8 CELL- THE UNIT OF LIFE

CHAPER NO.8 CELL:THE UNIT OF LIFE

A80

INTRODUCTION:Dear students today we are going to discuss about cell. In Biology cell is the basic structural, functional and biological unit of all known organisms. The study of cells is called cell biology. The word cell is derived from a Latin word cellula which means small room. Cells are the smallest units of life, and hence are often referred as the building blocks of life. The study of cells is called cell biology, Mor WE. The cell is a small membrane bound compartment that contains all the chemicals and molecules that help to support an organism's life.

DISCOVERY OF CELL In 1665, scientist Robert Hooke examined a thin slice of cork under his microscope and found a structure like a honey comb having hollow compartments. He named them cells. He wrote a book named Micrographia.He is known as Father of Cytology.

Anton Von Leeuwenhoek first saw and described a living cell. Robert Brown later discovered the nucleus. The invention of the microscope and its improvement leading to electron microscope revealed all the structural details of cell.

In 1838 Matthias Schleiden, a German botanist examined a large number of plants

and observed that all plants are composed of different kinds of cells which form the

tissue of the plant.

THEODORE SCHWAN British Zoologist reported that cells have a thin outer layer which is today known as plasma membrane.

Matthias Schleiden and Theodore Schwan together formulated the Cell Theory. This theory did not explain as to how new cells were formed. In 1855 Rudolf Virchow

explained that cells divide and new cells are formed from pre- existing cells (omnis

cellula-e-cellula) and gave the cell theory a final shape.

TYPES OF CELL

There are two types of cells: iS anc

Prokaryotic cells lack a membrane bound nucleus. These cells are represented by

bacteria, blue green algae. mycoplasma and PFPLO {Pleuro Pneumonia like Organisms}. They are generally smaller and multiply more rapidly than the eukaryotic cells. They may vary greatly in shape and size.The four basic shapes of bacterial cell are: Bacillus (rod like), Caccus (spherical),Vibrio (Comma shaped) and (spiral).

Most prokaryotic cells, particularly the bacteria cells have a chemically complex cell envelope that consists of a tightly bound a three layered structure glycocalyx. Each layer of envelope performs distinct functions. They act together as a single protective

unit. Prokaryotes have fluid matrix filling the cell, the cytoplasm. There is no well-

defined nucleus. The genetic material is basically naked. 70 s ribosome and flagella

are also present in prokaryotes.

Eukaryotic cells possess an organized nucleus. They include all the protists, plants,animals and fungi. In these cells there is an extensive compartmentalization of cytoplasm, through the presence of membrane bound organelles. In addition these cells have locomotors and cytoskeleton structures. Their genetic material is organized into chromosomes.

All eukaryotic cells are not identical. Plant and animal cells are different, as plantcells possess cell walls, plastids and a large central vacuoles, which are absent in animal cells. On the other hand animal cells have centrioles which are almost absent in plant cells.Eukaryotic (plant and animal) cells possess the following organelles:Cell membrane, cell wall(in plant cells), ribosomes , endoplasmic reticulum ,golgiapparatus , lysosomes , vacuoles , mitochondria , plastids ( in plant cells ) ,centrioles (in animal cells), nucleus , cilia and flagella ( in anima! cells), centrioles

and centrosomes ( in animal cells) and microbodies.

A. MULTIPLE CHOICE QUESTIONS:

1. Who discovered the cell?

a) G.N. Ramachandran

b) Robert Hooke

c) A.V. Leeuwenhock

d) None of these

2. Which scientist formulated cell theory?

a) Matthias Schleiden

b) Theodore Schwann

c) Both A and B

d) Robert Brown

3. ‘Omnis cellula-e-cellula’ means;

a) Cell is a basic unit of life

b) All organisms are composed of cells.

c) New cells are formed from preexisting cells.

d) None of these.

4. Prokaryotic cells are represented by;

a) Bacteria

b) Blue green algae

c) Mycoplasma

d) All of the above

5. Which organelle is absent in plant cells?

a) Centriole

b) Plastids

c) Cell wall

d) Golgi apparatus

B. FILLIN THE BLANKS

1. discovered the nucleus.

2. The genetic material in eukaryotic cells is organized into...................

3. Well organized nucleus is a unique character of......................cells.

C. TRUE AND FALSE

1. Prokaryotic cells lack a well organised nucleus.

2. Plastids are present in animal cells.

3. All eukaryotic cells are not identical.

A. MULTIPLE CHOICE QUESTIONS:

1. b (G.N. Ramachandran worked in the field of protein structure and A.V.

Leeuwenhoek described a live cell.

2. c ( Robert brown discovered the nucleus)

3. c (cells divide and produce new cells)

4. d (All these represent prokaryotic cells)

5. a ( Rest three organelles are found in plant cells)

B.FILL IN THE BLANKS

1. Robert Hooke

2. Chromosomes

3. Eukaryotic cells

C. TRUE AND FALSE

1. True

2. False(Plastids are found in plant cells)

3. True

PART-B SHORT ANSWER TYPE QUESTIONS

1. What are four basic shapes of bacterial cells?

2. Describe the structure of glycocalyx.

3. What are the main differences between prokaryotes and eukaryots?

PART-C LONG ANSWER TYPE QUESTIONS

1. Write a note on prokaryotic cells.

2. Give an account of eukaryotic cells.

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INTRODUCTION:Eukaryotic cells appeared on earth long = after Prokaryotic cells but they are much more advanced.Eukaryotic organisms unlike prokaryotic can be

unicellular or multi-cellular.

Eukaryotic Cell Definition :-“Eukaryotic cells are the cells that contain a membrane bound nucleus and organelles.”

What is a Eukaryotic Cell?

Eukaryotic cells have a nucleus enclosed within the nuclear membrane and form large and complex organisms. Protozoa, fungi, plants,and animals all have eukaryotic cells. They are classified under the

kingdom Eukaryota.They can maintain different environments in a single

cell that allows them to carry out various metabolic reactions. This helps

them grow many times larger than the prokaryotic cells.Characteristics of Eukaryotic Cell The features of eukaryotic cells are as follows:-The cell has mitochondria.Flagella and cilia are the locomotory organs in a eukaryotic cell.

A cell wall is the outermost layer of the eukaryotic cells.The cells divide by a process called mitosis.The eukaryotic cells contain a cytoskeletal structure.Eukaryotic cells have the nucleus enclosed within the nuclear membrane.The nucleus contains a single, linear DNA, which carries all the

genetic information.Eukaryotic Cell structure The eukaryotic cell structure comprises the following:-

1. Plasma Membrane The plasma membrane separates the cell from the outside

environment.It comprises specific embedded proteins, which help in the exchange of substances in and out of the cell.

2. Cell Wall It is composed of cellulose, hemicellulose, pectins, proteins, etc.

It provides shape to the cell and helps in cell-to-cell interaction.It is a protective layer that protects the cell from any injury or pathogen attacks.A cell wall is a rigid structure present outside the plant cell. It is,' however, absent in animal cells.

3. Cytoskeleton The cytoskeleton is present inside the cytoplasm, which consists of microfilaments, microtubules, and fibres to provide perfect shape to the cell, anchor the organelles, and stimulate the cell movement.

4. Endoplasmic Reticulum It is a network of small, tubular structures that divides the cell surface into two parts: luminal and extraluminal.Endoplasmic Reticulum is of two types:Rough Endoplasmic Reticulum contains ribosomes.Smooth Endoplasmic Reticulum that lacks ribosomes and is therefore smooth.

5. Ribosomes These are the main site for protein synthesis and are composed of proteins and ribonucleic acids.

6. Lysosomes They are known as “suicidal bags” because they possess hydrolytic enzymes to digest protein, lipids, carbohydrates, and nucleic acids.

Eukaryotic Cell Structure

7. Nucleus Ribosome production also takes place inside the nucleus.The nucleoplasm enclosed within the nucleus contains DNA and proteins.The nuclear envelop consists of two layers- the outer membrane and the inner membrane. Both the membranes are permeable to ions,molecules, and RNA material.

8. Golgi Apparatus It is made up of flat disc-shaped structures called cisternae.

They are arranged parallel and concentrically near the nucleus.It is absent in red blood cells of humans and sieve cells of plants.It is an important site for the formation of glycoproteins and glycolipids.

9. Mitochondria

They help in the regulation of cell metabolism.These are also known as “powerhouse of cells” because they produce

energy.it consists of an outer membrane and an inner membrane. The inner membrane is divided into folds called cristae.

10. PlastidsThese are double-membraned structures and are found only in plant

cells.Plastids are of three types:

Chloroplast that contains chlorophyll and is involved = in photosynthesis.Leucoplasts that are colourless and store oil, fats, carbohydrates, or proteins.: Chromoplast that contains a pigment called carotene that provides the plants yellow, red, or orange colours.

