10. Write any three significance of mitosis.
1. Genetic stability:
Daughter cells genetically identical to parent cells.
2. Growth:
As multicellular organisms grow, the number of cells making up their tissues increases. The new cells must be identical to the parent.
3. Repair of tissues:
Damaged cells must be replaced by identical new cells by mitosis.
| Image Video News |
11. Differentiate between mitosis and meiosis.
| Mitosis | Meiosis |
| Number of Chromosomes remain the same | Number of chromosomes is halved |
| Homologous chromosomes line up separately on the metaphase plate | Homologous in pairs at the chromosomes line up metaphase plate |
| Homologous chromosome do not pair up | Homologous chromosome pairup to form bivalent |
| One division | Two divisions |
| Chiasmata do not form and crossing over never occurs | Chiasmata form and crossing over occurs |
| Daughter cells are genetically identical | Daughter cells are genetically different from parent cells |
| Two daughter cells are formed | Four daughter cells are formed |
| Image Video News |
12. Given an account of G0 phase.
Some cells exit G₁ and enters a quiescent stage called Go. The cells remain metabolically active without proliferation.
Cells can exit for long periods in Go phase. In G, cells cease growth with reduced rate of RNA and protein synthesis.
G₁ phase is not permanent. Mature neuron and skeletal muscle remain permanently in Go.
G, cells are not dormant.
| Image Video News |
13. Differentiate cytokinesis in plant cells and animal cells.
| Cytokinesis in Animal Cells | Cytokinesis in Plant cell |
| The contractile mechanism contained in plasma membrane | Division of the cytoplasm often starts during telophase. |
| The ring consists of a bundle of microfilaments assembled from actin and myosin | Phragmoplast contains microtubules actin filaments and vesicles from Golgi apparatus and endoplasmic reticulum. |
| This fibri generates contractile force, that draws the ring inward forming a cleavage furrow in the cell | cell plate grows from centre towards lateral walls. |
| Image Video News |
14. Write about Pachytene and Diplotene of Prophase I
Prophase I
Pachytene:
Bivalent tetrads of meiosis I consist of 4 chromatids and 2 centromeres.
The homologous chromosomes are remain attached at the point called chiasmata.
The exchange of chromatids occurs of homologous chromosome of non sister chromatids is called crossing over.
Thus recombination is completed. This is mediated by the enzyme recombinase.
Diplotene:
The homologous chromosomes remains attached where crossing over has takes place. Its known as chiasmata.
Sister chromatids remain closely associated whereas the homologous chromosomes tend to separate from each other.
But are held together by chiasmata
This sub-stage may last for days or years depending on the sex and organisms.
| Image Video News |