How much useful energy can a cell get from sugar?

Cells turn energy from glucose into ATP, a molecule they use to do work. Oxygen changes how much ATP many cells can make from each glucose. Let's compare two routes in an on-screen model. Keep breathing normally.

1What "energy from food" really means

Glucose supplies energy; ATP carries it to useful work

You only need two ideas. Watch each one:

Glucose is a starting material

Cells rearrange glucose in a series of chemical reactions. Some of the released energy is captured in ATP. A cell is not a tiny fire.

Oxygen opens a further route

The first steps can make ATP without oxygen. In cells with mitochondria, oxygen lets later reactions capture much more energy from each glucose.

2Two routes through the model

Two ATP, or about thirty ATP per glucose

These are simplified yields per glucose. Real yields vary; we use 30 ATP for the oxygen-supported route so the comparison is easy to count.

Without oxygen

Glucose → 2 ATP

Glycolysis makes 2 ATP per glucose. Making lactate helps this route keep running; lactate still carries energy that other cells can use.

With oxygen

Glucose → about 30 ATP

Glycolysis plus mitochondrial reactions can make about 30–32 ATP per glucose. Complete oxidation produces carbon dioxide and water.

3Your turn — feed the cell some sugar

Count ATP from the route without oxygen

Choose a number of glucose molecules. This model uses the route without oxygen: 2 ATP for each glucose. Watch the count change; these are model totals, not a measurement of your body.

ATP made:
a trickle
a handful
1 GLUCOSE10 GLUCOSE

4Now compare two cells

More glucose, or more ATP per glucose?

Cell A gets 10 glucose molecules and uses the route without oxygen. Cell B gets only 2 glucose molecules and uses the oxygen-supported route. Predict which batch makes more ATP, then run the comparison.

Same counting rules:2 or 30 ATP per glucose

Guess before the batches run

Which batch will make more ATP in this model?