3 .5 GENETiC mODiFiCATiON AND BiOTEChNOlOGy
benefts or all GM crops. Instead it is better to select Figure 10 Wild plants growing next to a crop of GM maize
one claim rom the list given here and assess it or
one crop. Much o the evidence relating to potential These diseases currently reduce crop yields
benefts and also to risks is reely available. signifcantly and the only current method
o control is to reduce transmission by
Claims about environmental benefts o killing insect vectors o the viruses with
GM crops: insecticides.
Pest-resistant crop varieties can be produced A wide variety o concerns about GM crops
by transerring a gene or making a toxin have been raised. Some o these, such as the
to the plants. Less insecticide then has to be eect on armers incomes, cannot be assessed
sprayed on to the crop so ewer bees and on scientifc grounds so are not relevant
other benefcial insects are harmed. here. The remaining concerns can be grouped
into health risks, environmental risks and
Use o GM crop varieties reduces the need agricultural risks. To make overall j udgments
or plowing and spraying crops, so less uel is about the saety o GM crops, each risk needs
needed or arm machinery. to be assessed careully, using all the available
experimental evidence. This needs to be done
The shel-lie o ruit and vegetables can be on a case by case basis as it is not possible to
improved, reducing wastage and reducing the assess the risks and benefts o one GM crop
area o crops that have to be grown. rom experiments perormed on another one.
Claims about the health benefts o There is no consensus among all scientists or
GM crops: non-scientists yet about GM crops and it is
thereore important or as many o us as possible
The nutritional value o crops can be to look at the evidence or the claims and
improved, or example by increasing the counter- claims, rather than the publicity. Any o
vitamin content. the risks that are included here could be selected
or detailed scrutiny.
Varieties o crops could be produced lacking
allergens or toxins that are naturally present Claims made about health risks o GM crops:
in them.
Proteins produced by transcription and
GM crops could be engineered that produce translation o transerred genes could be
edible vaccines so by eating the crop a person
would be vaccinated against a disease.
Claims about agricultural benefts o
GM crops:
Varieties resistant to drought, cold and salinity
can be produced by gene transer, expending
the range over which crops can be produced
and increasing total yields.
A gene or herbicide resistance can be
transerred to crop plants allowing all other
plants to be killed in the growing crop by
spraying with herbicide. With less weed
competition crop yields are higher. Herbicides
that kill all plants can be used to create
weed-ree conditions or sowing non-GM
crops but they cannot be used once the crop
is growing.
Crop varieties can be produced that are
resistant to diseases caused by viruses.
193
3 Genetics
toxic or cause allergic reactions in humans or plants, plant-eating insects and organisms that
livestock that eat GM crops. eed on them where GM rather than non-GM
crops are being grown.
Antibiotic resistance genes used as markers
during gene transer could spread to Claims made about agricultural risks of
pathogenic bacteria. GM crops:
Transerred genes could mutate and cause Some seed rom a crop is always spilt and
unexpected problems that were not risk- germinates to become unwanted volunteer
assessed during development o GM crops. plants that must be controlled, but this could
become very dicult i the crop contains
Claims made about environmental risks of herbicide resistance genes.
GM crops:
Widespread use o GM crops containing a
Non-target organisms could be aected by toxin that kills insect pests will lead to the
toxins that are intended to control pests in spread o resistance to the toxin in the pests
GM crop plants. that were the initial problem and also to the
spread o secondary pests that are resistant to
Genes transerred to crop plants to make the toxin but were previously scarce.
them herbicide resistant could spread to wild
plants, turning them into uncontrollable Farmers are not permitted by patent law to
s u p e r- w e e ds . save and re-sow GM seed rom crops they
have grown, so strains adapted to local
Biodiversity could be reduced i a lower conditions cannot be developed.
proportion o sunlight energy passes to weed
Analysing risks to monarch butterfies o
Bt corn
Analysis odata on risks to monarch butterfies oBt crops.
Insect pests o crops can be controlled by spraying with insecticides
but varieties have been recently been produced by genetic engineering
that produce a toxin that kills insects. A gene was transerred rom the
bacterium Bacillus thuringiensis that codes or Bt toxin. The toxin is a
protein. It kills members o insect orders that contain butterfies, moths,
fies, beetles, bees and ants. The genetically engineered corn varieties
produce Bt toxin in all parts o the plant including pollen.
Bt varieties o many crops have been produced, including Zea mays.
In North America this crop is called corn, while in Britain it is known
as maize, or corn on the cob. The crop is attacked by various insect
pests including corn borers, which are the larvae o the moth Ostrinia
nubilalis. C oncerns have been expressed about the eects o Bt corn on
non-target species o insect. One particular species o concern is the
monarch butterfy, Danaus plexippus.
The larvae o the monarch butterfy eed on leaves o milkweed,
Asclepias curassavica. This plant sometimes grows close enough to
corn crops to become dusted with the wind-dispersed corn pollen.
There is thereore a risk that monarch larvae might be poisoned by Bt
toxin in pollen rom GM corn crops. This risk has been investigated
experimentally. D ata rom these experiments is available or analysis.
194
3 .5 GENETiC mODiFiCATiON AND BiOTEChNOlOGy
Data-based questons: Transgenic pollen and monarch larvae Survival of monarch larvae (%) 100
To investigate the eect o pollen rom Bt corn on the larvae o 75
monarch butterfies the ollowing procedure was used. Leaves were
collected rom milkweed plants and were lightly misted with water. A 50
spatula o pollen was gently tapped over the leaves to deposit a ne
dusting. The leaves were placed in water-lled tubes. Five three-day- 25
old monarch butterfy larvae were placed on each lea. The area o lea
eaten by the larvae was monitored over our days. The mass o the 0 23 4
larvae was measured ater our days. The survival o the larvae was 1 Time (days)
monitored over our days.
2
Three treatments were included in the experiment, with ve repeats Cumulative leaf 1.5
o each treatment: consumption per larva
leaves not dusted with pollen (blue) 1
leaves dusted with non-GM pollen (yellow) 0.5
leaves dusted with pollen rom Bt corn (red) 0
12 3
The results are shown in the table, bar chart and graph on the right. 4
Time (days)
1 a) List the variables that were kept constant in the [3] Source: Losey JE, Rayor LS, Carter ME (May 1999) .
experiment. Transgenic pollen harms monarch larvae.
Nature 399 (6733) : 214.
b) Explain the need to keep these variables constant. [2]
2 a) Calculate the total number o larvae used in the Treatment Mean mass of
experiment. surviving larvae (g)
[2]
b) Explain the need or replicates in experiments. [2] Leaves not dusted 0.38
with pollen
3 The bar chart and the graph show mean results and error bars.
Explain how error bars help in the analysis and evaluation Leaves dusted with Not available
non-GM pollen
o data. [2]
4 Explain the conclusions that can be drawn rom the [2] Leaves dusted with 0.16
percentage survival o larvae in the three treatments. pollen from Bt corn
5 Suggest reasons or the dierences in lea consumption [3] Actvt
between the three treatments.
Estatng te sze ofa cone
6 Predict the mean mass o larvae that ed on leaves dusted [2]
with non-GM pollen. A total of 130,000 hectares of Russet
Burbank potatoes were planted in
7 Outline any dierences between the procedures used in [2] Idaho in 2011. The mean density
this experiment and processes that occur in nature, which of planting of potato tubers was
might aect whether monarch larvae are actually harmed 50,000 per hectare. Estimate the size
by Bt pollen. of the clone at the time of planting and
at the time of harvest.
Clones
Clones are groups of genetically identical organisms,
derived from a single original parent cell.
A zygote, produced by the usion o a male and emale gamete, is
the rst cell o a new organism. Because zygotes are produced by
sexual reproduction, they are all genetically dierent. A zygote grows
and develops into an adult organism. I it reproduces sexually, its
195
3 Genetics
Activity ospring will be genetically dierent. In some species organisms can
also reproduce asexually. When they do this, they produce genetically
How many potato clones are there in identical organisms.
this photo?
The production o genetically identical organisms is called cloning and
a group o genetically identical organisms is called a clone.
Although we do not usually think o them in this way, a pair o
identical twins is the smallest clone that can exist. They are either
the result o a human zygote dividing into two cells, which each
develop into separate embryos, or an embryo splitting into two
parts which each develop into a separate individual. Identical twins
are not identical in all their characteristics and have, or example,
dierent fngerprints. A better term or them is monozygotic. More
rarely identical triplets, quadruplets and even quintuplets have
been produced.
Sometimes a clone can consist o very large numbers o organisms.
For example, commercially grown potato varieties are huge clones.
Large clones are ormed by cloning happening again and again,
but even so all the organisms may be traced back to one original
parent cell.
Figure 11 Identical twins are an example natural methods of cloig
of cloning
Many plant species and some animal species have
Figure 12 One bulb of garlic clones itself to natural methods of cloning.
produce a group of bulbs by the end of the
growing season Although the word clone is now used or any group o genetically
identical organisms, it was frst used in the early 20th century or plants
produced by asexual reproduction. It comes rom the Greek word or
twig. Many plants have a natural method o cloning. The methods used
by plants are very varied and can involve stems, roots, leaves or bulbs.
Two examples are given here:
A single garlic bulb, when planted, uses its ood stores to grow
leaves. These leaves produce enough ood by photosynthesis to grow
a group o bulbs. All the bulbs in the group are genetically identical
so they are a clone.
A strawberry plant grows long horizontal stems with plantlets
at the end. These plantlets grow roots into the soil and
photosynthesize using their leaves, so can become independent
o the parent plant. A healthy strawberry plant can produce ten
or more genetically identical new plants in this way during a
growing season.
Natural methods o cloning are less common in animals but some species
are able to do it.
Hydra clones itsel by a process called budding ( sub- topic 1 .6,
fgure 1 , page 51 ).
Female aphids can give birth to ospring that have been produced
entirely rom diploid egg cells that were produced by mitosis rather than
meiosis. The ospring are thereore clones o their mother.
196
3 .5 GENETiC mODiFiCATiON AND BiOTEChNOlOGy
Investigating actors afecting the rooting o stem-cuttings
Design o an experiment to assess one actor afecting the rooting o
stem-cuttings.
Stem-cuttings are short lengths o stem that are whether the cutting is placed in water or
used to clone plants artifcially. I roots develop compost
rom the stem, the cutting can become an
independent new plant. what type o compost is used
1 Many plants can be cloned rom cuttings. how warm the cuttings are kept
Ocimum basilicum roots particularly easily.
whether a plastic bag is placed over the
2 Nodes are positions on the stem where leaves cuttings
are attached. With most species the stem is cut
below a node. whether holes are cut in the plastic bag.
3 Leaves are removed rom the lower hal o You should think about these questions when
the stem. I there are many large leaves in the you design your experiment:
upper hal they can also be reduced.
1 What is your independent variable?
4 The lowest third o the cutting is inserted into
compost or water. C ompost should be sterile 2 How will you measure the amount
and contain plenty o both air and water. o root ormation, which is your dependent
variable?
5 A clear plastic bag with a ew holes cut in it
prevents excessive water loss rom cuttings 3 Which variables should you keep
inserted in compost. constant?
6 Rooting normally takes a ew weeks. Growth 4 How many dierent types o plant should
o new leaves usually indicates that the cutting you use?
has developed roots.
5 How many cuttings should you use or each
treatment?
Not all gardeners have success when trying
to clone plants using root cuttings. Successul
gardeners are sometimes said to have green
fngers but a biologist would reject this as
the reason or their success. Experiments can
give evidence about the actors that determine
whether cuttings root or not. You can design and
carry out an experiment to investigate one o
the actors on the list below, or another actor o
your own.
Possible actors to investigate:
whether the stem is cut above or below a node
how long the cutting is
whether the end o the stem is let in the air to
callus over
how many leaves are let on the cutting
whether a hormone rooting powder is used
197
3 Genetics
Figure 13 Sea urchin embryo ( a) 4-cell stage Cloning animal embryos
(b) blastula stage consisting of a hollow ball
of cells Animals can be cloned at the embryo stage by breaking
up the embryo into more than one group o cells.
Figure 14 Xenopus tadpoles
At an early stage o development all cells in an animal embryo are
198 pluripotent (capable o developing into all types o tissue) . It is thereore
theoretically possible or the embryo to divide into two or more parts
and each part to develop into a separate individual with all body parts.
This process is called splitting or ragmentation. Coral embryos have
been observed to clone themselves by breaking up into smaller groups o
cells or even single cells, presumably because this increases the chance o
one embryo surviving.
Formation o identical twins could be regarded as cloning by splitting,
but most animal species do not appear to do this naturally. However, it
is possible to break up animal embryos artifcially and in some cases the
separated parts develop into multiple embryos.
In livestock, an egg can be ertilized in vitro and allowed to develop into a
multicellular embryo. Individual cells can be separated rom the embryo
while they are still pluripotent and transplanted into surrogate mothers.
Only a limited number o clones can be obtained this way, because ater
a certain number o divisions the embryo cells are no longer pluripotent.
Splitting o embryos is usually most successul at the eight-cell stage.
There has been little interest in this method o artifcial cloning because
at the embryo stage it is not possible to assess whether a new individual
produced by sexual reproduction has desirable characteristics.
Cloning adult animals using diferentiated cells
Methods have been developed or cloning adult animals
using diferentiated cells.
It is relatively easy to clone animal embryos, but at that stage it
is impossible to know whether the embryos will have desirable
characteristics. Once the embryos have grown into adults it is easy to
assess their characteristics, but it is much more difcult to clone them.
This is because the cells that make up the body o an adult animal
are dierentiated. To produce all the tissues in a new animal body
undierentiated pluripotent cells are needed.
