Genetics help on number 6!

I am sooo confused! What is the difference between a & b and c & d? I was reading the lecture and I think I fugred out c & d. So I mainly need help with a & b.

Cellular Respiration

Humans would not be able to function on anaerobic cellular respiration alone. They need both of these processes to produce ATP in order to survive. The oxygen we need is produced through aerobic respiration. When it doesn’t happen, like in anaerobic, our muscles can shut down. Which is very bad obviously. That doesn’t really explain why we are most active. I believe that us mammals are more active because of our surrounding and environment. Crocodiles and cold blooded animals live in water, or at least like to be in water or kind of lone areas. This has made them adapt to a kind of boring and less active lifestyle. Mammals like us are more active because of our own surroundings. We like to be around other people and do a lot of activities. In the end like that, I don’t think ATP works that way. Just because cold blooded animals have more ATP, doesn’t mean they are supposed to be more active. It just means they produce more ATP.