LIWA

Ecosystems

ICSE Class 8 · Biology · Chapter 4

What this chapter covers

Key definitions

Biotic components are the living parts of an ecosystem, such as plants, animals and micro-organisms.

Abiotic components are the non-living parts of an ecosystem, such as air, water, soil, sunlight and temperature.

Ecology is the study of how living organisms interact with one another and with their non-living surroundings.

Producers are organisms that make their own food from simple substances using the energy of sunlight.

Consumers are organisms that cannot make their own food and so get it by eating other organisms.

Herbivores are animals that feed only on plants or plant parts.

Carnivores are animals that feed on the flesh of other animals.

Omnivores are animals that eat both plants and animals.

Decomposers are micro-organisms, mainly bacteria and fungi, that break down the dead bodies and waste of plants and animals into simple substances.

Symbiosis is a close relationship between two organisms of different kinds that live together, in which both partners benefit.

Parasitism is a relationship between two organisms of different kinds in which one, the parasite, lives on or inside the other, the host, and gets food from it while harming it.

Predation is a relationship in which one animal, the predator, hunts, kills and eats another animal, the prey.

Key points

Questions answered

Define an ecosystem. Name its two main components.
An ecosystem is a natural unit made up of all the living organisms in an area together with the non-living things around them, all interacting with one another. Its two components are biotic (living) and abiotic (non-living).
Why are green plants called producers?
Green plants make their own food from carbon dioxide and water using the energy of sunlight. All other organisms depend on this food, directly or indirectly.
What is the role of decomposers in a forest?
Decomposers, mainly bacteria and fungi, break down dead plants and animals into simple substances. This cleans the forest floor and returns minerals to the soil for plants to use again.
In the food chain Grass → Rabbit → Fox, name the producer, the primary consumer and the secondary consumer.
Grass is the producer, the rabbit is the primary consumer and the fox is the secondary consumer.
How is a food web different from a food chain? Why is a food web more stable?
A food chain is a single straight series of who eats whom, while a food web is many food chains joined together. A food web is more stable because if one food source disappears, animals can switch to another.
Why are there far fewer tigers than deer in a forest?
Each animal uses most of the energy from its food to stay alive, so only a little passes up the chain. Many deer are needed to support one tiger, so the numbers fall at each higher level of the pyramid of numbers.
A lichen is an example of which relationship? Explain how both partners benefit.
Symbiosis. The alga makes food using sunlight and shares it with the fungus, while the fungus holds water and protects the alga from drying out.
How is a parasite different from a predator? Give one example of each.
A parasite feeds on a living host slowly over a long time and usually keeps it alive, as Cuscuta does on a host plant. A predator kills its prey and eats it, as a tiger does with a deer.