The biologist John Gurdon carried out experiments on cloning in the rog
Xenopus as a postgraduate student in Oxord during the 1 950s. He removed
nuclei rom body cells o Xenopus tadpoles and transplanted them into egg
cells rom which the nucleus had been removed. The egg cells into which
the nuclei were transplanted developed as though they were zygotes. They
carried out cell division, cell growth and dierentiation to orm all the
tissues o a normal Xenopus rog. In 201 2 Gurdon was awarded the Nobel
Prize or Physiology or Medicine or his pioneering research.
Cloning using dierentiated cells proved to be much more diicult
in mammals. The irst cloned mammal was Dolly the sheep in 1 996.
Apart rom the obvious reproductive uses o this type o cloning,
there is also interest in it or therapeutic reasons. I this procedure
3 .5 GENETiC mODiFiCATiON AND BiOTEChNOlOGy
was done with humans, the embryo would consist of pluripotent
stem cells, which could be used to regenerate tissues for the adult.
Because the cells would be genetically identical to those of the
adult from whom the nucleus was obtained they would not cause
rejection problems.
Methods used to produce Dolly
Production of cloned embryos by somatic-cell nuclear transfer.
The production of Dolly was a pioneering
development in animal cloning. The method that
was used is called somatic-cell nuclear transfer. A
somatic cell is a normal body cell with a diploid
nucleus. The method has these stages:
Adult cells were taken from the udder of
a Finn Dorset ewe and were grown in the
laboratory, using a medium containing a low
concentration of nutrients. This made genes
in the cells inactive so that the pattern of
differentiation was lost.
Unfertilized eggs were taken from the ovaries
of a Scottish Blackface ewe. The nuclei were Figure 15 Dolly with Dr Ian Wilmut, the embryologist who led
removed from these eggs. One of the cultured the team that produced her
cells from the Finn Dorset was placed next
to each egg cell, inside the zona pellucida The embryos were then injected when about
around the egg, which is a protective coating seven days old into the uteri of other ewes that
of gel. A small electric pulse was used to could act as surrogate mothers. This was done
cause the two cells to fuse together. About in the same way as in IVF. O nly one of the 2 9
1 0% of the fused cells developed like a zygote embryos implanted successfully and developed
into an embryo. through a normal gestation. This was D olly.
egg without a
nucleus fused
with donor cell
using a pulse of
electricity
cell taken from udder of embryo resulting from
donor adult and cultured
in laboratory for six days fusion of udder cell and
egg transfered to the surrogate mother
uterus of a third sheep gives birth to lamb.
which acts as the Dolly is genetically
surrogate mother identical with the
sheep that donated
the udder cell
unfertilized egg taken from another (the donor)
sheep. Nucleus removed from the egg
Figure 16 A method or cloning an adult sheep using diferentiated cells
199
3 Genetics
Questions
1 Human somatic cells have 46 chromosomes, 3 The cheetah ( Acinonyx jubatus) is an endangered
while our closest primate relatives, the species o large cat ound in South and East
chimpanzee, the gorilla and the orangutan all Arica. A study o the level o variation o the
have 48 chromosomes. One hypothesis is that cheetah gene pool was carried out. In one
the human chromosome number 2 was ormed part o this study, blood samples were taken
rom the usion o two chromosomes in a rom 1 9 cheetahs and analysed or the protein
primate ancestor. The image below shows transerrin using gel electrophoresis. The
human chromosome 2 compared to chromosome results were compared with the electrophoresis
1 2 and 1 3 rom the chimpanzee. patterns or blood samples rom 1 9 domestic
a) Compare the human chromosome 2 cats ( Felis sylvestris) . Gel electrophoresis can
be used to separate proteins using the same
with the two chimpanzee chromosomes principles as in DNA profling. The bands on
the gel which represent orms o the protein
(fgure 1 7). [3] transerrin are indicated.
b) The ends o chromosomes, called telomeres,
have many repeats o the same short DNA
sequence. I the usion hypothesis were
true, predict what would be ound in the
region o the chromosome where the usion
is hypothesized to have occurred. [2] transferrin
HC
Figure 17
origin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
cheetahs
2 The pedigree in fgure 1 8 shows the ABO
groups o three generations o a amily.
I AB B OB transferrin
1 2 34
II B A B OO
1 2 3 45
III O A B O?
1 2 3 45
Figure 18 origin
a) Deduce the genotype o each person in the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
domestic cats
amily. [4] Figure 19
b) Deduce the possible blood groups o
individual III 5, with the percentage chance Using fgure 1 9, deduce with reasons:
o each. [2] a) the number o domestic cats and the
c) Deduce the possible blood groups and the number o cheetahs that were heterozygous
percentage chance o each blood group:
or the transerrin gene; [2]
(i) o children o individual III 1 and his b) the number o alleles o the transerrin gene
partner who is also in blood group O [2]
in the gene pool o domestic cats; [2]
(ii) o children o III 2 and her partner who c) the number o alleles o the transerrin gene
is in blood group AB. [2] in the gene pool o cheetahs. [1 ]
200
4 Ecology survival o living organisms including humans
depends on sustainable ecological communities.
Intrdutin Concentrations o gases in the atmosphere have
signifcant eects on climates experienced at the
Ecosystems require a continuous supply o Earths surace.
energy to uel lie processes and to replace
energy lost as heat. Continued availability
o carbon and other chemical elements in
ecosystems depends on cycles. The uture
4.1 Species, communities and ecosystems
Understandin Skis
Species are groups o organisms that can Classiying species as autotrophs, consumers,
potentially interbreed to produce ertile ofspring. detritivores or saprotrophs rom a knowledge o
their mode o nutrition.
Members o a species may be reproductively
isolated in separate populations. Testing or association between two species
using the chi-squared test with data obtained
Species have either an autotrophic or by quadrat sampling.
heterotrophic method o nutrition (a ew
species have both methods) . Recognizing and interpreting statistical
signicance.
Consumers are heterotrophs that eed on living
organisms by ingestion. Setting up sealed mesocosms to try to
establish sustainability. (Practical 5)
Detritivores are heterotrophs that obtain organic
nutrients rom detritus by internal digestion. Nature f siene
Saprotrophs are heterotrophs that obtain Looking or patterns, trends and discrepancies:
organic nutrients rom dead organic matter by plants and algae are mostly autotrophic but
external digestion. some are not.
A community is ormed by populations
o diferent species living together and
interacting with each other.
A community orms an ecosystem by its
interactions with the abiotic environment.
Autotrophs and heterotrophs obtain inorganic
nutrients rom the abiotic environment.
The supply o inorganic nutrients is maintained
by nutrient cycling.
Ecosystems have the potential to be
sustainable over long periods o time.
201
14 E co lo g y
Figure 1 A bird of paradise in Papua Species
New Guinea
Species are groups o organisms that can potentially
interbreed to produce ertile ofspring.
Birds o paradise inhabit Papua New Guinea and other Australasian
islands. In the breeding season the males do elaborate and distinctive
courtship dances, repeatedly carrying out a series o movements
to display their exotic plumage. One reason or this is to show to a
emale that they are ft and would be a suitable partner. Another
reason is to show that they are the same type o bird o paradise as
the emale.
There are orty-one dierent types o bird o paradise. Each o
these usually only reproduces with others o its type and hybrids
between the dierent types are rarely produced. For this reason
each o the orty-one types o bird o paradise remains distinct, with
characters that are dierent to those o other types. Biologists call
types o organism such as these species. Although ew species have
as elaborate courtship rituals as birds o paradise, most species have
some method o trying to ensure that they reproduce with other
members o their species.
When two members o the same species mate and produce ospring
they are interbreeding. Occasionally members o dierent species breed
together. This is called cross- breeding. It happens occasionally with birds
o paradise. However, the ospring produced by cross- breeding between
species are almost always inertile, which prevents the genes o two
species becoming mixed.
The reproductive separation between species is the reason or each
species being a recognizable type o organism with characters that
distinguish it rom even the most closely related other species. In
summary, a species is a group o organisms that interbreed to produce
ertile ospring.
Populations
Members o a species may be reproductively isolated in
separate populations.
A population is a group o organisms o the same species who live in the
same area at the same time. I two populations live in dierent areas
they are unlikely to interbreed with each other. This does not mean that
they are dierent species. I they potentially could interbreed, they are
still members o the same species.
I two populations o a species never interbreed then they may gradually
develop dierences in their characters. Even i there are recognizable
dierences, they are considered to be the same species until they cannot
interbreed and produce ertile ospring. In practice it can be very
difcult to decide whether two populations have reached this point and
biologists sometimes disagree about whether populations are the same or
dierent species.
202
4.1 SPecieS, com muni tieS an d ecoSyStem S
arph hrrph r av
Species have either an autotrophic or heterotrophic Glpgs rss
method o nutrition (a ew species have both methods) . The tortoises that live on
the Galpagos islands are
All organisms need a supply o organic nutrients, such as glucose and the largest in the world.
amino acids. They are needed or growth and reproduction. Methods o They have sometimes been
obtaining these carbon compounds can be divided into two types: grouped together into one
species, Chelinoidis nigra,
some organisms make their own carbon compounds rom carbon but more recently have been
dioxide and other simple substances they are autotrophic, which split into separate species.
means sel-eeding; Discuss whether each
o these observations
some organisms obtain their carbon compounds rom other indicates that populations
organisms they are heterotrophic, which means eeding on others. on the various islands are
separate species:
S ome unicellular organisms use both methods o nutrition. Euglena The Galpagos tortoises
gracilis or example has chloroplasts and carries out photosynthesis when
there is sufcient light, but can also eed on detritus or smaller organisms are poor swimmers and
by endocytosis. Organisms that are not exclusively autotrophic or cannot travel rom one
heterotrophic are mixotrophic. island to another so
they do not naturally
Figure 3 Arabidopsis Figure 4 Humming birds Figure 5 Euglena an interbreed.
thaliana the autotroph Tortoises rom
that molecular biologists are heterotrophic; the plants unusual organism diferent islands have
use as a model plant recognizable diferences
from which they obtain as it can feed both in their characters,
including shell size and
nectar are autotrophic autotrophically and shape.
Tortoises rom diferent
heterotrophically islands have been
mated in zoos and
trs pl lgl r hybrid ofspring have
been produced but they
Looking or patterns, trends and discrepancies: plants have lower ertility and
and algae are mostly autotrophic but some are not. higher mortality than
the ofspring o tortoises
Almost all plants and algae are autotrophic they make their own rom the same island.
complex organic compounds using carbon dioxide and other simple
substances. A supply o energy is needed to do this, which plants and Figure 2 Galpagos tortoise
algae obtain by absorbing light. Their method o autotrophic nutrition
is thereore photosynthesis and they carry it out in chloroplasts.
This trend or plants and algae to make their own carbon compounds
by photosynthesis in chloroplasts is ollowed by the majority o species.
However there are small numbers o both plants and algae that do not ft
the trend, because although they are recognizably plants or algae, they
203
14 E co lo g y
do not contain chloroplasts and they do not carry out photosynthesis.
These species grow on other plants, obtain carbon compounds rom
them and cause them harm. They are thereore parasitic.
To decide whether parasitic plants alsiy the theory that plants and
algae are groups o autotrophic species or whether they are just minor
and insignifcant discrepancies we need to consider how many species
there are and how they evolved.
The number o parasitic plants and algae is relatively small only
about 1 % o all plant and algal species.
It is almost certain that the original ancestral species o plant and
alga were autotrophic and that the parasitic species evolved rom
them. Chloroplasts can quite easily be lost rom cells, but cannot
easily be developed. Also, parasitic species are diverse and occur in
many dierent amilies. This pattern suggests that parasitic plants
have evolved repeatedly rom photosynthetic species.
Because o this evidence, ecologists regard plants and algae as groups o
autotrophs, with a small number o exceptional species that are parasitic.
data-base questions: Unexpected diets
Although we usually expect plants to be autotrophs and
animals to be consumers, living organisms are very varied
and do not always conorm to our expectations. Figures 6
to 9 show our organisms with diets that are unexpected.
1 Which o the organisms is autotrophic? [4]
2 Which o the organisms is heterotrophic? [4]
3 O the organisms that are heterotrophic, deduce which is a Figure 6 Venus y trap: grows in
consumer, which a detritivore and which a saprotroph. [4] swamps, with green leaves that
carry out photosynthesis and also
catch and digest insects, to provide
a supply o nitrogen
Figure 7 Ghost orchid: grows Figure 8 Euglena: unicell Figure 9 Dodder: grows parasitically
underground in woodland, eeding that lives in ponds, using its on gorse bushes, using small root-like
of dead organic matter, occasionally chloroplasts or photosynthesis, structures to obtain sugars, amino acids
growing a stem with owers above but also ingesting dead organic and other substances it requires, rom
ground matter by endocytosis the gorse
204
4.1 SPecieS, com muni tieS an d ecoSyStem S
csrs Figure 10 Red kite (Milvus milvus) is a
consumer that feeds on live prey but also
Consumers are heterotrophs that feed on living organisms on dead animal remains (carrion)
by ingestion.
Figure 11 Yellow-necked mouse (Apodemus
Heterotrophs are divided into groups by ecologists according to the favicollis) is a consumer that feeds mostly on
source o organic molecules that they use and the method o taking living plant matter, especially seeds, but also
them in. One group o heterotrophs is called consumers. on living invertebrates
Consumers eed o other organisms. These other organisms are either
still alive or have only been dead or a relatively short time. A mosquito
sucking blood rom a larger animal is a consumer that eeds on an
organism that is still alive. A lion eeding o a gazelle that it has killed is
a consumer.
Consumers ingest their ood. This means that they take in undigested
material rom other organisms. They digest it and absorb the products o
digestion. Unicellular consumers such as Paramecium take the ood in by
endocytosis and digest it inside vacuoles. Multicellular consumers such
as lions take ood into their digestive system by swallowing it.
Consumers are sometimes divided up into trophic groups according
to what other organisms they consume. Primary consumers eed on
autotrophs; secondary consumers eed on primary consumers and so on.
