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Why may a rise in testosterone above normal cause a subsequent decrease in the hormone?

This is a question from the AQA June 15 Biology A level past paper. Short answer: Raised testosterone causes a physiological decrease in GnRH as well as LH and FSH via negative feedback. Detailed answer: To ...
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Answered by Dhiluni K. • Biology tutor
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Outline some of the evidence for evolution

The fossil record provides a comprehensive array of evidence for evolution. For example Darwin studied Brachiopods, and within rocks you can see the clear change in the Brachiopods through time. The fossil r...
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Answered by Kelly T. • Biology tutor
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Describe the process by which a pathogen is destroyed after it has become attached to the surface of a phagocyte.

Pathogens are first recognised as a foreign body by the antigens on it's membrane, as they are non-self antigens. The body then triggers a response by attaching antibodies to these antigens. Phagocytes can d...
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Answered by Kelly T. • Biology tutor
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Describe the structure of DNA and where it is found inside a human cell

The DNA molecule is found within the nucleus of the cell, organised into chromosomes. In humans, there are 46 chromosomes. The DNA molecule consists of organic bases joined by sugars and phosphate molecules.
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Answered by Kelly T. • Biology tutor
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How are action potentials propagated along a neuron?

Electical impulses usually arrive at the dendrites of a neuron. These then pass through the cell body and a propagated down the longest part of the neuron, the axon. Resting potential This is the potential d...
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Answered by Ollie W. • Biology tutor
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