Download GCSE Osmosis PowerPoint

Movement Across
Membranes
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1. Diffusion
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Diffusion
Particles in liquids
and gases move in
random directions
with a certain
amount of kinetic
energy
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Diffusion
The overall effect of this is
that particles become evenly
distributed (equilibrium)
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Diffusion
Kinetic Energy can
be increased by
increasing the
temperature
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Examples from syllabus:
• Diffusion of CO2 into stomata of leaves
during photosynthesis.
• Diffusion of O2 into the alveoli of the lungs
• Diffusion of O2 to respiring cells
• Diffusion of glucose, amino acids etc. into
the villi during digestion.
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2. Osmosis
The cell membrane is partially
permeable – it allows small,
particles to pass through by simple
diffusion
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The cell membrane is partially
permeable – it allows small,
uncharged or high energy particles
to pass through by simple diffusion
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• Osmosis is simply a special case of
diffusion…
• …that applies to WATER only.
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Water Potential
‘Water potential’ is a measure of
the amount of kinetic (movement)
energy water molecules have
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Water Potential
Water potential (y) is a measure of
the amount of kinetic energy water
molecules have
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Water Potential
In pure water, water potential is at
its highest…
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Osmosis definition:
“Osmosis is the diffusion of water
molecules from areas of high water
potential to areas of lower water potential
through a partially permeable membrane”
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Osmosis
Osmosis is the diffusion of water
molecules from areas of high water
potential to areas of lower water potential
through a partially permeable membrane.
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Exam errors:
• Forgetting to use the term ‘water potential’
• Saying water ‘osmoses’ (it doesn’t; it diffuses)
• Not mentioning ‘selectively permeable
•
membrane’
Saying water moves ‘from high to low
concentration’ ( you can’t concentrate water! It
should be high to low water potential)
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Osmosis and Animal
Cells
Cells placed in
a solution of
higher water
potential
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Osmosis and Animal
Cells
Cells placed in
a solution of
higher water
potential
Cell
Water
bursts
enters by
(lysis)
osmosis
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Osmosis and Animal
Cells
Cells placed in
a solution of
lower water
potential
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Osmosis and Animal
Cells
Water leaves
by osmosis
Cells placed in
a solution of
lower water
potential Cell shrivels
(crenation)
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• This is the reason
why animals need
kidneys…
• …to keep the blood
•
water levels precisely
right.
This is called
OSMOREGULATION.
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Osmosis and Plant
Cells
Cells placed in
a solution of
higher water
potential
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Osmosis and Plant
Cells
Cells placed in
a solution of
higher water
potential
Cell
Water becomes
enters by TURGID
osmosis
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Turgid cells keep a plant supported
upright.
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Osmosis and Plant
Cells Cells placed in a
solution of lower
water potential
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Osmosis and Plant
Cells Cells placed in a
solution of lower
water potential
Cell shrivels
(PLASMOLYSED)
Water leaves
by osmosis
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• When plant cells lose
•
water and
plasmolyse…
…the plant is unable
to support itself and
starts to WILT.
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Osmosis and Plant
Cells
And when turgid the cell contents
exert outward pressure on the cell
wall
This helps to support plants and
keep them upright.
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Osmosis and Plant
Cells
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This plant is supported by turgid
cells, as well as wood.
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Examples of osmosis:
• Absorbing water in root hair cells of
plants.
• Absorbing water in the large intestine
(colon).
• Pallisade cells absorbing water for
photosynthesis.
• Seeds absorbing water prior to
germination.
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Explain why:
• Placing limp lettuce leaves in water for 20
minutes makes them ‘firm’ again.
• Pouring salt on slugs effectively kills them.
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Active Transport
Active transport moves
substances against a
concentration gradient.
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Active Transport
Movement involves the use
of ATP from aerobic
respiration to supply energy
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Active Transport
Structural changes in the carrier
proteins result in the movement of
material through the membrane.
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Examples of active transport:
• Uptake of minerals by roots
• Concentrating molecules in the vacuoles of
plants eg beetroot, rhubarb, mint etc.
• Impulses firing in nerves of animals.
• Exporting enzymes from cells into the gut.
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