Thursday, August 27, 2020

The fundamental unit of life


Wno 10ok different fr

earth is inhabited organisms, very

by different kinds of living was-

eubacterla, protista (Amoe

ter. hese living num

organisms archaebacteria,


living organisms are made up of microscon

L ), Tungi, plants and animals. The bodies of

atonm in the physical sciences. The

Lne cell has same central position in biology as an

1s the basic structural and functional unit of living organisms.

DNA tha

day cells share instance, all cells employ as

common fundamental properties. For the

genetic material, membrane, basic mechanisms for ener

are surrounded by and the same

a plasma use

metabolism. On the other hand, present-day cells have evolved a variety of diferent life-styles. Ma Re

Organisms, such as bacteria (both archaebacteria and eubacteria), protozoa (e8, amoeba) and yea

sists of single cells (called unicellular organisms) that are capable of independent sel-replicatio

C cOmplex organisms, called multicell ular organisms, are composed of collections of cells th

Lnclon in a coordinated manner, with different cells specialized to perform the particular tasks. T

Doay, for example, is composed of more than 200 different kinds of cells, each specialized

c dstinctive functions as memory, sight, movement and digestion. The diversity exhibited by

ltny irterent kinds of cells is striking; for example, consider the differences between bacteria and

cells of human brain.

All cells, whether they exists as one celled organisms (unicellular organisms) or as a part

mulicellular organisms are capable of carrying out certain basic functions such as nutrition, respiratie

rowth and reproduction. These functions are essential for the survival of the cells.

Discovery of cell

i ar org umber t o

adidual s short s The

5he espan ot e

n he orgsbon atn hasic d sf Cell biolngy

The fandamental most important stractral and pudae

are the anpects and c structure and fndos

is the study ot oels in al of

Discovery of Cell Hooke saw tat me cis

5a o

strucar consisting Se ot cork, Hobert

of ma eear ments. s a

1665 when ed

his cru e tained disconery from the bark selt ot a e Fig 21) Eooet


lsCell a means oBox

bvng 21) Robert s c sed


he ant. in indicated n of a

it L that

of because for he the irst first time time

smaller strue or units

Bax 21 studygea

Cell Theo

The word cell is derived trom

ile atin room". word 'cellula English w reservor


Robert Hooke (1639

1665 discovered and re

ells, while examinig iitive

f bottle cork un ade by onev- (Fig screw

21), microscope observed mad

Hooke co . bec


fo or porous rous strucure re of cork

Hooke s and

pubiis Figure 6. Dead cork cels

cells. He Hooke. as seen

led to p

resemble with blished microscope.

the un Hooke Rober

vork in a DOOK "Micro8e Figure 2.l. Robert s by

tmprOved micrOScope

1663. Durch microscOpist, nond made an

Leeuwenhoek uwenhoes ttb32-1/3, overed the a water

free ans, d rabbits, To irogs, ich tust and insect

n In 1674, T6/4, Anton von this microscope

discovere identied ified

2.3) he ana ered





Datterences beetween nucieds Naucleoid

aDie L. comparatively smaier

Ncies absent. in stze THE PUNOAMEN

1 t is theore is t. It it lhes lies free f re

t t

has is larger covering in size. membrane enve 2 A covenng asm

a of double

Nucie absent in lt become

3. lus is to to a a sin slngle DN Ao occurs irre

Euglena in

5. Nucleolus equa anda m

is present i Oanucleoid the

absent. DA membtahe cel sha.

to two or several DN 4. Its DNA contermt s

molecules ts DNA content is equal

associated with histone proteins to In it histones are S pa

chromatin A1s nalkea sms,

human being ca surface

Division of Labour organism such as à

e Figure 2.10, you will notice that an cel,

ells of different Li eg--hdiverse ner rigidity mechanical ter-

osteocyte (ooneE ce u o

Sperm, leucocyte (white blood cell),

labour within mlrtcentlu oguss, ese st

functtons. nuttatt Doay has

utrerernt the tact that there is

human a division of

perform ditterent movement and locomoion and Or pigme

tO pump blood, d stomach t parts of body

to digest food, yuuucaly

cells skeletal muscles muscles to perform contract raplay hythmical

al type of muscle called cardiac which sucn ds mucoous

ssly they special cells proenaye Ot p

Secrete never fatigue during life time of an organism. Stomach has

mucus for lubricating the food, nyarocnlonic

pepsiogen, zymogen cells (or Chief cells) to secrete a

parietal cells oxyntic cells to secrete

(HCI) activatino P, caled or killing germs of food. Skeletal muscle

striated pepsin and also for

and vont nto runctional

contraction depends on your will or corntrol. Dute to uus PrOp

or skeletal their

muscle y muscles,

cells, 1.e,

Lil you are able to move your hands and ten fingers in aes ways.

