Movement of materials
in and out of cells
Diffusion, Osmosis
& Active Transport
1
Contents
Solution
Diffusion
Osmosis
Osmosis and Food Preservation
Active Transport
2
Solution
Solution = Solute + Solvent
e.g. Brine = Salt + Water
Diffusion
Osmosis
3
Diffusion
(1/4)
is the movement of molecules from an area of
high concentration to an area of lower
concentration.
No permeable or semi-permeable membrane
is necessary for diffusion to occur.
In biology, dealing with living things
composed of cells, diffusion will always
take place across the cell membrane.
No energy used by the cell for diffusion to
take place i.e. it is a passive process.
4
Examples of diffusion:
(2/4)
• a bottle of perfume opened at one end of a
room
• a crystal of potassium permanganate in a
beaker of water
• a stink bomb
• gaseous exchange in alveoli and leaves
• absorption through villi of small intestine
• transpiration through stomata
5
Example of Diffusion
(3/4)
Carbon dioxide
Oxygen
Oxygen
Carbon dioxide
6
7
Osmosis
(1/2)
Cell wall - fully permeable (plant cell only) rigid.
Cell membrane - semi-permeable (plant +
animal cells) - elastic.
Solution = Solute + Solvent
e.g. Brine = Salt + Water
8
Osmosis
(2/2)
is the movement of solvent (always water)
from a dilute solution to a more
concentrated solution through a semipermeable membrane.
No energy used by the cell for osmosis to take
place i.e. it is a passive process.
9
Examples of osmosis:
• Water entering root hair cell
• Water moving from cell to cell in
transpiration
• Water moving between our body cells
and blood
• Water re-absorption in the nephron
10
Root hair cells
11
Problem caused by Osmosis
Animal cells have no cell walls.
Cell membranes are elastic.
If an animal cell is placed in distilled water,
water enters the cell by osmosis.
Cell swells.
May burst.
- problem!!
12
How is this problem solved?
In some animals e.g. Amoeba, a contractile
vacuole is used.
As excess water enters the cell, it is diverted
to this vacuole.
When vacuole is full, its contents are emptied
to the exterior.
This process requires energy.
13
Diagram of Amoeba
14
How it is solved in humans
By keeping the concentration of our blood
correct.
If there is less water in the blood than in the
cells, water will leave the cells and flow
into the blood.
If there is more water ……… (complete)
The kidneys control the concentration of the
blood = osmoregulation.
15
Kidney
16
Nephron
17
Red blood cells in solutions of
different concentrations
18
Plant cells in solutions of
different concentrations
19
Plant cell in concentrated soln.
Vacuole loses water.
Cell membrane shrinks and pulls away from
cell wall.
Gap forms between cell wall and cell
membrane.
This process is plasmolysis and the cell is said
to be plasmolysed.
20
Plant cell in distilled water
In a turgid cell the water has entered the
vacuole and pushed outward against the cell
wall (causes pressure = turgor pressure).
The cell wall pushes back against the cell
membrane.
The cell expands but does not burst.
Note: turgor pressure maintains structural
rigidity in herbaceous (non-woody) plants.
Can you explain how wilting occurs?
21
Osmosis & Food Preservation
SALTING - causes water to be drawn from
bacterial cells and denatures bacterial
enzymes - kills all bacteria.
SUGAR - in high concentrations causes water
to be drawn from bacterial cells - kills all
bacteria.
22
Active Transport
• is the movement of molecules (solute or
solvent) from a region of low concentration
to a region of higher concentration through
a semi-permeable membrane.
• This process requires energy - ATP from
respiration, which requires oxygen mitochondria.
• The movement is against the concentration
gradient.
23
Example of Active Transport
• Reabsorption in the nephron of the kidney
24
END
25