Maharashtra Board Class 11 Biology Important Questions Chapter 5 Cell Structure and Organization

Balbharti Maharashtra State Board 11th Biology Important Questions Chapter 5 Cell Structure and Organization Important Questions and Answers.

Maharashtra State Board 11th Biology Important Questions Chapter 5 Cell Structure and Organization

Question 1.
Define cell.
Answer:
Cell is defined as a structural and functional unit of life of all living organisms capable of independent existence and can perform all functions of life.

Question 2.
Write information about the instrument which is used for observing smaller organisms or cells.
Answer:

1. To observe cells or organisms of smaller size we use a microscope.
2. Larger cells can be seen through simple microscope but to observe smaller cells we require compound microscope.
3. Simple microscope can magnify image 50 to 100 times but a compound microscope can do so 1000 times or more.
4. In the microscope a beam of light is used to make things visible hence it is light microscope.
5. To observe interior of cell we need electron microscope which can magnify image 500000 times.

Question 3.
Write the shapes of the cells that can be observed.
Answer:
There is no typical shape of a cell. Cells may be spherical, rectangular, flattened, polygonal, oval, triangular, conical, columnar, etc.

Question 4.
1. Smallest cell
2. Longest cell in animals
3. Largest cell
Answer:
1. Mycoplasma (0.3 µm)
2. Nerve cell
3. Ostrich egg

Question 5.
Explain the term totipotency.
Answer:

1. Totipotency (totus – entire, potential – power) is the capacity or the potential of living nucleated cell, to differentiate into any other type of cell and thus, can form a complete new organism.
2. A cell is totipotent as it has the entire genetic information of the organism stored in its nucleus.
3. Embryonic animal cells are totipotent and are termed as stem cells.
4. Stem cells are used in curing many diseases. Therefore, they have great potential for medical applications.

Question 6.
Who proposed the cell theory?
Answer:
Schwann and Schleiden proposed the cell theory.

Question 7.
Give the postulates of modern cell theory.
Answer:
Postulates of modern cell theory:

1. All living organisms are made up of cells.
2. Cell is the basic structural and functional unit of life.
3. All cells arise from pre-existing cells. (Rudolf Virchow 1858 – “Omnis cellula-e-cellula”).
4. Total activities of cells are responsible for activity of an organism.
5. Cells show transformation of energy.
6. Cells contain nucleic acids; DNA and RNA in the nucleus and cytoplasm.

Question 8.
State the two general categories on which living organisms are grouped.
Answer:
Living organisms are grouped into two main categories the Prokaryotes and Eukaryotes.

Question 9.
State the general characteristics of prokaryotic cell.
Answer:
General characteristics of prokaryotic cell:
1. Prokaryotic cells are primitive type of cells.
2. It does not have membrane bound cell organelles (like endoplasmic reticulum, Golgi complex, mitochondria, etc.) and well-defined nucleus (nuclear membrane is absent).
3. Genetic material is in the form of nucleoid.

4. Cell envelope:
a. Prokaryotic cell has chemically complex protective cell envelope having glycocalyx, cell wall and plasma membrane.
b. In some bacteria, glycocalyx occurs in the form of a slime layer (loose sheath). Other bacteria may have a thick and tough covering called capsule. It helps in protection of bacterial cell.

5. Cell wall:
The Gram-positive bacteria show presence of peptidoglycan layer in the cell wall and Gram-negative bacteria show presence of murein in the cell wall. It gives mechanical strength to the cell.
[Note: In Gram-negative bacteria, cell wall is made up of two layers; inner layer of Murein or peptidoglycan and outer layer of Lipopolysaccharides.]

6. Cell membrane:
a. It is the innermost covering of the cell envelope, chemically composed of lipids and proteins.
b. It helps in intercellular communication.
c. Cell membrane shows infoldings called mesosomes which help in cell wall formation, cellular respiration and DNA replication.
d. The cyanobacteria show longer extensions called as chromatophores which carry photosynthetic pigments.

7. In motile bacteria either cilia or flagella are found. Both are driven by rotatory movement produced by basal body (which works as motor) of flagellum. Other parts of flagellum are filament and hook.

8. Some other surface projections are the tubular pili (which help in inter-cellular communication) and fimbriae (for clinging to support).

9. Ribosomes:
Bacterial cell cytoplasm contains dense particles called ribosomes which help in protein synthesis. Ribosomes are 70S type (composed of a larger sub-unit 50S and + smaller sub-unit 30S).

Question 10.
What is the difference between Gram-positive and Gram-negative bacterial cells? Name the technique used for differentiating such bacterial cells.
Answer:
The Gram-positive bacteria show presence of peptidoglycan layer in the cell wall and Gram-negative bacteria show presence of murein in the cell wall. The technique used for differentiating bacterial cells is Gram staining.
[Note: Murein is similar to peptidoglycan in structure and function. It is present in the cell walls of archaebacteria.

