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Biology

A Level

What causes cancer?

There are lots of different types of cancer which affect different tissues in the body, and two cancers of the same type may not have the same causes. This makes cancer interesting, but also potentiall...

Answered by Frederick H. • Biology tutor

8672 Views

Explain the principles of PCR

The Polymerase Chain Reaction (PCR) is a method of DNA amplification in vitro. It consists of 3 stages - denaturation, annealing and extending. PCR relies on the use of a thermophilic Taq polymerase en...

Answered by David B. • Biology tutor

5312 Views

State the differences between introns and exons.

Introns and exons are parts of genes - exons code for proteins, whereas introns do not, ie: exons are converted into messenger RNA to allow these parts of the gene to then be transcribed into protein. ...

Answered by David B. • Biology tutor

13936 Views

Explain what is meant by active transport

Avtive transport is the transport of molecules against their concentration gradient (that is, from a low concentration to a high concentration). This mechanism requires energy, and so ATP is used up.

Answered by Arantxa B. • Biology tutor

4236 Views

The surface run-off of nitrate from agricultural fertiliser into freshwater ponds and lakes can cause the death of the fish. Explain how this happens.

This question crops up a lot and may be up to a five mark question, if you learn the key points and terms you can be confident of getting all the marks you can here!