Category: Biology Second Paper

Amitosis is formed from the Greek words a meaning not, mito meaning thread and osis meaning state. The process in which a cell directly produces two daughter cells without any complex medium is called amitosis. Walter Flemming first used the term amitosis in 1882. In 1955 scientist Remak first observed amitosis cell division in red blood cells of chick embryos. Amitosis occurs in cells such as bacteria, yeast, amoeba, nostoc, cartilage of vertebrates, embryo membrane, endosperm of seeds etc.

Process of Amitosis cell division
At the beginning of amitosis, cells take in food and grow in size. Its nucleus is also enlarged. The nucleus enlarges and takes the shape of a dumbbell. The cytoplasm of the cell folds inwards. The nucleus then divides into two fragments. The cytoplasm folds further inward. Later the cytoplasm changes into two cells with nucleus
Significance of Amitosis
1. Amitosis is simple cell division process.
2. This process gave rise to complex and advanced cell division.
3. It increases the number of cells rapidly.
4. Lower organisms multiply in this manner.
5. It is very effective in the rapid growth of unicellular organisms.

The name Nucleus is derived from the Latin word Nux-nut. The dense, opaque and spherical organelle located in the protoplasm of the cell which carries the genetic material and controls the vital functions of the cell is called the nucleus. It is also called the nucleus, nucleus and brain of the cell. It is the largest cell organelle.

Dutch scientist Anthony von Leeuwenhoek was the first to observe the lumen or nucleus in the red blood cells of salmon. In 1831, Robert Brown discovered the nucleus from Rasna leaves. In 1882, scientist Strasburger gave the idea of ​​nucleoplasm. In 1953, scientist J. Hammerling sheds light on the function of hereditary characteristics of the nucleus.

Normally each cell has a nucleus. However, cells of Vaucheria, Botrydium, Sphaeroplea, Penicillium, Opalina, Osteoclasts and Paramecium are more numerous. Multinucleated plant cells are called sinocytes. Animal cells with multiple nuclei are called syncytium. Stem cells, stem cells and mammalian red blood cells (except camels) do not have a nucleus. Nucleus may occupy 10-15% of cell space. About 90% of sperm are nuclei.

The nucleus is usually round. But can be ellipsoidal, flattened, fusiform (rounded), toothed etc. Spherical nucleus is one micron in diameter. Cells with more cytoplasm have larger nuclei and cells with less cytoplasm have smaller nuclei.

 

Structure of Nucleus

The parts of the nucleus are:

1. Nuclear membrane or envelope: The membrane that covers the nucleus is called nuclear membrane or nuclear membrane. It is called the envelope, nucleolemma or karyotheca. The nuclear membrane is bilayered. Outer cover and inner cover. It is composed of phospholipids. The space between the two envelopes is called the perinuclear space. The distance between perinuclear spaces is 10-15 nm. Blisters originating from within the nuclear envelope are called nuclear blisters. The nuclear membrane contains nucleoplasmin. Nucleoplasmin mediates the exchange of various substances.

Function: The main function of the envelope is to separate the nucleoplasm, nucleolus and chromatin from the cytoplasm. Endoplasmic reticulum keeps the nucleus connected. Necessary materials transport from inside to outside and from outside to inside.

2. Nuclear Pore: The nuclear envelope consists of octagonal pores. These pores are called nuclear pores. Nuclear membrane has 300 pores. The number of nuclear pores per square micrometer is 40-145. The hole-to-hole distance is 1500 Å. The diameter of each pore is 9 nm. The pores are constricted and expanded by a protein network.

The nuclear pore contains the annulus. The annulus contains 8 granular edge proteins. Peripheral proteins are linked by spokes. At the center of the nuclear pore is a large protein called a transporter. The transporter is attached to the envelope by anchor proteins. Proteins can consist of subunits and fibers. Inside the nucleus is a fibrous cage. Proteins are attached to the fiber cage. Peripheral proteins associate with the transporter to form a wheel-like structure.

Function: It maintains contact with the cytoplasm and transports materials. The product passes through the nuclear pores into the cytoplasm.

