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Interactions Ch 2 Environment Learning outcome

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Background information i-Science – interact, inquire, investigate P5&6

Interactions Ch 2 - Environment
Learning outcome:

  • Describe the characteristics of a local environment

An organism is affected by its immediate surroundings or environment. The environment of an organism is made up of all the factors which affect its growth, development and survival.

The environment may be divided into the biotic and abiotic environments. The biotic environment is made up of biotic factors, that is, all the living things in the environment. The abiotic environment is made up of all the physical factors that affect the organism. These include the air, temperature and amount of water and light in the environment.

Abiotic environment:
- Air

- Light

- Water

- Minerals

- pH (acidity/alkalinity)

- Temperature

Biotic environment:
- All the living things in the environment

A local environment

The environment of a school’s eco-garden is an example of a local environment. The abiotic environment of the eco-garden is determined by various physical factors such as air, water, light and temperature. Some of these factors change with the time of the day and year. The eco-garden receives more light during the day than at night. The amount of rain the eco-garden receives will vary according to the seasons. Physical conditions may vary in the different locations of the eco-garden. For example, the open areas of the eco-garden receive more sunlight than the shady areas. The physical characteristics of the environment may be observed and measured using sensors (e.g. temperature, light and pH sensors) and dataloggers.

Soil is part of the abiotic environment of the eco-garden. Soil factors include soil type, temperature, pH and the air, water, mineral and organic (humus) contents of the soil. There are different types of soil. Clay is mainly made up of very fine particles of mostly hydrated aluminium silicates, while sand is mainly made up of larger particles of silicon dioxide. The particle size and chemical composition of the soil affect the types of plants growing in it and the animals living in it.
The biotic environment of the eco-garden is made up of organisms living in the eco-garden. These include plants, animals, fungi and micro-organisms such as bacteria. Common land plants which can be found in the eco-garden include grass, fern, money plant, allamanda, angsana, bougainvillea, coconut tree, cycad, desert rose, fig tree, heliconia, hibiscus, ixora, mango tree, palm, ginger plant, rain tree and spider lily.

Angsana tree

Spider lily

Coconut tree

Rain tree

Water plants in the pond can be classified as floating plants, partially submerged plants or submerged plants. Duckweeds, water hyacinths and water lettuces are floating plants. Arrowhead, cattail, cabomba, lotus and water lily are partially submerged plants, while Hydrilla and Elodea are submerged plants.

Water lettuce Lotus Hydrilla

The table below shows some examples of animals commonly found in the eco-garden during the day.

Places in the eco-garden

Examples of animals

On the tree branches

Birds (e.g. sunbird, mynah), ants

On the tree trunks

Ants, beetles, lizards

On the stems and leaves of plants

Ants, aphids, beetles, bugs, caterpillars, grasshoppers, locusts, praying mantises, spiders, slugs, snails

On the flowers

Bees, butterflies, hornets, wasps

In the air

Damselflies, dragonflies, bees, butterflies, birds

In the soil and leaf litter

Ants, beetles, centipedes, earthworms, millipedes, slugs, snails, woodlice

In rotting logs

Ants, beetles, termites, woodlice

In the pond

Backswimmers, dragonfly nymphs, fish, frogs, great diving beetles, pond skaters, toads, water boatman, water fleas, water scorpions, water snails

Great diving beetle Backswimmer Water scorpion

Organisms, populations and communities
Learning outcome:

  • Differentiate among the terms organism, population and community

Organisms are living things. Most organisms do not live alone. They live as a group. Thus, many organisms of the same species can be found in the same place at the same time. A population is defined as a group of organisms of the same species living at a given place at a particular time. This includes the young and adult organisms living in the same place at a given time. The grasshopper population in a school’s eco-garden, for example, would include all the adult grasshoppers and nymphs living in the eco-garden at a given time.

Different species of organisms often live in the same place at any given time. A community consists of the different populations living together in a particular place at a given time. An example is the marine community which is made up of different populations of marine organisms, including phytoplankton, zooplankton, fish and marine mammals, living together in the ocean. The different populations in a community interact and depend on one another.

Different habitats support different communities
Learning outcome:

  • Show an understanding that different habitats support different communities

A habitat is a place where an organism lives and reproduces. A habitat can be as big as an ocean or as small as a rock pool. Some organisms are the habitats of other organisms. A tree, for example, may be the habitat of other plants such as ferns, mosses and orchids, and animals such as ants, birds and lizards.

Different habitats have different abiotic and biotic environments. The community in one habitat can be very different from the community in another habitat.
A field community

Different plant populations make up the plant community in a field habitat. Cow grass, love grass, cupid shaving grass, kyllinga, mimosa and lalang are some grass populations which can be found in a field.

