Top answers

What is a proposed model for enzyme activity?

The lock and key model: Only substrates of a specific shape that is complementary to the active site of an enzyme can fit into the active site, in a way that is analagous to a key fitting into a lock.
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Answered by Alastair P. • Biology tutor
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How is the structure of alveoli suitably adapted for efficient gas exchange?

Very thin walls result in a short diffusion distance which makes gas exchange particularly favourable. Lots of branches and sacs result in a large surface area so gas exchange can be maximised.
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Answered by Alastair P. • Biology tutor
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What are the differences between exons and introns found in DNA.

Exons are coding regions of DNA, and are copied into mRNA and transcribed as proteins. Introns are non-coding regions of DNA, and are spliced out of pre-mRNA so are not copied into mRNA.
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Answered by Alastair P. • Biology tutor
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Explain what a hydrocarbon is, and suggest two properties of hydrocarbons that leave a fractioning column near the top.

A hydrocarbon is a molecule that contains only hydrogen and carbon atoms. Any two of the follwing properties are suitable answers: Low boiling points, low viscosities or high flammability.
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What is the difference between an aldehyde and a ketone, and what type of molecule can they each be reduced to?

Both aldehydes and ketones have a carbonyl functional group (C=O), however in aldhydes the carbonyl carbon atom is the terminal carbon of the chain, whereas in ketones the carbonyl carbon has two alkyl group...
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