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IGCSE: Biology - Human Respiration
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IGCSE: Biology - Human Respiration Triple award content course summary
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RESPIRATIONRespiration is the transfer of energy from glucose. It happens in every cell. Energy transferred by
respiration is used to make Adenosine triphosphate (ATP). ATP stores the energy, when it is needed it is
broken down to Adenosine diphosphate (ADP) and energy is released.
Aerobic respiration happens in mitochondria:
Glucose + Oxygen → Carbon dioxide + water
C6H12O6 + 6O2 → 6CO2 + 6H2O
Anaerobic respiration (without oxygen) Happens in cytoplasm:
Plants + Yeast : Glucose → Ethanol + Carbon dioxide
Animals: Glucose → Lactic acid
Why is aerobic respiration not good? Anaerobic respiration produces lactic acid, which causes low cell
pH this results in enzymes denaturing and eventually cell death.
Glucose comes from food. Starch is broken down by amylase enzymes to glucose, then absorbed
through sintes to blood then transported to cells.
Oxygen comes from air. When we breathe in it diffuses into blood through alveoli to be transported by
red blood cells.
Carbon dioxide is an excretory product of respiration. Diffuses out of blood through alveoli and released
when we breathe out.
PRACTICAL: Investigating the production of carbon dioxide by small living organisms.
Method:
Fill a boiling tube with a small amount of hydrogen carbonate
indicator.
Place a small gauze above the indicator, and place small
organisms on top of the gauze.
Stopper the boiling tube.
Observe the colour change of the hydrogen carbonate indicator,
from orange to yellow.
Measuring breathing rate: 1 minute. Control time and intensity
of exercise.
During exercise breathing rate increases, muscles contract more so it needs more energy and Oxygen.
CO2 is removed. During exercise the heart rate increases. The heart pumps more so more blood goes to
the muscle cells to give O2 and glucose.
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