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what is a food web?

When all the food chains in a habitat are joined up together they form a food web. Here is an example of a food web

Although it looks complex, it is just several food chains joined together. Here are some of the food chains in this food web:

grass → insect → vole → hawk

grass → insect → frog → fox

grass → insect → vole → fox

Food web - The producer is grass, which is eaten by rabbits, insects and slugs. The rabbit is eaten by the fox. The insects are eaten by frogs, voles and thrushes. Thrushes also eat the slugs. Frogs, voles and thrushes are eaten by a hawk. Frogs and voles are also eaten by the fox. (

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draw a food chain.


GrassGrasshopperFrogHawk grass (   A grasshopper (   a frog (   a hawk ( Producer   Consumer   Consumer   Consumer     Primary consumer   Secondary consumer   Tertiary consumer     Herbivore   Carnivore   Carnivore

food chain shows the different organisms that live in a habitat, and what eats what.

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describe the structure of DNA.

DNA  is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C).


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explain what what causes genetic variation.

Without genetic variation, some of the basic mechanisms of evolutionary change cannot operate.

There are three primary sources of genetic variation,

Mutations are changes in the DNA. A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations.

Gene flow  is any movement of genes from one population to another and is an important source of genetic variation.

Genetic shuffling (

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