CELL – BASIC UNIT OF LIFE
C E L L – BA S I C U N I T O F L I FE
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
Leeuw enhoek
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
Endosmosis 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 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 Envelop Nucleoplasm Nucleolus
T H E N U C L E U S I S E N C L O S E D
B Y A D O U B L E M E M B R A N E
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