Final answer:
Sexual reproduction in Volvox occurs under stressful environmental conditions, such as nutrient depletion, and results in the formation of resistant zygospores that can withstand adverse conditions.
Step-by-step explanation:
In Volvox, a colonial green algae, sexual reproduction occurs under certain environmental conditions. Sexual reproduction is often associated with periods when resources are scarce, such as when nutrients are depleted, or environmental changes occur that stress the organism. During sexual reproduction in Volvox, specialized reproductive cells, known as gametes, are produced. These gametes are capable of fusing with each other to form a zygote, which then develops into a resistant zygospore.
This zygospore can undergo meiosis, eventually leading to the release of haploid cells that will develop into new individuals. Sexual reproduction in protists, including Volvox, not only generates diversity but also creates cysts or spores that can withstand adverse conditions until the environment is more favorable.