A community of animals, plants and microorganisms, together with their habitat is called an ecosystem.

For example, a pond ecosystem may consist of a pond habitat, inhabited by aquatic plants, microorganisms in the mud at the bottom, fish in the water and a heron on the bank.

If one part of an ecosystem is changed, this may affect other living things in the ecosystem. For example, if a disease suddenly wipes out the plants in a pond, it might affect the fish and heron because they have less food to eat.

Humans affect the environment in positive and negative ways.

Cutting down trees and littering have a negative effect on animals and plants.

Protecting endangered species and cleaning lakes and seas has a positive effect on the environment.

At home you can help the planet by recycling waste and growing plants or vegetables.

Tropical rainforests are found between the Tropics of Cancer and Capricorn, 23.5° north and south of the equator.

What are rainforests like? The tropical rainforest contains far more species of plants and animals than any other biome. They cover approximately six per cent of the Earth's surface, and because they get 2,000 mm of rain per year and temperatures range from around 27 to 32°C, conditions are wet and hot all year round so it is a good environment for growth.

Animal cells and plant cells

Animal cells usually have an irregular shape, and plant cells usually have a regular shape. Cells are made up of different parts.How are plant and animal cells different?Plant cells have all the parts in the list above, plus a few extra structures:

• Cell wall - this is an outer structure that surrounds the cell and gives it support.

• Vacuole - this is a space within the cytoplasm of plant cells that contains sap.

• Chloroplasts - these contain chlorophyll and are the site of photosynthesis.