The cellular organelle that is considered the site of respiration is the
a. nucleus
b. lysosome
c. mitochondrion
d. rough er
e. golgi apparatus

c. mitochondrion

Explanation:

The mitochondrion is a double membrane-bound organelle present in eukaryotic cells only. It is the site for Kreb's cycle and oxidative phosphorylation and produces a large amount of energy stored in the form of ATP.  

Since Kreb's cycle and oxidative phosphorylation are second and final stages of aerobic cellular respiration respectively, the mitochondrion is called a site of respiration in cells.  

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.

1. b.

2. d.

3. a.

5. d.

6. c.

these are the only ones that i know, i hope this , and good luck.