Form 2 Science Chapter 4

Form 2 Chapter 4: INTERDEPENDENCE AMONG LIVING ORGANISMS AND THE ENVIRONMENT

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4.1 Interdependence among Living Organisms

Species

A group of organisms of the same kind that can interbreed to produce fertile offspring

Population

A group of the same species of organisms that live in the same place at the same

time

Community

Populations of different species in the same place that interact with one another

Habitat

The place where a particular organism lives

Provides an organism with air, food, shelter and a place to breed

Ecosystem

Is made up of living organisms and non-living things (water, air, temperature, light)

that interact with one another

Biotic components – the living things

Abiotic components – the non-living things

Interaction in an environment

For survival, living organisms that live together in an ecosystem are interdependent on

each other and also interdependent on the non-living components in their environment

such as air, water and sunlight for survival

The interdependence among living organisms and the environment creates a balanced

ecosystem.

A balanced ecosystem is a stable ecosystem because the living and non-living

components in it do not change very much over a period of time.

The example of interaction between living things and non-living things in a pond

Aquatic plants obtain sunlight for the process of photosynthesis

Aquatic plants obtain mineral salts from the soil in the pond

Aquatic plants depend on aquatic animals to obtain carbon dioxide for

photosynthesis

Aquatic animals depend on aquatic plants to supply oxygen for the process of

respiration

Small fishes and tadpoles eat aquatic plants

Big fishes eat the small fishes

The kingfisher eats the fish

Interaction between living things and non-living things in the environment is important as

it maintains

Balance in the environment (the number and types of living things within the

environment remain the same)

Balance in the carbon dioxide and oxygen cycles (oxygen and carbon dioxide content

in atmosphere remain the same)

In order to maintain a balanced ecosystem, the following factors need to be maintained

The number of individuals in the different population

The number of populations in the different communities

The composition of gases in the air and the quality of the air

The availability of water, soil and nutrients


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4.2 Interaction between Living Organisms

The organisms in a community interact with one another to obtain food, shelter,

protection, transport, support and many other necessities.

This interaction creates a balanced and stable environment.

There are three major types of interactions between living organisms:

Prey-predator

Symbiosis

Competition

4.2.1 Prey-predator

Also called as predation

In this interaction, a predator kills a prey for food.

A predator is an organism that hunts and eats another organism

Normally, the predators are larger than their prey

Predators are carnivores or omnivores. They have special adaptions such as powerful

jaws, sharp teeth, sharp claws, strong beaks or good vision.

A prey is the organism that is hunted and eaten by other organisms

A prey usually has the ability to run away with special adaptation such as monoscopic

vision and run fast.

In the prey-predator relationship, predator benefits while prey loses.

Examples:

Predator Prey

Tiger Deer

Kingfisher Fish

Lion Buffalo

Snake Chicken

Chicken Worms

Owl Rat

Guppy Mosquito larvae

4.2.2 Symbiosis

The relationship between two species of organisms that live closely together and interact

with each other

One organism always benefits by receiving food, a place to stay and shelter. The other

organism may benefit, be at a disadvantage or is not affected.

There are 3 types of symbiosis

Commensalism

Mutualism

Parasitism

Commensalism

Commensalism is a relationship between two organisms in which one organism (the

commensal) benefits from the other (the host) without damaging the host.

Examples of plants that live on trees to obtain sunlight are: the money plant, the

staghorn fern, the pigeon orchid and the bird’s nest fern. Though they take tree trunk

as a home, they do not harm the tree.


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Examples of animals that live on other animals to obtain food (that fall out of the

host's mouth), as well as for shelter and transport are

(a) Barnacles that live on the shells of crabs, cockles or snails

(b) Remora fish (commensal) that is often found attached under a shark. It feeds on

the scraps of food left by shark without harming the shark.

Mutualism

Mutualism is an interaction between two different organisms that live together in

which both organisms benefit. It can be between two animals, two plants or one

animals and one plant. They obtain nutrition and shelter from each other.

Examples:

Sea anemone and hermit crab

(i) The sea anemone has tentacles that can sting, and protects the hermit crab

with them.

(ii) The sea anemone obtains transport and food ( food bits that drop ) from the

hermit crab.

