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Cell : The Unit of Life

Match The Following

161. Match the following

A. Cristae	(i) Flat membranous sacs in stroma
B. Cisternae	(ii) Infoldings in mitochondria
C. Thylakoids	(iii) Disc-shaped sacs in Golgi apparatus.

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Long Answer Type

162. Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles ? State their function and draw labelled diagrams of both.

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Multiple Choice Questions

163. Which of the following is correct :

Cells of all living organisms have a nucleus.
Both animal and plant cells have a well defined cell wall.
In prokaryotes there are no membrane bound organelles.
Cells are formed by de novo from abiotic materials.

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Short Answer Type

164. What is a mesosome in prokaryotic cell? Mention the functions that it performs.

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Long Answer Type

165. What are the characteristics of prokaryotic cells?

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Short Answer Type

166. Multicellular organisms have division of labour. Explain.

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Long Answer Type

167. What is a centromere ? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.

Centromere is a primary constriction present in the chromosome. It provides orientation to chromosome and marks the space for attachment of chromosomal fibres during cell division. The centromere has disc shaped structures called kinetochores on the sides of it.

Depending upon the location of centromere in a chromosome, the chromosome is classified into the following four types :

(a) Telocentric: Centromere is present at the terminals.

(b) Acrocentric: Centromere is present near the terminals resulting in two short arms and two long arms.

(c) Sub- metacentric : Centromere divides the chromosomes into two unequal arms. It lies either below centre or above centre.

(d) Metacentric : Centromere divides the chromosomes into two equal arms with the centromere in the middle.