Question 11.
Write the constituents of prokaryotic cytoplasm.
Answer:
1. Cytoplasm of prokaryotes is a pool of all necessary materials like water, enzymes, elements, amino acids, etc.
2. Some inclusion bodies in form of organic (cyanophycean starch and glycogen) and inorganic granules (phosphate and sulphur) are also found.

Question 12.
Fill in the blanks.

1. Genetic material in bacterium is a single chromosome made up of circular and coiled _______.
2. The bacterial chromosome remains attached to _________.
3. The _________ model of replication is observed in bacterial cells.
4. _________ present in the bacterial cells are known as extrachromosomal self-replicating DNA.

Answer:

1. DNA
2. Mesosomes
3. Theta
4. Plasmids

Question 13.
What are eukaryotic cells?
Answer:
1. Eukaryotic cells are the cells possessing well-defined nucleus and membrane bound organelles (like mitochondria, endoplasmic reticulum, ribosomes, Golgi complex etc.).
2. Eukaryotes include protists, plants, animals and fungi.

Question 14.
Write a note on cell wall in Eukaryotic cells.
Answer:

• The rigid, protective and supportive covering, outside the cell membrane is called cell wall. It is present in plant cells, fungi and some protists.
• Algae show presence of cellulose, galactans, mannans and minerals like calcium carbonate in cell wall.
• In other plants, it is made up of hemicelluloses, pectin, lipids and protein.
• Microfibrils of plant cell wall show presence of cellulose which is responsible for rigidity.
• Some of the depositions of cell wall are silica (grass stem), cutin (epidermal walls of land plants), suberin (endodermal cells of root), wax, lignin.
• Function:
  • Provides support, rigidity and shape to the cell.
  • Protects the protoplasm against mechanical injury and infections.

Question 15.
Explain the structure of plant cell wall.
Answer:
In plants, cell wall shows middle lamella, primary wall and secondary wall

1. Middle lamella:
It is thin and present between two adjacent r cells. It is the first structure formed from cell plate during cytokinesis. It is mainly made up of pectin, calcium and magnesium pectate. Softening of ripe fruit is due to solubilization of pectin.
2. Primary wall:
In young plant cell, it is capable of growth. It is laid inside to middle lamella.
It is the only wall seen in meristematic tissue, mesophyll, pith, etc.
3. Secondary wall:
It is present inner to primary wall. Once the growth of primary wall stops, secondary wall is laid. At some places thickening is absent which leads to formation of pits.

Question 16.
Draw a well labelled diagram of a plant cell.
Answer:

Question 17.
Give an account of eukaryotic plasma membrane.
Answer:
Eukaryotic plasma membrane/ Cell membrane/ Biomembrane:

1. It is thin, quasi-fluid structure present both extracellularly and intracellularly.
2. Extracellularly, it is present around protoplast and intracellularly, it is present around most of the cell organelles in eukaryotic cell. It separates cell organelles from cytosol.
3. Thickness of bio-membrane is about 75A.
4. Cell membrane appears trilaminar (made up of three layers) when observed under electron microscope. It shows presence of lipids (mostly phospholipids) arranged in bilayer.
5. Lipids possess one hydrophilic polar head and two hydrophobic non-polar tails. Therefore, phospholipids are amphipathic.
6. Lipid molecules are arranged in two layers (bilayer) in such a way that their tails are sandwiched in between heads. Due to this, tails never come in direct contact with aqueous surrounding.
7. Cell membrane also shows presence of proteins and carbohydrates.
8. Ratio of proteins and lipids varies in different cells. For example, in human beings, RBCs show approximately 52% protein and 40% lipids.

Question 18.
Explain the structure of plasma membrane on the basis of Fluid mosaic model.
Answer:
Fluid mosaic model:

1. Fluid mosaic model was proposed by Singer and Nicholson (1972).
2. This model states that plasma membrane is made up of phospholipid bilayer and proteins.
3. Proteins are embedded in the lipid membrane like icebergs in the sea of lipids.
4. Phospholipid bilayer is fluid in nature.
5. Quasi-fluid nature of lipid enables lateral movement of proteins. This ability to move within the membrane is measured as fluidity.
6. Based on organization of membrane proteins they are of two types, as:

a. The intrinsic proteins occur at different depths of bilayer i.e. they are tightly bound to the phospholipid bilayer and are embedded in it. They span the entire thickness of the membrane. Therefore, they are known as transmembrane proteins. They form channels for passage of water.
b. The extrinsic or peripheral proteins are found on two surfaces of the membrane i.e. are loosely held to the phospholipid layer and can be easily removed.