Eukaryotic Cell Diagram Eukaryotic cell diagram mentioned below depicts different cell organelles present in eukaryotic cells. The nucleus, endoplasmic reticulum, cytoplasm, mitochondria, ribosomes, lysosomes are clearly mentioned in the diagram.

Eukaryotic Cell Cycle The eukaryotic cells divide during the cell cycle. The cell passes through different stages during the cycle. There are various checkpoints

between each stage.

1. Quiescence (GO)This is known as the resting phase, and the cell does not divide

during this stage. The cell cycle starts at this stage. The cells of the liver, kidney, neurons, and stomach all reach this stage and can remain there for longer periods. Many cells do not enter this stage and divide indefinitely throughout their lives.

2. Interphase In this stage, the cells grow and take in nutrients to prepare them

for the division. It consists of three checkpoints:

Gap 1 (G1) Here the cell enlarges. The proteins also increase.Synthesis (S) DNA replication takes place in this phase.

Gap 2 (G2) Ther cells enlarge further to undergo mitotic division.

3. Mitosis

Mitosis involves the following stages:-

Prophase

Prometaphase

Metaphase

Anaphase

Telophase

Cytokinesis

On division, each daughter cell is an exact replica of the original cell.Examples of Eukaryotic Cells Eukaryotic cells are exclusively found in plants, animals, fungi,protozoa, and other complex organisms. The examples of eukaryotic cells

are mentioned below:

1. Plant Cells The cell wall is made up of cellulose, which provides support to

the plant. It has a large vacuole which maintains the turgor pressure.The plant cell contains chloroplast, which aids in the process of photosynthesis.

2. Fungal Cells The cell wall is made of chitin. Some fungi have holes known as

septa which allow the organelles and cytoplasm to pass through them.

3. Animal Cells These do not have cell walls. Instead, they have a cell membrane. That is why animals have varied shapes. They have the ability to perform phagocytosis and pinocytosis.

4. Protozoa Protozoans are unicellular organisms. Some protozoa have cilia

for locomotion. A thin layer called pellicle provides supports to the

cell.

Let us know what we have Learnt!

PART: A VERY SHORT ANSWER TYPE QUESTIONS:

MCQ’s Prokaryotic Cells

1) Which of the following is not true of a Eukaryotic cell?

a. The cell wall is made up of peptidoglycans

b. 80S ribosome’s is present in the cytoplasm

c. Mitochondria contain circular DNA

d. Membrane bound organelles are present

2) Which one of the following is absent in eukaryote?

a. Nucleolus

b. Plastid

c. Mesosomes

d. Ribosomes

3) Which of the following are not Eukaryotic?

a. Plants

b. Fungi

c. Protests

d. Moneras

4) Which of these are absent in plant cell?

a. Large central Vacuole' cc. Centriole

b. Cell wall d. Plastid

5) What is the name of fluid part of the cytoplasm of Eukaryotic cells?

a. Protoplasm

b. Cytokine

c. Cytoplasmic Inclusion

d. Matrix

6) Which of the following is not available in animal cells?

a. Plastid

b. Mitochondria

c. Lysosomes

d. Centrosomes

Fill Ups

1) Eukaryotic cell is with nucleus.

2) Eukaryotic cellhas envelops organisition.

3) The functions of eukaryotic cell organellesto generate sig.

4) Eukaryotic cells have a well developed membrane.

5) slis the empty space in the cell.

True/False

1) Flagella is used for cell motility in eukaryotic cells.

2) The eukaryotic cell is the earliest type of cell.

3) Cytoplamic matrix is also called hyaloplasm.

PRT: B SHORT ANSWER TYPE QUESTIONS:

1) Which of the following is not true for a eukaryotic cell?

2) Write short note on eukaryotic cells?

3) Where is DNA located in eukaryotic cells?

4) Write shirt note on RNA Polymerases of eukaryotic cells?

PART: C LONG ANSWER TYPE QUESTIONS:

1) Give the salient features of eukaryotic cells?

2) When & how might the eukaryotic cell have arisen?

MCQ’s Fillups True/False

1) a 1) Organised 1) False

2) a 2) Two 2) False

3) d 3) Energy 3) True

4) c 4) Nuclear

5) d 5) Vacuole

6) a

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INTRODUCTION:Prokaryotic cells were here first and for billions of years were

the only form of life on Earth. All prokaryotic organisms are unicellular.

Prokaryotic Cell Definition :-

“Prokaryotic cells are the cells that do not have a true nucleus and membrane-bound organelles.”D.N.A. is naked, without

Histone Proteins.

What is a Prokaryotic Cell?

Prokaryotic cells are single-celled microorganisms known to be the earliest on earth. Prokaryotes include Bacteria and Archaea. The photosynthetic prokaryotes include cyanobacteria that perform

photosynthesis.A prokaryotic cell consists of a single membrane and therefore, all the reactions occur within the cytoplasm. They can be free- living or parasites.

Characteristics of Prokaryotic Cell

Prokaryotes are the simplest type of cell.

Oldest type of cell appeared about four billion years ago.The largest group of organisms.Unicellular organisms that are found in all environments.They lack a nuclear membrane.Mitochondria, Golgi bodies, chloroplast, and lysosomes are absent.The genetic material is present on a single chromosome.The cell wall is made up of carbohydrates and amino acids.The plasma membrane acts as the mitochondrial membrane carrying respiratory enzymes.They divide asexually by binary fission. The sexual mode of ' reproduction involves conjugation.The histone proteins, the important constituents of eukaryotic

chromosomes, are lacking in them.

PROKARYOTIC CELL STRUCTURE:A prokaryotic cell does not have a nuclear membrane. However,the genetic material is present in a region in the cytoplasm known as the

nucleoid. They may be spherical, rod-shaped, or spiral. A prokaryotic cell

structure is as follows:-

Capsule :- it is an outer protective covering found in the bacterial cells, in addition to the cell wall. It helps in moisture retention, protects the cell when engulfed, and heips in the attachment of cells to nutrients and surfaces.

Cell Wall :- It is the outermost layer of the cell which gives shape to the cell.

Cytoplasm :- The cytoplasm is mainly composed of enzymes, salts, cell

organelles and is a gel-like component.Cell This layer surrounds the cytoplasm and regulates the entry

Membrane :- and exit of substances in the cells.

Pili :- These are hair-like outgrowths that attach to the surface of other bacterial cells.

Flagella :- These are long structures in the form of a whip, that help

in the locomotion of a cell.

Ribosomes :- These are involved in protein synthesis.

Plasmids :- Plasmids are non-chromosomal DNA structures. These are not involved in reproduction.Nucleoid it is the region in the cytoplasm where the genetic

Region :- material is present.A prokaryotic cell lacks certain organelles like mitochondria,endoplasmic reticulum, and Golgi bodies.Prokaryotic Cell Diagram

The prokaryotic cell diagram given below represents a bacterial cell. It depicts the absence of a true nucleus and the presence of a flagellum that differentiates it from a eukaryotic cell.

COMPONENTS OF PROKARYOTIC CELLS:

The prokaryotic cells have four main components:-Piasma It is an outer protective covering of phospholipid

Membrane :- molecules which separates the cell from the surrounding environment.

Cytoplasm :- it is a jelly-like substance present inside the cell. All the cell organelles are suspended in it.

DNA :- It is the genetic material of the cell. All the prokaryotes possess a circular DNA. It directs what proteins the cell creates. It also regulates the actions of the cell.

Ribosomes :- Protein synthesis occurs here.

Some prokaryotic cells possess cilia and flagella which helps in locomotion.

REPRODUCTION IN PROKARYOTES:

A prokaryote reproduces in two ways:-

Asexually by binary fission Sexually by conjugation

BINARY FISSION:

The DNA of an organism replicates and the new copies attach to the cell membrane.

The cell wall starts increasing in size and starts moving inwards.A cell wall is then formed between each DNA, dividing the cell into two daughter cells.

RECOMBINATION:In this process, genes from one bacterium are transferred to the

genome of other bacteria. It takes place in three ways:CONJUGATION, TRANSFORMATION, AND TRANSDUCTION.Conjugation is the process in which genes are transferred between

two bacteria through a protein tube structure called a pilus.Transformation is the mode of sexual reproduction in which the DNA from the surroundings is taken by the bacterial cell and incorporated in its DNA.Transduction is the process in which the genetic material is transferred into the bacterial cell with the help of viruses.Bacteriophages are the virus that initiates the process.

Examples of Prokaryotic Cells:

The examples of the prokaryotic cells are mentioned below:

Bacterial Cells

Archaeal Cells

Bacterial Cells These are unicellular organisms found everywhere on earth from soil to the human body.They have different shapes and structures.The cell wall is composed of peptidoglycan that provides structure to the cell wall.Bacteria have some unique structures such as pili, flagella and capsule.They also possess extra chromosomal DNA known as plasmids.

