Cell Components: Cell wall, Cell membrane, Protoplasm, Cytoplasm and Nucleolasm - Biology Grade XI

Science Notes

Cell Components: Cell wall, Cell membrane, Protoplasm, Cytoplasm and Nucleolasm

Cell wall:

It is outermost layer of plant cell. It is a rigid and protective layer. It is composed of a different layer.

  • Middle lamella: It is present between the walls of adjacent cells. It acts as cementing materials between two cells. It is made up of carbohydrate, Ca and Mg.
  • Primary cell wall: It is found on either side of middle lamella. It is made up of middle lamella. It is made up of cellulose, hemicellulose. It is thin elastic and permeable.
  • Secondary cell wall: it is found on inner side of primary cell wall. It is thick non-elastic and rigid it is made up of cellulose lignin and pectin.
  • Function of cell wall: It provides rigidity to the cell. It protects the inner mass of the cell. Maintain the shape of the cell. Balance the osmotic pressure. It helps in absorption of water.

Cell membrane:

The most important structure of the cell is its membrane, for it is the cell membrane that controls and regulates what enters and leaves the cell. The cell membrane is made of two layers of lipids, called a lipid bilayer. The lipid bilayer is made of lipids (fats) and phosphates, normally called phospholipids Phospholipids have a polar end, and a non-polar end. In making membranes, the non-polar ends of both layers face each other, while the polar end faces the outside and inside of the cell. There are two theories for model of cell membrane

  • Sandwich Model: In this, there are two layers of protein outer and inner. In between two protein layers, there are two phospholipids layers. The heads of the phospholipids molecules face towards protein layer and the tails toward the centre.
  • Fluid Mosaic Model: In this model, there are 3 layers, two layers of protein and one layer of phospholipids. The phospholipids are liquid in nature. Therefore, molecules can exchange their position. This is called transition movement. The molecules can also interchange between two layers this is called flip-flop movement. The Proteins are of two types Peripheral protein (extrinsic protein): They are present either inner or outer surface.
  • Intrinsic protein: It is partially or completely embedded in phospholipids.
  • Function of cell membrane: It is the outer covering membrane of animal cell, which maintain cell shape, helps in diffusion, helps in osmosis endocytosis (intake of large molecules in to the cell) and exocytosis Expelling of large molecules of liquid or solid from the cell.

Protoplasm:

It is found inside cell membrane. It is a liquid mass viscous in nature. It contains several living and non-living things. It is divided into two parts

Cytoplasm:

It is a liquid mass present between the plasma membrane and nuclear membrane. it is differentiated into two layers The outer ectoplasm which is non-granular and inner endoplasm which is granular containing cell inclusions and cell organelles.

Nucleolasm:

It is liquid material within nuclear membrane.

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