Category: Biology Second Paper

Chromosomes are covered by a membrane called pellicle. Modern studies have found no attachment to the pellicle. Scientists Mc Clinton and Swanson mentioned the pellicle. But scientists Darlington, Novikoff and Rees deny Pellicol’s existence.

1. All embryo cells divide by the process of mitosis to become multicellular plants or animals. Without mitosis, embryos do not form.
2. The development and growth of various organs of the organism takes place in the process of mitosis.
3. All organelles in multicellular organisms divide by mitosis.
4. Plant roots, stems and leaves grow in the process of mitosis.
5. Cuttings, layering, grafting etc. are produced by division of mitosis.

1. The number of germ cells increases by mitosis in the process of spermatosis and oogenesis.
2. Lower plants reproduce by mitosis cell division. Chlamydomonas and Chlorella reproduce by mitosis.
3. Cuttings, layering, grafting etc. are produced by division of mitosis.
4. Genitalia of multicellular organisms are formed through mitosis cell division. This process is necessary to increase the number of reproductive cells.

 

1. Body structure and physical growth: The number of cells in the body increases through mitosis cell division. It forms the organism’s body and physical growth takes place.
2. Reproduction: The number of reproductive cells increases by mitosis in the process of spermatosis and oogenesis. Lower class plants reproduce by mitosis. Chlamydomonas and Chlorella reproduce by mitosis.
3. Chromosome Equality or Continuity: In the absence of mitosis cell division, the number of chromosomes in the body cells of the organism will not be equal. In this, the maternal quality will not remain intact in the organism’s body.
4. Balance of nucleus and cytoplasm: In the process of mitosis, the cytoplasm and nucleus of the organism are divided once. As a result, equality is maintained. So the balance of nucleus and cytoplasm is preserved (NP index = Nucleoplasmic index).
5. Propagation: Roots are produced by mitosis division by cutting, layering, grafting etc.
6. Wound healing: When a wound occurs anywhere in the organism, it is healed through mitosis. But if mitosis does not occur it will never be completed.
7. Reproduction: The lifespan of any cell in the living body is limited. After all these cells are destroyed, they are produced again and again in the process of mitosis.
8. Specific size-volume: The size and volume of the organism is determined by mitosis cell division.
9. Genital formation and increase in the number of reproductive cells: Genital formation occurs in multicellular organisms through mitosis cell division. This process is necessary to increase the number of reproductive cells.
10. Stability of qualitative characteristics: The quality of progeny cells produced by mitosis cell division is similar to that of the mother cell. That is, there is no change in quality. So the qualitative characteristics remain stable in the living world.
11. Cancer formation: Uncontrolled mitosis cell division is called neoplasia. If the neoplasia cells are confined to one place, it is called benign neoplasia. When the resulting cells spread to different parts of the body, it is called malignant neoplasia. Neoplasia causes cancer and tumors.
12. Continuous Replenishment: Cells that have a fixed lifespan are replenished through mitosis. Mitosis replaces old and damaged cells.
13. Maintenance of genetic homogeneity: In mitosis cell division, cell quality remains intact and no genetic changes occur. As a result, the genetic homogeneity or stability of the cells is maintained.
14. Orderly Growth: Orderly growth of the body occurs through mitosis cell division. In this, the number and quality of chromosomes of the offspring cells are the same, so the growth of the organism is orderly.
15. Red blood cell production: The lifespan of red blood cells is 120 days. Red blood cells are produced in the bone marrow and liver in the process of mitosis.
16. Chemical Balance: Nucleic acid, protein and other chemical substances balance is maintained as the number of chromosomes in the progeny cells created in the process of mitosis is equal.
17. Uncontrolled mitosis: Uncontrolled mitosis causes tumors and cancer in the body.

Termination of cell life due to external and internal causes is called death. Millions of cells die in the human body every day. Cell death occurs in two ways. Necrosis and apoptosis.
1. Necrosis: Cell death due to lack of nutrients or toxic substances is called necrosis. Deficiency of one or more of the micronutrients and macronutrients can cause cell death. Toxins enter the body in various ways, chemical reactions produce toxins, and excess drugs accumulate as toxins. These toxins can cause cell death.
2. Apoptosis: Apoptosis is genetically controlled death. In this process, unnecessary body cells or organs die. Apoptosis is the destruction or death of tissue between human fingers. Apoptosis causes red blood cells, white blood cells and platelets to die after a certain period of time. If these cells survive for a long time, they can become cancer. The role of apoptosis in human body is-
(i) Finger differentiation during embryonic development is by apoptosis.
(ii) Dorsal neural tube closure due to apoptosis.
(iii) Remnants of dying organelles (pro-nephrons) are removed from the body by apoptosis.
(iv) Wolffian ducts are removed by apoptosis during embryonic sex determination.
(v) Residual tissue between the umbilical cord and the sac is removed by apoptosis during embryonic development.

Apoptosis is genetically controlled death. In this process, unnecessary body cells or organs die. Apoptosis is the destruction or death of tissue between human fingers. Apoptosis causes red blood cells, white blood cells and platelets to die after a certain period of time. If these cells survive for a long time, they can become cancer. The role of apoptosis in human body is-
(i) Finger differentiation during embryonic development is by apoptosis.
(ii) Dorsal neural tube closure due to apoptosis.
(iii) Remnants of dying organelles (pro-nephrons) are removed from the body by apoptosis.
(iv) Wolffian ducts are removed by apoptosis during embryonic sex determination.
(v) Residual tissue between the umbilical cord and the sac is removed by apoptosis during embryonic development.

