GCSE Combined Science revision · Biology: homeostasis, inheritance and ecology

Higher: infertility and negative feedback

Higher only

The idea

In IVF, the woman is given FSH and LH to mature several eggs, which are collected and fertilised by sperm in the lab. The embryos grow into balls of cells and one or two are inserted into the uterus. IVF success rates are low and it can cause multiple births. Adrenaline, from the adrenal glands, prepares the body for 'fight or flight'. Thyroxine controls metabolic rate and is regulated by negative feedback: high levels reduce TSH release from the pituitary.

List the IVF steps in order.
Weigh IVF's benefits and drawbacks.
Explain negative feedback in steps.

Watch out Negative feedback reverses a change: too much thyroxine leads to less TSH, so less thyroxine.

See it worked

Worked example

Explain how negative feedback keeps thyroxine levels stable.

When thyroxine is high, the pituitary releases less TSH.
So the thyroid releases less thyroxine, and the level falls back.

Answer High thyroxine reduces TSH, so less thyroxine is made

Your turn

Question 1Calculator allowed1 mark

Which hormones are given to a woman at the start of IVF?

Question 2Calculator allowed1 mark

Which is an effect of adrenaline?

Question 3Calculator allowed3 marks

Give one advantage and one disadvantage of IVF.

Write your answer, then see a model answer

Advantage.
Disadvantage.

Answer It lets infertile couples have a child, but success rates are low, it is costly and stressful, and multiple births are a risk.

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