CELL – BASIC UNIT OF LIFE

Fundament unit of life

CELL – BASIC UNIT OF LIFE

Prokaryotic and Eukaryotic Cells

Multicellular Organisms

Cell Membrane and Cell Wall

Cell Organelles• Chloroplast• Mitochondria• Vacuoles• Endoplasmic Reticulum• Golgi Apparatus• Nucleus

Chromosomes • Basic Structure, Number

DISCOVERY OF CELL

In 1665 Robert Hooke – an English Scientist, Saw

Cells in a thin slice of cork with his crude

microscope.

He observed as “Honey – comb” like Structure

and named them as CELLULAE or CELLS

His discovery indicated for the first time that

living organisms consisted of number of small

structures or units.

Microscope

1665- Robert Hook discovery of cell

1674-A. Van Leeuwenhoek-studied living for the first

time.

1831-Robert Brown discovery and named Nucleus in a

cell

1838-39-M.J.Schleiden & Schwann formulated Cell

Theory

1855-Rudolf Virchow, Stated “Omnis cellula-e-cellula”

TO KNOW THE HISTORY OF CELL?

Robert Hook

Leeuwenhoek

Robert Brown

M.J.Schleiden

Schwann

Rudolf Virchow

Just as a building is made up of bricks the body of all

living organisms made up of cells.

Basing on the cellular organization some organisms are

made of single cells “Unicellular Organisms” e.g.

Chlamydomonas, Amoeba, Paramecium

Organisms which are made up of more than a cell

“multicellular”

Irrespective of unicellular or multicellular organisms

the cells perform similar basic functions for their

survival.

WHAT ARE LIVING ORGANISMS MADE UP

OF?

Cells are too small to be seen by necked eye.

They are studied with the help of microscopes.

Microscopes are high resolution instruments that

are used for observing fine details of very small

objects

Two common types of microscopes• Light microscope-magnification range from 100-1500• Electron microscope- magnification range from 1 lakh-

5 lakhs

GADGETS TO STUDY CELLS

Shape and size of cells vary but all of these are

ultimately determined by the specific function.

Shape and Size of cells

Some cell can change their

shapes amoeba, WBC but plants

and animals have almost fixed

shapes.

Smallest ell=

PPLO(mycoplasma)

Largest Cell-Ostrich egg

Longest animal cell-Nerve cell

A micrometer (μm) or micron is

one thousandth of a millimeter.

The Scale of Life

Unicellular

Made of Single Cell

Single cell able to

perform all the life

processes like obtaining

food, respiration,

excretion, growth and

reproduction.

Cannot be divided in to

cells, they are also called

acellular organisms

Amoeba, paramecium

UNICELLULAR VS. MULTICELLULAR

Multicellular

Made up of many number of

cells

Cells have a similar basic

structure and similar basic

life activities

Different shapes and

aggregated to form different

tissues

Tissues form organs and

organs give rise to organ

system that perform special

function.

Plants, Animals and Fungi

It performs all life function like intake of food

materials, excretion, metabolism, respiration,

irritability, etc.,

Division of Labour – Cell usually possesses a

number of components called cell organelles.

Each cell organelle performs different functions• Clearing waste material• Protein synthesis• Lipid synthesis

Cell is basic unit of life

A cell is a tiny mass of protoplasm which is

surrounded by a membrane and is capable of

performing all function of life.

A typical cell is formed of three parts• Plasma membrane-to create separate

environment • Nucleus-for its control• Cytoplasm-possessing metabolic machinery

What is Cell made up of?

The outer most delicate elastic membranous covering of the

cell that separates its contents from the external

environment is called Plasma Membrane

Plasma Membrane is Selectively Permeable (it allows entry

of certain substance restricting others)

It is made up of a bi-lipid layer and proteins are integrated

in out and inside.

Small carbohydrates are attached at placed to outer surface

of lipids and proteins.

Functions- Shape to contents of cell, Mechanical Barrier,

Semi-Permeable, Endocytosis, Recognition Centres, Flow of

Information, Osmosis, Cell Continuity, Modified to perform

special functions like absorption in microvilli.

