SCIENCE - FORM 2
Interdependence Among Living Organisms and the Environment
INTERDEPENDENCE AMONG LIVING ORGANISMS
1. A specific group of organisms that have the same characteristics is known as species.
2. Organisms from the same species mate together to produce offsprings, for example the species of
3. Organisms of the same species that live and reproduce in a particular habitat will form a
population. For example, in a pond habitat there are populations of fish, shrimps and water
4. A habitat is the place where on organism stays in its naturel state.
5. In a habitat, an organism can eat reproduce and get shelter.
6. Habitat of several organisms :
7. A community is formed when a few populations of different types of animals and plants live a
habitat. An example of a community is the population of animals ( fish ) and plants ( weeds ) living
together, interacting and influencing each other in a pond.
8. An ecosystem is formed when a community of living organisms in a habitat interacts with one
another as well as with the non-living environment.
9. An ecosystem consist of the living or biotic components in the environment.
10. The biotic components in an ecosystem are plants, animals and microorganisms.
11. The non-living components of an ecosystem or abiotic components consist of water, gases, light,
soil, temperature and rocks.
12. The eco-balance of the environment is closely related to the oxygen cycle, carbon dioxide cycle,
nitrogen cycle and food web.
13. Human beings are part of the ecosystem because they depend on living things and non-living
things in order to survive. If the ecosystem is interrupted, human lives will also be disturbed
14. A few elements in an ecosystem need to be maintained in order to keep the ecosystem balance :
(a) The size of each population.
(b) The composition of gases in air, water and soil.
(c) The composition of mineral salts in the soil.
15. The biotic and abiotic components are interdependent with one another to create a balanced
ecosystem which changes only slighly over time.
Interaction in an environment
1. Living things interact with each other and with non-living things in order to survive.
2. The interaction between living things and non-living things lead to balance in an ecosystem.
3. The example of interaction between living things and non-living things is shown below.
(a) Aquatic plants obtain mineral salts from the soil in the pond.
(b) Aquatic animals depend on aquatic plants to supply oxygen for the process of respiration.
(c) Aquatic plants depend on aquatic animals to obtain carbon dioxide for photosyntesis.
(d) Small fishes and tadpoles eat aquatic plants.
(e) Big fishes eat small fishes.
(f) Kingfisher eats fish.
(g) Water lettuce, water hyacinth, lotus and land plants obtain sunlight for the process of
4. Interaction between living things and non-living things is important as it maintains
(a) balance in a environment ( the number and types of living thing within the environment remain
the same ).
(b) balance in the carbon and oxygen cycles ( oxygen and carbon dioxide content in atmosphere
remain the same ).
INTERACTION AMONG LIVING ORGANISMS
(A) The various forms of interaction
1. Living things interact among themselves in order to obtain food and protection.
2. Interaction may involve animal and animal, plant and plant or animal and plant.
3. Interaction between living organisms in an ecosystem will :
(a) Create equilibrium in the environment.
(b) Control the size of a population in a community.
4. There are three types of interactions among organisms :
(b) Symbiosis that consits of commonsalism, mutualism and parasitism.
5. Predator-prey relationship.
(a) The animals that hunt other animals for food are called predators, while the hunted animals
(b) The predators which are carnivores have powerful jaws, sharp and strong teeth, good
stereoscopic vision, sharp claws or hard and strong beaks.
(c) The preys have a wide field of monoscopic vision to detect predators or are able to camouflage
with their surroundings in order to escape from the predators.
(d) The examples are tigers (predators) and horses (preys), eagles (predators) and rabbit (preys).
(e) Diagram 4.1 shows the predator-prey relationship.
INTERACTION AMONG LIVING THINGS
1. In symbiosis, different organism live together in a close relationship.
2. In symbiosis, 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.
3. There are three types of symbiotic relationship, i.e. commensalism. parasitism and mutualism.
1. Commensalism is a relationship between two organisms. One organism bnefits from the other. The
second organism is not adversely affected by the relationship.
2. For example, the staghorn fern grows on a tree. This helps it easily obtain sunlight. The plant that it
grows on is not adversely affected.
3. Examples of plants that live on trees to obtain sunlight are
(a) the staghorn fern
(b) the money plant
(c) the pigeon orchid
(d) the bird's nest fern
4. Examples of animals taht 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 that live on a shark
1. Parasitism is another type of interaction between two organism. Only one organism benefits. The
other organism is negatively or adversely affected.
2. A parasite is the organism that lives on or inside the other organism. The host is the organism on
which the parasite lives.
