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Biology

A Level

Describe the process of transcription

Transcription takes place in the nucleus and is the first stage of protein synthesis. RNA polymerase attaches to the DNA double helix at the promoter sequence and unwinds the helix by breaking the hydroge...

Answered by Jess D. • Biology tutor

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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 a...

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 ...

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 reprodu...

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 noradren...

Answered by Ammar L. • Biology tutor

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