Due to photosynthesis, plants convert Sunlight and Carbon Dioxide into Oxygen. All living things breathe in this gas (Oxygen).
If all humans had the same DNA, and one person got the cold, everyone would die at some point. The more diversity there is the more chance of surviving an outbreak or natural disaster or something. Think of the flu. there are HUNDREDS of strains out there. some are resistant to our medicines and others aren't.
The over-hunting of the Baleen Whales lowers the population significantly. Since Baleen Whales eat the penguins, less whales equals less penguins eaten; therefore the penguins' population remains about the same until breeding season, where a surplus of baby penguins are produced.
By the excretory system through the large intestine
Producers, herbivores, secondary consumers, apex predators