Populations of animals, such as ants, earthworms, grasshoppers, spiders, snails and millipedes, make up the animal community of a field habitat.
A leaf litter community can be found in a field. A leaf litter community is made up of populations of ants, earthworms and snails which feed on the leaf litter. Fungi and bacteria are also part of the leaf litter community.
A pond community

A pond is an aquatic habitat. Different populations live in or around the pond. The table below shows some plants which make up a local pond community.

Types of plants

Examples of plants

Free-floating plants

Duckweed, floating moss fern, mosquito fern, water hyacinth, water lettuce

Partially submerged plants

Arrowhead, cabomba, cattail, lotus, sedge, water lily, water shamrock

Submerged plants

Hydrilla, Elodea

The table below shows some animals which make up a local pond community.

Where are these animals found?

Examples of animals

In or around the pond

Frog, toad, mayfly, damselfly, dragonfly

On the surface of the pond

Pond skater, water cricket

Below the pond surface

Fish, dragonfly nymph, tadpole, great diving beetle, water boatman, water flea, water bug, backswimmer, worm, snail, water stick insect, water scorpion

Populations of micro-organisms, such as amoeba, paramecia, Euglena and other types of alga, are also part of the pond community. Bacteria live in the soil or water of the pond. They decompose dead and waste matter, thus helping to recycle the nutrients in the pond.

Factors affecting the survival of an organism
Learning outcome:

  • Identify the factors which affect the survival of an organism

    • Physical characteristics of the environment

    • Availability of food

    • Types of other organisms present

Physical characteristics of the environment

Physical factors such as temperature, the amount of light and water in the environment affect the survival of an organism.


Some organisms can live in the freezing cold of the Antarctic or in the hot hydrothermal vents in the deep ocean, but most organisms cannot survive in such extreme temperatures.

Water is present in the cells of organisms. When the temperature rises too much, plants and animals tend to lose water. Plants will wilt as a result and animals can get dehydrated.
The rate of evaporation of water increases when temperature increases and so there is less liquid water available for drinking.
Water freezes if the temperature drops to below its freezing point. Animals will not have enough liquid water to drink when it turns into ice. Ice will form inside the plant cells and cause the plants to die. Cold-blooded animals, such as amphibians and reptiles, cannot regulate their body temperatures and will be badly affected if there are any drastic changes in the surrounding temperature.
Many chemical reactions in the cells of organisms are not able to take place without enzymes, which are biological catalysts. Temperature affects the activity of enzymes. At low temperatures, enzyme activity decreases. When temperatures are too high, the enzymes are denatured.
Amount of light

Light is necessary for photosynthesis. Without light, plants and other photosynthetic organisms, such as phytoplankton, will not be able to make food. Animals and other organisms which depend directly or indirectly on these photosynthetic organisms for food will not be able to survive.

Most animals need light to look for food and to avoid danger. However, some organisms cannot tolerate high amounts of light. Direct exposure to sunlight will affect their growth, development and survival. Ferns and fungi do not grow well under direct sunlight. Animals like earthworms prefer the dark.
Amount of water

Water is a basic necessity of life. Water is one of the main components of cells. Many chemical reactions in the cells take place only when the reactants are dissolved in water. Since water can dissolve many substances, it forms the medium of transport in many organisms. Mineral salts from the soil dissolve in water before they are absorbed by plant roots and are transported to other parts of the plant. Food made by plants is dissolved in water and transported to the different parts of the plants. Digested food and nutrients are dissolved in water and transported to the different parts of the body of an animal.

Water is a raw material for photosynthesis. Water also keeps plant cells turgid so that plants will not wilt.
Many organisms live in water. The amount of water affects their survival. Aquatic organisms living in lakes and rivers would die if these bodies of water were to dry up. Water can dissolve oxygen and carbon dioxide. Dissolved oxygen is necessary for many aquatic organisms to carry out aerobic respiration. Dissolved carbon dioxide enables submerged water plants and alga to carry out photosynthesis.
Too much water can be harmful to living things. Over-watering a cactus will cause it to die. Floods can drown and kill many animals and plants. When animal cells absorb too much water, they can swell up and burst. The cell walls of plant cells prevent the cells from bursting when they take up too much water.
Availability of food

Food provides organisms with energy to carry out life processes and to do work. Food also provides nutrients, such as minerals, which enable organisms to grow healthily. Living things live in places where food is easily available. Organisms which cannot make their own food are adapted to finding and obtaining food. Organisms which make their own food can only survive in an environment where the conditions that are needed to make food, such as the availability of light, water and carbon dioxide, are met.