They have the ability to form tough, dormant structures known as endospores that helps them to survive under un-favourable conditions.The endospores become active when the conditions are favourable again.

Archaeal Cells Archae bacteria are unicellular organisms similar to bacteria in shape and size.They are found in extreme environments such as hot springs and

other places such as soil, marshes, and even inside humans.They have a cell wall and flagella. The cell wall of archaea does not contain peptidoglycan.The membranes of the archaea have different lipids with a completely different stereochemistry

Learnt!

MCQ’s Prokaryotic Cells

i. Which of the following is the typical feature of a Prokaryote cell

a. Abrence of DHA

b. Abrence of Nucleus

c. Abrence of RNA.

d. Abrence of cellwall

ii. The cell wall of enbacteria is made up of

a. cellulose

b. Peptidoglycan

c. Phospholipids

d. chitin

iii, Ribosomes in prokaryote cells are

a. 80s

b. 70s

c. 60s + 40s

d. 50s+Nos

iv. Extremely fine extracellular structures involved in cell to cell

contact is

a. Flagella

b. Cilia

c. Pili

d. Spinae

v. In some bacteria there is slimy layer outside to cell wall considered

as virulence factor is called

a. Capsule

b. Plasmid

c. Outer layer

d. Fimbriae

vi. What is the name of the region where double-strandel single circular DNA is found in Prokaryotic cell.

a. Protonucleus

b. Nucleus

c. Nucleoid

d. Nucleoplasm

vii. The two domains to which prokaryotics are classified into are

a. Bacteria & Protista

b. Bacteria & Archaea

c. Archaea & Eukarya

d. Eukarya & Monera

Fill Ups:

i. cell does not have a nuclear membrane.

ii, The nuclear region of prokaryotic cell is called

iii, Cells were discovered by Robert Hooke in .

iv. Prokaryotes are organisms

v. Prokaryotes proper us.nucle

True/False

i. True nucleus is seen in Prokaryotre cell.

ii, The example of a Prokaryotic cell is Blue-green algae.

iii, Bacteria & Algae are Prokaryotic cells.

iv. Circular genetic material of Prokaryotes are Plasmids.

v. Prokaryotes divide to reproduce by binary fission.

Short Q/A

i. What are the characteristics of Prokaryotic cell?

ii. How Prokaryotic cell is differs from eukaryotic cell?

iii, What is Mesosome in Prokaryotic cell? Mention the function that it performs.

iv, What are cell inclusions in prokaryotic cell?

Long Q/A

i. What are the differences between prokaryotic cell & Eukaryotic

cells?

ii. Differentiate Gram +ve & Gram -ve bacteria?

ANSWER- KEY: PART-A

Mca: Fill ups:

i. Absence of Nucleus i. Prokaryotic

ii. Peptidoglycan iit Nucleoid

iii, 70s iii, 1665

iv. Pili iv. Unicellular

v. Capsule v. Lack

vi. Nucleoid

vii, Bacteria & Archaea

True/False:

i. False

ii. True

iii. False

iv. True

v. True

A83

INTRODUCTION:Cell is the basic unit of life; structural as well as functional. The various structures present inside the cell are known as the Cell Organelles.Today in our topic we will discuss about Cell membrane, cell wall and endomembrane.

CELL MEMBRANE / PLASMA MEMBRANE:The cell membrane, also called the plasma membrane, is found in all cells and separates the interior of the cell from the outside environment. The cell membrane consists of a lipid bilayer that is semipermeable. The cell membrane regulates the transport of materials entering and exiting the cell.

The plasma membrane, or the cell membrane, provides protection for a cell. It also provides a fixed environment inside the cell, and that membrane has several different functions. One is to transport nutrients into the cell and also to

transport toxic substances out of the cell. Another is that the membrane of the cell, which would be the plasma membrane, will have proteins on it which interact with other cells. The cell membrane also provides some structural support for a cell. There are different types of plasma membranes in different types of cells.

PLASMA MEMBRANE or CELL MEMBRANE: STRUCTURE

Biological membranes have three primary functions:

(1) They keep toxic substances out of the cell;

(2) They contain receptors and channels that allow specific molecules,such as ions, nutrients, wastes, and metabolic products, that mediate cellular and extracellular activities to pass between organelles and between the cell and the outside environment; and

(3) They separate vital but incompatible metabolic processes conducted within organelles.

STRUCTURE OF PLASMA MEMBRANE:Membranes consist largely of a LIPID bilayer, which is a double layer of phospholipid, cholesterol, and glycolipid molecules that contains chains of fatty acids and determines whether a membrane is formed into long flat sheets or round vesicles. Lipids give cell membranes a fluid character,with a consistency approaching that of light oil. The fatty-acid chains

allow many small, fat-soluble molecules, such as oxygen, to permeate the

membrane, but they repel large, water-soluble molecules, such as sugar,

and electrically charged ions, such as calcium.Embedded in the lipid bilayer are large PROTEINS, many of which transport ions and water-soluble molecules across the membrane. Some proteins in the plasma membrane form open pores, called membrane

channels, which allow the free diffusion of ions into and out of the cell.Others, known as carrier proteins bind to specific molecules on one side of amembrane and transport the molecules to the other side. Sometimes one protein simultaneously transports two types of molecules in opposite directions.Most plasma membranes are about 50 percent protein by weight, while the membranes of some metabolically active organelles are 75 percent protein.

Attached to proteins on the outside of the plasma membrane are long carbohydrate molecules.The R.B.C. membrane is composed of 52% proteins, 40% lipids and 08%

cabohydrates.The cell membrane is primarily composed of a mix of proteins and lipids. |

Phospholipids are a major component of cell membranes. They form a lipid bilayer

in which their hydrophilic (attracted to water) head areas spontaneously arrange to

face the aqueous cytosol and the extracellular fluid, while their hydrophobic (repelled by water) tail areas face away from the cytosol and xtracellular fluid.Cholesterol is another lipid component of animal cell membranes. Cholesterol molecules are selectively dispersed between membrane phospholipids. This helps to keep cell membranes from becoming stiff by preventing phospholipids from being too closely packed together.

Glycolipids are located on cell membrane surfaces and have a Carbohydrate sugar

chain attached to them. They help the cell to recognize other cells of the body.

PROTEINS: The cell membrane contains two types of associated proteins.Peripheral membrane proteins are exterior to and connected to the membrane by interactions with other proteins.Integral membrane proteins are inserted into the membrane and most pass through the membrane.

FLUID MOSAIC MODEL OF PLASMA MEMBRANE

In the above model the quasi-fluid nature of the lipids, enables lateral movement of proteins within overall bilayer. Singer and Nicolson proposed this model.

CELL WALL:Cell wall is NON-LIVING rigid structure present outside the plasma

membrane of FUNGI and PLANTS.

It gives shape and protection from mechanical damage and infection.It helps in cell to cell interaction through plasmodesmata.It provide barrier to undesirable macromolecules.The plant cell wall is made up of CELLULOSE, HEMICELLULOSE,PECTIN

and PROTEINS.The Algal cell wall consists of CELLULOSE, GALACTANS, MANNANS and

MINERALS.FUNGAL cell wall is made up of CHITIN.In young plant cell the wall is living and can grow. Later secondary wall is formed.The middle lamella is layer made of CALCIUM PECTATE, which holds the

neighbouring cells together.

ENDOMEMBRANE:The membranes of different organelles are different in terms of structure and function. The membranes of many organelles considered as ENDOMEMBRANE SYSTEM because their functions are coordinated.

The ENDOMEMBRANE SYSTEM includes Endoplasmic reticulum, Golgi

complex, Lysosomes and Vacuoles.The other organelles are not coordinated with above, so they are not the part of endomembrane system.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A VERY SHORT ANSWER TYPE QUESTIONS:

MCQs:

Q1. Who proposed the fluid mosaic model of the plasma membrane?

a.) Benda

b.) Schleiden and Schwann

c.) Singer and Nicolson

d.) Robert Brown

Q2. Which of the following statements is not true for plasma membrane?

a.) itis present in both plant and animal cell.

b.) Lipid is present as a bilayer in it.

c.) Proteins are presently integrated as well as loosely associated with lipid bilayer.

d.) Carbohydrate is never found in it.

Q3. Which of the following are covered by a single membrane?

(a) Mitochondria

(b) Vacuole

(d) Plastid

Q4. Cell wall of which one of these is not made up of cellulose?

(a) Bacteria

(b) Hydrilla

(d) Cactus

Q5. The organelle that helps in the membrane biogenesis is:

(a) lysosome

(b) Golgi bodies

(d) ribosome

FILL IN THE BLANKS:

1. The function of endomembrane system is

2. The fungal cell wall is made up of

TRUE/FALSE:

1. Plasma membrane is a selective permeable membrane.

2. Middle lamella is made up of calcium pectate.

3. Mycoplasma has cell wall.

4. The cell wall of certain fungi is made of lignin.

ANSWER KEY: PART-A

MCQs:

1. C(Singer and Nicolson)

2. D (carbohydrate is never found in it)

3. C(lysosome)

4. A(bacteria)

5. C (endoplasmic reticulum )

FILL IN THE BLANKS:

1. Coordinated

2. Chitin

TRUE/FALSE:

1. True

2. True

3. False: Mycoplasma has NO cell wall, it is bound by plasma

membrane only.