Question 19.
Draw neat and labelled diagram of structure of plasma membrane proposed by Singer and Nicolson.
Answer:
Fluid mosaic model:

1. Fluid mosaic model was proposed by Singer and Nicholson (1972).
2. This model states that plasma membrane is made up of phospholipid bilayer and proteins.
3. Proteins are embedded in the lipid membrane like icebergs in the sea of lipids.
4. Phospholipid bilayer is fluid in nature.
5. Quasi-fluid nature of lipid enables lateral movement of proteins. This ability to move within the membrane is measured as fluidity.
6. Based on organization of membrane proteins they are of two types, as:

a. The intrinsic proteins occur at different depths of bilayer i.e. they are tightly bound to the phospholipid bilayer and are embedded in it. They span the entire thickness of the membrane. Therefore, they are known as transmembrane proteins. They form channels for passage of water.
b. The extrinsic or peripheral proteins are found on two surfaces of the membrane i.e. are loosely held to the phospholipid layer and can be easily removed.

Question 20.
Give the functions of plasma membrane.
Answer:
1. The significant function of plasma membrane is transport of molecules across it. Plasma membrane is selectively permeable.

2. Passive transport:
a. Many molecules move across the membrane without spending energy.
b. Some molecules move by simple diffusion along the concentration gradient i.e. from higher to lower concentration.
c. Neutral molecules may move across the membrane by the process of simple diffusion.
d. Water may also move by osmosis.

3. Active transport:
a. Few ions or molecules are transported against concentration gradient i.e. from lower to higher concentration.
b. This requires energy, hence ATP is utilized. As such a transport is an energy dependent process in which ATP is utilized, it is called Active transport e.g. Na⁺ /K⁺ pump.
c. Polar molecules cannot pass through non-polar lipid bilayer. Therefore, they require carrier proteins to facilitate their transport across the membrane.

Question 21.
Write a note on cytoplasm in Eukaryotic cell.
Answer:
Cytoplasm in Eukaryotic cell:

1. The cell contains ground substance called cytoplasmic matrix or cytosol.
2. This colloidal jelly like material shows streaming movements called cyclosis.
3. The cytoplasm contains water as major component along with organic and inorganic molecules like sugars, amino acids, vitamins, enzymes, nucleotides, minerals and waste products.
4. It also contains various membrane-bound cell organelles like endoplasmic reticulum, Golgi complex, mitochondria, plastids, nucleus, microbodies and cytoskeletal elements like microtubules.
5. Cytoplasm acts as a source of raw materials as well as seat for various metabolic activities taking place in the cell.
6. It helps in distribution and exchange of materials between various cell organelles.

Question 22.
Explain the endomembrane system of the cell.
Answer:

1. Cell organelles are compartments in the cell that carry out specific functions.
2. Some of these organelles coordinate with each other and complete the specific function of the cell.
3. Nuclear membrane, endoplasmic reticulum, Golgi complex, lysosomes and various types of vesicles and vacuoles form such a group and are together considered as endomembrane system of the cell.

Question 23.
Why mitochondria and chloroplasts are not considered as a part of endomembrane system?
Answer:
1. Organelles having distinct functions are not included in endomembrane system.
2. Mitochondria or chloroplast carry out specific type of energy conversions in the cell. Therefore, mitochondria and chloroplasts are not considered as a part of endomembrane system.

Question 24.
Describe the structure of Endoplasmic Reticulum.
Answer:

1. Endoplasmic reticulum is a network present within the cytosol.
2. It is present in all a cells except ova and mature red blood corpuscles.
3. Under the electron microscope, it appears like network of membranous tubules and sacs called cisternae.
4. This network of ER divides the cytoplasm in two parts viz. one within the lumen of ER called laminal cytoplasm and non-laminal cytoplasm that lies outside ER.
5. Membrane of ER is continuous with nuclear envelope at one end and extends till cell membrane. It thus acts as intracellular supporting framework and helps in maintaining position of various cell organelles in the cytoplasm.
6. Depending upon the presence or absence of ribosomes, endoplasmic reticulum is called rough endoplasmic reticulum (RER) or smooth endoplasmic reticulum (SER) respectively.

Question 25.
Label the diagram
Answer:

1. Endoplasmic reticulum is a network present within the cytosol.
2. It is present in all a cells except ova and mature red blood corpuscles.
3. Under the electron microscope, it appears like network of membranous tubules and sacs called cisternae.
4. This network of ER divides the cytoplasm in two parts viz. one within the lumen of ER called laminal cytoplasm and non-laminal cytoplasm that lies outside ER.
5. embrane of ER is continuous with nuclear envelope at one end and extends till cell membrane. It thus acts as intracellular supporting framework and helps in maintaining position of various cell organelles in the cytoplasm.
6. Depending upon the presence or absence of ribosomes, endoplasmic reticulum is called rough endoplasmic reticulum (RER) or smooth endoplasmic reticulum (SER) respectively.

Question 26.
Explain the structure, location and functions of Golgi complex.
Answer:
Golgi complex or Golgi apparatus or Golgi body act as a assembly, manufacturing cum packaging and transport unit of cell.
1. Structure of Golgi complex:
a. Golgi complex consists of stacks of membranous sacs called cistemae.
b. Diameter of cistemae varies from 0.5 to 1pm.
c. A Golgi complex may have few to several cistemae depending on its function.
d. The thickness and molecular composition of membranes at one end of the stack of a Golgi sac differ from those at the other end.
e. The Golgi sacs show specific orientation in the cell.
f. Each cistema has a forming or ‘cis’ face (cis: on the same side) and maturing or ‘trans’ face (trAnswer:the opposite side).
g. Transport vesicles that pinch off from transitional ER merge with cis face of Golgi cistema and add its contents into the lumen.

