Overview
What you’ll learn
- Describe physical factors in a habitat and give examples of adaptations.
- State that an ecosystem is a community plus its environment.
- Describe predator–prey, mutualism and parasitism.
- Interpret food chains and food webs, and outline photosynthesis and respiration.
- Explain how decomposers recycle nutrients and how people can affect biodiversity.
In 30 seconds
- 1An ecosystem is a community of organisms plus the environment they share.
- 2Abiotic factors are non-living: air, water, temperature, light, minerals, and acidity or alkalinity. An adaptation is a feature that helps survival.
- 3Predator–prey: one animal eats another. Mutualism: both benefit. Parasitism: one benefits and the host is harmed.
- 4Arrows in a food chain show energy transfer from food to feeder. A food web joins several chains.
- 5Photosynthesis makes food in plants. Respiration releases energy from food in living cells.
- 6Decomposers break down dead matter. Losing habitats can reduce biodiversity.
Notes · 1 of 5
Habitats, factors and adaptations
Where an organism lives, and the features that help it live there.
A habitat is the place where an organism lives. A population is a group of the same species there. A community is all the populations together. The ecosystem is that community plus the non-living environment.
- Abiotic (non-living) factors: air, water, temperature, light, minerals, and how acidic or alkaline the soil or water is. Biotic factors are the other living things.
- A thick coat helps a mammal where the temperature is low. A plant with a deep root can reach water where water is scarce.
- An adaptation can be a body feature or a behaviour, such as hunting at night when the light is low.
Changing one abiotic factor changes which organisms can live there. A pond that loses oxygen, or soil that becomes too acidic, can lose species even if nobody removes them by hand.
Notes · 2 of 5
How organisms interact
Name who benefits and who is harmed.
| Relationship | What happens | Example |
|---|---|---|
| Predator–prey | The predator eats the prey | A frog eats a grasshopper |
| Mutualism | Both benefit | Bees get food and flowers are pollinated |
| Parasitism | The parasite benefits; the host is harmed | A tick on a dog |
Predator numbers and prey numbers affect each other. If prey becomes scarce, predators have less food. A parasite usually lives on or in the host and does not kill it straight away.
Notes · 3 of 5
Food chains and food webs
The arrow points to the organism that gains the energy.
A producer makes its own food, usually a green plant. A consumer eats other organisms. The first consumer is the herbivore. Later consumers eat animals. Example: grass → grasshopper → frog → snake. The arrow means “energy is transferred to”.
| Role | Chain 1 | Chain 2 |
|---|---|---|
| Producer | grass | grass |
| First consumer | grasshopper | grasshopper |
| Later consumer | frog, then snake | spider |
Put the two chains together and you have a food web: the grasshopper is eaten by both the frog and the spider. One animal may eat several foods, and one food may be eaten by several animals. Energy is lost as heat at each step, so food chains are short.
Notes · 4 of 5
Photosynthesis, respiration and decomposers
Plants make food. All living cells release energy from food. Decomposers recycle what is left.
Photosynthesis in green plants: carbon dioxide + water → glucose + oxygen, using light energy. Respiration in living cells: glucose + oxygen → carbon dioxide + water, and energy is released. Respiration is not the same thing as breathing. The two processes move carbon dioxide in opposite directions.
Decomposers, such as many bacteria and fungi, break down dead organisms and waste. Nutrients return to the soil or water and can be used again by plants.
Notes · 5 of 5
People, biodiversity and climate
Changing a habitat changes the organisms that can live there.
Biodiversity is the variety of living things in a place. Clearing forest, draining a wetland or polluting a river removes habitats and food, so fewer species remain.
Burning fuels adds carbon dioxide to the air. A warmer climate can change rainfall and temperature, which are physical factors. Protecting habitats and cutting waste are ways to reduce the harm.
Revise
Key terms
The words examiners expect you to use precisely.
- Habitat
- The place where an organism lives.
- Population
- A group of organisms of the same species living in the same place.
- Community
- All the populations of living things in a habitat.
- Ecosystem
- A community of living things together with their environment.