4. False: The cell wall of certain fungi is made of CHITIN.

PART: B SHORT ANSWER TYPE QUESTIONS:

Q1. Give the biochemical composition of the plasma membrane. How are

lipid molecules arranged in the membrane?

Q2. Write the functions of the Cell wall and Cell membrane.

PART: C LONG ANSWER TYPE QUESTIONS:

Q1. Discuss structure of cell wall and cell wall depositions.

Q2. Differentiate between primary wall and secondary wall.

A84

INTRODUCTION:MITOCHONDRIA were named by Carl Benda in 1898 from his study of cell

internal structure and the first recorded information of mitochondria in plants in

cells was created by Friedrich Meves in 1904. In 1908, Friedrich Meves and

Claudius Regaud showed that they contain lipids and proteins.“Mitochondria are membrane-bound organelles present in the cytoplasm of all eukaryotic cells, that produces adinosine triphosphate (ATP), the main energy molecule used by the cell.”

PLASTIDS:Plastids are double-membrane organelles which are found in the cells of plants and algae.

What are Mitochondria?

Popularly known as the “Powerhouse of the cell,” mitochondria (singular:

mitochondrion) are a double membrane-bound organelle found in mos eukaryotic organisms. They are found inside the cytoplasm and essentially functions as the cell"s “digestive system.” They play a major role in breaking down nutrients and generating energy-rich molecules for the cell. Many of th biochemical reactions involved in cellular respiration take place within th mitochondria. The term mitochondrion is derived from the Greek words “mitos’and “chondrion” which means “thread” and “granules-like” respectively. It wa first described by a German pathologist named Richard Altmann in the yea 1890.Characteristics of Mitochondria:

The features of Mitochondria are as follows:-Mitochondria are organs of special importance. These organelles are

absolute requirements to sustain the physiological activities of the cells.

Typically sausage shaped or cylindrical shaped.Each mitochondrion is a double membrane - bound structure with the oute

membrane and the inner membrane dividing its lumen distinctly into two compartments, l.e., the outer compartment (perimitochondrial space) and the inner compartment matrix).They are present in almost all the cells of the body except in Red Blood Cells.They are freely floating in the cytoplasm and stay in the regions of high energy requirement.Mitochondria are self-replicable i.e. they can multiply on their own withou the requirement of cell to divide. Its characteristic feature helps replacemen of old, worn out and damaged mitochondria with new and healthy

mitochondria.Mitochondria have their own genetic material as single stranded DNA.

The mitochondria have many enzyme complex which in series help in formation of energy i.e. adenosine tri-phosphate (ATP).

Mitochondria Diagram The diagram of mitochondria below illustrates several structural features of mitochondria.

Structure of Mitochondria:The structure comprises the following:-The mitochondrion is a double-membrane, rod-shaped structure found i both plant and animal cell.

Its size ranges from 0.5 to 1.0 micrometre in diameter.The structure comprises an outer membrane, an inner membrane, and a gel like material called the matrix.

The outer membrane and the inner membrane are made of proteins and phospholipid layers separated by the inter membrane space.The outer membrane covers the surface of the mitochondrion and has a larg

number of special proteins known as porins. It is freely permeable to ions,

nutrient molecules, energy molecules like the ADP and ATP molecules.

1) Cristae The inner membrane of mitochondria is rather complex in structure. It has many folds that form a layered structure called cristae, and this helps in increasing the surface area inside the organelle. The cristae and the proteins of the inner membrane aids in the production of ATP molecules. The inne

membrane is strictly permeable only to oxygen and to ATP molecules.number of chemical reactions take place within the inner membrane o mitochondria.

2. Mitochondrial Matrix The mitochondrial matrix is a viscous fluid that contains a mixture of enzymes and proteins. It also comprises ribosomes, inorganic ions,

mitochondrial DNA, nucleotide cofactors, and organic molecules. The enzymes present in the matrix play an important role in the synthesis of ATP molecules.Functions of Mitochondria The most important function of mitochondria is to produce energy through

the process of oxidative phosphorylation. It is also involved in the following

process:-Regulates the metabolic activity of the cell.Promotes the growth of new cells and cell multiplication.Helps in detoxifying ammonia in the liver cells

Plays an important role in apoptosis or programmed cell death Responsible for building certain parts of the blood and various hormones like testosterone and oestrogen Helps in maintaining an adequate concentration of calcium ions within the

compartments of the cell It is also involved in various cellular activities like cellular differentiation,"cell signalling, cell senescence, controlling the cell cycle and also in cell growth.

PLASTIDS:

What are Plastids?

Plastids are double-membrane organelles which are found in the cells of plants and algae. Plastids are responsible for manufacturing and storing of food. These often contain pigments that are used in photosynthesis and different types of pigments that can change the colour of the cell.

Types of Plastids:There are different types of plastids with their specialized functions. Among them, a few are mainly classified based on the presence or absence of the Biological pigments and their stages of development.

Chloroplasts

Chromoplasts

Gerontoplasts

Leucoplasts

1. Chloroplasts:Chloroplasts are biconvex shaped, semi-porous, double membrane, cel

organelle found within the mesophyll of the plant cell. They are the sites fo

synthesizing food by the process of photosynthesis.

2. ChromoplastsChromoplasts are the name given to an area for all the pigments to be kept and synthesized in the plant. These can be usually found in flowering plants, ageing leaves and fruits. Chloroplasts convert into chromoplasts. Chromoplasts hav

carotenoid pigments that allow different colours that you see in leaves and fruits. The main reason for its different colour is for attracting pollinators.

3. Gerontoplasts These are basically chloroplasts that go with the ageing process. Geronoplast refer to the chloroplasts of the leaves that help to convert into different othe organelles when the leaf is no longer using photosynthesis usually in an autumn month.

4. Leucoplasts These are the non-pigmented organelles which are colourless. Leucoplasts ar usually found in most of the non-photosynthetic parts of the plant like roots.They act as storage sheds for starches, lipids, and proteins depending on the need of the plants. They are mostly used for converting amino acids and fatty

acids.Leucoplasts are of three types:

Amyloplasts — Amyloplasts are greatest among all three and they store and

synthesize starch.Proteinoplasts — Proteinoplasts help in storing the proteins that a plant needs and can be typically found in seeds. Elaioplasts - Elaioplast helps in storing fats and oils that are needed by the plant.

Inheritance of Plastids:There are many plants which are inherited from the plastids from just a single parent. Angiosperms inherit plastids from the female gamete while there are many gymnosperms that inherit plastids from the male pollen. Algae inherit plastids from one parent only. The inheritance of the plastids-DNA seems to be 100% uniparental. In hybridisation, the inheritance of plastid seems to be more erratic.

LET US KNOW WHAT WE HAVE LEARNT!

MCQs:

Q1.Cristare in mitochondria serves as sites for?

a. Oxidation reduction reaction

b. Protein Synthesis

c. Macromolecules breakdown

d. Flavoproteins are phosphorylated

Q2. Which of the following cell organelle can be viewed by a light

microscope?

a. Ribosome

b. Golgikodies

c. Endoplasmic Reticulum

d. Mitochondria

Q3. Mitochondria in the human sperm cell are occupied at which part?

a. Sperm head

b. Mid piece

c. Sperm Tail

d. Mitochondria in the Sperm

Q4. Leucoplasts are a type of:

a. Plastids

b. Endoplasmic reticulum

c. Nucleus

d. Golgi Apparatus

FILL IN THE BLANKS:

1. Mitochondria are of the Cell.

2. helps in storing fats and oils that are needed by the plant.

TRUE/FALSE:

1. Mitochondria are not membrane bound.

2. Yellow colour of mango is due to chloroplasts.

ANSWER KEY: PART-A

MCQs:

1. a (Oxidation reduction reaction)

2. d (Mitochondria)

3. b (Mid piece)

4. a(Plastids)

FILL IN THE BLANKS:

1. Power House

2. Elaioplasts

TRUE/FALSE:;

1. False: Mitochondria are double membrane bound cell organelles.

2. False: Yellow colour of mango is due to chromoplasts.

PART: B SHORT ANSWER TYPE QUESTIONS:

1. What are 3 facts about mitochondria?

2. | Why mitochondria are called the power house of the cell?

3. Write a short note on Plastids.

PART: C LONG ANSWER TYPE QUESTIONS:

Q1. Write down the structure and functions of Mitochondria?

A85

INTRODUCTION:The organelles are present inside the cell and they are performing specific function that regulates the cell activities.Let us discuss some important organelles.