2. Location of Golgi complex:
Golgi bodies are usually located near endoplasmic reticulum.

3. Functions of Golgi complex:
a. Golgi body carries out two types of functions, modification of secretions of ER and production of its own secretions.
b. Cistemae contain specific enzymes for specific functions.
c. Refining (modification) of product takes place in a sequential manner.
d. For example, certain sugar component is added or removed from glycolipids and glycoproteins that are brought from ER, thus forming a variety of products.
e. Golgi bodies also manufacture their own products. Golgi bodies in many plant cells produce non-cellulose polysaccharides like pectin.
f. Manufactured or modified, all products of Golgi complex leave cistemae from trans face as transport vesicles.

Question 27.
How transport vesicles identify their target cell or cell membrane?
Answer:
While transport vesicles are leaving from the trans face of the Golgi, certain markers get impregnated on their membrane. These markers help them to identify their specific target cell or cell organelle.

Question 28.
Label the diagrams and write down the details of concept in your words.
Answer:
Golgi complex or Golgi apparatus or Golgi body act as a assembly, manufacturing cum packaging and transport unit of cell.
1. Structure of Golgi complex:
a. Golgi complex consists of stacks of membranous sacs called cistemae.
b. Diameter of cistemae varies from 0.5 to 1pm.
c. A Golgi complex may have few to several cistemae depending on its function.
d. The thickness and molecular composition of membranes at one end of the stack of a Golgi sac differ from those at the other end.
e. The Golgi sacs show specific orientation in the cell.
f. Each cistema has a forming or ‘cis’ face (cis: on the same side) and maturing or ‘trans’ face (trAnswer:the opposite side).
g. Transport vesicles that pinch off from transitional ER merge with cis face of Golgi cistema and add its contents into the lumen.

2. Location of Golgi complex:
Golgi bodies are usually located near endoplasmic reticulum.

3. Functions of Golgi complex:
a. Golgi body carries out two types of functions, modification of secretions of ER and production of its own secretions.
b. Cistemae contain specific enzymes for specific functions.
c. Refining (modification) of product takes place in a sequential manner.
d. For example, certain sugar component is added or removed from glycolipids and glycoproteins that are brought from ER, thus forming a variety of products.
e. Golgi bodies also manufacture their own products. Golgi bodies in many plant cells produce non-cellulose polysaccharides like pectin.
f. Manufactured or modified, all products of Golgi complex leave cistemae from trans face as transport vesicles.

Question 29.
Write a note on lysosomes and make a list of lysosomal enzymes.
Answer:
Lysosomes:

1. Lysosomes are considered as dismantling and restructuring units of a cell.
2. These are membrane bound vesicles containing hydrolytic enzymes. The enzymes in lysosomes are used by most eukaryotic cells to digest (hydrolyse) macromolecules.
3. The lysosomal enzymes show optimal activity in acidic pH.
4. Lysosomes arise from Golgi associated endoplasmic reticulum.
5. Lysosomes are polymorphic in nature and are classified as primary lysosomes, secondary or hybrid lysosomes, residual body and autophagic vesicle.
6. The list of lysosomal enzymes includes:
   All types of hydrolases viz, amylases, proteases and lipases.

Question 30.
“Lysosomes are polymorphic in nature.” Justify the statement.
Answer:

1. Lysosomes are classified as, Primary lysosomes; which are nothing but membrane bound vesicles in which enzymes are in inactive state.
2. Secondary lysosomes or hybrid lysosomes, which are formed by fusion of lysosome with endocytic vesicle containing materials to be digested, represented as heterophagic vesicle. This is larger in size than primary lysosome.
3. When organic molecules or membrane bound old cell organelle to be recycled fuses with primary lysosome, autophagic vesicles are formed.
4. Residual body is the vesicle containing undigested remains left over in the heterophagic vesicle after releasing the products of digestion in the cytosol. Hence, lysosomes are polymorphic in nature.

Question 31.
“Lysosomes are called suicide bags of the cells”. Why?
Answer:

1. Lysosomes which bring about digestion of cell’s own organic material like a damaged cell organelle are called autophagic vesicle (suicide bags).
2. An autophagic vesicle essentially consists of lysosome fused with membrane bound old cell organelle or organic molecules to be recycled.
3. Thus, lysosomes are capable of destructing all kinds of material in the cell. Therefore, can digest its own cell organelles due to presence of lysosome. Hence, lysosomes are also called as suicide bags.

Question 32.
Write a note on vacuoles.
Answer:
The organelle which helps in maintaining turgidity of the cell and a proper internal balance of cellular contents is known as vacuole.

