This document discusses different modes of movement of substances across membranes, including diffusion, osmosis, and active transport. It defines diffusion as the net movement of molecules from an area of higher concentration to lower concentration down a gradient. Osmosis is defined as the net movement of water molecules from an area of higher water potential to lower water potential through a partially permeable membrane. Active transport is the movement of substances against a concentration gradient and requires energy. Examples of each process are provided. The effects of osmosis on plant and animal cells are also described.

1. Movement
of
Substances

2. Learning Outcome
• Define diffusion and describe the role of diffusion
in nutrients uptake and gaseous exchange in plants
and humans.
• Define osmosis and describe the effects of osmosis
on plant and animal tissues.
• Define active transport and discuss its importance
as an energy-consuming process (Pure)

3. Diffusion
• Diffusion is the net movement of molecules
from a region of higher concentration to a
region of lower concentration, down a
concentration gradient.
• Concentration gradient??
• Difference in concentrations of the substance between

4. Diffusion

5. Moving molecules
In which states are molecules able to diffuse?
Molecules in liquids and gases are constantly moving and bumping into each
other. This means that they tend to spread out.
gas (e.g. steam)liquid (e.g. water)solid (e.g. ice)

6. Diffusion in action: two gases

7. Diffusion in action: one gas

8. Dissolved substance diffuse throughout liquid in
which they are dissolved.

9. Diffusion
• Can starch diffuse
through the partially
permeable membrane?
• Can glucose diffuse
through the partially
permeable membrane?

10. Examples of diffusion
• Carbon dioxide diffuses from blood
capillary into alveoli and oxygen
diffuses from alveoli into surrounding
blood capillaries.
• The diffusion of carbon dioxide
through the stomata into the
mesophyll cells.
• The diffusion of water vapour from
the leaves during transpiration.

11. Diffusion: true or false?

12. Osmosis
•the net movement of water molecules
•from a region of higher water potential to a
region of a lower water potential
•through a partially permeable membrane
•Involves only water molecules

13. Concentrated Vs. Diluted
Solution A Solution B
1. 10% salt solution 2% salt solution
2. 80% sugar solution 100% distilled water
3. 50% salt solution 50% salt solution
Which direction would osmosis occur?

14. Osmosis in action!
Partially permeable membrane

15. Osmosis in Action!

16. Diffusion Osmosis
Both involve the movement of molecules
from a region of higher concentration
to a region of lower concentration
How are they alike?
1. Involves movement of
all types of molecules.
2. Do not involve a
partially permeable
membrane
1. Involves movement of only
water molecules
2. Involve the movement of
water molecules passing
through a partially
permeable membrane
How are they different?

17. Osmosis in Living Cells
•Animal Cell
•Plant Cell

18. What happens when water enters
an Animal Cell
Animal cell swells and
may burst.
Why?
Due to the
absence of a
cell wall.

19. What happens when water enters
a Plant Cell
Plant cell swells and
becomes turgid w/o
bursting.
Why?
Due to the
presence of a
cell wall.

20. What happens when water exits
an Animal Cell
Little spikes appear on the
plasma membrane. This
process is called
crenation.
The animal
cell
shrinks.

21. What happens when water exits
a Plant Cell
Vacuole decreases in size
and cell becomes soft and
flaccid.
What happens to
the plant?

22. The plant
• Therefore turgor pressure is
important
• To help maintain the shape of
tissues in plants
Wilts

23. MicroQues 3
Four plant cells were placed in 20% sucrose solution, 50% sucrose
solution, 80% sucrose solution and pure water separately.
In the table below,
(a) describe the appearance of the plant cells.
(b) identify the solution that the cells have been placed in.

24. Pure water
20% sucrose 50% sucrose 80% sucrose
Cell become
turgid.
No change. Cell become
flaccid.
Cell become
plasmolysed.
MicroQues 3

25. Lets Recap!
• What is diffusion?
• Name some examples of diffusion
• What is osmosis?
• Name some examples of osmosis

26. • What happens when an animal cell is placed into a
concentrated sugar solution?
• What happens when an animal cell is placed into
distilled water?
Lets Recap!

27. • What happens when a plant cell is placed into a
concentrated sugar solution?
• What happens when a plant cell is placed into
distilled water?
Lets Recap!

28. … Any other modes of transportation?
Besides diffusion & osmosis?
Active
Transport!

29. Active Transport
• Requires energy
• When substances move from a region of lower
concentration to a region of higher concentration
against a concentration gradient
• Occurs only in living cells as only living cells respire
• Respiration will release energy where part of it will
be used in active transport

30. Active transport is the process in which particles
move from a region of low concentration to a
region of high concentration, against the
concentration gradient, with the use of energy.

31. Lets recall…. In Sec 2…
Some examples of active transport
• The absorption of mineral salts from the surrounding
soil solution by root hair cells.
• The absorption of glucose and amino acids by the
epithelium cells in the small intestines of man, when
they are low in concentration.

32. Which of the following diagram illustrates the most likely
appearance of a red blood cell that has been placed in
distilled water?
Micro Ques 4
( D )

33. A strip of potato, originally 50 mm in length, was measured
after it was soaked in distilled water. Which of the following
graphs A, B, C or D best represents the results?
Micro Ques 5
( A )
length of potato
strips/mm

34. The apparatus shown in the diagram was set up. After one
hour, the water in the beaker turned red. What is the most
likely reason for this colour change?
Micro Ques 6
A Molecules of red ink move through the membrane by diffusion.
B Molecules of red ink move through the membrane by osmosis.
C Molecules of water move through the membrane by diffusion.
D Molecules of water move through the membrane by osmosis.
( A )

35. Factors affecting the rate of movement
of substances
Surface Area to Volume
Ratio

36. Surface Area to Volume Ratio
• Surface Area: measure of how much exposed area a
solid object has, expressed in square units (x2).
• Volume: how much three-dimensional space a
substance (solid, liquid, gas, or plasma) or shape occupies
and is expressed in cubed units (x3).
• Ratios (Surface Area:Volume):
make comparisons between two things.

37. Surface area and volume

38. Have you ever wondered why our body has such a
dense network of blood capillaries?
To increase the SA : Vol for faster rate of diffusion

39. Start working on your
Assignment
To-dos