Plasma Membrane-Cell Membrane

Plasma Membrane

Plasma membrane

SEM-Plasma membrane

Membranes act as physical

barriers between the organelles

of a cell and its cytoplasm and its

surrounding environment.

Impermeable – substances do not

pass through the membrane

Permeable – both solute and

solvent can pass through

Semipermeable – membrane

permeable to solvent but prevents

solutes passage

Selectively Permeable – if

membrane allows the passage of

solvent and some selected

solutes.

Transport Across the Membrane

Substances may pass across the membrane without or

with expenditure of energy-

Active Transport - substances pass the membrane with

consuming ATP

Passive Transport-substances pass the membrane

without consuming ATP

Bulk Transport – Large amounts of substances and food

particles across the plasma membrane

The process of bringing the bulk of materials from outside

by formation of endosomes is called endocytosis.

Bulk expulsion of materials as in secretion and excretion

is called exocytosis.

Active & Passive Transport

Active Transport

Passive Transport is of two types• Diffusion• Osmosis

Diffusion – The process of movement of substances

(solid, Liquid or Gas)from the region of higher

concentration to the region of its lower concentration

till spread uniformly in the given space is called

diffusion.

Passive Transport

Diffusion – Demonstration

Helps in spread of different

substances throughout

cytoplasm of cell.

Osmosis is a type of diffusion

where only solvent is allowed

to diffuse.

Diffusion helps in exchange

of respiratory gases between

the cells and their

environment.

Transpiration is diffusion

process

Flowers spread aroma

through diffusion to attract

insects and other animals for

pollination.

Importance of Diffusion

Defined as the diffusion of water or solvent across a

semipermeable membrane from a region of its higher

concentration to region of its lower concentration.

Plasma membrane functions as semipermeable

membrane.

Osmosis

Osmosis Osmosis - demonstration

Diffusion

It can take place in solid,

liquid and gases.

It does not involve any semi

permeable membrane.

It equalizes the

concentration of substances.

Different substances diffuse

independent of one another

Diffusion is not much

influenced by the presence

of other substances

How Diffusion differs from Osmosis ?

Osmosis

It takes place only in liquid

medium

It requires semi-permeable

membrane.

It does not equalize the

concentration of solvent on

the two sides of the

membrane

Only solvent undergoes

diffusion

It is influenced by the

concentration and type of

solute particles.

Osmotic solutions are those solutions which can cause

osmosis

They are three types• Hypotonic Solution, Isotonic Solution and Hypertonic

Solution

Hypotonic – which has an osmotic concentration lower

than another solution.

Isotonic – The solution has an osmotic concentration

similar to another solution.

Hypertonic – which has an osmotic concentration higher

than that of another solution.

Types of Osmotic Solutions

Osmosis is of two types • Endosmosis• Exosmosis

Endosmosis – Osmotic entry of water in to the cell or

system

Exosmosis – Osmotic withdrawal of water from a cell or

system

When we place the cell in higher concentration the

water comes out of the cell by a process called

exosmosis.

When we place the cell in lower concentration the

water enters in to the cell by a process called

endosmosis.

Types of Osmosis

En

dosm

os

is Exosm

osis

Rigid, semi elastic, semi transparent and

protective covering present outside the

plasma membrane in plant cells, fungi and

prokaryotes.

Made up of Cellulose in plants, Fungal

cellulose and Chitin in fungi

Extra deposition of lignin, suberin and

cutin may be present during secondary

thickening

A cementing layer called middle lamella is

present between the walls of two adjacent

cells

Cell wall possesses small pores through

which adjacent cells remain connected

called Plasmodesmata.

Cell Wall

Plasmodesmata.

Middle lamella.

It provides shape to the cells

It provides mechanical strength to plants

Protects against pathogens and mechanical injury

Growth of the cell wall determines the growth of the

cell

Cell wall prevents bursting of cell on endosmosis

Ability to withstand a lot of variation in nature.

What is the role of cell wall?

Does cell wall & Plasma membrane are similar in

function?

