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Biology unit 3
B3…read more

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B3 1.1 Osmosis
Membranes which only let some types of particles through are
called partially permeable.
Osmosis is the net movement of water from an area of high
concentration of water to an area of low concentration of water
along a concentration gradient.
Osmosis restores the balance of water in cells.
If solution outside the cell is more dilute, water will move in to the
cell and can make the cell swell and may burst.
If the solution outside is more concentrated, water will move out
of the cell. The cytoplasm may become too concentrate and the
cell may shrivel up and die.
Osmosis is important to plants. They gain water by osmosis
through their roots. Water moves into plant cells by osmosis,
making them turgid or stiff so that they are able to hold the plant
upright.…read more

Slide 3

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B3 1.2 Active Transport
Active transport is when substances are absorbed
against a concentration gradient.
Cells can absorb ions from very dilute solutions. It
also enables them to move substances, such as
sugars and ions, from one place to another through
cell membranes.
Active transport uses energy from respiration so
cells involved in active transport have lots of
mitochondria to provide the energy they need.
By using active transport, plants can absorb these
mineral ions, even though it is against a
concentration gradient.
Sugar such as glucose is always actively absorbed
out of your gut and kidney tubules into your blood.…read more

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B3 1.3 The Sports Drink
Most soft drinks contain water, sugar and mineral
Sports drinks contain sugars to replace the sugar
used in energy release during activity. They also
contain water and ions to replace the water and
mineral ions lost during sweating.
Evidence suggests that for normal levels of
exercise, water is at least as effective as a sports
drink.…read more

Slide 5

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B3 1.4 Exchanging
materials ­ the lungs
The effectiveness of an
exchange surface can be
increased by:
having a large surface area
being thin, which provides a
short diffusion path
having an efficient blood supply
to maintain a concentration
(diffusion) gradient
being ventilated, to make
gaseous exchange more efficient
by maintaining steep
concentration gradients…read more

Slide 6

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B3 1.5 Ventilating the Lungs
The lungs are in your thorax
protected by your rib cage and
separated from your abdomen by
the diaphragm.
When you breathe in, the
intercostal muscles contract to
move your ribs up and out and
flatten the diaphragm, increasing
the volume of your thorax. The
pressure decreases and air moves
When you breathe out, the
intercostal muscles relax and the
ribs move down and in, and the
diaphragm domes up, decreasing
the volume of your thorax. The
pressure increases and air is forced…read more

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