B9 Respiration

  • Created by: msahay
  • Created on: 21-08-17 12:25

B9.1 Aerobic respiration

Aerobic respiration

  • Called aerobic because it involes oxygen
  • Glucose reacts with oxygen that transfers energy for body cell usage
  • C02 and water are waste products
  • Exothermic reaction - heats up surroundings 
  • Takes place in the mitochondria
  • Glucose + Oxygen ---> C02 + Water + Energy transferred to surroundings

Mitochondria = organelle in cell. Has large surface area for enzymes involved in aerobic respiration

Need for respiration

  • Energy from respiration used in building large molecules and cell material
  • Energy from respiration used in breaking down molecules e.g. in digestion
  • Energy from respiration used in muscle contraction e.g. heartbeat, digestion, breathing
  • Energy from respiration used for maintaining constant body temperature
  • Plants = active transport of mineral ions from soil to root hair cells.
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B9.2 The response to excercise


  • Made of protein fibres that contract when energy is transferred from respiration
  • Many mitochondria = carry out aerobic respiration to provide energy for contraction
  • Muscles store glucose as glycogen which can be rapidly converted to glucose when energy is needed for exercise, when muscles have to contract

Glucose + Oxygen ---> C02 + Water + Energy transferred to the surroundings

Body's response to excercise 

During exercise:

  • muscles contract harder and faster
  • muscles need more glucose and oxygen to use in respiration for energy
  • muscles produce increased amounts of C02 which needs to be removed fast
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B9.2 The response to excercise 2

The changes taking place in the body during exercise 

  • Increased heart rate
  • Arteries carrying blood widen ---> increased flow of oxygenated blood to muscles ---> increased rate of oxygen and glucose for respiration ---> increased rate that C02 is removed
  • Increased breathing rate and depth of breathing ---> breathe more often and more air breathed ---> increased rate of oxygen to muscles ---> more C02 breathed out
  • Glycogen stored in muscles converted back to glucose for increased cellular respiration

Summary of body response to excercise 

  • an increase in the heart rate, in the breathing rate and in the breath volume
  • glycogen stores in muscles are converted to glucose for cellular respiration
  • the flow of oxygenated blood to the muscles increases.
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B9.3 Anaerobic respiration

Anaerobic respiration

  • Hardworking muscles for long duration = not enough oxygen ---> respire anaerobically (without oxygen)
  • Not as effective - glucose molecules are not broken down completely ---> less energy transferred
  • Equation - Glucose ---> Lactic acid + Energy transferred to the environment

Muscles can become fatigued and not contract efficiently because of the build-up of lactic acid, produced by cells in anaerobic respiration. Causes oxygen debt.

Oxygen Debt

  • The build-up of lactic acid has to be broken down to produce C02 and water using oxygen
  • Amount of oxygen needed to break down lactic acid = oxygen debt 

Heart rate and breathing rate stay high after exercise to supply body with extra oxygen needed to pay off oxygen debt. 

Equation = Lactic acid + Oxygen ---> C02 and Water 

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B9.3 Anaerobic respiration 2

Anaerobic respiration in plants 

Glucose ---> Ethanol + C02 + Energy transferred to the environment 

Yeast cells respire anaerobically to produce ethanol and C02 - known as fermentation - used in the manufacture of bread and alcoholic drinks

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B9.4 Metabolism and the liver

Metabolism = sum of all reactions taking place in a cell or body.

The energy that is transferred during respiration is used for enzyme-controlled reactions like the making of new molecules

Metabolic reactions

  • Conversion of glucose to starch, glycogen and cellulose
  • Formation of lipid molecules from glycerol and fatty acids
  • Use of glucose and nitrate ions to form amino acids to make proteins
  • Breakdown of excess proteins to form urea


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B9.4 Metabolism and the liver 2

The Liver

1. Lactic acid transported to liver. 

2. Liver converts lactic acid back to glucose 

3. Oxygen debt paid off = lactic acid converted to glucose + glucose broken down in aerobic respiration to form C02 and water

Oxygen debt not paid off = lactic acid converted to glycogen and stored

Summary : Blood flowing through the muscles transports lactic acid to the liver where it is converted back to glucose

Other uses of the liver 

  • Detoxifying substances like ethanol from alcoholic drinks
  • Passing breakdown products into the blood so they can be excreted in the urine via kidneys
  • Breaking down old cells and storing the iron to make more cells
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