Download S3 Biology Revision

S3 Biology Revision
Cell Structure
Cell
structure
Function
Cell type
Cell wall
Supports and strengthens cell
Plant cell, fungal cell or
bacterial cell
Cell
membrane
Controls which substances can
enter and leave the cell
All cell types
Cytoplasm
Location of many chemical
reactions
All cell types
Mitochondria
Location where aerobic respiration Animal cell, plant cell
occurs
or fungal cell
Chloroplasts
Site of photosynthesis.
Plant cell
Vacuole
Contains cell sap.
Plant cell
Ribosomes
Site of protein synthesis
All cell types
Plasmids
Contains genes that help cell to
function.
Bacterial cell
Nucleus
Controls activities of cell
Animal cell, plant cell
or fungal cell
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Cell Transport
Membrane Structure
Phospholipid
Diffusion
 Diffusion is the movement of molecules from an area of high
concentration to an area of low concentration.
 It does not require energy.
 Molecules move down a concentration gradient.
Oxygen
Glucose
Carbon
dioxide
Osmosis
 Osmosis is a special case of diffusion.
 It is the movement of water molecules from an area of high
concentration to an area of low concentration.
 It does not require energy and molecules move down a
concentration gradient.
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Active Transport
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Movement of molecules from an area of low concentration to an
area of high concentration, against a concentration gradient.
Requires energy.
Molecules travel through specific proteins in the membrane.
Mitosis
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Mitosis is cell division.
It is used for the growth and repair of cells.
It is important that the chromosome number remains the same in
the daughter cells so that no genetic information is lost.
Stage 1 - The replicated chromosomes
'condense'. Their DNA becomes tightly
coiled up and the replicated chromosomes
become visible as separate units. The
chromosomes shorten and thicken and can
now be seen as pairs of chromatids.
Stage 2 – The nuclear membrane breaks
down.
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Stage 3 - Rope-like structures called
spindle fibres attach themselves to the
centromere region of the sister
chromatid pairs. The spindle fibres line
sister chromatid pairs up in the centre of
the cell. This location is known as the
equator.
Stage 4 - The spindle fibres contract
and separate the sister chromatids from
each other. The sister chromatids are
pulled to opposite ends of the cell - the
cell poles.
Stage 5 - The separated sister
chromatids are now known as
chromosomes. Their DNA becomes more
loosely coiled (decondensed), and new
nuclear membranes form around them.
Two new nuclei are formed. Each nucleus
now contains four chromosomes (two sets
of two chromosomes) exactly the same
complement as the original parent cell.
Stage 6 - The cytoplasm of the cell then
divides in two to produce two daughter
cells. The daughter cells are genetically
identical because they each contain the
same diploid chromosome complement as
the original parent cell.
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DNA Structure
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Double helix.
Base pairing rules: Adenine always pairs with Thymine. Guanine
always pairs with Cytosine.
Enzymes
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Enzymes speed up chemical reactions.
They are reusable.
At high temperatures they become denatured.
Enzymes have an optimum (best) pH and temperature.
Enzymes are specific – they only work with one substrate.
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Genetic Engineering

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Genetic engineering is the transfer of DNA from one organism to
another using biotechnology. The organism receiving the DNA is
said to be genetically modified (GM).
Bacterial cells can be genetically modified so that they have the
gene for producing human insulin. As these modified bacteria grow,
they produce human insulin. This protein can be purified and
supplied to diabetics.
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