ScienceCBSE Class 8 · How Nature Works in Harmony

Habitats, Populations, Communities and Ecosystems: Class 8 Science

Updated 17 October 2026 · Fact-checked

A habitat is the place where an organism lives. Its living parts are biotic components and its non-living parts are abiotic components. The group of one kind of organism in a habitat is a population, all populations together form the community, and the community interacting with the abiotic components forms an ecosystem. Organisms interact by feeding, competition, mutualism, commensalism and parasitism.

Understand Habitats, Populations, Communities and Ecosystems

Habitat and its components (Activity 12.1). A habitat is simply the place where an organism lives; it can even be the bark of a tree. In a pond, fish, frogs, turtles, snakes, dragonflies, mosquitoes, snails, ducks and plants such as algae, diatoms, duckweed and lotus are biotic (living) components, while water, air, sunlight, temperature and soil are abiotic (non-living) components. A pond provides food, oxygen, shelter and space; fish take food (biotic need) from small plants and animals and oxygen (abiotic need) from water. Different organisms in one habitat use resources differently: a night-active snake and a day-active rodent share a forest that is warm by day and cool by night.

Population (Activity 12.2). A group of the same kind of organism in a habitat at a given time is a population. It can be recorded by counting organisms in a marked area, for example a 1 m x 1 m patch of a school garden. If all organisms were of one kind, they would have identical needs, leading to competition and scarcity.

Community. Different populations sharing the same habitat form a community: the plants, animals and microorganisms, the biotic components together. The levels, from small to large, are individual, population, community and ecosystem (Fig. 12.7). Pollination is an example of interdependence in a community: wind, water, insects, bats and birds carry pollen from stamens to carpels, which is essential for fruits and seeds.

Every organism matters (Activity 12.3). In a study, a pond with fish had fewer dragonflies than a pond without fish, because fish eat dragonfly larvae. Dragonflies eat flies, bees and butterflies, so the pond with fish had more bees and butterflies, which pollinate flowers, so the flowers near the pond with fish produced more seeds. Removing or adding one organism, for example by overfishing, changes the whole habitat.

Interactions and the ecosystem (Activity 12.4).

Biotic with abiotic: earthworms live in moist soil; a fish lays eggs in water.
Abiotic with abiotic: bright sunlight raises the day temperature and evaporates water; wind makes waves.
Among biotic components: a frog eats insects, a water snake eats fish, and frogs and fish compete for insect larvae.

The biotic and abiotic components interacting form an ecosystem. Aquatic ecosystems include ponds, rivers and lakes; terrestrial ecosystems include forests, farms and even a large tree. Ecosystems can be large or small, and overlap; farmland is a human-made ecosystem. Plants need sunlight, carbon dioxide and water to make food, soil provides nutrients, air provides oxygen and water is needed by all. Conversely, plants release oxygen, roots hold soil and prevent erosion, and plants retain soil moisture and help cool the atmosphere.

Types of relationships among organisms. *Competition* for food, water, space and sunlight controls population size. *Mutualism:* both benefit (honeybees and flowers). *Commensalism:* one benefits and the other is not affected (orchids on trees). *Parasitism:* one benefits and the other is harmed (ticks on a dog).

Elephant corridors. Loss of forest and waterholes drives elephants into farms; corridors connect forest habitats so animals can move safely.

Feeding relationships, food webs and human impact are in the next topic.

Habitats, Populations, Communities and Ecosystems: formulas and key facts

Components of a habitat: $B i o t i c : pl an t s, anima l s, mi cr oor g ani s m s ∣ A bi o t i c : ai r, w a t er, s u n l i g h t, t e m p er a t u r e, so i l$; Both are interdependent.
Levels of organisation in ecology: $I n d i v i d u a l > P o p u l a t i o n > C o mm u ni t y > E cosy s t e m$; Population: same kind. Community: different populations in one habitat.
Types of ecosystem: Aquatic: pond, river, lake | Terrestrial: forest, farm, large tree; Farmland is human-made.
Relationships between organisms: $M u t u a l i s m (+ +) ∣ C o mm e n s a l i s m (+ 0) ∣ P a r a s i t i s m (+ -) ∣ C o m p e t i t i o n$; Examples: bees and flowers; orchid on tree; tick on dog.
Interaction criteria in Table 12.3: $B i o t i c - abi o t i c ∣ A bi o t i c - abi o t i c ∣ B i o t i c - bi o t i c$; Three kinds of interactions.

How to solve Habitats, Populations, Communities and Ecosystems questions

Use this method for ecology questions.

1List the living and non-living parts: biotic and abiotic.
2Group individuals of the same kind: populations; all populations together: community.
3Name the ecosystem: living plus non-living interacting; aquatic or terrestrial.
4For each pair of organisms, decide the effect on each (+, 0, −) to name the relationship.
5For chain-of-effects questions, follow one change step by step.
6Mention one human impact and a protective action if asked.

Habitats, Populations, Communities and Ecosystems in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Counting a population

Suppose four groups each mark a 1 m x 1 m square in the school garden and count clover plants: 18, 22, 25 and 15 (invented counts).

