Download Diffusion and Osmosis

DIFFUSION AND OSMOSIS
DIFFUSION
• is the movement of liquid or a gas molecules
from a high concentration to a low
concentration until the substance is evenly
spread.
• important as it lets food and oxygen into a cell
and waste products such as carbon dioxide out
of the cell
How does a scent spread through
a gas?
MOLECULES IN SOLUTION TEND TO SLOWLY SPREAD APART
OVER TIME. THIS IS DIFFUSION.
How Does a Dye Spread
Through a Liquid?
How Does Heat Effect the Spread
of Dye Through a Liquid?
OSMOSIS
• osmosis is the movement of water molecules,
• from a region of high water concentration
to a region of low water concentration
• across a selectively permeable membrane.
SELECTIVELY PERMEABLE
• a membrane controls what goes in and out of the cell.
• permeable means it allows substances to go through it.
• a selectively permeable membrane is a membrane
with holes in it small enough for water to go through it
easily.
• big molecules like starch can not fit through easily
Model of a
Selectively Permeable Membrane
Water
Starch
Small molecules, such
as water can pass
through it.
Large molecules like starch
cannot pass through the
membrane
Osmosis – what will happen?
Water
Starch
The water molecules pass
both ways through the
membrane
The overall flow of water
molecules is from a region
with lots of water
molecules to region of less
water molecules.
Lots of water
molecules
Few water molecules
Until both sides have an
evenly balanced water
concentration.
WHICH MOLECULES WILL
DIFFUSE IN EACH OF THE
FIGURES BELOW?
1
2
5
3
6
4
ANSWERS
1
2
3
4
No Movement
5
6
No Movement
SUMMARY
• osmosis is the movement of water
molecules across a selectively permeable
membrane.
• the membrane only allows small molecules to
pass through it, large molecules can not pass
through the membrane.
• water molecules move into the region where
there are less water molecules
• the water acts to even up the concentration
of water on either side of the membrane.
PLANT CELLS IN WATER
Plant cell placed in
pure water
Water moves
Into the cell
in pure water – water will
move in swelling the
vacuole which pushes out
against the cell wall.
the cell does not burst
because of the cell wall.
PLANT CELL IN STRONG
SUGAR SOLUTION
Strong Sugar/Salt
Solution
In a strong salt or sugar
solution – water will move
out of the vacuole causing it
to shrink.
The cytoplasm can also
shrink away from the cell wall.
The plant cell is described as
flaccid.
ANIMAL CELLS IN DIFFERENT
SOLUTIONS
• a red blood cell in pure water, water will move
into the cell and the cell will burst (there is no
cell wall to prevent this happening)
• in a strong salt/sugar solution water will
move out and the cell will shrink