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Structural Organisation Of Cell

Structural Organisation Of Cell

Structural Organisation of Cell

Study which deals with the cell is called cytology.

Cell was first discovered by Robert Hooke in 1665 in sections of cork. He only coined the term 'Cell'.

The Cell Theory was given by Schleiden and Schwan. It states that :

  1. All living things are composed of cells and their products.

  2. All cells arise from pre - existing Cells.

  3. All cells are basically alike in Chemical Composition and Metabolic Activities.

  4. The function of an organism as a whole is the outcome of the activities and interaction of the Constituent Cells.

Types of Cells :

In a typical cell, the protoplasm consists of nucleus and cytoplasm.

Depending on the type of nucleus present, the cells are of two types:

  1. Prokaryotic cell (found in blue - green algae, bacteria and Pleuropneumonia like organisms (PPLO).

  2. Eukaryotic Cell.
Prokaryotic CellEukaryotic Cell
It is simple and primitive in nature. It is developed and comparatively complex in nature.
The nucleus is not well organized. It has no nuclear membrane and nucleolus. The nucleus is well organized. Nuclear membrane and nucleolus are present.
The cell has no membrane bound organelles except ribosomal granules. The cell contains almost all the membrane bound organelles.
Chromosomes are not formed in this cell during cell division. Chromosomes are formed in the nucleus during cell division.
Single DNA thread remains freely in the nuclear material. DNA is present in the nuclear reticulum or chromosomes.

On the basis of number of cells, the organisms are classified as Unicellular and Multi-cellular organisms.

Difference between Plant Cells and Animal Cells :

Plant CellAnimal Cell
A plant cell has a rigid wall on the outside. Cell wall is absent.
It is usually larger in size. An animal cell is comparatively smaller in size
It cannot change its shape An animal cell can often change its shape
Plastids are found in plant cells. Plastids are usually absent.
Plant cells exposed to sunlight possess chlorophyll containing plastids called chloroplasts. Chlorophyll is absent
A mature plant cell contains a large central vacuole. An animal cell often possesses many small vacuoles.
Nucleus lies on one side in the peripheral cytoplasm. Nucleus usually lies in the centre.
Mitochondria are comparatively fewer. Mitochondria are generally more numerous.
Cristae are tubular in plant mitochondria. Cristae are plate-like in animal mitochondria.
Plant cells do not burst if placed in hypotonic solution due to the presence of cell wall. Animal cells usually burst if placed in hypotonic solution unless and until they possess contractile vacuoles.
Centrioles are usually absent except in lower plants. Centrioles are found in animal cells.
Golgi apparatus consists of a number of distinct or unconnected units called dictyosomes. Golgi apparatus is either localized or consists of a well connected single complex.
Lysosomes are rare. Their activity is performed by specialized vacuoles. Typical lysosomes occur in animal cell.
Glyoxysomes may be present. They are absent.
Crystals of inorganic substances may occur inside the cell. Crystals usually do not occur in animal cells.
Reserve food is generally starch and fat. Reserve food is usually glycogen and fat.
Adjacent cells may be connected through plasmodesmata. Adjacent cells are connected through a number of junctions.

Huxley called protoplasm 'Physical basis of life'.

Ostrich egg is the largest cell in size.

Human nerve cell is the longest animal cell.

Largest acellular plant Acetabularia is 10 cm and animal is Amoeba, which is 1 mm.

In human beings, cells of kidney are the smallest.

Smallest cell is 0.1 - 0.3 µm in size. It is PPLO (Mycoplasma gallisepticum)





23 Jul, 2019, 00:14:57 AM