Category: Biology Second Paper

Plant cells such as trachyds, vessels, sutures, guard cells, stone cells, gland cells, rhizomes, diatoms, parenchyma, collenchyma etc.

Differentiation is the different shape and function of cells in different organs of multicellular organisms. The number of chromosomes in all human body cells is 44. So all cells have the same genome. But not all cells secrete hormones or enzymes.

Stem cell means that all the tissues of the whole body are formed from the cells of the embryo. The primary cells of the zygote and embryo are called stem cells. The unicellular zygote divides repeatedly to form a multicellular embryo. Embryo cells divide repeatedly to form organs such as brain, heart, lungs, liver, kidney, stomach, eyes, etc. Complete human body is formed by these organs. In the 19th century, the primary cells of the zygote and embryo were named stem cells.

Importance of stem cells

1. New cells are produced from stem cells to regenerate damaged organs or tissues.
2. Stem cells are used to repair organs that cannot function properly.
3. Can differentiate in different ways to form different types of cells and tissues.
4. Embryonic stem cells can be used to make new tissue.
5. Organs like heart, kidney, liver, lung etc. can be produced and used.
6. Can make meatballs for human consumption. So there will be no need to keep cows, buffaloes, sheep, goats, poultry etc. The United States has recently allowed the marketing of laboratory-grown chicken meat.
7. Organs like bone marrow, skin, liver etc. have some stem cells. They have the potential for regeneration and repair.

Cells can be divided into two types based on the structure of the organism.

1. Plant cell: All the cells that form the plant body are called plant cells. Plant cells contain cell wall and plastids. It has fewer mitochondria and usually no centrioles. Their stored food is starch and fat. It lacks microvilli and pinocytic cavities. It contains small and large cells. It maintains cell junctions through plasmodesmata.
2. Animal cell: All the cells that form the body of an animal are called animal cells. Animal cells do not have cell walls and plastids. It contains more mitochondria and centrioles are always present. Their stored food is glycogen and fat. It contains microvilli and pinocytic cavities. It does not contain glyoxysomes. It maintains cell junctions through desmosomes.

Dougherty (1975) divided cells into two groups based on the structure of the nucleus.

1. Prokaryotic cell: The word Prokaryotic is formed from Greek word pro meaning origin and karyon meaning nucleus. Prokaryotic means original nucleus or pseudonucleus. Cells that do not have a well-formed nucleus are called primitive cells. Adiocytes are small in size and less than 5 micrometers. Its cell wall consists of peptidoglycan. It contains 70S ribosomes. Primary cells do not contain chromosomes. It contains only DNA. Its nucleoid is called nucleoid or xenophore. It is low in histone proteins and non-enveloped. It does not undergo cytoplasmic movement or cyclolysis. However, transcription occurs in the cytoplasm. Protozoa like bacteria, blue green algae (BGA), mycoplasma (PPLO), spirochetes, rickettsia etc.

2. Eukaryotic cell: The word Eukaryotic is formed from the Greek word eu meaning actual and karyon meaning nucleus. Eukaryotic means true nucleus. Cells that have a well-formed nucleus are called true cells. Cysts are large in size and more than 5 micrometers. The actual cell size is 10 times larger than the original cell due to the presence of the nucleus alone. Its cell wall consists of cellulose. It contains 80S ribosomes. Cells contain chromosomes and DNA. Cyclosis occurs in its cytoplasm and transcription in the nucleus. Cell division in normal cells occurs in the process of mitosis and meiosis. Algae, fungi, bryophytes, pteridophytes, gymnosperms and angiosperms, somatic cells, germ cells, muscle cells, nerve cells etc.

A type of cell between protocell and protocell is called mesokaryotic cell. Mesokaryotic cells have a nuclear membrane. Its chromosomes are composed of DNA and acidic proteins. For example – Gymnodinium (Algae), Peridineum (Algae), Noctiluca (Protozoa) etc.