1. The vacuoles are bound by semipermeable membrane, called tonoplast membrane. This membrane helps in maintaining the composition of vacuolar fluid (cell sap), different from that of the cytosol.
2. Composition of cell sap differs in different types of cells.
3. In vacuoles along with excretory products other compounds are stored that are harmful or unpalatable to herbivores, thereby protecting the plants.
4. Attractive colours of the petals are due to storage of such pigments in vacuoles.
5. Generally, there are two or three permanent vacuoles in a plant cell.
6. In some large plant cells, a single large vacuole occupies the central part of the cell. It is called central vacuole. In such cells, vacuole can occupy about 90% of the total volume of the cell.
7. The cell sap of central vacuole is a store house of various ions and thus is hypertonic to cytosol.
8. Small vacuoles in seeds of certain plants store organic materials like proteins.
9. In animal cells, they are few in number and smaller in size.
10. Intake of food or foreign particle by phagocytosis involves formation of food vacuole.

Question 33.
What is the function of contractile vacuole in Paramoecium?
Answer:
Contractile vacuole performs excretion and osmoregulation in fresh water unicellular forms like Paramoecium.

Question 34.
What are microbodies? Mention their types and functions.
Answer:
Microbodies are minute membrane bound sacs found in both plant and animal cells. Microbodies contain various types of enzymes based on which they are classified into following types:
1. Sphaerosomes:
a. These are found mainly in cells involved in synthesis and storage of fats. For e. g. endosperm of oil seeds.
b. The membrane of sphaerosome is half unit membrane i.e. this membrane has only one phospholipid layer.

2. Peroxisomes:
a. Peroxisomes contain enzymes that remove hydrogen atoms from substrate and produce toxic hydrogen peroxide by utilisation of oxygen.
b. At the same time peroxisome also contains enzymes that convert toxic H₂0₂ to water. Conversion of toxic substances like alcohol takes place in liver cells by peroxisomes.

Question 35.
Draw a neat and labelled diagram and explain the functions of glyoxysomes.
Answer:

Glyoxysomes are membrane bound organelles containing enzymes that convert fatty acids to sugar. They are observed in cells of germinating seeds where the cells utilize sugar (formed by conversion of stored fatty acids) till it starts photosynthesising on its own.

Question 36.
Describe the structure of mitochondria.
Answer:
Mitochondrion is known as the power house of the cell. It plays significant role in aerobic respiration. Mitochondria are absent in prokaryotic cells and red blood corpuscles (RBCs).

The structure of mitochondrion:

1. Shape of the mitochondria may be oval or spherical or like spiral strip.
2. It is a double membrane bound organelle.
3. Outer membrane is permeable to various metabolites due to presence of a protein-Porin or Parson’s particles.
4. Inner membrane is selectively permeable to few substances only.
5. Both membranes are separated by intermembrane space.
6. Inner membrane shows several finger like or plate like folds called as cristae which bears numerous particles oxysomes and cytochromes / electron carriers.
7. Inner membrane encloses a cavity called inner chamber, containing a fluid-matrix.
8. Matrix contains few coils of circular DNA, RNA, 70S types of ribosomes, lipids and various enzymes of Krebs’ cycle and other pathways.

Question 37.
Label the diagram and write down the details of concept in your words.

Answer:
Mitochondrion is known as the power house of the cell. It plays significant role in aerobic respiration. Mitochondria are absent in prokaryotic cells and red blood corpuscles (RBCs).

The structure of mitochondrion:

1. Shape of the mitochondria may be oval or spherical or like spiral strip.
2. It is a double membrane bound organelle.
3. Outer membrane is permeable to various metabolites due to presence of a protein-Porin or Parson’s particles.
4. Inner membrane is selectively permeable to few substances only.
5. Both membranes are separated by intermembrane space.
6. Inner membrane shows several finger like or plate like folds called as cristae which bears numerous particles oxysomes and cytochromes / electron carriers.
7. Inner membrane encloses a cavity called inner chamber, containing a fluid-matrix.
8. Matrix contains few coils of circular DNA, RNA, 70S types of ribosomes, lipids and various enzymes of Krebs’ cycle and other pathways.

Question 38.
Identify and label the following structure. Write a note on it.

Answer:
1. The given structure is of Oxysome/ F₁ Particle.
2. A: Head (F₁)
B: Pedicel
C: Foot (Base / F₀)
3. Structure of Oxysome:
a. Inner membrane of mitochondria bears numerous particles called as Oxysomes (F₁ – F_o / Fernandez – Moran Elementary particles / Mitochondrial particles).
b. Each particle consists of head, stalk (Pedicel) and base.
c. Head (F₁) / lollipop head faces towards matrix and foot (F0) is embedded in inner membrane.
d. Head acts as an enzyme ATP synthase and foot (base) as proton channel. Oxysomes are involved in proton pumping and ATP synthesis.

Question 39.
What are plastids?
Answer:
Plastids are double membraned organelles containing DNA, RNA and 70S ribosomes.

