2.1.5 Biological Membranes COMPLETE Flashcards
Roles of the Cell surface membrane
- Barrier to operate cell contents
- Controls movement in and out the cell
- Selective permeability
- Cell Recognition
- Attachment of multiple cells forms tissue
- Cell signalling e.g. the receptor site for hormones
Roles fo internal membranes
- Compartmentalisation
- Isolate Enzymes
- Control Entry and exit
- Attachment of ribosomes ect.
- Isolate DNA
Phospholipids in the membrane
Gives the membrane fluidity
A barrier to large soluble molecules and ions
Allows lipid soluble molecules to pass through
Unsaturated fatty acids have kinks on tails which prevents close packing
Proteins in the membrane
Adds structural support
Used in transport i.e. channel proteins
Act as receptors
Helps cells adhere together
Cholesterol in the membrane
A barrier to stop prevent large water soluble molecules to pass through
Reduces the lateral movement of the phospholipids
Gives mechanical stability
Glycocalyx
Glycoproteins and Glycolipids Receptor sites for hormones Cell markers Act as antigens allowing the cell to recognise self Helps cells adhere together q
Effect of Temperature on Membranes
Increased temp= Increased kinetic energy
therefore membrane becomes more permeable as the phospholipid vibrate and move further apart.
Sometimes membrane breaks down
Effect of Organic Solvents on Membranes
Organic solvents are less polar than water so san dissolve lipids.
Ethanol dissolves lipids on the membrane so it breaks down. Thus becomes more permeable
Diffusion
A passive process which doesn’t require ATP
The net movement of molecules or ions from a. region of high concentration to a region of lower concentration
Factors affecting rate of diffusion
Temperature Ion Size SA Concentration gradient Stirring/ moving Distance
Facilitated Diffusion
Either Channel Proteins for certain ions, i.e. Ca2+ which have a hydrophilic lining
or Carrier Proteins for large polar molecules, glucose binds to the protein so it changes shape and the molecule moves across the membrane
Osmosis
The net movement of water from a high water potential to a region of lower water potential down the gradient across a partially permeable membrane
DEFINITION- Solute
The substance that dissolves in a liquid to form a solution
DEFINITION- Solvent
The liquid in which a solute dissolves in
DEFINITION- Solution
The mixture formed when a solute has dissolved in a solvent
Water Potential
The tendency of water molecules to leave a solution
Animal Cells in Low water potential
CRENATION
Water leaves the cell which disrupts metabolic reactions and enzymes are no longer able to work
Theres a reduction in cell volume
Animal Cells in High water potential
LYSIS
Water enters the cell
The cell membrane cannot withstand pressure and theres no cell wall so the cell bursts
Plant Cells in Low water potential
PLASMOLYSED
Volume decreases as water moves out the cell
Plasma membrane pulls back from the cell wall, if it rips the cell dies.
Plant Cells in High water potential
TURGID
Water enters the cell and volume increases
The cell contents expand and the cell wall is pushed out
Pressure then increase as cell wall pushes back
Active Transport
Movement of molecules or ions through a transport protein across membranes against their concentration gradient. Uses ATP
Examples of Active Transport
- In the roots of plants
- Gut
- Kidney
- Phloem
What will affect Active Transport
Temperature
Oxygen
Poisons
Bulk Transport
- An active process
- Endocytosis
- Exocytosis
- Phagocytosis
- Pinocytosis
Endocytosis
The bulk movement of material into a cell
Exocytosis
The bulk movement of material out of a cell
Phagocytosis
When the cell eats solid material
Pinocytosis
When the cell drinks liquid material
Examples of Bulk Transport
- Hormones
- Plant Cells
- Phagocytes
Cell Signalling
Molecules such as hormones have specific shapes that bind onto receptors on the cell surface membrane
These have complimentary shapes
This stimulates a reaction
