CELL – BASIC UNIT OF LIFE

Fundament unit of life

CELL – BASIC UNIT OF LIFE

Prokaryotic and Eukaryotic CellsMulticellular OrganismsCell Membrane and Cell WallCell 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 cell1674-A. Van Leeuwenhoek-studied living for the first time.1831-Robert Brown discovery and named Nucleus in a cell1838-39-M.J.Schleiden & Schwann formulated Cell Theory1855-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

UnicellularMade 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

MulticellularMade 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

Active Transport

Active Transport

Active Transport

Active 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

Endosmos

is Exosmosis

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 cellsIt provides mechanical strength to plantsProtects against pathogens and mechanical injuryGrowth of the cell wall determines the growth of the cellCell wall prevents bursting of cell on endosmosisAbility 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 Walloccurs in plant cellslies on the outside of

the cell Rigid and thickCell wall is permeableFormed 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 apparatusAll 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 presentCentrioles and

centrosomes are absentVacuoles large and lessNucleus lie on one sideCell is rigidGolgi contains

dictyosomesLarger in sizeStarch 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

Adhweat Gupta

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