Biology · Lesson 10

Respiration ≠ breathing

JAMBWAECNECO

What the syllabus asks

JAMB: respiration (aerobic, anaerobic), respiratory organs and surfaces, mechanism of gaseous exchange, energy and ATP

WAEC: respiration — definition, aerobic and anaerobic respiration, energy release and ATP, fermentation and its uses, oxygen debt, respiratory quotient, experiments on respiration, respiratory surfaces and their characteristics, gaseous exchange in Amoeba, insects, fish, amphibians, mammals and plants, mechanism of breathing in mammals, lung volumes, composition of inhaled and exhaled air, respiratory…

NECO: respiration — definition, aerobic and anaerobic respiration, energy release and ATP, fermentation and its uses, oxygen debt, respiratory quotient, experiments on respiration, respiratory surfaces and their characteristics, gaseous exchange in Amoeba, insects, fish, amphibians, mammals and plants, mechanism of breathing in mammals, lung volumes, composition of inhaled and exhaled air, respiratory…

What you will learn

Distinguish respiration from breathing and explain the role of ATP.
Write equations for aerobic and anaerobic respiration and compare their energy yields.
Describe the stages of aerobic respiration in outline.
Explain oxygen debt and the industrial uses of fermentation.
Calculate and interpret respiratory quotients and describe experiments on respiration.
State the features of respiratory surfaces and describe gas exchange in Amoeba, insects, fish, frogs and plants.
Describe the human respiratory system, the mechanism of breathing and lung volumes, and common respiratory diseases.

Key points

Respiration is the release of energy from food in every living cell; breathing only ventilates the lungs.
Energy is stored as ATP; ATP → ADP + P releases energy for movement, growth, active transport, nerves and warmth.
Aerobic: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 2880 kJ (38 ATP); glycolysis (cytoplasm), Krebs cycle (matrix), electron chain (cristae).
Anaerobic in muscle: glucose → lactic acid (2 ATP), causing fatigue and oxygen debt.
Yeast fermentation: glucose → ethanol + CO₂ (2 ATP); used in baking, brewing, yoghurt, garri, biogas.
RQ = CO₂/O₂: carbohydrate 1.0, protein 0.9, fat 0.7; > 1 shows anaerobic respiration.
Experiments: limewater/hydrogencarbonate for CO₂, respirometer with soda lime for O₂, vacuum flasks for heat — all with controls.
Respiratory surfaces: large, thin, moist, well supplied with blood, ventilated; small organisms use the body surface.
Insects: spiracles, tracheae, tracheoles; fish: gills with lamellae and counter-current flow; toads: skin, mouth, lungs.
Humans: nose, trachea (cartilage, cilia), bronchi, bronchioles, alveoli (thin, moist, capillaries).
Inhalation: external intercostals and diaphragm contract, thorax volume up, pressure down; tidal volume 500 cm³; exhaled air 16% O₂, 4% CO₂.
Plants exchange gases through stomata, lenticels and root hairs; smoking, TB, asthma and CO poisoning harm breathing.

Start here: What respiration really is

A footballer sprinting at the Moshood Abiola Stadium, a seed germinating in moist soil, a bacterium in yoghurt and a mango tree standing still: all of them are respiring every second of their lives. Ask most people what respiration is and they will say "breathing". In Biology this is wrong, and WAEC deliberately sets traps on it.

Respiration is the chemical breakdown (oxidation) of food substances, mainly glucose, inside living cells to release energy. It is carried out by every living cell, day and night.

Breathing (ventilation) is the physical process of moving air into and out of the lungs (or water over gills). It supplies the oxygen and removes the carbon dioxide.

Respiration	Breathing
Chemical process	Physical (mechanical) process
Occurs in all living cells	Occurs in lungs/gills of certain animals
Releases energy	Uses energy (muscle contraction)
Controlled by enzymes	Controlled by muscles and nerves
Occurs in plants, animals, microbes	Plants do not breathe

Why cells need energy

Muscle contraction (movement, heartbeat, breathing).
Building large molecules: proteins for growth, glycogen, fats.
Active transport of substances across membranes (e.g. glucose in the ileum, mineral ions into root hairs).
Transmitting nerve impulses.
Cell division.
Keeping a constant body temperature in mammals and birds.

Worked example 10.1

A student says, "Plants respire only at night because they photosynthesise in the day." Correct this statement.

Respiration happens in every living cell all the time, because cells always need energy.
In bright light, plants respire and photosynthesise together; photosynthesis is faster, so it hides the respiration.

Plants respire day and night

⚠️ Common mistake: writing "respiration is the intake of oxygen and removal of carbon dioxide". That is gas exchange, not respiration.

Try it yourself. Name the organelle where most of the energy from respiration is released.

Show solution

The mitochondrion.

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Practice questions

1. The end products of aerobic respiration are

carbon dioxide, water and energy
ethanol and carbon dioxide
lactic acid and energy
oxygen and glucose

Show answer

A: carbon dioxide, water and energy
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.

2. Yeast respiring anaerobically produces

lactic acid
oxygen and water
glucose
ethanol and carbon dioxide

Show answer

D: ethanol and carbon dioxide
Alcoholic fermentation — used in brewing and baking.

3. Glycolysis takes place in the

nucleus
ribosome
cytoplasm
mitochondrion

Show answer

C: cytoplasm
Glycolysis (glucose → pyruvate) occurs in the cytoplasm; the Krebs cycle is in the mitochondria.

4. The products of aerobic respiration are

ethanol and CO₂
carbon(IV) oxide, water and energy
oxygen and glucose
lactic acid and energy

Show answer

B: carbon(IV) oxide, water and energy
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.

5. Anaerobic respiration in muscles produces

lactic acid
ethanol
oxygen
starch

Show answer

A: lactic acid
Lactic acid builds up during strenuous exercise.

Key words

Respiration: The breakdown of food substances in living cells to release energy.
Breathing: The muscular movements that move air into and out of the lungs.
ATP: Adenosine triphosphate, the energy carrier molecule of cells.
Aerobic respiration: Respiration that uses oxygen and releases a large amount of energy.
Anaerobic respiration: Respiration without oxygen, releasing a small amount of energy.
Fermentation: Anaerobic respiration in yeast and some bacteria producing ethanol or lactic acid.
Oxygen debt: The extra oxygen needed after exercise to remove lactic acid.
Glycolysis: The first stage of respiration, in the cytoplasm, splitting glucose into two pyruvate molecules.
Krebs cycle: A cycle of reactions in the mitochondrial matrix releasing CO₂ and hydrogen.
Respiratory quotient (RQ): Volume of CO₂ produced ÷ volume of O₂ consumed.
Respiratory surface: A surface across which gases are exchanged between an organism and its environment.
Alveolus: A tiny air sac in the lung where gas exchange occurs.

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