Unit 2: Organisation of the organism

Fundimentals of Bio

Cells are the building blocks of life

Cell is the common basic structural and functional unit of living beings.

Robert Hooke discovered cells in 1665

Two Different Types of Cells :

M.J. Schleiden and Theodore Schwen (1838-39) first formed a theory “All plants and animals are composed of cells and cell is the basic unit of life”.

Later was changed in 1885 R.Virchow changed it to “all cells arise from pre-existing cells”

Electron Microscope was discovered in 1940

Different cells have different shapes depending on their functions

• Columnar - Epithelial cells

• Circular biconcave - RBCs

• Spindle shaped - Smooth muscle cells

• Oval - Ovum/egg cells

• Irregular - Ameba

• Branched - Nerve cells

• Spiral - Spirillum bacteria

• Rectangular - cells of spirogyra

• Rod shaped - Bacillus Bacteria

Cell Structure

Cell Walls (only in plants)

Plasma Membrane

Cytoplasm

Cell Organelles

Cell Organelles: Plasma Membrane

• It is the thin outer covering of a cell.

• It separates the contents of the cell from external environment.

• The plasma membrane is flexible and is made up of organic molecules called lipids and proteins.

• The plasma membrane allows the entry and exit of some materials in and out of the cells

• It also prevents the movement of some other materials.

• Therefore, the plasma membrane is called as a selectively permeable membrane.

• For e.g. when the concentration of CO2 inside the cell increases, the CO2 moves outside of the cells by diffusion.

• Similarly when the concentration of O2 inside the cell decreases the O2 moves from the outside to inside of the cell.

• Plasma membrane also helps in the transport of water in out of cells.

Osmosis and diffusion in cells

Osmosis -

Movement of water from Higher concentration to lower concentration thru plasma membrane

It is a pure mechanical process (which doesn’t require energy)

Diffusion -

IS the net movement of molecules

Isotonic solution -

Medium surrounding the cell has same water concentration as that of the cells. NO EXCHANGES OF WATER. In this case there is neither entry of water in the cell nor exit. So the cell remains Flaccid. (flaccid - not hard or firm)

Hypotonic Solution -

Medium surrounding the cell has higher water concentration that that of the cell. I.E. outside solution is very dilute in this case water moves inside the cell.

Water enters → Inside cell → swells up

So cell become turgid.

(Turgid - Swollen)

Hypertonic Solution -

Medium surrounding the cell has lower water concentration than that of the cell. I.E. outside solution is very concentration so cell becomes plasmolysed

Water comes → outside cell → shrinks up (Plasmolysis)