Ox peckers and buffaloes

Ox peckers eat the ticks and leeches that feed on buffaloes.

The Egyption Plover bird and crocodiles

The Egyption Plover bird eats leeches as well as food particles stuck between the

crocodile's teeth.

Nitrogen-fixing bacteria and leguminous plants

(i) Rhizobium bacteria live in the root nodules of leguminous plants. They

convert the nitrogen in the air and change it to nitrates for the use of the plants.

(ii) These bacteria obtain food and shelter from the leguminous plants.

Green algae and fungus

(i) The algae provide the fungus with food.

(ii) The fungus protects the algae and release carbon dioxide for the algae to

use during photosynthesis.

Symbiotic bacteria and herbivorous animals

(i) Symbiotic bacteria live in the digestive tract of herbivorous animals and help

in the digestion of cellulose.

(ii) The bacteria obtain food and shelter from the host.

Parasitism

Parasitism is another type of interaction between two organisms.

Only one organism benefits (parasite). The others organism is harmed or even

killed (host).

Examples:

Tapeworm is a parasite that obtains food and shelter from human. Human as a

host are harmed by losing nutrients, resulted loses weight and becomes weak.

Tick that live on a host feeds on the host’s blood

Stem borers and oil palm leaves

Tree barnacles and trees

Aphids and mustard plants

Mistletoe and a tree

A parasite may live outside the body (ectoparasite) or inside the body (endoparasite)

of other living organisms (host).


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4.2.3 Competition

Happens when organisms living in the same habitat compete for the same basic needs.

Animals compete to obtain food, water, breeding mate for reproduction and shelter.

Plants compete to obtain water, sunlight, minerals salts and living space.

Competition becomes more intense when basic resources are limited.

Stronger organisms are success, while weaker and smaller organisms are driven out.

2 types of competition are intraspecific competition and interspecific competition

Intraspecific competition is the competition between living organisms of the same

species for the same resources in an ecosystem.

Male deer compete for a mating partner

A pride of lions compete for food

Interspecific competition is the competition between living organisms of different species

for a limit resource in the same area.

Flowering plants compete with weeds to obtain water and minerals.

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

more easily

4.2.4 Importance of Interaction between Living Organisms and the

Environment

Interactions between living organisms and the environment are important because they

create a balanced ecosystem by maintaining the size of populations in it.

When a population of living organisms grows too large, the living organisms of the same

species will compete with each other for their basic needs.

The living organisms which are stronger able to adapt to the changes in the environment

will survive whereas the weaker ones will die. This reduces the size of the population.

4.2.5 Biological Control

Biological control is a method of reducing the number of pests using the natural

predator of the pests.

Biological control uses prey-predator or parasitism interaction

Biological control is used in agriculture to control pests that attack crops and fruit trees

without using chemical pesticides.

Types of Interactions

Prey-predator Symbiosis

Mutualism

Commensalism

Parasitism

Competition

Intraspecific competition

Interspecific competition


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For example:

Owls and snakes are used to control the rat population in oil palm plantations

Guppy fish are reared in ponds to control the population of mosquito larvae

Ducks are used to control snail and weed populations in paddy fields

Ladybugs are used to control the aphid population in fruit orchards

A Trichogramma wasp is laying its eggs in the eggs of a moth. The growing larvae of

Trichogramma wasp feed on the moth’s caterpillar and kill it. Caterpillars are pests

that destroy fruits leaves.

Advantages of biological control

Does not pollute the environment

Does not affect or kill other organism because the predator feeds on specific prey

Cost-effective over the long term (cheap and safe)

Does not affect the health of human

Disadvantages of biological control

The results are not instant. It takes time.

The introduction of new species may upset the balance of an ecosystem

Some predators attack the other organisms

The population of predators increases

Not every pest has its predator that can control it. Chemical control is often needed.

Biological control has its advantages and disadvantages. The implementation of

biological control should be planned and monitored closely to ensure that its

effectiveness is sustained.

4.3 Food Web

4.3.1 Food Chain

A food chain shows the feeding relationship between living organism

A food chain is an energy link showing the energy in food is passed from plants

(producers) to animals (consumers).

The sun is the main source of energy for all living organisms in a food chain.

Producers are all green plants that make food through photosynthesis.

