Ecology – JSS3 Intermediate Science Lesson Note (First Term)

Ecology is the study of how living things interact with one another and with their surroundings.

Behavioural objectives

1. Define ecology and ecosystem.
2. Name the biotic and abiotic components of an ecosystem, with examples.
3. Describe a food chain and identify producers, consumers and decomposers in it.
4. Distinguish between a food chain and a food web.
5. Explain how energy flows through an ecosystem.
6. State why damage to one organism affects the whole ecosystem.

What is an ecosystem?

An ecosystem is a community of living things together with the non-living parts of the place where they live.

• Neighbourhood idea: a neighbourhood needs people (living) and houses and roads (non-living) to work.
• Examples: a pond, a forest, a farm, a school garden and the space under a tree.

What are the components of an ecosystem?

An ecosystem has two components: biotic (living) and abiotic (non-living).

Biotic components

• Plants: grass, mango trees, maize and other green plants.
• Animals: ants, birds, goats, fish and humans.
• Fungi: mushrooms and moulds.
• Microbes: bacteria and other tiny organisms.

Abiotic components

• Sunlight: gives light and heat, and is the energy source for plants.
• Water: needed by every living thing.
• Soil: holds plants and supplies mineral nutrients.
• Air: supplies oxygen and carbon dioxide.
• Temperature: affects which organisms can live in a place.

Biotic and abiotic compared

• Teacher’s note: if the water (abiotic) is removed, the fish (biotic) cannot survive. The two parts depend on each other.

What is a food chain?

A food chain is a path that shows how energy passes from one living thing to another through feeding.

• Why it matters: every living thing needs energy, and that energy comes from food.
• Arrows: each arrow means “is eaten by” and points in the direction the energy moves.

What are the members of a food chain?

1. Producers: green plants that make their own food using sunlight. They start every food chain.
2. Consumers: animals that get energy by eating plants or other animals.
3. Decomposers: bacteria and fungi that break down dead plants and animals and return nutrients to the soil.

What are the levels of consumers?

• Primary consumers: eat plants, as in a grasshopper or a goat.
• Secondary consumers: eat primary consumers, as in a toad.
• Tertiary consumers: eat secondary consumers, as in a snake that eats a toad.
• Top consumers: sit at the end of the chain and have few or no natural enemies, as in a hawk or a lion.

Example of a food chain

• Chain: Grass → Grasshopper → Toad → Snake → Hawk.

What is a food web?

A food web is a network of many food chains joined together in one ecosystem.

• Reason: most animals eat more than one kind of food. A snake may eat a toad, a mouse or a small bird.
• Appearance: it looks like a spider’s web, with arrows pointing in different directions.
• Advantage: if one food source disappears, an animal can feed on another. This makes the ecosystem more stable.

Food chain and food web compared

How does energy flow in an ecosystem?

Energy flows in one direction, from the Sun to plants and then to animals.

Steps in energy flow

1. The Sun provides light energy.
2. Green plants capture the light and change it into chemical energy in food.
3. A primary consumer, such as a goat, eats the plant and takes in some of the energy.
4. A secondary consumer, or a human eating the goat, takes in a smaller amount.
5. Decomposers get energy from the dead remains of plants and animals.

Rules of energy flow

• One direction: energy does not move backward along the chain.
• Energy is lost: not all the energy is passed on to the next level.
• Plants: use some energy to grow.
• Animals: use some energy to run, breathe and keep warm, and lose some as heat.
• Top of the chain: much less energy reaches the top consumer than was present at the start.
• Result: there are many plants but only a few lions.

• Primary source of energy: the Sun is called this because nearly all the energy in food chains begins as sunlight.

Why must the parts of an ecosystem stay in balance?

Every organism in an ecosystem depends on others, so harm to one affects the rest.

• Chemical spraying: chemicals that kill all insects remove the food of insect-eating birds.
• Birds die: snakes may increase in number, or hawks may lack food.
• Link: everything in an ecosystem is connected.
• Care: farmers and communities should protect plants, water and animals to keep ecosystems healthy.

Evaluation

1. Define ecology and ecosystem.
2. List three abiotic components you can find in your school garden.
3. Name the producer, the primary consumer and the secondary consumer in: Grass → Grasshopper → Toad → Snake → Hawk.
4. State two differences between a food chain and a food web.
5. Why is the Sun called the primary source of energy, and why are there fewer lions than plants?

Assignment

Draw a food web of at least six living things found around your school or home. Label the producer, the consumers and the decomposers.