Cell death due to lack of nutrients or toxic substances is called necrosis. Deficiency of one or more of the micronutrients and macronutrients can cause cell death. Toxins enter the body in various ways, chemical reactions produce toxins, and excess drugs accumulate as toxins. These toxins can cause cell death.

1. Classification based on characteristics: Chromosomes are divided into two groups based on characteristics.

(i) Autosomes: All the chromosomes present in the body cells of organisms are called autosomes. The number of autosomes is 22 pairs or 44. It does not carry hereditary characteristics.

(ii) Sex Chromosomes: Chromosomes which determine the sex of an organism are called sex chromosomes. Sex chromosomes are called allosomes/heterochromosomes. The number of sex chromosomes is one pair or 2. X and Y.

In 1891, the scientist Henking observed that certain elements of the nucleus were involved in the production of spermatozoa in insects. He named it X-body. It is recognized as the X chromosome in sex determination. Later another sex chromosome was discovered in males. It is called Y chromosome. Sex chromosomes can be carriers of color blindness or hemophilia. This problem is called Sex Linked Inheritance.

2. Classification based on position of centromere: Chromosomes are divided into four parts based on the position of centromere.

(i) Metacentric Chromosome: Chromosome which lies in the center of centromere is called metacentric chromosome. During the anaphase phase of cell division, the metacentric chromosomes look like the English letter V. Amphibians have metacentric chromosomes. All chromosomes of Solanum nigrum are metacentric. Human chromosomes 1, 3, 6, 7, 8, 11, 16, 19, 20 and X are metacentric types.

(ii) Sub-metacentric chromosomes: Chromosome which is slightly away from the center of centromere is called sub metacentric chromosome. During the anaphase phase of cell division, the sub-metacentric chromosomes look like the English letter L. Human chromosomes 2, 4, 5, 9, 10, 12, 17 and 18 are of sub metacentric type.

(iii) Acrocentric Chromosome: Chromosome which is near the edge of centromere is called acrocentric chromosome. In the anaphase phase of cell division, acrocentric chromosomes look like the English letter O. All acrocentric chromosomes are sat-chromosomes. Human chromosomes 13, 14, 15, 21, 22 and Y are acrocentric types.

(iv) Telocentric Chromosome: Chromosome which is located at the extreme end of centromere is called telocentric chromosome. During the anaphase phase of cell division, the telocentric chromosomes look like the English letter I. Telocentric chromosomes are rare in organisms. Humans do not have telocentric chromosomes. Telocentric chromosomes are found in gymnosperms (Welwitschia) and onion (Allium).

[The dark purple variant of Typhonium trilobatum has 11 metacentric, 4 sub-metacentric and 2 acrocentric chromosomes]

 

3. Classification based on the number of centromeres: Chromosomes are of five types according to the number of centromeres.

(i) Acentric Chromosome: A chromosome which does not have a centromere is called an acentric chromosome. It is the fragile part of the chromosome. It does not participate in cell division as it does not have a centromere.

(ii) Monocentric Chromosome: Chromosome having only one centromere is called monocentric chromosome. Chromosomes in most species are monocentric.

(iii) Dicentric Chromosome: A chromosome having two centromeres is called a dicentric chromosome. Wheat, Bhutra, yeast and Dsophila fly have dicentric chromosomes.

(iv) Polycentric Chromosome: A chromosome having more than two centromeres is called a polycentric chromosome. Banana plants, Luzula purpurea, Spirogyra and roundworms have polycentric chromosomes.

(v) Diffuse Chromosomes: If the centromeres are isolated in a chromosome, it is called diffuse chromosome. Banana plants have diffuse chromosomes.

4. Classification of dye retention: Chromatin material is divided into two types based on dye retention.

(i) Euchromatin: The part of the chromosome which becomes light colored when stained with alkaline dye is called euchromatin. This region contains a large amount of DNA and plays an important role in heredity. It synthesizes mRNA.

(ii) Heterochromatin: The part of the chromosome which becomes dark when stained with alkaline dye is called heterochromatin. These regions contain small amounts of DNA and do not play a significant role in heredity. It does not synthesize mRNA.

Chromatin material is divided into two types based on dye retention.
(i) Euchromatin: The part of the chromosome which becomes light colored when stained with alkaline dye is called euchromatin. This region contains a large amount of DNA and plays an important role in heredity. It synthesizes mRNA.
(ii) Heterochromatin: The part of the chromosome which becomes dark when stained with alkaline dye is called heterochromatin. These regions contain small amounts of DNA and do not play a significant role in heredity. It does not synthesize mRNA.

Chromosomes are of five types according to the number of centromeres.
(i) Acentric Chromosome: A chromosome which does not have a centromere is called an acentric chromosome. It is the fragile part of the chromosome. It does not participate in cell division as it does not have a centromere.
(ii) Monocentric Chromosome: Chromosome having only one centromere is called monocentric chromosome. Chromosomes in most species are monocentric.
(iii) Dicentric Chromosome: A chromosome having two centromeres is called a dicentric chromosome. Wheat, Bhutra, yeast and Dsophila fly have dicentric chromosomes.
(iv) Polycentric Chromosome: A chromosome having more than two centromeres is called a polycentric chromosome. Banana plants, Luzula purpurea, Spirogyra and roundworms have polycentric chromosomes.
(v) Diffuse Chromosomes: If the centromeres are isolated in a chromosome, it is called diffuse chromosome. Banana plants have diffuse chromosomes.