3. The host is negatively affected by this interaction. The parasite may even kill the host.
4. A parasite obtains food, shelter and transport from the host.
5. For example, a tick that lives on a host feeds on the host's blood.
6. Other examples are
(a) stem borers and oil palm leaves
(b) tree barnacles and trees
(c) aphids and mustard plants
1. Mutualism is an interaction betwee two different organisms that live together in which both
organisms benefit. They obtain nutrition and shelter from each other.
2. For example,
(a) 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.
(b) ox peckers and buffaloes
Ox peckers eat the ticks and leeches that feed on buffaloes.
(c) the Egyption Plover bird and crocodiles
The Egyption Plover bird eats leeches as well as food particles stuck between the crocodile's
(d) 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.
(e) 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
(f) 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.
1. Competition occurs when organism compete for the same basic resources.
2. Plants compete to obtain water, sunlight, mineral salts and living space.
3. Animals compete to obtain water, food, living space and mates for reproduction.
4. Competition becomes more intense when basic resources are limted.
5. Stronger organisms are successful in controlling their terriroty. weaker and smaller organisms are
driven out of the area.
6. For example,
(a) flowering plants compete with weeds to obtain water and mineral salts.
(b) lions in a pride compete for food.
(c) plants in a tropical rainforest compete for basic needs. Taller trees obtain sunlight more easily.
7. Another example of competition occurs between Paramecium aurelia and Paramecium caudatum.
(a) Paramecium aurelia and Paramecium caudatum compete for food.
(b) Paramecium aurelia succeeds.Biological control
1. Biological control is a method in which a predator, which is a natural enemy to a certain pest
( prey ), is used to control the population of that pest in an area.
2. Biological control is usually used in agriculture to control populations of pests without the use of
3. The prey-predator interaction is applied in biological control.
4. Biological control has many advantages as compared to using pesticides. Biological control
(a) does not pollute the environment
(b) does not kill other organisms because natural enemies are used
(c) is cheap and safe to use
5. For example,
(a) owls and snakes eat rats
(b) fire ants eat aphids on leaves
6. The two types of interaction that happen in biological control are
(a) parasitism - the parasite destroys crops
(b) prey-predator - eventually removes the pest
7. Other examples of biological control are
(a) rearing guppies ina apond to eat mosquito larvae.
(b) rearing cats to eliminate rats.
Producer, consumers and decomposers
1. Producers are all green plants that make food through photosynthesis.
2. Consumers are animals that eat plants or other animals.
3. Decomposers are organism that decompose dead organism ( animals or plants ) and change them
into simple substances. Examples of decomposers are bacteria and fungi.
4. The sun is the main source of energy for all living organisms in a food chain.
1. A food chain is an energy link showing how energy in food is passed from plants ( producers ) to
animals ( consumers ).
2. A food chain shows the interaction of several organisms with each other.
3. When the organisms in a food chain die, they are decomposed by decomposers such as bacteria
and fungi, into simple minerals.
1. A food web consists of several food chains that are interlinked.
2. The organisms in a food web interact with each other.
3. Just as in a food chain, dead organisms are decomposed by decomposers.
Pyramid of numbers
1. A pyramid of numbers shows the number of organisms at each link of the food chain.
2. From the base of the pyramid to the top,
(a) the number of organisms decrease
(b) the size of the organisms increase
(c) more energy is lost
3. Producers' number is the most and forms the base of the pyramid.
4. The number of producers is always greater than the number of primary consumers in order to
provide sufficient food to the primary consumers.
5. 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.
6. Secondary producers make up the third level of the pyramid. Tertiary consumers make up the
fourth level of the pyramid and so on.
7. The final consumers are at the apex of the pyramid and are the least in number.
8. The flow of energy in a pyramid of numbers is the same as in a food chain.The flow of energy is a food web and pyramid of numbers
1. Green plants supply energy in the form of food, either directly or indirectly, to all organisms in a
2. The flow of energy in a food web and the pyramid of numbers starts with the producers and moves
to the consumers.
3. However, not all the energy in a producer is transferred to consumers.
4. Some energy is lost as heat when the organism carries out its life processes such as respiration,
reproduction, excreation and growth.Disturbances in the ecosystem
1. 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.
2. Disturbances at any level of a pyramid of numbers will cause the equilibrium in a food chain to be
disrubted. 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.
3. The increase or decrease in the number of organisms will affect the equilibrium of the ecosystem.
4. All living organisms in an ecosystem depend on one another. If one group of organisms is removed,
the balance of nature will be disturbed.
1. Photosynthesis is an a process that occurs in green plants, in which food is made from water and
carbon dioxide in the presence of cholophyll and sunlight.