In practice, most consumers do not ft neatly into any one o these groups
because their diet includes material rom a variety o trophic groups.
drvrs Sprrphs
Detritivores are heterotrophs that obtain Saprotrophs are heterotrophs that obtain
organic nutrients from detritus by organic nutrients from dead
internal digestion. organic matter by external digestion.
Organisms discard large quantities o organic Saprotrophs secrete digestive enzymes into the dead
matter, or example: organic matter and digest it externally. They then
absorb the products o digestion. Many types o
dead leaves and other parts o plants bacteria and ungi are saprotrophic. They are also
known as decomposers because they break down
eathers, hairs and other dead parts o animal carbon compounds in dead organic matter and
bodies release elements such as nitrogen into the ecosystem
so that they can be used again by other organisms.
eces rom animals.
Figure 12 Saprotrophic fungi growing over the surfaces of dead
This dead organic matter rarely accumulates leaves and decomposing them by secreting digestive enzymes
in ecosystems and instead is used as a source
o nutrition by two groups o heterotroph
detritivores and saprotrophs.
Detritivores ingest dead organic matter and then
digest it internally and absorb the products o
digestion. Large multicellular detritivores such as
earthworms ingest the dead matter into their gut.
Unicellular organisms ingest it into ood vacuoles.
The larvae o dung beetles eed by ingestion o
eces rolled into a ball by their parent.
205
14 E co lo g y Identifying modes of nutrition
TOK Classiying species as autotrophs, consumers, detritivores
or saprotrophs rom a knowledge otheir mode onutrition.
to wh exen do he lssifion
sysems (lbels nd egories) we By answering a series o simple questions about an organisms mode o
use se limis o wh we pereive? nutrition it is usually possible to deduce what trophic group it is in. These
questions are presented here as a dichotomous key, which consists o a
There are innite ways to divide up series o pairs o choices. The key works or unicellular and multicellular
our observations. Organisms can be organisms but does not work or parasites such as tapeworms or
organized in a number o ways by ungi that cause diseases in plants. All multicellular autotrophs are
scientists: by morphology (physical photosynthetic and have chloroplasts containing chlorophyll.
similarity to other organisms) ,
phylogeny (evolutionary history) and Feeds on living or recently Feeds on dead organic
niche (ecological role) . In everyday killed organisms = CONSUMERS matter = DETRITIVORES
language, we classiy organisms such
as domesticated or wild; dangerous or
harmless; edible or toxic.
Either ingests organic matter by endocytosis (no cell walls) or by taking it into its gut.
aiviy START HERE
cleruing
Cell walls present. No ingestion of organic matter. No gut. Enzymes not secreted.
Only requires simple
Secretes enzymes into ions and compounds
its environment to digest such as CO2
dead organic matter = AUTOTROPHS
= SAPROTROPHS
Figure 14 communiies
In a classic essay written in 1972, the A community is ormed by populations o diferent
physicist Philip Anderson stated this: species living together and interacting with each other.
The ability to reduce everything to An important part o ecology is research into relationships between
simple fundamental laws does not organisms. These relationships are complex and varied. In some cases
imply the ability to start from those the interaction between two species is o benet to one species and
laws and reconstruct the universe. At harms the other, or example the relationship between a parasite and its
each level ofcomplexity entirely new host. In other cases both species benet, as when a hummingbird eeds
properties appear. on nectar rom a fower and helps the plant by pollinating it.
Clearcutting is the most common All species are dependent on relationships with other species or their
and economically protable orm o long-term survival. For this reason a population o one species can
logging. It involves clearing every tree never live in isolation. Groups o populations live together. A group
in an area so that no canopy remains.
With reerence to the concept o
emergent properties, suggest why the
ecological community oten ails to
recover ater clearcutting.
206
4.1 SPecieS, com muni tieS an d ecoSyStem S
o populations living together in an area and interacting with each other
is known in ecology as a community. Typical communities consist o
hundreds or even thousands o species living together in an area.
Figure 13 A coral reef is a complex community with many interactions between the
populations. Most corals have photosynthetic unicellular algae called zooxanthellae living
inside their cells
Field work associations between species
Testing for association between two species using the chi-squared test with data
obtained by quadrat sampling.
Quadrats are square sample areas, usually marked The quadrat is placed precisely at the distances
out using a quadrat rame. Quadrat sampling determined by the two random numbers.
involves repeatedly placing a quadrat rame at
random positions in a habitat and recording the I this procedure is ollowed correctly, with a large
numbers o organisms present each time. enough number o replicates, reliable estimates o
The usual procedure or randomly positioning
quadrats is this:
A base line is marked out along the edge o the
habitat using a measuring tape. It must extend
all the way along the edge o the habitat.
Random numbers are obtained using either
a table or a random number generator on a
c a lc u la to r.
A frst random number is used to determine
a distance along the measuring tape. All
distances along the tape must be equally likely.
A second random number is used to determine
a distance out across the habitat at right angles
to the tape. All distances across the habitat Figure 15 Quadrat sampling of seaweed populations on a
must be equally likely. rocky shore
207
14 E co lo g y
population sizes are obtained. The method is only 2 C alculate the expected requencies,
suitable or plants and other organisms that are assuming independent distribution, or
not motile. Quadrat sampling is not suitable or each o the our species combinations.
populations o most animals, or obvious reasons. Each expected requency is calculated rom
I the presence or absence o more than one values on the contingency table using this
species is recorded in every quadrat during equation:
sampling o a habitat, it is possible to test or an
association between species. Populations are oten expected = _row tota_l colum_n total
grand total
requency
unevenly distributed because some parts o the 3 Calculate the number o degrees o reedom
habitat are more suitable or a species than others. using this equation.
I two species occur in the same parts o a habitat,
they will tend to be ound in the same quadrats. degrees o reedom = (m 1 ) (n 1 )
This is known as a positive association. There can where m and n are the number o rows
also be negative associations, or the distribution o and number o columns in the contingency
two species can be independent. table.
There are two possible hypotheses: 4 Find the critical region or chi-squared rom a
H0: two species are distributed independently table o chi-squared values, using the degrees
(the null hypothesis) . o reedom that you have calculated and a
H1: two species are associated (either positively signifcance level (p) o 0.05 (5%) . The critical
so they tend to occur together or negatively so region is any value o chi-squared larger than
the value in the table.
they tend to occur apart) .
We can test these hypotheses using a statistical 5 Calculate chi-squared using this equation:
procedure the chi-squared test. X2 = _( fo - fe) 2
fe
The chi-squared test is only valid i all the
expected requencies are 5 or larger and the where fo is the observed requency
sample was taken at random rom the population. fe is the expected requency and
Method for chi-squared test is the sum o.
1 Draw up a contingency table o observed 6 Compare the calculated value o chi-squared
requencies, which are the numbers o quadrats with the critical region.
containing or not containing the two species.
I the calculated value is in the critical
Species A Species A Row region, there is evidence at the 5% level
present absent totals or an association between the two species.
Species B present We can rej ect the hypothesis H0.
Species B absent I the calculated value is not in the critical
Column totals region, because it is equal or below the
value obtained rom the table o chi-
Calculate the row and column totals. Adding squared values, H0 is not rejected. There
the row totals or the column totals should give is no evidence at the 5% level or an
the same grand total in the lower right cell.
association between the two species.
208
4.1 SPecieS, com muni tieS an d ecoSyStem S
d-bs qss: Chi-squared testing
Figure 1 6 shows an area on the summit o C aer 3 Calculate the number o degrees o reedom. [2 ]
Caradoc, a hill in Shropshire, England. 4 Find the critical region or chi-squared at a
The area is grazed by sheep in summer and signifcance level o 5%. [2]
hill walkers cross it on grassy paths. There are 5 Calculate chi-squared. [4]
raised hummocks with heather (Calluna vulgaris)
growing in them. A visual survey o this site 6 State the two alternative hypotheses, H0 and
suggested that Rhytidiadelphus squarrosus, a species
o moss growing in this area, was associated H , and evaluate them using the calculated
1
value or chi-squared. [4]
with these heather hummocks. The presence or 7 Suggest ecological reasons or an association
absence o the heather and the moss was recorded between the heather and the moss. [4]
in a sample o 1 00 quadrats, positioned randomly.
8 Explain the methods that should have been
Results used to position quadrats randomly in the
Sps Frq area o study. [3]
Heather only 9
Moss only 7
Both species 57
Neither species 27
Questions
1 Construct a contingency table o observed
values. [4]
2 Calculate the expected values, assuming no
association between the species. [4] Figure 16 Caer Caradoc, Shropshire
Statistical signifcance
Recognizing and interpreting statistical signifcance.
Biologists oten use the phrase statistically that it is alse. A statistic is calculated using the
signifcant when discussing results o an results o the research and is compared with
experiment. This reers to the outcome o a range o possible values called the critical
a statistical hypothesis test. There are two region. I the calculated statistic exceeds the
alternative types o hypothesis: critical region, the null hypothesis is considered
to be alse and is thereore rejected, though
H is the null hypothesis and is the belie that we cannot say that this has been proved
0 with certainty.
there is no relationship, or example that two
means are equal or that there is no association When a biologist states that results were
or correlation between two variables. statistically signifcant it means that i the null
hypothesis (H0) was true, the probability o getting
H1 is the alternative hypothesis and is the results as extreme as the observed results would
belie that there is a relationship, or example be very small. A decision has to be made about
that two means are dierent or that there is an how small this probability needs to be. This is
association between two variables. known as the signifcance level. It is the cut-o
point or the probability o rejecting the null
The usual procedure is to test the null
hypothesis, with the expectation o showing
209
14 E co lo g y
hypothesis when in act it was true. A level o In the example o testing or an association
5% is oten chosen, so the probability is less than between two species, described on previous
one in twenty. That is the minimum acceptable pages, the chi-squared test shows whether
signicance level in published research. there is a less than 5% probability o the
dierence between the observed and the
I there is a dierence between the mean expected results being as large as it is
results or the two treatments in an without the species being either positively or
experiment, a statistical test will show negatively associated.
whether the dierence is signicant at the 5%
level. I it is, there is a less than 5% probability When results o biological research are displayed
o such a large dierence between the sample on a bar chart, letters are oten used to indicate
means arising by chance, even when the statistical signicance. Two dierent letters,
population means are equal. We say that there usually a and b, indicate mean results with a
is statistically signicant evidence that the statistically signicant dierence. Two o the same
population means dier. letter such as a and a indicates that any dierence
is not statistically signicant.
Figure 17 Grasses in an area of developing Ecosystems
sand dunes
A community forms an ecosystem by its interactions
210 with the abiotic environment.
A community is composed o all organisms living in an area. These
organisms could not live in isolation they depend on their non-
living surroundings o air, water, soil or rock. Ecologists reer to these
surroundings as the abiotic environment.
In some cases the abiotic environment exerts a powerul infuence over the
organisms. For example the wave action on a rocky shore creates a very
specialized habitat and only organisms adapted to it can survive. On clis,
the rock type determines whether there are ledges on which birds can nest.
There are also many cases where living organisms infuence the abiotic
environment. Sand dunes are an example o this. They develop along
coasts where sand is blown up the shore and specialized plants grow in
the loose wind-blown sand. The roots o these plants stabilize the sand
and their leaves break the wind and encourage more sand to be deposited.
So, not only are there complex interactions within communities, there are
also many interactions between organisms and the abiotic environment.
The community o organisms in an area and their non-living environment
can thereore be considered to be a single highly complex interacting
system, known as an ecosystem. Ecologists study both the components o
ecosystems and the interactions between them.
inorganc nutrents
Autotrophs and heterotrophs obtain inorganic nutrients
from the abiotic environment.
Living organisms need a supply o chemical elements:
Carbon, hydrogen and oxygen are needed to make carbohydrates,
lipids and other carbon compounds on which lie is based.
4.1 SPecieS, com muni tieS an d ecoSyStem S
Nitrogen and phosphorus are also needed to make many o these
compounds.
Approximately fteen other elements are needed by living
organisms. S ome o them are used in minute traces only, but they
are nonetheless essential.
Autotrophs obtain all o the elements that they need as inorganic
nutrients rom the abiotic environment, including carbon and nitrogen.
Heterotrophs on the other hand obtain these two elements and
several others as part o the carbon compounds in their ood. They do
however obtain other elements as inorganic nutrients rom the abiotic
environment, including sodium, potassium and calcium.
nr ls Reserves of an
element in the
The supply of inorganic nutrients is maintained by abiotic environment
nutrient cycling.
Element forming
There are limited supplies on Earth o chemical elements. Although part of a living
living organisms have been using the supplies or three billion years,
they have not run out. This is because chemical elements can be organism
endlessly recycled. Organisms absorb the elements that they require as
inorganic nutrients rom the abiotic environment, use them and then
return them to the environment with the atoms unchanged.
Recycling o chemical elements is rarely as simple as shown in this
diagram and oten an element is passed rom organism to organism
beore it is released back into the abiotic environment. The details
vary rom element to element. The carbon cycle is dierent rom the
nitrogen cycle or example. Ecologists reer to these schemes collectively
as nutrient cycles. The word nutrient is oten ambiguous in biology but
in this context it simply means an element that an organism needs.
The carbon cycle is described as an example o a nutrient cycle in sub-
topic 4.2 and the nitrogen cycle in Option C.
Ssbl f sss Figure 18 Living organisms have been recycling
for billions of years
Ecosystems have the potential to be sustainable over
long periods of time. 211
The concept o sustainability has risen to prominence recently because
it is clear that some current human uses o resources are unsustainable.
S omething is sustainable i it can continue indefnitely. Human use o
ossil uels is an example o an unsustainable activity. Supplies o ossil
uels are fnite, are not currently being renewed and cannot thereore
carry on indefnitely.
Natural ecosystems can teach us how to live in a sustainable way, so
that our children and grandchildren can live as we do. There are three
requirements or sustainability in ecosystems:
nutrient availability
detoxifcation o waste products
energy availability.
