This document defines key transport processes in biology - diffusion, osmosis, and active transport - and provides examples of each in plants and humans. Diffusion is the passive movement of molecules from high to low concentration down a gradient. Osmosis is the specific case of diffusion where water moves through a semi-permeable membrane from high to low water potential. Active transport moves molecules against a concentration gradient and requires energy. The document discusses the roles of these processes in nutrient/gas exchange and describes demonstrations of osmosis in plant and animal cells under varying conditions.

1.  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)

2. •Diffusion is the net movement of molecules
from a region of higher concentration to a
region of lower concentration, down a
concentration gradient.
•The difference in concentrations of the
substance between the two regions is
known as concentration gradient or
diffusion gradient.

3. Under
normal
condition
…

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

6. How does the ‘water baby’ works?

7. 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.

8. Osmosis is …
• 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

9. Concentrations of Solutions
 Dilute solutions:
- larger number of water molecules (solvent)
compared to another similar solution.
- dilute solutions have a higher water potential,
compared to another similar solution.
- Eg) 5% sugar solution means:
5% sugar molecules;
95% water molecules

10.  Concentrated solutions:
- smaller number of water molecules (solvent)
compared to another similar solution.
- concentrated solutions have a lower water
potential, compared to another similar solution.
- Eg) 10% sugar solution means:
10% sugar molecules;
90% water molecules
QUESTION:
Compare between a 5% and 10% sugar solution.
Which one has a higher water potential?

11. Osmosis
 Sugars such as starch molecules CANNOT
pass through the partially permeable
membrane (Too big)
 However, sugar such as glucose CAN pass
through the partially permeable membrane
(Small enough)

12. Partially
permeable
membrane
Higher water Lower water
potential potential

13. Another example of osmosis
5% sucrose solution 10% sucrose solution
Point A Point B
Partially permeable
membrane

14. Demonstrations of Osmosis
Question:
What will happen to the water level in glass
tube?

15. The surrounding
solution has a
higher water
potential than the
solution in the
visking tubing.
Increase.
Water enters the visking tubing by osmosis.
The Visking tubing swells and becomes firm
and turgid.

16. Surrounding
solution has a
lower water
potential than the
solution in the
visking tubing.
Decrease.
Water leaves the visking tubing by osmosis.
The Visking tubing shrinks
and becomes soft and flaccid.

17. The surrounding
solution has the
same water
potential as the
solution in the
visking tubing.
Water level and Visking tubing remain
unchanged.
No net movement of water molecules into and
out of the visking tubing.

18. MicroQues 1
Describe the changes that took place in the
water levels of the solution in the glass tube and
beaker.

19. MicroQues 1
Dilute solution
= high
____water potential
Concentrated solution
low
= ____ water potential
Decrease.
Water leaves the Visking tubing by osmosis.
The Visking tubing shrinks and becomes soft.

20. MicroQues 2(a)
State the similarities between osmosis and diffusion.
Both involves movement of substances.
Both involves movement of substances from a
region of its higher concentration to a region of
lower concentration.
Bothinvolves movement of substances down a
concentration gradient.

21. MicroQues 2(B)
State two differences between osmosis and diffusion.

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

23. Quiz Time
1. Which of the following processes causes juice
the chilli to curl outwards?
a. Diffusion
b. Transpiration
c. Osmosis
d. Plasmolysis
Watch video: Chilli bloom practical

24. Quiz Time
2. How could a lettuce, which has just wilted,
be made firm and crispy again?
a. Submerge in water
b. Submerge in a 20% sugar solution
c. Submerge in a 30% sugar solution
d. Submerge in a 50% salt solution

25.  The cell membrane of living cells are
partially permeable.
 The cell wall, however, is non-living, tough
and fully permeable.
 In a plant cell, the vacuole membrane
(tonoplast) is also partially permeable.
 The cell sap in the large central vacuole of a
plant cell is highly concentrated (low water
potential) as it contains a complex mixture of
substances.

26. Cells in a Solution with
High Water Potential
Water enters the cell by osmosis.
 Plant cell
Vacuole increases in size. Plant
cell becomes firm and turgid.
 Animal cell
Animal cell swells and may
burst. Why?

27. Why animal cell will burst?
 Due to the absence of a cell wall.
 Cell wall is strong and relatively inelastic.

28. Cells in a Solution with
Low Water Potential
Water leaves the cell by osmosis.
 Plant cell
Vacuole decreases in size and cell
becomes soft and flaccid.
Cytoplasm shrinks away from
cellulose cell wall, through a process
known as plasmolysis.
Watch animation: Plant cell when placed in low/high water potential

29. Cells in a Solution with
Low Water Potential
 Animal cell
The animal cell shrinks.
Little spikes appear on the
plasma membrane. This
process is called
crenation.
Watch animation: Animal cell when placed in low/high water potential

30. Importance of turgor pressure
in plants
• Help maintain shape of soft tissues in plants,
especially young stems and leaves
• Changes in movement of plants due to
turgor
• Plasmolysed leaves are flaccid and the cells
can die

31. 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.

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

33. Question
What happens to animal
and plant cells when placed
in solutions with differing
water potentials?

34. Active Transport (PURE)
 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

35. 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.

36. 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.

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

38. Micro Ques 5
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?
length of potato
strips/mm
( A )

39. Micro Ques 6
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?
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 )