5.3Chapter 5: Respiration and the Respiratory System

Anaerobic respiration — Alhussan Biology - Stage 8 Revision Notes & Topical Questions

5 min read 6 parts Lesson 3 of 12 2 quizzes

📚 Alhussan Biology - Stage 8 Hub / Topical Revision

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Lesson summary

Biology 5.3 Anaerobic respiration — Lactic Acid and Fermentation — Alhussan International Academy — Biology (Stages 7–9) notes: Describe anaerobic respiration in muscles and yeast, write the equations and explain how lactic acid and oxygen debt are linked.Anaerobic respiration = …

Aerobic summary
When it happens
After exercise
Graph of oxygen uptake
Use of lactic acid
Anaerobic respiration = respiration without oxygen ("anaerobic" means without oxygen)

Part 1 of 4Respiration without oxygen

Anaerobic respiration

Anaerobic respiration respiration without oxygen ("anaerobic" means without oxygen).

Aerobic summary

Aerobic summary most of the time muscles receive the glucose and oxygen they need, and glucose + oxygen → carbon dioxide + water (+ energy).

When it happens

When it happens when oxygen is too scarce, such as in muscles during intense exercise, because muscles can store fuel but cannot store oxygen.
A 100 m sprinter may not take a breath during the race, yet the muscles keep working using anaerobic respiration.

Part 2 of 4Anaerobic respiration in animals

Equation

Equation glucose → lactic acid (+ energy).
No carbon dioxide or water is made.

Energy

Energy the glucose is not completely broken down,
so much less energy is released per molecule than in aerobic respiration.
- (about 2 ATP instead of about 30 or more)
Each muscle cell uses many glucose molecules, so even a small amount of energy per molecule keeps it working.

Speed

Speed anaerobic respiration provides energy quickly, a burst for sprinting or escaping danger.
It cannot be used for long.

Feature	Aerobic respiration	Anaerobic respiration
Oxygen	Needed	Not needed
Energy per glucose	A lot	Less
Speed of energy release	Slower	Quicker
Waste product	Carbon dioxide and water	Lactic acid (in muscles)

Part 3 of 4Lactic acid and oxygen debt

Lactic acid

Lactic acid the waste product of anaerobic respiration, which is toxic when it builds up and causes muscle fatigue and sometimes cramp.

After exercise

After exercise breathing stays fast because the extra oxygen taken in breaks down the lactic acid in the muscles and liver into carbon dioxide and water.
This is the oxygen debt, and once it is repaid, breathing and heart rate return to normal.

Graph of oxygen uptake

Graph of oxygen uptake it rises during exercise, stays high in recovery while lactic acid is removed, and falls to the resting level.

Use of lactic acid

Use of lactic acid it can be changed back to glucose in the liver or used for energy when oxygen is available.

Athletes

Athletes a sprinter relies heavily on anaerobic respiration and builds a large oxygen debt,
whereas a marathon runner works mostly aerobically at a steady pace.
Training gives a bigger heart, more capillaries and mitochondria in muscles and bigger lung volume, so anaerobic respiration is needed later.

Part 4 of 4Anaerobic respiration in yeast and plants

Fermentation

Fermentation yeast and some plant tissues,
- such as roots in waterlogged soil, produce ethanol and carbon dioxide: glucose → ethanol + carbon dioxide (+ energy).

Uses

Uses bakers use the carbon dioxide to raise dough, and brewers use the ethanol to make beer and wine.

Feature	Aerobic	Anaerobic (animals)	Anaerobic (yeast)
Oxygen needed	Yes	No	No
Products	Carbon dioxide and water	Lactic acid	Ethanol and carbon dioxide
Energy released	Large	Small	Small

Key terms

Term	Meaning
Anaerobic respiration	Respiration without oxygen.
Lactic acid	The product of anaerobic respiration in muscles.
Fermentation	Anaerobic respiration in yeast giving ethanol and carbon dioxide.
Oxygen debt	The extra oxygen needed after exercise to break down lactic acid.
Fatigue	Tiredness of muscles from lactic acid build-up.
Ethanol	The alcohol produced by yeast fermentation.