Exchange of substances T2 Flashcards

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1
Q

Use Fick’s law of diffusion to explain the adaptations of mammalian gas exchange surfaces.
(5)

A
  • Rate of diffusion is proportional to surface area. Alveoli have large surface area.
  • Rate of diffusion is proportional to difference in concentration. Breathing maintains a difference in gas concentrations. As does blood flow.
  • Rate of diffusion is inversely (one increases the other decreases) proportional to diffusion distance. Walls of alveoli and capillaries one cell thick.
  • Diffusion distance is reduced due to flattened cells forming alveoli and capillary walls.
  • Rate of diffusion is proportional to diffusion constant. Cell membranes are permeable to non-polar gas molecules.
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2
Q

What is Fick’s law?

A

Rate of diffusion= surface area x difference in concentration/ thickness of gas exchange surface

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3
Q

Explain why animals need a heart and a circulatory system.

4

A
  • Heart needed to pump blood around the body.
  • Mass flow
  • Many animals have a small surface area to volume ratio.
  • Circulatory system needed to overcome limitations of diffusion.
  • Transport molecules in blood. (Plasma, white blood cells, red blood cells.)
  • Many animals have a high metabolic rate.
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4
Q

Describe and explain how the lungs of a mammal are adapted for rapid gas exchanged.
(5)

A
  • Alveoli one cell thick.
  • Endothelium walls of capillaries one cell thick.
  • Alveoli covered with capillaries.
  • Short diffusion distance.
  • Alveoli and capillaries provide large surface area.
  • Concentration gradient maintained by breathing/ventilation.
  • Large no. of red blood cells, haemoglobin binds to O2.
  • Concentration gradient maintained by blood flow.
  • Fick’s law.
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5
Q

Suggest how the heart of a daphnia enables organs to carry out effective gas exchange.
(2)

A
  • Blood carries oxygen.
  • Blood moving maintains concentration gradient.
  • Massflow.
  • Organs have a large surface area to volume ratio.
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6
Q

In mammals, blood passes through the heart twice for each circulation of the body. Suggest how this type of circulation enables mammals to carry out effective gas exchange.
(3)

A
  • One side of the heart transports blood to lungs, other the body.
  • Sep. of oxygenated and deoxygenated blood.
  • Maintaining concentration gradient.
  • Blood pressure lower to lungs, higher to body.
  • Mass flow.
  • Need good supply of oxygen as mammals have high metabolic rate.
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7
Q

Explain how the partial permeability of the surface membrane of the cells lining the bronchi allows osmosis to take place.
(2)

A
  • Partial permeability is a barrier to some solutes but not water.
  • Enables a concentration gradient of water/solutes.
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8
Q

Histamine increases the permeability of capillary walls so that large molecules can pass through. Explain how this change in permeability results in swelling around the bite.
(4)

A
  • Proteins can move into tissue fluid.
  • Lowers water potential of tissue fluid.
  • Increases tendency to draw water out.
  • Reduces tendency to reabsorb water.
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