Distinguish between Mitosis and Meiosis on the basis of the following three aspects
- Site of occurrence
- Nature of division of chromosome
- Number of cells produced
Explain the following phenomena related to meiotic cell division
- Separation of chromosome and chromatid
- Crossing over
Or
Distinguish between the cytokinesis of plant cells with the cytokinesis of animal cells on the basis of the following aspects :
- Process
- Time of initiation
- Role of Golgi bodies
Establish the interrelationships among genes, DNA and chromosome.
WBBSE
Class X
Life Science
02 (a) Cell Division and Cell Cycle
5
2022
Distinguish between Mitosis and Meiosis on the following three aspects
| Aspect | Mitosis | Meiosis |
|---|---|---|
| Site of occurrence | Occurs in somatic (body) cells of plants and animals | Occurs in reproductive or germ cells (testes, ovaries, spore mother cell) |
| Nature of division of chromosome | Equational division (chromosome number remains same in daughter cells as parent) | Reductional division (chromosome number is reduced to half in daughter cells) |
| Number of cells produced | Two identical diploid daughter cells | Four non-identical haploid daughter cells |
Phenomena related to meiotic cell division
1. Separation of Chromosome and Chromatid
- In Meiosis I, homologous chromosomes are separated which reduces the chromosome number by half in the gametes/spores.
- In Meiosis II, the chromatids of each chromosome separate, similar to what happens in mitosis.
2. Crossing Over
Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes during Prophase I of meiosis. This process results in new genetic combinations and increases genetic variation among offspring.
Or
Differences between Cytokinesis of Plant Cells and Animal Cells
| Aspect | Plant Cell Cytokinesis | Animal Cell Cytokinesis |
|---|---|---|
| Process | Formation of a cell plate by fusion of vesicles at the centre, which later develops into a new cell wall (phragmoplast method) | Formation of a cleavage furrow (constriction forms at the periphery and moves inward dividing the cell) |
| Time of initiation | Begins during late telophase, generally after karyokinesis | Begins in late anaphase or early telophase, often overlaps with end of nuclear division |
| Role of Golgi bodies | Golgi vesicles collect at the equator and form the cell plate (which becomes the new cell wall) | Golgi bodies do not play a direct role in animal cell cytokinesis |
Interrelationship among Genes, DNA, and Chromosome
- Chromosomes are the gene-bearing, nucleoprotein filaments found in the nucleus of cells. They are composed mostly of chromatin and carry genes arranged linearly.
- DNA is the chemical substance that forms chromosomes and is structured as a double helix. DNA coils and folds to form chromatin reticulum, which condenses to create chromosomes.
- Genes are specific segments of DNA that carry the information necessary for the synthesis of proteins and determine hereditary traits. Each gene occupies a definite position (locus) on a chromosome.
- Thus, chromosomes are made up of DNA, and genes are functional segments of DNA located on chromosomes.
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