NCERT Solutions for Class 11 Biology Chapter 10 Cell Cycle and Cell Division free download in PDF for or to Study online without downloading files. Download Solutions of other subjects and study notes related to all chapters.
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Cell Cycle and Cell Division: Solutions
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Important Notes on Cell Cycle and Cell Division
- Specialised kind of cell division that reduces the chromosomes number by half, hence it is called reductional division.
- Occurs during gametogenesis in plants and animals.
- Involves two sequential cycles of nuclear and cell division called Meiosis I and Meiosis II.
- It results in 4 haploid daughter cells.
- Interphase occurs prior to meiosis which is similar to interphase of mitosis except the S phase is prolonged.
Significance of Meiosis
- Format ion of gametes: In sexually reproducing organisms.
- Genetic variability: Variations are very important for evolution.
- Maintenance of chromosomal number: By reducing the chromosome number in gametes. Chromosomal number is restored by fertilisation of gametes.
- Since the number of chromosomes in the parent and progeny cells is the same, it is called as equational division. Mitosis is divided into four sub stages.
- Replicated chromosomes, each consisting of 2 chromatids, condense and become visible.
- Microtubules are assembled into mitotic spindle.
- Nucleolus and nuclear envelope disappear.
- Centriole moves to opposite poles.
- 2. Metaphase
- Spindle fibres attached to kinetochores (small disc-shaped structures at the surface of centromere) of chromosomes.
- Chromosomes line up at the equator of the spindle to form metaphase plate.
- 3. Anaphase
- Centromeres split and chromatids separate.
- Chromatids move to opposite poles due to shortening of spindal fibres.
- 4. Telophase
- Chromosomes cluster at opposite poles.
- Nuclear envelope assembles around chromosomes clusters’.
- Nucleolus, Golgi Complex, E.R. reforms.
Significance of Mitosis
- Growth-addition of cells.
- Maintenance of surface/volume ratio. Maintain Nucleo-cytoplasmic ratio.
- Maintenance of chromosomes number.
- Reproduction in unicellular organisms, lower plants and some insects.
- Repair and wound healing.
- Vegetative reproduction in plants takes place by mitosis.