Consumers are animals that eat plants or other animals.

Primary consumer normally is an herbivore that eats the plants.

Secondary consumer is a carnivore that eats the primary consumer.

Tertiary consumer is a carnivore that eats the secondary consumer.

Decomposers are organism that decompose dead organism (animals or plants) and

change them into simple substances such as bacteria and fungi. These simple

substances can be used again by green plants as nutrient.

Normally we don’t show the decomposers in a food chain or a food web. Otherwise, it

will become too complex.

Examples of food chains are given below:

a) Grass Rabbits Eagles

b) Green plants Goats Human Beings

c) Paddy plants Rats Snakes Eagles


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4.3.2 Food Web

A food web consists of several food chains that are interlinked

In a real ecosystem, feeding relationship among living organisms is complex.

Most living organisms eat more than one type of food. Therefore, food chains are

interconnected.

The food web helps to maintain a balanced ecosystem by controlling the number of living

organisms at each level of a food chain.


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4.3.3 Pyramid of numbers

A pyramid of numbers shows the relative number of organisms at each level of a food

chain

From the base to the peak:

Number of organisms decrease

Size of organisms increase

More energy is lost

Producers' number is the most and forms the base of the pyramid.

The number of producers is always greater than the number of primary consumers in

order to provide sufficient food to the primary consumers.

The number of primary producers is greater than the number of secondary producers.

Therefore, primary producers make up the second level of the pyramid, the level above

the producers.

Secondary producers make up the third level of the pyramid. Tertiary consumers make

up the fourth level of the pyramid and so on.

The final consumers are at the apex of the pyramid and are the least in number.

The animals at the higher levels tend to be larger in size.


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4.3.4 Energy flow

A food chain or food web shows the energy transfer from one living organism to another

The arrows in a food chain or a food web represent the feeding relationship as well as

the energy flow from one organism to another.

All energy in a food web comes from the Sun

During photosynthesis, plants convert light energy from the Sun into chemical energy

(stored as food)

When the consumers eat the plants, the chemical energy is transferred to them

Meanwhile, the consumers also lose energy in the form of heat through respiration,

growth, metabolism, excretion, defecation and other life processes.

Thus, not all of the energy is passes to the next level as some energy are used and lost.

4.3.5 Disturbances in the ecosystem

The numbers of organisms in an ecosystem must be maintained at equilibrium to

ensure that all organisms have sufficient food supply. This situation will ensure that the

balance of nature in an ecosystem is maintained.

However, a food web is not permanent in any community. Some animals and plants may

die. Some animals may leave the community while some may move into the community.

When one population of living organisms in a food web is missing or decreases in

number, it will affect the other living organisms. The food web becomes imbalanced.

If new living organisms are introduced into a food web, the food web will become

imbalanced too.

Disturbances at any level of a pyramid of numbers will cause the equilibrium in a food

chain to be disrupted. The number or organisms at each level of a pyramid of numbers

will not be balanced.

For example, if all the frogs in the area are captured.

(a) The number of snakes will decrease because of a shortage of food.

(b) The number of caterpillars will increase because of a shortage of predators.

(c) The number of leaves will decrease because of the increase in caterpillars.

The increase or decrease in the number of organisms will affect the equilibrium of the

ecosystem.

It would take a long time for the ecosystem to become balanced again.


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4.4 Photosynthesis

Photosynthesis is a process by which the chlorophyll in green plants absorbs light

energy to make food from carbon dioxide and water.

Light comes from the Sun or other light source

Water is absorbed from the soil by the roots

Carbon dioxide enters the leaves through the stomata (small pores on the leaves)

Chlorophyll is the green pigment in the leaves that absorbs light energy.

Products of photosynthesis:

Glucose – converted into starch and stored in other parts of the plant

Oxygen – released into the air

The glucose produced is brought to other parts of the plant to be

(a) Oxidised through the process of respiration to provide energy.

(b) Stored as starch, if in excess.

Photosynthesis is important to maintain the equilibrium of an ecosystem

The importance and role of photosynthesis:

Enable green plant to make own food

Supply food to animals

Remove carbon dioxide from the atmosphere

Regulate and maintain carbon dioxide content in atmosphere

Increase oxygen content in atmosphere


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Natural Gas Cycle

Natural gas cycles maintain the content of gases in the air.

