BIOLOGY · Stage 8 · Chapter 5: Respiration and the Respiratory System
Biology 5.2 Aerobic respiration in animals and plants — Alhussan International Academy - Biology (Stages 7-9) 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
Section 1 of 6Why energy is needed
- Life processes
- animals and plants grow, reproduce, move, excrete, replace worn-out cells and heal damaged tissues.
- Body temperature
- mammals and birds keep the same body temperature in a hot desert, a temperate woodland or on ice and snow.
- Energy needed
- all these processes need energy, which comes from food.
- 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.
Section 2 of 6Controlled release of energy
- 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
- they need a controlled way of releasing the energy stored in food so they can use it to grow, move and reproduce.
- 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.
- which releases energy in a controlled way.
Section 3 of 6Equation for aerobic respiration
- Word equation
- glucose + oxygen → carbon dioxide + water (+ energy).
- Symbol equation
- C6H12O6 + 6O2 → 6CO2 + 6H2O.
- Energy
- it is not usually included in the equation because it is not a substance, and it is released and not created.
- Exothermic
- energy is released to the surroundings, which is why we feel warm after exercise.
- ATP
- the energy is used to make ATP, a short-term energy store for muscle contraction, active transport, growth and keeping warm.
Section 4 of 6Where respiration happens
1Mitochondria3 points
- 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.
2Numbers of mitochondria3 points
- 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.
Section 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
- the two processes are almost opposites and together keep oxygen and carbon dioxide in the air in balance.
- Breathing
- the movement of air into and out of the lungs, which brings oxygen for respiration and removes the carbon dioxide produced.
Section 6 of 6Evidence and uses of the energy
- Evidence
- germinating seeds release heat in a flask, exhaled air turns limewater cloudy and living organisms in a sealed container use up oxygen.
- 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
- muscle contraction, building proteins, active transport, cell division, nerve impulses and keeping a constant body temperature in mammals and birds.
- Exercise
- muscles respire faster, so breathing and heart rate increase to deliver more glucose and oxygen.
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