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Nervous and Chemical Co-ordination
Nervous Chemical

Nature of Message Electrochemical impulse Hormones

Route of Transmission Specific Nerve Cells General blood system

Type of effects Rapid but short term Usually slower but generally
longer lasting

The Nervous System
Follows a similar pattern of response to the endocrine system:
Stimulus ­ Receptor…

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Neurones may only form one synapse
with another neurone, but relay neurones in the brain will have thousand of synaptic
connections. Some neurones may influence or be influenced by others. Therefore synapses
are very important for integrating information in the CNS. Other chemicals in the body often
affect neurotransmitters. Alcohol…

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The pituitary gland is located at the base of the brain just below part of the brain called the
HYPOTHALAMUS. The pituitary gland secretes a number of chemical messengers called
hormones into the blood.

The Eye

The sense organs are specialised receptor cells grouped together to perform a specific

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Aqueous and Vitreous Humour ­ this is a jelly like, translucent liquid that helps
maintain the shape of the eye.
Suspensory Ligament ­ ring of strong fibres supporting the lens.
Ciliary Muscle ­ pulls on ligament to change the shape of the lens
Ciliary Body ­ Thick edge of the…

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Visual Defects:

Both natural and artificial
selection can only arise because organisms are different from one another.

Genetic Variation:
Much of this is due to genes:
Many different alleles or different version of the same gene exist
Genes can also mutate
The way that homologous chromosomes line up at…

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Genetic Code:
DNA molecules carry a code that tells cells how to make proteins. The code is carried as a
sequence of base pairs and controls the order in which amino acids are put together to form
new proteins. Groups of three base pairs form CODONS that code for…

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3. The new nucleotides are joined together by the enzyme: DNA polymerase
4. The two new identical daughter strands are formed containing one parent strand and
one new polynucleotide strand
DNA replication has to occur before a cell can divide either by mitosis or meiosis. It means
that until cell…

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Diseases include:
Cystic Fibrosis
Huntington's chorea
Hemophilia ­ this is an inherited sex-linked disease and only men can have it because the
gene is only found on the Y chromosome

Patterns of Inheritance
Genetic Cross Diagram:

This diagram works with dominant
and recessive alleles

Codominance: Sometimes both alleles have…

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Cell Division:

Characteristic Meiosis Mitosis

Role in Living Things Sexual Reproduction Growth and Repair, Asexual

Number of Chromosomes in 46 46
Parent Cells

Number of Chromosomes in 23 46
Daughter Cells

Number of Daughter Cells 4 2

Described as... HAPLOID DIPLOID

Daughter Cells are... Sperm or egg are different…

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N.B Cancer results from uncontrolled cell division. The extra cells invade adjacent tissues,
compete for nutrients and may eventually cause death.

Selective Breeding
Also called artificial selection:
1. From your existing stock select the ones, which have the best characteristics.
2. Breed them with each other.
3. Select the BEST…



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