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Co-ordination and control.
Hormones are chemical messengers which travel in the blood to activate target cells.

The nervous system uses electric impulses to enable you to react to your surroundings
and co-ordinate what you do. A stimulus is a change in your environment which you may need
to react to.…

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Each month the lining of the womb thickens ready to support a developing baby. At the
same times an egg starts maturing in the ovary.
Ovulation is when the egg is released from the ovary (14 day)
I f the egg is not fertilised, the lining of the womb and…

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5) The eggs are checked to make sure they have been fertilised and the early embryos
are developed properly
6) The embryos are then placed in the uterus of the mother.



Homeostasis

Humans need to maintain a constant internal environment, controlling levels of
water, ions, blood, sugar and blood.

Ion…

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You need energy to fuel the chemical reactions in the body that keep you alive. These
reactions are called your metabolism, and the speed at which they occur is your
metabolic rate. Muscle needs more energy than fatty tissue, which means people with
higher proportion of muscle to fat in…

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Drugs

A drug is a substance that alters the way in which you body works. Drugs change the
chemical processes in your body, so you become addicted to them. Recreational drug is
a drug used non-medically for personal enjoyment .

What is an addiction?
Some drugs change the chemical processes…

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damaged, it's harder for your body to eject stuff that shouldn't be there, which makes chest
infections more likely.
Nicotine gums or patches are given to help stop smoking. This gradually reduced the dose
of the nicotine that the body is craving for.


Pathogens

Infectious diseases are cause by microorganisms.…

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Some medicines relieve the symptoms of disease but do not kill the pathogens:
Antibiotics cure bacterial diseases by killing the bacteria
Antibodies can't destroy viruses, because they reproduce rapidly using your own body cells.

Changing Pathogens

In the 1940s Antibiotics treated killer diseases.
Unfortunately they were over used and the…

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Vaccination
You can be immunised against a disease by injecting a small amount of dead pathogens.
They carry antigens, which cause your body to produce antibodies. Then your body will
respond rapidly to future infection by the same pathogens by making the correct antibody.
You become immune to the disease.…

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the ability to go for a long time without water - they don't store water in their humps, but
they lose very little through urination and sweating
the ability to tolerate body temperatures up to 42ºC
slit-like nostrils and two rows of eyelashes to help keep the sand out

Desert…

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Reproduction

Sexual reproduction:
2 parents are needed
Offspring will have "pairs" of chromosomes
This will cause genetic variation

Asexual reproduction:
Only 1 parent needed (no gametes)
Off springs are genetically identical to parent ("clones")

An alternative form of genes is called alleles.
For example, there are genes which decided whether:…

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