The plasma membrane is composed mainly of phospholipids and proteins. Phospholipids have a hydrophilic head and hydrophobic tails, forming a bilayer. Various proteins are embedded in the membrane including channel proteins that form channels and carrier proteins that transport substances. Cholesterol molecules are also present and make the membrane more flexible. The plasma membrane is selectively permeable due to its structure, allowing some substances like oxygen, water and ions to pass through easily via protein channels and carriers while blocking other larger molecules. It regulates the movement of substances into and out of cells that are essential for cellular functions and waste removal.

1. 1
Chapter 3
Movement Of Substances
Across The Plasma Membrane

2. 3.1 Structure of
Plasma Membrane

3. The necessity of movement
of substances across a
plasma membrane
3

4. 4
Substances Required (需要)
By The Cells
• Glucose
• Amino acids
• Fats
• Vitamins
• Minerals
• Water
• Oxygen

5. 5
Substances That Have To Be
Eliminated(清除)By The Cells
• Products of cellular respiration (carbon
dioxide)
• Products of protein breakdown (urea, uric
acid and ammonia)
• Excess ions
• Excess water

6. Plasma membrane

7. VIDEOCLIPS:
• FLUID MOSAIC MODEL - WITH
MOVEMENT
• FLUID MOSAIC MODEL – WITHOUT
MOVEMENT
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8. The structure of the plasma
membrane
• Plasma membrane are composed mainly
of phospholipids and proteins.
8

9. Plasma membrane are composed mainly
of phospholipids and proteins

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Each phospholipid molecule consists of two
parts:
(a) a polar head - hydrophilic (loves water /
attracted to water)
(b) a pair of non-polar tail – hydrophobic
(hates water/repels water)
Hydrophilic head
Hydrophobic tails
Hydrophilic head

11. There are various types of protein
molecules embedded partially or fully
within the membrane.
The protein molecules are widely
dispersed between the phospholipid
bilayer.
The protein molecules with channels or
canals are known as channel proteins,
the protein molecules that function as
carriers are called carrier proteins

12. Some proteins and lipids have
carbohydrate chains attached to them,
known as glycoprotein and glycolipid
respectively
Glycoprotein and glycolipid act as
receptors to hormones such as
insulin,
It stabilise the membrane by forming
hydrogen bonds with water and act as
antigens for cell identification.

13. There are also cholesterol molecules found
between the phospholipid molecules
Cholesterols make the phospholipid bilayer
stronger, more flexible and less permeable
to water-soluble substances such as ions.
The phospholipid bilayer, proteins and
cholesterols are not static but form a
dynamic and flexible structure. This
contributes to the ‘fluid’ characteristic of
the plasma membrane and makes the
plasma membrane more flexible.

14. Permeability of a plasma membrane
A membrane is said to be permeable to a
substance if the membrane allows the
substance to pass through it freely.
The plasma membrane is a selectively
permeable membrane.
The plasma membrane has a selectively
permeable property due to its building
structure.
 The phospholipid bilayer and protein
determine the membrane permeability
towards specific substances

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