Cell Wall

occurs in plant cells

lies on the outside of

the cell

Rigid and thick

Cell wall is permeable

Formed of Cellulose,

Hemi cellulose and

Pectin.

Provide protection and

strength to the cell

Plasma Membrane

Occurs in plant & animal

cells

Lies on the outside of

animal cells and inside in

plants

Flexible and thin

Selectively Permeable

Lipids and Proteins with

small number of

carbohydrates

Hold cellular contents and

control of passage materials

Nucleus – The Cell Brain

Dense protoplasmic body that

contains hereditary information

controlling cell activities as well as for

transfer to next generation

It lies in median or central position

In mature plant cell it lies towards

periphery

In prokaryotes nuclear membrane is

absent

It is called Nucleoid.

Cells like RBC, Sieve Elements lack

Nucleus

Cells without Nucleus cannot survive

for longtime

One nucleus (uninucleate) is present

in most of cells but some cells may

have more than one (multi nucleate)

Nuclear Envelop is a double

membrane covering which separates

the nucleus from the cytoplasm. It

contains many Nuclear pores.

Nuclear pores allow exchange of

materials between the nucleus and

cytoplasm

Nucleoplasm – It is colorless, dense

sap found inside the nucleus in which

chromatin and nucleolus are

suspended.

Nucleolus – a round structure found in

side the nucleus, it is rich in RNA and

protein. It is site of ribosome

formation.

What is Nucleus made up of?

Nuclear EnvelopNucleoplasmNucleolus

THE NUCLEUS IS ENCLOSED BY A DOUBLE MEMBRANE

Nuclear Pore Complex-Diagram

Does cell wall & Plasma membrane are similar in

function?

Nucleus

It represent the whole

eukaryotic complex that

contains genetic

information

It is covered by a two

membrane envelop

It controls the structure

and working of cells

Nucleolus

It is a component of

nucleus

It is without a covering

membrane

It synthesizes ribosomal

subunits

Chromatin Material – An intervened mass of thread-like structure made of DNA and Proteins. During Cell Division, Chromatin becomes highly condensed, thick and rod like structures, Known as Chromosomes.

Thread like structures which are formed by condensation of

chromatin during cell division are called chromosomes they

referred as hereditary vehicles

Chromosomes are made of DNA & Proteins

A chromosome consists of two similar threads called

Chromatids

Two chromatids are attached at the center by a centromere

On either side of centromere chromatids are called arms

Chromosomes

Chromosome number is fixed for each species

In most organisms they occur in homologous pair

In each pair, one chromosome belongs to father parent

while other belongs to mother parent

Presence of two sets of chromosomes is called Diploid• 2n=46 ( in human)

Presence of singe set of chromosomes is called Haploid• n=23 (in human)

Chromosomes-Number

Nucleus contains all the genetic

information not only for the cell but

also the whole organism

It functions as control centre of the

cell as it controls cell metabolism

and cell activities

Ribosomes are formed by nucleolus

part of nucleus

Nucleus us brings about cell

differentiation by which a cell

attains a specific structure and

function.

Division of nucleus is essential for

cell division

Reshuffling of chromosomes and

changes in genes produce variations

Role of Nucleus in a Cell

Prokaryotes (singular ) are a group of organisms that

lack a cell nucleus or any other membrane-bound

organelles. They differ from the eukaryotes, which

have a cell nucleus. Prokaryotes are the single-celled

organisms, such as bacteria, and are roughly one

micrometre in diameter.

A eukaryote is an organism whose cells contain

complex structures inside the membranes. The

defining membrane-bound structure that sets

eukaryotic cells apart from prokaryotic cells is the

nucleus, or nuclear envelope, within which the genetic

material is carried

Prokaryotes & Eukaryotes

Bacteria Plant Cell

Prokaryotes do not have a nucleus that houses its genetic

material.

Prokaryote cell consists of a large DNA molecule compacted

in an area of cytoplasm called the nucleoid region.  

The nucleoid region is protected and encased by the cell

wall, or cell membrane, the outer layering of the cell

(similar to human's skin).  Finally,

Flagellum a rudder-like device, affords the prokaryote the

luxury of mobility.  

