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
draw a food chain.
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).
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.