TRANSPORT ACROSS CELL MEMBRANES examQs

• Explain the function of this ATP hydrolase (in Na/K pump). [2]

  Hydrolyses ATP to ADP and Pi, releasing energy

  energy allows for transport of ions against concentration gradient
• The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum. Explain how. [2]

  Maintains a diffusion gradient/concentration gradient for sodium ions

  sodium ions move in by facilitated diffusion/co-transport and bring glucose with it
• Describe and explain two features you would expect to find in a cell specialised for absorption. [2] (ANY 2)

  Many mitochondria, to make more ATP

  many carrier/channel proteins so fast rate of absorption

  microvilli so provide large surface area for absorption
• The movement of substances across cell membranes is affected by membrane structure. Describe how. [5]

  cholesterol affects fluidity/permeability/rigidness

  phospholipid bilayer allows transport of non-polar substances

  phospholipid bilayer prevents transport of polar substances

  carrier proteins allow for active transport of substances

  carrier/channel proteins allow facilitated diffusion/co-transport of substances

  shape of channel/carrier protein determines which substances move
• Give two similarities in the movement of substances by diffusion and by osmosis. [2]


  both have movement down a gradient

  both are passive OR both don't use energy from ATP
• Suggest how the increase in temperature of the water caused the release of the red pigment (from beetroot, out of cell surface membrane). [2]

  Damage to cell surface membrane

  causes proteins in cell membrane to denature

  increases fluidity/damage to the phospholipid bilayer
• NHE3 actively transports one sodium ion into the cell in exchange for one proton (hydrogen ion) out of the cell. Use your knowledge of transport across cell membranes to suggest how NHE3 does this. [3]

  Co-transport

  uses hydrolysis of ATP

  sodium ion and proton bind to the carrier protein

  protein changes shape (allows movement of the sodium ion across membrane)
• High absorption of salt from the diet can result in a higher than normal concentration of salt in the blood plasma entering capillaries. This can lead to a build-up of tissue fluid. Explain how. [2]

  more salt results in higher blood pressure

  so more tissue fluid forced out of capillary at arteriole end

  OR

  high salt content so lower water potential of the tissue fluid

  so less water returns to capillary by osmosis
• Contrast the processes of facilitated diffusion and active transport. [3]

  Facilitated diffusion takes place down a concentration gradient whereas active transport can take place against a concentration gradient

  facilitated diffusion doesn't require ATP but active transport does

  Facilitated diffusion involves carrier or channel proteins whilst active transport only involves carrier proteins