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B6.2B6. Respiration and Gas Exchange

Respiration — Combined Science 0653 - Biology Revision Notes & Topical Questions

5 min read 11 parts Lesson 3 of 8 1 quiz

📚 Combined Science 0653 - Biology Hub / Topical Revision
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Lesson summary

B6.2 Respiration — COMBINED SCIENCE notes: Define respiration, state the uses of energy and describe aerobic respiration and its equation.Respiration = a chemical process that breaks down nutrient molecules, specifically glucose, to release the energy stored in their bonds.Enzyme…

  • Energy is released from glucose
  • Complete breakdown
  • Word equation
  • Balanced equation
  • Photosynthesis link
  • Independent variable

Part 1 of 9What respiration is

What respiration is
Respiration
Respiration a chemical process that breaks down nutrient molecules, specifically glucose, to release the energy stored in their bonds.
Enzymes
  • Enzymes respiration is controlled by enzymes.
Where
  • Where it takes place in all living cells, and most of the aerobic reactions take place in the mitochondria.
Two types
  • Two types respiration can be aerobic, with oxygen, or anaerobic, without oxygen.

Part 2 of 9Energy is released

  • Energy is released from glucose
    • it is never made, produced or created.

Part 3 of 9Uses of energy in humans

  • Muscle contraction
  • Protein synthesis
  • Cell division, to make new cells
  • Growth
  • Active transport across cell membranes
  • Generation of nerve impulses
  • Maintaining a constant internal body temperature

Part 4 of 9Respiration is not breathing

Respiration
  • Respiration a series of chemical reactions that release energy inside cells.
Breathing
  • Breathing the movement of air in and out of the lungs, which supports respiration.

Part 5 of 9Aerobic respiration

Aerobic respiration
Aerobic respiration the chemical reactions in cells that use oxygen to break down nutrient molecules and release energy.
Complete breakdown
  • Complete breakdown glucose is broken down completely, so a relatively large amount of energy is released.
Products
  • Products carbon dioxide and water, as well as useful cellular energy.

Part 6 of 9Equations for aerobic respiration

Word equation
  • Word equation glucose + oxygen → carbon dioxide + water.
Balanced equation
  • C6H12O6 + 6O2 → 6CO2 + 6H2O.
Photosynthesis link
  • Photosynthesis link the equation is the reverse of the photosynthesis equation.

Part 7 of 9Journey of glucose and oxygen

1
Food is digested into glucose.
2
Blood carries glucose and oxygen to the cells.
3
Mitochondria use them in aerobic respiration, releasing energy.
4
Carbon dioxide travels in the blood back to the lungs.
5
It is breathed out.

Part 8 of 9Investigating temperature and respiration in yeast

Indicator
  • Indicator methylene blue does not damage living yeast, and it loses its blue colour as the yeast uses up oxygen.
Rate
  • Rate the faster the dye turns colourless, the faster the respiration.
Independent variable
  • Independent variable temperature, set with water baths.
Dependent variable
  • Dependent variable the time taken for the dye to change from blue to colourless.
Controlled variables
  • Controlled variables volume and concentration of the dye, the yeast suspension and the glucose, and pH using a buffer solution.
Results below 40 °C
  • Results below 40 °C the rate rises because molecules have more kinetic energy and enzymes and substrates collide more often.
Results above 40 °C
  • Results above 40 °C the rate falls because the enzymes denature.

Part 9 of 9More from the specification

More from the specification
Chemical Nature of Cellular Respiration
  • Respiration is an enzyme-mediated catabolic process occurring inside living cells that releases chemical energy from nutrient molecules like glucose to synthesize ATP.
Anaerobic Respiration in Mammalian Muscle
  • Under severe oxygen deficits, muscles respire anaerobically via: Glucose → Lactic Acid, yielding limited ATP and triggering muscle fatigue due to localized intracellular acidification.
Repaying the Oxygen Debt Post-Exercise
  • Continued rapid breathing and elevated heart rate after vigorous exercise transport accumulated lactic acid to the liver,
    • where aerobic oxidation converts it back into glucose.

Key terms

TermMeaning
RespirationChemical reactions in cells that release energy from nutrient molecules.
Aerobic respirationRespiration that uses oxygen.
MitochondrionThe organelle where most aerobic respiration takes place.
GlucoseThe sugar broken down in respiration.
Independent variableThe variable that is changed on purpose.
Dependent variableThe variable that is measured.
Methylene blueA dye that loses its colour as yeast uses oxygen.

Avoid these mistakes

1
Saying respiration is breathing — respiration releases energy in cells.
2
Saying energy is made or produced in respiration — it is released.
3
Forgetting that respiration is enzyme-controlled — extreme temperature or pH slows it.
4
Saying only animals respire — all living cells respire, including plants.

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