3. Nucleoplasm: The clear, granular and jelly-like semi-fluid substance inside the nuclear membrane is called nucleoplasm or karyolymph. It is called protoplasmic juice or nucleo juice of nucleus. It is mainly composed of proteins. It contains DNA polymerase, RNA polymerase, phosphoprotein, histone protein, nucleotide triphosphatase, nucleoside phosphorylase, kinase, dehydrogenase, endonuclease, lipid and mineral salts.

Function: It contains nucleolus and chromosomes. Helps in various biological functions. The nucleoplasm serves as the main site of enzyme activity.

4. Nucleolus: The dense, bright and spherical material seen inside the nucleus is called nucleolus. Each nucleolus consists of three parts. Pars Amorpha, Nucleonima and Matrika. The surrounding part of the nucleolus is called pars amorpha, the central part is called nucleonema and the liquid part inside is called matrix. It is attached to a chromosome called the organizer. The location of the chromosome where the nucleolus is attached is called the SAT or satellite. Nucleolus contains DNA, RNA, proteins, lipids, enzymes, phosphorus, sulphur, potassium etc. In 1781, the scientist Felice Fontana first observed the nucleolus. Nucleolus was named by Bowman in 1840. The SAT gene located on the satellite of the chromosome plays a direct role in the production of nucleolus. Cells that do not synthesize proteins do not have a nucleolus. Spermatozoa, red blood cells and white blood cells do not contain nucleolus.

Function: Nucleolus synthesizes different types of RNA. It synthesizes and stores proteins. It acts as a storehouse of nucleotides. It creates ribosomes.

5. Chromatin: The fine thread-like structure found inside the nucleus is called nuclear reticulum or chromatin fibers. The unit of chromatin is the nucleosome. A necklace-like structure formed by enclosing histone proteins is called a nucleosome. Each human cell contains about 3×107 nucleosomes. It is called chromatin because it contains some basic color (fluorescent color) when the cell is stained. Chromatin is characterized by two regions due to its ability to absorb color. Euchromatin and Heterochromatin. The darker colored denser region of chromatin is called heterochromatin and the lighter colored less dense region is called euchromatin. Chromatin is divided into thick and short sections called chromosomes. Each chromatin contains DNA, histone proteins and non-histone proteins.

Function: Chromatin contains DNA. It acts as a carrier and carrier of hereditary characteristics. It plays a key role in the variation and mutation of organisms.

Function of Nucleus

1. Biological function: The nucleus is called the brain of the cell. It controls all biological functions of cells.
2. Heredity: DNA molecules present in chromosomes control the heredity of organisms.
3. Protein synthesis: Nucleolus forms ribosomes and ribosomes make proteins.
4. Metabolism: Nucleus is the organelle that regulates cell metabolism.
5. Regulation of enzyme activity: Nucleoplasm serves as the main site of enzyme activity.
6. Variation and mutation: It causes variation and mutation in organisms. As a result, evolution takes place in the living world.
7. Metabolism: The nuclear membrane acts as a medium of exchange. It exchanges essential substances between cytoplasm and nucleoplasm.
8. Cell division: It plays an important role in cell division.
9. Differentiation: Nucleus controls cell differentiation during embryonic development.
10. Shape the cell: The nuclear membrane forms the various structural components of the cytoplasm. These elements help in cell shape.

 

Role of nucleus in the growth of organisms

1. The nucleus is called the brain of the cell. It controls all biological functions of cells. It also regulates the growth of organisms.
2. Nucleolus forms ribosomes and ribosomes make proteins. These proteins make up the organism’s body.
3. The nucleus is the cell’s metabolic control organelle. It boosts the metabolism of organisms and helps in growth.
4. The nucleoplasm serves as the main site of enzyme activity. Nucleus promotes growth of organisms by regulating enzyme activity.
5. The nucleus carries out the exchange of essential substances. These substances help in cell growth.
6. Nucleus controls cell mitosis cell division. The number of body cells increases in the process of mitosis. Physical growth of the organism occurs when the number of body cells increases.

