B2: topic 2-Life processes

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Aerobic Respiration

Aerobic respiration equation:

glucose+oxygen --> carbon dioxide+water (+energy)

Respiration: A chemical reaction where energy is released through glucose being broken down which happens in all living cells.

Enzymes in cells catalyse:


-Protein Synthesis

-Aerobic Respiration

The energy released by respiration is used to make large molecules from smaller ones.

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Anearobic Respiration

Anearobic respiration equation:

Glucose --> Lactic acid (+energy)

Anearobic respiration does not need oxygen.

It does release energy from glucose, but the amount is much lower. It does happen, but only when there is not enough oxygen for aerobic respiration.

Much less energy is released by anaerobic respiration than by aerobic respiration. The lactic acid that forms causes muscle fatigue and pain.

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Exercise and breathing

During exercise, the muscle cells respire more than they do at rest. This means:

-Oxygen and glucose must be delivered to them more quickly

-Waste carbon dioxide must be removed more quickly

This is achieved through an increase in heart and breathing rate, and the stroke volume (the volume of blood pumped each beat)

Total cardiac output can be measured using this calculation:

Cardiac Output= stroke volume x heart rate

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After effects of exercise

Excess post-exercise oxygen debt (EPOC):

During hard exercise when anaerobic respiration occurs with aerobic respiration, an oxygen debt builds up. This is because Glucose is not completely broken down to form harmless products like water or carbon dioxide; some of its broken down into lactic acid.

This is why we pant after exercise; the extra oxygen helps to break down this lactic acid. The increased heart rate also allows the blood to pump the lactic acid away from the heart to the liver where it is broken down.

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The circulatory system: transport

-Carries glucose, oxygen and carbon dioxide around the body in the blood:

  • Glucose needed for respiration comes from broken down food in the digestive system
  • Oxygen comes from the air we breathe in.
  • Carbon Dioxide is breathed out.


Smallest of the blood vessels, the capillaries are always near cells to supply them ith glucose and oxygen, and take away the waste CO2. This is called diffusion.

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The circulatory system: diffusion.

A movement of particles from an area of higher concentration to an area of lower concentration.

When cells respire they use up oxygen and glucose. so the concentration of this is low. However, they have a high concentration in the blood, so they diffuse from the capillaries into the cells. 

However, when cells respire they produce a lot of carbon dioxide, so they have a high concentration of this in the cells. They have a low concentration in the blood because it diffuses from the cells into the blood.

The bigger the difference in concentration, the faster the rate of diffusion.

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