TRANSPORT ACROSS MEMBRANES EXAM QUESTIONS

• Name and describe five ways substances can move across the cell-surface membrane into a cell.

  • Simple diffusion of small, non polar molecules down a concentration gradient
  • Facilitated diffusion down a concentration gradient via a channel proteins or carrier protein
  • Osmosis of water down a water potential gradient
  • Active transport against a concentration gradient via a carrier protein using ATP
  • Co transport of 2 different substances using a carrier protein
• The movement of sodium ions out of the cell allows the absorption of glucose into the cell lining the ileum. Explain how.

  • Maintains a concentration gradient for sodium
  • Sodium moves in by facilitated diffusion and brings glucose with it
• Describe and explain two features you would expect to find in a cell specialized for absorption.

  • Folded membrane / microvilli so there is a large surface area for absorption
  • Large number of co transport / carrier / channel proteins so there is a faster rate of diffusion
  • Large number of mitochondria for aerobic respiration
• The movement of substances across cell membranes is affected by membrane structure. Describe how.

  • The phospholipid bilayer allows the movement / diffusion of non polar / lipid soluble substances
  • Carrier proteins allow active transport
  • Channel / carrier proteins allow facilitated diffusion / co transport
  • Number of channel / carrier proteins determines how much movement there is
  • Cholesterol affects fluidity, rigidity
• Give two similarities in the movement of substances by diffusion and by osmosis.

  • Movement down a concentration from high concentration to low concentration
  • Both passive processes - not active
• Suggest and explain two ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients.

  • The membrane is folded so there is a larger surface area for fast diffusion
  • Large number of carrier / channel proteins in the membrane for facilitated diffusion
• Compare and contrast the processes by which water and inorganic ions enter cells.

  • Comparison : Both move down the concentration gradient
  • Contrast : Ions can move against a concentration gradient by active transport
• Contrast the processes of facilitated diffusion and active transport.

  • Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins
  • Facilitated diffusion does not use ATP where as active transport does
  • Facilitated diffusion takes place down a concentration gradient whereas active transport takes place against a concentration gradient