 

Role of nucleus in reproduction of organisms

1. Nucleus controls cell mitosis cell division. Genitalia of multicellular organisms are formed in the process of mitosis. Participates in reproductive work.
2. Nucleus controls cell meiosis cell division. In the process of meiosis, sperm and ovum are formed from the generative mother cells. Participates in sperm and egg production.
3. Nucleus Cell Mitosis causes cell division. Mitosis plays an important role in cell division. Roots are produced by vegetative propagation by cuttings, layering, grafting etc. of plants.

Role of nucleus in the heredity of organisms

1. Nucleus helps cell meiosis in cell division. In the process of meiosis, sperm and ovum are formed from the generative mother cells. Sperm and egg play a major role in heredity through sexual intercourse.
2. Nucleus contains chromosomes. Chromosomes contain DNA. DNA acts as the container and carrier of heredity. It carries hereditary characteristics. It transfers the characteristics of the parent to the offspring.

 

 

1. Amitosis is simple cell division process.
2. This process gave rise to complex and advanced cell division.
3. It increases the number of cells rapidly.
4. Lower organisms multiply in this manner.
5. It is very effective in the rapid growth of unicellular organisms.

At the beginning of amitosis, cells take in food and grow in size. Its nucleus is also enlarged. The nucleus enlarges and takes the shape of a dumbbell. The cytoplasm of the cell folds inwards. The nucleus then divides into two fragments. The cytoplasm folds further inward. Later the cytoplasm changes into two cells with nucleus

Amitosis is formed from the Greek words a meaning not, mito meaning thread and osis meaning state. The process in which a cell directly produces two daughter cells without any complex medium is called amitosis. Walter Flemming first used the term amitosis in 1882. In 1955 scientist Remak first observed amitosis cell division in red blood cells of chick embryos. Amitosis occurs in cells such as bacteria, yeast, amoeba, nostoc, cartilage of vertebrates, embryo membrane, endosperm of seeds etc.

In animal cells, the small organelles near the nucleus that contain microtubules and form spindle fibers during cell division are called centrioles. The junction of two centrioles located side by side is called a centrosome. In 1887 scientist Von Benden discovered it. Named after scientist Theodor Bovery in 1888.

Centrioles are present in animal cells. Most plant cells do not have it. Algae, fungi, bryophyta, pteridophyta, gymnosperms etc. plants have centrioles. Each cell has only one centriole. It is absent in protozoa, diatoms, yeasts, plant and mammalian red blood cells.

Centrioles are cylindrical and small organelles. It looks like a cylindrical barrel with two openings. It is 0.3-0.5 µm in length and about 0.15-0.25 µm in diameter. Each centriole consists of three main parts. These are-

1. Cylinder wall: At the center of the centriole there is a structure like a bullock cart wheel. It is called cart wheel model. The center of the cart wheel model is called the hub. The central rod is surrounded by walls or cylinder walls. Its wall is made up of 9 bundles or microtubules. Surrounding the centriole are 9 pericentriolar satellites above and below the microtubule.
2. Triplets: The centriole consists of 9 clusters of triplet molecules or triplets surrounding a cavity. Each tertiary microtubule has three equidistant subtubules. That is, each centriole (3×9) has 27 subtubules. Microtubules are attached to a central axis like the spokes of a wheel. Scientist Threadgold (1968) identified three subducts internally as A, B and C. The diameter of each subchannel is 250Å.
3. Linker: Linker is a type of protein fiber. The dense protein fibers that connect the tertiary tubules are called linkers. Channel A is connected to channel B and channel B is connected to channel C by connectors.

Centrioles are arranged in pairs. Each pair of centrioles is called diplosomes. The dark fluid surrounding the centriole is called the centrosphere.

Chemical structure of centriole

The main chemical component of centriole is protein. Also contains lipids and ATP.

