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MCBN 171: Calculate the Surface area-to-Volume ratio of a Cube 4 mm and a Cube 8 mm.: Molecular And Micro Biology Assignment, NWU, South Africa

University North-West University (NWU)
Subject MCBN 171: Molecular And Micro Biology


(a)Calculate the surface area-to-volume ratio of a cube 4 mm and a cube 8 mm.

(b)What is the significance of a large surface-area-to-volume ratio for a cell?

(d)  Which exact type of microscope would you use to study

(i) changes in the shape of a living human white blood cell?

(ii) details of the surface texture of human hair?

(iii)detailed structure of an organelle of a human liver cell?

(e)Cyanide binds with at least one of the molecules involved in the synthesis of ATP. Following exposure of a cell to cyanide, most of the cyanide would be expected to be found in the

A. ribosome

B.  mitochondria

C.   lysosome

D. peroxisomes

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Mammalian red blood cells are sensitive to a change in salt concentration of the external environment. If they are transferred from plasma to a less concentrated solution they swell. If they swell sufficiently they burst, in which case they are said to be haemolyzed. In an experiment to find the percentage of human red blood cells haemolyzed at different concentrations, the following results were obtained:

Salt concentration (g/l) % red blood cells haemolyzed
3.2 100
3.4 97
3.6 81
3.8 53
4.0 30
4.2 13
4.4 3

(a)     Plot the results on a graph paper, making sure the dependent variable is on the vertical axis. The graph should be drawn on graph paper (a freehand graph) which has to be scanned and submitted with the assignment as an attachment

(b) Explain why red blood cells swell and burst when placed in a dilute salt solution

(c)Explain why a plant cell does not burst under the same situation as in 2 above

(d)At what concentration is the proportion of haemolyzed to non-haemolyzed cells equal?

Indicate your answer clearly on the graph

(e)Amoeba is a protest that lives in freshwater. What osmotic problem(s) are faced by a unicellular organism like and how does it overcome them?

(e) How do marine organisms osmotically adapt to living in an environment which has such a high salinity?


A range of concentrations of sucrose solutions is used to find the concentration of the solution which causes no change in weight or size of tissue immersed in it. The result of such an investigation are given in the figure below:

a. Write down the solute concentration of the potato chip. Explain

b. What is happening to the cells in the sucrose solution of 0.3 M? Explain.

c. What is happening to the cells in a sucrose solution of 0.8 M? Explain (2)

The turgidity of tissue immersed in solutions can be demonstrated as follows: Identical potato chips are left in (A) water and in (B) 20% sucrose solution.

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