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

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What is the primary mechanism by which the injection prevents pregnancy?

Increases sperm production
Stimulates thick cervical mucus production
Blocks the transfer of progesterone
Enhances ovulation frequency

The correct answer is: Stimulates thick cervical mucus production

The primary mechanism by which the injection prevents pregnancy is by stimulating thick cervical mucus production. When the cervical mucus is thickened, it becomes more difficult for sperm to swim through the cervix and reach an egg. This barrier significantly reduces the chances of fertilization occurring since sperm has an essential role in this process. In addition to thickening cervical mucus, contraceptive injections typically contain hormones that can also inhibit ovulation, though that is not the mechanism highlighted in this context. By concentrating on cervical mucus, the injection provides a mechanical barrier to sperm, which adds to its effectiveness in preventing pregnancy.