GCSE Biology Edexcel B2 Topic 2

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B2 Topic 2 Organisms and Energy
Respiration: this is the process used by all living organisms to release energy from organic molecules. This
energy is used for:
o Building up larger molecules like proteins
o contract muscles (exercise)
o maintain a steady body temperature
Respiration is the process of breaking down glucose to release energy which goes on in every living cell.
Aerobic respiration
During aerobic respiration, oxygen is used to release energy from molecules such as glucose. The word
equation is:
o glucose + oxygen carbon dioxide + water + (energy)
Delivering oxygen and glucose and removing waste gases
In humans, oxygen and glucose needed for respiration are carried around the body and into tissues by the
bloodstream. The blood must also carry the waste carbon dioxide from respiring cells.
All these substances move between respiring cells and tiny blood vessels called capillaries by a process
called diffusion.
Diffusion: The movement of particles from an area of higher concentration to an area of lower concentration.
In respiring cells, oxygen and glucose levels fall as they are used up in aerobic respiration. At the same time,
carbon dioxide levels in the cells rise. As a result, the carbon dioxide diffuses out of the cells and into the
capillaries and oxygen and glucose diffuse out of the capillaries and into the cells.
Gas exchange
Lung tissue is spongy and full of tiny air sacs called alveoli. These are surrounded by capillaries and oxygen
that enters the body
through the lungs moves into
the blood by diffusion.
Carbon dioxide also
leaves the blood by
diffusion into the air
spaces. As one gas is
entering the bloodstream,
another one is leaving it and
thus it is called gas

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Anaerobic respiration
As you work harder your need for energy increases and thus you respire more. During exercise, muscles use
up oxygen and glucose very quickly so the blood supply to the muscles must increase (as that carries glucose
and oxygen).
The amount of blood circulated by the heart depends on heart rate and stroke volume. If we multiply heart
rate by stroke volume we get the cardiac output.
The cardiac output is the volume of blood circulated by the heart in a given time.…read more

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The cuticle protects the leaf with its wax but it doesn't block out sunlight.
Limiting factors
Many factors affect the rate of photosynthesis: the concentration of carbon dioxide, light intensity,
temperature and water availability.
The rate of reaction varies, dependent upon the conditions. These conditions are known as limiting factors.
Limiting factors limit the rate at which a reaction can take place.
Limiting factor: These stop a reaction from occurring any faster.…read more

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Root hair cells are found on the surface of plant roots. They have millions of long thin extensions which reach
into the surrounding soil to get all the mineral salts and water possible.
They take in water by osmosis. This gives the plant a big surface area for absorbing water from the soil.
However, they take in minerals by active transport, which is the movement of particles against the
concentration gradient.…read more

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This is used to catch small invertebrates through an inlet tube by sucking sharply on a second tube connected
to the container.
Sweep net
This is used for catching insects in long grass. It is a net lined with strong cloth.
It should be quickly swept through the grass and the insects collected should be put into a container.
Pond net
This is a net used for catching insects, water snails etc. from ponds.…read more


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