- Adaptation
- A feature that helps an organism survive in its environment.
- Abiotic factor
- A non-living factor in a habitat, such as air, water, temperature, light, minerals, or acidity.
Show 10 more key termsShow fewer key terms
- Producer
- An organism that makes its own food, usually a green plant.
- Consumer
- An organism that obtains food by eating other organisms.
- Food chain
- A line of organisms showing the transfer of energy from food to feeder.
- Food web
- A set of linked food chains in one ecosystem.
- Photosynthesis
- The process in green plants that makes glucose from carbon dioxide and water, using light energy, and releases oxygen.
- Respiration
- The process in living cells that releases energy from food. It is not the same as breathing.
- Decomposer
- An organism, such as a fungus or many bacteria, that breaks down dead matter and returns nutrients.
- Mutualism
- A relationship in which both organisms benefit.
- Parasitism
- A relationship in which one organism benefits and the host is harmed.
- Biodiversity
- The variety of living things in an area.
Revise
Common mistakes
Where students most often lose marks in this chapter — and what to do instead.
Mistake: Drawing the food-chain arrow from the eater to the food.
The arrow shows where the energy goes, not who is chasing whom.
Instead: The arrow points to the organism that receives the energy.
Mistake: Saying an ecosystem is only the animals.
The environment is part of the definition.
Instead: Ecosystem = community + environment.
Show 5 more mistakesShow fewer mistakes
Mistake: Calling breathing the same thing as respiration.
Breathing moves air. Respiration releases energy inside cells.
Instead: Respiration happens in living cells and releases energy from food.
Mistake: Saying both partners benefit in parasitism.
That is mutualism.
Instead: In parasitism the host is harmed.
Mistake: Putting a decomposer as the producer at the start of a chain.
Producers make food by photosynthesis. Decomposers break down dead matter.
Instead: The producer is usually a green plant.
Mistake: Saying one food chain shows every feeding link in a habitat.
Most organisms have more than one food.
Instead: A food web shows those extra links.
Mistake: Calling a frog an abiotic factor because it lives in the pond.
A frog is alive. Abiotic means non-living.
Instead: Abiotic factors include air, water, temperature, light, minerals, and acidity or alkalinity.
Check yourself
Quick quiz
10 questions with instant explanations. About 5 minutes.
Question 1 of 3
- Question 1: current question
- Question 2: not answered
- Question 3: not answered
Define an ecosystem
An ecosystem is a community plus
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Practise
Topical questions
Exam-style practice in three tiers, from recall to data questions.
- 5Foundation
- 5Standard
- 5Challenging
15 questions worth 36 marks, each with a model answer, mark scheme and examiner tips.
Practise topical questionsExam practice
Practice paper
A 30-mark paper set out like a school paper, with a separate mark scheme. Give yourself 40 min.
Question paper
Chapter 4 Practice Paper
30 marks · 40 min · 6 pages
10 multiple-choice questions and structured questions with answer lines. Chapter 4.
Mark scheme
PROChapter 4 Practice Paper — mark scheme
Answers · Marking points · 3 pages
Model answers with a mark for each creditworthy point — for marking at home or in class.
Where this chapter is tested
Each school sets its own scope — check your assessment outline.
Questions
Frequently asked questions
What is an ecosystem in Sec 2 Science?
A community of living things together with the environment they live in. A habitat is the place. A population is one species in that place.
Which way do food chain arrows point?
Towards the organism that receives the energy. Grass → grasshopper means the grasshopper gets energy from the grass.
What is the difference between mutualism and parasitism?
In mutualism both organisms benefit. In parasitism the parasite benefits and the host is harmed.
Is respiration the same as breathing?
No. Breathing moves air. Respiration is the release of energy from food inside living cells.
Is ecosystems in the Sec 2 EOY?
Most schools that follow the usual G2/G3 scheme teach this chapter in Sec 2 and include it in the Sec 2 end-of-year paper. A few schools move a topic across the two years, so check your school’s assessment outline.
Up next
Chapter 5: Electrical Systems