Explain the following terms: [4 MARKS]
(i) Cell cycle                 (ii) Diploid cell              (iii) Chromosome number


i) 2 Marks
ii) 1 Mark
iii) 1 Mark

(i) Cell cycle: Genetically controlled series of changes that occur in a newly formed cell by which it duplicates its contents, undergoes growth and division to form two daughters is called cell cycle. The cell cycle consists of two stages or period:
(a) a long non-dividing growing I-phase or interphase, and 
(b) a short dividing M-phase. Both the stages have sub-stages. Interphase consists of a series of changes that take place in a newly formed cell and its nucleus before it becomes capable of division again. Therefore, it is also called intermitosis. It is also called resting stage because there is no apparent activity related to cell division. The interphase stage is also regarded as the energy phase. At the end of interphase, the cell becomes ready for equitable division into two equal daughter cell. Interphase occupies 75-90% of the total generation time. However, the non-dividing stage of the mature cell and its nucleus is also called interphase. It lasts throughout the life of the cell.

(ii) Diploid cell: Any cell having two of each type of chromosome is called a diploid cell.

(iii) Chromosome number: It is the number of each type of chromosome characteristic of species.

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