🌿 Interactions Within the Environment

5.1 Organism, Population and Community

Organism

1. An organism is a living thing.

Population

2. A population is a group of living things of the same kind living together. Organisms of the same species tend to live together.

3. The organisms that live together reproduce so that their species continues to exist.

4. The adults and young of a particular species make up a population.

5. The number of organisms in a population is known as the population size.

6. Factors that affect the population size include birth, death, diseases and movement of organisms into and out of their habitat.

Ecosystem Hierarchy — From Individual to Community

🌍

DID YOU KNOW?

A single tree can be home to hundreds of different species — insects, birds, fungi, and more. All together they form a community!

Community

7. A community is made up of several populations living together in the same environment.

8. The animals in a community depend on one another.

9. The plants provide food for the plant-eaters, while the meat-eaters feed on the plant-eaters. Plant-and-animal eaters feed on plants and other animals.

How Organisms in a Community Depend on Each Other

5.2 Different Habitats Support Different Communities

Habitat

1. A specific place where organisms live together and are able to find their basic needs easily is their habitat. The mangrove swamp, single tree, seashore, pond, garden, field and leaf litter are some examples of habitats.

Different Habitats — Different Communities

Mangrove Swamp Habitat

2.

(a) The mangrove trees, egrets, crocodiles, snakes and mudskippers live in the mangrove swamp habitat.
(b) The plants in the mangrove swamp habitat provide shade to the mangrove floor keeping the habitat cool.
(c) Due to the moving waters from the open sea, food is available to the organisms in the mangrove swamp.

Mangrove Swamp — A Rich Habitat

🌊

DID YOU KNOW?

Mangrove trees have special roots that stick out of the mud. These help them breathe in waterlogged soil and provide homes for crabs, fish, and mudskippers!

Single Tree / Forest Habitat

3.

(a) A single tree habitat provides shelter to animals such as birds, squirrels, ants and ferns.
(b) The leaves of the tree provide shade keeping the habitat cool.
(c) The habitat is exposed to wind, which provides air to the organisms in the habitat.

🌳

DID YOU KNOW?

A single large tree can support an entire ecosystem — from insects in the bark to birds in the canopy and fungi at the roots!

Seashore Habitat

4.

(a) Hermit crabs, seaweeds, starfish, clams and mussels live in the seashore habitat. Birds such as seagulls can be found looking for food on the seashore during the daytime.
(b) These organisms are directly exposed to natural elements such as the wind and rain.

Seashore — Where Land Meets Sea

Pond Ecosystem Habitat

5.

(a) The pond habitat supports the plants and animals that live in or around the pond.
(b) Organisms that live in the pond include fish, snails and cabomba.
(c) Organisms that live in the floor / bottom of the pond are prawns and nymphs of dragonflies.
(d) Organisms that live around / near the pond are frogs, ducks and dragonflies.
(e) Organisms that can be found on the water surface of the pond are water boatmen, pond skaters and backswimmers.
(f) Three types of plants in the pond habitat include the floating plants such as the water hyacinth, the fully-submerged plants such as the cabomba and hydrilla, and the partially-submerged plants such as the water lotus.
(g) The pond habitat also supports communities of microorganisms such as algae and amoebae.

Pond Ecosystem — Different Zones, Different Life

🏞️

DID YOU KNOW?

Pond skaters can walk on water because of surface tension — the water molecules hold together like an invisible skin!

Garden Habitat

6.

(a) Organisms that live in the garden habitat usually feed on leaves and other parts of the plants.
(b) Organisms living in the garden habitat include butterflies, beetles and snails / ladybirds / caterpillars / bees / ants.
(c) Organisms that live in the garden soil include earthworms and crickets.
(d) Plants in the garden include the flowering plants such as roses and non-flowering plants such as ferns.
(e) The garden habitat is exposed directly to natural elements like the wind and rain.
(f) Air is allowed to flow freely in the garden.
(g) The garden soil is full of nutrients so plants can grow healthily.

Field Habitat

7.

(a) Organisms such as birds, snakes, rats and grasshoppers live in the field habitat.
(b) The sunny weather during the day and cool weather during the night provide optimal living conditions for the organisms.
(c) Food is abundant in the field habitat as a great intensity of light is available for plants to carry out photosynthesis.
(d) Air flows freely in the field habitat.

Leaf Litter Habitat

8.

(a) A leaf litter habitat is formed when the dried leaves that have withered and fallen from trees and plants pile up.
(b) Cockroaches, centipedes, millipedes and snails live in the leaf litter habitat. The dark and damp / moist / wet conditions of this habitat support these organisms.
(c) The air is stagnant and the temperature in the leaf litter is almost constant.
(d) The decomposed leaves in this habitat are the main source of food for the organisms living here.
(e) Fungi and bacteria decompose the leaves.

🍂

DID YOU KNOW?

Leaf litter acts like a blanket on the forest floor, keeping moisture in and providing food for decomposers that enrich the soil!

5.3 Factors that Affect the Survival of Organisms

1. A natural habitat provides an organism with a suitable environment to live in. A favourable environment allows the organisms to survive well.

2. Living factors and non-living / physical factors may affect the survival of organisms in their habitat.

3. Living factors that affect the survival of an organism include food and other organisms.

4. Non-living factors that affect the survival of an organism include temperature, air, light and water.

5. Organisms tend to lose water and may dehydrate and die if their environment becomes too hot. This can reduce the number of organisms in an environment.

6. The primary supply of energy for plants is light energy from the Sun. Plants use this energy to make food through photosynthesis.

7. Plants then provide food for other organisms including animals and humans.

Physical Factors of the Environment

8.

(a) The animals use the oxygen produced by the plants during photosynthesis.
(b) Carbon dioxide that is produced by the animals during respiration is used by the plants for photosynthesis.

9.

(a) Habitats such as the river / mangrove swamp / seashore / ocean / pond habitat have abundant water supply to support many types of aquatic and land organisms.
(b) Hot and dry habitats such as the hot desert do not support as much diversity of living things because water is scarce.

10.

(a) The survival of an organism is affected by interactions with other organisms.
(b) An organism may compete with other organisms for resources, such as air / food / water / sunlight.
(c) An animal feeds on other organisms and may in turn be eaten by other animals.

11.

(a) Organisms that feed on dead organisms or solid wastes from organisms are the decomposers. They break down the dead organisms or solid wastes into simpler substances to be returned to the soil as nutrients for plants.
(b) Examples of decomposers are fungi and bacteria.

📝 Chapter 5 Summary

Key Concepts to Remember

An organism is a single living thing.
A population is a group of the same species living together.
Population size changes due to birth, death, and movement.
A community has several populations depending on each other.
Plants feed plant-eaters → plant-eaters feed meat-eaters (food chain).
A habitat is a specific place where organisms find their basic needs.
Different habitats support different communities of organisms.
Mangrove swamp — cool, food-rich habitat with moving waters from the sea.
Single tree — provides shelter and shade; wind brings air.
Seashore — exposed to wind and rain; home to crabs, starfish, seagulls.
Pond ecosystem — zones include: around, surface, in water, floor/bottom.
Pond plants: floating (water hyacinth), fully-submerged (cabomba), partially-submerged (water lotus).
Garden — exposed to wind and rain; rich soil with nutrients.
Field — abundant light for photosynthesis; day/night temperature cycle.
Leaf litter — dark, damp habitat; decomposed leaves provide food.
Factors affecting survival: living (food) and non-living (temperature, air, light, water).
Decomposers (fungi, bacteria) break down dead matter into nutrients for plants.