Question 40.
Draw a labelled diagram of the organelle which plays a significant role in synthesis of starch in plants. Write a note on its structure.
Answer:
Chloroplast plays a significant role in synthesis of starch in plants.
Structure of chloroplast:

1. In plants, chloroplast is found mainly in mesophyll of leaf.
2. Chloroplast is lens shaped but it can also be oval, spherical, discoid or ribbon like.
3. A cell may contain single large chloroplast as in Chlamydomonas or there can be 20 to 40 chloroplasts per cell as seen in mesophyll cells.
4. Chloroplasts contain green pigment called chlorophyll along with other enzymes that help in production of sugar by photosynthesis.
5. Inner membrane of double membraned chloroplast is comparatively less permeable.
6. Inside the cavity of inner membrane, there is another set of membranous sacs called thylakoids.
7. Thylakoids are arranged in the form of stacks called grana (singular: granum).
8. The grana are connected to each other by means of membranous tubules called stroma lamellae.
9. Space outside thylakoids is filled with stroma.
10. The stroma and the space inside thylakoids contain various enzymes essential for photosynthesis.
11. Stroma of chloroplast contains DNA and ribosomes (70S).

Question 41.
Insulin is the protein hormone synthesized by pancreatic cells. Name the component that performs the role of protein factory and draw their labelled structure as seen in prokaryotes and eukaryotes.
Answer:
Ribosomes are the protein factories that synthesize proteins using genetic information.

Question 42.
Give the detailed information on ribosomes found in eukaryotic cell.
Answer:

1. Ribosomes are protein factories of cell and were first observed as dense particles in electron micrograph of a cell by scientist Palade in 1953.
2. Ribosomes lack membranous covering around them and are made up of Ribosomal RNA and proteins.
3. In a eukaryotic cell, ribosomes are present in mitochondria, plastids (in plant cells) and in cytosol.
4. Ribosomes are either found attached to outer surface of Rough Endoplasmic Reticulum and nuclear membrane or freely suspended in cytoplasm.
5. Both are of 80S type. Each ribosome is made up of two subunits- a large (60S) and a small (40S) subunit.
6. Bound ribosomes generally produce proteins that are transported outside the cell after processing in ER and Golgi body. e.g. Bound ribosomes of acinar cells of pancreas produce pancreatic digestive enzymes.
7. Free ribosomes come together and form chains called polyribosomes for protein synthesis.
8. Free ribosomes generally produce enzymatic proteins that are used up in cytoplasm, like enzymes required for breakdown of sugar.
9. Both types of ribosomes (bound and free) can interchange position and function.
10. Number of ribosomes is high in cells actively engaged in protein synthesis.

Question 43.
What is Svedberg unit?
Answer:
The particle size of ribosomes is measured in terms of Svedberg unit (S). It is a measure of sedimentation rate of a particle in ultracentrifuge. It is thus a measure of density and size of a particle. 1S = 10^-13 sec.

Question 44.
Describe the structure of nucleus.
Answer:
Nucleus is known as the master cell organelle as it regulates various metabolic activities through synthesis of various proteins and enzymes.
The nucleus in eukaryotic cell is made up of nuclear envelope, nucleoplasm, nucleolus and chromatin network.
1. Nuclear envelope:
a. Nuclear envelope is a double layered delimiting membrane of nucleus.
b. Two membranes are separated from each other by perinuclear space (10 to 50nm).
c. Outer membrane is connected with endoplasmic reticulum at places and harbours ribosomes on it.
d. The inner membrane is lined by nuclear lamina- a network of protein fibres that helps in maintaining shape of the nucleus.
e. The two membranes along with perinuclear space help in separating nucleoplasm from cytoplasm. However, nuclear membrane is not continuous.
f. There are small openings called nucleopores on the nuclear membrane.
g. The nucleopores are guarded by pore complexes which regulate flow of substances from nucleus to cytoplasm and in reverse direction.

2. Nucleoplasm or karyolymph:
a. The nucleoplasm or karyolymph contains various substances like nucleic acids, protein molecules, minerals and salts.
b. It contains chromatin network and nucleolus.

3. Nucleolus:
a. Nucleolus is made up of rRNA and ribosomal proteins and it is known as the site of ribosome biogenesis.
b. The rRNA and ribosomal proteins are transported to cytoplasm and are assembled together to form ribosomes.
c. Depending on synthetic activity of a cell, there are one or more nucleoli present in the nucleoplasm. For e.g. cells of oocyte contain large nucleolus whereas sperm cells contain small inconspicuous one.
d. Nucleolus appear as dense spherical body present near chromatin network.

Question 45.
Write the functions of the controlling unit of the cell.
Answer:
Nucleus is known as the controlling unit of the cell.
Functions of the nucleus:
1. The nucleus contains entire genetic information; hence play important role in heredity and variation.
2. It is the site for synthesis of DNA, RNA and ribosomes.
3. It plays important role in protein synthesis.

