OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What happens to the uterus lining if no fertilised egg is present by day 28?

It thickens further
It starts to break down
It remains unchanged
It produces additional hormones

The correct answer is: It starts to break down

The uterus lining, or endometrium, is designed to prepare for a potential pregnancy each menstrual cycle. By day 28 of the cycle, if a fertilized egg has not implanted, the hormone levels, particularly progesterone, begin to fall. This decrease in hormone levels signals the body that pregnancy has not occurred. As a result, the thickened endometrial lining, which has developed to support a potential embryo, starts to break down. This breakdown leads to menstruation, where the lining is shed from the body. The process is a crucial part of the menstrual cycle, helping to reset the body for a new cycle in which fertilization could occur. Thus, the breakdown of the uterus lining is essential for reproductive health.