class xi bio

8/12/2019 Class XI Bio

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ClassXIIth Chemist ry Electrochemistry 1

SAVANT EDUCATION GROUP E-17, East of Kailash, New Delhi 110065. Ph.: +91 -11 -26224417 www.savantgroup.org

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Cell: The Unit of Life

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Pre requisites

Basic Knowledge of cell and Cell organelles _ __________________________________________

Slide 1

Prokaryotic cell:

A cell which has an incipient nucleus and lacksmembrane bound organelles .In addition to the chromosomal or genomic DNA,many bacteria contain a small circular DNA in thecytoplasm; it is called a plasmid .The cell membrane forms infoldings calledmesosomes .

__________________________________________ Slide 2

Cell Envelope Glycocalyx. It forms the outermost layer.

Cell wall Cell wall is made up of pepdidoglycans , i.e.,made of repeating units of N acetyl

glucosamine , cross linked by short peptidechains. Based on the response of the cell wall to thestaining technique developed by Gram,bacterial cells are of two types:

Slide 3

Gram Positive Bacteria Gram Negative Bacteria

These bacteria retain apurple/blue colour afterwashing with alcohol. Cell wall is thick, about20 -80 nm in thickness. Peptidoglycan is about70 -80% of the cell wall. Mesosomes areabundant .Resistant to lysozymeaction.

These bacteria do notretain any colour afterwashing with alcohol. Cell wall is thin about 8 12 nm in thickness. Peptidoglycan is about 20-30% of the cell wall. Mesosomes are lessabundant. Suscepti ble to lysozymeaction

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Flagella The motile bacterial cells are provided withthin filamentous extension, called flagella. Each flagellum has three parts namely

filaments hook and basal body . Thefilament is the longest portion. Pili and FImbriae

These are also surface extensions of bacterialcells; but they are not concerned with motilityof cells.

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312 Cell: T he Unit of Life Biology (XI)


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Pili are elongated, tubular structure made ofprotein pilin, they are involved in theformation of conjugation bridges for transfer ofDNA into the recipient cells. Fimbriae are small bristle like fibres.

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Ribosomes The ribosomes are found attached to theplasma membrane of the cell. They are of 70S type and consist of 50 S and30 S subunits .

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Slide 6

Prokaryotic Cell Structure

Slide 7(a)

Eukaryotic Cells

Cell Membrane

Its presence was first recognized by Naigeli &Cramer (1855) who gave the term Plasmamembrane

It was experimentally confirmed by EOverton (1899) suggesting that it is made upof lipid.Cell membrane is composed of lipid bilayers,and proteins.

___________________________________________ Slide 4 (b)

The lipids are arranged within the membrane,with the polar head towards the outer sides(outer and inner surfaces) and thehydrophobic tails towards the inner part; thismakes the non polar tail of saturatedhydrocarbons protected from the aqueousenvironment. Cell membranes also have proteins andcarbohydrates. Membrane proteins are classified as integraland peripheral proteins.

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Fluid Mosaic Model. Fluid mosaic model of plasma membrane wasproposed by Singer and Nicolson; it is thewidely accept ed model.


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According to this model, the quasi - fluidnature of lipid enables the lateral movementof proteins within the overall bilayer. The fluid nature of the membranes is alsoimportant for certain functions like cell growth,endocytosis, formation of i ntercellular

junctions, cell division etc. ___________________________________________

Slide 9

___________________________________________ Slide 10

Transport across the Cell Surface Membrane

PASSIVE TRANSPORT DIFFUSIONFACILITATED DIFFUSION

ACTIVE TRANSPORT

Slide 11

Diffusion Facilitated diffusion

It is the movement ofions/molecules of anysubstance from aregion of higherconcentration to theregion of lowerconcentration, untilequilibrium is reached.

It refers to themovement ofions/molecules acrossthe membrane with thehelp of transmembraneproteins.

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Active Transport Passive transport

This type of transportoccurs with the

utilization of metabolicenergy. It can occur evenagainst concent rationgradient. It occurs rapidly.

This method oftransport occurs without

any expenditure ofenergy. It occurs only followingthe concentrationgradient. It occurs slowly .

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Endoplasmic Reticulum

First observed by Porter, Claude and Fullum .

Garnier earlier named it ergastoplasmPorter (1952) coined the term Endoplasmicreticulum


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Notes: -

Slide 14

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Common functions of RER and SER:

Both serve as channels for transport of proteins,lipids and sterols.

They also provide some mechanical support tothe cells.

