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Transcript
Movement Across
Membranes
1
1. Diffusion
2
Diffusion
Particles in liquids
and gases move in
random directions
with a certain
amount of kinetic
energy
3
Diffusion
The overall effect of this is
that particles become evenly
distributed (equilibrium)
4
Diffusion
Kinetic Energy can
be increased by
increasing the
temperature
5
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.
6
2. Osmosis
The cell membrane is partially
permeable – it allows small,
particles to pass through by simple
diffusion
7
The cell membrane is partially
permeable – it allows small,
uncharged or high energy particles
to pass through by simple diffusion
8
• Osmosis is simply a special case of
diffusion…
• …that applies to WATER only.
9
10
11
12
Water Potential
‘Water potential’ is a measure of
the amount of kinetic (movement)
energy water molecules have
13
Water Potential
Water potential (y) is a measure of
the amount of kinetic energy water
molecules have
14
Water Potential
In pure water, water potential is at
its highest…
15
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”
16
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.
17
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)
18
Osmosis and Animal
Cells
Cells placed in
a solution of
higher water
potential
19
Osmosis and Animal
Cells
Cells placed in
a solution of
higher water
potential
Cell
Water
bursts
enters by
(lysis)
osmosis
20
Osmosis and Animal
Cells
Cells placed in
a solution of
lower water
potential
21
Osmosis and Animal
Cells
Water leaves
by osmosis
Cells placed in
a solution of
lower water
potential Cell shrivels
(crenation)
22
• This is the reason
why animals need
kidneys…
• …to keep the blood
•
water levels precisely
right.
This is called
OSMOREGULATION.
23
Osmosis and Plant
Cells
Cells placed in
a solution of
higher water
potential
24
Osmosis and Plant
Cells
Cells placed in
a solution of
higher water
potential
Cell
Water becomes
enters by TURGID
osmosis
25
Turgid cells keep a plant supported
upright.
26
Osmosis and Plant
Cells Cells placed in a
solution of lower
water potential
27
Osmosis and Plant
Cells Cells placed in a
solution of lower
water potential
Cell shrivels
(PLASMOLYSED)
Water leaves
by osmosis
28
• When plant cells lose
•
water and
plasmolyse…
…the plant is unable
to support itself and
starts to WILT.
29
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.
30
Osmosis and Plant
Cells
31
This plant is supported by turgid
cells, as well as wood.
32
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.
33
Explain why:
• Placing limp lettuce leaves in water for 20
minutes makes them ‘firm’ again.
• Pouring salt on slugs effectively kills them.
34
Active Transport
Active transport moves
substances against a
concentration gradient.
35
Active Transport
Movement involves the use
of ATP from aerobic
respiration to supply energy
36
Active Transport
Structural changes in the carrier
proteins result in the movement of
material through the membrane.
37
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.
38