C.5 pOpULaTiOn eCOLOgy ( aHL)
actvt 5 Push enter. The calculator selects quadrat 8, 13 and 11.
Note that three quadrats may not be sufcient to be
Us th T-84 to rt rdom umbrs representative o the whole area.
A student has divided a 50 m2 area into 25 quadrats and Screen 1
wants to select three quadrats randomly without bias.
She decides to use her calculator to randomly select the Screen 2
quadrats or her. Figure 1
For steps 1 to 3 below see screen 1
1 On the Ti-84, press the MATH button
2 Scroll over until the PRB button is highlighted
3 Push 5 so that randlnt is selected.
For steps 4 and 5 below see screen 2
4 Type in 1 or the lowest number, 25 or the highest
number and 3 or the number o quadrats. The comma
button is ound above the number 7.
The Lincoln index
Use o the capture-mark-release-recapture method to estimate the population
size o an animal species.
One sampling technique used to determine population density is the Lincoln index or the
capture-mark-release-recapture method.
1 Capture as many individuals as possible in the 3 Release all the marked individuals and
area occupied by the animal population, allow them to settle back into their habitat.
using netting, trapping or careful searching
e.g. careful searching
for banded snails
(Cepaea nemoralis)
4 Recapture as many individuals as possible and count
how many are marked and how many unmarked.
24 marked
2 Mark each individual, without making them 16 unmarked
more visible to predators.
5 Calculate the estimated population size by
e.g. marking the inside
of the snail shell witha using the Lincoln index:
dot of non-toxic paint.
population size = n1 n2
Figure 2 n3
n 1 = number caught and marked initially
n 2 = total number caught on the second occasion
n 3 = number of marked individuals recaptured
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C ECOLOGY AND CONSERVATION
Estimating commercial fsh populations
Analysis o the eect o population size, age and reproductive status on
sustainable fshing practices.
Fish are an important ood resource. Because they population is in decline, then the proportion
are an open access resource on the high seas, the o older fsh will be higher. In addition to
incentives are limited or conservation. population size inormation, the age structure o
the population is important inormation when
An important component o managing fsh is establishing sustainable levels o harvesting.
clear data about fsh populations. The concept Figure 5 shows a technician holding an otolith
o maximum sustainable yield is related to the (ear bone) o a fsh. The otolith contains rings,
sigmoid growth curve. When the population size similar to the rings o a tree, that can be used to
is low, the rate o population growth will increase determine the age o the fsh.
until environmental resistance begins to limit
population size. At point 2 in the graph in fgure 3
the population is growing at its maximum rate.
This is the point at which the maximum sustainable
yield occurs. I fsh were harvested at this rate, then
fshing would be able to continue indefnitely.
Number 3
2 Figure 5
1 There are a number o practices that are
associated with sustainable fshing and each
Time practice is inormed by population size data.
Most practices depend upon international
Figure 3 Population growth curve cooperation.
Figure 4 shows a graph o sustainable yield versus Restrictions exist on the catching o younger
intensity o fshing. I there is no fshing, then the fsh. Regulations or international agreements
yield o fsh would be zero. I there is very high- oten restrict the net mesh size allowing
intensity fshing, it may be that the population younger fsh to escape.
o fsh becomes extinct and there is no yield.
The maximum o the curve in fgure 4 would Quotas are agreed upon or species with low
correspond to point 2 on the S-curve in fgure 3. stocks and moratoria declared on the fshing o
all endangered species.
maximum
Sustainable yield Closed seasons are oten declared to allow
undisturbed breeding and exclusion zones
zero maximum are agreed upon in which all fshing is
banned.
Figure 4 Intensity o fshing
Methods o fshing that are particularly
I a population is growing, then the relative damaging are oten banned, or example drit
number o younger fsh will be higher. I a nets, which catch many species o fsh other
than target species.
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C.5 pOpULaTiOn eCOLOgy ( aHL)
Evaluating methods o determining population size
Evaluating the methods used to estimate the size of commercial stock of marine
resources.
The frst stage in the conservation o fsh is species do not orm shoals. A common method
obtaining reliable estimates o fsh stocks. This or estimating stocks is based on data obtained
is difcult or marine species because most rom fsh catches. The age structure o landed
fsh species are highly mobile and unevenly fsh can be used to estimate population size. The
distributed, so random sampling methods are numbers o the target species o fsh o each age
ineective. Capture-mark-release-recapture are counted. Spawning rates can be deduced,
methods are useul in lakes and rivers, but the rom which estimates o the total can be made.
numbers o recaptured fsh are usually too small Violators o regulations designed to control the
in the open ocean or reliable estimations. Fish age o fsh landed oten do not report what they
can be temporarily stunned and then counted land or they dump the restricted fsh as bycatch
in lakes and rivers with an electric shock, but beore landing so biased estimates might be
not in the ocean. Echo sounders can be used ormed by using age structure as a method o
to estimate the size o shoals o fsh, but many estimating fsh stocks.
The J shaped population growth curve exponential growth
The exponential growth pattern occurs in an ideal, population size
unlimited environment.
time
I a population experiences ideal conditions, than the population will
grow exponentially. A graph o population size over time will resemble Figure 6
a J shape (fgure 6).
relative population density
Figure 7 shows the population growth o a culture o the unicellular
organism Paramecium aurelia, kept in controlled conditions, including 0 2 4 6 8 10 12 14 16 18
a constant supply o ood. The graph illustrates a pattern called the time (days)
sigmoid, or S-shaped, growth curve.
Figure 7 Population growth of a
The S-curve is representative o what happens when a population culture of Paramecium aurelia
colonizes a new habitat. With a low level o environmental resistance,
a population will grow exponentially initially. As the environment
begins to oer resistance, the population reaches a transition point
where the growth rate begins to slow down until it reaches the
carrying capacity.
Factors that infuence population size
The phases shown in the sigmoid curve can be explained
by relative rates of natality, mortality, immigration and
emigration.
With limited environmental resistance, a population will grow exponentially.
At this stage birth rate (natality) is higher than death rate (mortality) .
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C ECOLOGY AND CONSERVATION
As population density increases, various density-dependent actors
begin to limit population growth. Examples o such limiting actors
include competition or resources, a build-up o the toxic by-products o
metabolism, an increase in predation or an increase in the incidence o
disease. The initial result is that natality slows in relation to mortality.
This is the transition phase on the curve, when the slope begins to
decrease. It is important to recognize that the population is still growing
at this point. The plateau phase begins when mortality and natality rates
equal out.
An important variable aecting population size is migration.
Immigration increases the size o a population. As an example, an island
that is close to the mainland will most likely have regular replenishment
o a population through immigration.
Emigration decreases the size o a population. Emigration occurs when
population members leave an area. The Norway lemming (Lemmus
lemmus) is renowned or its emigration patterns rom areas o high
population density or poor habitat. This occurs in seasons with high
population levels.
transitional Where curve slopes
phase downward, mortality
exceeds natality
K
carrying capacity
Data-based questions exponential plateau Natality rate approaches
phase phase mortality rate
Two male and eight emale ring-
necked pheasants were released Mortality rates begin
on Protection Island. Figure 9 to increase
shows how the population grew.
Natality exceeds mortality
a) Explain the changes in
population size: time
i) in the frst our years; [3] sigmoid (s-shaped) population
growth curve
ii) rom year 4 to year 6. [3]
Figure 8
b) Predict with reasons what
population of ring-neckedwould have happened to the Carrying capacity
pheasants /no. of birdspopulation ater year 6. [4]
Population growth slows as a population reaches the
2250 carrying capacity of the environment.
2000
1750 The maximum size o a population that an environment can support is
1500 its carrying capacity. It is represented by the variable K. In the sigmoid
1250 growth pattern, when a population reaches its carrying capacity, the
1000 population will stop growing and natality and mortality will be equal.
This is reerred to as the plateau phase o the S-curve. At this point, an
750 equilibrium population is oten maintained.
500
250 However, some years can see a boom and bust pattern where
populations ar exceed the carrying capacity. Higher rates o mortality
0 will return the population to the carrying capacity o the environment or
01234567 the population may crash well below the carrying capacity.
time /years
Figure 9
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C.5 pOpULaTiOn eCOLOgy ( aHL)
Discussing the actors that infuence population growth
Discussion o the efect o natality, mortality, immigration and emigration
on population size.
The logistic growth curve is a model o population Natality has the greatest impact on population
growth and is somewhat idealized. size. Knowing the age structure is important
when recording natality. Age and health status
There are a number o causes o mortality: can both aect natality rates in dierent ways.
Predicting whether natality rates will rise or
senescence, or death rom age related illness all depends on knowledge o population age
structure.
predation
I a population lacks genetic diversity, then
disease environmental resistance can have a
disproportionately negative eect on population;
injury or example, a relatively disproportionate number
might die in an epidemic. Immigration can
shortage o ood or water diversiy the gene pool and allow some members
o the population to survive the selection pressure.
density independent actors such as In the case o the migrations ound in Norway
earthquakes, volcanic eruption, fre or storms. Lemmings, emigrating individuals are more likely
to be individuals who are weaker and unable to
The impact o mortality on population growth will deend territory; i.e., they have the lowest
depend on the age o the individual; i.e., whether reproductive ftness.
the death occurred beore or ater reproductive
age. While density dependent actors tend to aect
the very young, the old and the weak individuals,
density independent limiting actors aect all
groups equally including the individuals who are
at the peak o their reproductive potential.
Modelling population growth
Modelling the growth curve using a simple organism such as yeast or species
o Lemna.
Population growth can be studied using model
species such as yeast (Saccharomyces cerevisiae) or
duckweed (Lemna sp) .
Duckweed (Lemna sp.) are stemless water plants
(see fgure 1 0) . Each plant grows one to our lea-
like structures called thalli. Duckweeds reproduce
asexually by growing new thalli rom older thalli
and when they reach a certain size, they break
ree rom the parent plant.
A number o experiments are possible: Figure 10 Duckweed (stemless water plant) on pond
together with pond skaters which also inhabit the
What is the carrying capacity o a given surace flm
container?
What conditions o light, nutrients or container
surace area are ideal or population growth?
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C ECOLOGY AND CONSERVATION
Top-down and bottom-up limiting factors
Limiting factors can be top-down or bottom-up.
A limiting actor is an environmental selection pressure that limits
population growth. There are two categories o limiting actor: top-down
and bottom-up.
The population o organisms in an ecosystem can be infuenced by the
availability o resources such as nutrients, ood and space. All such
actors are reerred to as bottom-up limiting actors.
Predation is reerred to as a top-down limiting actor.
A keystone species exerts top-down infuence on its community by
preventing species at lower trophic levels rom monopolizing critical
resources, such as competition or space or ood sources.
Case study of bottom-up and top-down limiting factors
Bottom-up control of algal blooms by shortage of nutrients and top-down
control by herbivory.
The distinction between bottom-up control Nutrient enrichment through human
and top-down control can be illustrated by the activity, known as eutrophication, can have
example o ree-living marine algae growing in a bottom-up impact on the build-up o algae
coral ree communities. Free-living algae blooms populations. Fishing practices which remove
can disrupt coral ree communities by blocking herbivorous ish rom coral rees can have
sunlight and preventing photosynthesis in the a top-down impact on algae populations.
symbiotic zooxanthellae. Coral-ree ecosystems Figure 1 2 summarizes the impacts on coral ree
are generally nutrient- poor. This explains the communities o either actor as well as both
selection pressure or the symbiotic relationship actors in combination.
between zooxanthellae and coral. The absence o
nutrients represents a bottom-up limiting actor to declining coral-reef resiliency
ree-living algae population growth.
I N CR E ASI N G grazing activity (top-down control)
Coral are also populated by grazing sh which sets HUMAN IMPACT high reduced
limits to the growth o ree-living algae blooms.
Parrotsh graze on ree-living algae and thus have declining coral-reef resiliency MASSIVE FORMS OF TURF ALGAE
a top-down limiting eect (gure 1 1 ) . nutrient levels (bottom-up control) CORALS & CRUSTOSE
CORALLINE ALGAE
elevated low
CRUSTOSE FRONDOSE
CO R ALLI N E M ACR O ALG AE
ALGAE
Figure 12
Figure 11 Parrotfsh grazing on algae is an example o
a top-down limiting actor
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C.6 THe niTrOgen anD pHOSpHOrUS CyCLeS (aHL)
C.6 Th to d hoshous ccls (aHL)
Understanding Applications
Nitrogen-fxing bacteria convert atmospheric The impact o waterlogging on the nitrogen
nitrogen to ammonia. cycle.
Rhizobium associates with roots in a Insectivorous plants as an adaptation or low
mutualistic relationship. nitrogen availability in waterlogged soils.
In the absence o oxygen denitriying bacteria Skills
reduce nitrate in the soil.
Drawing and labelling a diagram o the nitrogen
Phosphorus can be added to the phosphorus cycle.
cycle by application o ertilizer or removed by
the harvesting o agricultural crops. Assess the nutrient content o a soil sample.
The rate o turnover in the phosphorus cycle is Nature o science
much lower than the nitrogen cycle.
Assessing risks and benefts o scientifc
Availability o phosphate may become limiting research: agricultural practices can disrupt the
to agriculture in the uture. phosphorus cycle.
Leaching o mineral nutrients rom agricultural
land into rivers causes eutrophication and leads
to increased biochemical oxygen demand.
Nitrogen fxation
Nitrogen-fxing bacteria convert atmospheric nitrogen to
ammonia.
The atmosphere is 78% nitrogen gas in the orm o the diatomic
molecule N2. Nitrogen in this orm cannot be taken up by plants.
