Biology Class 11 NCERT Solutions: Chapter 10 Cell Cycle and Cell Division Part 1

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Q: 1. What is the average cell cycle span for a mammalian cell?

Answer:

The average cell cycle span for a mammalian cell is approximately 24 hours.

Image shows the cell cycle span

Image Shows the Cell Cycle Span

Image shows the cell cycle span

Q: 2. Distinguish Cytokinesis from karyokinesis.

Answer:

Difference between Cytokinesis and Karyokinesis
Difference between cytokinesis and karyokinesis

Cytokinesis

Karyokinesis

(i)

Cytokinesis is the biological process involving the division of a cell’s cytoplasm during mitosis or meiosis.

(i)

Karyokinesis is the biological process involving the division of a cell’s nucleus during mitosis or meiosis.

(ii)

It is divided into four stages-prophase, metaphase, anaphase, and telophase.

(ii)

Stages such as prophase, metaphase, anaphase, and telophase are not present in karyokinesis.

Q: 3. Describe the events taking place during interphase.

Answer:

Interphase 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) phase

(ii) S phase

(iii) phase

phase - It is the stage during which the cell grows and prepares its DNA for replication. In this phase, the cell is metabolically active.

S phase - 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.

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

Interphase and mphase

Interphase and Mphase

Interphase and mphase

Q: 4. What is (quiescent phase) of cell cycle?

Answer:

or quiescent phase is the stage wherein cells remain metabolically active, but do not proliferate unless called to do so. Such cells are used for replacing the cells lost during injury.

Image shows the stage of cell cycle

Image Shows the Stage of Cell Cycle

Image shows the stage of cell cycle

Q: 5. Why is mitosis called equational division?

Answer:

Mitosis is the process of cell division wherein the chromosomes replicate and are equally distributed into two daughter cells. The chromosome number in each daughter cell is equal to that in the parent cell, i.e., diploid. Hence, mitosis is known as equational division.

Image shows the mitosis

Image Shows the Mitosis

Image shows the mitosis

Q: 6. Name the stage of cell cycle at which one of the following events occur:

(i) Chromosomes are moved to spindle equator

(ii) Centromere splits and chromatids separate

(iii) Pairing between homologous chromosomes takes place

(iv) Crossing over between homologous chromosomes takes place

Answer:

(i) Metaphase

(ii) Anaphase

(iii) Zygotene of meiosis I

(iv) Pachytene of meiosis I