Cells are divided into two groups based on the number of chromosomes.
1. Haploid cells: Cells which have haploid (n) number of chromosomes are called haploid cells. Haploid cells divide by the process of meiosis. These cells have half the number of chromosomes. For example, sperm and egg.
2. Diploid cells: Cells which have diploid (2n) number of chromosomes are called diploid cells. Diploid cells divide in the process of mitosis. Diploid cells have the same number of chromosomes. For example, root, stem, muscle, xylem, phloem etc.

Cells are divided into two types based on physiological function.

1. Organism: The cells that form the body of multicellular organisms are called organelles. It is diploid in nature. Cells divide in the process of mitosis. That is, an equal number of chromosomes divides. Body cells such as root, stem, leaf, xylem, phloem, muscle cell, nerve cell (neuron), epithelial cell, blood cell etc.
2. Germ cells: Cells which take part in the reproduction of an organism are called germ cells. It is haploid in nature. Germ cells divide by the process of meiosis. Germ cells have half the number of chromosomes. That is, the reductive division of chromosomes takes place. Sperm and ovum are the units of sexual reproduction and spores or molecules are the units of asexual reproduction.

Cells are divided into two types based on physiological function.

1. Organism: The cells that form the body of multicellular organisms are called organelles. It is diploid in nature. Cells divide in the process of mitosis. That is, an equal number of chromosomes divides. Body cells such as root, stem, leaf, xylem, phloem, muscle cell, nerve cell (neuron), epithelial cell, blood cell etc.
2. Germ cells: Cells which take part in the reproduction of an organism are called germ cells. It is haploid in nature. Germ cells divide by the process of meiosis. Germ cells have half the number of chromosomes. That is, the reductive division of chromosomes takes place. Sperm and ovum are the units of sexual reproduction and spores or molecules are the units of asexual reproduction.

1. Viruses, virions and prions have no cellular location.
2. Bacteria, archaebacteria and blue-green algae do not have a well-structured nucleus.
3. Many algal and fungal cells are multinucleated.
4. The protoplasm of many cells is dead.
5. Red blood cells and cytoplasm are without nucleus.
6. Connective tissue contains a lot of extracellular matrix.

In 1838-39 German botanist Jacob Schleiden, zoologist Theodor Schwann and later in 1855 Rudolf Virchow provided the theory of cells called cell theory. Cell theory is called Cell doctrine.

Fundamentals of Cell theory

1. All organisms are made up of cells.

2. Cell is the basic unit of life.

3. Cell is the structural, organizational and physiological unit of an organism.

4. It is the unit of inheritance.

5. New cells are formed from old cells.

6. All body functions take place inside cells.

7. The biological functions of the body depend on the functions of all cells.

8. All members of the same species have the same chemical nature of cells.

9. Cells contain the genetic information of organisms and are transmitted from cell to cell during cell division.

10. All biological functions of multicellular organisms are the sum of interactions of body cells.

The units of cell measurement are meter (M), decimeter (dm), centimeter (cm), millimeter (mm), micrometer or micron (µ), nanometer (nm) and angstrom (Å).
1 meter = 100 cm = 1000 mm = 1,000,000 micrometers = 1,000,000,000 nanometers
1 cm = 10 mm = 1/100 meter
1 mm = 1/10 cm = 1/1000 meter
1 micrometer = 1/10,000 cm = 1/1,000,000 meter
1 nanometer = 1/10,000,000 cm = 1/1,000,000,000 meter
1 nm = 0.001 µm = 10 Å
Cells larger than 100 μm are visible to the naked eye.
A light microscope can see from 0.2 μm to a maximum of 40 μm and a magnification of up to 2,000 times.
Electron microscopes can see from 0.5 μm to 20 μm at a maximum magnification of 500,000 times.
Electron microscopes use electron beams at shorter wavelengths. So many tiny objects are visible.