Golgi apparatus

Golgi bodies were first detected by Camillo Golgi. Found in all cells except RBC of mammals andmuscle cellsAlso known as Golgisome, Id iosome orLipochondriaIn pant cells the Golgi complex consists of manyunconnected units known as dictyosomes

Slide 16

___________________________________________ Slide 17

Function of Golgi apparatus It packages the materials for intracellular tra nsportas well for secretion to the outside. Many proteins synthesized by ribosomes aremodified in the cisternae of Golgi apparatus. It is the site of formation of glycoproteins andglycolipids. Golgi cisternae form the primary lysosomes bybudding.


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Notes: -

Slide 18

Lysosomes

Discovered by Christian de Duve (1955) fromliver cells of rats. Contain about 50 different hydrolyzing (digestive)enzymes called acid hydrolases like nucleases,phosphatases .Single -membrane spherical bodies having a sizeof 0.08 m. Polpularly called as suicide bags,

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Lysosome ___________________________________________

Slide 20

Mitochondria

First seen by Kolliker (1850) in muscles .Benda (1898) stained these organelles withcrystal violet and renamed them mitochondria. These are double membrane bound, sausage shaped semi -autonomous organelles.

The electron micrograph shows that the boundarymembranes are separated by a fluid filled spacecalled outer compartment. The outer membrane is smooth but the innersmooth projects in the form of many folds calledcristae into the matrix.

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The matrix is rich in enzymes, a circular DNAmolecule and many small ribosomes .The inner membrane and the cristae bear anumber of particles, which have a spherical head

piece (F 1 subunit) and a stalk (F 0 subunit) thatis embedded in the lipid of the membrane. The F 0 F 1 combination functions as ATPsynthetase. The main function of mitochondria is aerobicrespiration and ATP synthesis .

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Slide 22

Mitochondria


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Notes: -

Slide 23

___________________________________________

Slide 24Plastids

Plastids are double membrane boundorganelles of different shapes, that are found onlyin plant cells and contain pigments and storageproducts. These are three types of plastids, depending ontheir colour and functions.

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(i) Leucoplasts These are the oval, spherical, rod like orfilamentous and colourless plastids, usuallyfound in storage organs (tubers, fruits,

rhizomes etc.) that are mostly not exposed tosunlight. Their main function is to store nutrients likestarch (amyloplasts), proteins (aleuroplasts)and fats (elaioplasts).

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(ii) Chromoplasts These are the coloured plastids containingmainly the yellow, red and orange pigments(carotene and xanthophylls).

(iii) Chloroplasts These are the green plastids containingmainly chlorophylls and very little of caroteneand xanthophylls .Chloroplasts may be lens shaped, oval,spherical, discoid, ribbon-like or cup shaped.

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Each chloroplast has a double membranecovering, enclosing the colourless matrixcalled stroma. The stroma contains a small, circular, double-helical DNA, ribosomes and several enzymes.Many flat membranous structure calledthylakoids occur in the form of stacks ofcoins called grana , whose number is about 40

1 00 in a chloroplast. The grana are interconnected by stromalamellae .


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Notes: -

Slide 28

Chloroplast ___________________________________________

Slide 29

Ribosomes

Ribosomes were first observed by Palade underelectron microscope, as dense particles. They are mad e up of ribonucleic acid (RNA) andproteins ; they have no boundary membrane. Each ribosome consists of two subunits a largesubunit of 60S and as small subunit of 40S andthe whole ribosome is of 80S type .The main functions of ribosomes is to synthesiseproteins.

Slide 30

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Slide 31Cilia and Flagella

Cilia and flagella are hair like, movableprojections/outgrowths of cell membrane. Cilia are much smaller, but more in number whileflagella are larger than cilia and few in number percell. The ultra-structure (as seen under an electronmicroscope) shows that cilia and flagella aremembrane bound cylindrical structures havingfour parts namely

(i) Rootlets,(ii) Basal body, (iii) Basal plate and (iv) Shaft or axoneme.


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Notes: -

Slide 32

The cilia and flagella are attached with the help ofrootlets. A basal body lies at the base of eachcilium/flagellum in the cytoplasm; it shows ninemicrotubule triplets along the periphery(9 + 0organisation).

A basal plate separates the axoneme from thebasal body .

