Resources and environment, Year 10: ecosystems

Interdependence (in an ecosystem)

提示It begins with a prefix meaning "between".

为什么In a pond the plants need sunlight, water and nutrients. The animals need the plants. The decomposers need the dead remains, and by rotting them they put nutrients back for the plants. Geography questions on any ecosystem, from a pond to a rainforest, are built on these links.

litter

提示The same word is used for rubbish dropped in the street.

为什么Leaves fall and join the store on the ground. Decomposers rot it, which moves the nutrients into the soil. Roots take them up and they become part of the living plants again. Nutrients keep going round this loop; they are not used up.

Decomposers work faster when it is warm and moist

提示Think about what bacteria and fungi need in order to be active.

为什么This is how climate controls the nutrient cycle. Where it is hot and wet all year, dead material rots within weeks. Where it is very cold, it can lie for years. The same idea explains the soils of every global ecosystem.

It rises, because fewer water fleas are being eaten

提示Ask who has just lost its main predator.

为什么The change then spreads. More water fleas graze more algae, so the algae fall. The heron has less to eat, so it may leave or go hungry. One change to one part has altered every level of the chain.

It shows all the feeding links, so every species affected can be traced

提示Most animals have more than one thing on the menu.

为什么A chain follows one route only. In real ecosystems most consumers eat several things and are eaten by several others. A web shows which animals can switch to another food and which have no alternative.

A biome (global ecosystem)

提示A short word that starts with the Greek for "life".

为什么Tropical rainforest, hot desert, tundra and temperate deciduous forest are all examples. Climate is the main control: temperature and rainfall decide which plants can grow, and the plants decide which animals can live there.

Hot desert

提示Daytime here is scorching and plants are few.

为什么Air that rose at the Equator sinks again at about 30° north and south. Sinking air warms up, so clouds cannot form and rain is rare. That is why the great dry regions of the world line up along the two tropics.

It has a wet season and a dry season

提示Rainforest gets a soaking in every month; here the pattern splits in two.

为什么It is warm all year. In the wet months the grasses grow tall. In the dry months they die back and fires are common, which is one reason trees are scattered and not packed together.

hot desert; coniferous forest; tundra

提示One is the driest, one is evergreen with needles, one is treeless and frozen below the surface.

为什么The ecosystems lie in belts that roughly follow the lines of latitude, because temperature and rainfall change with distance from the Equator. Coniferous forest is also called taiga or boreal forest, and lies at about 50° to 60° north.

Temperate deciduous forest

提示Think of oak and beech, and what they do each autumn.

为什么The UK has warm summers, mild winters and rain all year. That suits broad-leaved trees which drop their leaves in winter to save water and energy. Most of this forest was cleared for farming long ago.