6. (a) The diagram shows part of a testis - Scottish Highers Human Biology - Question 6 - 2019

1. Testosterone stimulates and promotes sperm production and the development of male gametes.
2. It triggers the development of secondary sexual characteristics, including the growth of facial hair and deepening of the voice.

When testosterone levels are low, the hypothalamus detects this and increases the secretion of gonadotropin-releasing hormone (GnRH). This, in turn, stimulates the pituitary gland to release luteinizing hormone (LH), which stimulates the interstitial cells to produce more testosterone, thus restoring the balance.

AI: In artificial insemination, a number of sperm are collected over a period of time and then introduced directly into the female reproductive tract, increasing the likelihood of fertilisation.

ICSI: Intra-cytoplasmic sperm injection involves directly injecting a single sperm into an egg, which enhances the chances of successful fertilisation, especially in cases of low sperm count.