2. The equation below shows the process of photosynthesis.
3. 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.
4. Photosynthesis is a natural process. Only green plants carry out photosynthesis.
1. A green leaf that has been exposed to sunlight is plucked.
2. A knife is used to cut it into several small pieces.
3. The leaf pieces are put in boiling water and boiled for five minutes.
4. The leaf pieces are boiled in alcohol for a few minutes.
5. The leaf pieces are soaked in hot water for a while.
6. The leaf pieces are placed on a white tile. A few drops of iodine solution are dripped onto the leaf
The leaf becomes dark blue when tested with iodine solution.
1. The leaf pieces are boiled in water to kill the cells abd break the cell walls.
2. The leaf pieces are boiled in alcohol to remove chlorophyll.
3. The leaf pieces are soaked in hot water to soften them.
4. Plants store food in the form of starch in leaves.
Starch is a product of photosynthesis. It can be tested with iodine solution.
1. Two potted plants are placed in the dark for two days.
2. The apparatus as shown in the Figure above is prepared. The apparatus is placed under the sun for
3. A leaf is plucked from each plant and tested for the presence of starch.
4. The observations are recorded in the table.
1. The green plant in apparatus A carried out photosynthesis. It produced starch in the presence of
2. The green plant in apparatus B did not carry out photosynthesis because there was no carbon
dioxide in the air in the bell jar.
3. Both plants were placed in the dark for two days before the experiment to remove starch from the
4. The sodium hydroxide solution absorbed carbon dioxide from the air.
1. The hypothesis made can be accepted.
2. Carbon dioxide is needed for photosynthesis.
1. The green plant in apparatus A did not carry out photosynthesis because no water was supplied.
2. The green plant in apparatus B carried out photosynthesis as water was supplied.
3. Water is absorbed by the plant through the roots.
1. The hypothesis made can be accepted.
2. Water is necessary for photosynthesis.
1. A green potted plant is kept in the dark for two days.
2. A part of one leaf is covered with black paper as shown in the Figure above. Paper clips are used to
hold the black paper in place.
3. The plant is placed under the sun for two days.
4. At the end of the experiment, the leaf is plucked and tested for the presence of starch.
5. The observations are recorded in the table below.
1. A part of the leaf was covered to prevent exposure to sunlight.
2. Photosynthesis does not take place without sunlight.
3. Sunlight supplies energy to the plant to break water molecules.
1. The hypothesis made can be accepted.
2. Sunlight is needed for photosynthesis.
1. The green parts of the left have chlorophyll, which enables the plant to carry out photosynthesis.
2. The equation that represents photosynthesis is :
1. The hypothesis made can be accepted.
2. Chlorophyll is needed for photosynthesis.
The importance of photosynthesis
1. Photocynthesis is important to maintain the equilibrium of an ecosystem.
2. The importance and role of photosynthesis are :
(a) supplies food to animals
(b) removes carbon dioxide from the atmosphere
(c) enables green plants to make theor own food
(d) regulates and maintains carbon dioxide content in the atmosphere
(e) increase oxygen content in the atmosphere; this gas is used by organisms for respiration as
well as in the processes of combustion, rusting and decomposition
Natural gas cycles
1. Natural gas cycles maintain the content of gases in the air.
2. The carbon and oxygen cycles are two natural gas cycles.
The carbon cycle
1. 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 continously.
2. The carbon cycles maintains the content of carbon dioxide in the air.
3. The processes that release carbon dioxide into the air include :
(a) respiration or breathing.
4. Photosynthesis, which takes place in green plants, removes carbon dioxide from the air.
The oxygen cycle
1. 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 continously.
2. The oxygen cycle maintains the content of oxygen in the air.
3. The processes that use oxygen include :
(a) respiration or breating
4. Photosynthesis is the only process that release oxygen into the air.
5. The following is a summary of the processes that are involved in the carbon dioxide and oxygen
6. Rusting uses up oxygen but does not release carbon dioxide.
THE ROLE HUMANS IN MAINTAINING THE BALANCE OF NATURE
1. Human beings have a very close relationship with the ecosystem.
2. Human beings are a part of the ecosystem that depend on living and non-living things for survival.
3. Human beings interact with the ecosystem to obtain needs and to lead comfortable lives.
4. We obtain our needs in many ways. At the same time, we also disturb the balance of nature.
5. Human activities bring about an imbalance and decline in the ecosystem. Human activities that
destroy the balance of nature are
(a) forestry / logging
(h) illegal hunting
6. The large scale exploration of forests for agriculture, industry, settlement and insfrastructure
construction has resulted in the loss of wide forest tracts.
