Notes
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Cell:
The body of all living organisms is made up of minute component called cell. The number of cells are different and specific for every living organism.
(1) Cell is the fundamental structural and functional unit of living organisms. Cellular organization is the primary characteristic of all living organisms.
Structural organization of Book -Flow Chart
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Structural organization of Living organisms -Flow Chart
Cell ->Tissue -> Organ -> Organ System -> Body – Living Organisms.
History of cell science :
(1) Robert Hooke in 1665 discovered cells.
(2) M. J. Schleiden and Theodore Schwann in 1838, gave a theory about cellular structure.
(3) Rudolph Virchow in 1885, stated that all cells are formed from pre-existing cells.
Measurement and observation of cells:
(1) Anton van Leeuwenhoek constructed first microscope in 1673. For the first time he observed live bacterial and protozoan cells under this microscope.
(2) Cells are minute in size and can be seen only with a compound microscope.
(3) The units used for measuring the sizes of cellular structure is micrometre and nanometre.
1 centimetre =10 millimetres.
1 millimetre = 1000 micrometres.
1 micrometre (or micron) = 1000 nanometres.
Shapes of the cells:
(1) The shapes of cells show great variation which is mainly related to their functions.
(2) Circular, rod-shaped, columnar, spiral, oval, rectangular, etc. are the different shapes of the cells observed.
Components of the cell:
(1) Every cell has many cell components which are specific in their function. These components are called cell organelles. They carry out different life processes.
(2) Cell organelles are studied with the help of the electron microscope which has magnifying power of (2 x 109) i.e. two billion times their actual size.
(3) Cells are of two main types, viz.
- Prokaryotic cells (in microbes).
- Kukaryotic cells, (Plant cells and Animal cells.)
(4) Cell wall: The outermost covering of a cell which is seen only in plant cells. Cell wall gives definite shape to the cells, Animal cells lack the cell wall.
(5) The plasma membrane : or cell membrane is a thin extremely delicate and flexible covering, In plant cells it is inside the cell wall. In animal cell it is the outermost covering of the cells.
(6) Cytoplasm : The liquid part in the cell, except the nucleus is called cytoplasm. It is present in the space between the plasma membrane and nucleus. In the cytoplasm the cell organelles are scattered.
(7) Cell organelles :
- Nucleus :
- Structure : Porous double membrane around it. Lodges chromosomes and genes.
- Functions : Gives orders of protein synthesis.
- Peculiarities : Controls all functions of the cell.
- Endoplasmic reticulum and the ribosomes attached to it :
- Structure : Sprawling net-like.
- Functions : Ribosomes : Protein synthesis.
- Peculiarities : Transport system of the cell.
- Golgi bodies:
- Structure : several flat sacs.
- Functions : The proper distribution of proteins.
- Peculiarities :
- Plastids:
- Structure : With double membrane.
- Functions : Performing photosynthesis.
- Peculiarities : Present only in plant cells.
- Mitochondria:
- Structure : Spindle shaped, with double membrane.
- Functions : Produce energy.
- Peculiarities : Power house of the cell.
- Vacuoles :
- Structure : Empty space like a bubble.
- Functions : Throw out waste products of the cell.
- Peculiarities : Only one big vacuole in plant cells. Many small ones in animal cells.
- Lysosomes :
- Structure : Spherical bag with enzymes.
- Functions : Destroy cell by lysis.
- Peculiarities : Suicidal bags of the cell.
Plant Cell :
- Plant cells have cell wall made up of cellulose.
- The cytoplasm of the plant cells is lesser, granular and not dense.
- There is a single large vacuole located in centre which pushes the cytoplasm to one end.
- There are no lysosomes.
- The mitochondria are few in number.
- Plastids are present only in plant cells.
- Single or more but large vacuoles present.
- The vacuoles are filled up with cell sap.
Animal Cell :
- Animal cells do not have cell wall.
- The cytoplasm of animal cells is more granular and dense.
- The cytoplasm is uniformly distributed in the cell.
- Lysosomes are present in the animal cells,
- The mitochondria are greater in number as compared to the plant cells.
- Plastids are absent in the animal cells.
- Vacuoles are few and temporarily formed.
- The vacuoles are filled with food or excretory matter,
Prokaryotic cell : Prokaryotic cells are about 1 to 10 um in size
- The nucleus of prokaryotic cell is not distinct.
- Due to the absence of nuclear membrane, the nuclear material comes in contact with the cytoplasm.
- The cell organelles if present are without membranes.
- There is indistinct nucleoid in which prokaryotic DNA is present. There is a single chromosome.
- Mitochondria are absent in prokaryotic cells.
- Chlorophyll is present in the vesicles and not in plastids.
- Prokaryotic cells are found in blue-green algae and bacteria.
Eukaryotic cell : Eukaryotic cells are about 5 to 100 pm in size.
- The nucleus of eukaryotic cell is distinct, with nuclear membrane, nucleoli and nucleoplasm.
- Due to the presence of nuclear membrane, nucleoplasm and cytoplasmn never come in physical contact with each other.
- The cell organelles are always bound with membranes.
- The nucleus is distinct with more than one chromosomes.
- Mitochondria are present in eukaryotic cells.
- Chlorophyll is always inside the chloroplasts.
- Eukaryotic cells are found in highly evolved plants and animals.
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