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Diffusion, osmosis; cell
membranes
Lab 4
Solution
• Making a saline
water solution by
dissolving salt (NaCl)
in water. The salt is
the solute and the
water the solvent.
Concentration
• These glasses containing red dye demonstrate
qualitative changes in concentration. The solutions
on the left are more dilute, compared to the more
concentrated solutions on the right.
Diffusion-Brownian movement
• The rate of diffusion is dependent on such factors as the
temperature, the size of the molecule, concentration
gradient and the type of medium.
Diffusion and differentially
permeable membranes
• A differentially permeable membrane prevents the movements of
some molecules but not others.
•
Osmosis
• Special case of diffusion
• Osmosis is the diffusion of water across a differentially
permeable membrane.
• Water molecules follows its concentration gradient and
moves from the area of higher concentration to the area
of lower concentration.
Osmosis and the rate of
diffusion along a concentration
gradient
• Isotonic- two solutions have equal concentrations of
solutes.
• Hypotonic- a solution with a lower concentration of solutes,
especially those solutes that do not pass across the
surrounding membranes.
• Hypertonic- a solution with a high concentration of solutes.
Osmotic effects on cells
In an isotonic solution
Animal
cells
In an hypertonic solution
In an hypotonic solution
plasma
membrane
nucleus
Water mainly enters the cell, which may
burst (lysis)
No net movement of water
Water mainly leaves the cell, which
shrivels (crenation)
Plant
cells
cell
wall
central
vacuole
nucleus
plasma
membrane
chloroplast
No net movement of water
Vacuoles fill with water
turgor pressure develops
chloroplasts - next to the cell wall
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Vacuoles lose wate
the cytoplasm shrinks(plasmolysis)
chloroplasts- in the center of the cell
Cellular membranes
Thickness: 6-10 nm
● Functions:
1. retarding diffusion of selected molecules
2. housing receptor molecules that detect other cells or
organelles
3. providing sites for active and passive transport of
selected molecules
4. organizing life processes by providing surfaces to
accommodate chemical reactions
5. helping maintain the integrity of cells
●
Procedure 9.2
Procedure 9.3
Procedure 9.4 (Start this one first)
Procedure 9.5
Procedure 9.6 (Observe only)
Procedure 9.7 (Observe only)
Procedure 9.8
Procedure 10.1
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