TRANSPORTATION OF MATERIALS IN LIVING
THINGS
Osmosis
This is the movement of water molecules
from a region of higher concentration
to a region of lower concentration through a semi- permeable membrane.
A partially-permeable membrane is a membrane that allows small particles such as water molecules to pass
through it, but not larger particles such as sugar molecules
and ions from salts. Examples
of semi-permeable membranes are cell membranes and a pig’s bladder.
For osmosis to take place
there must be:
1.
Two solutions with different
concentrations; and
2.
A partially permeable membrane
to separate them.
Effects of osmosis
in animal cell
Red blood cells in Isotonic
Solution
Ø If the red blood cell placed in isotonic solution, the cell will neither
gain nor lose water
Ø This means that the movement of water into and out the cell by osmosis
will be the same
Red blood
cell in hypotonic solution
Ø If the red blood cell placed in hypotonic solution, the cell will gain water
by osmosis
Ø This will cause the cell to swell and eventually burst due building
up of osmotic pressure in cytoplasm
Ø Under extreme condition the red blood cell become haemolysed
Haemolysis is the process by which red blood cell burst when placed in hypotonic solution
Red blood
cell in hypertonic solution
Ø If the red blood cell placed in hypotonic solution, the cell will lose water by osmosis
Ø This will cause the cell to shrink
and became crenated
Crenation is process
by which red blood cell loses water and shrink
when placed in hypertonic solution
Effect of osmosis in plant cells
Plant cell in isotonic solution
Ø If the plant cell placed in isotonic solution, the cell will neither gain nor loses
water
Ø This means that the movement of water into and out the cell by osmosis
will be the same
Plant cell in hypotonic solution
Ø If the plant cell placed in hypotonic solution, the cell gain water by osmosis
Ø The cell does not burst due to the
presence of rigid cell wall
Ø The cell become firm and
rigid and is said to be turgid. Turgidity is the
condition where by a plant cell is full of water such that it can no longer absorb any more water from surrounding
Plant cell in hypertonic solution
Ø If the plant cell placed in hypotonic solution, the cell will lose water by osmosis
Ø This will cause the cell to
shrink and became flaccid
Ø This cause the plant to became floppy and wilt due to lack an internal support
Ø Under extreme case the plant became plasmolysed
Plasmolysis
is
the process by which plant cell loses water,
shrink and becomes flaccid when placed in hypertonic solution
Osmosis in unicellular organisms
Unicellular organisms that live in fresh water, for example amoeba and euglena, are hypertonic to their
surrounding so water enters the organisms by osmosis. These organisms have a contractile vacuole.
The contractile
vacuole collects the excess water and removes it from the cell. This prevents
the cell from bursting
Sample practical question
Aim of the experiment: To demonstrate the process of osmosis using potato cubes
Materials: Three raw potatoes, sugar solution, water and beakers or dishes
Procedures
1.
Boil one of the potatoes
(boiling kills the cells).
2.
Cut each potato in half and make
a shallow hole in each half
3.
Place each potato half in a
beaker or dish that has water. The water should not cover the potato.
4.
Put some sugar solution in the
shallow hole in the one raw potato
and the boiled potato. Leave the other potato empty. Label the set-ups
(a),(b) and (c)
5.
Mark the level of water in each beaker
or dishes
6.
Leave the setups undisturbed overnight
Observation
Diffusion
Diffusion is the
net movement of particles from the region of high concentration to low concentration until the particles are
evenly distributed.
Factors affecting
the rate of Diffusion
i.
Concentration gradient; A huge
difference between the concentration
of the molecules in two regions leads to a faster rate of diffusion
ii. Surface area to volume
ration; the higher the ratio the greater the rate of diffusion
iii. Temperature; increase in temperature increases the rate of diffusion and decrease in temperature decreases the rate of diffusion
iv. Thickness of the membrane;
thin membrane enhances the higher rate of diffusion than the thick
membrane
v. Size of molecules; small and light molecules diffuses faster than large and heavy molecules
The role of diffusion in living things
i.
Absorption; digested food example amino acids and
glucose diffuse across the walls of
the ileum to the blood system. Also plants absorb most of mineral salts by diffusion
ii. Gaseous exchange; the process
of gaseous exchange in plants and animals occurs
through diffusion
iii. Excretion of waste; waste
products move out of the cell through diffusion
Sample
practical question
Experiment: Demonstrating
Diffusion using Potassium Permanganate Crystals
Materials:
i. Glass beaker or clear glass container
ii.
Potassium permanganate crystals
iii.
Water
iv.
Stirring rod or glass rod
v. Stopwatch or timer
vi. Paper or cardboard
Procedure:
1.
Fill the glass beaker or container
with water, about two-thirds full.
2.
Add a few potassium
permanganate crystals to the water. The crystals will slowly dissolve, turning the water purple.
3.
Use the stirring rod to gently stir the water and potassium permanganate mixture.
4.
After stirring, observe the
initial distribution of the purple color in
the water.
Questions to Explore:
1.
What happens when potassium
permanganate crystals are added to water?
2.
Why does the water turn purple when potassium permanganate is added?
3.
Describe the initial distribution of the purple color in the water after stirring.
4.
What do you think will happen to the purple
color in the water over time? Why?
5.
How does the purple color spread
throughout the water? What process is responsible for this movement?
6.
What do you notice about the
movement of the purple color particles in the water? Is it uniform,
or does it show any specific pattern?
7.
How can you explain the process
responsible for the spreading of the purple color in the water?
8.
Does the movement of the purple color particles depend
on the presence of an external force, like stirring?
Why or why not?
9.
What factors do you think can
affect the rate of color spreading in the water? How can you design an experiment to test this?
10.
Can you compare the diffusion process
observed here to any natural
processes you know of? How are they similar or different?
Differences between
diffusion and osmosis
|
DIFFUSION |
OSMOSIS |
|
Diffusion is
the movement of materials from the area
of their higher
concentration to the area of their
lower concentration |
Osmosis is
the movement of only solvents or
water from the area of their lower concentration
to the area of their higher
concentration through a semi permeable membrane |
|
Diffusion can
operate in any medium |
Osmosis operates only in liquid medium |
|
Diffusion is applicable to all types
substances (solids liquids and gases) |
Osmosis is applicable only to the solvent part of the solution |
|
Diffusion does
not require a semi permeable membrane |
Osmosis requires the semi permeable membrane |
|
It helps to equalize the concentration
of the diffusing substances throughout the available space |
It does not equalize the concentration of the
substance on two sides of the system |
