Cell Structure and it's Functions

Cell have various type of structures like cylindrical, elliptical, spherical, transverse etc.

Cell Components:

1) Cell membrane:

• It is also called as Plasma membrane.
• It is the outermost layer of the cell.
• It is semipermeable membrane.
• In plant cell it is found within cell wall.
• It is made up of phospholipid molecules.

Function:

• Control the molecular activities between cell and it's other medium which interacts with cell. 

2) Cell Wall:

• Only present in Plant cell.
• it is made up of non living substance
• Cell wall of algae and plants are made up of Cellulose.
• Cell wall of fungi and bacteria are made up of Carbohydrates.
• Cell Wall of fungi is made up of => Chitin
•  Cell wall of bacteria is made up of => Peptidoglycan

Function:

• It protect nucleoplasm and cell membrane from external attack.

3) Protoplasm:

• Name was given by Purkinje (in 1839).
• Whole fluid present inside plasma membrane is Protoplasm.
• It is made up of water, ions, salt and organic molecules
• It is a living part of cell.
• It is divided into two parts
• Cytoplasm: Present between nuclear membrane and cell membrane.
• Nucleoplasm: Present inside nuclear membrane.

4) Mitochondria:

• It was discovered by => Altman and Benda (in 1886).
• Altman called it Bioplast and Benda called it Mitochondria.
• It's shape is cylindrical having Diameter (0.2 -1  micrometer) and Length (1 - 1.4 micrometer).
• It surrounded by double membrane(outer and inner membrane).
• Outer membrane is oily and smooth.
• Inner membrane has many folds called cristae (in plant cell it is called tubuli) and inner compartment where fluid is present called matrix.
• Function: 

• It is a site of aerobic respiration and they produce cellular energy in the form of ATP (Adenosine Tri Phosphate).
• Hence Mitochondria is called as Power house of cell.  

5) Golgi Bodies: 

• It was discovered by => Camillo Golgi (in 1898).
• It is also called as Golgi apparatus.
• It is made up of group of tubes and vesicles.
• In plant it is more in number and here it is known as Dictyosomes.

Function:

• It work as storage, processing and packaging of material and packages are brought to their destination, hence Golgi apparatus is called as traffic controller of cellular molecules. 
•  It is also involved in synthesis of cell wall, plasma membrane and lysosome.
• It help in the synthesis of carbohydrate from simple sugar which combine with Protein made by Ribosome forming Glycoprotein. 

 
6) Endoplasmic Reticulum:

• It was invented by => Porter (in 1945).
• It membranous network of tubules like structure found in cytoplasm is called Endoplasmic Reticulum.
• It is of two types:
• Rough walled ER: At it ribosome is to be found and it is help in protein synthesis.
• Smooth walled ER: At it ribosome is absent and it is responsible for lipid secretion. In animal cell lipid like steroidal hormones are synthesized by smooth walled ER.

7) Ribosome:

• It was discovered by => G. E. Palade (in 1955).
• It was firstly seen by Calede (in 1941) and called microsome, later it is called ribosome by Palade.
• Diameter of it varies from 150 Å to 250 Å.
• Chemically it is composed of RNA and Protein.
• Eukaryotic ribosomes are 80S  while Prokaryotic ribosomes are 70S. (Here S=> Svedberg Coefficient)

Function:

• It's main function to synthesize the protein, hence Ribosome is called as Factory of Protein. 

8) Lysosome: 

• It was discovered by => De Duve.
• It contain hydrolytic enzyme, which is able to digest every organic substance.
• It help in intracellular digestion that's why Lysosome is called Digestive Vesicle.
• Lysosome is not found in RBC of mammal.

Function:

• It destroy every foreign substance like bacteria etc. inside the cell.
• It replaces old and weak cell organelles, so that new cell organelles originates inside cell.
• If there is need it destroy entire damaged or dead cell, also it destroy itself, hence Lysosome is called as suicide bag of cell.

9) Centrosome:

• It was discovered by => Boveri (in 1888).
• It is only found in animal cell.
• It is not bounded by membrane, it consist of two Centriole.
• Sometimes it is called as diplosome.

Function:

• It help in the cell division and it form spindle fiber between pole during cell division.  

10) Plastid:

•  It is only found in plant cell.
• It's shape is like mitochondria, it has two membrane.
• It is of three types a) Chloroplast b) Chromoplast c) Leucoplast.

a) Chloroplast:

• Found in green colored plant.
• Made up from green colored substance called as Chlorophyll (In Chlorophyll Mg metal is present).
•  By the help of chlorophyll Photosynthesis is done in the presence of sunlight by the plant and trees, thus Chlorophyll is called as Kitchen of the cell.
• Chloroplast is bounded by two membrane having grana and stroma.
•  Grana => It contain chlorophyll molecule and it is a site of light reaction.
•  Stroma => It contain photosynthetic enzyme and it is a site of dark reaction.
• Chloroplast also contain pigments like genthophyll and carotene.
•  The leaf of plant becomes yellow because of formation of carotene.
• Chloroplast also contain double standered  circular DNA molecule and ribosome.
• ribosome in chloroplast is smaller (70S) than cytoplasmic ribosome (80S).

 b) Chromoplast:

• It is colored plastid usually red, yellow or orange color.
• It is found in colored part of plant like flower, fruit, seeds etc.
• Chloroplast are of different kind

1.  Lycopene: In tomato it provide red color.
2. Carotene: Provide yellow or orange color in plant eg:- Carrot
3. Betanin: Found in sugar beet root.

 c) Leucoplast:

• It is colorless plastid.
• It store food in the form of starch, fat and protein.
• It is found in roots and underground stems.
• Amyloplast store starch.
• Elaioplast store oil & fats.
• Aleuroplast store protein.

 

11) Vacuole:

• It is surrounded by semipermeable membrane called as Tonoplast.
• It contains water, sap, excretory product and other material not useful for the cell, means it contain dead organelles of cell.
• In plant it is longer in size & in animal it is smaller in size.

Function:

• It help in osmoregulation & it store toxic metabolic waste.

12) Nucleus:

• It was invented by => Robert Brown (in 1831).
• It is spherical or elliptical.
• It is centrally located major structure found in cell, in plant cell it is shifted towards periphery.
• It control all activity of cell, hence it is called Control Room of cell.
• Components of nucleus:

a) Nuclear membrane:

• It is a double layered membrane.
• It is connected with ER.
• It is made up of protein & fat.
• It has small holes through which cytoplasm & nucleoplasm exchange in cell.

b) Nucleoplasm:

• It is made up from protein, phosphorous & nucleic acid.
• Within nucleoplasm nucleolus and chromatin material is found.

 c) Nucleolus:

• Nucleolus is rich in protein & RNA.
• It synthesize r-RNA & transport it to other place.
• It collect ribosome inside it. 

 d) Chromatin:

• Chromatin is thin thread like structure forming network.
• It is made up of histone protein, DNA & RNA.
• DNA is main component of chromatin which causes genetic character in organism.
• During cell division chromatin breaks into pieces & form Chromosome. 

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