14 E co lo g y
Figure 19 Sunlight supplies energy to a forest Nutrients can be recycled indefnitely and i this is done there should
ecosystem and nutrients are recycled not be a lack o the chemical elements on which lie is based. The waste
products o one species are usually exploited as a resource by another
ativity species. For example, ammonium ions released by decomposers are
absorbed and used or an energy source by Nitrosomonas bacteria in the
cve eosystems soil. Ammonium is potentially toxic but because o the action o these
Organisms have been ound bacteria it does not accumulate.
living in total darkness in
caves, including eyeless Energy cannot be recycled, so sustainability depends on continued
fsh. Discuss whether energy supply to ecosystems. Most energy is supplied to ecosystems
ecosystems in dark caves as light rom the sun. The importance o this supply can be illustrated
are sustainable. by the consequences o the eruption o Mount Tambora in 1 81 5 .
Figure 20 shows a Dust in the atmosphere reduced the intensity o sunlight or some
small ecosystem with months aterwards, causing crop ailures globally and deaths due to
photosynthesizing plants starvation. This was only a temporary phenomenon, however, and
near artifcial lighting in a energy supplies to ecosystems in the orm o sunlight will continue
cave that is open to visitors or billions o years.
in Cheddar Gorge. Discuss
whether this is more or Mesocosms
less sustainable than
ecosystems in dark caves. Setting up sealed mesocosms to try to establish
sustainability. (Practical 5)
Figure 20
Mesocosms are small experimental areas that are set up as
ecological experiments. Fenced-o enclosures in grassland or
orest could be used as terrestrial mesocosms; tanks set up in
the laboratory can be used as aquatic mesocosms. Ecological
experiments can be done in replicate mesocosms, to fnd out the
eects o varying one or more conditions. For example, tanks could
be set up with and without fsh, to investigate the eects o fsh on
aquatic ecosystems.
Another possible use o mesocosms is to test what types o ecosystems
are sustainable. This involves sealing up a community o organisms
together with air and soil or water inside a container.
You should consider these questions beore setting up either aquatic
or terrestrial mesocosms:
Large glass jars are ideal but transparent plastic containers could
also be used. Should the sides o the container be transparent or
opaque?
Which o these groups o organisms must be included to make up
a sustainable community: autotrophs, consumers, saprotrophs and
detritivores?
How can we ensure that the oxygen supply is sufcient or all the
organisms in the mesocosm as once it is sealed, no more oxygen
will be able to enter.
How can we prevent any organisms suering as a result o being
placed in the mesocosm?
212
4.2 enerGy Flow
4.2 eg f
Understanding Skills
Most ecosystems rely on a supply o energy Quantitative representations o energy fow
rom sunlight. using pyramids o energy.
Light energy is converted to chemical energy in Nature of science
carbon compounds by photosynthesis.
Use theories to explain natural phenomena:
Chemical energy in carbon compounds fows the concept o energy fow explains the limited
through ood chains by means o eeding. length o ood chains.
Energy released by respiration is used in living
organisms and converted to heat.
LoivrNminsag ootrugearnneeirsgomyf.s scacnineotncconevert heat to other
EHxepaetriismloesnttarlodmeseigcnos: aycscteumraste. quantitative
amEthrneeeeaelrsegsunysrgeeltonmhstisoeaenl.stosboiendtwochsemaeinnosstriaosnpehdxiptcheleerivmbeioelsmnrtaesssstrioct
higher trophic levels.
Sunlight and ecosystems
Most ecosystems rely on a supply o energy rom
sunlight.
For most biological communities, the initial source of energy is
sunlight. Living organisms can harvest this energy by photosynthesis.
Three groups of autotroph carry out photosynthesis: plants,
eukaryotic algae including seaweeds that grow on rocky shores, and
cyanobacteria. These organisms are often referred to by ecologists
as producers.
Heterotrophs do not use light energy directly, but they are indirectly
dependent on it. There are several groups of heterotroph in ecosystems:
consumers, saprotrophs and detritivores. All of them use carbon
compounds in their food as a source of energy. In most ecosystems all
or almost all energy in the carbon compounds will originally have been
harvested by photosynthesis in producers.
The amount of energy supplied to ecosystems in sunlight varies around
the world. The percentage of this energy that is harvested by producers
and therefore available to other organisms also varies. In the Sahara
Desert, for example, the intensity of sunlight is very high but little of it
becomes available to organisms because there are very few producers.
In the redwood forests of California the intensity of sunlight is less than
in the Sahara but much more energy becomes available to organisms
because producers are abundant.
213
14 E co lo g y
ativity dt-bse questions: Insolation
cynobteri in ves Insolation is a measure o solar radiation The two maps in fgure 2
show annual mean insolation at the top o the Earths atmosphere
Cyanobacteria are (upper map) and at the Earths surace (lower map) .
photosynthetic bacteria that
are oten very abundant Questions
in marine and reshwater
ecosystems. Figure 1 1 State the relationship between distance rom the equator and
shows an area ogreen
cyanobacteria on an area insolation at the top o the Earths atmosphere. [1 ]
owall in a cave that is
illuminated by artifcial light. 2 S tate the mean annual insolation in Watts per square metre
The surrounding areas are or the most northerly part o Australia
normally dark. Ithe artifcial
light was not present, what a) at the top o the atmosphere [1 ]
other energy sources could [1 ]
be used by bacteria in caves? b) at the Earths surace.
[2]
3 Suggest reasons or dierences in insolation at the Earths
surace between places that are at the same distance rom
the equator.
4 Tropical rainorests are ound in equatorial regions o all [5]
continents. They have very high rates o photosynthesis.
Evaluate the hypothesis that this is due to very high
insolation. Include named parts o the world in your
a n s w e r.
Figure 1
0 40 80 120 160 200 240 280 320 360 400 w/m2
Figure 2
214
4.2 enerGy Flow
Energy conversion activit
Light energy is converted to chemical energy in carbon Bush d st fs
compounds by photosynthesis.
Figure 3
Producers absorb sunlight using chlorophyll and other photosynthetic Figure 3 shows a bush re in
pigments. This converts the light energy to chemical energy, which is used to Australia.
make carbohydrates, lipids and all the other carbon compounds in producers. What energy conversion is
happening in a bush re?
Producers can release energy rom their carbon compounds by cell Bush and orest res
respiration and then use it or cell activities. Energy released in this way occur naturally in some
is eventually lost to the environment as waste heat. However, only some ecosystems.
o the carbon compounds in producers are used in this way and the Suggest two reasons or this
largest part remains in the cells and tissues o producers. The energy in hypothesis: There are ewer
these carbon compounds is available to heterotrophs. heterotrophs in ecosystems
where res are common
Energy in food chains compared to ecosystems
where res are not common.
Chemical energy in carbon compounds fows through ood
chains by means o eeding.
A ood chain is a sequence o organisms, each o which eeds on the previous
one. There are usually between two and ve organisms in a ood chain. It is
rare or there to be more organisms in the chain. As they do not obtain ood
rom other organisms, producers are always the rst organisms in a ood
chain. The subsequent organisms are consumers. Primary consumers eed
on producers; secondary consumers eed on primary consumers; tertiary
consumers eed on secondary consumers, and so on. No consumers eed on
the last organism in a ood chain. Consumers obtain energy rom the carbon
compounds in the organisms on which they eed. The arrows in a ood chain
thereore indicate the direction o energy fow.
Figure 4 is an example o a ood chain rom the orests around Iguazu
alls in northern Argentina.
Figure 4
Respiration and energy release
Energy released by respiration is used in living organisms
and converted to heat.
Living organisms need energy or cell activities such as these:
Synthesizing large molecules like DNA, RNA and proteins.
Pumping molecules or ions across membranes by active transport.
Moving things around inside the cell, such as chromosomes or vesicles,
or in muscle cells the protein bres that cause muscle contraction.
ATP supplies energy or these activities. Every cell produces its own
ATP supply.
215
14 E co lo g y
All cells can produce ATP by cell respiration. In this process carbon
compounds such as carbohydrates and lipids are oxidized. These
oxidation reactions are exothermic and the energy released is used
in endothermic reactions to make ATP. So cell respiration transers
chemical energy rom glucose and other carbon compounds to ATP. The
reason or doing this is that the chemical energy in carbon compounds
such as glucose is not immediately usable by the cell, but the chemical
energy in ATP can be used directly or many dierent activities.
The second law o thermodynamics states that energy transormations
are never 1 00% efcient. Not all o the energy rom the oxidation
o carbon compounds in cell respiration is transerred to ATP. The
remainder is converted to heat. S ome heat is also produced when ATP is
used in cell activities. Muscles warm up when they contract or example.
Energy rom ATP may reside or a time in large molecules when they
have been synthesized, such as DNA and proteins, but when these
molecules are eventually digested the energy is released as heat.
data-base questions 20
Figure 5 shows the results o an experiment in respiration rate (mW g1) 15
which yellow- billed magpies (Pica nuttalli) were
put in a cage in which the temperature could 10
be controlled. The birds rate o respiration
was measured at seven dierent temperatures, 5
rom 1 0 C to +40 C. Between 1 0 C and
30 C the magpies maintained constant body
temperature, but above 30 C body temperature
increased.
a) Describe the relationship between external
temperature and respiration rate in yellow- 0 -10 0 10 20 30 40 50
temperature (C)
billed magpies. [3]
b) Explain the change in respiration rate as Figure 5 Cell respiration rates at diferent temperatures in
temperature drops rom +1 0 C to 1 0 C. [3] yellow-billed magpies
c) Suggest a reason or the change in d) Suggest two reasons or the variation in
respiration rate as temperature increased
rom 30 C to 40 C. respiration rate between the birds at each
[2] temperature. [2]
Heat energy in ecosystems
Living organisms cannot convert heat to other forms
of energy.
Living organisms can perorm various energy conversions:
Light energy to chemical energy in photosynthesis.
Chemical energy to kinetic energy in muscle contraction.
Chemical energy to electrical energy in nerve cells.
Chemical energy to heat energy in heat-generating adipose tissue.
They cannot convert heat energy into any other orm o energy.
216
4.2 enerGy Flow
Heat losses from ecosystems acivi
Heat is lost rom ecosystems. thikig bu g
chgs
Heat resulting rom cell respiration makes living organisms warmer.
This heat can be useul in making cold-blooded animals more active. What energy conversions
Birds and mammals increase their rate o heat generation i necessary to are required to shoot a
maintain their constant body temperatures. basketball?
According to the laws o thermodynamics in physics, heat passes rom What is the nal orm o the
hotter to cooler bodies, so heat produced in living organisms is all eventually energy?
lost to the abiotic environment. The heat may remain in the ecosystem or
a while, but ultimately is lost, or example when heat is radiated into the
atmosphere. Ecologists assume that all energy released by respiration or use
in cell activities will ultimately be lost rom an ecosystem.
expiig h gh f fd chis
Use theories to explain natural phenomena: the
concept o energy fow explains the limited length
o ood chains.
I we consider the diet o a top carnivore that is at the end o a ood
chain, we can work out how many stages there are in the ood chain
leading up to it. For example, i an osprey eeds on sh such as salmon
that ed on shrimps, which ed on phytoplankton, there are our
stages in the ood chain.
There are rarely more than our or ve stages in a ood chain. We
might expect ood chains to be limitless, with one species being eaten
by another ad innitum. This does not happen. In ecology, as in all
branches o science, we try to explain natural phenomena such as the
restricted length o ood chains using scientic theories. In this case it
is the concept o energy fow along ood chains and the energy losses
that occur between trophic levels that can provide an explanation.
Energy losses and ecosystems Figure 6 An inrared camera image o an
Arican grey parrot (Psittacus erithacus)
Energy losses between trophic levels restrict the length shows how much heat is being released to the
o ood chains and the biomass o higher trophic levels. environment by dierent parts o its body
Biomass is the total mass o a group o organisms. It consists o the cells and Figure 7 The osprey (Pandion halietus) is a
tissues o those organisms, including the carbohydrates and other carbon fsh-eating top carnivore
compounds that they contain. Because carbon compounds have chemical
energy, biomass has energy. Ecologists can measure how much energy is 217
added per year by groups o organisms to their biomass. The results are
calculated per square metre o the ecosystem so that dierent trophic levels
can be compared. When this is done, the same trend is always ound:
the energy added to biomass by each successive trophic level is less. In
secondary consumers, or example, the amount o energy is always less per
year per square metre o ecosystem than in primary consumers.
The reason or this trend is loss o energy between trophic levels.
Most o the energy in ood that is digested and absorbed by
organisms in a trophic level is released by them in respiration or
41 E co lo g y
activity use in cell activities. It is thereore lost as heat. The only energy
available to organisms in the next trophic level is chemical energy in
Slmon nd soy carbohydrates and other carbon compounds that have not been used
up in cell respiration.
Most salmon eaten by
humans is produced in sh The organisms in a trophic level are not usually entirely consumed
arms. The salmon have by organisms in the next trophic level. For example, locusts
traditionally been ed on sometimes consume all the plants in an area but more usually only
sh meal, mostly based on parts o some plants are eaten. Predators may not eat material rom
anchovies harvested othe the bodies o their prey such as bones or hair. E nergy in uneaten
coast oSouth America. These material passes to saprotrophs or detritivores rather than passing to
have become scarce and organisms in the next trophic level.
expensive. Feeds based on
plant products such as soy Not all parts o ood ingested by the organisms in a trophic level are
beans are increasingly being digested and absorbed. Some material is indigestible and is egested
used. In terms oenergy ow, in eces. Energy in eces does not pass on along the ood chain and
which othese human diets is instead passes to saprotrophs or detritivores.
most and least efcient?
Because o these losses, only a small proportion o the energy in
1 Salmon ed on sh meal the biomass o organisms in one trophic level will ever become part o
the biomass o organisms in the next trophic level. The fgure o 1 0% is
2 Salmon ed on soy beans oten quoted, but the level o energy loss between trophic levels is
variable. As the losses occur at each stage in a ood chain, there is less and
3 Soy beans. less energy available to each successive trophic level. Ater only a ew
stages in a ood chain the amount o energy remaining would not be
enough to support another trophic level. For this reason the number o
trophic levels in ood chains is restricted.
