Anaerobic respiration and oxygen debt

Last time

Before we start: last time, in Respiration, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Running out of oxygen

In a hundred-metre sprint, your muscles need energy faster than your blood can bring oxygen. So they switch to respiring without oxygen. Yeast does the same in bread dough. Today: anaerobic respiration in muscles and in yeast, and the oxygen debt.

Anaerobic respiration

Anaerobic respiration is the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen. It releases much less energy per glucose molecule than aerobic respiration. Because the glucose is only partly broken down.

In muscles

In human muscles. Glucose gives lactic acid. No carbon dioxide, and no water, are made.

In yeast

In yeast. Glucose gives alcohol, which is ethanol, plus carbon dioxide. The balanced equation: C six H twelve O six gives two C two H five O H plus two C O two.

Using yeast

In bread making, the carbon dioxide from yeast makes the dough rise. The alcohol evaporates when the bread is baked. In making biofuel and drinks, the alcohol is the product that is wanted.

Aerobic or anaerobic?

Here is the comparison. Oxygen, products, and how much energy. Aerobic releases far more energy from each glucose molecule.

Oxygen debt

During hard exercise, lactic acid builds up in the muscles and the blood. The oxygen debt is the extra oxygen needed after exercise to remove it. The blood carries lactic acid to the liver, where it is broken down by aerobic respiration.

Why you keep panting

After exercise, you keep breathing fast and deep, and the heart rate stays high. This supplies the extra oxygen to the liver to remove the lactic acid. Lactic acid can cause muscle fatigue and cramp.