CELL:CELL:THE UNIT THE UNIT

OF OF LIFELIFE

What is a cell?What is a cell?

A cell is the smallest unit that is A cell is the smallest unit that is capable of performing life capable of performing life functions. functions.

All living organisms are composed All living organisms are composed of cells. of cells.

Examples of cell:Examples of cell:

Amoeba Proteus

Plant Stem

Red Blood Cell

Nerve Cell

Bacteria

Cell TheoryCell Theory

All living things are made up of cells. All living things are made up of cells. Cells are the smallest working units of all Cells are the smallest working units of all

living things. living things. All cells come from preexisting cells through All cells come from preexisting cells through

cell division. cell division.

Discovery of cell:Discovery of cell:

In 1665, In 1665, Robert HookeRobert Hooke examined a thin slice examined a thin slice of a cork under a of a cork under a microscope.  He saw microscope.  He saw that it was made of that it was made of thousands of tiny thousands of tiny chambers.  These chambers.  These chambers reminded chambers reminded him of the tiny rooms him of the tiny rooms in a monastery, called in a monastery, called cells.cells.

TYPES OF CELL:TYPES OF CELL:

There are two types of There are two types of cells: cells:

Prokaryotic cellProkaryotic cell Eukaryotic cellEukaryotic cell

Characteristics of Prokaryotic cell:Characteristics of Prokaryotic cell:

Cells that lack a membrane-Cells that lack a membrane-bound nucleus are called bound nucleus are called prokaryotes (from the Greek prokaryotes (from the Greek meaning before nuclei). meaning before nuclei).

Cells in the monera Cells in the monera kingdom such as bacteria kingdom such as bacteria and cyanobacteria (also and cyanobacteria (also known as blue-green algae) known as blue-green algae) are prokaryotes. are prokaryotes.

They don't have a They don't have a membrane-bound nucleus membrane-bound nucleus and their genetic and their genetic information is in a circular information is in a circular loop called a plasmid. loop called a plasmid.

Bacterial cells are very Bacterial cells are very small, roughly the size small, roughly the size of an animal of an animal mitochondrion (about 1-mitochondrion (about 1-2µm in diameter and 10 2µm in diameter and 10 µm long). µm long).

Characteristics of Eukaryotic cell:Characteristics of Eukaryotic cell:

Eukaryotic cells (from the Eukaryotic cells (from the Greek meaning truly Greek meaning truly nuclear) comprise all of the nuclear) comprise all of the life kingdoms except life kingdoms except monera. monera.

They can be easily They can be easily distinguished through a distinguished through a membrane-bound nucleus. membrane-bound nucleus.

Eukaryotic cells also Eukaryotic cells also contain many internal contain many internal membrane-bound structures membrane-bound structures called organelles. These called organelles. These organelles such as the organelles such as the mitochondrion or mitochondrion or chloroplast chloroplast

Following are the Important Cell-Following are the Important Cell-organelles:organelles:

Cell membraneCell membrane Cell wallCell wall Endoplasmic reticulumEndoplasmic reticulum Golgi apparatusGolgi apparatus LysosomeLysosome VacuolesVacuoles MitochondriaMitochondria PlastidsPlastids Ribosomes Ribosomes Cilia and FlagellaCilia and Flagella Centrosome and centriolesCentrosome and centrioles NucleusNucleus MicrobodiesMicrobodiesLet us study about each of them individually………………………………Let us study about each of them individually………………………………

Cell membrane:Cell membrane: Outer membrane of cell that Outer membrane of cell that

controls movement in and out of controls movement in and out of the cellthe cell

Double layer Double layer It is a multipurpose covering It is a multipurpose covering

composed of phospholipids and composed of phospholipids and proteins. proteins.

Apart from the plasma membrane, Apart from the plasma membrane, an eukaryotic cell also shows an eukaryotic cell also shows intracellular and subcellular intracellular and subcellular membranes around its organelles membranes around its organelles and vacuoles. and vacuoles.