A. Claude (1941), first observed ribosomes and called them as microsomes.

B. Robinson and Brown (1953) first discovered ribosomes, in plant cells (roots of Vicia).

C. Palade (1955) isolated ribosomes from animal cells and detected RNA.

D. Roberts (1958) coined the term ribosome.

The ribosome word is derived from — ‘ribo’ ribonucleic acid and ‘somes’ from

the Greek word ‘soma’ which means ‘body’.

The location of the ribosomes in a cell determines what kind of protein it makes. If the ribosomes are floating freely throughout the cell, it will make proteins that will beutilized within the cell itself. When ribosomes are attached to endoplasmic reticulum,it is referred to as rough endoplasmic reticulum or rough ER. Proteins made on the rough ER are used for usage inside the cell or outside the cell.

On average in a mammalian cell, there can be about 10 million ribosomes.

FUNCTIONS OF RIBOSOMES:

1. They assemble amino acids to form specific proteins, proteins are essential to carry out cellular activities.

2. In the process of production of proteins, the DNA produces mRNA by the

process of DNA transcription.

3. The genetic message from the mRNA is translated into proteins during DNA

translation.

4. The sequences of protein assembly during protein synthesis are specified in

the mRNA.

5. The mRNA is synthesized in the nucleus and is transported to the cytoplasm

for further process of protein synthesis.

6. In the cytoplasm, the two subunits of ribosomes are bound around the polymers of mRNA; proteins are then synthesized with the help of transfer RNA.

7. The proteins that are synthesized by the ribosomes present in the cytoplasm

are used in the cytoplasm itself. The proteins produced by the bound ribosomes are transported outside the cell.

Cilia and Flagella are complex filamentous cytoplasmic structures which grow

through a cell wall.They are minute, especially differentiated appendices of the cell.Flagella (singular = flagellum) are long, hair-like structures that extend from the plasma membrane and are used to move an entire cell.Cilia (singular = cilium) are short, hair-like structures that are used to move a cells (Such as paramecia) or substances along the outer surface of the cell (for example, the cilia of cells lining the Fallopian tubes that move the ovum toward the uterus, or cilia lining the cells of the respiratory tract that trap particulate matter and move it toward the nostrils).The terms cilium (meaning an eyelash) and flagellum (meaning a whip) are often used simply.Generally, cilia are shorter than flagella (<10 um compared to >40um).Cilia are present on the surface of the cell in much greater numbers (ciliated cells often have hundreds of cilia but flagellated cells usually have a single flagellum).The real difference, however, lies in the nature of their movement. Cilia row like oars. The movement is biphasic, consisting of an effective stroke in which the cillum is held rigid and bends only at its base and a recovery stroke in which the

bend formed at the base passes out to the tip.Flagella wriggle like eels. They generate waves that pass along their length,usually from base to tip at constant amplitude.Thus the movement of water by a flagellum is parallel to its axis while a cilium moves water perpendicular to its axis and, hence, perpendicular to the surface of the cell.

STRUCTURE OF CILIA AND FLAGELLA:

Despite their different pattern of beating, cilia and flagella are indistinguishable

structurally.All cilia and flagella are built on a common fundamental plan:

1. A bundle of microtubules called the axoneme which is covered by a membrane

that is part of the plasma membrane.

2. The axoneme is attached with the basal body which is an intracellular granule

lying in the cell cortex and which originates from the centrioles.

3. Each axoneme is filled with ciliary matrix, in which are embedded two central

singlet microtubules, each with the 13 protofilaments and nine outer pairs of

microtubules, called doublets. This is known as the 9 + 2 array.

4. Each doublet contains one complete microtubule, called the A sub fiber,

containing all the 13 protofilaments. Attached to each A sub fiber is a B sub fiber with 10 protofilaments.

5. Subfibre A has two dynein arms which are oriented in a clockwise direction.

Doublets are linked together by nexin links.

6. Dynein is an ATPase that converts the energy released by ATP hydrolysis into

the mechanical work of ciliary and flagellar beating.

7. Each sub fiber A is also connected to the central microtubules by radial spokes

terminating in fork-like structures, called spoke knobs or heads.This regular arrangement of microtubules and associated proteins with the nine-way pattern is also seen in centrioles. But unlike centrioles, cilia and flagella have a central pair of microtubules, so that the overall structure is called the 9 + 2 axoneme.

IMPORTANT POINT: Eukaryotic flagella diverge from prokaryotes in composition.

Flagella in eukaryotes contain far more proteins and bear some similarity to motile

cilia, with the same general motion and control patterns.WORKING OF CILIA AND FLAGELLA:In eukaryotes The ATP produced are used by mitochondria near the base of the cilium or flagellum as fuel, the dynein arms push on the adjacent outer doublets, forcing a sliding movement to occur between adjacent outer doublets. Because the arms are activated in a strict sequence both around and along the axoneme and because the amount of sliding is restricted by the radial spokes and inter-doublet links, sliding is converted into bending.

In prokaryotes Bacterial flagella use a different method. Like the propeller of a boat, the motion of the bacterial flagellum is completely driven by the rotary motor at its base. The bacterial flagella itself is a specialized piece of extracellular cell wall, made of one protein named as flagellin that different from tubulin or dynein. Cilia and flagella are full of cytosol all the way to their tips and use the ATP in that cytosol to generate

force all the way along their length.

FUNCTIONS OF CILIA:Cilia are used for locomotion in unicellular organisms, such as protozoans (e.g., Paramecium).

Motile cilia use their rhythmic undulation to throw away substances, as in clearing

dirt, dust, micro-organisms and mucus, to prevent disease.Cilia play important roles in the cell cycle as well as animal development, such as in the heart.

Cilia selectively allows only some proteins to function properly.Cilia also play a major role in cellular communication and molecular trafficking.Non-motile cilia serve as sensory apparatus for cells, detecting signals. They play crucial roles in sensory neurons. Non-motile cilia can be found in the kidneys to sense urine flow, as well as in the eyes of the hotoreceptors of the retina. They also provide habitats or living areas for symbiotic microbiomes in animals. Cilia have also been reported to participate in vesicular secretion of ectosomes.

FUNCTIONS OF FLAGELLA:Flagella are generally used for locomotion of cells, such as the spermatozoon and Euglena (protozoan).It has an active role to help the cell for feeding and eukaryotic reproduction.In prokaryotes such as bacteria, flagella serve as propulsion mechanisms; they're the chief way for bacteria to swim through fluids.It also provides a mechanism for pathogenic bacteria to aid in colonizing hosts

and therefore transmitting diseases.

It also function as bridges or scaffolds for adhesion to host.as Centrosome is an organelle that contains two cylindrical structures called centrioles.Both are composed of two centrioles arranged at right angles to each other, and

covered by a dense, highly organized mass of protein which is known as the

pericentriolar material (PCM). The PCM contains proteins responsible for

microtubule nucleation and anchoring — including y-tubulin, pericentrin and ninein

(these are the names of proteins).

FUNCTIONS OF CENTROSOME:Centrosomes arrange the microtubules, so it is also called the microtubules organizing center. The centrosomes duplicate before cell division.

CENTRIOLE:Eukaryotic cells contain two cylindrical, rod-shaped, microtubular structures,called centrioles, near the nucleus.They lack a limiting membrane and DNA or RNA and occur in most algal cells ,

moss cells, some fern cells, and most animal cells.They are absent in prokaryotic cells, red algae, yeast, cone-bearing

(gymnosperms) and flowering plants ( angiosperms) and some non-flagellated or

non-ciliated protozoans (such as amoebae).

Centrioles form a spindle of microtubules, the mitotic apparatus during mitosis or

meiosis and sometimes get arranged just beneath the plasma membrane to form

and bear flagella or cilia in flagellated or ciliated cells.When a centriole bears a flagellum or cilium, it is called the basal body

STRUCTURE OF CENTRIOLE:

1. Centrioles and basal bodies are cylindrical structures which are nearly 0.16-0.27 um in diameter usually 0.28—0.69 um in length.

2. They are visible under a light microscope, but the details of the centriole structure were seen only under an electron microscope.

3. Each cell has a pair of centrioles in the centrosome, a region near the nucleus.

The members of each pair of centrioles are at right angles to one another.

4. They are small -sub-microscopic microtubular sub cylinders with a configuration of nine triplet fibrils and the ability to form their own duplicates, astral poles and basal bodies, without having DNA and a membranous cover.

5. A centriole consists a whorl of nine peripheral fibrils. Fibrils are absent in the center. The arrangement is, therefore, called 9 + 0. Fibrils run parallel to one

another but at an angle of 40°. Each fibril is made up of three sub-fibers. So, it is

called a triplet fibril.

6. Each sub-fiber has a diameter of nearly 25 nm. From outside to inside the three

sub-fibers of a triplet fibril are named as C, B and A. Sub-fibre A are complete

with 13 proto-filaments while B and C sub-fibers are incomplete due to sharing of

some microfilaments.

