1. AS Biology FOUNDATION Chapter 4 CELL MEMBRANES and TRANSPORT
Visit
For 100’s of free powerpoints
AS Biology. Foundation. Cell membranes and Transport

2. AS Biology. Foundation. Cell membranes and Transport
The Cell
AS Biology. Foundation. Cell membranes and Transport

3. AS Biology. Foundation. Cell membranes and Transport
Learning Objectives
Describe the fluid mosaic model of membrane structure and explain the underlying reasons for this structure.
Outline the roles of phospholipids, cholesterol, glycolipids, proteins and glycoproteins in membranes.
Outline the roles of the plasma membrane, and the roles of membranes within cells.
Describe and explain how molecules can get in and out of cells (cross cell membranes) by the processes of diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis.
Describe the effects on animal and plant cells of immersion in solutions of different water potential.
Describe the features of the gaseous exchange surface of mammalian lung.
Describe the features of root hairs that enable the uptake of ions by active transport.
AS Biology. Foundation. Cell membranes and Transport

4. Key words you should know
Phospholipids Solution Pinocytosis
Polar Solute Micropinocytosis
Hydrophilic Solvent Exocytosis
Hydrophobic Partially permeable Gaseous exchange
Micelles Water potential Alveoli
Phospholipid bilayer Solute Potential Root hair
Fluid mosaic model Pressure Potential Surface area
Glycoproteins Turgid Epidermis
Glycolipids Plasmolysis Passive transport
Cholesterol Plasmolysed
Proteins Incipient plasmolysis
Transport proteins Active transport
Enzymes Carrier protein
Receptor molecules Bulk transport
Diffusion Endocytosis
Concentration gradient Phagocytosis
Facilitated diffusion Phagocytes
Osmosis Phagocytic vacuoles
AS Biology. Foundation. Cell membranes and Transport

5. AS Biology. Foundation. Cell membranes and Transport
All living things are surrounded by a membrane.
A cell membrane is also known as plasma membrane.
Controls exchange of materials such as nutrients and waste between cells and their environment.
Has other important functions for example to enable cells to receive hormones.
To understand the function of anything in biology, you must study the structure first!
AS Biology. Foundation. Cell membranes and Transport

6. Cell Membranes from Opposing Neurons (TEM x436,740).
Nerve cell
Gap between cells
Cell membrane {
} cell membrane
7nm wide
Nerve cell
AS Biology. Foundation. Cell membranes and Transport

7. Cell membranes are made of PHOSPHOLIPIDs
HYDROPHILIC heads (water liking) -Attracted to the water
called POLAR
HYDROPHOBIC tails (water fearing) -Not attracted to the water
called NON-POLAR
A Phospholipid
AS Biology. Foundation. Cell membranes and Transport

8. AS Biology. Foundation. Cell membranes and Transport
Phospholipids are important structural components of cell membranes. Phospholipids are modified so that a phosphate group (PO4-) replaces one of the three fatty acids normally found on a lipid. The addition of this group makes a polar "head" and two nonpolar "tails".
AS Biology. Foundation. Cell membranes and Transport

9. AS Biology. Foundation. Cell membranes and Transport
A phospholipid
HYDROPHILIC HEAD
At the other end of the phospholipid is a phosphate group and several double bonded oxygens. The atoms at this end of the molecule are not shared equally. This end of the molecule has a charge and is attracted to water. It is POLAR
HYDROPHOBIC TAILS
The two long chains coming off of the bottom of this molecule are made up of carbon and hydrogen. Because both of these elements share their electrons evenly these chains have no charge. They are NON POLAR. Molecules with no charge are not attracted to water; as a result water molecules tend to push them out of the way as they are attracted to each other. This causes molecules with no charge not to dissolve in water.
3D model of a Phospholipid
AS Biology. Foundation. Cell membranes and Transport

10. A Phospholipid Bilayer
Phospholipids can form:
BILAYERS
-2 layers of phospholipids with
hydrophobic tails protected inside by the hydrophilic heads.
The PHOSPHOLIPID
BILAYER is the basic
structure of membranes.
AS Biology. Foundation. Cell membranes and Transport

11. AS Biology. Foundation. Cell membranes and Transport

12. Structure of the cell membrane
Phospholipids
Cell membranes are made mainly of phospholipids. They have:
HYDROPHILIC heads (water liking)
-Attracted to the water POLAR
HYDROPHOBIC tails (water fearing)
-Not attracted to the water NON-POLAR
Phospholipids can form BILAYERS
-2 layers of phospholipids with
hydrophobic tails protected
inside by the hydrophilic
heads.
The PHOSPHOLIPID BILAYER is
the basic structure of membranes.
AS Biology. Foundation. Cell membranes and Transport

13. AS Biology. Foundation. Cell membranes and Transport
Diagram representing the cell membrane Remember the membrane is 7nm wide
AS Biology. Foundation. Cell membranes and Transport

