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Explain the transmission of a nerve impulse across a cholinergic synapse referring to action potentials. (6)

When an action potential reaches the terminal of a pre-synaptic cleft, voltage-gated calcium channels are stimulated to open, causing an influx of Ca+ ions in the pre-synaptic neuron. This infux of Ca+ ions ...
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Answered by Sarah W. • Biology tutor
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Describe how phagocytic white blood cells destroy bacteria. (4)

The phagocyte recognises antigens on the surface of the bacteria as foreign, causing it to be attracted to the bacteria. The phagocyte then engulfs the bacteria, forming a vesicle around it. Lysozomes fuse w...
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Answered by Sarah W. • Biology tutor
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Why does a base substitution in DNA not always result in the formation of non-functional proteins?

Protein structure is determined by amino acid sequence. Each amino acid is coded for by a triplet of RNA bases. These are transcribed from a DNA molecule. If a DNA base is substituted for another base, then ...
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Answered by Abby R. • Biology tutor
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What type of blood does the pulmonary artery contain?

Deoxygenated blood
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An extract of DNA contains 4000 base pairs. The extract is identified to contain 300 guanine bases. How many adenine bases can be found in the DNA extract?.

3700
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