Biology : The Cell

 

p style=”text-align: justify;”>The Cell: Foundation Of All Living Things

Cells are the basic units of life. They are the smallest parts of a living organism that can lead an independent existence. Singly, or in association with other cells, they make up the bodies of all living things.

Structure of Cell: Every cell is surrounded by a membrane or a living covering. Within the membrane is the protoplasm.

  1. Parts of the Protoplasm: The nucleus controls and directs the activities of all the other parts of the cell. The remainder is known as cytoplasm, where any vital activities of the cell take place. Following are the parts of a Cell-
  • (i) Cell Wall :Found only in plant cells, it consists of non-living substances, eg, linguin, pectin, cellulose etc.,
  • (ii) Cell membrane (Plasmalemma) :This is the outer membrane of the cytoplasm, found both in animals and plants. It consists of living substances such as proteins,
  •  (iii) Endoplasmic reticulum (ER): It is a network of tubes or channels of membrane in the cytoplasm, which helps in protein synthesis and conduction of material,
  • (iv) Ribosomes: They are extremely small, dense, granular, spherical bodies found in free state in the cytoplasm, composed of RNA and proteins. They help in the synthesis of protein from amino acids,
  • (v) Golgi apparatus (Golgi bodies): They are bag-like structures formed of stacks of membrane. Their functions include secretion of various substances, secretion of pectic material of cells wall in plants, and helping in the formation of cell during cell division,
  • (vi) Vacuoles: Are fluidfilled sacs within a cell. In animals they are tiny. Their functions include osmo-regulation and maintenance of cell turgidity, 
  • (vii) Mitochondria: Rod-like or spherical semi-solid structures containing DNA in its matrix along with some enzymes, which are found in all cells. They synthesise ATP (energy storing molecules),
  • (viii) Plastids: Small bodies found in the cells of higher plants. They are of two types, viz, Leucoplasts, which are colourless and store starch, protein or lipids; and Chromoplasts, which are coloured and are of two varieties: (i) Non-photosynthetic chromoplasts, which provide colour to flowers, fruits and leaves, (ii) Photosynthetic chromoplasts, which manufacture food from carbon  dioxide and water in the presence of sunlight, in green plants,
  • (ix) Nucleus: Each nucleus is bound by the nuclear membrane, which contains nucleoplasm. Nucleoplasm consists of chromatin and nucleoli. Chromatin consists of DNA, RNA and proteins. The nucleus controls all cell activities and is responsible for the transfer of heredity characters and also assists in cell division,
  • (x) Centrosome: A rather dense area of protoplasm, it lies close to nucleus. It is usually found in animal cells. In the middle of the centrosome are two small dot-like bodies called centroils. They form a spindle during cell division and lower plants,
  • (xi) Cilia and flagella: These are fine extensions of the cell surface and are similar in structure. Their functions are to help in locomotion or movement, and in some animals they also help in feeding,

Animal Cell

An animal cell typically contains several types of membrane- bound organs, or organelles. The nucleus directs activities of the cell and carries genetic information from generation to generation. The mitochondria generate energy for the cell. Proteins are manufactured

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