The document covers the basic principles of cell transport mechanisms, specifically diffusion and osmosis, highlighting their importance for cellular function and water regulation. It explains the differences between isotonic, hypotonic, and hypertonic solutions as they relate to plant and animal cells, and describes how these processes are critical for maintaining cell integrity. Key terms and concepts are defined, leading to an understanding of how water molecules move across membranes and the implications for biological systems.

1. General Biology 1/2
Science, Technology, Engineering, and Mathematics
General Biology 1
Science, Technology, Engineering, and Mathematics
Lesson 4.2
Cell’s Transport
Mechanism I: Diffusion
and Osmosis

2. 2
Water is a very
essential substance
for life to persist.

3. 3
When a plant is not
watered for days, it wilts
because its cells lack
sufficient water.
Animals drink water not
just to quench thirst when
feeling hot, but also to
help cells in performing
daily biochemical
processes.

4. 4
Water has various
properties that help
sustain life.

5. 5
How do water molecules cross
the membrane?

6. Learning Competency
At the end of the lesson, you should be able to do the
following:
6
Explain the transport mechanisms in cells
(diffusion and osmosis) (STEM_BIO11/12-Ig-h-
13).

7. Learning Objectives
At the end of the lesson, you should be able to do the
following:
7
● Explain the difference between diffusion and
osmosis as molecules cross the membrane.
● Differentiate hypotonic, isotonic and hypertonic
solutions for animal and plant cells.

8. 8
How does diffusion affect the
movement of substances into
and out of the cell?

9. 9
Cell’s Transport Mechanism I
D
I
F
F
U
S
I
O
N
Simple Diffusion
Facilitated
Diffusion
Area of
higher
concentratio
n

10. 10
Cell’s Transport Mechanism I
D
I
F
F
U
S
I
O
N
Simple Diffusion
Facilitated
Diffusion
Equilibrium is
achieved

11. 11
Cell’s Transport Mechanism I
D
I
F
F
U
S
I
O
N
Simple Diffusion
Facilitated
Diffusion
Diffusion involves the movement of molecules in a solvent from an area of
higher solute concentration to an area of lower solute concentration which
eventually results in the state of dynamic equilibrium.

12. 12
Cell’s Transport Mechanism I
D
I
F
F
U
S
I
O
N
Simple Diffusion
Facilitated
Diffusion
passive
transport
no energy
required
movement of
molecules
high to low
concentratio
n
state of
dynamic
equilibrium

13. 13
Cell’s Transport Mechanism I
D
I
F
F
U
S
I
O
N
Simple Diffusion
Facilitated
Diffusion
Molecules such as ions and water
outside the cell are being
transported across the cell
membrane through channel
proteins via facilitated diffusion.

14. 14
Cell’s Transport Mechanism I
D
I
F
F
U
S
I
O
N
Simple Diffusion
Facilitated
Diffusion
The channel protein
facilitates the movement of
molecules hence the term
“facilitated diffusion”.

15. 15
How does osmosis play an
important role in different
cellular processes?

16. 16
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
Semi-permeable
membrane
High water, low
solute
concentration
Low water, High
solute
concentration

17. 17
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
Movement is from
the region of high
water
concentration to
one with lower
water
concentration.

18. 18
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
Osmosis is similar
to diffusion.
However, osmosis
refers to the
movement of
water from
higher to lower
concentration.

19. 19
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
Tonicity
relative
concentration of
solutes in fluids
ability of a
surrounding solution
to cause a cell to gain
or lose water
depends on the
concentration of
solutes
can be isotonic,
hypotonic, or
hypertonic

20. 20
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
solute
molecules
outside the
cell
solute
molecules
inside the cell
Isotonic solution
Solutions of equal solute
concentration

21. 21
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
Isotonic solution
is when water
molecules move at
the same rate in both
directions.

22. 22
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
solute
molecules
outside the
cell
solute
molecules
inside the cell
Hypotonic solution
has lower solute concentration
and has higher water
concentration (i.e., less solute,
more water).