A fluid mosaic model was given A fluid mosaic model was given by singer and nicholson.by singer and nicholson.

Cell Wall:Cell Wall: A cell wall is a characteristic feature A cell wall is a characteristic feature

of plant cells, bacteria and fungi. The of plant cells, bacteria and fungi. The composition however varies in composition however varies in different groups. different groups.

cell wall is chiefly composed of cell wall is chiefly composed of insoluble polysaccharides, most insoluble polysaccharides, most common constituent is cellulose, common constituent is cellulose, pectin, hemicellulose, lignin and pectin, hemicellulose, lignin and xylan may also be present. xylan may also be present.

The cell wall is generally deposited The cell wall is generally deposited in two layers a primary wall and a in two layers a primary wall and a secondary wall. secondary wall.

the cell wall is involved in some the cell wall is involved in some specific functions such as :specific functions such as :

Protection against the attack of Protection against the attack of pathogens pathogens

Providing mechanical support Providing mechanical support Allowing movement of materials in Allowing movement of materials in

and out of the cell and out of the cell

Cytoplasm:Cytoplasm: The term cytoplasm can be used to describe The term cytoplasm can be used to describe

the matrix of a cell found between its plasma the matrix of a cell found between its plasma membrane and the nucleus. It encloses membrane and the nucleus. It encloses various cell organelles and inclusions. various cell organelles and inclusions.

The cytoplasm is a semi viscous jelly-like The cytoplasm is a semi viscous jelly-like substance. It consists of an aqueous, almost substance. It consists of an aqueous, almost transparent structureless ground substance transparent structureless ground substance called hyaloplasm or cytosol. called hyaloplasm or cytosol.

Cytoplasm serves the following functions Cytoplasm serves the following functions It is the seat of all metabolic and bio-It is the seat of all metabolic and bio-

chemical processes taking place in a cell. chemical processes taking place in a cell. It is involved in the storage of raw materials It is involved in the storage of raw materials

or reserve food required by the cell. or reserve food required by the cell. It brings about exchange of materials It brings about exchange of materials

between the cell organelles. between the cell organelles. It exchanges materials with the surrounding It exchanges materials with the surrounding

environment such as extra cellular fluid. environment such as extra cellular fluid.

Endoplasmic Reticulum(ER):Endoplasmic Reticulum(ER): This is a complex network of tubes, the This is a complex network of tubes, the

lumen of which is filled with fluid. Two lumen of which is filled with fluid. Two types of endoplasmic reticula are seen. types of endoplasmic reticula are seen. They are:They are:

Tubes with a smooth surface are called Tubes with a smooth surface are called smooth endoplasmic reticula. They smooth endoplasmic reticula. They secrete lipids. secrete lipids.

Tubes with spherical bodies (ribosomes) Tubes with spherical bodies (ribosomes) attached are known as rough endoplasmic attached are known as rough endoplasmic reticula. reticula.

The functions of the endoplasmic The functions of the endoplasmic reticulum are to form the skeletal reticulum are to form the skeletal framework of the cell, to provide a framework of the cell, to provide a pathway for the distribution of nuclear pathway for the distribution of nuclear material from one cell to the other and to material from one cell to the other and to synthesize fats, steroids and cholesterol synthesize fats, steroids and cholesterol with the help of enzymes secreted by the with the help of enzymes secreted by the cell. cell.

Golgi apparatusGolgi apparatus Also known as Golgi Complex Also known as Golgi Complex

or Golgi Bodies, they consist of or Golgi Bodies, they consist of tiny, elongated, flattened sacs tiny, elongated, flattened sacs (cisternae), which are stacked (cisternae), which are stacked parallel to one another along parallel to one another along with some vacuoles and clusters with some vacuoles and clusters of vesicles. of vesicles.

The function of the golgi body is The function of the golgi body is to secrete certain hormones and to secrete certain hormones and enzymes. It also forms enzymes. It also forms lysosomes and peroxisomes. The lysosomes and peroxisomes. The golgi body is usually found close golgi body is usually found close to the nucleus. to the nucleus.