14. AS Biology. Foundation. Cell membranes and Transport
Fluid mosaic model
Cell membranes also contain proteins within the phospholipid bilayer.
This ‘model’ for the structure of the membrane is called the:
FLUID MOSAIC MODEL
FLUID- because individual phospholipids and proteins can move around freely within the layer, like it’s a liquid.
MOSAIC- because of the pattern produced by the scattered protein molecules when the membrane is viewed from above.
AS Biology. Foundation. Cell membranes and Transport

15. Diagram of a cell membrane
AS Biology. Foundation. Cell membranes and Transport

16. TEM of freeze-fractured cell membrane.
The fracture occurs between the two phospholipid layers.
You can clearly see the exposed proteins sticking out of the two layers.
Individual phospholipids are too small to see.
AS Biology. Foundation. Cell membranes and Transport

17. Cell Membranes from Opposing Neurons (TEM x436,740).
} Phospholipid Bilayer
7nm wide
AS Biology. Foundation. Cell membranes and Transport

18. Features of the fluid mosaic model
Double layer – BILAYER of phospholipids which can move about by ………………………… in their own ……………………….
Phospholipid tails point inwards forming a ……. ………. ………………………… interior. The phospholipid heads point outwards facing the aqueous (water containing) medium surrounding the membrane.
Some phospholipids fatty acid tails are ……………………….. – straight so fit together tightly. Some are ………………………… – bent so fit together ……………………. The more unsaturated tails there are the more ……………… the membrane becomes. The lower the temp, the ……………….fluid.
Most protein molecules …………………. like icebergs in the layers, some are fixed to ………………………. inside the cell and don’t float.
Some proteins are embedded in the outer layer, some in the inner layer and some ………………… the two layers. Hydrophobic and Hyrdophilic parts of the protein molecules sit next to the …………………………… and ………………………….. portions of the ……………………………… of the membrane. This ensures the proteins stay in the membrane.
The membrane is ……nm thick on average.
Some phospholipids have carbohydrates attached to them called- ………………………..
Some of the proteins have carbohydrates attached to them called– ……………………
The membrane also contains molecules of ………………………………..
AS Biology. Foundation. Cell membranes and Transport

19. Features of the fluid mosaic model
Double layer – BILAYER of phospholipids which can move about by DIFFUSION in their own MONOLAYER
Phospholipid tails point inwards forming a NON-POLAR HYDROPHOBIC interior. The phospholipid heads point outwards facing the aqueous (water containing) medium surrounding the membrane.
Some phospholipids fatty acid tails are SATURATED – straight so fit together tightly. Some are UNSATURATED – bent so fit together loosely. The more unsaturated tails there are the more ‘fluid’ the membrane becomes. The lower the temp, the less fluid.
Most protein molecules float like icebergs in the layers, some are fixed to structures inside the cell and don’t float.
Some proteins are embedded in the outer layer, some in the inner layer and some span the two layers. Hydrophobic and Hyrdophilic parts of the protein molecules sit next to the Hydrophobic and Hydrophilic portions of the phospholids of the membrane. This ensures the proteins stay in the membrane.
The membrane is 7nm thick on average.
Some phospholipids have carbohydrates attached to them – GLYCOLIPIDS
Some of the proteins have carbohydrates attached to them – GLYCOPROTEINS
The membrane also contains molecules of CHOLESTEROL
AS Biology. Foundation. Cell membranes and Transport

20. Roles of components of cell membranes
Using the following headings produce a table on A4 to summarise roles of t he
different types of molecules found in the cell membrane. Try not to copy, pick
out the relevant information and write it in note form You may want to use
bullet points, different coloured pens etc basically whatever helps you to remember them.
There will be a short test on this next lesson! Use pages
Component Function
Phospholipids
Cholesterol
Proteins
Glycolipids and Glycoproteins
AS Biology. Foundation. Cell membranes and Transport

21. AS Biology. Foundation. Cell membranes and Transport
Summary
Cell membranes have a basic structure composed of a PHOSPHOLIPID BILAYER.
Phospholipds have HYDROPHOBIC (non-polar) tails and HYDROPHILIC (polar) heads.
The best model of the cell membrane is called the FLUID MOSAIC MODEL
The average thickness of the membrane is 7nm.
The fatty acid tails of phospholipids can be SATURATED (straight) or UNSATURATED (bent)
Proteins can float or be fixed and also have hydrophobic and hydrophilic portions.
Some proteins and phospholipids have carbohydrates attached to them to form GLYCOPROTEINS AND GLYCOLIPIDS.
Phospholipids form the bilayer, act as barrier to most water soluble substances
Cholesterol regulates the fluidity of the membrane, gives mechanical stability and help to prevent ions from passing through the membrane.
Proteins act as transport proteins to act as channels for substances to move into or out of the cell. Some act as membrane enzymes and some have important roles in membranes of organelles.
Glycolipids and Glycoproteins help to stabilise membrane structure, some act as receptor molecules eg for hormones and neurotransmitters or as antigens for other cells to recognise them.
AS Biology. Foundation. Cell membranes and Transport

22. Movement of selected molecules across the cell membrane
AS Biology. Foundation. Cell membranes and Transport

23. AS Biology. Foundation. Cell membranes and Transport
Moving amoeba
AS Biology. Foundation. Cell membranes and Transport