Nitrogen would quickly become a limiting actor or ecosystems i it were
not or the bacteria involved in the nitrogen cycle. The bacteria Rhizobium
and Azotobacter can fx nitrogen gas and convert it to ammonia ( NH3) , a
orm that living things can use. Once in this orm, it can be absorbed by
plants and then it can enter ood chains. Other bacteria convert ammonia
to nitrates, another bioavailable orm o nitrogen.
Nitrogen fxation by Rhizobium Figure 1
Rhizobium associates with roots in a mutualistic relationship.
The bacteria o the genus Rhizobium convert atmospheric nitrogen
into a usable organic orm. These bacteria are oten not ree-living but
live in a close symbiotic association in the roots o plants such as the
legume amily. B ecause both organisms beneft, the symbiosis is an
example o mutualism.
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C ECOLOGY AND CONSERVATION
Figure 2 SEM of a root nodule Figure 1 is a photo o root nodules on the roots o white clover, Triolium
Figure 3 repens, caused by the nitrogen-xing bacteria Rhizobium triolii. The
bacteria convert (x) atmospheric nitrogen in the soil to ammonia
(NH3) . The host plant cannot carry out this process itsel, but it is vital or
the production o amino acids, the building blocks o proteins. In return
the plant passes carbohydrates produced during photosynthesis to the
bacteria or use as an energy source.
Rhizobium inect the plant through root hairs, orming an inection
thread, which conveys them rom the entry point to the nodule site.
Once they are within the nodule, they divide repeatedly and swell. The
scanning electron micrograph in gure 2 shows that the outside o the
nodule is composed o plant tissue.
Denitrifcation
In the absence of oxygen, denitrifying bacteria reduce
nitrate in the soil.
The ammonia produced by nitrogen xation is converted to nitrite (NO2)
by the genus o bacteria known as Nitrosomonas. These bacteria have
a double membrane and use electrons gained rom the oxidation o
ammonia to produce energy. Nitrites are produced rom this oxidation.
The energy is used to x carbon dioxide into organic carbon molecules.
This means that Nitrosomonas are a genus o chemoautotrophs as they
use the energy ound in ammonia, an inorganic molecule.
Nitrites are converted to nitrates by the genus o bacteria known as
Nitrobacter ( gure 3 ) . Nitrobacter sp are an example o chemoautotrophs
as they derive energy rom nitrites which are inorganic compounds.
They oxidize nitrites as an energy source or carbon xation and convert
it to nitrates. Nitrate is a orm o nitrogen that is bioavailable to plants.
D enitrication is the reduction o nitrate ( NO3) to nitrogen ( N2) .
D enitriying bacteria, such as Pseudomonas denitrifcans can use oxygen as
an electron acceptor. However, when oxygen is in short supply, instead
o using O2 as an electron acceptor in electron transport, denitriying
bacteria use nitrate as an electron acceptor, releasing gaseous nitrogen as
the product.
When this occurs, the bioavailability o nitrogen within the ecosystem
becomes reduced.
Summary o the nitrogen cycle
Drawing and labelling a diagram of the nitrogen cycle.
The nitrogen cycle is an example o a nutrient cycle. When constructing
nutrient cycle diagrams, also known as systems fow diagrams, three
things are represented: pools, fuxes and processes. Compartments such
as litter, biomass and the atmosphere are reerred to as pools as they
represent concentrations or stores o the nutrient. They are usually
represented by shapes. In some systems fow diagrams, the size o the
stock is indicated by varying the size o the shape.
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C.6 THe niTrOgen anD pHOSpHOrUS CyCLeS (aHL)
Arrows are used to represent the direction o fuxes, or fows, o the Waterlogging leads
nutrient. In some nutrient cycle diagrams, the thickness o arrows is to denitrifcation
used to indicate rates o fow.
The impact of waterlogging
Processes are usually written over fow arrows. on the nitrogen cycle.
nitrogen xation by living nitrogen gas in nitrogen xation by Soil can become inundated
organisms the atmosphere non-living processes by water through fooding or
irrigation with poor drainage.
denitrication e.g. e.g. lightning and The consequence is waterlogging.
Oxygen is in short supply in
by Pseudomonas uptake and the Haber process waterlogged soils. This decreases
denitricans assimilation available aeration and avours
the process o denitrication by
nitrates by plants plant animal Pseudomonas.
NO3
protein transfer of protein Excessive irrigation can then lead
to two problems related to the
nitrication nitrogen in the food nitrogen cycle. I the excess water
fows o the eld and enters water
mutualistic free-living e.g. by nitrifying chain death and courses as runo, the nutrient
bacteria such as decomposition enrichment o the body o water
nitrogen-xing nitrogen-xing Nitrobacter can lead to eutrophication, a
problem discussed later in this
bacteria in root bacteria in the soil, sub-topic. S econdly, waterlogging
can lead to the loss o bioavailable
nodules, e.g. e.g. Azotobacter nitrites nitrogen through denitrication.
Rhizobium
NO2
nitrication decomposers; mainly
bacteria and fungi)
e.g. by nitrifying
bacteria such as
Nitrosomonas ammonia
NH3
Figure 4 The nitrogen cycle, showing the roles o Rhizobium, Azotobacter, Nitrosomonas,
Nitrobacter and Pseudomonas denitrifcans
Carnivorous plants are adapted to low nitrogen soils
Insectivorous plants as an adaptation for low nitrogen availability in waterlogged soils.
Wetlands such as swamps and bogs have
permanently waterlogged soils and would
thereore have nitrogen-decient soils.
One adaptation o bog plants is to become
carnivorous and obtain nitrogen through the
extracellular digestion o animals.
In gure 5, the fy has been attracted by the Figure 5 A hoverfy has been captured by the lea o the
droplets at the tips o the tentacles, which extend carnivorous plant Drosera rotundifolia, the sundew
rom the lea surace. Insects stick to the tips o the
longer tentacles, which bend over bringing them
inward towards the shorter tentacles. Enzymes
secreted by the tentacles digest the animal and the
products are absorbed by the modied lea. Note
that the plant is not truly carnivorous as it obtains
its energy and carbon rom photosynthesis rather
than the tissue o the animal.
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C ECOLOGY AND CONSERVATION
The phosphorus cycle
The rate of turnover in
the phosphorus cycle
is much lower than the
nitrogen cycle.
All living things require
phosphorus to produce molecules
phosphate decomposers runo dissolved such as ATP, D NA and RNA.
in soil and leaching in waterways Phosphorus is required to
maintain skeletons in vertebrates.
plant and Phosphorus is a component o
animal wastes cell membranes as well.
weathering mining plant and Phosphorus cycles through
(phosphate fertilizers animal wastes various orms in a biogeochemical
phosphate cycle depicted in fgure 6.
rocks and detergents) shallow ocean
sediments Phosphorite (fgure 7) is a
geologic uplift sedimentary rock that contains
high levels o phosphate-bearing
deep ocean sediments minerals.
Figure 6 Weathering and erosion o such
rocks releases phosphates into the
soil. Phosphorus in the orm o phosphates is readily taken up by plants,
where it enters ood chains.
The largest stocks o phosphate occur in marine sediments and in
mineral deposits.
Turnover rate reers to the amount o phosphorus released rom one
stock to another per unit time. Phosphate is only slowly released to
ecosystems by weathering and so has a relatively low turnover rate
in comparison to nitrogen.
Figure 7 Efect o agriculture on soil phosphorus
Phosphorus can be added to the phosphorus cycle by
application of fertilizer or removed by the harvesting of
agricultural crops.
Human activity impacts the phosphorus cycle. Phosphate is mined
and converted to phosphate- based ertilizer. The ertilizer is then
transported great distances and applied to crops. Phosphorus in the
biomass o crops is transerred rom felds in one area to markets in
other areas.
Waterlogging o soils in poorly drained irrigated crops can dissolve
phosphate and bring it into solution. Runo containing phosphate
rom ertilizer can contribute to resh water eutrophication.
652
C.6 THe niTrOgen anD pHOSpHOrUS CyCLeS (aHL)
Peak phosphorus
Availability of phosphate may world phosphate rock production 160 106
become limiting to agriculture in (metric tonnes) 140
the future. 120
100
The depletion o phosphate resources that 80
can be mined is a concern because o the 60
role it plays in ertilizer or modern intensive 40
arming practices. Peak phosphorus is the 20
point in time at which the maximum global
phosphate production rate is reached and 1900 1920 1940 1960 1980 2000
then begins to all because o the depletion year
o reserves. Figure 8 shows a graph o world
phosphate rock production against time Figure 8
rom 1 900 to 2009 obtained rom the US
Geological S urvey. This graph suggests that
the point o peak phosphorus production is
approaching.
There is a lack o agreement on the amount
o available phosphate rock reserves though
many agree that the problem will become
acute within 50 to 1 00 years.
Without ertilizer, amine would most certainly result because yields
per unit o armland would plummet without the addition o ertilizer.
There are no alternative sources o phosphate and no synthetic way
o creating it, unlike ammonia which can be created by the industrial
conversion o plentiul supplies o atmospheric nitrogen. Exploring
alternative ways o conducting agriculture and conserving nutrients is
one possible solution.
Eutrophication and biochemical oxygen demand Figure 9 Algal bloom in marshland
by the Thames Estuary, London,
Leaching of mineral nutrients from agricultural land into England
rivers causes eutrophication and leads to increased
biochemical oxygen demand. 653
When rain alls on agricultural land, water-soluble nutrients that have
been added to crops such as phosphates and nitrates can dissolve in the
water and the resulting runo can enter water courses and streams. In
addition to crops, nutrients rom manure and urine o livestock can also
contribute to nutrient enrichment o bodies o water.
The nutrient enrichment o water is known as eutrophication. The nutrients
avour the growth o algae leading to algal blooms (see fgure 9) . The algal
blooms block light to the plants below.
When the mats o algae die and the plants below them die, it leads to a
loss o oxygen, because o bacterial activity on the dead organic matter.
This is called biological oxygen demand (BOD) . The higher the BOD
the more anoxic a body o water becomes and the more limiting the
habitat becomes or certain fsh species.
Eutrophication can also occur due to the release o untreated sewage.
C ECOLOGY AND CONSERVATION
Data-based questions: Sewage release into a river Relative concentrations oxygen
Figure 1 0 shows changes in the biotic and abiotic nitrate
actors at increasing distances rom an untreated
sewage outall into a river.
1 Outline the relationship between distance silt suspended
rom untreated sewage outall and: solids
a) numbers o bacteria [2]
b) oxygen concentrations [2]
c) numbers o algae. [2 ] distance from outfall
2 Explain the relationship between:
algae
a) numbers o bacteria and concentrations
o oxygen [2] Relative numbers
b) numbers o algae and concentrations o protozoa
nitrate [2] bacteria
c) numbers o algae and concentrations o
oxygen. [2]
3 Predict, with reasons, the changes in BOD distance from outfall
o water as it fows downstream rom where Figure 10
untreated sewage enters the river. [3]
Solutions to disruptions to the phosphorus cycle
Assessing risks and benefts o scientifc research: agricultural practices can
disrupt the phosphorus cycle.
Modern agriculture involves the harvesting o phosphorus annually in urine. Many washing
crops and shipping o the crops to markets outside powders also contain phosphates that contributed
o the ecosystem. As a consequence nutrients to the phosphate load in sewage treatment plants,
including phosphate are removed rom the eld but alternative ormulations o detergents have
in the crop biomass and have to be replaced reduced this component o the problem.
by adding ertilizer. D emand or ood due to
population growth and increasing afuence leads One biological solution is the seeding o the
to increasing pressure on the land. Higher levels sludge that settles in sewage treatment plants
o inputs are used to get more produce out o with particular groups o bacteria that selectively
the same area o land. This is known as intensive accumulate phosphorus. The bacterial/sludge
agriculture and it requires even greater inputs mass can then be removed and used as ertilizer.
o ertilizer. C oncerns about the uture limited
availability o phosphate deposits that can be Phosphorus can also be removed by chemical
mined (see section on peak phosphorus) as precipitation with iron chloride or alum. This
well as the ertilizer pollution (see section on can lead to additional quantities o sludge and
eutrophication) are leading scientists to search the chemicals are expensive, but this is a more
or solutions. straightorward solution than biological removal
and gives higher yields o phosphate.
One possible solution to the supply problem is Livestock production can lead to an additional
the recovery o phosphorus rom sewage. People problem associated with the phosphorus cycle.
can excrete between 200 and 1 ,000 grams o Runo that comes in contact with livestock arm
654
C.6 THe niTrOgen anD pHOSpHOrUS CyCLeS (aHL)
manure might result in eventual phosphate Bfts possbl hmul cts
pollution and eutrophication.
1. Less release o 1. Traces o phytase
The development o genetically modifed phosphorus to the in pork might cause
organisms is very expensive, so it is only likely environment in pig allergies in human
to be done i there are clear benefts. The manure. consumers.
EnviropigTM has been proposed as a solution to
the phosphate pollution problem. This pig has 2. Less risk o phosphorus 2. Phytase gene might
been genetically engineered with DNA rom E.
coli to produce phytase in its saliva. This enzyme deciency in growing transer to wild species
digests normally insoluble phytate in pig eed,
leading more phosphate to be absorbed by the pigs. by cross-breeding.
pig and less to be released into the manure o
the pig. 3. Less need to deplete 3. The genetic
world mineral modication might
phosphate reserves cause suering to the
by its use as a dietary pigs in some way that is
supplement in pig eed. unexpected or difcult
to detect.
Soil testing
Assess the nutrient content o a soil sample.
Garden supply companies commonly sell soil quality assessment kits.
The kits involve adding a chemical to a sample o soil that reacts with
the nutrient in question i present. A colour is produced that can be
visually compared to a key or the concentration can be quantifed in a
colorimeter (fgure 1 1 ) .