Lysosomes:Lysosomes: These are tiny, spherical, These are tiny, spherical,

sac-like structures scattered sac-like structures scattered all over the cytoplasm. Their all over the cytoplasm. Their main function is digestion. main function is digestion.

They contain powerful They contain powerful destructive enzymes capable destructive enzymes capable of digesting all organic of digesting all organic material, and hence called material, and hence called “digestive bags”. “digestive bags”.

““suicide bag” is a sobriquet suicide bag” is a sobriquet that is often used for that is often used for Lysosomes.Lysosomes.

Vacuoles:Vacuoles:

Membrane-bound sacs Membrane-bound sacs for storage, digestion, for storage, digestion, and waste removaland waste removal

Contains water solutionContains water solution Help plants maintain Help plants maintain

shapeshape

Mitochondria:Mitochondria: These may be cylindrical, rod-These may be cylindrical, rod-

shaped or spherical and distributed shaped or spherical and distributed in the cytoplasm. in the cytoplasm.

Each mitochondrion is bound by a Each mitochondrion is bound by a double membrane. double membrane.

The inner membrane is folded into The inner membrane is folded into ridges called cristae, which increase ridges called cristae, which increase the surface area of the membrane. the surface area of the membrane.

It is in the mitochondria that the It is in the mitochondria that the sugar is finally burnt during cellular sugar is finally burnt during cellular respiration. The energy thus released respiration. The energy thus released is stored as high-energy chemicals is stored as high-energy chemicals called ATP (adenosine triphosphate). called ATP (adenosine triphosphate). Hence, mitochondria are termed as Hence, mitochondria are termed as the “power house” or the “power the “power house” or the “power plant” of the cell. plant” of the cell.

Plastids:Plastids: These organelles are found only in plant cells.These organelles are found only in plant cells. Plastids are of three typesPlastids are of three types:: Chloroplasts Chloroplasts Chromoplasts Chromoplasts Leucoplasts Leucoplasts ChloroplastsChloroplasts They are green and found in leaves. The green colour They are green and found in leaves. The green colour

is due to the presence of chlorophyll.is due to the presence of chlorophyll.

ChromoplastsChromoplasts They are yellow, orange and red, and found in flowers They are yellow, orange and red, and found in flowers

and fruits.and fruits.

LeucoplastsLeucoplasts They are colourless and found in roots, seeds and They are colourless and found in roots, seeds and

underground stems.underground stems. The function of the chloroplast is to trap solar energy The function of the chloroplast is to trap solar energy

for photosynthesis. Chromoplasts impart colour to for photosynthesis. Chromoplasts impart colour to flowers to attract insects for pollination. Leucoplasts flowers to attract insects for pollination. Leucoplasts store food in the form of carbohydrates, fats and store food in the form of carbohydrates, fats and proteins.proteins.

Ribosomes:Ribosomes:

These are spherical, These are spherical, granular particles which granular particles which occur freely in the matrix occur freely in the matrix or remain attached to the or remain attached to the rough endoplasmic rough endoplasmic reticulum. reticulum.

Ribosomes contain RNA Ribosomes contain RNA (ribonucleic acid) and (ribonucleic acid) and proteins proteins

Their function is to Their function is to provide the surface for provide the surface for protein synthesis. protein synthesis.

Cytoskeleton:Cytoskeleton:

An elaborate network of An elaborate network of filamentous filamentous proteinaceous structures proteinaceous structures present in cytoplasm.present in cytoplasm.

They are involved in They are involved in many functions as many functions as mechanical support, mechanical support, motility, maintenance of motility, maintenance of shape of cell etc.shape of cell etc.

Cilia and Flagella:Cilia and Flagella: Hair-like outgrowths of the Hair-like outgrowths of the

cell membranecell membrane Covered by plasma Covered by plasma

membranemembrane Their core axoneme Their core axoneme

possesses a no. of possesses a no. of microtubules parallel to microtubules parallel to long axis.long axis.