(a) Find the total number of clover plants in the 4 m2 surveyed. (b) Find the mean per square metre. (c) Estimate the clover plants in a garden bed of 30 m2 with the same density. (d) Why can this be only an estimate?

Try it first, then show the solutionSolution

Total = 18 + 22 + 25 + 15 = 80.
Mean = 80 ÷ 4 = 20 per m2.
20 × 30 = 600 plants.
The density may differ in other parts of the bed, and populations change with time.

Answer: (a) 80; (b) 20 per m2; (c) about 600; (d) density differs from place to place and over time.

Memory hook: A population is a count at a place and time.

Naming relationships

Imagine you observe bees on flowers, an orchid growing on a tree branch, a tick on a dog and two plants competing for light.

(a) Name each relationship. (b) State who benefits and who is harmed in each. (c) Which two of these involve no feeding on another organism?

Try it first, then show the solutionSolution

Bees and flowers: mutualism; orchid on tree: commensalism; tick on dog: parasitism; two plants for light: competition.
Mutualism: both benefit; commensalism: orchid benefits, tree unaffected; parasitism: tick benefits, dog harmed; competition: both are affected by the shared limited resource.
The orchid on the tree (gets support) and the two plants competing for light involve no feeding on another organism; bees take nectar and ticks take blood.

Answer: (a) Mutualism, commensalism, parasitism, competition; (b) as above; (c) the orchid on the tree and the competing plants.

Memory hook: Plus-plus, plus-zero, plus-minus.

Tricks to remember Habitats, Populations, Communities and Ecosystems

Short memory aids. Say each one aloud once, then use it on a question the same day.

Bio = life
Biotic have life; abiotic have none (a = not).
Use it when: Component questions.
Same kind: Pop. Many kinds: Com.
Population = same species; Community = many populations.
Use it when: Differentiating terms.
Orchid on tree: O for 'OK for tree'
Commensalism: one OK (unaffected), one gains.
Use it when: Types of interaction.
Tick = takes
Parasite takes and harms.
Use it when: Parasitism.

Habitats, Populations, Communities and Ecosystems: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Population versus community · 2 marks · Short answerBoard level

Differentiate between a population and a community with one example each from a pond.

Try it first, then show the solutionSolution

A population is a group of the same kind of organism in a habitat at a given time, e.g. all the fish of one kind in the pond. (1)
A community is made of different populations sharing a habitat, e.g. fish, frogs, snails and plants of the pond together. (1)

Answer: Population: one kind (fish); community: all populations of the pond together.

Example 2: Identify the relationship · 1 mark · MCQBoard level

A tick on a dog is an example of
(a) mutualism
(b) commensalism
(c) parasitism
(d) competition

Try it first, then show the solutionSolution

The tick benefits and the dog is harmed (skin irritation).

Answer: (c)

Example 3: Ripple effect of fish in a pond · 5 marks · Long answerHarder board level

Pond A has fish and many flowering plants around it. Pond B has no fish and fewer flowering plants.
(a) Compare dragonflies in the two ponds and explain. (1)
(b) Compare bees and butterflies and explain. (1)
(c) How does this affect seed production? (1)
(d) What might overfishing do? (1)
(e) Name two biotic and two abiotic components of such a pond. (1)

Try it first, then show the solutionSolution

(a) Pond A has fewer dragonflies because fish eat dragonfly larvae. (1)
(b) Pond A has more bees and butterflies because fewer dragonflies are there to eat them. (1)
(c) More pollinators move pollen between flowers, so plants near Pond A produce more seeds. (1)
(d) It would reduce fish, increase dragonflies, reduce pollinators and perhaps seeds, changing the balance. (1)
(e) Biotic: fish, plants, dragonflies; abiotic: water, sunlight, temperature, soil (any two each). (1)

Answer: Fish reduce dragonflies, so pollinators and seeds increase; overfishing would reverse these effects.

Example 4: Elephants and corridors · 4 marks · Case-basedHarder board level

Read the passage and answer.

In some states elephants enter farms when vegetation is scarce and waterholes dry up. Forests have been cut for roads and buildings. Ecologists have marked corridors between forest patches.
(a) Give two reasons why elephants enter farms. (1)
(b) How does cutting trees make things worse? (1)
(c) What is the purpose of a corridor? (1)
(d) Name the ecosystem type of the farm and say whether it is natural or human-made. (1)

Try it first, then show the solutionSolution

(a) Scarcity of vegetation and drying of waterholes in their habitat; farms offer food such as bananas and sugarcane. (1)
(b) Forests shrink and dry up, so animals lose habitat and move into human habitats. (1)
(c) Corridors connect forest habitats so animals can move safely. (1)
(d) Terrestrial; human-made. (1)

Answer: (a) Scarce food and water; (b) habitat loss; (c) safe movement; (d) terrestrial, human-made.

Example 5: Classify the interactions · 4 marks · Case-basedHOTS / competency

Read the passage and answer.