Biomass, measured in grams, also diminishes along ood chains, due
to loss o carbon dioxide and water rom respiration and loss rom the
ood chain o uneaten or undigested parts o organisms. The biomass
o higher trophic levels is thereore usually smaller than that o lower
levels. There is generally a higher biomass o producers, the lowest
trophic level o all, than o any other trophic level.
decomposers secondary consumer Pyramids of energy
(16,000 kJ m2 yr1) (200 kJ m2 yr1)
Quantitative representations oenergy ow using
primary consumer pyramids oenergy.
(2,500 kJ m2 yr1)
The amount o energy converted to new biomass by each trophic level in
plankton an ecological community can be represented with a pyramid o energy.
(150,000 kJ m2 yr1) This is a type o bar chart with a horizontal bar or each trophic level.
The amounts o energy should be per unit area per year. Oten the units
Figure 8 An energy pyramid for an aquatic are kilojoules per metre squared per year (kJ m-2 yr-1) . The pyramid
ecosystem (not to scale) should be stepped, not triangular, starting with the producers in the
lowest bar. The bars should be labelled producer, frst consumer, second
secondary consumer consumer and so on. I a suitable scale is chosen, the length o each bar
(3,000 MJ m2 yr1) can be proportional to the amount o energy that it shows.
primary consumer Figure 8 shows an example o a pyramid o energy or an aquatic
(7,000 MJ m2 yr1) ecosystem. To be more accurate, the bars should be drawn with relative
widths that match the relative energy content at each trophic level. Figure
producers 9 shows a pyramid o energy or grassland, with the bars correctly to scale.
(50,000 MJ m2 yr1)
Figure 9 Pyramid of energy for grassland
218
4.2 enerGy Flow
dt-bs qustis: a simple food web
A sinkhole is a surace eature which orms when an underground
cavern collapses. Montezuma Well in the Sonoran desert in Arizona is
a sinkhole flled with water. It is an aquatic ecosystem that lacks fsh,
due in part to the extremely high concentrations o dissolved CO2. The
dominant top predator is Belostoma bakeri, a giant water insect that can
grow to 70 mm in length.
Figure 1 0 shows a ood web or Montezuma Well.
1 C ompare the roles o Belostoma bakeri and Ranatra montezuma
within the ood web. [2]
2 Deduce, with a reason, which organism occupies more [2]
than one trophic level.
3 Deduce using P values:
a) what would be the most common ood chain in this web [2]
b) what is the preerred prey o B. bakeri? [1 ]
4 Construct a pyramid o energy or the frst and second
trophic levels. [3]
5 Calculate the percentage o energy lost between the frst and
second trophic levels. [2]
6 Discuss the difculties o classiying organisms into [2]
trophic levels.
7 Outline the additional inormation that would be required to [1 ]
complete the pyramid o energy or the third and ourth
trophic level.
Ranatra montezuma Belostoma bakeri
235,000 kJ ha1 yr1 588,000 kJ ha1 yr1
P = 1.0 gm2 yr1 P = 2.8 gm2 yr1
Telebasis salva
1,587,900 kJ ha1 yr1
P = 7.9 gm2 yr1
Hyalella montezuma
30,960,000 kJ ha1 yr1
P = 215 gm2 yr1
phytoplankton - Metaphyton piphyton
234,342,702 kJ ha1 yr1 427,078,320 kJ ha1 yr1
P = 602 g C m2 yr1 P = 1,096 g C m2 yr1
Figure 10 A food web for Montezuma Well. P values represent the biomass stored
in the population of that organism each year. Energy values represent the energy
equivalent of that biomass. Arrows indicate trophic linkages and arrow thickness
indicates the relative amount of energy transferred between trophic levels
219
14 E co lo g y
4.3 carbon yling
Understanding Appliations
Autotrophs convert carbon dioxide into Estimation o carbon fuxes due to processes in
carbohydrates and other carbon compounds. the carbon cycle.
In aquatic habitats carbon dioxide is present as Analysis o data rom atmosphere monitoring
a dissolved gas and hydrogen carbonate ions. stations showing annual fuctuations.
Carbon dioxide diuses rom the atmosphere or Skills
water into autotrophs.
Construct a diagram o the carbon cycle.
Carbon dioxide is produced by respiration and
diuses out o organisms into water or the Nature o siene
atmosphere.
Making accurate, quantitative measurements:
Methane is produced rom organic matter it is important to obtain reliable data on the
in anaerobic conditions by methanogenic concentration o carbon dioxide and methane
archaeans and some diuses into the in the atmosphere.
atmosphere.
Methane is oxidized to carbon dioxide and
water in the atmosphere.
Peat orms when organic matter is not ully
decomposed because o anaerobic conditions
in waterlogged soils.
Partially decomposed organic matter rom past
geological eras was converted into oil and gas
in porous rocks or into coal.
Carbon dioxide is produced by the combustion
o biomass and ossilized organic matter.
Animals such as ree-building corals and molluscs
have hard parts that are composed ocalcium
carbonate and can become ossilized in limestone.
carbon fxation
Autotrophs convert carbon dioxide into carbohydrates
and other carbon compounds.
Autotrophs absorb carbon dioxide from the atmosphere and convert
it into carbohydrates, lipids and all the other carbon compounds
that they require. This has the effect of reducing the carbon dioxide
concentration of the atmosphere. The mean CO2 concentration of the
atmosphere is currently approximately 0.039% or 390 micromoles per
mole (mol/mol) but it is lower above parts of the Earths surface where
photosynthesis rates have been high.
220
4.3 carBon cyclinG
dt-bse quests: Carbon dioxide concentration
The two maps in fgure 1 were produced 4 a) Deduce the part o the Earth that had the
by NASA. They show the carbon dioxide
concentration o the atmosphere eight kilometres lowest mean carbon dioxide concentration
above the surace o the Earth, in May and
October 201 1 . between May and October 201 1 . [1 ]
1 State whether October is in the spring or b) Suggest reasons or the carbon dioxide
all(autumn) in the southern hemisphere. [1 ] concentration being lowest in this area. [2 ]
2 a) Distinguish between carbon dioxide [1 ]
concentrations in May and October
in the northern hemisphere.
b) Suggest reasons or the dierence. [2]
3 a) Distinguish between the carbon
dioxide concentrations in May between
the northern and the southern
hemisphere. [1 ]
b) Suggest reasons or the dierence. [2 ] Figure 1
carbon dioxide in solution
In aquatic habitats carbon dioxide is present as a
dissolved gas and hydrogen carbonate ions.
C arbon dioxide is soluble in water. It can either remain in water as atvt
a dissolved gas or it can combine with water to orm carbonic acid pH hges k ps
(H2CO3) . Carbonic acid can dissociate to orm hydrogen and hydrogen Ecologists have monitored
pH in rock pools on sea
carbonate ions (H+ and H C O - ) . This explains how carbon dioxide can shores that contain animals
3 and also photosynthesizing
algae. The pH o the
reduce the pH o water. water rises and alls in
a 24-hour cycle, due to
Both dissolved carbon dioxide and hydrogen carbonate ions are absorbed changes in carbon dioxide
by aquatic plants and other autotrophs that live in water. They use them concentration in the water.
to make carbohydrates and other carbon compounds. The lowest values o about
pH 7 have been ound during
Absorption of arbon dioxide the night, and the highest
values o about pH 10 have
Carbon dioxide difuses rom the atmosphere or water been ound when there was
into autotrophs. bright sunlight during the
day. What are the reasons or
Autotrophs use carbon dioxide in the production o carbon compounds these maxima and minima?
by photosynthesis or other processes. This reduces the concentration The pH in natural pools or
o carbon dioxide inside autotrophs and sets up a concentration articial aquatic mesocosms
gradient between cells in autotrophs and the air or water around. could be monitored using
Carbon dioxide thereore diuses rom the atmosphere or water into data loggers.
autotrophs.
221
In land plants with leaves this diusion usually happens through
stomata in the underside o the leaves. In aquatic plants the entire
surace o the leaves and stems is usually permeable to carbon dioxide,
so diusion can be through any part o these parts o the plant.
14 E co lo g y
Release of carbon dioxide from cell respiration
Carbon dioxide is produced by respiration and difuses out
o organisms into water or the atmosphere.
Carbon dioxide is a waste product o aerobic cell respiration. It is
produced in all cells that carry out aerobic cell respiration. These can be
grouped according to trophic level o the organism:
non-photosynthetic cells in producers or example root cells in plants
animal cells
saprotrophs such as ungi that decompose dead organic matter.
Carbon dioxide produced by respiration diuses out o cells and passes
into the atmosphere or water that surrounds these organisms.
data-base questions: Data-logging pH in an aquarium
Figure 2 shows the pH and light intensity pH sensor (pH) light intensity 100
in an aquarium containing a varied 7.50 pH 90
community o organisms including 80
pondweeds, newts and other animals. 7.45 light intensity /arbitrary units
The data was obtained by data logging
using a pH electrode and a light meter. 70
The aquarium was illuminated articially
to give a 24-hour cycle o light and dark 7.40 60
using a lamp controlled by a timer.
50
7.35 40
1 Explain the changes in light 30
intensity during the experiment. [2]
7.30 20
10
2 Determine how many days the 7.25 0
6.02:45:09
data logging covers. [2] 0.14:02:31 0.23:13:11 3.08:23:50 4.17:34:30
06 February 2013 14:02:31 absolute time (d.hh:mm:ss)
3 a) Deduce the trend in pH in
Figure 2
the light. [1 ]
4 a) Deduce the trend in pH in darkness. [1 ]
b) Explain this trend. [2] b) Explain this trend. [2]
Methanogenesis
Methane is produced rom organic matter in anaerobic
conditions by methanogenic archaeans and some
difuses into the atmosphere.
In 1 776 Alessandro Volta collected bubbles o gas emerging rom mud in
a reed bed on the margins o Lake Maggiore in Italy, and ound that it
was infammable. He had discovered methane, though Volta did not give
it this name. Methane is produced widely in anaerobic environments, as
it is a waste product o a type o anaerobic respiration.
Three dierent groups o anaerobic prokaryotes are involved.
1 Bacteria that convert organic matter into a mixture o organic acids,
alcohol, hydrogen and carbon dioxide.
222
4.3 carBon cyclinG
2 Bacteria that use the organic acids and alcohol to produce acetate, Figure 3 Waterlogged woodlanda typical
carbon dioxide and hydrogen. habitat for methanogenic prokaryotes
3 Archaeans that produce methane rom carbon dioxide, hydrogen and
acetate. They do this by two chemical reactions:
CO2 + 4H2 CH4 + 2H2O
CH COOH CH + CO
3 42
The archaeans in this third group are thereore methanogenic. They
carry out methanogenesis in many anaerobic environments:
Mud along the shores and in the bed o lakes.
Swamps, mires, mangrove orests and other wetlands where the soil
or peat deposits are waterlogged.
Guts o termites and o ruminant mammals such as cattle and sheep.
Landfll sites where organic matter is in wastes that have been
buried.
Some o the methane produced by archaeans in these anaerobic
environments diuses into the atmosphere. Currently the concentration
in the atmosphere is between 1 .7 and 1 .85 micromoles per mole.
Methane produced rom organic waste in anaerobic digesters is not
allowed to escape and instead is burned as a uel.
oxidatin f methane
Methane is oxidized to carbon dioxide and water
in the atmosphere.
Molecules o methane released into the atmosphere persist there
on average or only 1 2 years, because it is naturally oxidized in
the stratosphere. Monatomic oxygen (O) and highly reactive
hydroxyl radicals (OH) are involved in methane oxidation. This
explains why atmospheric concentrations are not high, despite large
amounts o production o methane by both natural processes and
human activities.
Peat frmatin Figure 4 Peat deposits form a blanket on a
boggy hill top at Bwlch Groes in North Wales
Peat forms when organic matter is not fully decomposed
because of anaerobic conditions in waterlogged soils.
In many soils all organic matter such as dead leaves rom plants is
eventually digested by saprotrophic bacteria and ungi. Saprotrophs
obtain the oxygen that they need or respiration rom air spaces
in the soil. In some environments water is unable to drain out
o soils so they become waterlogged and anaerobic. Saprotrophs
cannot thrive in these conditions so dead organic matter is not ully
decomposed. Acidic conditions tend to develop, urther inhibiting
saprotrophs and also methanogens that might break down the
organic matter.
223
14 E co lo g y
data-base questions: Release of carbon from tundra soils
Soils in tundra ecosystems typically contain large either 7 or 1 5C. Some samples were kept moist (M)
amounts o carbon in the orm o peat. This and others were saturated with water (W) . The
accumulates because o low rates o decomposition initial carbon content o the soils was measured
o dead plant organic matter by saprotrophs. To and the amount o carbon dioxide given o during
investigate this, ecologists collected samples o soil the experiment was monitored. The bar chart in
rom areas o tussock vegetation near Toolik Lake fgure 5 shows the results.
in Alaska. Some o the areas had been ertilized
with nitrogen and phosphorus every year or the 1 a) State the eect o increasing the [2]
previous eight years (TF) and some had not (TC). temperature o the soils on the rate
The soils were incubated or 1 00-day periods at o release o carbon.
40 b) Explain the reasons or this eect. [2]
TC 2 a) Compare the rates o release o carbon in
30 TF
percentage of initial C moist soils with those in soils saturated
with water. [2]
20 b) Suggest reasons or the dierences. [2]
10 3 Outline the eects o ertilizers on rates o
0 release o carbon rom the soils. [2]
7M
4 Discuss whether dierences in temperature,
Figure 5
amount o water in the soil or amount o
7W 15M 15W ertilizer have the greatest impact on the
treatment group
release o carbon. [2]
Large quantities o partially decomposed organic matter have
accumulated in some ecosystems and become compressed to orm a dark
brown acidic material called peat. About 3% o the Earths land surace
is covered by peat and as the depth is ten metres or more in some places,
the total quantities o this material are immense.
