biology = whole organisms
microbiology = whole tiny organisms
cellular biology = whole cells of complex organisms
molecular biology = The machinery inside of cells
biochemistry = The chemicals of organisms, both inside and outside of cells
organic chemistry = chemistry involving carbon and hydrogen.
There’s more chemistry, and underlying chemistry is physics. Biology is an application of chemistry, and chemistry is an application of physics.
When you look at molecular biology, you see what looks like program counters and 3d printers. Most of the bits inside of cells are literally physical machines, aided along by the right shape to have a static or magnetic charge necessary to pull the right pieces out of the semi-random soup and move, attach, or detach them.
When you exercise, you literally dump calcium into pockets in a muscle cell, and those fit into a lock on a little machine that ratchets down a little rope, each click caused by an ATP molecule floating in, connecting, getting snapped, and having a tiny bit of electric charge transferred.
The fun thing is that ATP is also required to pump the calcium out of that little pocket, so when you’ve depleted ATP. There is a complex loop for making ATP, and a whole of of ways to keep that cycle (ctric acid or Krebs cycle) going, but the fastest way to make ATP is oxygen and glucose.
Oxygen input often lags behind, and you can always burn up oxygen faster than you can replenish it. When this happens, muscle cells get stuck contracted, and they keep trying to contract, competing for ATP in this depleted state. This is one of the ways a muscle cramp occurs.
This rambling brought to you by brain inputs triggered by talking to Khai about his AP biology test today, and how excited he is about all of the machinery inside of cells.