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Describe the process of DNA replication

DNA replicates by a semi-conservative method. When replication needs to occur, DNA helicase separates the two strands of DNA by breaking the hydrogen bonds between the strands. Each free strand now acts as a...
PB
Answered by Parisha B. • Biology tutor
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a) Name a hormone secreted by the ovaries (1 mark). b) A female takes a contraceptive pill that increases the body's levels of progesterone. Explain what effects this has on the female's body and what effects that it has on her other hormones (3 marks)

a) Oestrogen or Progesterone b) FSH stimulates follicles in the ovaries to mature while progesterone has a "maintenance" function as it maintains the lining of the uterus. Progesterone also has an ...
TH
Answered by Tom H. • Biology tutor
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Describe evolution by natural selection and how this may lead to speciation?

A given population of biological organisms will show considerable genetic variation. This is initially (relatively speaking) a result of random mutation. However, as factors affecting survival and reproducti...
MK
Answered by Mark K. • Biology tutor
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Compare the differences between the sympathetic and the parasympathetic nervous system.

The sympathetic nervous system is most active in times of stress and acts to increase activity, such as by increasing heart rate, ventilatory rate and dilates pupils. It uses the neurotransmitter noradrenali...
AL
Answered by Ammar L. • Biology tutor
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Outline how the first neurone communicates with the second neurone at a synapse.

The neurotransmitter e.g. Acetylcholine is excocytosed at the presynaptic membrane, the neurotransmitter diffuses across the synaptic cleft, down its concentration gradient, then attaching to complementary r...
MG
Answered by Maria G. • Biology tutor
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