Figure 6 Coal at a power station Fossilized organic matter
224 Partially decomposed organic matter from past geological
eras was converted into oil and gas in porous rocks or
into coal.
Carbon and some compounds o carbon are chemically very stable and
can remain unchanged in rocks or hundreds o millions o years. There
are large deposits o carbon rom past geological eras. These deposits are
the result o incomplete decomposition o organic matter and its burial
in sediments that became rock.
Coal is ormed when deposits o peat are buried under other
sediments. The peat is compressed and heated, gradually turning into
coal. Large coal deposits were ormed during the Pennsylvanian sub-
period o the Carbonierous. There was a cycle o sea level rises and
alls; coastal swamps ormed as the level ell and were destroyed and
buried when the level rose and the sea spread inland. Each cycle has
let a seam o coal.
4.3 carBon cyclinG
Oil and natural gas are ormed in the mud at the bottom o seas and
lakes. Conditions are usually anaerobic and so decomposition is oten
incomplete. As more mud or other sediments are deposited the partially
decomposed matter is compressed and heated. C hemical changes occur,
which produce complex mixtures o liquid carbon compounds or gases.
We call these mixtures crude oil and natural gas. Methane orms the
largest part o natural gas. Deposits are ound where there are porous
rocks that can hold them such as shales and also impervious rocks
above and below the porous rocks that prevent the deposits escape.
combustion Figure 7 Carbon dioxide is released by
combustion of the leaves of sugar cane
Carbon dioxide is produced by the combustion of biomass
and fossilized organic matter. Figure 8 Kodonophylluma Silurian coral, in
limestone from Wenlock Edge. The calcium
I organic matter is heated to its ignition temperature in the presence carbonate skeletons of the coral are clearly
o oxygen it will set light and burn. The oxidation reactions that occur visible embedded in more calcium carbonate
are called combustion. The products o complete combustion are carbon that precipitated 420 million years ago in
dioxide and water. shallow tropical seas
In some parts o the world it is natural or there to be periodic fres in Figure 9 Chalk cliffs on the south coast of
orests or grassland. Carbon dioxide is released rom the combustion o England. Chalk is a form of limestone that
the biomass in the orest or grassland. In these areas the trees and other consists almost entirely of 90-million-year-
organisms are oten well adapted to fres and communities regenerate old shells of tiny unicellular animals called
rapidly aterwards. fo ra m in ife ra
In other areas fres due to natural causes are very unusual, but humans 225
sometimes cause them to occur. Fire is used to clear areas o tropical
rainorest or planting oil palms or or cattle ranching. Crops o sugar
cane are traditionally burned shortly beore they are harvested. The dry
leaves burn o, leaving the harvestable stems.
Coal, oil and natural gas are dierent orms o ossilized organic
matter. They are all burned as uels. The carbon atoms in the carbon
dioxide released may have been removed rom the atmosphere by
photosynthesizing plants hundreds o millions o years ago.
limestone
Animals such as reef-building corals and molluscs have
hard parts that are composed of calcium carbonate and
can become fossilized in limestone.
Some animals have hard body parts composed o calcium carbonate
( C aC O 3) :
mollusc shells contain calcium carbonate;
hard corals that build rees produce their exoskeletons by secreting
calcium carbonate.
When these animals die, their sot parts are usually decomposed
quickly. In acid conditions the calcium carbonate dissolves away but in
neutral or alkaline conditions it is stable and deposits o it rom hard
animal parts can orm on the sea bed. In shallow tropical seas calcium
14 E co lo g y
carbonate is also deposited by precipitation in the water. The result is
limestone rock, where the deposited hard parts o animals are oten
visible as ossils.
Approximately 1 0% o all sedimentary rock on Earth is limestone. About
1 2% o the mass o the calcium carbonate is carbon, so huge amounts o
carbon are locked up in limestone rock on Earth.
carbon yle diagrams Diagrams can be used to represent the carbon
cycle. Text boxes can be used or pools and labeled
Construct a diagram of the carbon cycle. arrows or fuxes. Figure 1 0 shows an illustrated
diagram which can be converted to a diagram o
Ecologists studying the carbon cycle and the text boxes and arrows.
recycling o other elements use the terms pool and
fux. Figure 1 0 only shows the carbon cycle or
terrestrial ecosystems. A separate diagram could
A pool is a reserve o the element. It can be be constructed or marine or aquatic ecosystems,
organic or inorganic. For example the carbon or a combined diagram or all ecosystems. In
dioxide in the atmosphere is an inorganic pool marine and aquatic ecosystems, the inorganic
o carbon. The biomass o producers in an reserve o carbon is dissolved carbon dioxide
ecosystem is an organic pool. and hydrogen carbonate, which is absorbed by
producers and by various means is released back
A fux is the transer o the element rom into the water.
one pool to another. An example o carbon
fux is the absorption o carbon dioxide
rom the atmosphere and its conversion by
photosynthesis to plant biomass.
CO2 in
cell respiration atmosphere photosynthesis
in saprotrophs in pcreoldl urecseprsiration
and detritivores
combustion of fossil fuels cell respiration carbon in
in consumers organic
compounds
in producers
death
carbon in dead egestion fe e d i n g
organic matter
incomplete
decomposition
and fossilization
of organic matter
coal oil and gas
Figure 10 Carbon cycle
226
4.3 carBon cyclinG
carbon fuxes
Estimation o carbon fuxes due to processes in the carbon cycle.
The carbon cycle diagram in gure 1 0 shows Pess F u x/g g t es
processes that transer carbon rom one pool to e - 1
another but it does not show the quantities o these Photosynthesis
fuxes. It is not possible to measure global carbon Cell respiration 120
fuxes precisely but as these quantities are o great Ocean uptake 119.6
interest, scientists have produced estimates or Ocean loss
them. Estimates are based on many measurements Deorestation and land use 92.8
in individual natural ecosystems or in mesocosms. changes 90.0
Burial in marine sediments
Global carbon fuxes are extremely large so Combustion o ossil uels 1.6
estimates are in gigatonnes (petagrams) . One
gigatonne is 1 ,01 5 grams. Table 1 shows estimates Table 1 0.2
based on Ocean Biogeochemical Dynamics, Sarmiento 6.4
and Gruber, 2006, Princeton University Press.
dt-bse quests: Oak woodland and carbon dioxide concentrations
Carbon fuxes have been measured since 1 998 in 1 Calculate whether the carbon pool in the
deciduous woodland at Alice Holt Research Forest biomass o the orest increases or decreases
in E ngland. The trees are mainly oaks, Quercus on more days in the year. [1 ]
robur and Quercus petraea, with some ash, Fraxinus 2 Deduce the months in which the carbon pool
excelsior. They were planted in 1 93 5 and are now
nearly 20 metres tall. o biomass in the orest was highest
and lowest. [2]
Carbon dioxide concentrations are measured 3 Explain the reasons or increases in the [4]
20 times a second. From these measurements carbon pool o biomass in the orest
the net ecosystem production can be deduced. during part o the year and decreases in
This is the net fux o carbon dioxide between other parts.
the orest and the atmosphere. Positive values
indicate an increase in the carbon pool o 4 State the annual carbon fux to or rom the
the orest and negative values indicate a orest. [2]
decrease due to net loss o carbon dioxide. The 5 Suggest a reason based on the data or [1 ]
graph shows the daily average net ecosystem encouraging the planting o more
production or several years and also the oak orests.
cumulative net ecosystem production.
20 25
20
15
15
10
10
daily average NEP (kg CO2 ha1 h1)
cumulative NEP (t CO2 ha1)
55
0
0 0 50 100 150 200 250 300 530
5
5 10
10 15
day ofyear
227
14 E co lo g y
Environmental monitoring
Making accurate, quantitative measurements: it is important to obtain reliable data
on the concentration o carbon dioxide and methane in the atmosphere.
Carbon dioxide and methane concentrations carbon dioxide concentrations to rise rom
in the atmosphere have very important 397 micromoles per mole in 201 4 to a level
eects. Carbon dioxide concentrations aect above 600 by the end o the century.
photosynthesis rates and the pH o seawater. B oth
gases infuence global temperatures and as a result Reliable data are an essential prerequisite or
the extent o ice sheets at the poles. Indirectly evaluating hypotheses and predictions such as
they thereore aect sea levels and the position o these. Reliable measurements o atmospheric
coast lines. Through their eects on the amount carbon dioxide and methane concentration are
o heat energy in the oceans and the atmosphere needed over as long a period as possible beore
they aect ocean currents, the distribution o we can evaluate the past and possible uture
rainall and also the requency and severity o consequences o human activity.
extreme weather events such as hurricanes.
Data on concentrations o gases in the atmosphere
Consider these hypotheses and predictions: is collected by the Global Atmosphere Watch
programme o the World Meteorological
The carbon dioxide concentration o the Organization, an agency o the United Nations.
atmosphere is currently higher than at any Research stations in various parts o the world
time in the past twenty million years. now monitor the atmosphere, but Mauna Loa
Observatory on Hawaii has records rom the
Human activities have increased the carbon longest period. Carbon dioxide concentrations
dioxide and methane concentrations in the have been measured rom 1 959 onwards and
Earths atmosphere. methane rom 1 984. These and other reliable
records are o immense value to scientists.
Human activity will cause atmospheric
Trends in atmospheric carbon dioxide
Analysis o data rom atmosphere
monitoring stations showing
annual fuctuations.
Data rom atmosphere monitoring stations is
reely available allowing any person to analyse
it. There are both long-term trends and annual
fuctuations in the data. The Mauna Loa
Observatory in Hawaii produces vast amounts
o data and data rom this and other monitoring
stations are available or analysis.
Figure 11 Hawaii from space. Mauna Loa is near the
centre of the largest island
228
4.4 climate cHanGe
4.4 c hg
Understandin Applications
Carbon dioxide and water vapour are the most Correlations between global temperatures and
signicant greenhouse gases. carbon dioxide concentrations on Earth.
Other gases including methane and nitrogen Evaluating claims that human activities are not
oxides have less impact. causing climate change.
The impact o a gas depends on its ability to Threats to coral rees rom increasing
absorb long-wave radiation as well as on its concentrations o dissolved carbon dioxide.
concentration in the atmosphere.
Nature of science
The warmed Earth emits longer-wave radiation
(heat) . Assessing claims: assessment o the claims
that human activities are not causing climate
Longer-wave radiation is reabsorbed by change.
greenhouse gases which retains the heat in the
atmosphere.
Global temperatures and climate patterns are
infuenced by concentrations o greenhouse
gases.
There is a correlation between rising atmospheric
concentrations o carbon dioxide since the start
o the industrial revolution two hundred years ago
and average global temperatures.
Recent increases in atmospheric carbon
dioxide are largely due to increases in the
combustion o ossilized organic matter.
greenhouse ases
Carbon dioxide and water vapour are the most signicant
greenhouse gases.
The Earth is kept much warmer than it otherwise would be by gases
in the atmosphere that retain heat. The effect of these gases has been
likened to that of the glass that retains heat in a greenhouse and they are
therefore known as greenhouse gases, though the mechanism of heat
retention is not the same.
The greenhouse gases that have the largest warming effect on the Earth
are carbon dioxide and water vapour.
Carbon dioxide is released into the atmosphere by cell respiration
in living organisms and also by combustion of biomass and fossil
229
14 E co lo g y
uels. It is removed rom the atmosphere by photosynthesis and by
dissolving in the oceans.
Water vapour is ormed by evaporation rom the oceans and also
transpiration in plants. It is removed rom the atmosphere by rainall
and snow.
Water continues to retain heat ater it condenses to orm droplets o
liquid water in clouds. The water absorbs heat energy and radiates it
back to the Earths surace and also refects the heat energy back. This
explains why the temperature drops so much more quickly at night in
areas with clear skies than in areas with cloud cover.
Figure 1 Satellite image of Hurricane Andrew in other greenhuse gases
the Gulf of Mexico. Hurricanes are increasing in
frequency and intensity as a result of increases Other gases including methane and nitrogen oxides have
in heat retention by greenhouse gases less impact.
Although carbon dioxide and water vapour are the most signicant
greenhouse gases there are others that have a smaller but nonetheless
signicant eect.
Methane is the third most signicant greenhouse gas. It is emitted
rom marshes and other waterlogged habitats and rom landll
sites where organic wastes have been dumped. It is released during
extraction o ossil uels and rom melting ice in polar regions.
Nitrous oxide is another signicant greenhouse gas. It is released
naturally by bacteria in some habitats and also by agriculture and
vehicle exhausts.
The two most abundant gases in the Earths atmosphere, oxygen and
nitrogen, are not greenhouse gases as they do not absorb longer-wave
radiation. All o the greenhouse gases together thereore make up less
than 1 % o the atmosphere.
Assessing the impact f greenhuse gases
The impact of a gas depends on its ability to absorb
long-wave radiation as well as on its concentration in the
atmosphere.
Two actors together determine the warming impact o a greenhouse gas:
how readily the gas absorbs long-wave radiation; and
the concentration o the gas in the atmosphere.
For example, methane causes much more warming per molecule
than carbon dioxide, but as it is at a much lower concentration in the
atmosphere its impact on global warming is less.
The concentration o a gas depends on the rate at which it is released
into the atmosphere and how long on average it remains there. The rate
at which water vapour enters the atmosphere is immensely rapid, but it
remains there only nine days on average, whereas methane remains in
the atmosphere or twelve years and carbon dioxide or even longer.
