What do muscles form after being exercised extensively?

The concept of keystone species is controversial among ecologists because most organisms are highly interdependent. if each of the trophic levels is dependant on all others how can we say one is most important

Cassandra made a venn diagram to compare and contrast the two stages of cellular respiration. which belongs in the area marked x? energy is released. oxygen is used up. glucose is broken down. carbon dioxide is used up.

Can someone i have no idea of how to do this.