Key area 2: transport across cell membranes

• what is the cell membrane made up of?

  a bilayer of phospholipids with protein scattered throughout

  
• what does selectively permeable mean?

  allows certain (small soluble) molecules to pass through but not others (large insoluble molecules)
• what is the cell membrane described as ?

  selectively permeable
• What substances can pass through the cell membrane (small soluble)?

  glucose, fatty acids, amino acids
• what substances cannot pass through the cell membrane (large insoluble)?

  cells, proteins, fats, startch
• what is diffusion?


  The movement of particles from an area of high concentration to an area of low concentration, down a concentration gradient
• what is a concentration gradient?


  the difference in the concentration of a substance between two areas
• when does diffusion stop?

  when the concentration of the substance is equal in both areas
• what is passive transport?

  Movement of molecules across a cell membrane without the use of energy, down a concentration gradient (e.g osmosis/diffusion)
• what is osmosis?


  The movement of water molecules from an area of high concentration to an area of low concentration through a selectively permeable membrane
• what kind of transport does osmosis use?

  passive transport down a concentration gradient, no energy is required
• What happens when a plant cell is placed in pure water?

  it becomes turgid as water enters the cell
• what does turgid mean?

  when the vacuole becomes swollen and pushes against cell, but the cell wall stops it from bursting
• what does plasmolysed mean?

  the vacuole has shrunk
• what happens when an plant cell is placed in 95% sugar?

  it becomes plasmolysed as water moves out
• what happens when an animal cell is placed in strong sugar solution?

  water moves out and the cell shrinks, shrivels and looses weight
• what happens when an animal cell is placed in pure water?

  water moves in and the cell bursts as there is no cell wall to support it
• what is active transport?

  the movement of molecules against a concentration gradient, from an area of low concentration to an area of high concentration (requires energy)
• what type of energy is needed for active transport?

  ATP from respiration