Soil nutrient defciencies oten produce characteristic symptoms in
leaves. Figure 1 2 summarizes some o these characteristic signs.
a healthy corn plant leaf is deep green
and glossy
a leaf from a plant with nitrogen deciency Figure 11
yellows down the midvein starting at the tip and
moving back towards the stem
a leaf displaying phosphorus deciency
turns red-purple along the leaf margins
a leaf from a potassium-deprived plant features
ring and yellowing along the leaf margins
Figure 12
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C ECOLOGY AND CONSERVATION
TOK
in what ways does technology enhance our ablty to know the world?
The original method o colorimetry involved visually comparing the test sample
to a known colour standard. However, the subjectivity o the perception o the
experimenter, inconsistencies in the light sources, and the ading o colour
standards limit the accuracy and reliability o results.
In 1931 the Commission Internationale de lEclairage developed a system to
quantiy the light that humans perceive by matching the three primary colours
that make up all colours with three values, called the tristimulus values which
approximately correspond to red, blue and green. They are also known as RBG
values. Any visible colour can be quantifed using these three values, and this
has allowed or objective measuring and comparing o colours. A colorimeter
or spectrophotometer can be used to measure the amount o light absorbed
by a coloured sample in reerence to a colourless sample or blank. Modern cell
phone applications or measuring RBG values make quantifcation o colour
even more accessible.
656
QUeSTiOnS
Questions
1 Lecanora muralis is a species of lichen that grows a food addition area enclosed within a
on walls and roofs in northwest Europe. In 1 976 predator exclusion area.
ecologists did a survey of the distribution of
L. muralis in a sector of Leeds, an industrial city in The areas were monitored from 1 986 to 1 996.
the north of England. Wind direction in this area In spring 1 996 all fences were dismantled and
is variable and levels of air pollution decrease food addition was stopped.
from the centre of the city outwards. L. muralis
was found growing on three habitat types: As a further experiment, spring and summer mark-
recapture population estimates of the squirrels
sandstone blocks, used to build the tops of walls were conducted from spring 1 996 to spring 1 998.
The results for these two years are shown below.
walls constructed using cement or concrete The areas are labelled according to the conditions
imposed during the previous ten years.
roofs made of asbestos cement.
Like many lichens, this species does not tolerate 30
high levels of sulphur dioxide, an acidic gas that is control
a major component of acid rain. Acid rain can be
neutralized by alkaline materials, including cement squirrels hectare-1 25 predator exclusion
and concrete. The results of the survey are shown food addition
in the map below. L. muralis was found north of
the lines shown on the map for each of the three food addition plus
types of habitat. The grid lines are 1 km apart. 20 predator exclusion
outskirts of city sandstone 15
cement or concrete 10
asbestos cement
5
0 summer spring summer spring
spring 19 9 6 19 97 19 97 19 9 8
19 9 6
Source: Karels et al., Nature, (2000) , 408, pages 460463
a) State the squirrel population in the food
addition plus predator exclusion area in
spring 1 996. [1 ]
b) Describe the effect of ending food addition
on the squirrel population. [2]
city centre c) Scientists believed that the number of
Source: Oliver Gilbert, Lichens, 2000, Harper Collins, page 56
ground squirrels in the boreal forests was
a) (i) Deduce which habitat type allows limited by an interaction between food
L. muralis to tolerate the highest level and predators that acted primarily through
of sulphur dioxide pollution. Give a changes in reproduction. Using the data,
reason for your answer. [2] discuss this hypothesis. [3]
(ii) Suggest a reason for the differences in
tolerance between the habitat types. [1 ] 3 Destruction of subtidal and intertidal kelp
b) Explain the value of a survey of this kind, (seaweed) and seagrass beds has been observed
especially if it is repeated at regular intervals. [3] over a wide geographical range. Removal of sea
urchins (Strongylocentrotus sp.) by experimental
2 The Kluane boreal forest ecosystem project manipulation and accidental oil spill has resulted
was a large-scale ten-year experimental in the rapid development of marine vegetation.
manipulation of food and predators on an arctic The presence and absence of kelp beds has a major
ground squirrel (Spermophilus parryii plesius) effect on the structure of the marine community.
population. A survey was carried out of two of the western
Three areas were set up: Aleutian Islands with and without sea otters
( Enhydra lutris) . S ea urchin size, density and
a food addition area biomass were measured. Densities and biomass
a predator exclusion area were recorded per 0.25 m2. Data was collected
657
C ECOLOGY AND CONSERVATION
rom Amchitka Island (with sea otters) anddensity of sea urchins/number 0.25 m2sea urchin biomass/g 0.25 m2 egg development/arbitary unitshigher the value the more developed the eggs
Shemya Island (without sea otters) . were. The 0 m beach distance is based on the
mean high tide line.
Amchitka Island
20 urchin number 400 20
urchin biomass 15
15 300 10
10 200 5
5 100 0
4 -2 0 2 4 6 8 10 12
3 50 beach distance/m
2 4.0
1 10 3.0
10 20 30 40 50 60 70 80 90 oxygen concentration/ppm2.0
diameter of sea urchin/mm 1.0
Shemya Island 0.0
-2 0 2 4 6 8 10 12
density of sea urchins/number 0.25 m2 20 urchin number 400 beach distance/m
urchin biomass sea urchin biomass/g 0.25 m2 28
15 300
10 200
5 100
4 temperature/C
3 50 27
2
1 10
10 20 30 40 50 60 70 80 90 26
diameter of sea urchin/mm
Source: reprinted with permission from J A Estes and J F Palmisano, 25
Science, (1974) , 185, pages 10581060, copyright 1974 AAAS -2 0 2 4 6 8 10 12
beach distance/m
a) (i) State the diameter o sea urchins
Figure 3 from Penn and Brockmann. 1994. Biol. Bull. 187:
with the most requent biomass on 373384. with permission from the Marine Biological
Laboratory, Woods Hole, MA.
Amchitka Island. [1 ]
(ii) Suggest, giving a reason, which island a) State the optimum distance above the high
would have the oldest sea urchins. [1 ]
b) Compare the sea urchin densities and biomass tide line or egg laying. [1 ]
on Shemya Island and Amchitka Island. [2 ]
b) Describe the eect o oxygen concentration
c) Deduce the trophic level o the sea urchins and temperature on egg development. [2]
in this marine community. [1 ] c) Scientists believe that egg development
was infuenced by oxygen concentration,
d) Explain the observed dierences in sea temperature o the sand and distance rom
urchin populations on the two islands. [2] the mean high tidal line.
4 The horseshoe crab ( Limulus polyphemus) (i) Evaluate this study with respect to
lay their eggs in the sand on beaches in the
intertidal zone. The nesting site is selected on these three actors. [2]
the basis o distance above the mean high tide
line, oxygen concentration and temperature o (ii) State one other possible actor that
the sand. Egg development was assessed ater might infuence egg development. [1 ]
1 0 days and recorded as an arbitary unit; the
658
D Human pHYsIOLOGY
CIEtroLdLctioB I O L O G Y
Health in humans depends on physiological A balanced diet is required with digestion
mechanisms working eciently. The study o regulated by both nervous and hormonal
disease both helps understand normal physiology mechanisms. The chemical composition o the
and how treatments may be developed. Many blood is regulated by the liver. Heart unction is
physiological mechanisms are involved in regulated by both internal and external actors.
homeostasis. To achieve a state o equilibrium, Red blood cells transport respiratory gases and
hormones need to be secreted at a variable rate. respiratory gases infuence blood pH.
D.1 Human nutrition
udertdig alictio
Essential nutrients cannot be synthesized by Production o ascorbic acid by some mammals,
the body, thereore they have to be included in but not others which need a dietary supply.
the diet.
Cause and treatment o phenylketonuria (PKU) .
Dietary minerals are essential chemical elements. Lack o Vitamin D or calcium can aect
Vitamins are chemically diverse carbon compounds bone mineralization and cause rickets or
that cannot be synthesized by the body. osteomalacia.
Breakdown o heart muscle due to anorexia.
Some atty acids and some amino acids are Cholesterol in blood as an indicator o the risk
essential. o coronary heart disease.
Lack o essential amino acids aects the skill
production o proteins.
Determination o the energy content o ood by
Malnutrition may be caused by a defciency, combustion.
imbalance or excess o nutrients in the diet.
Use o databases o nutritional content o oods
Appetite is controlled by a centre in the and sotware to calculate intakes o essential
hypothalamus. nutrients rom a daily diet.
Overweight individuals are more likely to suer
hypertension and type II diabetes.
Starvation can lead to breakdown o body tissue.
ntre of ciece induce the symptoms in laboratory rats and mice
were entirely unsuccessul.
Falsifcation o theories with one theory being
superseded by another: scurvy was thought
to be specifc to humans, because attempts to
659
D Human pHysiology
Essentil nutrients
Essential nutrients cannot be synthesized by the body,
therefore they have to be included in the diet.
Nutrients are chemical substances, ound in oods, that are used in the
human body. S ome nutrients are essential in the human diet, because
oods are the only possible source o the nutrient. This includes some
amino acids, some unsaturated atty acids, some minerals, calcium,
vitamins and water.
Other nutrients are non-essential, either because another nutrient can
be used or the same purpose or because they can be made in the body
rom another nutrient. Glucose, starch and other carbohydrates are non-
essential, because they are used in respiration to provide energy and
lipids can be used instead.
Some essential nutrients are conditionally essential. In adults, vitamin K
is produced by the metabolism o symbiotic bacteria in the intestine.
Because inants do not have colonies o such bacteria at birth, they are
oten given a supplementary injection o vitamin K.
ascorbic cid is n essentil nutrient in
some nimls
Production of ascorbic acid by some mammals, but not
others which need a dietary supply.
Vitamin C is a compound called ascorbic acid. It is needed or the
synthesis o the collagen fbres that orm part o many tissues in the
body, including skin and blood vessel walls. The vast maj ority o plants
and animals, including most mammals, can synthesize vitamin C. The
pathway by which it is synthesized in vertebrates is shown in fgure 1
b e lo w.
Mutations that led to genes that no longer produce the protein
necessary to make vitamin C have occurred several times in
evolutionary history ( see fgure 2 ) . In all cases studied so ar, the
inability to synthesis vitamin C is due to mutations in the GLO gene
which codes or the production o the enzyme L-gulono--lactone
oxidase. In fgure 1 , this is the enzyme that catalyses the fnal reaction
in the pathway.
A group o fsh called teleost, or ray-fnned, fsh have lost the ability to
produce vitamin C. Examples o fsh rom this diverse group include
cod, salmon and herring. Most mammals can synthesize vitamin C:
examples include carnivores such as dogs and cats. However, many
primates including humans, chimpanzees and apes cannot synthesize
vitamin C, though more primitive primates such as lorises and lemurs
can. Only a ew species o bats can synthesize vitamin C.
A variety o symptoms develop as a result o vitamin C defciency,
which are collectively known as scurvy. The symptoms o scurvy can
be alleviated by intake o dietary sources o the compound.
660
D.1 Human nutrition
D-Glucose-1-P UDP-D-Glucose O elephant
dog
O N NH cat
crow
HO O O P O- PPi HO O OO O sheep
HO UTP O OPO PO OH pig
OH O- horse
OH OH HO bat
OH HO OH OH rabbit
1 N AD + mouse
2 rat
N ADH guinea pig
squirrel
D-Glucuronate U D P- D - G l u cu ro n a te galago
HCO
H C OH UDP H2O O O- O lemur
3 owl monkey
HO C H HO O O POP O- O N NH marmoset
H C OH HO OH O-O O HO O macaque
H C OH O gibbon
OH orangutan
gorilla
COO- human
N ADPH Figure 2 Phylogenetic distribution o the
ability to synthesize vitamin C in mammals.
4 Lineages able to synthesize vitamin C are in
N ADP+ black, those incapable are in purple
L-Gulonate L-Gulono-1, 4-lactone L-Ascorbic acid
CH2OH CH2OH CH2OH
H C OH H C OH H C OH
HO C H
H2O CH O2 H2O2 CH
H C OH 5 GLO enzyme
H C OH C OH
H C OH O O
COO-
H C OH C OH
Figure 1
CO CO
Essential fatty acids and amino acids Figure 3 Sunfower seeds (Helianthus
annuus) . Sunfower seeds can be eaten
Some fatty acids and some amino acids are essential. as a source o dietary linoleic acid
O the 20 amino acids in proteins, about hal are essential in humans, 661
because they cannot be synthesized in sufcient quantities, but the other
hal can be made rom other simpler nitrogen compounds. Threonine
and arginine are conditionally essential. Threonine is an essential amino
acid that can be synthesized by the body i phenylalanine is present.
Sufcient arginine can normally be produced by a healthy individual.
The synthesis pathway o arginine is not active in prematurely born
inants and so they must obtain it through their diet.
There are some omega-3 and omega-6 atty acids that are essential in
the diet because they cannot be synthesized in the body. The omega-3
and omega-6 reers to the position o a double bond in relation to
the end o the molecule. Alpha-linolenic acid and linoleic acid are used
in the biosynthesis o a number o other compounds. They are needed
D Human pHysiology
throughout the body, but the development o the brain and the eye
involves particularly large quantities. However, there is little or no
evidence that supplementation o a normal balanced diet with omega-3
atty acids, or example rom fsh oils, enhances brain or eye development.
Essential amino acids Phenylalanine
Histidine Tryptophan
Isoleucine Valine
Leucine Threonine (only i phenylalanine is not in the diet)
Lysine Arginine (required in the diet o inants)
Methionine
Essential amino acids are needed for protein
synthesis
Lack o essential amino acids afects the production
o proteins.
