The liver is doing respiration.

I saved a boy from drowning, mouthtomouth respiration.

The only creatures that have got conscious control of their breath are the diving animals and the diving birds.

And if you watched the videos on respiration, you know that we need the oxygen in order to metabolize our food, in order to turn our food into ATPs that can then drive other types of cellular functions or anything that we have to do move, or breathe, or think, or everything that we have to do.

Now the interesting thing is we can account whether we get to the 38 ATPs promised by cellular respiration.

So actually, photosynthesis is happening during the day, but at all times, plants are also capable of doing cellular respiration, just like humans are, so humans and plants have actually more in common than you might think.