Q30 of 50 Page 5

Describe with a diagram the fluid mosaic organisation of the plasma membrane.

Fluid mosaic organisation: It was proposed in the early 1970s by S.J. Singer and G. Nicolson. According this model, plasma membrane is composed of a bilayer of phospholipids. There are two types of proteins-intrinsic and extrinsic are embedded in the lipid bilayer. These proteins are:

(i) Intrinsic proteins -They completely cover the lipid bilayer.’


(ii) Extrinsic proteins – These occur either on the outer surface or on the inner surface of lipid layer.


The “fluid” part of the term comes from the belief that the proteins are able to flow and move around in the membrane.

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Write short note on the following:

(a) Golgi apparatus (b) Mitochondria

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Draw a diagram of a plant cell and Label at least eight important organelles in it.

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Give an illustrated account of nucleus.

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Carry out the following osmosis experiment:

Take four peeled potato halves and scoop each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup into a trough containing water.


Now


(a) keep cup A empty;


(b) put one teaspoon sugar in cup B;


(c) put one teaspoon salt in cup C.


(d) put one teaspoon sugar in the boiled potato cup D;


Keep these for 2 hours. Then observe the four potato cups and answer the following


(i) Explain why water gathers in the hollowed portion of B and C.


(ii) Why is potato A necessary for this experiment?


(iii) Explain why water does not gather in the hollowed out portions of A and D?