Prokaryotes & Eukaryotes

Prokaryotes & Eukaryotes

Prokaryotes

Small in size, 1-10μm.

Organized nucleus is

absent.

A single DNA molecule is

present suspended in

cytoplasm, nucleolus is

absent

Membrane bound cell

organelles are absent

Typical vacuoles are absent

Mitosis is absent

Bacteria, Cyanobacteria

Eukaryotes

Larger in size, 5-100 μm

Organized nucleus is

present with nuclear

envelop, Nucleolus is

present, several DNA

molecules are present

Membrane bound cell

organelles are present

Typical vacuoles are

present

Mitosis is present

Plants, Animals, Fungi

Eukaryotic (Animal ) Cell

The contents of a cell except for the nucleus. It

includes cytosol, organelles, vesicles, and the

cytoskeleton

Cytoplasm has two parts, cytosol and cell organelles

Cytosol – is the fluid part of cytoplasm,

homogeneous and crystallocolloidal liquid that

contains substances water, ions, enzymes, vitamins,

amino acids, carbohydrates, lipids, proteins etc.,

Cell Organelles – Submicroscopic structure which

are specialized to perform specific cellular

functions.

Cell organelles may be bounded by a membrane as

in Eukaryotes but prokaryotes lack membrane bound

organelles

Virus lack cytoplasm as well as membrane

Cytoplasm

The endoplasmic reticulum (ER) is a network of interconnecting

membranes distributed throughout the cytoplasm.

The internal compartment, called the lumen, is a separate part

of the cell with a distinct protein and ion composition.

The ER’s folding generates a surface area much greater than

that of the plasma membrane.

At certain sites, the ER membrane is continuous with the outer

nuclear envelope membrane.

Depending upon the presence or absence of ribosomes on the

surface, there are two types of E.R.

Rough E.R. – Characterized by the presence of ribosomes on its

surface

Smooth E.R. – Devoid of ribosomes on its surface

Endoplasmic Reticulum

Endoplasmic Reticulum

Protein Synthesis – Rough E.R. is the site of Protein

synthesis

Lipid Synthesis – Smooth E.R. helps in lipid synthesis

Proteins and lipids synthesized on E.R. are used for

making cell membrane

Transport – helps in intercellular and intracellular

transport of substances

Support – it gives internal support to the cytoplasm

SER in liver cells takes part in detoxifying many

poisons and drugs

Functions of E.R.

SER

Ribosomes are absent

Synthesize lipids and steroids

Mainly formed of vesicles

and tubules

RER

Ribosomes are present

Synthesize proteins

Formed by cisternae

Golgi complex is an organelle of membrane bound sacs,

tubules and vesicles secrete complex biochemical

Golgi is a single complex in animal cells.

In plants they form separate units called dictyosomes.

Membrane bound sacs of Golgi are called cisternae.

Cisternae occurs in stacks, tubes and vesicles occur on

their periphery

Golgi Complex

Golgi Apparatus

Golgi apparatus is involved in repair and

synthesis of cell membranes

Lysosomes are formed by Golgi apparatus

All types of substances which are to be secreted

or excreted are packed in vesicles by Golgi

apparatus for passage to the outside

Takes part in storage, modification and

packaging of various biochemical produced by

different components of the cell

Components of cell wall are synthesized by

Golgi apparatus

Complex and special sugars are made by Golgi

apparatus

Functions of Golgi

Lysosomes

Lysosomes generally found in animal cells they lack in plant cell

Are small spherical vesicles covered by single membrane

contain digestive enzymes for intracellular digestion and waste

disposal

These enzyme are synthesized by R.E.R

In damaged cell, lysosomes burst to release enzymes for

digestion of cellular components

Functions

Destruction of foreign particles

Intracellular Digestion

Removal of cell debris

Time of metamorphosis

Organs are digested by Lysosomes

Lysosomes-suicide bags

Lysosomes-Kuffer cells

Mitochondria is rod-shaped cell organelles of aerobic

eukaryotes which take part in the Krebs cycle.