I there is a shortage o one or more essential amino acids in the diet
then the body cannot make enough o the proteins that it needs. This
condition is known as protein defciency malnutrition. Essential amino
acids may be lacking due to an overall insufciency o protein in the diet
or to an imbalance in the types o protein. For example, protein defciency
malnutrition causes a lack o blood plasma proteins, with the result that
Data-based questions: Protein defciency malnutrition
Figure 4 shows the incidence o stunting, wasting b) Identiy the regions o the world where
and developmental disability or eight regions the trend has been most pronounced.
o the world. The statistic used is YLD per 1 ,000,
which is years lost to disease per thousand c) Suggest reasons or this.
members o the population. The chart shows the
results or males in the years 1 990 and 2000. The 6 Predict with a reason what the pattern might
fgures or emales showed the same trends. have been in 201 0.
1 a) Identiy the region with the greatest evidence Whole world YLD 2000
o protein defciency malnutrition. S. + C. America YLD 1990
Eastern Mediterranean
b) Suggest reasons or this.
Africa
2 a) Determine the percentage dierence in S.E.Asia + W.Pacic
YLD or the year 2000 between the region China + E.Asia(part)
with the highest rate and the region with India + S.E.Asia(part)
the lowest rate.
E.Europe
b) What could be done to narrow the dierence? W.Europe + Other
3 a) Outline what the data reveals about the developed areas
worldwide trend in protein defciency
malnutrition. 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50
YLD/1000
Figure 4 YLD due to protein defciency malnutrition
662
D.1 Human nutrition
fuid is retained in tissues. This causes swelling (edema) , which is oten very H
obvious in the abdomen. Child development may be both mentally and
physically retarded, with stunted growth and developmental disabilities. HH
Adults may undergo serious weight loss (wasting) . HO C
C OH
Essential minerals
O C O
Dietary minerals are essential chemical elements. C
Minerals are needed in the diet in relatively small quantities milligrams H
or micrograms per day rather than grams. They can be distinguished
rom vitamins by their chemical nature. CC
Minerals are chemical elements, usually in ionic orm; or example, HO OH
calcium is required in the diet in the orm o Ca2+ ions. I any mineral
is lacking rom the diet, a deciency disease results. The consequences vitamin C
o deciency diseases can be serious, even though the quantities o the
mineral needed in the diet are small. An example o this is the mineral O
iodine. It is needed by the thyroid gland or synthesis o the hormone
thyroxin. This hormone stimulates the metabolic rate and ensures that H3C N
enough energy is released in the body. A lack o iodine causes iodine NH
deciency disorder (IDD) . I a pregnant woman has IDD, her baby may
be born with permanent brain damage, and i children suer rom IDD H3C N N O
ater birth, their mental development and intelligence are impaired.
Tens o millions o people worldwide have been aected in this way by CH2
IDD. Iodine supplementation can be done easily by adding the mineral H OH
to salt sold or human consumption. It costs about ve cents per person
to iodize salt and prevent IDD in a population. There are other types o H OH
nutrient supplementation that have considerable benets, or little cost,
in populations where deciencies exist. H OH
Vitamins CH2
Vitamins are chemically diverse carbon compounds that OH
cannot be synthesized by the body.
vitamin B2
Vitamins are organic compounds that are needed in very small amounts
because they cannot be synthesized by the body but must be obtained H3C CH3 CH3 CH3 OH
rom the diet. They serve a variety o roles such as co-actors or
enzymes, anti-oxidants and hormones. The word vitamin is derived rom CH3
the words vital amine as the rst vitamins to be discovered contained vitamin A
an amino group. Other vitamins discovered since do not necessarily
contain an amino group such as vitamins A, C, D and E. Figure 5 shows Figure 5
j ust some o the range o structures o vitamins. Vitamin C is derived
rom a monosaccharide, vitamin A is hydrophobic and contains a
hydrocarbon ring and chain. Vitamin B 2 contains nitrogen rings and is
readily converted to the nucleotide FMN (favin mononucleotide) by the
addition o a phosphate to the carbohydrate within the molecule.
Vitamins are oten broadly categorized as at soluble and water soluble. The
water soluble vitamins have to be constantly consumed and any excess is
lost in urine. The at soluble vitamins can be stored in the body.
663
D Human pHysiology
TOK Waer soluble viamins Fa soluble viamins
A
to wha exen should ehical consrains limi C ascorbic acid
he pursui o scienifc knowledge? E
B1 thiamin
During the Second World War, experiments were B2 ribofavin K
conducted both in England and in the US using B3 niacin
conscientious objectors to military service as B pantothenic acid D (conditionally essential)
volunteers. The volunteers were willing to sacrice
their health to help extend medical knowledge. A 5
vitamin C trial in England involved 20 volunteers.
For six weeks they were all given a diet containing B pyridoxine
70 mg o vitamin C. Then, or the next eight months, 6
three volunteers were kept on the diet with 70 mg,
seven had their dose reduced to 10 mg and ten B7 biotin
were given no vitamin C. All o these ten volunteers B9 olic acid
developed scurvy. Three-centimetre cuts were B12 cobalamin
made in their thighs, with the wounds closed up
with ve stitches. These wounds ailed to heal. Types of malnutrition
There was also bleeding rom hair ollicles and rom
the gums. Some o the volunteers developed more Malnutrition may be caused by a deciency,
serious heart problems. The groups given 10 mg or imbalance or excess o nutrients in the diet.
70 mg o vitamin C ared equally well and did not
develop scurvy. Malnutrition is the outcome o a poor diet. Diets can be low in
overall quantity with low protein and calorie content. They can
Experiments on requirements or vitamin C have be unbalanced and ail to provide essential nutrients or they
also been done using real guinea pigs, which can contain excess ats and refned carbohydrates. Malnutrition
ironically are suitable because guinea pigs, like is oten associated with poverty. S tarvation is a consequence
humans, cannot synthesize ascorbic acid. During o a diet lacking in adequate protein and carbohydrates.
trial periods with various intakes o vitamin C, Increasingly, obesity is observed in developing countries as well
concentrations in blood plasma and urine were as in the lower socio-economic classes o developed nations as
monitored. The guinea pigs were then sacriced a consequence o unhealthy diets with excess at and refned
and collagen in bone and skin was tested. The carbohydrates.
collagen in guinea pigs with restricted vitamin C
had less cross-linking between the protein bres The appetite control centre
and thereore lower strength.
Appetite is controlled by a centre in the
1 Sometimes, people are paid to participate in hypothalamus.
medical experiments, such as new drug trials.
What are some o the ethical issues associated In the hypothalamus o the brain there is a centre that is
with being paid to be a subject in an experiment? responsible or making us eel satisfed when we have eaten
enough ood (satiated) . It is called the appetite control centre.
2 For some drug trials, there is the potential The small intestine secretes the hormone PYY336 when it
or the subject to be harmed. What are the contains ood. The pancreas secretes insulin when the blood
associated ethical issues related to risks to glucose concentration is high. Adipose tissue secretes the
volunteers in drug trials? hormone leptin when amounts o stored at increase. I the
appetite control centre receives these hormones, it reduces the
3 Some experiments on humans were done desire to eat. This helps to us to avoid health problems due to
against the subjects will or without the overeating, including excessive blood glucose levels and obesity.
subjects knowledge. Once the data is generated
rom these experiments, it cannot become Consequences of being overweight
unknown. What are the associated ethical
issues with people other than the original Overweight individuals are more likely to suer
experimenter using the inormation gathered hypertension and type II diabetes.
under these conditions?
Unhealthy diets with excess at and refned carbohydrates
664 have health consequences. Two examples o nutrition related
diseases are diabetes and hypertension.
D.1 Human nutrition
There are several diseases involving excessive excretion o urine, all o
which are orms o diabetes. In the commonest orm, sugar is present in
the urine. This is diabetes mellitus, and it aects hundreds o millions
o people worldwide. There are two ways in which this sort o diabetes
can develop:
Auto-immune destruction o insulin-secreting cells in the pancreas
(type I diabetes) .
Decreased responsiveness o body cells to insulin due to burn-out
(type II diabetes) .
Prevalence rates o type II diabetes are rising rapidly in many countries.
The study o the rates and distribution o a disease, to try to fnd its
causes, is known as epidemiology. Epidemiological studies o type II
diabetes have implicated increased blood concentrations o atty acids,
linked to the ollowing risk actors:
diets rich in at and low in fbre
obesity due to overeating and lack o exercise
genetic actors which aect at metabolism.
There is huge variation between ethnic groups in rates o type II
diabetes, rom less than 2 per cent in China to 50 per cent among
the Pima Indians. The symptoms are not always recognized, so not
all people with diabetes are diagnosed. The main symptoms are:
elevated levels o blood glucose
glucose in the urine this can be detected by a simple test
dehydration and thirst resulting rom excretion o large volumes
o urine.
Unless careully managed, diabetes can cause other health problems
to develop, several o which relate to the cardiovascular system:
atherosclerosis (narrowing o arteries by atty deposits)
hypertension (raised blood pressure, discussed below)
coronary heart disease (narrowing o the coronary arteries with the
associated risk o heart attacks) .
There also seems to be a link between these cardiovascular problems
and blood lipid concentrations. Links have been suggested between
high concentrations o cholesterol, high concentrations o LDL and
low concentrations o HDL. There has been much controversy about
the role o cholesterol, in particular in the development o coronary
heart disease (CHD) .
There is a clear correlation between excessive weight gain and
hypertension, though the relationship is complex. Weight gain can
increase the release o several hormones as well as cause changes in
body physiology and anatomy all o which can lead to hypertension:
weight gain leads to higher cardiac (heart) output which can raise
blood pressure
abdominal obesity can increase vascular resistance which can raise
blood pressure
665
D Human pHysiology
Figure 6 weight gain is associated with arteries becoming stier and narrower
which can raise blood pressure.
Hypertension can also be caused by high salt intake. Circulating salt has
an osmotic eect.
Efects o strvtion
Starvation can lead to breakdown of body tissue.
Starvation occurs due to the severe lack o intake o essential and non-
essential nutrients. In the absence o dietary intake o energy sources, the
body will frst access glycogen stores. However, i no glucose is available,
the body will break down its own muscle tissue to utilize the resulting
amino acids as energy sources. The amino acids are sent to the liver
where they are converted to glucose. This results in a loss o muscle mass.
In fgure 6, the child is suering rom marasmus. His thin limbs indicate
that muscle tissue has been broken down as an energy source by his body.
anorexi
Breakdown of heart muscle due to anorexia.
The medical term anorexia means reduced appetite. As body weight in a person with anorexia alls,
Anorexia nervosa is a psychiatric illness, with causes not only is skeletal muscle digested, but heart
that are complex. It involves voluntary starvation muscle deteriorates. To some degree, the skeletal
and loss o body mass. The amounts o carbohydrate muscle mass reduces disproportionately aster
and at consumed are too small to satisy the bodys than the cardiac mass. Lack o protein, electrolytes
energy requirements, so protein and other chemicals and micronutrients may result in the deterioration
in the body are broken down. There is wasting o o muscle fbres. The lack o dietary intake also
muscles, resulting in loss o strength. Hair becomes alters the electrolyte balance; i.e., concentrations
thinner and can drop out. The skin becomes dry and o calcium, potassium and sodium. Both skeletal
bruises easily. A fne growth o body hair tends to muscle and cardiac muscle do not contract
develop. Blood pressure is reduced, with slow heart normally under these circumstances. There is
rate and poor circulation. In emales, inertility is oten reduced blood pressure, a slower heart rate
another common consequence, with no ovulation and reduced heart output in patients.
or menstrual cycles.
Data-based questions: Changes in heart dimensions in patients with anorexia
The data in fgure 7 shows the dimensions o c) the let atrium
various structures in subjects with normal diet
and in patients with anorexia. d) the base o the aorta. [5]
1 Calculate the percent change in the mean 2 Identiy the part o the heart with the largest
dimensions o decrease in dimension due to anorexia. [1 ]
a) the let ventricle 3 Suggest what might be the symptoms o
this change in the aected patient. [3]
b) the let ventricle wall
Normal mean Left ventricle Left atrium Base of aorta Ventricle wall
Anorexia range 47 mm 29 mm 27 mm 9 mm
mean ( 35 57 ) ( 19 40 ) ( 20 37 ) ( 6 11 )
range 38 mm 26 mm 21 mm 8 mm
(3844) ( 17 34) ( 18 26 ) (69)
Figure 7
666
D.1 Human nutrition
The guinea ig as a model organism for studying scurvy
Falsifcation o theories with one theory being superseded by another: scurvy was
thought to be specifc to humans, because attempts to induce the symptoms in
laboratory rats and mice were entirely unsuccessul.
In 1 907, two scientists, Holst and Frolisch,
published a research paper on their success in
developing an animal model or the study o
scurvy. They caused scurvy by eeding guinea
pigs ( Cavia porcellus) with whole grains. They
cured scurvy in the guinea pigs through dietary
modifcation including eeding resh cabbage
and lemon juice. The ideas within their paper
were somewhat unpopular with the scientifc
community as the concept o nutritional
defciencies was unheard o at the time. The use
o the term vitamin did not begin until later.
Their animal model allowed or the systematic Figure 8 Dermatitis in a guinea pig fed exclusively on rabbit
study o the actors that led to the scurvy, as well pellets. This is one of a number of symptoms of scurvy seen
as the preventive value o dierent substances. in guinea pigs with the disease
Substituting guinea pigs or pigeons, an animal
model that had been used in beriberi research, was
a lucky coincidence, as the guinea pig was later
shown to be among the very ew mammals capable
o showing scurvy-like symptoms, while pigeons,
as seed-eating birds, were later shown to make
their own vitamin C and could not develop scurvy.
phenylketonuria
Cause and treatment o phenylketonuria (PKU) .