7. The adjacent triplet fibrils are connected by C—A proteinaceous linkers. The

center of centriole possesses a rod-shaped proteinaceous mass known as the

hub. The hub has a diameter of 2.5 nm. From the hub, develops 9 protein strands

towards the peripheral triplet fibrils. They are Known as spokes.

8. Each spoke has a thickening called X before uniting with A sub-fiber. Another

thickening known as Y is present nearby. It is attached both to X thickening as

well as C —A linkers by connectives.

9. The presence of radial spokes and peripheral fibrils, the centriole gives a

cartwheel type shape in T.S.

FUNCTIONS OF CENTRIOLE:Centrioles are mainly involved in the formation of the spindle, which functions during cell division(or cell reproduction)

The absence of centrioles causes divisional errors then there is delay in the

mitotic process.A single centriole makes the anchor point, or basal body, for each individual cilium or flagellum.Basal bodies direct the formation of cilia and flagella

LET US KNOW WHAT WE HAVE LEARNT!

PART: A_ VERY SHORT ANSWER TYPE QUESTIONS:

MCQs:

1. Centrosome is found in:

(a) cytoplasm

(b) chromosome

(d) Lysosomes

2. Two cylindrical rod shaped structures present in Eukaryotic cell:

(a) centrioles

(b) genes

(d) ribosomes

3. Who coined the term ribosome?

(a) Robert Brown

(b) Roberts

(d) Leeuwenhoek

4. Centriole Takes Part in the Formation of:

(a) Nucleus

(b) Spindle

(d) To start cell division

5. Bacterial flagella are made up of protein:

(a) tublin

(b) flagellin

(d) None of these

FILL IN THE BLANKS:

1. Centrioles are involved in the formation of the .

2. Flagella are generally used for of cells.

TRUE/ FALSE:

1. Nucleus controls the hereditary characteristics of an organism.

2. A bundle of microtubules called the axoneme.

ANSWER KEY: PART-A

MCQs:

1. a) Cytoplasm

2. a) Centrioles

3. b) Roberts

4. b) Spindle

5. b) Flagellin

FILL IN THE BLANKS:

1. Centrioles are involved in the formation of the spindle apparatus.

2. Flagella are generally used for Locomotion of cells.

TRUE/ FALSE:

1. TRUE

2. TRUE

PART: B SHORT ANSWER TYPE QUESTIONS:

1. What are the functions of Ribosomes?

2. What are the functions of centriole?

3. What is the difference between 70S and 80S ribosomes?

PART: C LONG ANSWER TYPE QUESTION:

1. Explain the structure and functions of cilia and flagella.

A86

Nucleus is a specialized double membrane’ bound protoplasmic body which contains all the genetic information for controlling cellular metabolism and transmission to the

posterity. A nucleus in non-dividing or metabolic phase is call interphase nucleus. It directs and controls all the cellular

functions.

Discovery: It was first described by Robert Brown (1831 A.D.) in the root cells of orchid cells.

Occurrence: A true nucleus is present in all the eukaryotes except mature

mammalian RBCs, sieve tube cells of phloem, tracheids and vessels of xylem.

Position: The nucleus is generally centric.

Number: Mostly the cells are monokaryotic but may be anucleate,binucleate, multinucleate.

Shape: It varies widely. Generally spherical, oval, discoidal, kidney shaped,

horse shoe shaped, bilobed, multilobed, long and beaded moniliform and branched.

CHEMICAL COMPOSITION OF NUCLEUS

Proteins =80%

DNA =12%

RNA=5%

Lipids = 3%

Enzymes like polymerases are abundantly present and help in synthesis of

DNA and RNA.Minerals in traces like Ca, Mg, Na and K.A typical interphase nucleus is 5-25 ym in diameter. It has four components

1. Nuclear Envelope

2. Nucleoplasm

3. Nucleolus

4. Nuclear Chromatin

1. Nuclear Envelope: It bounds the nucleus in the outside. The nuclear envelope separates the nucleus from the cytoplasm. It is made up of two lipoprotein and trilaminar membranes, each of which is 60-90A thick.The inner membrane is smooth. The outer membrane may be smooth of its

cytoplasmic surface may bear ribosomes like the rough endoplasmic reticulum. The two membranes of the nuclear envelope are separates by an electron transparent perinuclear space. Nuclear envelope contains a large number of pores (1000-10000)

Functions of Nuclear envelope:

1. It regulates the nucleo-cytoplasmic interactions.

2. It allows the passage of inorganic ions and small organic molecules

3. It helps in pinocytosis and phagocytosis.

2. Nucleoplasm: It is a transparent, semifluid and colloidal substance which

fills the nucleus. It contains nucleosides and a number of enzymes which are required for the synthesis and functioning of DNA, RNA, nucleoproteins, etc.Some of the proteins present in nucleoplasm are essential for spindle formation.

3. Nucleolus: It is a darkly stained granular naked organelle with no limiting

membrane. It is associated with nucleolar organizer region of the chromosome. It is seat of biogenesis of r-RNA and also stores r-RNA so it is called ribosome factory. It plays important role in spindle formation during cell division.

4. Nuclear Chromatin: It is a darkly stained network of long and fine

threads, called chromatin fibers. Chromatin fibers are distributed throughout the nucleoplasm. They are differentiated into two region-euchromatin and heterochromatin. Chromatin fibers contain DNA which

acts as a genetic material.

LET US SEE WHAT WE HAVE LEARNT! |

PART A: VERY SHORT ANSWER TYPE QUESTIONS:

A. MULTIPLECHOICE QUESTIONS:

1) Nucleus is discovered by :

a) Erclab

b) Robert Hook

c) Robert Brown

2) Nucleus is absent in:

a) RBCs of mammals

b) Seive tube cells of phloem

c) Both a and b

3) Nucleolus is found in:

a) Protoplasm

b) Nucleus

c) Cytoplasm

4) Nuclear material without nuclear membrane is observed in:

a) Eukaryotes

b) Bacteria and cyanobacteria

c) Bacteria and green algae

5) Controlling centre of cell is:

a) Ribosomes

b) Nucleus

c) Nucleolus

1) ......... is the principal site for the development of r-RNA.

2) Incipient nucleus with no nuclear membrane is called .........

1) Nuclear membrane regulates the nucleo-cytoplasmic interactions.

2) Nucleoplasm possesses cyclosis.

3) A nucleolus is darkly stained granular naked organelle with no limiting

membrane.

ANSWER KEY |

PART A: VERY SHORT ANSWER TYPE QUESTIONS:

(A MULTIPLECHOICE QUESTIONS: _

1) c (Robert Brown) —

2) c (Both a and b ,RBCs of mammals and sieve tube cells of phloem)

3) b (Nucleus)

4) b (Bacteria and cyanobacteria)

5) b (Nucleus) It controls the cellular metabolism

1) Nucleolus

2) Nucleoid

1) True

2) False (Nucleoplasm is a gel-like sticky material covered by nuclear envelope and supports the chromosomes and nucleoli so do not show cyclosis (streaming movement)).

3) True

PART-B: SHORT ANSWER TYPE QUESTIONS

1) Why nucleus is called director of the cell?

2) Name four components of nucleus.

3) List two functions of nuclear membrane.

PART-C: LONG ANSWER TYPE QUESTIONS

1) Draw the well labeled diagram of nucleus

2) Give the functions of components of nucleus.

A87

INTRODUCTION:CHROMOSOMES are rod shaped or threadlike deeply stainable condensed chromatin fibres which are hereditary vehicles as they store and transmit coded hereditary information. Chromosomes appear only during karyokinesis. They are meant for equitable distribution of genetic material.The number is fixed and is the same in all the individuals of a species. There is a single set in gametophytic or haploid forms and two sets in sporophytic

or diploid forms. Size and shape of individual chromosomes are quite distinct. The shape is more clearly is more clearly visibly in late prophase and metaphase (as well as anaphase) when primary constriction or centromere becomes distinct. During prophase and metaphase, theChromosomes are replicated. There are two chromosome halves or chromatids.

The two chromatids are attached to each other by a narrow area called centromere or primary constriction. Anaphasic chromosomes do not have chromatids. The two parts of chromosome or chromatid on either side of primary construction are called arms. The two arms are equal in isobrachial chromosomes and unequal’ in heterobrachial chromosomes. The ratio between the two arms of a chromosome is called centromeric ratio.Based on the position of centromere, chromosomes are of four types

(i) Telocentric: Centromere terminal in the area of telomere.

(ii)Acrocentric: Centromere inner to telomere (subterminal).

(iii) Submetacentric: Centromere submedian.

(iv) Metacentric: Centromere median.

Some chromosomes have additional non-staining sub terminal constriction, called secondary constriction and such chromosomes are called SAT-chromosomes. In human karyotype, there are five pairs of

SAT-chromosomes (13, 14, 15, 21 and 22).

