B7.1 Biology

B7.1 gcse revision full

  • Created by: callum
  • Created on: 08-06-11 14:50

Why do we need the sun?

The Sun provides:

- Thermal energy that helps to keep the Earths atmosphere warm.

- Light energy that green plants use to make food chemicals.

Amimals, fungi and bacteria depend, directly or indirectly on plants for food.

So life on Earth is dependant on the suns energy.

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How do plants harness the suns energy?

Only the green parts of plants absorb light energy. They use it to make food in a process called Photosynthesis.

Plants absorb on a tiny amount of the suns energy.

The new material made by photosynthesis consists of chemicals such as carbohydrates, fats and proteins. These chemicals form new plant cells and any food stores inside those cells. You can think of both as a store of energy.

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How organisms feed?

Organisms that make their own food are called Autotrophs.

most are green plants.

Organisms that cant make their own food are called Heterotrophs. These include animals bacteria and fungi. They depend on food produced by Autotrophs.

If heterotrophs feed on plants we call them herbivores.

If heterotrophs feed on animals that have eaten plants we call them carnivores.

If heterotrophs feed on waste produced by animals and plants we call them decomposers.

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How are food and energy transferred between organi

When an amimal eats a plant or waste, the energy that is stored in it is transferred to the animal.

A food chain shows what eats what. Food chains also show the direction of energy transfer.

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Pyramid of numbers.

A Pyramid of numbers shows the number of organisms at each feeding level in an ecosystem.

It gives you now idea of the biomass at each level.


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Pyramid of biomass.

A Pyramid of biomass shows you the mass of organisms at each feeding level in an ecosystem. So it shows you hao much food is availible to the next level.

A pyramid of biomass is bigger at the base because some of the mass does not pass onto the next level.


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How is energy lost from food chains.

There is less biomass at each level in a food chain. So there is less energy. The energy that is not passed on is:

- in uneaten parts.

- Used for life processes such as movement and keeping warm.

- Lost to the surroundings as heat energy.

- In waste products.

As there is less food and energy at each feeding level, There is a limit to the length of food chains.

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What is in soil?

Soil contains:

- biomass that includes the living organisms and decaying materials.

- inorganic particles such as sand, silt and clay.

- Air.

- water ith dissolved mineral ions.

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