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Vaccines have become an effective way to prevent certain diseases, however for some viruses it is difficult to develop a vaccine. Describe possible difficulties of developing a permanent vaccine for the influenza virus.

The influenza virus has a very high mutation rate. This means that its surface proteins (antigens) will change. Since a vaccine contains a specific antigen, if the virus switches to a different antigen, then...
NL
Answered by Nancy L. • Biology tutor
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Explain the stages of the cardiac cycle

The cardiac cycle consists of series of chamber systole and diastole. Systole is the name given to a period when cardiac muscle contract to cause blood ejection from the respective chamber to another. Diasto...
AB
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Give one piece of evidence that supports the theory that mitochondria evolved from prokaryotic cells. (1 mark)

Size: mitochondria are 2uM in diameter, similar to bacteria. Also applies to genome size and content, suggesting an 'endosymbiosis' event.
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Answered by Lauren M. • Biology tutor
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How does DNA lead to the production of proteins?

Proteins are encoded by the information stored in the DNA genetic material. This happens in two stages: transcription and translation. During transcription, the DNA unravels and exposes it's sequence, allowi...
MS
Answered by Millie S. • Biology tutor
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What is an enzyme? Explain their importance?

Enzymes are specific proteins that catalyse a specific reaction or breakdown of a substance. They allow a variety reactions to take place without using as much energy (improve efficiency). Useful to think ab...
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Answered by William W. • Biology tutor
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