Cilia are small hair-like Cilia are small hair-like structures which work like structures which work like oars. Flagella are longer hair oars. Flagella are longer hair like structures which beat like structures which beat anteriorly or posteriorly.anteriorly or posteriorly.

Flagella are of two types: 1.) Flagella are of two types: 1.) Whiplash 2.)TinselWhiplash 2.)Tinsel

Centrosome and Centrioles:Centrosome and Centrioles:

Present only in animal cellsPresent only in animal cells Made up of two centrioles Made up of two centrioles

(cylindrical structures).(cylindrical structures). The central part of proximal The central part of proximal

region of centriole is also region of centriole is also proteinaceous and called proteinaceous and called hub.hub.

Function:formation of Function:formation of spindle fibres.spindle fibres.

Nucleus:Nucleus: This is a prominent, spherical or This is a prominent, spherical or

oval structure found at the centre oval structure found at the centre of the cell. It is the controlling of the cell. It is the controlling centre of all cell activities and has centre of all cell activities and has been described as the brain of the been described as the brain of the cell. It regulates all metabolic and cell. It regulates all metabolic and hereditary activities of the cell.hereditary activities of the cell.

The nucleus is composed of the The nucleus is composed of the following structures: following structures:

Nuclear Membrane Nuclear Membrane Nucleoplasm Nucleoplasm Nucleolus Nucleolus Chromatin network Chromatin network

Nuclear MembraneNuclear Membrane This is a double-layered membrane which separates the nucleoplasm from the This is a double-layered membrane which separates the nucleoplasm from the

cytoplasm. The nuclear membrane has minute pores which allow the selective cytoplasm. The nuclear membrane has minute pores which allow the selective transfer of material between the nucleoplasm and the cytoplasm.transfer of material between the nucleoplasm and the cytoplasm.

NucleoplasmNucleoplasm Within the nuclear membrane, completely filling up the space, is a clear, semi-Within the nuclear membrane, completely filling up the space, is a clear, semi-

solid, granular substance or matrix called the nucleoplasm. The nucleolus and the solid, granular substance or matrix called the nucleoplasm. The nucleolus and the chromatin network lie suspended in the nucleoplasm.chromatin network lie suspended in the nucleoplasm.

NucleolusNucleolus This dense, spherical granule found in the nucleus contains RNA (ribonucleic acid) This dense, spherical granule found in the nucleus contains RNA (ribonucleic acid)

which is responsible for protein synthesis in the cytoplasm.which is responsible for protein synthesis in the cytoplasm. Chromatin NetworkChromatin Network These are very fine thread-like, coiled filaments uniformly distributed in the These are very fine thread-like, coiled filaments uniformly distributed in the

nucleoplasm. At the time of cell division, the chromatin becomes thick and ribbon nucleoplasm. At the time of cell division, the chromatin becomes thick and ribbon like and are known as chromosomes. The chromosomes contain genes, which are like and are known as chromosomes. The chromosomes contain genes, which are composed of DNA (deoxy-ribonucleic acid). Genes are responsible for storing and composed of DNA (deoxy-ribonucleic acid). Genes are responsible for storing and transmitting hereditary characteristics from one generation to another. A gene is the transmitting hereditary characteristics from one generation to another. A gene is the functional unit of a chromosome. Genes are arranged in single linear order along functional unit of a chromosome. Genes are arranged in single linear order along the chromosome. One gene may be responsible for a single characteristic, or a the chromosome. One gene may be responsible for a single characteristic, or a single characteristic may be transmitted by a set of genes.single characteristic may be transmitted by a set of genes.

Types of chromosomes based on the Types of chromosomes based on the position of centromere:position of centromere:

Microbodies:Microbodies:

Small sac like structures which contain various Small sac like structures which contain various hydrolytic enzymes.hydrolytic enzymes.

1- Nucleus 2- Chromosomes

3- Mitochondria

4- Ribosomes

5- Chloroplasts

6- Vacuoles

7- ER

8- Cell Membrane

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