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Biology Revision
Classification:

Classification is organising living organisms into groups
Biologists classify organisms into groups based on how closely related they are to one
another
They are divided into 5 kingdoms: plants, animals, fungi, protocists and prokaryotes.
Plants make their food by photosynthesis. This is because they contain chlorophyll and…

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Variation is differences within a species. There are two causes of variation; genes and
the environment.
All plants and animals have characteristics, meaning that in some way they are all
similar to their parents.
The characteristics are determined by the genes inherited from their parents
The combining of genes from…

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Before scientists can publish their work it has to undergo peer review. This is when
other scientists read and review the work, to check it's valid and that experiments are
carried out to the highest possible standard.


Speciation and Genes:

Speciation is the development of a New Species
Speciation occurs…

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Sickle cell anaemia is also caused by a recessive allele. This is a genetic disorder
characterised by funny-shaped red blood cells.
The red blood cells can get stuck in the capillaries, which deprive the body cells of
oxygen. Symptoms include tiredness, painful joints and muscles, fever and anaemia.

Homeostasis:

Homeostasis…

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The affected cells are called target cells. They have right receptors to respond to that
hormone- target organ.
Hormones travel at same speed as blood and have long lasting effects.

Neurones transmit information around the body
Neurones-the nerve cells- transmit information as electrical impulses.
They have branched endings called dendrons-…

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Relay neurones are many short dendrons and axons carry nerve impulses from sensory
neurones to motor neurons.
Sensory neurones are long dendrons and short axons carry nerve impulses from the
receptors in the sense organs to the CNS.

Reflexes are an automatic response to certain stimuli- they can reduce the…

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Phototropism- the growth of a plant in response to light. Shoots grow towards the
light.
Gravitropism (geotropism) - the growth of a plant in response to gravity. Roots grow
downwards
Auxin is the plant hormone that controls growth at the tip of shoots and roots.
It is produced in the…

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Drugs have a big effect on what happens in your body.
Drugs can be beneficial or harmful.
Most drugs are chemical substances and affect the central nervous system
Tolerance develops when taking drugs so the body gets used to having it therefore you
have to have a higher dose to…

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The eyes- they produce a chemical called lysozyme which kills bacteria on the surface
of the eye.
The stomach- It kills of pathogens which you may eat in food. Killed by hydrochloric
acid in stomach.

Bacteria can mutate meaning that mutations cause them to become resistant to an
antibiotic. If…

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Fertilisers which contain nitrates are essential to modern farming. Without the nitrates
wouldn't grow as well. This is because crops take nitrates out of the soil and these
nitrates need to be replaced.
Some of the fertiliser finds its way into rivers, lakes and seas. This can easily happen if…

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