Phenylketonuria (PKU) is a genetic disease. It difculties, hyperactivity and seizures in older
is caused by mutations o a gene coding or the children. Other consequences are a lack o skin and
enzyme that converts phenylalanine into tyrosine. hair pigmentation.
The mutations produce alleles o the gene PKU babies are unaected at birth because the
that code or enzymes unable to catalyse mothers metabolism has kept phenylalanine and
the conversion reaction. Only one normal tyrosine at normal levels. This gives an opportunity
allele is needed or satisactory conversion or early diagnosis and treatment. A test should be
o phenylalanine to tyrosine, so this allele is carried out at about 24 hours ater birth, by which
dominant. The symptoms o PKU only occur in time blood phenylalanine concentrations will have
individuals with two recessive mutant alleles. started to rise. Treatment involves eating a diet low
Phenylalanine then accumulates in the body and in phenylalanine or the rest o the persons lie.
there can also be a defciency in tyrosine. Meat, fsh, nuts, cheese, peas and beans can only
be eaten in small quantities. Tyrosine supplements
The consequences o PKU are potentially very may be needed. I a suitable diet is rigorously
serious. The high phenylalanine levels cause adhered to, the harmul consequences o PKU can
reduced growth o head and brain, with mental be avoided.
retardation o young children and severe learning
667
D Human pHysiology
H
HO
NC C
H OH
CH2
phenylalanine
phenylalanine
hydroxylase
H
HO
NC C
H OH
CH2
OH Figure 10 A new born baby being tested for PKU using the Guthrie test
tyrosine
Figure 9 Synthesis of tyrosine from phenylalanine
Vitamin D defciency
Lack o Vitamin D or calcium can afect bone mineralization and cause rickets
or osteomalacia.
Vitamin D is needed or calcium absorption Ultraviolet light has some harmul
rom ood in the intestines, so the symptoms consequences, including mutations that
o vitamin D defciency are similar to those o can lead to skin cancer. Melanin in the skin
calcium, with children developing the skeletal intercepts and absorbs light, including the
deormities known as rickets. Vitamin D does ultraviolet wavelengths. Dark skins thereore
not ft the defnition o a vitamin very well, give good protection against cancer, but they
as it can be synthesized in the skin. This only also reduce vitamin D synthesis. In indigenous
happens when sunlight, or another light source human populations, skin colour balances the
containing ultraviolet light with wavelengths twin risks o vitamin D defciency and cancer
in the range 29031 0 nm, strikes the skin. I or other damage due to ultraviolet light. Ater
teenagers and adults spend enough time outside, population migrations there can be problems.
with their skin uncovered, no vitamin D is In the 1 970s immigrants with dark skin rom
required in the diet. Children, pregnant women the Indian subcontinent living in the United
and elderly people are recommended to eat Kingdom started to show symptoms o vitamin
1 0 g per day, to supplement the amount made D defciency. Immigrants rom northern E urope
in their skin. There are ew dietary sources with light skin living in Australia were ound
o vitamin D. Oily fshes including herring, to have high rates o malignant melanoma.
mackerel, sardines and tuna are rich sources. Australians with light skin were then advised to
Eggs and liver also contain some, and certain stay out o bright sunlight, cover their skin or
oods such as margarine and milk are artifcially apply sun-block creams.
ortifed with vitamin D.
668
D.1 Human nutrition
Blood cholesterol and heart disease
Cholesterol in blood as an indicator of the risk of coronary heart disease.
Cholesterol is a normal component o plasma thereore presumably has little eect on CHD
membranes in human cells, but nevertheless it rates.
has developed a reputation or being a harmul
substance. This is because research has shown The liver can synthesize cholesterol so dietary
a correlation between high levels o cholesterol cholesterol is not the only source.
in blood plasma and an increased risk o
coronary heart disease. Advice is oten given Genetic actors are more important than dietary
to minimize dietary cholesterol intake, but it is intake and members o some amilies have high
not certain that this will actually lower the risk cholesterol levels even with a low dietary intake.
o coronary heart disease (CHD) , or a variety
o reasons. Drugs can be more eective at reducing blood
cholesterol levels than reductions in dietary
Much research has involved total blood intake.
cholesterol levels, but only cholesterol in LDL
(low-density lipoprotein) is implicated in CHD. There is a positive correlation between
dietary intake o saturated ats and intake o
Reducing dietary cholesterol oten has a very cholesterol, so it is possible that saturated ats,
small eect on blood cholesterol levels and not cholesterol, cause the increased risk o
CHD in people with high cholesterol intakes.
Calorimetry Figure 11
Determination of the energy content of food
by combustion.
The determination o the energy content o a substance is called calorimetry.
Figure 1 1 shows an experimental set-up or a simple calorimeter. It is based
on the knowledge o the specifc heat capacity o water. It takes 4.1 86 J o
heat energy to raise the temperature o 1 gram o water by 1 degree Celsius.
Q = mass o water specifc heat capacity change in temperature
The apparatus consists o a thermometer to detect the change in
temperature and a vessel containing a known mass o water (1 ml o
water has a mass o 1 g) . The sample to be tested or its energy content
is ignited and placed below the container containing the water and the
temperature change is noted.
acvy
Using the experimental results below, estimate the energy content
o the nut per gram.
Sample data:
Mass o nut = 0.60 g
Volume o water = 25 ml
Initial water temperature = 20 C
Final water temperature = 65 C
669
D Human pHysiology
monitoring personal dietary intake
Use of databases of nutritional content of foods and software to calculate intakes
of essential nutrients from a daily diet.
When nutritionists refer to a balanced diet, they are image generated by entering a record of the contents
referring to a combination of foods that will provide of a typical breakfast into the free software Super
essential and non-essential nutrients in the correct Tracker available from the US Department of
balance. Figure 1 2 shows a food wheel showing Agriculture (USDA) .
a healthy balanced diet. The wheel shows what
proportion of the diet should be made up by each
of the major food groups. Fresh fruit and vegetables
should make up the largest part of the diet, followed
by carbohydrates, proteins and then dairy products.
Fats and sugars are on the chart, not because they
are encouraged or required but because they should
make up the smallest part of the diet.
Computer applications can be used to keep a record Figure 12
of the food consumed by an individual. Based
on information entered in databases about the
composition of the foods consumed, the nutrient
intake of an individual can be tracked and compared
to the recommended intake. Figure 1 3 shows an
Figure 13
670
D.2 Digestion
D.2 D
udertdig applictio
Nervous and hormonal mechanisms control the The reduction o stomach acid secretion by
secretion o digestive juices. proton pump inhibitor drugs.
Exocrine glands secrete to the surace o the Dehydration due to cholera toxin.
body or the lumen o the gut. Helicobacter pylori inection as a cause o
The volume and content ogastric secretions are stomach ulcers.
controlled by nervous and hormonal mechanisms.
skill
Acid conditions in the stomach avour some
hydrolysis reactions and help to control Identifcation o exocrine gland cells that
pathogens in ingested ood. secrete digestive juices and villus epithelium
cells that absorb digested oods rom electron
The structure o cells o the epithelium o the micrographs.
villi is adapted to the absorption o ood.
ntre of ciece
The rate o transit o materials through the large
intestine is positively correlated with their fbre Serendipity and scientifc discoveries: the role
content. ogastric acid in digestion was established by
William Beaumont while observing the process o
Materials not absorbed are egested. digestion in an open wound caused by gunshot.
Regltio of digetive ecretio 671
Nervous and hormonal mechanisms control the secretion
o digestive juices.
Under natural conditions, there are gaps between meals. Animals may
go or long periods o time between meals. In order to conserve energy,
animals do not have their digestive systems active constantly. In the case
o the ght or fight response, conserving energy or muscle use creates
the need to divert energy rom the digestive process. In both cases, nerves
and hormones ensure resources are devoted to digestion only when
needed. Consider the example o gastric juice secretion in the stomach.
Regltio of gtric ecretio
The volume and content o gastric secretions are
controlled by nervous and hormonal mechanisms.
Both nerves and hormones are involved in controlling the secretion o
digestive juices. Gastric juice secretion is an example o this. The sight or
D H um an pH ysiology
672 smell o ood causes the brain to send nerve impulses via the vagus nerve
rom the medulla. Gland cells in the stomach wall are stimulated to
secrete components o gastric juice. I chemoreceptors in the stomach
wall detect peptides in the stomach contents or i stretch receptors
detect distension o the stomach, impulses are sent to the brain. The
brain responds by sending impulses via the vagus nerve to endocrine
cells in the wall o the duodenum and the part o the stomach nearest
to the duodenum, stimulating them to secrete gastrin. The hormone
gastrin stimulates secretion o acid and pepsinogen by two types o
exocrine gland cell in the stomach wall. Two other hormones, secretin
and somatostatin, inhibit gastrin secretion i the pH in the stomach alls
too low.
Exocrine glands
Exocrine glands secrete to the surface of the body or the
lumen of the gut.
The passage through which ood passes rom mouth to anus is called the
alimentary canal. Digestive juices are added to ood in the alimentary
canal at several points. Exocrine glands secrete the juices, including
salivary glands, the pancreas, gland cells in the stomach wall and in the
wall o the small intestine. The composition o the juices secreted by the
glands is dierent, refecting the processes that occur in each part o the
alimentary canal (see table 1 ) .
Digetive fuid source Compoition
saliva salivary glands
water, electrolytes, salivary amylase,
gastric juice stomach mucus, lysozyme
pancreatic juice pancreas water, mucus, enzymes including
pepsin, rennin and hydrochloric acid
water, bicarbonate, enzymes including:
amylase, lipase, carboxypeptidase,
trypsinogen
Table 1
Unlike endocrine glands, which secrete directly into the bloodstream,
exocrine glands secrete into ducts. Figure 1 shows the arrangement o
cells in part o an exocrine gland. Secretory cells are in groups around
the duct branch. Each group o cells is called an acinus. The structure
o the individual exocrine gland cells that secrete digestive enzymes
is revealed in electron micrographs (gure 2) . There is extensive
endoplasmic reticulum or synthesis o enzymes. There are numerous
mitochondria to provide ATP or protein synthesis and other cell
activities. There are also large numbers o secretory vesicles containing
enzymes. The process o exocytosis o these vesicles can sometimes be
seen in progress where the plasma membrane o the cell is in contact
with the duct.
D.2 Digestion
secretory vesicles
one acinus
secretory cells basement membrane
wall of duct
lumen of duct Figure 2 An exocrine cell
Figure 1 An exocrine gland
adpttions of the villus
The structure of cells of the epithelium of the villi
is adapted to the absorption of food.
Figure 3 shows a longitudinal cross-section through the ileum, the site o a
signifcant amount o the absorption that takes place in the small intestine.
The inner surace o the ileum has numerous olds. Each o the olds is
covered in tiny projections called villi. Absorption takes place through
the epithelial cells covering each villus.
Each epithelial cell covering the villus adheres to its neighbours Figure 3 Longitudinal section through the
through tight junctions, which ensure that most materials pass into ileum wall
the blood vessels lining the villi through the epithelial cell.
The cell surace membrane on the intestinal lumen side has a number o
extensions called microvilli. The collection o microvilli on the intestinal
side o the epithelial cells is termed the brush border. The unction o
the brush border is to increase the surace area or absorption.
Relatively high amounts o ATP are required to drive active transport apical glucose Na+ lumen
processes. Thus epithelial cells have large numbers o mitochondria. s u rfa ce glucose Na+ of gut
Pinocytic vesicles are oten present in large numbers due to microvillus
absorption o some oods by endocytosis. tight
junction
The surace acing the lumen o the intestine is reerred to as the Na+ driven
intestinal
apical surace and the surace acing the blood vessels is reerred to glucose epithelium
symport
as the basal surace. These suraces have dierent types o proteins
involved in material transport. carrier
longitudinal protein
muscle layer mediating
villi fa c i l i t a t e d K-
diusion of ATP ADP+P1
glucose
basal Na+- K+ extracellular
s u rfa ce uid
glucose Na+ ATPase
mucosa circular
muscle layer
Figure 4 Transverse section of ileum
Figure 5
673
D Human pHysiology
Identifcation o exocrine glands
Identifcation o exocrine gland cells that secrete digestive juices and villus
epithelium cells that absorb digested oods rom electron micrographs.
Data-based questions: Adaptations of villus epithelium cells
The electron micrograph shows part o two villus b) Explain the unction o these structures. [2 ]
epithelium cells. False colour has been used to
distinguish between some o the structures that c) Calculate the magnication o the [3]
are present. electron micrograph, assuming that
these structures are 0.85mm long.
2 a) Identiy which structures are [1 ]
mitochondria.
b) Explain the need or large numbers o
mitochondria in villus epithelium cells. [2]
3 Large numbers o vesicles are visible in the
cytoplasm o the cells.
a) State the name o the process used to
orm these vesicles. [1 ]
b) Predict the contents o the vesicles. [2]
4 Part o the junction between the two cells
has been coloured blue.
Figure 6 Micrograph of villus epithelium cell a) State the name o this structure. [1 ]
1 a) Identiy the structures that have been b) Explain its unction. [2]
coloured orange. [1 ]
Figure 7 is an electron micrograph showing two
elongated, acinar cells o the exocrine human
pancreas. Arranged in rounded glands, these cells
secrete an alkaline, enzyme-rich fuid into the
duodenum via the small duct (in blue) at top o
image. Acinar cells are oten pyramidal-shaped cells.
Vesicles and granules will oten be ound at the
surace next to the duct. In this image, granules o
pancreatic enzymes are being carried through the
cytoplasm towards the duct at the top.
Figure 7
674
D.2 Digestion
Discovering the chemical nature of digestion in the stomach
Serendipity and scientifc discoveries: the role o gastric acid in digestion was
established by William Beaumont while observing the process o digestion in an
open wound caused by gunshot.