Certain secondary constrictions are involved in the formation of nucleoli and are called nucleolar organising regions (NORs) and suchchromosomes are called nucleolar chromosomes.

NUCLEOSOME:Chromatin fibre is formed of a chain of repeated units called nucleosomes. Each nucleosome is formed of a core complex called nu body wrapped by DNA strand (of 166 to 200 base pairs). Core complex

is formed of HISTONE OCTOMER of four types of histone molecules (2 molecules each) -H2A, H2B, H; and Hg.

SPECIAL TYPES OF CHROMOSOME These are /argest-sized chromosome, so called giant chromosomes.For example: lampbrush chromosomes of oocytic nuclei of

Salamandra are as long as 5900um (5.9mm). So these are even visible with naked eye. Each chromosome is formed of a main

central axis and several pairs of lateral loops laying the appearance of a brush, so called lampbrush chromosome.

These are second largest-sized chromosomes. These are about 200um or more in length (normal chromosome is about 7.5um. So these are called giant chromosomes. These are multi-stranded or polytenic chromosomes and may be formed as many as 512 to 1024

chromatids. It is due to a process called endomitosis. Each chromosome is with a specific pattern of dark-coloured bands and

alternatively arranged light-coloured interbands. One or more bands give rise to swelling called puffs or bulbs. Some chromonemata give rise to a number of large-sized loops, called Balbiani rings.

CHROMOSOME FUNCTIONS Chromosome contains genes. All the hereditary information is located in the genes.They control cellular differentiation.Sat chromosomes produce nucleoli for synthesis of ribosomes.

Their haploid or diploid number respectively brings about gametophytic and sporphytic characteristics to the individual.Chromosomes form a link between the offspring and the parents.

Some chromosomes called sex chromosomes (e.g., X and Y or Xand 0) determine the sex of the individual.Through the process of crossing over, chromosomes introduce

variations.

A. MULTIPLE CHOICE QUESTIONS:

1) Kinetochore is present in:

a. Mitochondria

b. Chromosome

c. Lysosome

2) Ina cell that is not dividing the chromosome are visible as a tangle

of thread called:

a. Chromatin

b. Microtubule

c. Microfilament

3) Chromosome are always exist:

a. In pairs

b. Singly

c. In association with mitochondria

4) Chromosome whose arms are equal are called:

a. Metacentric

b. Acrocentric

c. Acentric

5) Tips of chromosomes are called:

a. Centromere

b. Chromomeric

c. Telomere

FILL UPS

1) Some chromonemata give rise to a number of large sized loops

called...........

2) Chromosomes are observable during.......or.......

TRUE/FALSE

1) Lampbrush chromosomes are called giant chromosomes.

2) Chromatin fibre is formed of a chain of repeated unit called

nucleosomes.

3) Chromosome does not contain genes.

PART A: VERY SHORT ANSWER TYPE QUESTIONS:

1) (b) Chromosome

2) (a) Chromatin

3) (a) In pairs

4) (a) Metacentric

5) (a) Telomere

FILL UPS °

1) Balbiani ring

2) M-phase or Nuclear division

TRUE/FALSE a

1) TRUE

2) TRUE

3) FALSE (Chromosome contain gene as all the hereditary information is located in the genes)

PART B: SHORT ANSWER TYPE QUESTIONS:

1) What are SAT chromosomes?

2) Define nucleosomes.

3) Name two special types of chromosomes?

PART C: LONG ANSWER TYPE QUESTIONS:

1) What is centromere? How does the position of centromere form

the basis of classification of chromosome? Support your with

diagram.

2) List the functions of chromosomes.

A88

INTRODUCTION:The cell is the structural and fundamental unit of life.Plant and animal cells are eukaryotic, so they contain membrane bound organelles like the nucleus, mitochondria etc. Plant Cell and Animal Cell do not look exactly the same.

All cells arise from pre-existing cells.

Animal cell: Animal cells do not have a cell wall. Animal cell is composed of a

cell membrane, cells have cytoplasm in it, different type of cellular activities

occurs in cytoplasm. Animal cells have different oraganelles like mitochondria,

nuclueus, ribosome, golgi apparatus, endoplasmic reticulum. Mitochondria are

the power house of cell.

PLANT CELL: Itis found in the organisms within the plant kingdom.

Plant cell contains the rigid cell wall. Cell wall provides the protection.

Plant cell contain large central vacuoles. Chloroplasts present, help in food

synthesis.

MCQs:

1. Component of plant cell absent in animal cell is:

[a] cytoplasm

[b] cell membrane

[c] cell wall

[d] nucleus

2. The main site of different types of cellular activities is;

[a] mitopchondria

[b] nucleus

[c] cytoplasm

[d] plasma-membrane

3. Chloroplast is found in:

[a] plant cell only

[b] Animal cell only

[c] both of these

[d]none of these

4. The functional unit of Life is called:

[a] cell

[b] egg

[c] nucleus

[d] none of these

5. The power house of cell is called:

[a] cell wall

[b] mitochondria

[c] ribosome

[d] nucleus

FILL IN THE BLANKS:

1. cell does not have a plastids.

2. All cells arise from cells.

TRUE/FALSE:

1. Cell is structural functional unit of an organism.

2. Both animal and plant cells are eukaryotes.

MCQs:

1. c_ cell wall

2. c cytoplasm

3. a plant cell only

4. a cell

5. b mitochondria

FILL IN THE BLANKS:

1. Animal cell

2. Pre-existing

TRUE/FALSE:

1. True

2. True

1. Write down the function of cell wall.

2. What is cytoplasm?

3. Write function of chloroplast.

1. Differentiate between plant cell and animal cell.

A89

INTRODUCTION:Dear students we have discussed the chapter; Cell: The Unit of Life.Now in this assignment we will discuss about the NCERT exercise questions.

NCERT EXERCISE QUESTIONS

Q: 1 Which of the following is not correct?

[a] Robert brown discovered the cell .

[b] Schleiden and scgwann formulated the cell theory

[c] Virchow explained that cells are formed from pre-existing cells

[d] A uniceller organism carries out its

life actiivites within a single cell .

Q:2 New cells generate from:

[a] bacterial fermentation

[b] regeneration of old cells

[c] pre-existing cells

[d] Abiotic material

Q: 3 Match the following :

COLUMN [1] COLUMN [2]

[A] Cristae [1] Flat membranous sacs in stroma

[B] Cisternae [2] Infoldings in mitochondria

[C] Thylakoids [3] Disk shaked sacs in Golgi-apparatus

ANS: A-1, B-3, C-2

Q: 4 Which of following is correct?

[a] cells of all living organism have a nucleus

[b] Both animal and plant cells have a well-defined cell wall

[c] In prokaryotes there are no membrane bound organelles

[d] cells are formed de novo from abiotic material

Q: 5 what is a mesosome in a prokaryotic cell? Mention the functions that it

perform.

ANS: Mesosome is a membranous structure in prokaryotic cell which is formed by the

extensions of the plasma membrane into the cell in the form of vesicles, tubules and

lamellae. Mesosome is equal to mitochondria in eukaryotes as it performs aerobic

cellular respiration in prokaryotes. It helps in DNA replication and distribution of genetic material to daughter cells. Mesosome also helps in respiration by increasing the surface area of the plasma membrane and enzymatic content. It helps in cell wall formation.

Q: 6 How do neutral solutes more across the plasma membrane. Can the polar molecules also move across it in the same way, If not then how are these transported across the membrane?

ANS: Neutral solutes move across the membrane by the process of simple diffusion

along the concentration gradient i.e, from higher concentration to the lower

concentration. Polar molecules cannot pass through the nonpolar lipid layer. They

require carrier protein of the membrane to facilitate their transport across the

membrane. In facilitated diffusion, molecules are transported along concentration gradient by the help of ion channels and aquaporin. It does not involve energy expenditure.

Q: 7 Name two cell organelles that are double membrane bound. What are the

characteristics of these two organelles? State their function and draw labeled

diagram of both.

ANS: Mitochondria and Chloroplast are double membrane bound organelles.

MITOCHONDRIA: Mitochondria are cylindrical shaped cell organelles and contain two

membranes; outer and inner. The inner compartment is called the matrix containing

DNA, RNA, ribosome etc. Outer membrane forms the continuous limiting boundary of

the organelle. Inner membrane forms number of infoldings, called the cristae which

increases the surface area. Oxysomes are present on inner mitochondrial membrane.

Mitochondria are semi-autonomous organelles i.e, have their own DNA and ribosomes.

FUNCTIONS OF MITOCHONDRIA:

1. Mitochondria are essential for aerobic respiration.

2. Mitochondria provide intermediates for synthesis of important biomolecules such

as chlorophyll cytochrome etc.

