The Fundamental Unit of Life : All you need to know

Cell

It is the struc­tur­al and func­tion­al unit of life.

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→ Cell is termed as the struc­tur­al unit of life as it pro­vides struc­ture to our body.

→ Cell is con­sid­ered as the func­tion­al unit of life as all the func­tions of the body take place at cell level.

Discovery of cell:

→ Dis­cov­ered by Robert Hooke in 1665.

→ Robert Brown in 1831 dis­cov­ered the nucle­us in the cell.

Cell Theory:

Cell the­o­ry states that:

→ All liv­ing organ­isms are com­posed of cells.

→ Cell is the fun­da­men­tal unit of life.

→ All new cells come from pre-exist­ing cells.

Types of Organisms on the Basis of Number of Cells

There are two kinds of organ­isms on the basis of cells:

(i) Unicellular Organisms: 

The organ­isms that are made up of sin­gle cell and may con­sti­tute a whole organ­ism, are named as uni­cel­lu­lar organisms.

For exam­ple: Amoe­ba, Para­me­ci­um, bac­te­ria, etc.

(ii) Multicellular Organisms: 

The organ­isms which are com­posed of a col­lec­tion of cells that assume func­tion in a coor­di­nat­ed man­ner, with dif­fer­ent cells spe­cial­ized to per­form par­tic­u­lar tasks in the body, are named as mul­ti­cel­lu­lar organisms.

For exam­ple: Plants, human beings, ani­mals, etc.

Shape and Size of Cells

→ Cells vary in shape and size. They may be oval, spher­i­cal, rec­tan­gu­lar, spin­dle shaped, or total­ly irreg­u­lar like the nerve cell.

→ The size of cell also varies in dif­fer­ent organ­isms. Most of the cells are micro­scop­ic in size like red blood cells (RBC) while some cells are fair­ly large like nerve cells.

Types of Cells

The cells can be cat­e­go­rized in two types:
1. Prokary­ot­ic Cell  2. Eukary­ot­ic Cell

1. Prokaryotic cell

Prokary­ot­ic cells are cells in which true nucle­us is absent. They are prim­i­tive and incom­plete cells. Prokary­otes are always uni­cel­lu­lar organ­isms. For exam­ple, archae­bac­te­ria, bac­te­ria, blue green algae are all prokaryotes.

2. Eukaryotic Cell

Eukary­ot­ic cells are the cells in which true nucle­us is present. They are advanced and com­plete cells. Eukary­otes include all liv­ing organ­isms (both uni­cel­lu­lar and mul­ti­cel­lu­lar organ­isms) except bac­te­ria and blue green algae.

Difference Between Prokaryotic and Eukaryotic Cells:

Structure of Cell

Cell is gen­er­al­ly com­posed of three basic components:

1. Cell wall  and cell membrane
2. Nucle­us
3. Cyto­plasm

(i) Cell membrane or Plasma membrane:

Func­tion:
As it is selec­tive­ly per­me­able mem­brane, it allows the flow of lim­it­ed sub­stances in and out of the cell.

(ii) Cell wall:

Func­tions:

→ It deter­mines the shape and rigid­i­ty to the plant cell.

→ It pro­tects the plas­ma membrane.

→ It pre­vents des­ic­ca­tion or dry­ness in cell.

→ It helps in the trans­port of varous sub­stances in and out of the cell.

(iii) Nucleus:

Func­tions:

→ Nucle­us con­trols all the meta­bol­ic activ­i­ties of the cell.

→ It reg­u­lates the cell cycle.

→ Nucle­us is the store­house of genes.It is con­cerned with the trans­mis­sion of hered­i­tary traits from the par­ent to offspring.

(iv) Cytoplasm:

Func­tions:
→ Pro­to­plasm acts as a store of vital chem­i­cals like amino acids, pro­teins, sug­ars, vit­a­mins, etc.
→ It is the site of cer­tain meta­bol­ic reac­tions, like gly­col­y­sis, syn­the­sis of fat­ty acids, nucleotides, etc.

Cell organelles:

Inside the cell there are dif­fer­ent parts per­form­ing dif­fer­ent activ­i­ties to keep the cell alive anf func­tion­able. These part are called Cell organelles. They are explained below:

1. Golgi Apparatus:

Func­tions:

→ Its main func­tion is to store, mod­i­fy, pack­age and dis­patch the substances.

→ It is also involved in the syn­the­sis of cell wall, plas­ma mem­brane and lysosomes.

2. Endoplasmic Reticulum:

Func­tions:

→ It gives inter­nal sup­port to cell.

→ It helps in trans­port of var­i­ous sub­stances from nuclear mem­brane to plas­ma mem­brane or vice versa.

→ RER helps in syn­the­sis and trans­porta­tion of proteins.

→ SER helps in syn­the­sis and trans­porta­tion of lipids.

3. Ribosomes:

Func­tion:

They play a major role in the syn­the­sis of proteins.

4. Mitochondria:

Func­tions:

→ They are the sites of cel­lu­lar res­pi­ra­tion, hence pro­vide ener­gy for the vital activ­i­ties of liv­ing cells.

→ They store ener­gy releas­es dur­ing reac­tions, in the form of ATP (Ener­gy cur­ren­cy of the cell). There­fore, they are also called ‘pow­er house’ of the cell.

5. Centrosome and Centrioles:

Func­tion:
Cen­tri­oles help in cell divi­sion and also help in the for­ma­tion of cil­ia and flagella.

6. Plastids:

Func­tion:

→ Chloro­plas­ts trap solar eber­gy and utilise it to man­u­fac­ture food for the plant.

→ Chro­mo­plas­ts impart var­i­ous colours to flow­ers to attract insects for pollination.

→ Lecuo­plas­ts help in the stor­age of food in the form of starch, pro­teins and fats.

7. Lysosomes:

Func­tions:

→ Lyso­somes help in diges­tion of for­eign sub­stances and worn-out cell organelles.

→ They pro­vide pro­tec­tion against bac­te­ria and virus.

→ They help to keep the cell clean.

→ Dur­ing the dis­tur­bance in cel­lu­lar metab­o­lism, for exam­ple when the cell gets dam­aged, lyso­somes may burst and the enzymes digest their own cell. There­fore, lyso­somes are also known as sui­cide bags of a cell

8. Vacuoles:

Func­tion:

→ They help to main­tain the osmot­ic pres­sure in a cell.

→ They pro­vide turgid­i­ty and rigid­i­ty to the plant cell.

9. Peroxiomes:

Func­tion:

→ They are spe­cial­ized to car­ry out some oxida­tive reac­tions, such as detox­i­fi­ca­tion or removal of tox­ic sub­stances form cell.

Difference Between Animal Cell and Plant Cell: