The document discusses cell membranes and their structure and functions. It describes membranes as a fluid mosaic model consisting of a phospholipid bilayer with integral and peripheral membrane proteins. The hydrophobic and hydrophilic properties of phospholipids help maintain membrane structure. Membrane proteins function in hormone binding, enzyme activity, transport, and cell communication. The document defines passive transport mechanisms of diffusion and osmosis, and explains active transport requiring ATP. Vesicles transport materials within cells, and membrane fluidity allows shape change during endocytosis and exocytosis.
2. Membranes
2.4.1 Draw and label a diagram to show the structure of
membranes.
2.4.2 Explain how the hydrophobic and hydrophilic properties of
phospholipids help to maintain the structure of cell membranes.
2.4.3 List the functions of membrane proteins.
Include the following: hormone binding sites, immobilized
enzymes, cell adhesion, cell-to-cell communication, channels for
passive transport, and pumps for active transport.
3. Membranes
2.4.4 Define diffusion and osmosis.
Diffusion is the passive movement of particles from a region of
high concentration to a region of low concentration.
Osmosis is the passive movement of water molecules, across a
partially permeable membrane, from a region of lower solute
concentration to a region of higher solute concentration.
4. Membranes
2.4.5 Explain passive transport across membranes by simple
diffusion and facilitated diffusion.
2.4.6 Explain the role of protein pumps and ATP in active
transport across membranes.
2.4.7 Explain how vesicles are used to transport materials within a
cell between the rough endoplasmic reticulum, Golgi apparatus
and plasma membrane.
2.4.8 Describe how the fluidity of the membrane allows it to
change shape, break and re-form during endocytosis and
exocytosis.
5. The Fluid Mosaic Model
In 1972, Singer and Nicolson proposed a model for the
membrane structure in which a mosaic of protein molecules float
in a fluid lipid layer.
This is know as the Fluid Mosaic Model of Membranes.
The model shows membranes to consist of a Phospholipid
Bilayer, with proteins molecules within the fluid bilayer.
Parts of the membrane model include:
– Phospholipid bilayer
– Protein molecules
– Cholesterol molecules
– Glycoprotein molecules
7. The Fluid Mosaic Model
The phospholipid bi-layer consists of a double layer of
phospholipid molecules.
The phospholipid molecules have a hydrophilic end (water loving)
and a hydrophobic end (water hating).
Phospholipids are amphipatic.
Hydrophilic Phosphate head Hydrophobic fatty acid tail
8. Fluidity of Membranes
Phospholipids in membranes are in a fluid state.
This allows membranes to change shape in a way that would be
impossible if they were solid.
The fluidity also allows vesicles to be pinched off from
membranes or fuse with them.
9. Membrane Proteins
Membrane proteins can be:
– Integral Proteins
• Protein molecules embedded in the fluid phospholipid bilayer.
– Peripheral Proteins
• Protein molecules spread over the surface of the membrane.
11. Membrane Proteins
Membrane proteins can have many different functions:
– Hormone binding sites
– Enzymes
– Electron carriers
– Channels for passive transport
– Pumps for active transport
13. Diffusion
Diffusion is the passive movement of particles from a region of
higher concentration to a region of lower concentration, as a
result of random motion of particles.
Diffusion is a passive process (no energy is required).
A membrane is not essential.
There are a number of types of diffusion.
15. Diffusion
Some substances can diffuse through membranes.
Small uncharged particles pass between the lipid molecules.
– eg: oxygen, carbon dioxide
Ref: Advanced Biology Roberts etal.
16. Diffusion Through Channel Proteins
Some substances pass through channel proteins.
Channel proteins are concerned with transporting ions through
membranes.
– Eg: water soluble substances, water, ions
Movement is passive (no energy is required).
Ref: Advanced Biology Roberts etal.
17. Facilitated Diffusion Through Channel Proteins
Some substances are larger and require carrier proteins to move
them through the membrane.
Carrier proteins carry molecules which are polar and larger.
