List two functions of testosterone.

Explanation

**Step-by-Step Text Solution:**

1. **Identify Testosterone**: Testosterone is a steroid hormone that plays a crucial role in male physiology. It is secreted by the Leydig cells (also known as interstitial cells) located in the testes.

2. **Function 1 - Growth of Secondary Sexual Characteristics**: One of the primary functions of testosterone is to stimulate the development of secondary sexual characteristics in males. This includes features such as the growth of facial hair (beard), a deeper voice (low pitch), and other male-specific traits that develop during puberty.

3. **Function 2 - Stimulation of Spermatogenesis**: Another important function of testosterone is its role in spermatogenesis, which is the process of sperm formation. Testosterone is essential for the maturation and production of sperm cells in the male reproductive system.

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