Complete revision notes for Topic 12 of the CIE IGCSE Biology course: Respiration. Explanations with diagrams for every specification point. These notes are written for candidates taking the Extended paper.
Respiration is a chemical process that involves the breakdown of nutrient molecules
(specifically glucose) in order to release the energy stored within the bonds of these
molecules.
Respiration can take place with oxygen (aerobically) or without oxygen (anaerobically).
Much less energy is released for each glucose molecule broken down anaerobically
compared to the energy released when it is broken down aerobically.
Respiration occurs in all living cells. Most of the chemical reactions in aerobic respiration
take place in the mitochondria.
State the uses of energy in the body of humans: muscle contraction, protein synthesis, cell
division, active transport, growth, the passage of nerve impulses and the maintenance of a
constant body temperature
State that respiration involves the action of enzymes in cells
Respiration is a series of reactions that are controlled by enzymes. You need to be able to
state this in an exam!
12.2 Aerobic respiration
Define aerobic respiration as the chemical reactions in cells that use oxygen to break down
nutrient molecules to release energy
Aerobic respiration requires oxygen and is defined as the chemical reactions in cells that use
oxygen to break down nutrient molecules to release energy.
It is the complete breakdown of glucose to release a relatively large amount of energy for
use in cell processes.
It produces carbon dioxide and water as well as releasing useful cellular energy.
State the word equation for aerobic respiration as glucose + oxygen → carbon dioxide +
water
State the balanced chemical equation for aerobic respiration as
C6H12O6 + 6O2 → 6CO2 + 6H2O
There are usually 3 marks given for the aerobic respiration chemical equation in an exam:
One for getting the correct formula for glucose and oxygen
One for getting the correct formula for carbon dioxide and water
, One for balancing the equation correctly
Investigate the effect of temperature on the rate of respiration of germinating seeds
To investigate the effect of temperature on the rate of respiration of germinating seeds the
respirometer can be set up and the tubes submerged in a series of water baths set at
different temperatures, e.g. 10℃, 15℃, 20℃, 25℃, 30°C
The seeds should be kept in the water bath for 15 minutes before the start of the
experiment to ensure they have acclimated to the temperature
As respiration is an enzyme-controlled reaction, it is unlikely to work faster beyond
around 40℃ as the enzymes will denature
Investigate the uptake of oxygen by respiring organisms, such as arthropods and
germinating seeds
We can investigate aerobic respiration in living organisms by measuring the amount of
oxygen that they take from the air
This is done by measuring the change in volume in an enclosed tube containing the
organisms
However, as they respire the organisms release carbon dioxide, which increases the gas
volume
The carbon dioxide must therefore be removed from the tube using a chemical
like soda lime or sodium hydroxide, otherwise it will make the experiment results
inaccurate
Any small organisms can be used in the apparatus, including seeds or arthropods.
The apparatus (shown below) is known as a respirometer:
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