230
4.4 climate cHanGe
lon-waveenth emissions from Earth TOK
The warmed Earth emits longer-wave radiation. Qusos xs bou h ry
o sf phoo. wh
The warmed surface of the Earth absorbs short-wave energy from the osqus gh hs hv or h
sun and then re-emits it, but at much longer wavelengths. Most of the pub prpo d udrsdg
re-emitted radiation is infrared, with a peak wavelength of 1 0,000 nm. o s?
The peak wavelength of solar radiation is 400 nm.
Much o what science investigates
Figure 2 shows the range of wavelengths of solar radiation that pass involves entities and concepts beyond
through the atmosphere to reach the Earths surface and warm it (red) everyday experience o the world,
and the range of much longer wavelengths emitted by the Earth that such as the nature and behaviour
pass out through the atmosphere (blue) . The smooth red and blue curves o electromagnetic radiation or the
show the range of wavelengths expected to be emitted by bodies of the build-up o invisible gases in the
temperature of the Earth and the sun. atmosphere. This makes it difcult
or scientists to convince the general
spectral intensity public that such phenomenon
actually exist particularly when
the consequences o accepting their
existance might run counter to value
systems or entrenched belies.
UV Visible I n fra re d
0.2
1 10 70
wavelength (m)
Figure 2
greenhouse ases
Longer-wave radiation is reabsorbed by greenhouse gases which retains
the heat in the atmosphere.
2530% of the short-wavelength radiation from A far higher percentage of the longer-wavelength
the sun that is passing through the atmosphere radiation re-emitted by the surface of the Earth is
is absorbed before it reaches the Earths surface. absorbed before it has passed out to space. Between
Most of the solar radiation absorbed is ultraviolet 70% and 85% is captured by greenhouse gases in
light, which is absorbed by ozone. 7075% of solar the atmosphere. This energy is re-emitted, some
radiation therefore reaches the Earths surface and towards the Earth. The effect is global warming.
much of this is converted to heat. Without it the mean temperature at the Earths
surface would be about 1 8C.
Key
short-wave radiation
from the sun
long-wave radiation
from earth
Figure 3 The greenhouse efect
231
14 E co lo g y
Greenhouse gases in the Earths atmosphere individual gases. The wavelengths re-emitted by
only absorb energy in specifc wavebands. the E arth are between 5 and 70nm. Water vapour,
Figure 4 below shows total percentage absorption carbon dioxide, methane and nitrous oxide all
o radiation by the atmosphere. The graph also absorb some o these wavelengths, so each o them
shows the bands o wavelengths absorbed by is a greenhouse gas.
percent100 Total absorption
and scattering
75 1
10 70
50
25
0
0.2
Water vapour
major components Carbon dioxide
Oxygen and ozone
Methane
0.2 1 10 Nitrous oxide
wavelength (m) 70
Figure 4
global temperatures and carbon dioxide concentrations
Correlations between global temperatures and carbon dioxide concentrations
on Earth.
I the concentration o any o the greenhouse gases Antarctica. During this part o the current Ice Age
in the atmosphere changes, we can expect the there has been a repeating pattern o rapid periods
size o its contribution to the greenhouse eect to o warming ollowed by much longer periods o
change and global temperatures to rise or all. We gradual cooling. There is a very striking correlation
can test this hypothesis using the carbon dioxide between carbon dioxide concentration and global
concentration o the atmosphere, because it has temperatures the periods o higher carbon
changed considerably. dioxide concentration repeatedly coincide with
periods when the Earth was warmer.
To deduce carbon dioxide concentrations and
temperatures in the past, columns o ice have The same trend has been ound in other ice cores.
been drilled in the Antarctic. The ice has built up Data o this type are consistent with the hypothesis
over thousands o years, so ice rom deeper down that rises in carbon dioxide concentration increase
is older than ice near the surace. Bubbles o air the greenhouse eect. It is important always
trapped in the ice can be extracted and analysed to remember that correlation does not prove
to fnd the carbon dioxide concentration. Global causation, but in this case we know rom other
temperatures can be deduced rom ratios o research that carbon dioxide is a greenhouse gas.
hydrogen isotopes in the water molecules. At least some o the temperature variation over
the past 800,000 years must thereore have been
Figure 5 shows results or an 800,000 year period due to rises and alls in atmospheric carbon dioxide
beore the present. They were obtained rom concentrations.
an ice core drilled in Dome C on the Antarctic
plateau by the European Project or Ice Coring in
232
4.4 climate cHanGe
C O 2 /p p m v 300
250
200
ure -380
(temperat - 410 warm
proxy) 9C
D/% -440 cold
0
800,000 600,000 400,000 200,000
age (years before present)
Figure 5 Data from the European Project for Ice Coring in the Antarctic Dome C ice core
d-bs qusos: CO concentrations and global temperatures
2
Figure 6 shows atmospheric carbon dioxide 0.6
concentrations. The red line shows direct temperature anomaly (C) Annual average
measurements at Mauna Loa O bservatory. 0.4 Five year average
The points show carbon dioxide 0.2
concentrations measured rom trapped air in
polar ice cores. 0
380
parts per million by volume 360 Direct measurments -0.2
Ice core measurments -0.4
340
1880 1900 1920 1940 1960 1980 2000
320
Figure 7
300
280 2 Compare the trends in carbon [2]
dioxide concentration and global
260 temperatures between 1 880 and 2008. [1 ]
1750 1800 1850 1900 1950 2000 [1 ]
3 Estimate the change in global average
Figure 6 temperature between [2]
Figure 7 shows a record o global average a) 1 900 and 2000
temperatures compiled by the NASA Goddard b) 1 905 and 2005
Institute or Space Studies. The green points are 4 a) Suggest reasons or global average
annual averages and the red curve is a rolling
ve-year average. The values are given as the temperatures alling or a ew
deviation rom the mean temperature between years during a period with an
1 961 and 1 990. overall trend o rising temperatures.
1 Discuss whether the measurements o [2] b) Discuss whether these alls [2]
carbon dioxide concentration rom indicate that carbon dioxide
ice cores are consistent with direct concentration does not infuence
measurements at Mauna Loa. global temperatures.
233
14 E co lo g y
greenhouse ases and climate patterns
Global temperatures and climate evaporation o water rom the oceans and
patterns are infuenced by thereore periods o rain are likely to be more
concentrations o greenhouse gases. requent and protracted. The amount o rain
delivered during thunderstorms and other intense
The surace o the Earth is warmer than it bursts is likely to increase very signicantly. In
would be with no greenhouse gases in the addition, higher ocean temperatures cause tropical
atmosphere. Mean temperatures are estimated to storms and hurricanes to be more requent and
be 3 2 C higher. I the concentration o any o the more powerul, with aster wind speeds.
greenhouse gases rises, more heat will be retained
and we should expect an increase in global average The consequences o any rise in global average
temperatures. temperature are unlikely to be evenly spread. Not
all areas would become warmer. The west coast
This does not mean that global average o Ireland and Scotland might become colder i
temperatures are directly proportional to the North Atlantic Current brought less warm
greenhouse gas concentrations. Other actors have water rom the Gul Stream to north-west Europe.
an infuence, including Milankovitch cycles in the The distribution o rainall would also be likely to
E arths orbit and variation in sunspot activity. Even change, with some areas becoming more prone
so, increases in greenhouse gas concentrations will to droughts and other areas to intense periods o
tend to cause higher global average temperatures rainall and fooding. Predictions about changes to
and also more requent and intense heat waves. weather patterns are very uncertain, but it is clear
that just a ew degrees o warming would cause very
Global temperatures infuence other aspects proound changes to the Earths climate patterns.
o climate. Higher temperatures increase the
data-base questions: Phenology temperature was obtained rom the records o
35 German climate stations.
Phenologists are biologists who study the timing
o seasonal activities in animals and plants, such as 1 Identiy the year in which:
the opening o tree leaves and the laying o eggs
by birds. Data such as these can provide evidence a) the leaves opened earliest [1 ]
o climate changes, including global warming. [1 ]
b) mean temperatures in March and
The date in the spring when new leaves open on April were at their lowest.
horse chestnut trees ( Aesculus hippocastaneum) has
been recorded in Germany every year since 1 951 . 2 Use the data in the graph to deduce the
Figure 8 shows the dierence between each ollowing:
years date o lea opening and the mean date o
lea opening between 1 970 and 2000. Negative a) the relationship between temperatures in
values indicate that the date o lea opening was
earlier than the mean. The graph also shows the March and April and the date o opening
dierence between each years mean temperature
during March and April and the overall mean o leaves on horse chestnut trees. [1 ]
temperature or these two months. The data or
b) whether there is evidence o global [2]
warming towards the end o the
2 0th century.
4 dierence in mean -15 Figure 8 The relationship
3 temperature / C -10 between temperature and
2 dierence in date of -5 horse chestnut leaf opening
1 leafopening / days in Germany since 1951
0 0
-1 5 Key:
-2 10 temperature
-3 15 leaf opening
-4 2000
1980 1990
1970 year
234
4.4 climate cHanGe
Industrialization and climate change Figure 9 During the industrial revolution
renewable sources of power including
There is a correlation between rising atmospheric wind were replaced with power generated
concentrations o carbon dioxide since the start o the by burning fossil fuels
industrial revolution two hundred years ago and average
global temperatures. TOK
The graph o atmospheric carbon dioxide concentrations over the past wh osus upb
800,000 years shown in gure 5 indicates that there have been large v of rsk?
fuctuations. During glaciations the concentration dropped to as low as In situations where the public is at risk,
1 80 parts per million by volume. During warm interglacial periods they scientists are called upon to advise
rose as high as 300 ppm. The rise during recent times to concentrations governments on the setting opolicies
nearing 400 ppm is thereore unprecedented in this period. or restrictions to oset the risk. Because
scientic claims are based largely on
Atmospheric carbon dioxide concentrations were between 260 and inductive observation, absolute certainty
2 80 ppm until the late 1 8th century. This is when concentrations is difcult to establish. The precautionary
probably started to rise above the natural levels, but as the rise was principle argues that action to protect
initially very slight, it is impossible to say exactly when an unnatural rise the public must precede certainty o
in concentrations began. Much o the rise has happened since 1 950. risk when the potential consequences
or humanity are catastrophic. Principle
In the late 1 8th century the industrial revolution was starting in some 15 othe 1992 Rio Declaration on the
countries but the main impact o industrialization globally was in the Environment and Development stated
second hal o the 2 0th century. More countries became industrialized, the principle in this way:
and combustion o coal, oil and natural gas increased ever more rapidly, Where there are threats oserious or
with consequent increases in atmospheric carbon dioxide concentration. irreversible damage, lack oull scientic
certainty shall not be used as a reason
There is strong evidence or a correlation between atmospheric orpostponing cost-efective measures
carbon dioxide concentration and global temperatures, but as already to prevent environmental degradation.
explained, other actors have an eect so temperatures are not
directly proportional to carbon dioxide concentration. Nevertheless,
since the start o the industrial revolution the correlation between
rising atmospheric carbon dioxide concentration and average global
temperatures is very marked.
Burning fossil fuels
Recent increases in atmospheric carbon dioxide are
largely due to increases in the combustion o ossilized
organic matter.
As the industrial revolution spread rom the late 1 8th century
onwards, increasing quantities o coal were being mined and burned,
causing carbon dioxide emissions. Energy rom combustion o the coal
provided a source o heat and power. D uring the 1 9 th century the
combustion o oil and natural gas became increasingly widespread in
addition to coal.
Increases in the burning o ossil uels were most rapid rom the
1 950s onwards and this coincides with the period o steepest rises
in atmospheric carbon dioxide. It seems hard to doubt the conclusion
that the burning o ossil uels has been a major contributory
actor in the rise o atmospheric carbon dioxide concentrations to higher
levels than experienced on Earth or more than 800,000 years.
235
14 E co lo g y
data-base questions: Comparing CO emissions were higher in the year 2 000: Qatar, United
2
Arab Emirates, Kuwait and Bahrain. Suggest
The bar chart in gure 1 0 shows the cumulative CO
2
emissions rom ossil uels o the European Union
and ve individual countries between 1 950 and reasons or the dierence. [3]
2000. It also shows the total CO emissions including 3 Although cumulative CO2 emissions rom
2 combustion o ossil uels in Indonesia and
orest clearance and other land use changes.
1 Discuss reasons or higher cumulative CO2 Brazil between 1 950 and 2000 were relatively
emissions rom combustion o ossil uels in
low, total C O2 emissions were signicantly
the United States than in Brazil. [3] higher. S uggest reasons or this. [3]
2 Although cumulative emissions between 4 Australia ranked seventh in the world or
1 950 and 2000 were higher in the United
S tates than any other country, there were emissions o CO2 in 2000, but ourth when
our countries in which emissions per capita all greenhouse gases are included. Suggest a
reason or the dierence. [1 ]
30% Figure 10
25% CO2 from fossil fuels
CO2 from fossil fuels & land-use change
percent of world total 20%
15%
10%
5%
0% U.S. EU-25 Russia China Indonesia Brazil
Assessing claims and counter-claims
Assessing claims: assessment of the claims that human activities are not causing
climate change.
Climate change has been more hotly debated than Global climate patterns are very complex
almost any other area o science. A search o the and it is dicult to make predictions about
internet will quickly reveal diametrically opposed the consequences o urther increases in
views, expressed very vocierously. The author greenhouse gas concentrations. There can
Michael Crichton portrayed climate change be tipping points in climate patterns where
scientists as eco-terrorists who were prepared to sudden massive changes occur. This makes
use mass murder to promote their work in his prediction even more dicult.
novel S tate o Fear. What reasons could there The consequences o changes in global climate
be or such erce opposition to climate change patterns could be very severe or humans
science and or what reason do climate change and or other species so many eel that
scientists deend their ndings so vigorously? there is a need or immediate action even
These questions are worth discussing. There are i uncertainties remain in climate change
many actors that could be having an infuence: science. Companies make huge prots rom
Scientists are trained to be cautious about their coal, oil and natural gas and it is in their
claims and to base their ideas on evidence. interests or ossil uel combustion to continue
They are expected to admit when there are to grow. It would not be surprising i they paid
uncertainties and this can give the impression or reports to be written that minimized the
that evidence is weaker than it actually is. risks o climate change.
