What is the 2nd phase of cellular respiration? what happens?

The second phage of cellular respiration is transition stage.

Process take place in transition stage:

The transition stage take place in mitochondria. The pyruvate is combined with NAD+ to form NADH and acetyl co-enzyme molecules.

After transition stage, Krebs cycle starts.

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands