Most people cannot afford an African safari or a trip to the Amazon flooded forest. But they can afford a ticket to the zoo. It's a part of human nature to care more about an issue when you focus on an individual who is affected, and it's the same case with helping wildlife; seeing an animal in person is more likely to instill a sense of awe and respect for that species than simply reading nature facts or even watching footage on a nature show. Zoos give people an opportunity to experience a taste of the natural world and develop a sense of urgency for protecting it.
An oft-used argument against zoos is that they take away an animal's freedom; however, life in the wild can hardly be considered "free." As Yann Martel says in his novel _Life of Pi_, "Animals in the wild lead lives of compulsion and necessity within an unforgiving social hierarchy in an environment where the supply of fear is high and supply of food low and where territory must constantly be defended and parasites forever endured."
Zoo animals are usually born in captivity, or they suffered some debilitating injury; either way, they would not last long in the wild. Zoos at least give them a high quality of life and longevity that they would not enjoy otherwise. These animals become ideal ambassadors of their species to the human public. We can learn to appreciate them in person, and in turn this can inspire people to work toward helping their species in the wild.
Zoos accredited by the Association of Zoos and Aquariums (AZA) take good care of their animals. These animals have a guaranteed food source, their diet and health are monitored by veterinarians and nutritionists, and their keepers provide enrichment to keep their enclosures stimulating. Modern enclosures are not at all like the cages used in zoos of old. Old exhibits were built to be cleaned and sterilized easily with little more than a hose. With the advancements made in animal health and exhibit upkeep, modern exhibits look and feel like the animal's natural habitat, with actual horticulture and foliage.
Zoos also dedicate their resources to wildlife conservation, such as by tracking the gene pools of endangered species and running extensive education programs for the public of all ages. Zoos enable us to learn first-hand about our fellow creatures and to take an active interest in their survival.