Answer:
1. Providing structure --> Collagen makes skin strong yet flexible.
2. Maintaining homeostasis --> Insulin controls the concentration of sugar in the blood.
3. Fighting Disease --> IgA prevents the buildup of viruses and bacteria in the gut.
4. regulating chemical reactions --> Pepsin works in the stomach to speed up the breakdown of food.
The horse and donkey, though closely related by sharing a common ancestor, are different species. They have different number of chromosomes hence pairing of homologous chromosomes during fusion of gametes becomes complicated. The mule will have an extra chromosome from the horse hence will have abnormalities such as sterility. A Mule is unable to reproduce due to this same phenomenon. Homologous chromosomes are not well paired for meiosis I.