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___________________________________________ Slide 34

Centrosome and Centrioles

Centrosome is the organelle usually found nearthe nucleus of animal cells, motile algal cell, sexcells or p rimitive land plants, etc. It consists of a pair of centrioles at right angles toeach other, surrounded by an amorphous

pericentriolar cytoplasm called centrospheres orkinoplasm. Each centriole has a cartwheel like organization,with nine evenly spaced microtubule -triplets alongthe periphery, connected to the centralproteinaceous hub by radial spokes, also made ofproteins. All the microtubules in a centriole are formed of

protein tubulin . ___________________________________________

Slide 35


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Notes: -

Slide 36 (a)

Nucleus

Reported by Robert Brown (1831) in orchid cells. Stasburger (1882) proved that nucleus arisesfrom pre existing nucleus by division. An interphase nucleus shows the following parts:

Nuclear membrane Chromatin reticulum Nucleolus Nucleoplasm

Chromatin Network is a network of thenucleoprotein fibres called chromatin.

___________________________________________ Slide 3 6(b)

Chromatin contains DNA, some basic proteinscalled histones, non histone proteins and RNA .A single human cell has approximately two metrelong fibre of DNA (chromatin) distributed amongall the forty six chromosomes. When the cell starts division, the chromatincondenses into individual, rod - like structure,called chromosomes.

Slide 3 6(c)


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Notes: -

Chapter Assignment

1 Marks Questions

1. Who was the first to describe a live cell? 2. Who discovered nucleus? 3. Name the scientists who are credited as

formulators of the cell theory.

4. What is middle lamella? 5. What is scientific contribution of Christian de

Duve? 6. What is the location of intrinsic proteins in the cell

membrane? 7. Give two alternative names for cell membrane. 8. Golgi apparatus in plant and invertebrate cells

consists of several separate units. What are thesecalled?

9. What does the term axoneme refer to? 10. What do you mean by perinuclear space?

11. What Schleiden observe? 12. What was Schwanns observation? 13. Who first showed that cells arise only from pre-

existing cells? 14. Name the structure that helps in the motility of

bacterial cells. 15. Name two surface extensions in bacterial cells,

that are not concerned with motility. 16. Name the two subunits of prokaryotic ribosomes. 17. Name any two groups of organisms where gas

vacuoles are present.

18. Why are mitochondria/chloroplasts not consideredwith the endomembrane system?

19. Name the site of synthesis of glycoproteins andglycolipids i n a cell.

20. Name the membrane boundary of vacuoles.

21. What is a centrosome? 22. Who coined the term chromatin? 23. What is the function of nucleolus? 24. Where are nucleoli formed from ?2 mark questions

25. Mention two functions of glycocalyx in bacteria. 26. Describe briefly the cell wall of bacteria. 27. What are pili in bacteria? 28. What are fimbriae? Mention their utility. 29. What are inclusion bodies in prokaryotic cells?

Explain. 30. What is meant by s econdary wall? Explain. 31. What do you understand by endomembrane

system? 32. What is centrosome? Explain .

33. What is pinosome? How does it differ fromphagosome?

34. What are polysomes? What is their function? 35. Differentiate between primary and secondary cell

wall.36. What is middle lamella? What is its made of? 37. What are plasmadesmata? What is their function?38. What are cis and trans faces of Golgi

apparatus? 39. What types of enzymes do lysosomes contain?

What is their function?


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Notes: -

3 mark questions

40. What is Gram staining? Explain briefly. 41. What is a mesosome? What are its functions? 42. Give a brief account of flagella in bacteria. 43. Describe briefly the prokaryotic ribosomes. 44. Write a note on prima ry wall layer of plant cell.

45. Define a vacuole. What are the various types ofvacuoles found in cells? Explain.

46. Mention briefly about the biogenesis ofmitochondria.

47. List various functions of cytoskeleton. 48. Who proposed cell theory? Enumerate the

components of cell theory as we understandtoday.

5 mark questions

49. What are the differences between Gram positiveand Gram negative bacteria?

50. List various functions of plasma membrane. 51. Give the various functions of Golgi apparatus. 52. Discuss the structure and functions of lysos omes. 53. Describe the similarities between mitochondria

and chloroplasts.

54. Describe with the help of a diagram theultrastructure of cilia and flagella.

55. Represent diagrammatically any five differentshapes of cells and name them.

56. What are mesosomes? What are their differentforms? Mention their important functions.

57. Describe the fluid mosaic model of membrane. 58. Differentiate between active and passive transport

across the membrane. Describe the differentmethods of passive transport.

59. Describe the st ructure of mitochondri a along witha diagram.

60. Describe the structure of chloroplasts.


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