The carbon and oxygen cycles are two natural gas cycles.

The carbon cycle

The carbon cycle is the circulation of carbon dioxide on Earth. It involves the use and

return of carbon dioxide to the air. These processes take place continuously.

The carbon cycle maintains the content of carbon dioxide in the air.

The processes that release carbon dioxide into the air include :

(a) Respiration or breathing.

(b) Combustion.

(c) Decomposition.

Photosynthesis, which takes place in green plants, removes carbon dioxide from the air.

The oxygen cycle

The oxygen cycle is the circulation of oxygen on Earth. It involves the use and return of

oxygen to the air. These processes take place continuously.


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The oxygen cycle maintains the content of oxygen in the air.

The processes that use oxygen include :

(a) Respiration or breathing

(b) Combustion

(c) Decomposition

(d) Rusting

Photosynthesis is the only process that release oxygen into the air.

Rusting uses up oxygen but does not release carbon dioxide

4.5 Importance of Conservation and Preservation of Living

Organisms

Conservation – to use natural resources wisely with minimal disturbances to the living

organisms and the ecosystem

Preservation – to maintain living organisms and the ecosystem in their original and

balanced state


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Ways to conserve and preserve living things:

Control pollution to preserve habitats

Manage natural resources wisely to protect flora and fauna by setting up forest

reserves and marine park and establish wildlife sanctuaries centres

Avoiding excessive mining

Replanting after logging, and practising selective logging

Educate through the mass media to increase public awareness on the importance of

conservation and preservation of living organisms and their environment

Practise sustainable development

Practise 3R

Reuse

Recycle

Reduce

Manage forests properly to minimise deforestation and illegal logging and to prevent

the occurrence of forest fires

Introduce legislation on wildlife protection

To protect endangered species

To control commercial hunting

To prevent overfishing

The importance of conservation and preservation of living organisms are:

Maintaining the balance of the ecosystem :

The presence of animals and plants maintain the composition of oxygen and

carbon dioxide in the atmosphere.

Trees help in the control of land erosions and floods by holding firmly the soil

particles.

The humidity in the forest helps to decompose dead organisms.

Economy

Forest products such as teak wood, orchid and rattan; as well as herbs can be

obtained.

Wildlife supplies such as leather, horns and meat can be obtained from the forest.

Some forest trees or wild animals are also used for scientific research.

Recreation

People can enjoy the beauty of the natural environment.

In the tropical forest, the air is fresh and unpolluted; therefore it is good for

relaxation.

4.6 Maintaining the Balance of Nature

Human beings have a very close relationship with the ecosystem.

Human beings are a part of the ecosystem that depends on living and non-living things

for survival.

Human beings interact with the ecosystem to obtain needs and to lead comfortable lives.

We obtain our needs in many ways. At the same time, we also disturb the balance of

nature.

Human activities bring about an imbalance and decline in the ecosystem.


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Activity Effects

Deforestation When trees are cut down and forest are cleared, - the concentration of carbon dioxide in the atmosphere increase, cause greenhouse effect and global warming - natural habitats are destroyed causing animals and plants become extinct - soil erosion occurs - depletion of water catchment areas causes flash flood

Agriculture When farming is carried out intensively without practising conservation, - soil erosion and depletion of minerals in the soil can occur - excessive use of fertilisers and pesticides cause water and soil pollution

Overfishing & overhunting

- Extinction of animals - Decline in biological diversity

Industrialisation - Air pollution and acid rain due to releasing smoke, haze and acidic gases into the atmosphere - Water and soil pollution due to releasing of excessive toxic chemicals into the environment

Poor waste management

- Rivers and lakes are often used as rubbish dumpsites - Decaying matter gives out bad smells and attract pests - Causes soil, water and air pollution

If we continue to exploit and destroy nature, there will be no more fresh air, fresh water,

food and suitable place to live.

Therefore, human activities must not result in any permanent damage to wildlife, habitats

and natural resources.

We need a stable, productive and balanced ecosystem so that we

Get enough food and water for our daily needs

Live healthily and fight against diseases

Continue to conserve and preserve other living organisms and natural resources on

the Earth

Form 2 Science Chapter 4

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