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Kerala PSC - Study Material : Biology (Structure of the Cell)

Kerala PSC - Study Material : Biology (Structure of the Cell)

  • Cell wall found only in plant cells. It consists of non-living substances. eg: lignin, pectin, cellulose etc.
  • Cell membrane (Plasma membrane)
  • It is the outer membrane of the cytoplasm found both in animals and plants.
  • Plasma membranes are composed of phospholipids and protein.
  • Cytoplasm : It is a jelly like semi-solid ground substance in which various cell organelles are suspended. It helps in exchange of materials between cell organelles.
  • Protoplasm : Cytoplasm together with the nucleus form the protoplasm - the living matter of the cell.
  • Ribosomes : Small, dense, granular, spherical bodies found attached to the endoplasmic reticulum or  in free state in the cytoplasm, composed of RNA and proteins. They help in synthesis of proteins.
  • Endoplasmic Reticulum (ER) provides an ultra structural skeletal framework and mechanical support to the cell. So it is called Skeleton of the cell.
  • Rough endoplasmic reticulum is the normal 'ER' with ribosomes attached to it. Only rough ER is involved in protein synthesis.
  • Smooth endoplasmic reticulum - without ribosomes in it.
  • Nucleus : The nucleus is the most prominent structure. It contains the genetical materials and also controls all cellular activities.
  • Golgi bodies : Bag like structures formed of membrances. Their functions include secretion of various substances.
  • Golgibodies : are often called traffic police of the cell because it plays a critical role in sorting many cellular protein and guiding them to their destination.
  • Vacuole : A fluid filled sac within a cell. The watery fluid enclosed in the vacuole is called 'Cell Sap'. It is slightly acidic or neutral. Osmo-regulation is the main function. Membrane of vacuole is called tonoplast.
  • Mitochondria : Rod like or spherical, semi-solid structures containing DNA. They are the sites of cellular respiration.
  • Mitochondria is the power house of the cell. It is also a double-membrane bound organelle. The inner membrane is thrown into folds called cristae to increase the surface area.
  • Peroxisomes and glyoxysomes are known as microbodies. They are enzyme bags.
  • Lysosomes are sac like structure bounded by a single membrane. It is known as suicidal bags, as they contain hydrolysing enzymes. Occasionally they digest the whole cell or part of it.
  • Plastids : Small discoid bodies found in the cytoplasm of higher plants. They are of many types.
  • Chloroplasts : are the centres of photosynthetic activity. it is found only in photosynthetic activity. It is found only in photosynthetic plant cell. Chloroplast is a green plastid.
    1. (i) Leucoplasts : Colourless starch storing particles
    2. (ii) Chromoplasts : Are Coloured particles which give colour to fruits and flowers.
  • Centrosome : A rather dense are of protoplasm, lies close to nucleus. It is found in animal cell only.
  • Plant cell is different from animal cell as it contains cell wall and chloroplasts and devoid of centrioles which help in cell division.
  • Adenosine Triphosphate (ATP provides energy for all kinds of activities of a cell.
  • ATP is called the 'universal biological energy currency'.
  • Energy is stored in the mitochondria as ATP molecules.
  • Chromosome is thread like structure found in the nucleus.
  • It becomes visible during cell division.
  • Each Chromosome is made up of two chromatids joined together at a point called centromere.
  • Genes are hereditary units which are the particular segments of DNA (Deoxyribonucleic acid) and carry genetic information from generation to generation.
  • Chromosome is made up of DNA & proteins.
  • Chromosomes, other than the sex chromosomes are called autosomes.
  • Number of autosomes in a cells is 44 (22 pairs) and number of sex chromosomes is 2.
  • Microfilaments - are fine thread like fibrils, made up of one of the major protein components, actin of muscle cells.
  • Microtubules - are straight tubular structure that provide some rigidity to the cell.
  • DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid) are two different nucleic acids found in the cells of every living organism. Both have significant roles to play a cell biology.
  • DNA is found mainly in the nucleus of the cell, while RNA is found mainly in the cytoplasm of the cell.
  • The structure of DNA was first deduced by J.D. Watson and F.H. Crick in 1953.
  • Apoptosis - It is the programmed cell death or cells suicide. This occur when the cell has fulfilled its biological functions.

Cell Division

  • Cell division is the process by which a parent cell divides into two or more daughter cells.
  • Rudolf Virchow was the first to suggest that new cells are formed from the division of the pre-existing cells.
  • Time taken for one cell division is called cell cycle.
  • Human cell cycle is 24 hours.
  • Cell division is of two types : Mitosis and Meiosis.
  • Mitosis occur in body cells, results in formation of two daughter cells with equal number of chromosomes.
  • Mitosis is called equational division.
  • Meiosis occurs in reproductive cells. It causes a reduction in number of chromosomes in the cell. 
  • Meiosis is called reduction division.
  • Division of nucleus during cell division is called Karyokinesis.
  • Division of cytoplasm is called cytokinesis
  • Two complete set of Chromosome is called diploid (found in somatic cell / body cell).
  • Single set of chromosome in cell is called haploid (found in gametes - sperm/ovum)
  • Exchange of genetic material between two non sister chromatids takes place during meiotic cell division is called crossing over.
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