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Cell Structure Part 1

Cell structure (Part 1):
Every cell is made up of cell wall or plasma membrane, nucleus and cytoplasm containing different cell organelles.

Cell wall:
Plant cells are surrounded by a rigid outer covering called the primary cell wall, which is made up of cellulose. Cellulose is a complex polysaccharide made up of pectin arranged in a jelly like matrix. The primary cell wall helps in maintaining the shape of cell.

A secondary cell wall is formed by deposition of cellulose, hemi cellulose, lignin, suberin etc. on the primary wall.


Plasma membrane:
Outer most covering of cell that separates the contents of the cell from its external environment is called plasma membrane. It is selectively permeable or semi permeable and allows entry or exit of some materials in and out of the cell.

Plasma membrane is made up of organic molecules like lipids and globular proteins. Lipids contain phospholipids, glycol lipids and cholesterol.

Lipids form a bilayered arrangement where outer surface is hydrophilic and inner surface is hydrophobic. Protein molecules are scattered amongst the bilayered lipid layer. Peripheral proteins are present at surface and removed very easily and called as extrinsic proteins. Integrated proteins are difficult to remove and called as intrinsic proteins.


Function of plasma membrane:
  • Transport of material
  • Transport of water

Transport across the membrane occurs in two main ways – active transport and passive transport.

Passive transport:
It is based on concentration gradient and materials are transported from more concentration to less concentration, hence energy is not requiring for transportation of material. Passive transport occurs by two ways – simple diffusion and facilitated diffusion.

Simple diffusion – Movement of carbon dioxide, oxygen and water (osmosis process) occurs across the cell membrane through simple diffusion.
Facilitated diffusion – Carrier molecules are involved in movement of materials from low concentration to high concentration but energy is not required is called facilitated diffusion.


Active transport:
It occurs against the concentration gradient and hence energy is required by carrier molecules to transport materials from low to high concentration.

Comparison between Prokaryotic cell and Eukaryotic cell:
Prokaryotic cell Eukaryotic cell
Lacing well organized nucleus A well organized nucleus is present
Smaller in size Bigger in size as compare to Prokaryotic cell
Cell division is very rapid Cell division  is slow
All genetic material occurs as a circular DNA and is arranged in a region called nucleoid Genetic material is organized into chromosomes and forms a complex with protein
Example – Bacteria, Blue green algae Example – Plant and animal cells

Self study:
Example-1: Match the following
(A) (B)
Cell wall energy is required
Plasma membrane made up of rigid outer covering
Active transport energy is not required
Passive transport selectively permeable or semi permeable

Answer:
(A) (B)
Cell wall made up of rigid outer covering
Plasma membrane selectively permeable or semi permeable
Active transport energy is required
Passive transport energy is not required

Example-2:  Cell is made up of ………………..
a)  Plasma membrane or cell wall
b)  Nucleus
c)  Cytoplasm
d) 
All of above

Answer: Cell is made up of plasma membrane or cell wall, nucleus and cytoplasm

Example-3: Plasma membrane contains ………………………
a)  Carbohydrate
b) 
Lipids and Proteins
c)  Enzymes
d)  Hormones

Answer: Plasma membrane contains lipids and proteins.

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