Alexis St. Martin was a Canadian ur trader process o digestion. He continued to conduct
who received a gunshot wound to his side. He investigations over an eleven-year period.
survived the accident, but the wound healed He published his results in 1 833. Beaumont
in such a way that the inside o his stomach is credited with overturning the notion that
could be seen rom the outside. William digestive processes within the stomach are
Beaumont, the surgeon who frst treated the solely physical providing evidence through his
wound, used the opportunity to study the experiments o the chemical nature o digestion.
The role of acid conditions in the process Figure 8 Interior o stomach
of digestion
Acid conditions in the stomach avour some
hydrolysis reactions and help to control pathogens in
ingested ood.
Acid is secreted by the parietal cells o the stomach. The acid disrupts
the extracellular matrix that holds cells together in tissues. It also
leads to the denaturing o proteins, exposing the polypeptide chains
so that the enzyme pepsin can hydrolyse the bonds within the
polypeptides.
Pepsin is released by chie cells as the inactive pepsinogen. The acid
conditions within the stomach convert the inactive pepsinogen to
pepsin. This ensures that the cells that produce pepsinogen are not
digested at the same time as the protein in the diet.
Bacterial infection as a cause of ulcers Figure 9 Helicobacter pylori bacteria on
the surace o the human gut. Colonies o
Helicobacter pylori inection as a cause o stomach H. pylori occur on the stomach mucous
ulcers. membrane in people who sufer rom
gastritis. This bacteria has been linked to
Stomach ulcers are open sores, caused by partial digestion o the stomach ulcer ormation. H. pylori may also
stomach lining by the enzyme pepsin and hydrochloric acid in gastric be a actor or gastric cancer as its presence
juice. Stomach cancer is the growth o tumours in the wall o the increases the risk o stomach tumours
stomach. Until recently, emotional stress and excessive gastric j uice
secretion were believed to be a major contributory actor in the
development o stomach ulcers, but a bacterium, Helicobacter pylori, has
been shown to be a more signifcant cause. This bacterium also seems
to be associated with stomach cancer.
675
D Human pHysiology
proton um inhibitors
The reduction o stomach acid secretion by proton pump inhibitor drugs.
There are several disease conditions o the The production o the acidic environment within
stomach that are made worse by the release the stomach is achieved by a proton pump called
o acid. Stomach acid is corrosive so the body the H+, K+-ATPase. This pump uses one ATP
produces a natural mucus barrier which protects molecule to exchange two protons rom the
the lining o the stomach rom being attacked by cytoplasm or two potassium ions in the lumen
the acid. surrounding the parietal cell. One therapy that
is increasingly prescribed or gastric diseases is
In some people this barrier may have broken proton pump inhibitors or PPIs.
down allowing the acid to damage the stomach,
causing bleeding. This is known as an ulcer. In PPIs bind irreversibly to a single pump. The eect
others there may be a problem with the circular on the overall acid production system is not
muscle at the top o the stomach that prevents permanent as the pumps are normally recycled
fuid rom escaping the stomach. I the muscle is and replaced with new pumps.
not unctioning, the acid escapes and irritates the
esophagus. This is called acid refux which can The PPIs are consumed in an inactive orm. Acid
cause a symptom reerred to as heartburn. conditions in the vicinity o the parietal cells convert
them to the active orm close to their target.
Egestion
Materials not absorbed are egested.
Dietary bre is the edible parts o plants that are resistant to being
digested and are not absorbed rom the small intestine. Examples include
cellulose and lignin. As a consequence, there is a raction o ingested
ood which never leaves the digestive tube. In addition, secretion into
the digestive tube occurs. Some o what is added is excretory products
such as bilirubin rom the breakdown o red blood cells. A large volume
o water is added to the tube in the process o digestion by secretions in
the mouth, stomach and small intestine, and has to be reclaimed in the
large intestine. The excretory products, the unabsorbed
water and undigested dietary bre are egested as eces.
ingestion bloodstream
The role o dietary fbre
digestion absorption The rate o transit o materials through the
nutrients large intestine is positively correlated with
mouth waste anus their fbre content.
products
Dietary bre is material such as cellulose, lignin and
pectin that cannot be readily digested. There are two
secretion categories o dietary bre: soluble and insoluble. A
salivary glands egestion healthy balanced diet contains bre as it increases the
( d efecation ) bulk o material passing through the intestines and
helps to prevent constipation as it draws water into the
liver
pancreas gall bladder intestine. The higher the water content o the intestine,
accessory digestive organs the aster the movement o ecal matter.
Figure 10 There are other possible benets o bre in the diet.
The risk o various diseases o the large intestine may
676
D.2 Digestion
be reduced, including bowel cancer, hemorrhoids and appendicitis. TOK
The presence o bulky material in the stomach and intestines may
increase eelings o satiety, reducing the desire to eat and the risk o Wha rl d crvam play
obesity. Absorption o sugars may be slowed down, helping to prevent cc?
the development o type II diabetes. Foods o plant origin contain
dietary bre, especially whole-grain bread and cereals, vegetables such Thirty years ago, it was widely believed
as cabbage and salads such as celery. Foods made rom cultured ungi that emotional stress and liestyle
(mycoprotein) also contain dietary bre. actors caused stomach ulcers. It is now
recognized about 80 per cent oulcers
Daa-bad qu: Dietary fbre and mean residence time are caused by inection rom Helicobacter
pylori. The theory that ulcers were the
Figure 1 1 shows the correlation between digestible matter content consequence oan inection was put
(meaning less dietary bre) and mean residence time (the length o orward in the early 1980s by Barry
time in the intestine) . Marshall and Robin Warren, two little-known
Australian scientists. By the mid-1980s,
1 Using the curve, determine the digestible matter content o a they worked out an inexpensive treatment
that cured about 75 per cent opatients.
eces which has a mean residence time o 40 hours. [1 ] By 1988, they had shown denitively that
antibiotics which killed H. pylori would
2 Explain the relationship between digestibility and mean [3] cure ulcers or good. But the treatment
residence time. did not become widely available until the
early 1990s. Marshall attributes the slow
90 percent digestible matter take-up otheir discovery to at least three
80 dierent actors. The rst problem is the
70 20 40 60 80 inertia oexisting belies. Doctors and drug
60 mean residence time (h) companies had convinced themselves
50 that they already knew the cause oulcers:
40 emotional stress. Marshall and Warrens
30 inectious-agent theory had to displace
20 the mindset. Also the blockbuster drugs o
10 the time, Smith Kline Beechams Tagamet
and Glaxos Zantac were both very good at
0 putting ulcers into remission. The second
0 problem lay in the way unding is allocated.
Research grants are oten awarded or
Figure 11 three-year stints. When, in 1988, Marshall
and Warren demonstrated that antibiotics
Dehydration due to cholera could cure ulcers, many researchers who
might have conrmed their result were
Dehydration due to cholera toxin. already locked into research on acid-
lowering drugs. Third, Marshall says that
C holera is a disease caused by inection by the bacterium Vibrio cholera. initially, they ound it difcult or their
The bacterium releases a toxin that binds to a receptor on intestinal publications to be noticed. Pharmaceutical
cells. The toxin is then brought into the cell by endocytosis. Once companies und an enormous amount o
inside the cell, the toxin triggers a cascade response that ultimately drug research in universities and hospitals.
leads to the efux o Cl- and HCO3- ions rom the cell into the Pharmaceutical companies understandably
intestine. Water ollows by osmosis leading to watery diarrhoea. Water tend to concentrate their eorts on
is drawn rom the blood into the cells to replace the fuid loss rom the conservative research that tends toward
intestinal cells. Quite quickly severe dehydration can result in death i lucrative ongoing treatments rather than
the patient does not receive rehydration. speculative ventures that might produce
cheaper, permanent cures.
677
D Human pHysiology
D.3 Functions of the liver
uderstdig applictios
The liver removes toxins rom the blood and Causes and consequences o jaundice.
detoxifes them. Dual blood supply to the liver and dierences
Components o red blood cells are recycled by between sinusoids and capillaries.
the liver.
ntre of sciece
The breakdown o erythrocytes starts with
phagocytosis o red blood cells by Kuper cells. Educating the public on scientifc claims:
scientifc studies have shown that high-
Iron is carried to the bone marrow to produce density lipoprotein could be considered good
hemoglobin in new red blood cells. cholesterol.
Surplus cholesterol is converted to bile salts.
Endoplasmic reticulum and Golgi apparatus in
hepatocytes produce plasma proteins.
The liver intercepts blood rom the gut to regulate
nutrient levels.
Some nutrients in excess can be stored in the liver.
hepatic vein carries blood from the Blood spply to the liver
liver on to the heart with levels of
food adjusted Dual blood supply to the liver and dierences between
l i ver sinusoids and capillaries.
hepatic artery Figure 1 illustrates the blood vessels that serve the liver. B lood arrives
brings oxygenated at the liver rom two sources.
blood to the liver
hepatic portal vein carries blood The hepatic artery branches o rom the aorta bringing oxygen-rich
containing digested food from the blood rom the heart.
intestines to the liver
Most o the blood circulating in the liver comes rom the hepatic
Figure 1 Blood fow to and rom the liver portal vein which brings blood rom the stomach and the intestines to
the liver. The blood can be rich in nutrients that have been absorbed
678 rom digested ood depending on how recently the individual has
eaten. Because the hepatic portal vein has travelled rom the heart to
the stomach or the intestine rst, its oxygen content is relatively low.
Within the liver, the vein subdivides into divisions called sinusoids.
Sinusoids are like capillaries but are wider and the walls are not
continuously lined with cells (gure 2) . This allows the blood fowing
through to come in contact with the hepatocytes (liver cells) , and also
allows proteins such as albumin to enter and leave the blood. The
hepatic artery subdivides into arterioles, which join with the sinusoids
at various points, providing oxygenated blood. The sinusoids merge
with venules that lead to the hepatic vein. This carries blood away
rom the liver to the vena cava.
part of a lobule hepatocytes D.3 FunCtions oF tHe liver
branch of sinusoid
hepatic artery
phagocytic
Kuper cells
microvilli on
cell surface
interlobular bile duct bile canal cell central branch
of hepatic vein
vein from hepatic
portal vein
Figure 2 Circulation within the liver
proceing of nutrient by the liver
The liver intercepts blood from the gut to regulate nutrient
levels.
One o the main unctions o the liver is to regulate the quantity o
nutrients circulating in the blood. It plays a key role in the regulation
o circulating glucose by either storing glucose as glycogen or breaking
glycogen down to glucose. Because the body cannot store proteins or
amino acids, excess quantities o these in the diet are broken down in
the liver to be utilized as energy sources. The liver processes the resulting
nitrogenous waste.
The liver is responsible or managing circulating lipids which arrive
in a variety o orms. Some orms such as chylomicrons arriving
rom the intestine are broken down. The liver processes lipids in one
orm and distributes it in other orms. For example, very low density
lipoproteins (VLDL) are synthesized in hepatocytes. Their purpose is
to transport the triglycerides synthesized in the liver into blood plasma
or storage or use in the body. S urplus cholesterol is converted into
bile salts.
storage of nutrient in the liver
Some nutrients in excess can be stored in the liver.
When levels o glucose are high, insulin is released. The insulin
stimulates hepatocytes to take up the glucose and store it as glycogen.
When the levels o blood glucose all, hormones such as glucagon will be
released. This release will result in the breakdown o glycogen, glycerol,
amino acids and atty acids in the liver releasing glucose to the blood
stream.
Iron, retinol (vitamin A) and calcierol (vitamin D) are stored in the liver
when in excess and released when there is a defcit in the blood.
679
D Human pHysiology
Recycling o red blood cells
Components o red blood cells are recycled by the liver.
The typical liespan o an erythrocyte (red blood cell) in an adult is
about 1 20 days. The old and damaged erythrocytes undergo changes in
their plasma membrane which make them susceptible to recognition
by macrophages. At the end o their liespan, they are removed rom
circulation and are broken down in the spleen and in the liver. The liver
is involved in the breakdown o erythrocytes and hemoglobin. Most o
the breakdown products are recycled.
Figure 3 The role o Kupfer cells in the breakdown
o erythrocytes
The breakdown o erythrocytes starts with phagocytosis
o red blood cells by Kupfer cells.
As red blood cells age, they swell and some are enguled by Kuper cells,
which are macrophages which line the sinusoids in the liver. Inside the
Kuper cell, the hemoglobin molecule is split into globin chains and a
heme group. Amino acids rom the globin chains are recycled, while the
heme group is urther broken down into iron and bilirubin. The Kuper
cells release bilirubin to the blood. The iron is bound to transerrin and
transported to the liver and spleen or storage or to the bone marrow to
be used in the synthesis o new red blood cells.
Figure 3 is a scanning electron micrograph (SEM) o Kuper cells in the
liver. Here, within a sinusoid ( coloured blue) o the liver, Kuper cells
( yellow, at right) are seen. Kuper cells are capable o phagocytosis,
whereby they trap and engul oreign particles and substances. Note
their long arm-like extensions o cytoplasm called flopodia.
The transport o iron to bone marrow
Iron is carried to the bone marrow to produce hemoglobin
in new red blood cells.
Hemoglobin is synthesized in red blood cells. It is here that iron is added
to the heme group.
Iron is essential or red blood cell unction as it is a component o the
hemoglobin molecule but it is toxic at high concentrations. When iron is
absorbed rom the intestine or when it is released during the breakdown
o damaged red blood cells, it is transerred in the blood bound to a
protein. The protein bound to iron is called transerrin. Cells have
receptors or the transerrin molecule. Red blood cells are ormed rom
stem cells in the bone marrow. D eveloping red blood cells have relatively
high levels o transerrin receptors. Once bound, the receptor-iron
complex enters the cell and the iron is either incorporated into the heme
molecule or it is transerred to a storage molecule called erritin.
