CELL – BASIC 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
 D I S C OV E RY O F C E L L
 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
 TO KNOW THE
HISTORY OF CELL?
 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”

Leeuw Rudolf
M.J.Schleiden Virchow
enhoek

Robert Schwann
Hook
Robert
Brown
 WHAT ARE LIVING
O RG A N I S M S M A D E U P O F ?
 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.
G A D G E T S TO S T U DY C E L L S
 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
 Shape and Size of cells
 Shape and size of cells vary but all of these are ultimately
determined by the specific function.
 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 VS.
M U LT I C E L L U L A R

 Unicellular  Multicellular

 Made of Single Cell  Made up of many number of cells

 Single cell able to perform all the  Cells have a similar basic
life processes like obtaining food, structure and similar basic life
respiration, excretion, growth and activities
reproduction.  Different shapes and aggregated
 Cannot be divided in to cells, they to form different tissues
are also called acellular organisms  Tissues form organs and organs

 Amoeba, paramecium give rise to organ system that

perform special function.

 Plants, Animals and Fungi

 Cell is basic unit of life
 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
 What is Cell made up of ?
 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
Plasma Membrane-Cell Membrane

 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

SEM-Plasma membrane

Plasma membrane
Transport Across the 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.
 Active & Passive Transport
 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 Transport
 Passive 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.

Diffusion – Demonstration
 Importance of Diffusion
 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.
 Osmosis
 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 - demonstration
 How Diffusion differs from
Osmosis ?
 Diffusion  Osmosis

 It can take place in solid,  It takes place only in liquid

liquid and gases. medium

 It does not involve any semi  It requires semi-permeable

membrane.
permeable membrane.
 It does not equalize the
 It equalizes the concentration
concentration of solvent on the
of substances.
two sides of the membrane
 Different substances diffuse
 Only solvent undergoes
independent of one another
diffusion
 Diffusion is not much
 It is influenced by the
influenced by the presence of
concentration and type of
other substances solute particles.
 Types of Osmotic Solutions
 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 Osmosis
 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.
Endosmosis

Exosmosis
 Cell Wall
 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

Plasmodesmata.
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. Middle lamella.
 What is the role of cell wall?
 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.

Does cell wall & Plasma membrane
are similar in function?

 Cell Wall  Plasma Membrane

 occurs in plant cells  Occurs in plant & animal cells

 lies on the outside of the  Lies on the outside of animal

cell cells and inside in plants

 Rigid and thick  Flexible and thin

 Cell wall is permeable  Selectively Permeable

 Formed of Cellulose, Hemi  Lipids and Proteins with small

cellulose and Pectin. number of carbohydrates

 Hold cellular contents and

 Provide protection and
control of passage materials
strength to the cell
 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)
What is Nucleus made up of ?
Nuclear Envelop
 Nuclear Envelop is a double membrane
Nucleoplasm
Nucleolus 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.
THE NUCLEUS IS ENCLOSED
BY A DOUBLE MEMBRANE
Nuclear Pore Complex-Diagram
 Does cell wall & Plasma membrane
are similar in function?

 Nucleus  Nucleolus
 It represent the whole eukaryotic  It is a component of nucleus
complex that contains genetic
information
 It is covered by a two membrane
 It is without a covering
envelop
membrane
 It controls the structure and
 It synthesizes ribosomal subunits
working of cells

 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.
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-Number
 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)
Role of Nucleus in a Cell
 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
Prokaryotes & Eukaryotes
 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
Plant Cell
Bacteria
Prokaryotes & Eukaryotes
 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

 Small in size, 1-10μm.  Larger in size, 5-100 μm

 Organized nucleus is absent.  Organized nucleus is present

 A single DNA molecule is with nuclear envelop,

present suspended in Nucleolus is present, several

cytoplasm, nucleolus is absent DNA molecules are present

 Membrane bound cell  Membrane bound cell

organelles are absent organelles are present

 Typical vacuoles are absent  Typical vacuoles are present

 Mitosis is absent  Mitosis is present

 Bacteria, Cyanobacteria  Plants, Animals, Fungi

Eukaryotic (Animal ) Cell
Cytoplasm
 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

Endoplasmic Reticulum
 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
Functions of E.R.
 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
 SER  RER
 Ribosomes are absent  Ribosomes are present
 Synthesize lipids and steroids
 Synthesize proteins
 Mainly formed of vesicles and
 Formed by cisternae
tubules
Golgi Complex
 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 Apparatus
Functions of Golgi
 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

Lysosomes
Lysosomes-suicide bags
 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
Lysosomes-Kuffer cells
 Intracellular Digestion
 Removal of cell debris
 Time of metamorphosis
 Organs are digested by Lysosomes
Mitochondria (power House of a Cell)

 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
Lysosomes-suicide bags
Plastids
 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

 Leucoplasts  Chromoplasts (non green)

 colorless  Brown or reddish in colour
 Cylindrical to round in shape  Irregular in shape
 Found in un exposed cells  in exposed & un exposed cell
 Take part in storage of food  Do not storage food
 Can change to other types  Provide coloration of organs
Chloroplast-kitchen of the cell
 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 Chloroplast
Lysosomes-suicide bags
Plastids-functions
 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.
Ribosomes-Translation factory
 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

 Centrosome-central apparatus
 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
 Vacuoles-store house of the cell
 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
 Differences between Plant and
Animal Cell
 Cell wall is present  absent
 Plastids are present  absent
 Centrioles and centrosomes  Centrioles and centrosomes
are absent are present

 Vacuoles large and less  Vacuoles small and many

 Nucleus lie on one side  Nucleus lies in the centre

 Cell is rigid  Cell is flexible

 Golgi contains dictyosomes  In the form of vesicles

 Larger in size  Smaller in size

 Starch is stored  Glycogen is stored

Plant and Animal Cell
 Prepared by
R.V.Raghavendra Rao

PGTBiology

JNV Kiltampalem

Vizianagaram

Email-raghubloom@gmail.com

Phone-9490811620