components e human body, the cell itself has got division of labour. In fact, each cell has got certaln Spe

within it known as cell organelles (Table 2.5). Each kind of cell organelle pertor

t starch) synthesis laKIng of

by new material in the cell such as protein synthesis by ribosomes, fooa (8u


nus, cell clearing

a is able to live and perform functions up the waste substances from the cell by the lyscOsomes

its because of these organelles. These organelles toge

cOnstitute the basic building blocks called cells. Quite interestingly, all cells are designed to have the s

c structure, no matter what their function is or what organism they are tound in.

lable 2.5. Differences between organs and organelles.

Organs Organelles

hey are found in multicellular organisms.

hey 1. They are found in all eukaryotic cells.

are large sized or macroscoplc. 2. They are very small sized, either microscopic or Ce

3. They submicroScopic.

may be external

organismns. or internal to the body of an 3. They are mostly internal (i.e., intracellular). cel

4. The mi

organs are formed of tissues, (

of cells arnd cells tissues

formed comprise

are organelles. .

of An organelle is made up of micromolecules

. Organs macromolecules. and

coordinate to form organ systems,

Organ while 5. Organelles

systems form the body coordinate

of an organism. to produce the cell.

Cell Shape

The basic shape of eukaryotic

function of the cell

cell. is spherical,


Variable the shape but the shape

irregular of the cell of cell

or shape be is ultimately

may variable determined

occurs in Amoeba (i.e.,

(Fig. frequently by the speu

2.9) and white changing

blood cells its shape)

leucocytes. or th

or In fact, leucoc


80 movement of

the spontaneous

Thus, diffusion is concentration to one of

of high

molecules from a region concentration is finally

until uniform in Amoeba

lower concentration, phase than

faster in the gaseous cell

achieved. Diffusion is

liquids and solids. Activity 2.3diffusion of ink in

Something similar to such CO2 gets

flor example, a gas ashappens in cells when the

 inside a cell. n

accumulated in high of CO2 islcell, the concentrationexternal environment of there lis a

nside of the cell. As soon asow compared to of

as outside aconcentration of CO%, inside anddifference of from region of its high D

of the cell, i.e., Figure 2.16.

cell, CO2 moves out concentration by the process di

concentration to region of low.

 the cell O

similar way, oxygen (O,)when

of diffusion. In a of diffusion2.16) by the process(e.g., Amoeba ; Fig. cell decreases.

concentration of O2 inside the

the level or diffusion. Thealso follows the law of

2. Osmosis. Water through selectivewater molecules 

spontaneous movement of called osmosis.

plasma membrane) is

permeable membrane (e.g., cell is

plasma membrane of the

across the osmosis

The movement of water Thus,

substance dissolved in water.

affected by amount of through

water concentration

from region of high (Fig.

is the passage of water a concentrations

region of low water

semi-permeable membrane to a by which

a diffusion process

purely mechanical

2.17). Osmosis is a amount of energy.

without spending any

cells absorb water animal cell (e-g,

will happen if you put an

Let what into

us see (eg., Rheo leaves) a

RBCs) cells

or plant following

red blood cells or of the

prepared in water ? One

solution of sugar or salt


three things could higher water

the cell has a

medium surrounding solution,

1. If the dilute

i.e., if solution is a very

concentration than the cell, solution is called

Such dilute

water by osmosis. a

the cell will gain

hypotonic solution. plasma membrane

free to pass across the

The net

While water molecules are than leave.

will enter the cell

directions, more water situation, celln both the cell. In such ahat water enters 2.18A). Such(over all) result isinflated turgid (, become orhaemolysed. (Fig. 2.19B).is likely to swell up,ultimately burst, i.e.,swollen RBCs may exactly the samethe cell is ofmedium surrounding movement of2. If the there will be no netconcentrationthe cell, Fig. 2.19 A).

water as (Fig. 2.18B andplasma membrane solutionwater across the solution (eg, Ringer'scalled isotonicSuch solution isa cells).solution for the animalbothmembrane inwater crosses the movementIn this case, overallgoing out, so there is nosame as the amountmaintain the same size.


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