680
D.3 FunCtions oF tHe liver
Jaundice
Causes and consequences of jaundice. concentration o bilirubin in blood plasma is 1 .2
mg dl-1. A concentration higher than 2.5 mg dl-1
When red blood cells are broken down in the results in jaundice.
liver and the spleen, hemoglobin is released.
Macrophages digest the hemoglobin releasing Jaundice is a condition in which the skin and eyes
heme and globin. The globin is digested into are discoloured due to the deposition o excess
amino acids which are recycled. The heme group bilirubin (pigment) in skin tissues. Figure 5 shows
is urther converted to iron and a yellow pigment an 81 -year-old man' s hand ( bottom) exhibiting
called bilirubin. Bilirubin is also released rom the jaundice as a result o taking the antibiotic
breakdown o other proteins such as myoglobin Augmentin to treat a sinus inection. A normal
and cytochrome. Any bilirubin produced outside person's hand is seen at top or comparison.
o the liver is transported to the liver bound to the Jaundice is not a disease in itsel, but is a
protein albumin. symptom o many disorders o the liver and
biliary system. Treatment is aimed at correcting
B ilirubin is relatively insoluble, so in the liver, it the underlying cause.
is reacted with glucaronic acid to make it soluble.
The water soluble orm is secreted into passages
called canaliculi along with water, electrolytes,
bicarbonate, cholesterol, phospholipids and
salts. This mixture is called bile. Figure 4 shows
a micrograph o a human liver cell (red-brown) ,
also known as hepatocyte, and a bile canaliculus
(green). Hepatocytes secrete a green-brown
fuid called bile. Bile is drained away rom the
liver through a dense network o bile canaliculi
towards the gall-bladder. Ater a meal, bile is
expelled rom the gall-bladder and enters the
duodenum where it plays an important role in the
breakdown and digestion o atty compounds.
Figure 4 Figure 5
When a disease intereres with the normal Jaundice is seen in liver diseases such as hepatitis
metabolism or excretion o bilirubin, it can build or liver cancer. It can occur due to obstruction o
up in the blood. The result is a condition known the bile duct by gallstones or pancreatic cancer.
as jaundice. The key symptom o jaundice is a Jaundice in newborns is relatively common. There
yellowing o the eyes and o the skin. The normal are dierent causes o newborn jaundice:
Newborns have a relatively high turnover o
red blood cells.
A newborns liver is oten still developing and
may not be able to process the bilirubin ast
enough.
Some newly born inants do not eed properly
and the lack o intestinal contents means that
excreted bilirubin can be reabsorbed.
Jaundice itsel is not a disease. Treatment to
remove bilirubin involves exposure to ultraviolet
light either under a special bili lamp or by
exposing the skin to the sun. Figure 6 shows
681
D Human pHysiology
a newborn baby undergoing bili therapy. The FPO
ultraviolet light converts the excess bilirubin < 839 211 _ph D. 3 . 6 >
into products that can be excreted. The eyes are
covered to prevent any possible damage to the Figure 6
retina.
The underlying cause needs to be addressed
to stop the jaundice. There can be signicant
consequences to extended periods o elevated
serum bilirubin in inants including a orm o
neurological damage called kernicterus in which
brain damage results in deaness and cerebral
palsy. Adult patients with j aundice normally j ust
experience itchiness.
Conversion of cholesterol to bile salts
Surplus cholesterol is converted to bile salts.
Although cholesterol is absorbed rom ood in the intestine, a large
quantity is synthesized each day by hepatocytes (liver cells) . Cholesterol
is a raw material needed or the synthesis o vitamin D as well as or
the synthesis o steroid hormones. It is a structural component o
membranes and it is used in the production o bile.
The liver regulates the amount o circulating lipids such as cholesterol and
lipoproteins, either synthesizing them as required, or breaking them down
and secreting cholesterol and phospholipids in the bile. The amount o
cholesterol synthesized by the body varies to some degree with diet. Excess
saturated at in the diet increases the production o cholesterol.
Data-based questions: Lipase and bile 4 The results in the graph show that in addition
The graph in gure 7 shows the rate o bile fow to HCO3 and bile salt, another solute is
into the gall bladder at dierent levels o bile salt secreted into the bile. Explain how this
secretion. The eect o a hormone, secretin, is
also shown. conclusion can be drawn rom the results in
Look at gure 7. the graph. [2]
1 a) State the relationship between the rate o Rate of ow of bile
bile salt secretion and the rate o bile fow, x
x
without secretin. [1 ] x
x
b) Suggest the cause o this relationship. [1 ] x
x
2 Suggest when the rate o secretion o bile salt x
by liver cells needs to be highest. [1 ] Key
x x with secretin
3 S e cre tin causes H C O ( hydro gen carbonate)
3 without secretin
ions to be secreted into the bile. Using only Rate of bile salt secretion
the data in the graph, outline the eect o Figure 7 The efect o bile salts and secretin on the rate
o ow o bile
secretin on bile fow. [2]
682
D.3 FunCtions oF tHe liver
Claims about cholesterol
Educating the public on scientifc claims: scientifc
studies have shown that high-density lipoprotein could
be considered good cholesterol.
Lipids are transported in the blood in vesicles known as lipoproteins.
There are fve types o lipoproteins. Lipoproteins are composed o
a hydrophilic exterior o phospholipids, proteins and cholesterol
and a core o cholesterol and ats (triglycerides) . Chylomicrons
transport lipids rom the intestine to the liver. O ther lipoproteins
are synthesized in the liver. S ome o the lipoproteins change their
density as molecules are selectively removed rom them.
Daa-bad q: Composition of various lipoproteins
lpp Dy Dam % % % %
ca (g m-1) (m) P Ch Phphpd tgyd
HDL 1.0631.210 515 33 30 29 8
LDL 1.0191.063 1828 25 50 21 4
IDL 1.0061.019 2530 18 29 22 31
VLDL 0.951.006 3080 10 22 18 50
Chylomicrons 1001000 <2 84
<0.95 8 7
Table 1
Source of data: http://www.learn.ppdictionary.com/exercise_and_lipoproteins3.htm
1 State the relationship between density and 2 Compare the cholesterol content o HDLs
i) % triglycerides [1 ] and IDLs. [2]
ii) % protein [1 ] 3 Suggest, with a reason, why levels o HDLs
iii) % cholesterol. are reerred to as good cholesterol levels
[1 ] and levels o LDL are reerred to as bad
cholesterol. [3]
production of lasma roteins by heatocytes Figure 8
Endoplasmic reticulum and Golgi apparatus in
hepatocytes produce plasma proteins.
The rough endoplasmic reticulum o hepatocytes within the liver
produce 90% o the proteins in blood plasma, including such proteins as
fbrinogen and albumin. Albumin is a carrier protein that binds to such
things as bilirubin. For this reason it is reerred to as a transport protein,
though it also plays a role in maintaining osmotic balance in the blood.
Fibrinogen is a protein that is essential or clotting.
The act that hepatocytes are actively involved in protein synthesis
explains the characteristic appearance o hepatocytes. They show
extensive networks o ER and Golgi body providing evidence o high
levels o protein synthesis. It has been estimated that there are 1 3 million
ribosomes attached to the ER o a typical liver cell.
683
D Human pHysiology
Detoxifctio by the liver
The liver removes toxins rom the blood and detoxies them.
An important role o the liver is detoxifcation. Liver cells absorb toxic
substances rom the blood and convert them into non-toxic or less
toxic substances, using a range o chemical conversions. For example,
alcohol is converted into a less toxic substance by the enzyme ethanol
dehydrogenase. The liver converts toxic ammonia into urea. The liver
also works to detoxiy biochemicals which are oreign to the organisms
normal biochemistry such as poisons or drugs. One means by which the
liver does this is to convert hydrophobic compounds into more easily
excreted hydrophilic compounds.
D.4 the hear
udertdig applictio
Structure o cardiac muscle cells allows Use o articial pacemakers to regulate the
propagation o stimuli through the heart wall. heart rate.
Signals rom the sinoatrial node that cause Use o debrillation to treat lie-threatening
contraction cannot pass directly rom atria to cardiac conditions.
ventricles.
Causes and consequences o hypertension and
There is a delay between the arrival and thrombosis.
passing on o a stimulus at the atrioventricular
node. skill
This delay allows time or atrial systole beore Measurement and interpretation o the heart
the atrioventricular valves close. rate under dierent conditions.
Conducting bres ensure coordinated Interpretation o systolic and diastolic blood
contraction o the entire ventricle wall. pressure measurements.
Normal heart sounds are caused by the Mapping o the cardiac cycle to a normal
atrioventricular valves and semilunar valves electrocardiogram (ECG) trace.
closing causing changes in blood fow.
Analysis o epidemiological data relating to the
ntre o ciece incidence o coronary heart disease.
Developments in scientic research ollowed
improvements in apparatus or instrumentation:
the invention o the stethoscope led to
improved knowledge o the workings o the
heart.
684
D.4 tHe Heart
Cardiac muscle cells Figure 1
Structure of cardiac muscle cells allows propagation mitochondrion intercalated discs
of stimuli through the heart wall. desmosomes opening of
transverse
Cardiac muscle tissue is unique to the heart. Like skeletal muscle, cardiac tubule
muscles are striated in appearance. The arrangement o the contractile gap junctions
proteins actin and myosin is similar to what is seen in skeletal muscle.
However, cardiac muscle cells are shorter and wider than skeletal muscles cardiac
and most commonly have just one nucleus per cell. Cardiac muscle nucleus muscle bre
contraction is not under voluntary control and many o the cardiac cells sarcolemma
contract even in the absence o stimulation by nerves or the entire lie o
the organism. For these reasons, they have special structural eatures. cardiac muscle bres
The cells are Y-shaped and are joined end to end in a complex network Figure 2
o interconnected cells. Where the end o one cell contacts the end o
another cell, there is a specialized junction called an intercalated disc. This
structure appears only in cardiac muscle. The intercalated disc consists
o a double membrane containing gap junctions which provide channels
o connected cytoplasm between the cells. This allows or the rapid
movement o ions and a low electrical resistance. Being interconnected
because o their Y-shapes and being electrically connected due to gap
junctions allows a wave o depolarization to pass easily rom one cell
to a network o other cells leading to the synchronization o muscle
contraction; that is, the network o cells contract as i it was one large cell.
Figure 1 shows a coloured transmission electron micrograph (TEM) o
cardiac muscle brils (orange and blue) . Mitochondria (red) supply the
muscle cells with energy. The muscle brils, or myobrils, are crossed
by transverse tubules (narrow dark blue lines) . These tubules mark
the division o the myobrils into contractile units (sarcomeres) . In the
centre is the intercalated disc (wavy dark blue line) .
The sinoatrial node
Signals from the sinoatrial node that cause contraction
cannot pass directly from atria to ventricles.
The cardiac cycle is a repeating sequence o actions in the heart which
result in the pumping o blood to the lungs and all other parts o the
body. The cycle represents all o the events rom the beginning o one
heartbeat to the beginning o the next. Cardiologists reer to contraction
o the hearts chambers as systole and relaxation as diastole. Figure 3
shows the sequence in which systole and diastole occur in the atria and
ventricles. Figure 4 provides details o the events and pressure changes
that occur in the stages in the cardiac cycle.
Within the wall o the right atrium, there is a collection o uniquely
structured cardiac cells that spontaneously initiate action potentials
without stimulation by other nerves. The initiation occurs rhythmically.
This is the sinoatrial (or SA) node. The SA node is sometimes reerred
to as the pacemaker o the heart. Because gap junctions allow electric
charges to fow reely between cells, the contraction which originated
in the SA node spreads very rapidly across the entire atrium as i it were
one cell. This causes the atria to undergo systole, i.e. they contract.
685
D Human pHysiology
(a) atrial systole oxygenated Signals rom the sinoatrial node that cause contraction within the atria
blood cannot pass directly rom the atria to ventricles. Instead the signal
deoxygenated rom the S A node reaches the atrioventricular ( AV) node. From there
blood the signal spreads throughout the heart via specialized heart muscle
tissue called Purkinje fbres. This signal causes the ventricles to undergo
(b) ventricular systole bicuspid systole. This snaps the atrioventricular valves shut. Ater the ventricles
valve are emptied the semilunar valves close.
tricuspid
valve The ventricles begin diastole, the atrioventricular valves open and
the ventricles start flling with blood. Finally, all our chambers are
in diastole and flling. When the atria are flled and the ventricles are
70 per cent flled, the cycle has ended.
left atrium systole systole diastole diastole
left ventricle diastole pressure in
semi-lunar aorta
16 valves closed
semi-lunar pressure
valves open in ventricle
12 bicuspid
pressure/kPa valve open
8
(c) diastole pressure in atrium
semilunar valves bicuspid
4 valve closed
0
time/s 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
atrial systole ventricular systole atrial and ventricular diastole
Figure 4 The pressure changes inside the heart during the cardiac cycle
Figure 3 The cardiac cycle The atrioventricular node
There is a delay between the arrival and passing on
of a stimulus at the atrioventricular node.
There are mechanisms in place to stagger the contraction o the atria
and the ventricle. The fbres which connect the S A node to the AV
node carry the action potential relatively slowly. There is a delay o
approximately 0.1 2 s between arrival o the stimulus rom the SA node
and initiation o the impulse with the ventricles.
The cells o the AV node take longer to become excited than the cells
o the S A node. There are a number o eatures o the AV node that lead
to the delayed initiation o contraction o ventricles by the AV node.
The AV node cells have a smaller diameter and do not conduct as quickly.
There is a relatively reduced number o Na+ channels in the
membranes o AV node cells, a more negative resting potential and a
prolonged reractory period within the cells o the AV node.
