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Cell Cycle and Cell Division

Short Answer Type

41. Name the stage of cell cycle at which one of the following events occur.

1. Chromosomes are moved to spindle equator.

2. Centromere splits and chromatids separate.

3. Pairing between homologous chromosomes takes place.

4. Crossing over between homologous chromosomes takes place.

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42. Describe the following

1. Synapsis
2. Bivalent
3. Chiasmata.

Draw diagrams to illustrate your answer.

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43.

Discuss with your teacher about.

1. haploid insects and lower plants where cell division occurs, and

2. Some haploid cells in higher plants where cell division does not occur.

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44. Find examples where the four daughter cells from meiosis are equal in size and where they are found unequal in size.

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45. Analyse the events during every stage of cell cycle and notice how the following two parameters change.

1. Number of chromosomes per cell.

2. Amount of DNA content (C) per cell.

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Long Answer Type

46. List the main differences between meiosis and mitosis.

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47. Describe the events taking place during interphase.

Interphase is the resting stage of the cell cycle. It covers 95% of the total duration of a cell cycle. It involves a series of changes that prepare a cell for division. It is the period during which the cell experiences growth and DNA replication in an orderly manner. Interphase is divided into three phases.

(i) G₁phase

(ii) S phase

(iii) G₂phase

G₁phase - It is the interval between mitosis and initiation of DNA replication. It is the stage during which the cell grows and prepares its DNA for replication. In this phase, the cell is metabolically active but there is no replication of the DNA.

S phase - It is known as the synthesis phase as it is the stage during which DNA synthesis occurs. In this phase, the amount of DNA (per cell) doubles, but the chromosome number remains the same.

G₂phase - In this phase, the cell continues to grow and prepares itself for the division. The proteins and RNA required for mitosis are synthesised during this stage.