CELL: THE UNIT OF LIFE

 

Function :

• Passive transport.
  • Simple diffusion
  • Facilitated diffusion.
  
  
• Active transport.
• Phagocytosis
• Exocytosis.
• Pinocytosis.

Cell wall :

• A non-living rigid structure called cell wall present outside the plasma membrane of plant and fungal cell.
• Algae have a cell wall made of cellulose, galactans, mannans and minerals like calcium carbonate.
• Plant cell wall consists of cellulose, hemicelluloses, pectins and proteins.
• The cell wall of young plant is called primary cell wall.
• On maturity secondary cell wall formed inner to it.
• The middle lamella is a layer of calcium pectate which holds or glues the neighboring cells.
• The cell wall and middle lamella may traversed by plasmodesmata; the cytoplasmic connection between two adjacent cell.

The endomembrane system :

Endoplasmic reticulum :

• Network or reticulum of tiny tubular structures scattered in the cytoplasm, called endoplasmic reticulum.
• It divides the intracellular space into two distinct compartments:
  • Luminal (inside the ER)
  • Extra luminal (cytoplasm).
  
  
• The ER shows ribosomes attached to their outer surface called Rough Endoplasmic reticulum (RER).
• Endoplasmic reticulum without ribosome called SER (smooth endoplasmic reticulum)

Function:

• RER present in the cell actively involved in protein synthesis.
• SER is the site for synthesis of lipid, glycogen and steroid hormones.

Golgi apparatus:

• Camillo Golgi (1898) first observed this organelle, and named after him.
• It consists of many flat, disc shaped sacs or cisternae.
• These are staked parallel to each other.
• The Golgi cisternae are concentrically arranged near the nucleus with distinct convex cisor the forming face and concave transor the maturing face.

Function:

• Principally responsible for packing of materials to be delivered intra-cellular target or intercellular target.
• Materials are packed in the form of vesicles, from the ER fuse with the cis face of the Golgi apparatus and move towards the trans face.
• Important site for the formation of glycoprotein and glycolipids.

Lysosomes:

• Membrane bound vesicular structure.
• Formed by Golgi body.
• Rich in all type hydrolytic enzymes, optimally active in acidic pH.
• These enzymes are capable to digesting carbohydrates, proteins, lipids and nucleic acids.

Vacuoles:

• The vacuole is the membrane-bound space found in the cytoplasm.
• It contains water, sap, excretory product.
• Vacuole is bounded by a single membrane called tonoplast.
• In plant cells the vacuole can occupy 90% of the volume.
• Tonoplast facilitates active transport of material from cytoplasm into the vacuole.
• In Amoeba the contractile vacuole is important for excretion and osmoregulation.
• In many protists, food vacuoles are formed by engulfing the food particles.

Mitochondria:

• The number of mitochondria varies according to the physiological activity of the cell.
• Each mitochondrion is a double membrane bound structure with outer and inner membrane, dividing its lumen into two aqueous compartments
  • Outer compartment.
  • Inner compartment.
  
  
• The inner compartment is called the matrix.
• The inner membrane forms a number of infoldings called the cristae towards the matrix.
• The cristae increase the surface area.
• Two membranes have their own specific enzymes associated with the mitochondrial function.
• Mitochondria are the site of aerobic respiration.
• They produce cellular energy in the form of ATP, hence called ‘power house’ of the cell.
• The matrix also possess single circular DNA molecule and a few RNA molecules, ribosomes (70S), they synthesize their own protein.
• Mitochondria divide by fission.

 

CBSE Biology (Chapter Wise) Class XI ( By Mr. Hare Krushna Giri ) 
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