Theory question 102
Transport in Plants(a) What is transpiration?
(b) (i) Name two types of transpiration (ii) List four factors which affect the rate of transpiration
(c) Describe the mechanisms of opening and closing of the stomata. (d) State:
(i) two similarities and (ii) two differences between transpiration and sweating
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(a) Transpiration is the loss of water in the form of vapour from the aerial parts of a plant, mainly through the stomata of the leaves.
(b)(i) Any two: stomatal; cuticular; lenticular.
(ii) Any four: light intensity; temperature; humidity; wind; availability of soil water; leaf surface area; thickness of cuticle; number/position of stomata (sunken, hairy leaves).
(c) Opening: in light the guard cells photosynthesise (and take in K+ ions/convert starch to sugar), so their solute concentration rises; water enters them from neighbouring cells by osmosis; they become turgid; the thin outer walls stretch more than the thick inner walls, so the cells curve apart and the pore opens.
Closing: in darkness or water shortage the solute concentration of the guard cells falls; water leaves by osmosis; the guard cells become flaccid and straighten, closing the pore.
(d)(i) Both lose water from the body; both cool the organism; water passes out through pores.
(ii) Transpiration occurs in plants through stomata/lenticels vs sweating occurs in mammals through sweat pores; transpiration loses only water vs sweat contains water, salts and urea; water lost as vapour vs lost as liquid; transpiration mainly by day vs sweating day and night.
Explain stomatal movement through osmosis and turgor.