Initial Set-Up of a Model of the Mass Flow Hypothesis for Translocation

Topics: Glucose, Leaf, Sucrose Pages: 2 (530 words) Published: December 13, 2012
02 II (2)| (a) The figure below shows the initial set-up of a model of the mass flow hypothesis for translocation in the phloem.Model of mass flow hypothesis (i) It was observed that the dye moved from osmometer X to osmometer Y during the course of the experiment. Explain this observation according to the mass flow hypothesis. (3 marks) (ii) Explain the function of tubing M in this model. In plants, which tissue serves the same function as tubing M? (3 marks) (iii) Indicate which osmometer represents photosynthetic mesophyll cells in plants during the growing season. Explain your choice. (1 mark) (iv) If a small amount of invertase is added to osmometer X, what will happen to the rate of movement of the dye? Explain your answer. (4 marks) (b) In terms of water relations, explain why animal cells store glycogen instead of simple sugars. (5 marks) (c) Round seeds and wrinkled seeds are two phenotypes of garden pea. The wrinkled phenotype is attributed to the absence of a starch-forming enzyme in the seeds. In terms of water relations, explain why the lack of the starch-forming enzyme will lead to the wrinkled appearance of the garden pea seeds at maturity. (HINT: Garden pea seeds become dehydrated at maturity.) (4 marks)(Total: 20 marks)|

2.(a)(i)the concentrated sucrose solution in X has a lower water potential than the water in flask A (1)-water from flask A moved into X by osmosis (1)
generated a hydrostatic pressure that forced the contents in X (with the dye) to move into Y (1) via the tubing L
(ii)tubing M channelled water from flask B to flask A (1)
this resulted in a continual supply of water for mass flow (1)
M = *Xylem (1)
(iii)X, sucrose formed by the photosynthetic mesophyll cell resembles the low water potential condition in X (1) (accept correct alternatives)
(N.B. No mark for the correct choice of osmometer if...
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