Function of Cetriole

1. Cell Division: Centriole helps in cell division. It plays a special role in cell division.
2. Mucous fibers production: During cell division, it produces mucous fibers. In the prometaphase state, the nucleus is formed. It acts as a carrier of chromosomes.
3. Aster-rays: It produces aster-rays during cell division. Aster rays are formed during prometaphase in animal cells.
4. Polar movement of chromosomes: It helps in the marginal movement of chromosomes. During anaphase, the cytoplasm contracts and the chromosomes move towards the poles.
5. Formation of microtubules: It produces microtubules. Microtubules form the cytoskeleton.
6. Sperm formation: It forms the tail of the sperm. As a result spermatozoa become motile.
7. Formation of flagella: Cilia and flagella form the basal body.

1. Mitogens: Substances that stimulate cell division are called mitogens. Cytokinin stimulates plant cell division. Steroids, lymphokines, EGF (Epidermal growth factor), PDGF (Platelet derived growth factor) etc. stimulate animal cell division. Cell division occurs due to these chemical elements.
2. Gene regulation: Cell division is a gene regulation process. Cell division begins when the amount of DNA in the nucleus doubles.
3. Increase in cell number: Cells divide to increase the number of cells. Cells do not increase in number unless they divide.
4. Increase in cell volume: Cell division occurs to increase cell volume. Cells divide repeatedly to increase cell volume.
5. Cell Metabolism: Different types of metabolism take place in cells. Cell division is necessary for carrying out metabolism.
6. Nucleo-Cytoplasmic Ratio: Nucleo-cytoplasmic ratio is maintained through cell division.

The process by which a cell divides to form two or more new cells is called cell division. Rudolf Virchow (1858) said, ‘As trees come from trees, so animals come from animals, right

Only cells are created from such cells. Life of unicellular or multicellular organisms starts from a single cell. In 1882, Walter Flemming first observed cell division in the marine Triturus maculosa. A human cell replicates and divides only 4-60 times. During human life, body cells divide about 10 quadrillion or 10¹⁵ times.

Long, cylindrical, hollow and unbranched organelles present in the cytoplasm of cells are called microtubules. In 1953, Robert and Franchi discovered it from animal nerve cells. In 1953, scientists Ledbetter and Porter first observed their location in plant cells.

Microtubules are the sub-structural components of flagella and cilia. It is attached to the centromere of the chromosome. Spindle fibers contain microtubules. It is present in centriole and basal body.

Microtubules are long, cylindrical and hollow organelles. Its diameter is 10-20 mm and length is few microns. One end of them is marked as ‘+’ and the other end as ‘-‘. Each microtubule contains 13 prototubules. Each prototubule is composed of dimeric proteins. Each dimeric protein molecule consists of α and β ubulin.

Functions/importance of microtubules

1. Microtubules provide cell shape and mechanical strength.
2. It plays the role of cytoskeleton.
3. It forms the circulatory system or transport system of the cytoplasm.
4. Assists in cellular movement.
5. It acts as spindle fibers during cell division.
6. Helps in opposite pole movement of chromosomes.
7. Helps in cell wall formation.
8. Helps in the formation and movement of cilia and flagella.
9. Centrioles form in animal cells.
10. It binds to the cell membrane and nuclear membrane to maintain biological connections.
11. It helps in the secretion of essential substances.
12. It helps in the transmission of nerve impulses between nerve cells.
13. It indicates the arrangement of microfibrils.
14. It helps in communication and transportation.

The specific point in the cell cycle at which cell division stops is called a checkpoint or decision point. Cell cycle check points are:
1. G1/S Check Point: The cell cycle stops at the G1/S checkpoint when the cell is not suitable for division and the cell’s DNA is damaged. The cell cannot enter the S phase from the G1 phase. Here cell shape, cell hormones and DNA damage are checked.
2. G2/M Check Point: Cell cycle stops at G2/M checkpoint if damaged DNA of the cell is not repaired and DNA replication is not completed. The cell cannot enter the M phase from the G2 phase. Here the cell and nucleus size and DNA damage are checked.
3. M Check Point: Cell cycle stops at M Check Point when spindle fiber formation of cell is not complete and beam fiber is not properly attached to kinetochore. As a result, the process of mitosis does not occur.