3. Mitochondria regulate the calcium ion concentration in the cell.

4. Synthesis of many amino acids takes place here.

CHLOROPLAST: They are green coloured plastids which are disc shaped. The

spaces limited by inner membrane of chloroplast is called stroma. Stroma has

organized flattened membranous sacs called the THALAKOID. Thalakoids are arranged in stacks called GRANA. Matrix of a chloroplast contains DNA, RNA,riobosomes and enzymes.

FUNCTIONS OF CHLOROPLAST:

1. Photosynthesis is performed by chloroplast.

2. Chloroplast stores starch grains.

3. Maintains balance of CO: concentration in the air.

4. Keeps oxygen balance constant in atmosphere by liberating O2 into the

atmosphere used during respiration and combustion.

Q: 8 What are the characteristics of prokaryotic cells?

ANS : The characteristics of prokaryotic cells are as follows:The prokaryotes cell is essentially a single envelope system.

Prokaryotes lack membrane bound cell organelles.Prokaryotes have 70s ribosomes.

e DNA is naked and lies coiled in cytroplasm. It is not covered by nuclear

membrane and is turned as nucleaid.

e Nuclear components like nuclear envelope, nucleolus, and nucleoplasm are absent. Cell wall is present in bacteria and cyanobacteria but absent in mycoplasma.

Multiplies by asexual reproduction.

Q: 9 Multicellular organisms have division of labor. Explain.

ANS: Division of labor is differentiation of certain components or parts to perform

different functions for increased efficiency and higher survival.Multicellular organisms often possess millions of cells are grouped together to form specific tissue organ system, with each specialized to perform particular function. Every cell of a multicellular organism cannot obtain food from outsides.The organism requires a system for obtaining food, its digestion and distribution.Therefore a digestive system and system of transport are also required. Certain cells of the body take over the function of reproduction. Other takes part in repair and replacement of worn out portions for optimum functioning of cells. A multicellular organism also requires an internal favorable environment. So a multicellular organism comes to have division of labor.

Q: 10 Cell is the basic unit of life. Discuss in brief.

ANS: Cell is fundamental, structural and functional unit of life as no living

organism can have life without being cellular. All life begins as a single cell. An organism single cell is capable of independent existence and perform all essential functions of life, while in multicellular organism each group of cells is specialized for specific function. Life passed from one generation to the next in front of cells and new cells always arise from division of pre-existing cells. Cells are totipotent i.e, single cell has ability to form whole organism.The activities of an organism are sum total of activities of its cells. Therefore cell is the basic unit of life.

Q: 11 What are nuclear pores? State their function.

ANS: Nuclear envelope bounds the nucleus from outside and separates it from

cytoplasm; it consists of two membranes, with outer membrane continuous with

endoplasmic reticulum. The nuclear pores at a number of places, which are produced by the fusion of its two membranes. These nuclear pores are the passage through which movement of RNA and protein molecules takes place in both directions between the nucleus and the cytoplasm.

Q: 12 Both lysosomes and vacuoles are endomembrane structure, yet they

differ in terms of their function, comment.

ANS: Organelles, of endomembrane system such as lysosomes and vacuoles

function in close co-ordination with one another but are specialized to perform

different functions. Lysosomes break down the ageing and dead cells. They help

in digestion of food as they contain hydrolytic digestive enzymes. They are

involved in cell division also. Vacuoles on other hand help in excretion and

osmoregulation in Amoeba or provide buoyancy mechanical strength in

prokaryotes. (Air- vacuoles)

Q: 13 Describe the structure of following with the help of labeled diagrams:

(1) Nucleus (2) Centrosome

ANS: NUCLEUS: Nucleus is double membrane bound principal cell organelle,

which contains all genetic information for controlling cellular metabolisim and

transmission of genetic information. Nucleus is differentiated into following four parts :

[a] Nuclear envelope: It is a double membrane envelope that surround the nucleus and separates the latter from the cytoplasm.

[b] Nucleaplasm: Its clear, non- staining fluid material present in the nucleus,which

contains raw materials (nucleotides ) enzymes (DNA/RNA polymerase) and metal ions

for the synthesis of RNA’ s and DNA.

[c] Nucleolus: It is a naked, round and slightly irregular structure which is attached to the chromatin at a specific region.

[d] Chromatin: It has the ability to get stained with certain basic dyes. It is known to be hereditary DNA protein fiberilar complex.

CENTROSOME It is an organelle usually containing two cylindrical structures called centrioles. It is present near the nucleus. Centrioles are surrounded by amorphous pericentriolar,centrosphere. The complex formed by centrosphere and centrioles is called centrosome. In a centrosome, the two centrioles lie perpendicular to each other. T.S. of

centriole gives a Cartwheel like appearance due to presence of peripheral fibrils,

spokes and hub.

Q: 14 What is a centromere? How does the position of centromere form the basis

of classification of chromosome? Support your answer with a diagram, showing

the position of centromere on different types of chromosome.

ANS: A chromosome consists of two identical halves, the chromatids. The chromatids

held together at one point called the centromere. The centromere is also called as primary constriction.Chromosome is classified into four types according to position of centromere on chromosome:

1. Metacentric chromosome: In this type centromere is in the middie and the two

arms of chromatids are almost equal in length.

2. Sub-metacentric chromosome: The centromere is slightly away from middle

point, so one arm of chromatids is slightly shorter than the other.

3. Acrocentric chromosome: The centromere is near the end and one arm of the

chromatids is extremely short and other arm is extremely long .

4. Telocentric chromosome: The centromere is at the tip of chromatids. These

chromosomes are not present in humans.

A90

RECAPITULATION:All cells arise from pre-existing cells.Animal cells plant cells both are eukaryotic type cells.Cells have cell organelles in cytoplasm that is nucleus, nucleolus Golgi apparatus, mitochondria, endoplasmic reticulum.

Plant cells have a cell wall outside the cell membrane.Plasma membrane is selectively permeable and facilitates

transport of several molecules.

NUCLEUS: It is main controlling center of the cell, nucleus contains nucleoli and chromatin network .It controls activities of organelles.NUELEOLUS: tt is a spherical structure present in nucleoplasm it is a

site for achive ribosomal RNA synthesis

ENDOPLASMIC RETICULUM: It is network of tiny structure scattered inthe cytoplasm .It is of two type’s smooth endoplasmic reticulum and rough endoplasmic reticulum.

They help in transport of substances.

Golgi apparatus: It is present near nucleus. It consists of cisternal

tubules, vesicles. It is a membranous organelle.

Chloroplast: It is found in plant cells. They are responsible for trapping

lignt energy essential for photo synthesis.

Chromatin: interphase nucleus has an indistinct work of nucleoprotein

fibers called chromatin.

Chromosome: On the basis of position of centromere, chromosome can be classified into following different types:

(1) Acrocentric: In this type centromere is situated close to its end forming One short and one long arm

(2) Telocentric: In this type chromosome has terminal centromere .

(3) Metacentric: It has middie centromere and forming two equal arms of

chromosome.

(4) Sub-metacentric: It has centromere slightly away from the middle of the chromosome, so chromosome has one shorter and one longer arm.

LET US KNOW WHAT WE HAVE LEARNT!

TEST YOUR KNOWLEDGE

MCQs: (1 Mark each)

1. Cell was first observed and described by

a) Anton van leeuwenhoek

b) Robert brown

c) Robert Virchow

d) Schleiden and Schwann

2. Cell theory was proposed by :

a) Robert brown

b) Robert Virchow

c) Schleiden and Schwann

d) Stanger and Nicolson

3. Which organelle is the site of protein synthesis :

a) Mitochondria

b) Golgi bodies

c) Ribosomes

d) Chloroplast

4. Endoplasmic reticulum is continuous with :

a) Mitochondria

b) Cell wall

c) Nucleus wall

d) Golgi bodies

5. Prokaryotic cells do not have :

a) Nucleus

b) Membrane bound organelles

c) Centrioles

d) All of these

FILL IN THE BLANKS: (1 mark each)

6. The endoplasmic reticulum bearing ribosomes on their outer surface

are Called 00... cee cee cee cee tte eee

7. Ribosomes are of two types 70S and..............0......

8... IS the living matter of cell.

9. The cell is the basic structural and functional unit of ............

10. Single celled organisms are called...............

TRUE / FALSE: (1 Mark each)

11. Plasma membrane is selectively permeable.

12. Ribosomes are also known as protein factories of the cell.

13. Presence of cell wall is characteristic feature of animal cell.

14. There is a cell membrane around all cells.

15. Chromosomes are found in the cytoplasm.

SHORT ANSWER TYPE QUESTIONS: ee

16. Write about cell theory.

17. Define cell, unicellular and multicellular organisms.

LONG ANSWER TYPE QUESTION

18. Differentiate between prokaryotic cell and eukaryotic cell.

Chapter 8 Cell: The Unit Of Life

Plus One

Friday 5 February 2021

Chapter 8 Cell: The Unit Of Life

Chapter 8 Cell: The Unit Of Life

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