Question 46.
Write a note on chromatin material.
Answer:

1. Nucleus contains genetic information in the form of chromosomes which are DNA molecules associated with proteins.
2. In a non-dividing cell, the chromosomes appear as thread like network and cannot be identified individually. This network is called chromatin material.
3. The chromatin material contains DNA, histone and non-histone proteins and RNA.
4. In some regions of chromatin, DNA is more and is genetically active called euchromatin.
5. Some regions that contain more of proteins and less DNA and are genetically inert, are called
   heterochromatin.

[Note: Heterochromatin is a region in chromatin that is highly compacted during interphase and is generally not accessible for transcription of genes.]

Question 47.
What is the significance of having constant chromosome number in a species?
Answer:
Constant chromosome number in a species is important in phylogenetic studies.

Question 48.
Explain the cytoskeletal system of a cell.
Answer:

1. The cytoskeleton is a supportive structure built from microtubules, intermediate filaments, and
   microfilaments.
2. Microtubules are made up of protein- tubulin.
3. Microfilaments are made up of actin.
4. Intermediate filaments are composed of fibrous proteins.

Question 49.
Compete the following concept map representing the functions of cytoskeleton.
Answer:

Question 50.
Explain in detail the structures of components that help in locomotion of unicellular organisms.
Answer:

1. Cilium or flagellum helps in locomotion of unicellular organisms.
2. They consist of basal body, basal plate and shaft.
3. Basal body is placed in outer part of cytoplasm. It is derived from centriole. It has nine peripheral triplets of fibrils.
4. Shaft is exposed part of cilia or flagella. It consists of two parts- sheath and axoneme.
5. Sheath is covering membrane of cilium or flagellum.
6. Core called axoneme possesses 11 fibrils (microtubules) running parallel to long axis.
7. It shows 9 peripheral doublet microtubules and two single central microtubules (9+2).
8. The central tubules are enclosed by central sheath.
9. This sheath is connected to one of the tubules of peripheral doublets by a radial spoke.
10. Central tubules are connected to each other by bridges.
11. The peripheral doublet microtubules are connected to each other through linkers or inter-doublet bridge.

Question 51.
Draw a labelled diagram of the structure of cilia.
Answer:
Cilia act as oars causing movement of cell.

Question 52.
Spindle apparatus is formed during cell division. Write the information on the components of cell which help in formation of this.
Answer:

1. Centrioles and centrosomes play significant role in formation of spindle apparatus during cell division.
2. Centrosome is usually found near the nucleus of an animal cell.
3. It contains a pair of cylindrical structures called centrioles.
4. The cylinder (centriole) are perpendicular to each other and are surrounded by amorphous substance called pericentriolar material.
5. Each cylinder of centriole is made up of nine sets of triplet microtubules made up of tubulin.
6. Evenly spaced triplets are connected to each other by means of non-tubulin proteins.
7. At the proximal end of centriole, there is a set of tubules called hub.
8. The peripheral triplets are connected to hub by means of radial spokes. Due to this proximal end of centriole looks like a cartwheel.
9. Centriole forms basal body of cilia and flagella.

Question 53.
Draw a labelled diagram of the structure of centriole.
Answer:

Question 54.
Match the column I with column II.

Column I	Column II
1. Mitochondria	(a) Synthesis of protein
2. Nucleus	(b) Photosynthesis
3. Chloroplast	(c) Respiration
4. Ribosomes	(d) Nucleoplasm

Answer:

Column I	Column II
1. Mitochondria	(c) Respiration
2. Nucleus	(d) Nucleoplasm
3. Chloroplast	(b) Photosynthesis
4. Ribosomes	(a) Synthesis of protein

Question 55.
Distinguish between Plant cell and Animal cell.
Answer:

Plant cell	Animal cell
(a) Cell wall is present.	Cell wall is absent.
(b) Plastids present.	Plastids absent.
(c) Chloroplast present.	Chloroplast absent.
(d) Centrioles are present only in lower plant forms.	Centrioles are present in all animal cells.
(e) Lysosomes absent.	Lysosomes present in all animal cells.
(f) Two or three large and permanent vacuoles.	Small and temporary vacuoles are present.
(g) Carbohydrates stored as starch.	Carbohydrates stored as glycogen.

Question 56.
Label the A, B, C, and D in above diagram and write the functions of organelles A and B.
Answer:
1. A: Mitochondria B: Endoplasmic Reticulum
C: Golgi complex D: Amyloplast
2. Functions of Mitochondria: Mitochondrion is known as the power house of the cell. It plays significant role in aerobic respiration. Mitochondria are absent in prokaryotic cells and red blood corpuscles (RBCs).
3. Functions of Endoplasmic Reticulum: Refer Q.33.

