1. Cell Structure and
Function
Chapter 7
Part 2

2. The Cell Membrane
 The
cell membrane is
called selectively
permeable because it
regulates what enters and
leaves the cell.
 A double layer of
phospholipids makes up
the membrane
(phospholipid bilayer).

3.  Phospholipids
are
arranged with the
polar head
(hydrophilic) facing
out in the bilayer, and
the non-polar tails
(hydrophobic) facing
the interior of the
bilayer.

4. Membrane Proteins
Various proteins are embedded in the lipid bilayer.
 Some membrane protein functions:
•
•
•
•
Marker proteins – identifies the cell type
Receptor proteins – binds to substances outside the
cell and allow chemical messages to be transmitted
across the cell membrane
Enzymes – assists in chemical reactions
Transport proteins – helps moves substances
across the cell membrane

6. 7.3 Cell Transport

Passive Transport – movement
across a membrane without using
energy.
•

Diffusion is the simplest type of passive
transport.
Particles will move down the
concentration gradient
•
Movement from an area of high
concentration to an area of low
concentration is known as diffusion.

7. 
Equilibrium will be reached when the
concentration of a substance is equal
throughout the space.

8. Facilitated Diffusion
• Small, uncharged molecules can easily pass
through the cell membrane.
• However, some molecules cannot easily
diffuse across the cell membrane.
• Facilitated diffusion is
diffusion using transport
proteins without using
energy.

9. Diffusion Demonstration
 What
molecules will move through the
cell membrane?

10. Osmosis
 The
diffusion of water through a
selectively permeable membrane.
 Water will move down the
concentration gradient from where
water is in high concentration to where
water is in low concentration.

12. 
Water moves in and out of the cell at
the same rate
•
•
•
Equal water concentration inside and
outside the cell
Cell will not change size
ISOTONIC SOLUTION

13. Direction of Water Movement

Water moves out of the cell
•
•
•
Lower water concentration outside the cell
Cell shrinks
HYPERTONIC SOLUTION

14. 
Water moves into the cell
•
•
•
Lower water concentration inside the cell
Cell swells
HYPOTONIC SOLUTION

15. Practice Problem
A
cell contains 5% NaCl. The cell’s
membrane is permeable to water, but not
NaCl.
• If this cell is placed in a solution containing
•
10% NaCl, what will happen to the cell?
Why?
What type of solution is this cell in?

16. More Practice Problems
The cell membrane of a cell is permeable to water but not to NaCl. The cell
contains 2% NaCl. You place this cell in 3 different solutions.



Beaker 1 contains a solution that is 5% NaCl.
Beaker 2 contains a solution that is 1% NaCl.
Beaker 3 contains a solution that is 2% NaCl.
Answer the following questions:
A. What will happen to the cell in beaker 1? What direction does the water
move? What type of a solution is it in?
B. What will happen to the cell in beaker 2? What direction does the water
move? What type of solution is it in?
C. What will happen to the cell in beaker 3? What direction does the water
move? What type of solution is it in?

17. Active Transport

Cells must move some substances against
their concentration gradient
•
•

from an area of low concentration to an area of high
concentration
usually requires a transport protein pump
Or move molecules that are too large to be
transported through the membrane
This REQUIRES ENERGY from ATP!

19. Bulk Transport (Movement in
Vesicles)
 Move
substances such as proteins and
polysaccharides, which are too large to
be transported by carrier proteins

20.  Endocytosis
– vesicle pinches in from
the cell membrane surrounding materials
to be brought into the cell.

21.  Exocytosis
– vesicle moves to the
outside of the cell, fuses with the cell
membrane and releases it’s contents.

22. 7.4 Homeostasis and Cells
 Unicellular
organisms carry out all
functions necessary for life.
 Our cells, however, cannot live on their
own.
• They must become specialized for a certain
job, and communicate with each other to
maintain homeostasis.

23. Cell Specialization
 Different cells have different jobs
 Examples:
• Muscle cells – movement
• Nerve cells – send/receive messages
• Red Blood cells – carry gasses to and from
cells
red blood cell
nerve cell

24. Levels of Organization
 Cells → Tissues → Organs → Organ
Systems