4.2 Respiration

4.2.1 Aerobic and anaerobic respiration

FSL: GCSE Biology Revision "Respiration"

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- Cellular respiration is an exothermic reaction which is continuously occurring in living cells.
- The energy transferred supplies all the energy needed for living processes.
- Respiration in cells can take place aerobically (using oxygen) or anaerobically (without oxygen), to transfer energy.
- Organisms need energy for:

• Chemical reactions to build larger molecules (ex. amino acids building proteins, glucosde building glycogen, in animals and plants)
• Movement (ex. skeletal muscle contration in animals)
• Keeping warm (ex. mammals and birds [warm-blooded])
• Plants taking up mineral ions (ex. active transport, nirated for amino acids, magnesium to make cholophyll)

Respiration equation

C6H12O6 + 6O2 → C6H12O6 + 6H2O + energy
- Energy is released, not produced.

Mitochondria

- Mitochondria are found in almost all plant, animal, fungal, and algal cells.
- Folded inner membrane provides a large surface area for the enzumes involved in aerobic respiration.

Exam question

Explain why aeroic respiration is an exothermic reaction, whereas photosynthesis is not. [4 marks]
Aerobic respiration is an exothermic reaction because:

• aerobic respiration transfers energy to the environment
• photosythesis takes in energy from the environment
• exothermic reaction products have less energy than reactants
• endothermic reaction products have more energy than reactants

4.2.2 Response to Exercise

GCSE Biology Revision "Exercise"

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- During exercise the human body reacts to the increased demand for energy.
- Glucose is stored as insoluble glycogen stored in the muscles and the liver.
- Glycogen is broken down into glucose, used as a rapid energy source, to release energy during aerobic respiration.
- The heart rate, breathing rate and breath volume increase during exercise to supply the muscles with more oxygenated blood.
- Your skin goes red because the body attemps to radiate excess heat into the air, so blood is diverted to the surface.
- If there is not as much oxygen, than anaerobic respiration will occur in muscles.
- The incomplete oxidation of glucose causes a build up of lactic acid and creates an oxygen debt.
- During long, vigorous periods of activity muscles get fatigued and stop contracting efficiently.
- Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose.
- Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.

4.2.3 Metabolism (and the Liver)

GCSE Biology Revision "Metabolism"

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- Metabolism is the sum of all the reactions in a cell or the body.
- The energy transferred by respiration in cells is used by the organism, for the enzyme controlled processes in metabolism that synthesise new molecules.
- Examples of photosynthesis include:

• Converting glucose to starch, glycogen, and cellulose
• Forming lipids (1 glycerol and 3 fatty acids)
• Glucose and nitrate ions form amino acids
• Respiration/photosynthesis
• Deamination (breakdown of excess proteins/amino acids to form urea for excretion)

Deamination

1. Excess amino acids are transported via blood to the liver.
2. Amine group is removed creating ammonia (toxic).
3. Ammonia is converted into urea.
4. Urea is filtered by the kidneys forming urine (excess water and salts).
5. Then excreted through urethra.

Role of the Liver: Break down of Lactic Acid

1. Blood flowing through the muscles transports the lactic acidd to the liver.
2. Oxidised into carbon dioxide and water OR (but less common): converted back to glucose.
3. The glucose is either used in respiration or stored as glycogen in muscles.

Example Exam Question

Compare and contrast aerobic and anaerobic respiration in humans [6 marks]

- Aerobic respiration releases carbon dioxide and water, while anaerobic respiration releases lactic acid.
- Aerobic respiration releases seven times as much energy per glucose molecule than anaerobic respiration (and is therefore more efficient).
- Aerobic respiration happens in mitochondria, anaerobic happens in the cytoplasm.
- Lactic acid needs to be broken down in the liver in anaerobic respiration.
- Oxygen is required to pay back the oxygen debt in anaerobic respiration.
- Both release energy and require glucose as a reactant.

Other roles of the liver

- Breaking down old worn blood cells.
- Detoxification - breakdown of ethanol (alcohol).
- Storing the iron until it is neeed to synthesis more blood cells.