5.2Chapter 5: Respiration and the Respiratory System

Aerobic respiration in animals and plants — Alhussan Biology - Stage 8 Revision Notes & Topical Questions

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Lesson summary

Biology 5.2 Aerobic respiration in animals and plants — Alhussan International Academy — Biology (Stages 7–9) notes: Write the equation for aerobic respiration, explain where and why it happens, and compare it with photosynthesis and breathing.Life processes — animals and plants …

Body temperature
Energy needed
Burning sugar
Word equation
Symbol equation
Exothermic

Part 1 of 6Why energy is needed

1Life processes

Life processes animals and plants grow, reproduce, move, excrete, replace worn-out cells and heal damaged tissues.

2Body temperature

Body temperature mammals and birds keep the same body temperature in a hot desert, a temperate woodland or on ice and snow.

3Energy needed

Energy needed all these processes need energy, which comes from food.

4Food

Food plants make their own food and animals eat plants or other animals, and food provides the energy cells need for the chemical reactions of life.

Part 2 of 6Controlled release of energy

Burning sugar

Burning sugar burning sugar in oxygen releases energy in an uncontrolled way, with a flame and hotter surroundings, which is no use to cells.

Cells

Cells they need a controlled way of releasing the energy stored in food so they can use it to grow, move and reproduce.

Aerobic respiration

Aerobic respiration the breakdown of food molecules such as glucose using oxygen,

which releases energy in a controlled way.
- ("aerobic" means using oxygen)
The waste products are carbon dioxide and water.

Part 3 of 6Equation for aerobic respiration

Word equation

Word equation glucose + oxygen → carbon dioxide + water (+ energy).

Symbol equation

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.

Energy

Energy it is not usually included in the equation because it is not a substance, and it is released and not created.

Exothermic

Exothermic energy is released to the surroundings, which is why we feel warm after exercise.

ATP

ATP the energy is used to make ATP, a short-term energy store for muscle contraction, active transport, growth and keeping warm.

Part 4 of 6Where respiration happens

Mitochondria

Mitochondria aerobic respiration takes place in these specialised structures in both animal and plant cells.
Plants respire too, in roots, stems and leaves, day and night.
In daylight photosynthesis produces more oxygen than respiration uses, so plants give out oxygen overall.

Numbers of mitochondria

Numbers of mitochondria cells that use a lot of energy,
- such as muscle cells, liver cells, sperm cells and cells making seeds and fruit, have many mitochondria.
Cells storing fats or oils have very few, because they use very little energy.
Heart muscle has many mitochondria for this reason.

Part 5 of 6Respiration compared with photosynthesis and breathing

Feature	Respiration	Photosynthesis
Reactants	Glucose and oxygen	Carbon dioxide and water
Products	Carbon dioxide and water	Glucose and oxygen
Energy	Released	Absorbed from light
Where	All living cells	Cells with chloroplasts
When	Always	Only in light

Balance

Balance the two processes are almost opposites and together keep oxygen and carbon dioxide in the air in balance.

Breathing

Breathing the movement of air into and out of the lungs, which brings oxygen for respiration and removes the carbon dioxide produced.

Part 6 of 6Evidence and uses of the energy

Evidence

Evidence germinating seeds release heat in a flask, exhaled air turns limewater cloudy and living organisms in a sealed container use up oxygen.

Practical

Practical living peas warm up in a vacuum flask as respiration releases energy, but boiled (dead) peas do not.
Controls are the number and mass of peas, the starting temperature and disinfecting the peas so microbes do not respire.

Uses

Uses muscle contraction, building proteins, active transport, cell division, nerve impulses and keeping a constant body temperature in mammals and birds.

Exercise

Exercise muscles respire faster, so breathing and heart rate increase to deliver more glucose and oxygen.

Key terms

Term	Meaning
Respiration	Chemical reactions in cells that release energy from food.
Aerobic	Using oxygen.
Mitochondrion	The organelle where aerobic respiration mostly takes place.
ATP	A molecule that stores and transfers energy in cells.
Exothermic	A reaction that releases energy to the surroundings.
Glucose	A sugar that is the main fuel for respiration.