2.4 Membranes
Topic 2 Cells
Membranes
2.4.1 Draw and label a diagram to show the structure of
membranes.
2.4.2 Explain how the hydrophobic and hydroph...
Membranes
2.4.4 Define diffusion and osmosis.
Diffusion is the passive movement of particles from a region of
high concent...
Membranes
2.4.5 Explain passive transport across membranes by simple
diffusion and facilitated diffusion.
2.4.6 Explain th...
The Fluid Mosaic Model
In 1972, Singer and Nicolson proposed a model for the
membrane structure in which a mosaic of prote...
The Fluid Mosaic Model
Ref: Advanced Biology Roberts etal.
The Fluid Mosaic Model
The phospholipid bi-layer consists of a double layer of
phospholipid molecules.
The phospholipid mo...
Fluidity of Membranes
Phospholipids in membranes are in a fluid state.
This allows membranes to change shape in a way that...
Membrane Proteins
Membrane proteins can be:
– Integral Proteins
• Protein molecules embedded in the fluid phospholipid bil...
Membrane Proteins
Ref: IB Biology OSC
Membrane Proteins
Membrane proteins can have many different functions:
– Hormone binding sites
– Enzymes
– Electron carrie...
Membrane Proteins
Ref: Allott
Diffusion
Diffusion is the passive movement of particles from a region of
higher concentration to a region of lower concen...
Diffusion
Ref: Allott
Diffusion
Some substances can diffuse through membranes.
Small uncharged particles pass between the lipid molecules.
– eg:...
Diffusion Through Channel Proteins
Some substances pass through channel proteins.
Channel proteins are concerned with tran...
Facilitated Diffusion Through Channel Proteins
Some substances are larger and require carrier proteins to move
them throug...
Osmosis
Osmosis is the passive movement of water molecules from a region
of lower solute concentration to a region higher ...
Active Transport
Active transport is the movement of substances across a
membrane using energy from ATP.
Active transport ...
Active Transport
Active transport allows cells to take up nutrients when their
concentrations outside the cell are low.
Al...
Exocytosis and Endocytosis
Sometimes substances need to be moved into or out of a cell
that can’t be done by diffusion or ...
Exocytosis
Sometimes large molecules need to be expelled from the cell.
This is done by a process called:
– Exocytosis
The...
Exocytosis
Ref: Biology Key Ideas
Endocytosis
Small molecules can enter and leave cells through the plasma
membrane by diffusion or active transport.
Someti...
Endocytosis
Ref: Biology Key Ideas
Transportation Using Vesicles
Ref: Advanced Biology Roberts etal.
Phagocytic Intake and Digestion
1. Small particles are taken in by
phagocytosis to form a phagocytic
vesicle.
2. A lysosom...
IBO guide:
2.4.1 Draw and label a diagram to show the structure of
membranes.
The diagram should show the phospholipid bil...
IBO guide:
2.4.2 Explain how the hydrophobic and hydrophilic properties of
phospholipids help to maintain the structure of...
IBO guide:
Osmosis is the passive movement of water molecules, across a
partially permeable membrane, from a region of low...
IBO guide:
2.4.7 Explain how vesicles are used to transport materials within a
cell between the rough endoplasmic reticulu...
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2.4 membranes

  1. 1. 2.4 Membranes Topic 2 Cells
  2. 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. 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. 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. 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
  6. 6. The Fluid Mosaic Model Ref: Advanced Biology Roberts etal.
  7. 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. 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. 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.
  10. 10. Membrane Proteins Ref: IB Biology OSC
  11. 11. Membrane Proteins Membrane proteins can have many different functions: – Hormone binding sites – Enzymes – Electron carriers – Channels for passive transport – Pumps for active transport
  12. 12. Membrane Proteins Ref: Allott
  13. 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.
  14. 14. Diffusion Ref: Allott
  15. 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. 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. 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. 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. 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. 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. 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. 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.
  23. 23. Exocytosis Ref: Biology Key Ideas
  24. 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
  25. 25. Endocytosis Ref: Biology Key Ideas
  26. 26. Transportation Using Vesicles Ref: Advanced Biology Roberts etal.
  27. 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. 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. 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. 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. 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.

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