The types of other organisms present

Organisms interact with other organisms in their environment. The organisms are interdependent and affect one another’s survival. Plants provide many animals with food and shelter. Some animals, in turn, help in the pollination and dispersal of seeds. Decomposers, like bacteria and fungi, break down dead organic and waste matter so that plants can absorb nutrients from them. Organisms may compete or co-operate and form food and symbiotic relationships.


As many resources in an environment are limited and finite, organisms have to compete for them. Resources such as food and water are essential for the survival of organisms. Organisms which eat the same type of food will compete for food. This competition exists among different species and within the same species. Tigers mark extensive areas of territory for their own use and will challenge other tigers which try to hunt in their territories. The presence of cheetahs will affect the survival of lions in the same habitat because both compete for similar types of food.

Plants that grow too close together will not be able to grow well because they have to compete for light, water, mineral salts and space. Fruits and/or seeds are, therefore, adapted for dispersal.

Organisms do not just compete for survival. Organisms of the same species co-operate because in many instances, co-operation enhances their survival. African wild dogs hunt in packs to increase their chances of catching a prey which may be larger in size than them. Deer and cattle live in herds and watch out for one another to protect themselves from predators. It is easier for a predator to bring down a lone prey than one that is in a large group. Social animals, like ants and bees, live in large groups called colonies, where each animal specialises in some specific tasks to ensure the survival of the whole colony. Human beings compete and co-operate with one another to ensure our survival too.


Symbiosis or symbiotic relationship is the relationship between organisms of two different species living together. Mutualism and parasitism are examples of symbiosis.

In mutualism, both species living together benefit from the relationship. Lichen consists of a fungus and an alga living together. The alga carries out photosynthesis and supplies the fungus with food. The fungus supplies the alga with water and minerals which it had absorbed. Together, they can survive in harsh environments.


Mutualism exists between:

  • oxpeckers and large mammals like giraffes;

  • clownfish and sea anemones;

  • plants and fungi which live on plant roots;

  • nitrogen-fixing bacteria and leguminous plants.

Parasitism is a form of symbiosis in which one species benefits at the expense of the other. The parasite is the species which benefits and it harms the host. Tapeworms are parasites which live in the intestines of some animals. They obtain food and nutrients from their hosts, which are, in turn, harmed by their presence.

Unfavourable environments
Learning outcome:

  • Discuss the effect on organisms when the environment becomes unfavourable

An environment becomes unfavourable when conditions change such that organisms in the environment find it difficult to survive. The environment can become unfavourable due to changes in the abiotic or biotic environments.

Droughts, floods and fires can make environments unfavourable. They affect both the abiotic and biotic environments.
During a drought, the amount of water is drastically reduced due to increasing temperature and/or decreasing rainfall. Floods occur due to heavy rainfall or rising sea levels. During floods, rivers, lakes and other water bodies overflow and soil gets washed away. Animals may fall sick or die due to water-borne diseases, such as typhoid and cholera, or drown. Fires cause the temperature of the surroundings to rise drastically. Plants and animals get burned by the fire and are harmed by the smoke and toxic gases which pollute the air.
The environment of native species can become unfavourable due to the introduction of non-native species. The new species may upset the ecological balance by spreading new diseases, competing with native species for food and other resources, or preying on the native species. The native species may become endangered or extinct as a result.
The removal of native species can make the environment unfavourable too. Over-fishing and over-hunting remove a large number of organisms from the environment. This upsets the ecological balance and makes the environment unfavourable for other organisms which have symbiotic or food relationships with the organisms removed.
When the environment becomes unfavourable, some organisms may move to new environments which are more favourable, while others try and adapt to the new unfavourable conditions. Those that are unable to adapt cannot survive and will die.
Internet links

  • Habitats

  • Environment

  • Terrarium and aquarium
Projects /Field trips

  • Organise field trips to nature reserves. Study the abiotic and biotic environments and the interactions between the different factors that make up the environments.

  • Set up and maintain an aquarium or terrarium in class.

Recommended reading

  • A Guide to the Botanic Gardens Jungle (Publisher: Singapore Science Centre)

  • A Guide to the Bukit Timah Nature Reserve (Publisher: Singapore Science Centre)

  • A Guide to the Coral Reef Life of Singapore (Publisher: Singapore Science Centre)

  • A Guide to the Freshwater Life in Singapore (Publisher: Singapore Science Centre)

  • A Guide to the Mangroves of Singapore I – Animal Diversity (Publisher: Singapore Science Centre)

  • A Guide to the Mangroves of Singapore II – Ecosystem and Plant Diversity (Publisher: Singapore Science Centre)

  • A Guide to Pond Life (Publisher: Singapore Science Centre)

  • A Guide to Seashore Life (Publisher: Singapore Science Centre)

  • Chek Jawa Guidebook (Publisher: Simply Green)

  • The Usborne Living World Encyclopedia (Publisher: Usborne)

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