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Explain how the physical properties of water enable organisms to survive over a range of temperatures.

Water has a very high specific heat capacity due to the collective forces of the many hydrogen bonds. A lot of energy goes into breaking these bonds rather than raising the temperature of the water, hence pr...
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Answered by Arunima B. • Biology tutor
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Tetrodotoxin (TTX) is a chemical found in pufferfish which binds to voltage-gated sodium channels causing inactivation via a conformational change. Poisoning can result in paralysis leading to death. How might this occur? (4 marks)

This question asks about nerve action potential generation. There are a couple of clues - these include 'voltage-gated sodium channels' and 'paralysis' which suggests the idea of failure of impulse transmiss...
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Answered by Rafee A. • Biology tutor
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Describe methods of solute transport across a cell membrane.

For non-polar small molecules simple diffusion down a concentration gradient through the phospholipid bilayer is possible as it is soluble in the hydrophobic fatty acid tails of the membrane. An example of t...
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Answered by Ayano F. • Biology tutor
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Describe the process of natural selection

Within a population of a species there will be variation between individuals. These variations arise because of mutations causing differences in alleles and phenotypes. Some individuals will have an allele w...
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Answered by Harry R. • Biology tutor
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Describe the role of the Loop of Henle

The Loop of Henle is an important part of the kidney nephron in forming concentrated urine. It is a long loop, which forms something known as a hairpin countercurrent mechanism. It is called countercurrent b...
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Answered by John A. • Biology tutor
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