7. Improperly planned conversion of forest areas have resulted in the destruction of habitats.
8. Loss of natural habitats has threatened plants and animals with extinction.
9. Human beings need a stable and productive ecosystem to ensure our survival.
10. All our needs can only be obtained continously, and over a long period of time, if the ecosystem is
stable and productive.
11. Before starting on a project, we should carefully plan the project with full responsibility, so as to
avoid adversely disturbing any member of the ecosystem, including ourselves.
Human activities cause pollution and have raised the following environmental issues :
(a) the greenhouse effect
(b) the thinning of the ozone layer.
(c) acid rain.
The greenhouse effect
1. The green house effect occurs because a layer of carbon dioxide in the atmosphere prevents a
portion of head from escaping to outer space.
2. The greenhouse effect raises Earth's temperature. This is known as global warming. This
phenomena causes changes in the weather and climate the world over.
3. Climatic change as a result of global warming causes the melting of icebergs in both poles. The sea
level increases and this results in the flooding of low-lying coastal areas.
The thinning of the ozone layer
1. The ozone layer absorbs ultraviolet rays and prevents them from reaching the Earth.
2. Chemicals such as chlorofluorocarbons ( CFCs ) are used in the manufacture of aerosol sprays,
refrigerators and air conditioners. These chemicals are pollutants that break down ozone
molecules in the ozone layer.
3. As a result, the ozone layer has thinned. Ultraviolet rays that reach the Earth as a result have
adversely affected human health by causing :
(a) skin cancer.
(c) the immune system to function improperly.
1. Gases such as sulphur dioxide and nitrogen dioxide dissolve in rainwater and form acid rain.
2. Acid rain can
(a) destroy the habitats of living things
(b) lower the soil pH value and make it unsuitable for plants. River water that is polluted by acid
rain is no longer suitable for aquatic organisms.
Controlling environmental pollution
1. Managing environmental pollution can save our Earth.
2. The following are steps we can take to reduce environmental pollution.
(a) use unleaded petrol
(b) make nuclear testing illegal
(c) create special places to burn rubbish
(d) tighten laws regarding the disposal of toxic waste from factories
(e) fix catalytic converters on the exhaust pipes of vehicles to reduce the emission of dangerous
(f) stop the use of chlorofluorocarbons ( CFCs ) by replacing it with hydrochloroflourocarbons
( HCFCs )
(g) fix equipment to clean the air that dissolves toxic and acidic gases before releasing them into
(h) create special places for the disposal of toxic chemical waste from factories
3. An ecosystem that is stable and productive supplies all our needs. Therefore we should be
responsible for ensuring that nature always remains in balance.CONSERVATION AND PRESERVATION OF LIVING ORGANISMS
1. Conservation is the systematic and wise use of the Earth's resources. The aim is to ensure that the
Earth's naturel resources such as forest and seas are not destroyed and can still be used in the
2. Preservation is an effort to ensure that the Earth's resources are maintained in good condition.
3. The steps that can be taken by the government and the public in conserving and preserving the
Earth's resouces include :
(a) Creating forest reserves, forest gardens and botanical gardens.
(b) Replanting the trees that have been cut down in all the forest areas and to practise selective
(c) Constructing breeding centres for animals that are at the brim of extinction.
(d) Reinforcing the Wildlife Protection Act and National and logging at certain areas.
(e) Reinforcing laws than ban illegal trading of animals and plants.
(f) To conduct awareness campaigns among the public.
4. The importance of preservation of living organisms are as follows :
(a) Maintaning the balance of the ecosystem :
i. The presence of animals and plants maintain the composition of oxygen and carbon
dioxide in the atmosphere.
ii. Trees help in the control of land erosions and floods by holding firmly the soil particles.
iii. the humadity in the forest helps to decompose dead organisms.
i. Forest products such as teak wood, orchid and rattan; as well as herbs can be obtained.
ii. Wildlife supplies such as leather, horns and meat can be obtained from the forest.
iii. Some forest trees or wild animals are also used for scientific reseach.
i. People can enjoy the beauty of the natural environment.
ii. In the tropical forest, the air is fresh and unpolluted; therefore it is good for relaxation.
5. Serious involvement of the private sectors in the protection of living organism must be fully
supported. For examples, the World Wildlife Fundand the Malaysian Nature Society.
6. The tropical forest is also a home to some of the aboriginal communities.
7. Aboriginal communities survive by hunting animals, catching fish, collecting foresh products and
building homes using forest materials such as bamboo and rattan.
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