A student's table lists: A. Honeybees collect nectar from flowers and pollinate them. B. Orchids grow on a tree branch for support. C. Ticks feed on a dog's blood. D. Frogs and fish eat the same insect larvae.
(a) Name the relationship in each. (2)
(b) For B, why is the tree said to be unaffected? (1)
(c) Suggest what would happen to the fish and frog populations if the larvae become scarce. (1)

Try it first, then show the solutionSolution

(a) A mutualism; B commensalism; C parasitism; D competition. (2)
(b) The orchid gets physical support without taking food from or harming the tree (as the chapter's figure indicates). (1)
(c) Competition for scarce larvae would increase and the numbers of fish and frogs would be limited, as competition controls population sizes. (1)

Answer: (a) Mutualism, commensalism, parasitism, competition; (b) tree not harmed; (c) populations limited by scarce food.

Where students lose marks in Habitats, Populations, Communities and Ecosystems

The slips examiners see most often, and what to write instead.

Mistake: Using population and community interchangeably.
Both refer to groups.
Wrong working
A community is all the fish in a pond.
Right working
All the fish of one kind form a population; the community includes all populations in the pond.
Do this: Population: one kind; community: many kinds.
Usually costs: 1 mark.
Mistake: Listing only living things in an ecosystem.
Abiotic components are forgotten.
Wrong working
Ecosystem: plants, animals and microbes.
Right working
Ecosystem: biotic and abiotic components interacting.
Do this: Add air, water, soil, sunlight.
Usually costs: 1 mark.
Mistake: Calling commensalism harmful to one partner.
Confused with parasitism.
Wrong working
In commensalism one organism is harmed.
Right working
In commensalism one benefits and the other is not affected.
Do this: Commensalism: + and 0.
Usually costs: 1 mark.
Mistake: Saying farms are not ecosystems.
Ecosystems seem natural.
Wrong working
Only forests and ponds are ecosystems.
Right working
Farms and parks are human-made ecosystems.
Do this: Both types exist.
Usually costs: 1 mark.

Exam tips

Define each term with a pond example.
Mention both biotic and abiotic components in any ecosystem answer.
Name the relationship and say who benefits or is harmed.
For population counts, state the area and time, then compute the mean per square metre.
Use the pond-fish-dragonfly-pollinator story as a model of indirect effects.

Practice questions on Habitats, Populations, Communities and Ecosystems

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 2 marks · Very short answerBoard level
Define habitat. Name two biotic and two abiotic components of a forest habitat.
Hint
Place where an organism lives.
Answer
A habitat is the place where an organism lives (1). Biotic: trees, birds; abiotic: soil, sunlight (any two each) (1).
Q2 · 1 mark · MCQBoard level
Orchids growing on trees for support are an example of
(a) parasitism
(b) mutualism
(c) commensalism
(d) competition
Hint
The tree is unaffected.
Answer
(c)
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Removing one organism from a pond can change the number of plant seeds produced around it.
Reason (R): Organisms in a community are connected through feeding and pollination.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Fish, dragonflies, bees and seeds.
Answer
(a) R explains A.
Q4 · 4 marks · Short answerHarder board level
A group counts mouse populations in four equal fields with 12, 16, 9 and 15 mice. (a) Find the total. (b) Find the mean per field. (c) If each field is 2 hectares, find the density per hectare. (d) Name the level of organisation formed by the mice together with the grass and hawks of the fields.
Hint
Mean = total ÷ 4.
Answer
(a) 12 + 16 + 9 + 15 = 52. (b) 52 ÷ 4 = 13. (c) 13 ÷ 2 = 6.5 mice per hectare. (d) A community (with the abiotic parts, an ecosystem) (1 mark each).
Q5 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
A farmer finds that her crop field with millet is visited by mice, and a hawk often hunts there. A student says the field cannot be an ecosystem because it was made by humans.
(a) Identify the biotic and abiotic components. (b) Evaluate the student's statement. (c) Name two interactions you would expect. (d) Why can an ecosystem be small or large?
Hint
Farmland is a human-made ecosystem.
Answer
(a) Biotic: millet, mice, hawk; abiotic: soil, water, sunlight. (b) Wrong: farmland is a human-made ecosystem. (c) Mice feed on millet; the hawk feeds on mice; or competition among mice. (d) An ecosystem can be a pond or a large tree, so it can be of any size (1 mark each).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is a habitat?Show answer
The place where an organism lives.
2.What is a community?Show answer
Different populations sharing the same habitat.
3.Give an example of mutualism.Show answer
Honeybees and flowers.
4.Give an example of parasitism.Show answer
Ticks on the body of dogs.
5.Name two aquatic ecosystems.Show answer
Pond, river or lake.

Habitats, Populations, Communities and Ecosystems: frequently asked questions

Can a tree be a habitat?

Yes. A habitat could be as small as the bark of a tree, and a large tree can also be an ecosystem.

How do plants influence abiotic factors?

They release oxygen, hold soil with roots, retain soil moisture and help cool the atmosphere.

What is competition?

Organisms compete for common resources such as food, water, space or sunlight, which helps control population size.

Why is pollination important?

It transfers pollen from stamens to carpels and is essential for the formation of fruits and seeds.