236
4.4 climate cHanGe
oppsitin t the climate change science
Evaluating claims that human activities are not causing climate change.
Many claims that human activities are not causing Global warming is continuing but not with equal
climate change have been made in newspapers, on increases each year. Humans are emitting carbon
television and on the internet. One example o this is: dioxide by burning ossil uels and there is strong
evidence that carbon dioxide causes warming, so
Global warming stopped in 1 998, yet the claim is not supported by the evidence.
carbon dioxide concentrations have continued
to rise, so human carbon dioxide emissions Claims that human activities are not causing
cannot be causing global warming. climate change will continue and these claims need
to be evaluated. As always in science, we should
This claim ignores the act that temperatures on base our evaluations on reliable evidence. There
Earth are infuenced by many actors, not just is now considerable evidence about emissions o
greenhouse gas concentrations. Volcanic activity greenhouse gases by humans, about the eects o
and cycles in ocean currents can cause signicant these gases and about changing climate patterns.
variations rom year to year. B ecause o such Not all sources on the internet are trustworthy
actors, 1 998 was an unusually warm year and and we need to be careul to distinguish between
also because o them some recent years have been websites with objective assessments based on
cooler than they otherwise would have been. reliable evidence and others that show bias.
d-bs qusos: Uncertainty in temperature rise projections
Figure 1 1 shows computer-generated orecasts 6 AI B
or average global temperatures, based on eight 5 AI T
dierent scenarios or the changes in the emissions 4 AI FI
o greenhouse gases. The light green band includes 3 A2
the ull range o orecasts rom research centres 2 B1
around the world, and the dark green band shows 1 B2
the range o most o the orecasts. Figure 1 2 shows IS92a
orecasts or arctic temperatures, based on two o
the emissions scenarios.
1 Identiy the code or the least optimistic 0
1990 20002010202020302040205020602070208020902100
emissions scenario. [1 ]
Figure 11 Forecast global average temperatures
2 State the minimum and maximum orecasts
or average global temperature change. [2] 7 Discuss whether the uncertainty in temperature
3 Calculate the dierence between the A2 orecasts justies action or inaction. [4]
and B2 orecasts o global average
temperature rise. 8 Discuss whether it is possible to balance
[2] environmental risks with socio-economic
4 Compare the orecasts or arctic and livelihood risks or whether priorities need
temperatures with those or global
average temperatures. to be established. [4]
[2] 7
6 A2
5 Suggest uncertainties, apart rom [2] 5 B2
greenhouse gas emissions, which 4
aect orecasts or average global 3
temperatures over the next 1 00 years. 2
1
6 Discuss how much more condent we can be 0
in orecasts based on data rom a number o 2000 2020 2040 2060 2080 2100
dierent research centres, rather than one. [3 ]
Figure 12 Forecast arctic temperature
237
14 E co lo g y
coral reefs and arbon dioxide
Threats to coral rees rom increasing concentrations o dissolved carbon dioxide.
In addition to its contribution to global warming, make their skeletons. Also, i seawater ceases to
emissions o carbon dioxide are having eects be a saturated solution o carbonate ions, existing
on the oceans. Over 500 billion tonnes o carbon calcium carbonate tends to dissolve, so existing
dioxide released by humans since the start o the skeletons o ree-building corals are threatened.
industrial revolution have dissolved in the oceans. In 201 2 oceanographers rom more than 20
The pH o surace layers o the Earths oceans is countries met in Seattle and agreed to set up a
estimated to have been 8.1 79 in the late 1 8th global scheme or monitoring ocean acidication.
century when there had been little industrialization.
Measurements in the mid-1 990s showed that it had There is already evidence or concerns about
allen to 8.1 04 and current levels are approximately corals and coral rees. Volcanic vents near
8.069. This seemingly small change represents a the island o Ischia in the Gul o Naples have
30% acidication. Ocean acidication will become been releasing carbon dioxide into the water
more severe i the carbon dioxide concentration o or thousands o years, reducing the pH o the
the atmosphere continues to rise. seawater. In the area o acidied water there are
no corals, sea urchins or other animals that make
Marine animals such as ree-building corals that their skeletons rom calcium carbonate. In their
deposit calcium carbonate in their skeletons place other organisms fourish such as sea grasses
need to absorb carbonate ions rom seawater. and invasive algae. This could be the uture o
The concentration o carbonate ions in seawater coral rees around the world i carbon dioxide
is low, because they are not very soluble. continues to be emitted rom burning ossil uels.
Dissolved carbon dioxide makes the carbonate
concentration even lower as a result o some
interrelated chemical reactions. Carbon dioxide
reacts with water to orm carbonic acid, which
dissociates into hydrogen and hydrogen carbonate
ions. Hydrogen ions react with dissolved
carbonate ions, reducing their concentration.
CO2 + H2O H2CO3 H+ + H C O -
3
H+ + C O 2 - H C O -
3 3
I carbonate ion concentrations drop it is more Figure 13 Skeleton ofcalcium carbonate from a reef-building coral
dicult or ree-building corals to absorb them to
activity TOK
Draw a graph o oceanic wht re the potentil impcts of funding bis?
pH rom the 18th century
onwards, using the gures The costs o scientic research is oten met by grant agencies. Scientists submit
given in the text above, and research proposals to agencies, the application is reviewed and i successul,
extrapolate the curve to the research can proceed. Questions arise when the grant agency has a stake in
obtain an estimate o when the study's outcome. Further, grant applications might ask scientists to project
the pH might drop below 7. outcomes or suggest applications o the research beore it has even begun. The
sponsor may und several diferent research groups, suppressing results that
238 run counter to their interests and publishing those that support their industry.
For example, a 2006 review o studies examining the health efects o cell phone
use revealed that studies unded by the telecommunications industry were
statistically least likely to report a signicant efect. Pharmaceutical research,
nutrition research and climate change research are all areas where claims o
unding bias have been prominent in the media.
QueStionS
Questions
1 The total solar energy received by a grassland is Area of tree mortality/km2 4 Warm/dry
5 l05 kJ m-2 yr-1. The net production o the Drought Index 3 long-term average
grassland is 5 1 02 kJ m-2 yr-1 and its gross 2
production is 6 1 02 kJ m-2 yr-1. The total 1
energy passed on to primary consumers is 0
60 kJ m-2 yr-1. Only 1 0 per cent o this energy 1
is passed on to the secondary consumers. 2
3 Cool/moist
a) Calculate the energy lost by plant [2] 2000
respiration. 1500
1000
b) Construct a pyramid o energy or this 500
grassland. [3] 0
1930 1940 1950 1960 1970 1980 1990 2000
Figure 15 Tree mortality and drought index
2 Figure 1 4 shows the energy fow through a a) Identiy the two periods when the drought
temperate orest. The energy fow is shown per
square metre per year (kJ m-2 yr-1) . index remained high or three or more
lost years. [2]
5 , 2 23 ,12 0
b) (i) Compare the beetle outbreaks in the
1 970s and 1 990s. [2]
sunlight (ii) Suggest reasons or the dierences
energy
5,266,800 respiration between the outbreaks. [2]
24,024
Figure 14 c) Predict rates o destruction o spruce
green 172 consumers trees in the uture, with reasons or
plants your answer.
[4]
14,448 storage
decomposers (e.g. wood)
5,036
a) The chart shows that 99.1 7 per cent o the 4 Figure 1 6 shows monthly average carbon
dioxide concentrations or Baring Head, New
Zealand and Alert, Canada.
sunlight energy in the temperate orest is 390
385
lost. Predict with a reason whether a greater CO2 concentration/ppm 380 Key
375 Alert station,
or lesser percentage o sunlight energy 370 Canada
365 Baring Head,
would be lost in desert. [2] 360 New Zealand
355
b) Only a small part o the net production 350
o plants in the temperate orest passes to 345
herbivores. Explain the reasons or this. [2] 340
335
3 Warmer temperatures avour some species 330
o pest, or example the spruce beetle. Since
the rst major outbreak in 1 992, it has killed 76 78 80 82 84 86 88 90 92 94 96 98 00 02 04
approximately 400,000 hectares o trees in year
Alaska and the C anadian Yukon. The beetle
normally needs two years to complete its lie Figure 16
cycle, but it has recently been able to do it in
one year. The graphs in gure 1 5 show the a) Suggest why scientists have chosen such
drought index, a combination o temperatures areas as Mauna Loa, Baring Head and Alert
and precipitation, and the area o spruce trees as the locations or monitoring stations. [1 ]
destroyed annually.
b) Compare the trends illustrated in both
graphs. [2]
c) Explain why the graphs show dierent
patterns. [3]
239
41 e c o lo G y
5 Figure 1 7 shows the concentration o CO2 in the above tundra root taiga
atmosphere, measured in parts per million (ppm) .
ground above
In a orest, concentrations o CO2 change over the ground root
course o the day and change with height. The
soil
top o the orest is reerred to as the canopy.
soil
height/m 320 330 320 310 310 ppm grasslands deciduous forest
30 320
above above
Top forest canopy ground ground
20 soil root root
soil
10 340350 305
360
0 6 330
0
340
350 savannah equatorial forest
12 18 24 above above
time of day / hours gro u n d ground
Figure 17 soil soil
root root
a) (i) State the highest concentration o CO2
reached in the canopy. [1 ]
(ii) Determine the range o concentration
ound in the canopy. [2]
b) (i) State the time o day (or night) Figure 18 The distribution of nitrogen in the three organic
matters compartments for each of six major biomes
when the highest levels o CO2 are
detected. [1 ] a) Deduce what the above ground
compartment consists o in an ecosystem. [1 ]
(ii) The highest levels o CO2 are detected
just above the ground. Deduce two b) State which biome has the largest above
reasons why this is the case. [2] ground compartment. [1 ]
c) Give an example o an hour when CO2 c) Explain why it is difcult to grow crops in
concentrations are reasonably uniorm over
an area where equatorial orest has been
the ull range o heights. [1 ] cleared o its vegetation. [2]
d) State the name o the process carried out
6 Within an ecosystem, nitrogen can be stored by decomposers and detritus eeders that
in one o three organic matter compartments:
above ground, in roots and in the soil. releases CO2 into the atmosphere. [1 ]
Figure 1 8 shows the distribution o nitrogen
in the three organic matter compartments or e) Suggest why most o the nitrogen in a
each o six major biomes.
tundra ecosystem is in the soil. [1 ]
f) Explain why warming due to climate
change might cause a release o CO2 rom
tundra soil. [2]
240
5 EvOLutIOn and BIOdIvErsItY
CIEoLLcioB I O L O G Y
There is overwhelming evidence or the theory comparing their base or amino acid sequences.
that the diversity o lie has evolved, and Species are named and classifed using an
continues to evolve by natural selection. The internationally agreed system.
ancestry o groups o species can be deduced by
5.1 Evidence for evolution
ueig applicio
Evolution occurs when heritable characteristics Comparison o the pentadactyl limb o
o a species change. mammals, birds, amphibians and reptiles
with dierent methods o locomotion.
The ossil record provides evidence or
evolution. Development o melanistic insects in
polluted areas.
Selective breeding o domesticated
animals shows that artifcial selection ne of ciece
can cause evolution.
Looking or patterns, trends and discrepancies:
Evolution o homologous structures by adaptive there are common eatures in the bone
radiation explains similarities in structure when structure o vertebrate limbs despite their
there are dierences in unction. varied use.
Populations o a species can gradually diverge
into separate species by evolution.
Continuous variation across the geographical
range o related populations matches the
concept o gradual divergence.
241
5 Evolution and biodivErsity
Figure 1 Fossils o dinosaurs show there were Evolution in summary
animals on Earth in the past that had diferent
characteristics rom those alive today Evolution occurs when heritable characteristics
of a species change.
There is strong evidence or characteristics o species changing over
time. Biologists call this process evolution. It lies at the heart o a
scientifc understanding o the natural world. An important distinction
should be drawn between acquired characteristics that develop during
the lietime o an individual and heritable characteristics that are
passed rom parent to ospring. Evolution only concerns heritable
characteristics.
The mechanism o evolution is now well understood it is natural
selection. Despite the robustness o evidence or evolution by natural
selection, there is still widespread disbelie among some religious
groups. There are stronger objections to the concept that species can
evolve than to the logic o the mechanism that inevitably causes
evolution. It is thereore important to look at the evidence or
evolution.
Figure 2 Many trilobite species evolved over Evidence from fossils
hundreds o millions o years but the group is
now totally extinct The fossil record provides evidence for evolution.
In the frst hal o the 1 9 th century, the sequence in which layers
or strata o rock were deposited was worked out and the geological
eras were named. It became obvious that the ossils ound in the
various layers were dierent there was a sequence o ossils. In the
2 0th century, reliable methods o radioisotope dating revealed the
ages o the rock strata and o the ossils in them. There has been a
huge amount o research into ossils, which is the branch o science
called palaeontology. It has given us strong evidence that evolution
has occurred.
The sequence in which ossils appear matches the sequence in which
they would be expected to evolve, with bacteria and simple algae
appearing frst, ungi and worms later and land vertebrates later still.
Among the vertebrates, bony fsh appeared about 420 million years
ago (mya) , amphibians 340 mya, reptiles 320 mya, birds 250 mya
and placental mammals 1 1 0 mya.
The sequence also fts in with the ecology o the groups, with
plant ossils appearing beore animal, plants on land beore
animals on land, and plants suitable or insect pollination beore
insect pollinators.
Many sequences o ossils are known, which link together existing
organisms with their likely ancestors. For example, horses, asses
and zebras, members o the genus Equus, are most closely related to
rhinoceroses and tapirs. An extensive sequence o ossils, extending
back over 60 million years, links them to Hyracotherium, an animal
very similar to a rhinoceros.
242
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