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B2: Additional Biology
B2 exam:
13th January 2011…read more

Slide 2

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All cells have:
Nuclei (singular = nucleus)
A cell membrane
A cytoplasm
Mitochondria (singular = mitochondrion)
Only plant cells have:
A cellulose cell wall
A vacuole…read more

Slide 3

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All organelles (parts of a cell) have a job to do:
Nuclei hold DNA and tell the cell how to behave.
Ribosomes are where protein synthesis
(creation) happens.
Mitochondria release energy during respiration.
The vacuole holds the cell's shape when it is not
joined to other cells.
The cell membrane controls the entry and exit of
substances in a cell.
The cellulose cell wall strengthens the cell.
Chloroplasts contain chlorophyll for
photosynthesis.…read more

Slide 4

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These are both ways of moving substances into
and out of cells. There is another method,
called active transport, which is sometimes
Diffusion is the net (overall) movement of a
substance from an area of high concentration
to one of lower concentration.
Osmosis is the same as diffusion, but only with
the movement of water, and across a partially-
permeable membrane.…read more

Slide 5

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If there is a large difference between the
concentrations of a substance inside and
outside a cell, this is called a high
concentration gradient. With a small
difference, it is a shallow concentration
Active transport is the moving of salts against
the concentration gradient.…read more

Slide 6

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A cell can behave in three ways in osmosis:
In an isotonic solution, the concentrations are
the same, so the cell isn't affected.
In a hypotonic solution, the cell takes in lots of
water and becomes turgid (swollen).
In a hypertonic solution, the cell lets out lots of
water and becomes flaccid (limp).
Plant cells, with cell walls, swell up or shrivel;
animal cells, with no cell walls, explode or
shrivel so much that they become useless -
they can only survive an isotonic solution.…read more

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