– Eg: glucose, amino acids
Carrier proteins are specific for certain substances.
Movement is passive (no energy is required). Ref: Advanced Biology Roberts etal.
18. Osmosis
Osmosis is the passive movement of water molecules from a region
of lower solute concentration to a region higher solute
concentration, across a partially permeable membrane.
Simply put, Osmosis is the diffusion of water.
Osmosis is a passive process (no energy is required).
A membrane is essential.
19. Active Transport
Active transport is the movement of substances across a
membrane using energy from ATP.
Active transport can move substances against the concentration
gradient:
– From a region of lower concentration to an area of higher concentration
Protein pumps in the membrane are used for active transport.
Each pump only transports particular substances, so cells can
control what is absorbed.
20. Active Transport
Active transport allows cells to take up nutrients when their
concentrations outside the cell are low.
Also allows cells to get rid of wastes when the outside
concentration is higher.
Ref: Advanced Biology Roberts etal.
21. Exocytosis and Endocytosis
Sometimes substances need to be moved into or out of a cell
that can’t be done by diffusion or active transport.
These substances are usually larger.
These methods rely on the fluidity of the plasma membrane.
Examples include:
– Exocytosis:
• Moving substances out of the cell
– Endocytosis:
• Moving substances into the cell
22. Exocytosis
Sometimes large molecules need to be expelled from the cell.
This is done by a process called:
– Exocytosis
The vesicle containing the material to be expelled moves to the
plasma membrane.
The vesicle fuses with the plasma membrane.
The vesicle then opens to the exterior of the cell, releasing its
contents out of the cell.
24. Endocytosis
Small molecules can enter and leave cells through the plasma
membrane by diffusion or active transport.
Sometimes larger molecules need to be taken into a cell.
This is done by a process called:
– Endocytosis
Two types of Endocytosis are:
– Phagocytosis
• Large solid particles
– Pinocytosis (sometimes referred to as cell drinking)
• Liquids
27. Phagocytic Intake and Digestion
1. Small particles are taken in by
phagocytosis to form a phagocytic
vesicle.
2. A lysosome fuses with the
vesicle and discharges its contents
into it.
3. The lysosome enzymes digest
the particles and the products of
digestion are absorbed into the
surrounding cytoplasm.
4. The vesicle membrane fuses
with the plasma membrane and
any indigestible matter is expelled.
Ref: Advanced Biology Roberts etal.
28. IBO guide:
2.4.1 Draw and label a diagram to show the structure of
membranes.
The diagram should show the phospholipid bilayer, cholesterol,
glycoproteins, and integral and peripheral proteins. Use the term
plasma membrane, not cell surface membrane, for the membrane
surrounding the cytoplasm. Integral proteins are embedded in the
phospholipid of the membrane, whereas peripheral proteins are
attached to its surface. Variations in composition related to the
type of membrane are not required.
Aim 7: Data logging to measure the changes in membrane
permeability using colorimeter probes can be used.
29. IBO guide:
2.4.2 Explain how the hydrophobic and hydrophilic properties of
phospholipids help to maintain the structure of cell membranes.
2.4.3 List the functions of membrane proteins.
Include the following: hormone binding sites, immobilized
enzymes, cell adhesion, cell-to-cell communication, channels for
passive transport, and pumps for active transport.
2.4.4 Define diffusion and osmosis.
Diffusion is the passive movement of particles from a region of
high concentration to a region of low concentration.
30. IBO guide:
Osmosis is the passive movement of water molecules, across a
partially permeable membrane, from a region of lower solute
concentration to a region of higher solute concentration.
2.4.5 Explain passive transport across membranes by simple
diffusion and facilitated diffusion.
2.4.6 Explain the role of protein pumps and ATP in active
transport across membranes.
31. IBO guide:
2.4.7 Explain how vesicles are used to transport materials within a
cell between the rough endoplasmic reticulum, Golgi apparatus
and plasma membrane.
2.4.8 Describe how the fluidity of the membrane allows it to
change shape, break and re-form during endocytosis and
exocytosis.