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UNIT 2 BIOLOGY NOTES
3.2.1- Living organisms vary, and this variation is influenced by genetic
and environmental factors
Variation exists between members of a species (a group of organisms which can interbreed
and produce fertile offspring
It is important to take a random sample (each individual is chosen entirely by…

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A gene is a chemical code that contains the instructions for making a
complete protein or polypeptide/a section of DNA that contain coded
information as a specific sequence of bases, the code for polypeptides
that determine the nature and development of organisms
Different forms of genes are known as alleles,…

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Crossing over takes place during first prophase division-two of the
chromatids on a homologous pair of chromosomes can cross over the
point at which they cross is known as the chiasma
When the chromosomes separate during anaphase, parts of the
chromatids are swapped from one chromatid to another
This means…

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Starch is a polysaccharide made of -glucose, and are joined by glycosidic bonds-it is made
of amylose and amlopectin
Starch and glycogen are used as a storage molecules, as they are compact and insoluble, and
so osmosis is prevented
Although both starch and glycogen are branched, glycogen has far more…

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Translation then begins-the start codon attaches to a ribosome, which reads the sequence
until the end codon
tRNA have complementary bases on one end, and an amino acid on the other, which join to
form an amino acid chain, which forms a primary then tertiary structure
Mitosis is used for…

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3.2.6- In complex multicellular organisms, cells are organised into tissues,
then organs, then systems
when cells become specialised for different functions it is called cell differentiation
Unspecialised cells tissue organ system

3.2.7- Factors such as metabolic rate and size affect the requirements of
organisms and this gives rise to adaptations…

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The cuticle prevents gas exchange, the stomata (mainly on the underside of the leaf)
provides an opening for gases to enter and escape, controlled by guard cells
Guard cells close the stoma when they are not
turgid (and have therefore lost water), which
prevents water loss and during times when…

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In a plant, the water first enters via osmosis, due to the root hair cell, which increase the
surface area for osmosis of water
The water enters, as mineral ions are taken into the cell via active transport, which lowers
the water potential, meaning water moves in by osmosis
For…

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As water moves out, it is replaced by the water in the xylem vessels, as there is a cohesive
force between water molecules, as water leaves the plant, a column of water is drawn up as
a result, due to the tension the column of water is under
The xylem…

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3.2.10- Adaptation and selection are major components of evolution and
make a significant contribution to the diversity of living organisms
Antibiotics are used to treat bacterial infections (not viral)
One way in which antibiotics work is to cause osmotic lysis, by preventing cell walls from
forming
They can also work…

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