Commonly called “Power House of the Cell” because they

contain enzymes necessary for the total oxidation of food and

for release of high amount of energy in the form of ATP

It is bounded by two membrane- outer membrane is smooth and

porous while inner membrane is folded inwards to form Cristae

Cristae contains oxysomes they are partially embedded in inner

membrane

Mitochondria enclose a matrix having DNA, ribosomes and

enzymes.

DNA and ribosomes make the mitochondria semi-autonomous as

they are able to manufacture some of their own proteins and

enzymes.

Mitochondria (power House of a Cell)

Mitochondria

Lysosomes-suicide bags

Plastids are large cell organelles found only in plant

cells which are specialized to synthesize and store

organic substances.

Plastids are classified on the basis of pigment present

in them two types• Leucoplasts – colorless plastids (amyloplasts,

aleuroplast, elaioplasts• Chromoplasts – Coloured Plastids. Green & Non green

plastids

Plastids

Leucoplasts

colorless

Cylindrical to round in

shape

Found in un exposed cells

Take part in storage of

food

Can change to other types

Chromoplasts (non green)

Brown or reddish in colour

Irregular in shape

in exposed & un exposed

cell

Do not storage food

Provide coloration of organs

Bounded by two membranes. Inside of chloroplast is

clearly marked into a colorless matrix called Stroma

and Membranous system called Grana.

Each granum consists of stack of membrane bounded,

flattened sacs called thylakoids

Thylakoids pigments like chlorophyll, carotenoids and

phycobillins

Stroma contains enzymes for dark reaction, DNA, RNA

and ribosomes, latter make the chloroplasts

semiautonomous.

Chloroplast-kitchen of the cell

Chloroplast Chloroplast

Lysosomes-suicide bags

Chromoplasts provide color to fruits and flowers and

attract the animals to help in pollination and fruit

dispersal

Leucoplasts take part in storage of protein, starch and

oil

Chloroplasts trap solar energy to manufacture food

through photosynthesis

Oxygen is being consumed in combustion and

respiration. Carbon dioxide is being produced inn the

two process. Chloroplasts maintain the balance of the

two gases by absorbing carbon dioxide and oxygen in

photosynthesis.

Plastids-functions

Ribosomes are small rounded bodies found either in

free state in the cytoplasm or attached to the surface of

Endoplasmic Reticulum

They are composed of ribonucleic acid (RNA) and

proteins

They are not bounded by a membrane

They are present in both prokaryotes (70s=50s+30s)

eukaryotes (80s=60s+40s)

Absent in mammalian R.B.Cs.

Ribosomes are the site of protein synthesis in the cell

Ribosomes-Translation factory

It is a small naked organelle

present near the nucleus in the

cells of animals and some lower

plants.

It has sheath of special

cytoplasm called centrosphere.

It encloses two micro cylinders

called centrioles.

Two centrioles like right angles

to each other.

It has nine triplet fibrils

present obliquely on the

periphery.

They form astral spindle fibers

and produce basal bodies that

form cilia and flagella

Centrosome-central apparatus

Membrane bound non-cytoplasmic sacs that contain

non-living solid or liquid contents. They are of three

types- sap vacuoles, food vacuoles and contractile

vacuoles

Covering membrane of sap vacuole is called tonoplast

The fluid filled content of the vacuole is called cell sap

or tonoplasm

Recently digestive enzymes are reported in vacuole of

plant cell

Vacuoles-store house of the cell

Vacuoles-store house of the cell

Differences between Plant and Animal Cell

Cell wall is present

Plastids are present

Centrioles and

centrosomes are absent

Vacuoles large and less

Nucleus lie on one side

Cell is rigid

Golgi contains

dictyosomes

Larger in size

Starch is stored

absent

absent

Centrioles and

centrosomes are present

Vacuoles small and many

Nucleus lies in the

centre

Cell is flexible

In the form of vesicles

Smaller in size

Glycogen is stored

Plant and Animal Cell

R.V.Raghavendra Rao

PGTBiology

JNV Kiltampalem

Vizianagaram

Email-raghubloom@gmail.com

Phone-9490811620

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