23. 23
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
Hypotonic solution
can cause the cell to
swell or even burst
due to the intake of
water more than the
cell can
accommodate.

24. 24
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
solute
molecules
outside the
cell
solute
molecules
inside the cell
Hypertonic solution
has higher solute concentration
and has lower water
concentration (i.e., more solute,
less water).

25. 25
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
Hypertonic solution
can cause an animal
cell to shrink or
shrivel due to water
loss.

26. 26
Cell’s Transport Mechanism I
O
S
M
O
S
I
S
Isotonic Hypotonic Hypertonic
Plant cells, relative to animal cells, do not change cell size that much with
varying concentrations of water.

27. 27
Marine fishes and other types of
animals drink water but excrete
salts across their gills. Why do
they do this?

28. Check Your
Understanding
28
Identify the correct term being described in each of
the following statements.
1. It refers to the relative concentration of solutes in
fluids separated by a selectively permeable
membrane.
2. It refers to a solution where water is drawn out of
the cell.
3. It is one of the components of a homogeneous
mixture that is usually solid.

29. Check Your
Understanding
29
Classify the following situations based on the tonicity
of the surrounding environment. Write if it is isotonic,
hypotonic, or hypertonic.
1. It can be observed that plants wilt and are almost
dying along a salted roadside.
2. Paramecia live in freshwater environments and use
their contractile vacuoles to get rid of excess water.

30. Check Your
Understanding
30
Classify the following situations based on the tonicity
of the surrounding environment. Write if it is isotonic,
hypotonic, or hypertonic.
3. Some animals must drink the saltwater to get the
water into their bodies, but they maintain it by
making the salts concentrated and excreted from
the body.

31. Let’s Sum It Up!
● Diffusion is the movement of molecules down their
concentration gradient, i.e., from an area of higher
concentration to an area of lower concentration.
● A solution contains both the solute, which is usually
solid and a solvent, which is usually a liquid. A solute
added in a solvent will naturally diffuse to form a
solution.
31

32. Let’s Sum It Up!
● Diffusion is an example of passive transport in
which molecules are moved across the membrane
without spending energy.
● Facilitated diffusion involves the movement of
molecules across the membrane but with the aid of
either channel or carrier proteins. These molecules
are usually those that cannot cross due to their
molecular size or chemical nature.
32

33. Let’s Sum It Up!
● Osmosis is the diffusion of water across a selectively
permeable membrane from high to low
concentration.
○ Solutions with an equal solute concentration are
said to be isotonic.
○ Hypotonic solution has a lower concentration of
solutes than inside the cell.
○ Hypertonic solution is one with a higher
concentration of solute outside of the membrane.
33

34. Let’s Sum It Up!
34
Diffusion and osmosis both involve movement of molecules without
spending energy.

35. Challenge Yourself
35
35
You took a fresh sample of human blood
and observed it under the microscope. You
added a solution that your laboratory
technician gave you. To your surprise, the
specimen becomes clear and void of cells.
What could have happened to the cells?

36. Photo Credit Bibliography
36
● Slide 1: Rhizomnium punctatum lamina by Kristian
Peters -- Fabelfroh 09:12, 28 February 2007 (UTC) is
licensed under CC BY-SA 3.0 via Wikimedia Commons
.
Hoefnagels, Marielle. Biology: The Essentials. 2nd ed. McGraw-
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Mader, Sylvia S., and Michael Windelspecht. Biology. 11th ed.
McGraw-Hill Education, 2014.
Reece, Jane B, Martha R. Taylor, Eric J. Simon, Jean L. Dickey,
and Kelly Hogan. Biology Concepts and
Connections. 8th ed. Pearson Education South Asia
Pte Ltd., 2016.
Simon, Eric J., and Jane B. Reece. Campbell Essential Biology.
5th ed. Pearson Education Inc., 2013.
Starr, Cecie, Christine A. Evers, and Lisa Starr. Biology Today
and Tomorrow. 4th ed. Cengage Learning Asia Pte Ltd,
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