There are ewer gap j unctions between the cells o the AV node.
There is relatively more non-conductive connective tissue in the node.
686
D.4 tHe Heart
The delay in conduction
This delay allows time or atrial systole beore the
atrioventricular valves close.
The delay in the initiation o contraction caused by the AV node is
important because it ensures that the atria contract and empty the
blood they contain into the ventricles frst beore the ventricles contract.
The contraction o ventricles causes the AV valves to snap shut, so that
contraction o the ventricles too early would lead to too small a volume
o blood entering the ventricles.
superior vena cava
Coordination of contraction
Conducting fbres ensure coordinated contraction right atrium left atrium
o the entire ventricle wall. SA node
Purkinje
Once through the AV bundle, the signal must be conducted rapidly AV node bres
in order to ensure the coordinated contraction o the ventricle. AV bundle
The atrioventricular bundle receives the impulse rom the bundle branches
AV node and conducts the signal rapidly to a point where Purkinje bres
it splits into the right and let bundle branches. The bundle
branches conduct the impulses through the wall between the
two ventricles. At the base, or apex o the heart, the bundle
branches connect to the Purkinje fbres which conduct the
signal even more rapidly to the ventricles. These fbres have a
number o modifcations that acilitate them conducting signals
at such a high speed:
They have relatively ewer myofbrils.
They have a bigger diameter. inter-ventricular heart apex
They have higher densities o voltage-gated sodium channels. septum
They have high numbers o mitochondria and high glycogen stores.
Figure 5
The contraction o the ventricle begins at the apex.
The invention of the stethoscope
Developments in scientifc research ollowed improvements in apparatus or
instrumentation: the invention o the stethoscope led to improved knowledge o the
workings o the heart.
Stethoscopes are one o the most recognizable some patients were inested with vermin
symbols o the medical proession. They were and i the patient was a emale, modesty was
invented in the 1 9th century by Rene Lannec an issue. While these variables were the main
though the original design has been signifcantly pressure behind the development o the tool,
modifed since then. Though not widely there were unintended benefts o the device. It
practised, practitioners would place their ears became one o the frst tools that allowed or the
directly on the chest o patients to listen to the non- invasive investigation o internal anatomy.
heart beat. In the 1 9th century, many patients Dierent types o heart abnormalities result
were too obese or sounds to be heard by this in dierent sounding heartbeats which can be
method, washing was not the social norm and detected through the stethoscope.
687
D Human pHysiology
120 semilunar Causes o the sound o the heartbeat
semilunar valves close
Normal heart sounds are caused by the
pressure (mm Hg)100 valves open atrioventricular valves and semilunar valves
closing causing changes in blood fow.
80 aortic pressure
60 A normal heartbeat has two sounds, both o which are caused
by the closing o valves. When the atrioventricular valves snap
40 ventricular pressure AV valves shut, there is a lub sound. Ater the ventricles are emptied the
20 AV valves semilunar valves close, causing the second sound, the dub sound.
0 close open
heart sounds atrial pressure
Figure 6 1st 2nd
lub dub
Figure 7 Variables afecting the heart rate
Measurement and interpretation o the heart rate under
dierent conditions.
A number o variables that can infuence heart rate can be assessed
in the school laboratory setting. Some examples include types o
exercise, intensity o exercise, recovery rom exercise, relaxation,
body position including lying down, breathing and breath holding,
exposure to a cold stimulus and acial immersion in water.
Detecting heart rate can be done in a number o ways.
Figure 7 shows how to detect the pulse o an artery in the wrist.
The researcher uses ngers rather than the thumb. The side o
the neck below the jaw has an artery where determining pulse is
relatively easy. D ata- logging equipment including hand- grip heart
monitors, ear clips, EKG sensors and wrist watches can eed data into
computers. The built-in cameras on some tablet computers can be
used as a device to detect heart rate.
Data-based questions: Cold exposure and heart rate
The resting heart rate o a sample o students cardiovascular response 100
was determined through monitoring by a wrist 90
band that measured heart rate. An ice pack was 80
then placed on the orearm o these students or 70
one minute. The heart rate was measured at the 60
end o the one minute o cold exposure and then 50
again at the end o each minute or two minutes 40
o recovery.
1 Determine the mean resting heart rate. [1 ] 30
2 Calculate the percent decline in mean heart 20
10
rate with cold exposure. [2]
3 Evaluate the conclusion that cold exposure 0 rest after 1 minute 1 minute 2 minutes
of cold exposure into recovery into recovery
suppresses heart rate. [2]
Figure 8
688
D.4 tHe Heart
artifcil pcemkers
Use o artifcial pacemakers to regulate the heart rate.
Artifcial pacemakers are medical devices that are surgically ftted in
patients with a malunctioning sinoatrial node, the part o the heart
that initiates the heartbeat, or in patients with a block in the signal
conduction pathway within the heart, which impairs the nerve
impulses generated by the node. The purpose o the device is to
maintain the rhythmic nature o the heart beat when the heart does
not beat ast enough or when there is a ault in the hearts electrical
conduction system.
Pacemakers can either provide a regular impulse or discharge only
when a heartbeat is missed so that it beats normally. The most
common, basic pacemaker monitors the hearts rhythm and when a
heartbeat is not detected, the ventricle is stimulated with a low voltage
pulse. More complex orms stimulate both the atria and the ventricles.
Figure 9 shows an X-ray o the chest o a male patient with a heart
pacemaker (upper right) . The heart is the blue mass at centre right, in
between the lungs (white) . The pacemaker has leads (running rom
upper right to lower centre) to supply regular electrical impulses to
the heart.
Figure 9
Relting the crdic cycle to the ECG trce
Mapping o the cardiac cycle to a normal electrocardiogram (ECG) trace.
Cardiac muscle contracts because it receives QRS
electrical signals. These signals can be detected complex
and quantifed using an electrocardiogram (ECG
or EKG) . Data-logging ECG sensors can be used R
to produce a pattern as shown in fgure 1 0.
The P-wave is caused by atrial systole, the PR ST T
QRS wave is caused by ventricular systole. The P segment segment
T- wave coincides with ventricular diastole.
Interval analysis can be perormed on the EKG PR interval Q
signal, or example on the times between the S
beginning o P and Q (PQ) , QRS, and Q to
the end o T (QT) intervals. The height o QT interval
the R-wave can be compared when the body
changes position rom standing to lying down.
The overall pattern can be compared beore and
ater mild exercise.
Specialists can use changes to the size o 0 0.1 0.2 0.3
peaks and lengths o intervals to detect heart time/s
p a t h o l o g y.
Figure 10 An ECG trace
689
D Human pHysiology
Explaining the use o a defbrillator
Use o defbrillation to treat lie-threatening cardiac conditions.
Cardiac arrest occurs when the blood supply to the
heart becomes reduced and heart tissues are deprived
o oxygen. One o the rst negative consequences
o this is abnormalities in the cardiac cycle such
as ventricular brillation. This is essentially the
twitching o the ventricles due to rapid and chaotic
contraction o individual muscle cells.
When rst responders reach a scene where Figure 11 First responders applying a defbrillator to the
a victim is not breathing, they will apply the chest o a man who is undergoing cardiac arrest
two paddles o a debrillator to the chest o the
patient, setting up a diagonal line between the
two paddles with the heart in the middle. The
device will rst detect whether brillation is
happening and i it is, an electric discharge is
given o to restore a normal heart rhythm.
Hypertension and thrombosis
Causes and consequences o hypertension and thrombosis.
Atherosclerosis is hardening o the arteries caused by Figure 12 A normal artery (top) can be compared to
the ormation o plaques, or atheromas, on the inner an artery where a plaque has ormed (bottom)
lining o arteries (gure 1 2) . Plaques are areas that
are swollen and accumulate a diversity o debris. The Chronic high blood pressure can lead to stroke
plaques oten develop because o high circulating by weakening blood vessels in the brain
levels o lipids and cholesterol. The plaques can causing them to narrow, leak or rupture. It can
reduce the speed at which blood moves through also lead to blood clots in the arteries leading
vessels. This can trigger a clot, or thrombosis, which to the brain potentially causing a stroke.
can block the blood fow through the artery and
deny the tissue access to oxygen. I this occurs on
the surace o the heart, the consequence can be a
myocardial inarction, or heart attack.
Greater resistance to the fow o blood can slow
the fow o blood. The result is greater pressure on
the walls o arteries, also known as hypertension.
Hypertension has a number o consequences.
Damage to the cells that line arteries can cause
a cascade o events that ultimately leads to the
arteries becoming narrower and sti.
Constant high blood pressure can weaken Chronic high blood pressure is one o the most
an artery causing a section o the wall to common causes o kidney ailure as it damages
enlarge and orm a bulge called an aneurysm. both the arteries leading to the kidney and the
An aneurysm can burst and cause internal capillaries within the glomerulus.
bleeding. They can orm in any artery in the
body but are most common in the aorta. There are a number o actors that are correlated with
a greater incidence o thrombosis and hypertension.
690
D.4 tHe Heart
Having parents who have experienced heart Sedentary liestyle, i.e. a lack o exercise is
attacks indicates a genetic precondition to correlated with obesity and prevents the
either condition. return o venous blood rom the extremities
leading to a greater risk o clot ormation.
Old age leads to less fexible blood vessels. In
children, the normal ranges are lower than
or adults.
Risk in emales increases post-menopause
correlated with a all in estrogen levels.
Males are at greater risk compared with emales
correlated with lower levels o estrogen.
Smoking raises blood pressure because
nicotine causes vasoconstriction.
A high-salt diet, excessive amounts o alcohol
and stress are also correlated with hypertension.
Eating too much saturated at and cholesterol Figure 13 A blood clot (thrombus) in the coronary artery,
promotes plaque ormation. showing red blood cells (purple) in a fbrin mesh (threads) .
The coronary artery supplies blood to the heart
Height aects blood pressure.
Interpreting blood pressure measurements
Interpretation of systolic and diastolic blood pressure measurements.
Blood pressure, or more accurately arterial pressure
is the pressure that circulating blood puts on
the walls o arteries. During each heartbeat, the
pressure o blood within arteries varies rom a peak
during the ventricle systole to a minimum near the
beginning o the cardiac cycle when the ventricles
are lled with blood and are in systole.
Blood pressure measurements are oten quoted Figure 14
in the pressure unit mm Hg. An example blood
pressure would be 1 20 over 80. The higher
number reers to the pressure in the artery caused by
ventricular systole and the lower number reers to
the pressure in the artery due to ventricular diastole.
Figure 1 4 shows a pregnant woman having prevents blood rom entering the orearm. The
her blood pressure measured. Monitoring cu is slowly defated and the nurse listens or the
blood pressure during pregnancy is important. occurrence o a sound. This occurs when the cu
High blood pressure during pregnancy is called pressure is lowered below the systolic pressure.
pre-eclampsia and it can be a lie-threatening The sound is caused by the opening and closing
condition i it is not treated. o the artery. The cu is urther defated until
normal blood fow returns and there is no longer
To measure blood pressure, a cu is placed on the a sound. The absence o sound occurs when the
bicep and infated so that it constricts the arm and cu pressure is less than the diastolic pressure.
691
D Human pHysiology
Blood preure sytolic Diatolic sphygmomanometer
category
90 or less 60 or less column of mercury 300
Hypotension (low 280
blood pressure)
indicating pressure 260 no sounds
Normal in mm Hg 240 (artery is closed)
220
Pre-hypertension sounds heard
200 (artery is opening
High blood and closing)
pressure (Stage 1 Less than 120 Less than 80 180
hypertension) 120139 8089 no sounds
140159 9099 160 (artery is open)
High blood
pressure (Stage 2 140 systole
hypertension) 120
Hypertension 100 diastole
crisis 80
Table 1 60
40
20
0
inatable
160 or higher 100 or higher rubber cu
Higher than 180 Higher than 110 artery sounds are heard
air valve with stethoscope
squeezable bulb
inates cu with air
Figure 15
Data relating to coronary heart disease
Analysis of epidemiological data relating to the incidence of coronary heart disease.
Coronary heart disease (CHD) refers to the Gender groups, age groups, groups that differ
damage to the heart as a consequence of reduced in their level of physical activity, groups with
blood supply to the tissues of the heart itself. This different genotypes, groups with differing medical
is often caused by narrowing and hardening of the histories all can have different probabilities of
coronary artery. experiencing CHD. Epidemiology is the study
of the patterns, causes and effects of diseases in
Ethnic groups can differ in their predisposition groups of individuals or populations.
to CHD because of differing diets and lifestyles.
Data-baed quetion: Hypertension 4 Evaluate the impact of differences
High blood pressure (hypertension) is a major risk between systolic and diastolic pressure
factor for coronary heart diseases. In a major study,
more than 31 6,000 males were followed for 1 2 on death rate. [3]
years to investigate the effects of high blood pressure
(BP) . Figure 1 6 shows the relationship between 81
systolic and diastolic blood pressure and the effect
on the death rate per 1 0,000 persons year1. coronary heart 43 44
36
disease death rate / 37 35
10, 000 persons year-1
1 Determine the death rate for a systolic blood 32 26 25 25 25 25
24
pressure between 1 40 and 1 59 mmHg and a >160
21 17 14 13 13 12 140159
diastolic blood pressure between 75 and
79 mmHg. [1 ] 10 12 9 9 9
>1009098908975797074 <70
2 Describe the effect of systolic blood pressure and 120139
diastolic blood pressure on the death rate. [2 ] <120 Systolic BP / mm Hg
3 Calculate the minimum difference between Diastolic BP / mm Hg
systolic and diastolic blood pressure where Figure 16 The efect o blood pressure on coronary heart
disease
the death rate is highest. [1 ]
692
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