SCIENCE F2 CHAPTER 2 (2.3)

SCIENCE FORM 2
(CHAPTER 2 :
ECOSYSTEM)

2.3 Interdependence Among Living Organisms

2.3 Interdependence Among Living Organisms

Species

a species a species of a species of
of fish water plant frog

1. Species is a group of organisms that have the same shape, structure
(common characteristics) and can reproduce to breed springs .

2. In the figure above, fish, frog and water plant are three different
species.

Population

A population is a number or group of organisms of
the same species that live together in a habitat.

A A population
population of water plants

of fishes

A
population

of frogs

Community

A community is made up of many populations
living together in a particular place (habitat).

All the fishes, frogs, tadpoles, water plants, snails, grass
and butterflies made up the community.

Habitat

A habitat is a natural living place of certain plants and
animals.

air food space shelter Place to breed

It is a habitat for water lily.

It is a habitat for frog.

It is a habitat for water snail.

It is a habitat for water plant.

Ecosystem

An ecosystem refers to the community of
organisms living in the same habitat, together
with the non-living environment.

air

water

soil

All the living organism and the non-living environment
such as water , soil and air made up an ecosystem.

2.4 Interaction Between Living Organisms

PREY-PREDATOR

1. Prey-predator is a relationship where an animal captures and eat
other animals.

2. A predator is an organism that kill and eats another organism.

3. A prey is the organism that is eaten.

For example, snake is a predator, rat is
its prey.

SYMBIOSIS

Symbiosis happen between two or more different species which
live close together and interact with each other.
There are three types of symbiosis:
• Commensalism
• Mutualism
• Parasitism

Commensalism

Commensalism is a relationship between two organisms
which only benefits one organism without harming the
other.

Remora fish is the commensal, it feeds on the
scraps of food left by the shark. The shark is
unharmed.

-The staghorn fern grows on a tree. This helps it easily obtain
sunlight to process photosyntesis.

-Examples of plants that live on tress to obtain sunlight are:

(i) the money plant
(ii) the pigeon orchid
(iii) the bird’s nest fern

Mutualism

a. Mutualism is an interaction between two different
organisms that live together in which both organisms
benefits.

b. They obtain nutrition and shelter from each other.

The Egyptian Plover bird and crocodiles.
the Egyptian Plover bird eats fleas and ticks crocodile as well
as food particles stuck between crocodile's teeth.

- Lichen consists of fungi and algae living together. The algae
produce food and the fungi provide shelter.

Parasitism

Parasitism is an interaction between two organisms that
benefits one organism only and harms the other.

Example
-Tapeworm is a parasite, it
lives in human intestine.

Tapeworm obtains food and
shelter from humans.
Human loses weight and
becomes weak.

Competition

Competition is a relationship where organisms
compete with each other for food, light, water,
shelter, mate or minerals.

Competition Intra-specific
competition

Inter-specific
competition.

• Stronger organisms are successful in controlling their territory.

Weaker and smaller organisms are driven out of the area.
• Examples:

a. Flowering plants compete with weeds to obtain water and
mineral salt.

b. Lions in a pride compete for food

c. Plants in a tropical rainforest compete for basic needs. Taller
trees obtain sunlight more easily.

Intra-specific competition.
Competition among organisms of the same species.

Examples :
a.flowering plants compete with weeds to obtain water
and mineral salt.
b.lions in a pride compete for food
c.plants in a tropical rainforest compete for basic
needs. Taller trees obtain sunlight more easily.

Inter-specific competition.
Competition among organisms of different species.

Summary Species 1 Species 2

Type of interaction (+) (-)
Competition (+) (-)
Prey predator (+) (-)
Parasitism (+) (0)
(+)
Commensalism (+)
Mutualism ©NgFL/SMK DC

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Biological Control

Biological control is a method in which a
predator, the natural enemy to a certain
pest, is used to control the population of
the pest in an area. The aphid is a pest to

the gardeners,
damaging his plants.

The ladybirds helps the
gardener by ridding him
of these pests

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Biological control has many advantages as
compared with using pesticides.

Advantages Disadvantages

It does not pollute the Takes a long time
environment. before any effect is
seen

It does not kill other The balance of the
organism except the ecosystem might be
pests disrupted

It is cheap and safe to
use.

Biological Control

(Owls is a natural (When the eggs (Rearing
predator of rats in hatch, the guppies in a
Oil Palm) ichneumon larvae pond to eat
feed on the body mosquito
of the host.) larvae.)

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Factors that influence
population size in an ecosystem

Factors that cause population size
to change:
Disease
The presence of predators
Sources of food
Change of weather

a) Disease – The population of animals
and plant decreases when a disease
strikes.

Example 1 : poultry
affected by a disease

Example 2 : Panama disease,
also called banana wilt, a
devastating disease of
bananas caused by the soil-
inhabiting fungus

b) Presence of

predators – when the
number of predators
increases, the number
of prey decreases.

C) Sources of food –if

the sources of food
decreases, animal can
threatened by
extinction

D) Change of
weather – Droughts
cause soil to
become dry and
infertile and
increase the risk of
forest fires.

CHANGES IN
ECOSYSTEM

Changes in
ecosystem such as

:

limited animal increase or
water migration decrease in
supply population size

Upset the balance between
population.

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