Cell membrane

• What is the role of cholesterol in cell membrane


  Cholesterol provides membrane stability and flexibility, preventing the membrane from becoming too rigid or too fluid
• What are glycoproteins and glycolipids responsible for

  glycoproteins and glycolipids are involved in cell recognition,communication and the immune response
• What is meant by selective permeability of the cell membrane


  it means the cell membrane regulates what enters and exits the cell allowing small non-polar molecules like oxygen to pass while restricting larger or charged molecules
• How is cell signalling related to the cell membrane

  receptor proteins on the membrane detect signals and trigger a cellular response
• What are endocytosis and exocytosis

  these are processes where the cell use vesicles to transport large molecules or particles into (endocytosis)or out of (exocytosis)
• What is passive transport

  Passive transport includes diffusion, faciliated diffusion and osmosis, where substances move along their concentration gradient without energy
• What is active transport

  active transport requires ATP to move substances against their concentration gradient often using carrier proteins
• How does water move across the cell membrane

  Water moves by osmosis from an area of higher water potential to an area of lower water potential
• What affects water potential?

  Water potential is influenced by solute concentration and pressure
• What are glycoproteins and their function

  • A recognition site for chemicals
  • made up carbohydrates and protein
  • attached to a protein
• What are glycolipids


  • acts as a receptor site to identify other cells
  • triggers a immune resposne
  • attached to a hydrophillic head from a phospholipid
• instrinsic protein

  • transporting substances such as charged or large molecules that cannot diffuse across the membrane
  • receptors for hormones and neurotransmitters or enzyme for catalyzing reactions
• Extrinsic proteins

  • not all they way through the membrane surface or bound to an instrinsic protein
  • the Extrinsic on the extracellular side of the membrane act as receptors for hormones or transmitters
  • extrinsic proteins on the cytosolic side of the membrane and is involved in cell signalling or chemical reactions
• What is role phospholipids ?

  • acts as barrier to most substances helping control what enters/exits the cell
  • the smaller and less polar a molecule the easier and faster it will diffuse across a cell membrane
  • small, non-polar molecules such as oxygen and carbon dioxide rapidly diffuse across a membrane
  • small polar molecules such as water and urea also diffuse across but much more slowly
• How does the temperature affect membrane structure?

  As the temperature increases, the kinetic energy of the phospholipid increases creating a gap between the bilayer. This means more molecules can pass through the gaps increasing the permeability of the membrane.
• How does solvents like alcohol affect the membrane structure?

  Solvents like alcohol or are less polar or benzene which is not polar and this can move into the bilayer disrupting the structure.
• A fluid membrane is needed for:


  • diffusion accross the membrane
  • membranes to fuse to vesicles
  • cells to move and change shape via phagocytosis
• What is diffusion?


  Difffusion is the net movement of particles down a concentration gradient: from a region of higher concentration to region of lower concentration
• What is an example of a passive transport?


  • Diffusion
  • Osmosis
• Factors that increase the rate of diffusion


  Diffusion is directly proportional to the surface area and difference in concentration. Therefore increasing the surface or increasing the difference in concentration will increase the rate of diffusion
• Factors that decrease the rate of diffusion


  The rate of diffusion is inversely proportional to the length of the diffusion path. Increasing the distance of the diffusion path will decrease the rate
• What is facillated diffusion


  • Polar or large molecules cannot pass straight through the bilayer
  • Carrier proteins or protein channels allow the molecules to pass through
  • Passive process
• What is osmosis


  Osmosis is the net movement of water molecules from a higher water potential to a lower potential across a partially-permeable membrane
• What is water potential?

  The tendency of water molecules in a system move
• The more solute you have in water the what?

  The more negative the kilopascals become
• What is the highest water potential?


  0 kilopascal - Pure water
• Why is it that the greater the amount of solute, the lower the water potential?

  This is because water molecules bind to the solute molecules reducing the number of water molecules that are free to diffuse
• How does pressure potential affect water potential?


  The greater the pressure, the higher water potential
• Only things that are what affect the osmotic concentration

  only things that are soluble
• Explain why dissolving more solute decrease the water potential of a solution?


  More solute will be in the concentration than water which means more water will be attracted to the solute clustering around it.Therefore less water to move, therefore lower water potential.
• Glucose can also be absorbed by an active process which requires metabolic energy. What is the immediate source of this energy in cells?

  ATP
• Explain why glucose cannot pass through a cell membrane by simple diffusion.

  Glucose is too large to pass through the phospholipid bilayer
• The students concluded that the red pigment began to leak out of the beetroot cells at any pH below pH6. Suggest and explain why a low pH might cause the red pigment to leak out of the beetroot cells.

  A lower pH changes the tertiary structure of the membrane proteins producing gaps for molecules to pass through therefore the permeability is increased letting the pigment leak through.
• How does the fluid mosaic model describe the structure of plasma membranes? 2 marks


  It describes it as having a phospholipid bilayer, the hydrophillic phosphate heads facing outwards and the hydrophobic fatty acids tails facing inwards.
• plasmalysed


  when water exits the plant cell due to its surrounderings have a higher water potential
• lysis


  when too much water goes into the animals cell causing it to burst
• Exocytosis


  • Exocytotic vesicle fused with the plasma membrane
  • Release the products out
  • requires ATP
• Endocytosis


  • The product the cell is trying the ingest approaches it
  • The plasma membrane move its membrane to create a endocytic vesicle
• Tonoplast


  • Vacuole membrane
• What is not a role of an intracellular membrane?

  • cell to cell signalling