1.2-diffusion_and_osmosis as active transport.ppt

Diffusion and
Osmosis
Section 1.2

The Cell Membrane
 The cell membrane is:
Selectively permeable
 Permeable = Pass through (Latin)
 Cell membrane = Gate-Keeper that
determines what can and can’t enter the
cell.

The Gate Keeper: The Cell
Membrane
 Who comes in for the
party?
 Small molecules like
water, carbon dioxide,
or oxygen can easily
pass through the
pores of the
membrane.
 Who gets bounced?
 Large molecules like
glucose
 Charged molecules
like salts.

Molecule Movement
 Recall cells are small because they need to
obtain sufficient nutrients and dispose of their
wastes.
 This is done by the cell membrane by three
means:
1. Diffusion
2. Osmosis
3. Active Transport (Senior Science)

Definitions.
 Solution = A homogenous, liquid mixture
of two or more substances.
 Solvent = The dissolving agent of a
solution. Water is the most versatile
solvent known.
 Solute = Substance that is dissolved in a
solution.

Diffusion
 The process by which molecules tend to move
from an area of higher concentration to an area
of lower concentration.
 Concentration= amount of substance in a given
volume.
 Think of the perfume example (high low)
 Think of the food-dye example (high low)

Why Diffusion?
 Kinetic molecular theory-
Molecules are always moving
 Collisions occur between molecules, which
causes the molecules to move away from one
another.
 If there is space these molecules want to spread
out evenly.

Diffusion and the Cell
 Movement of molecules by diffusion is how the
cell fulfills its needs.
 Nutrients: Low concentration in the cells, high
concentration outside of the cells.
 What direction will the nutrients diffuse?
 From outside the cell to inside the cell.
 High to Low Concentration!!

Diffusion and the Cell
 Wastes: High concentration in the cell,
low outside of the cell.
 What direction will the wastes move?
 From inside the cell to outside the cell.
 High to Low concentration

How Diffusion Works
https://www.youtube.com/watch?v=VY0mZU
DvbH4

A special case of diffusion:
Osmosis
 Water moves through the pores of the cell
membrane like other molecules.
 The movement of water from a high
concentration to a low concentration (thru a
semi-permeable membrane) is called: Osmosis
 Osmosis = movement of water (the solvent)
 Diffusion = movement of dissolved materials
(the solutes)

Osmosis is the movement of water (red dots) through a
semipermeable membrane to a higher concentration of
solutes (blue dots).

https://www.youtube.com/watch?v=w3_8FSrqc-I
How Osmosis Works – Video

Osmosis – a cure for the flu?
 Who here has taken penicillin to combat
sickness?
 Penicillin weakens bacterial cell walls
 Water is at higher conc. outside the cell…
which way will water move?
 With a weak cell wall, the bacterial cell
swells and…POP!

**Summary**
 Both osmosis and diffusion involve the
movement of molecules from an area of
high concentrations to a area of low
concentrations.
 Osmosis = movement of water (the
solvent)
 Diffusion = movement of dissolved
materials (the solutes)

Water Balance
 The cell membrane doesn’t actually control the
movement of water.
 The environment around the cell determines the
direction of water movement.
 For example, a cell is placed in a salt water tide pool.
The sun evaporates some water.
 The concentration of water inside the cell is higher than
outside.
 What happens?
 Water leaves the cell.
 Possible shrinking of the cell.

Water Balance
 On the contrary imagine it rains.
 A higher concentration of water outside
the cell is the result.
 What happens?
 Water moves into the cell
 Possible swelling of the cell.

Water Regulation
 Without other mechanisms the cell would burst
or shrivel.
 Plant vacuoles store water even when the
environment is dry.
 The cell wall is rigid to prevent bursting or
shriveling.
 Animals can increase or decrease their amount
of water intake and outtake (Urine
concentration/amount of water that is drank)

Hypertonic Solution – More
water inside cell than outside
Plasmolysis
Plasmolysis
Cells shrink
and die

Iso-osmotic Solution – same
concentration of water inside and outside
cell
Animal cell
Plant cell
No net gain or
loss of water

Hypotonic Solution – more water
outside cell than inside
Cytolysis –
cell swells and
bursts
Builds up turgor
pressure – cell
becomes stiff,
keeping plant
upright

 What would happen
to a cell placed in
pure water?
90% water
10%
solute
100% water
Cell’s are about 90% water.
Human Red Blood Cell Before: After

 What would
happen to a cell
placed in a 20%
salt solution?
90% water
10% solute
Cell’s are about 90% water.
80% water
Human Red Blood Cell Before: After

1.2-diffusion_and_osmosis as active transport.ppt

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1.2-diffusion_and_osmosis as active transport.ppt