Cell and Cell Structure Part-2

Structural Organization of the cell

Plasma Membrane or Cell Membrane

  • It is a biological membrane and outer covering of cell which separates a cell’s contents from its outside surrounding or external environment.
  • It consists of a bilayer membrane made of phospholipids.
  • It is selectively permeable in nature, i.e. it allows or permits the entry and exit of some materials in and out of the cell.
  • This membrane is flexible which enables cells to engulf in food and other from the external environment and this process called endocytosis. Example-Amoeba gets its food through this process.
  • Function-It prevents the movement of some other material not required for the cell due to its selectively permeable property.

Diffusion

  • It is the process of movement of molecules from a high-concentration region to a low-concentration region.
  • Example- Oxygen and Carbon dioxide moves across the cell membrane by diffusion.

                              

Osmosis

  • The process of movement of water through a semi-permeable membrane is called osmosis.
  • Since not all molecules can flow through the membrane, osmosis is a selective process.
  • The only free-moving molecule across this membrane is often water.
  • Example- Plant cell tend to obtain water through osmosis.

                                                    

Types of solution

  • Isotonic solution- Medium has exactly the same water concentration as the cell; there will be no net movement of water across the cell membrane.
  • Hypotonic solution- These solutions are ones that contain lower solute concentration than the surrounding fluid and can cause the cell to rupture due to an excess of water entering the cell.
  • Hypertonic solutions-These solutions have a higher solute concentration than the surrounding fluid and therefor the movement of water occur out of the cell, shrinking it.

Cell wall

  • There is a cell wall in plant cells, which distinguishes them from animal cells.
  • It is made up of cellulose and gives a rigid structure to the plant.
  • Due to its rigidity it provides structural support to plants.
  • Cells of plants, fungi and bacteria can withstand in surrounding condition than animal cells due to presence of cell walls.
  • When a living plant loses water through osmosis due to shrinkage or contraction of contents of the cell away from cell wall and the process is known as plasmolysis.
  • Function-Protects the cell membrane, responsible for maintaining the shape and size of the cell and prevents the cell from becoming flaccid and from drying out.

Nucleus

  • It refers to the brain of cell as it controls all the activities of cell.
  • It has double-layered covering called nuclear membrane.
  • The nuclear membrane has pores that enable material to move from inside the nucleus to its outside, i.e., to the cytoplasm.
  • Chromosome-The genetic material found in the nucleus is called chromosomes. It has linked proteins and DNA. They are found as chromatin strands. They are visible as rod-shaped structure only when the cell is about to divide. There are 23 pairs of chromosomes in human cells (46).
  • Chromatin-The genetic material found inside a cell's nucleus is called chromatin, a structure like a thread. DNA and protein components make up its structure. DNA contains the hereditary information needed for the structure and function of the organism.
  • Function- Controls all the metabolic activities of cell and regulate the cell cycle, helps in transfer of hereditary characters from parents to their offspring’s.

 

Cytoplasm

  • It was discovered by Kolliker in 1862.
  • Fluid found inside the cell is called cytoplasm.
  • It gives structure to the cell and contains different organelles of the cell.
  • Function-Site of many metabolic pathways such as glycolysis and helps in exchange of material between cell organelles.