Question 57.
Draw a labelled diagram of an animal cell.
Answer:

Question 58.
Classify the following organelles / cellular components on the basis of presence or absence in prokaryotic and eukaryotic cells.
(Ribosomes, Nucleus, Plasma membrane, Mitochondria, mRNA, Endoplasmic Reticulum, Golgi complex, Centrioles, Nucleoid)
Answer:

Prokaryotic cell	Ribosomes, Plasma membrane, mRNA, Nucleoid
Eukaryotic cell	Ribosomes, Plasma membrane, mRNA, Nucleus, Mitochondria, Endoplasmic Reticulum, Golgi complex, Centrioles

Question 59.
Apply Your Knowledge

Question 1.
After learning organization of cell, to test one of the postulates of cell theory, Ananya requested her teacher to guide and allow her to perform a small experiment. The aim of the experiment Avas to form new cells in the laboratory using isolated cellular organelles from other cells. Though Ananya did not succeed to form new cells, teacher-guided and motivated her explaining why experiment performed by them failed.
1. Which postulate Ananya was willing to test and why new cells failed to form from the isolated organelles from other cells?
2. From the above mentioned data could you guess which type of cells they were trying to form whether eukaryote or prokaryote?
Answer:
1. The postulate Ananya was willing to test was, ‘all cells arise from pre-existing cells’. According to this postulate, to form new cells, pre-existing cells are must; therefore, cellular organelles did not form new cells.
2. The cells which Ananya and her teacher were trying to form were eukaryotic cells, as cellular organelles are present in eukaryotes.

Question 2.
A mix bacterial culture was given to different teams of students and was asked to write their observation regarding the shapes of bacterial cells they observed under microscope. Students discussed the characteristics among their respective teams and mentioned major types of shapes they observed.
1. Which types of bacterial shapes were observed by the students?
2. Mention why they were named in a specific manner with respect to their shapes?
Answer:
1. The bacterial shapes observed by the students are cocci, bacilli, vibrios, spirilla.
2. Under microscope, cocci appear spherical shape, bacilli appear rod shape, vibrios appear comma shape and spirilla appear twisted, therefore they are named accordingly.

Question 60.
Quick Review:

Question 61.
Exercise

Question 1.
Define cell.
Answer:
The first microscope was made by two Dutch spectacle makers Hans and Zacharias Janssen.
[Note: The Dutch scientist Anton van Leeuwenhoek made microscopes capable of magnifying single-celled organisms in a drop of pond water.]

Question 2.
Write a note on microscope.
Answer:
Cell is defined as a structural and functional unit of life of all living organisms capable of independent existence and can perform all functions of life.

Question 3.
Write a short note on totipotency.
Answer:

1. Totipotency (totus – entire, potential – power) is the capacity or the potential of living nucleated cell, to differentiate into any other type of cell and thus, can form a complete new organism.
2. A cell is totipotent as it has the entire genetic information of the organism stored in its nucleus.
3. Embryonic animal cells are totipotent and are termed as stem cells.
4. Stem cells are used in curing many diseases. Therefore, they have great potential for medical applications.

Question 4.
What are the characteristics of cells in which genetic material is known as nucleoid?
Answer:
General characteristics of prokaryotic cell:
1. Prokaryotic cells are primitive type of cells.
2. It does not have membrane bound cell organelles (like endoplasmic reticulum, Golgi complex, mitochondria, etc.) and well-defined nucleus (nuclear membrane is absent).
3. Genetic material is in the form of nucleoid.

4. Cell envelope:
a. Prokaryotic cell has chemically complex protective cell envelope having glycocalyx, cell wall and plasma membrane.
b. In some bacteria, glycocalyx occurs in the form of a slime layer (loose sheath). Other bacteria may have a thick and tough covering called capsule. It helps in protection of bacterial cell.

5. Cell wall:
The Gram-positive bacteria show presence of peptidoglycan layer in the cell wall and Gram-negative bacteria show presence of murein in the cell wall. It gives mechanical strength to the cell.
[Note: In Gram-negative bacteria, cell wall is made up of two layers; inner layer of Murein or peptidoglycan and outer layer of Lipopolysaccharides.]

6. Cell membrane:
a. It is the innermost covering of the cell envelope, chemically composed of lipids and proteins.
b. It helps in intercellular communication.
c. Cell membrane shows infoldings called mesosomes which help in cell wall formation, cellular respiration and DNA replication.
d. The cyanobacteria show longer extensions called as chromatophores which carry photosynthetic pigments.

7. In motile bacteria either cilia or flagella are found. Both are driven by rotatory movement produced by basal body (which works as motor) of flagellum. Other parts of flagellum are filament and hook.

8. Some other surface projections are the tubular pili (which help in inter-cellular communication) and fimbriae (for clinging to support).

9. Ribosomes:
Bacterial cell cytoplasm contains dense particles called ribosomes which help in protein synthesis. Ribosomes are 70S type (composed of a larger sub-unit 50S and + smaller sub-unit 30S).

Question 5.
Which technique is used to differentiate between Gram positive and Gram negative bacteria?
Answer:
The Gram-positive bacteria show presence of peptidoglycan layer in the cell wall and Gram-negative bacteria show presence of murein in the cell wall. The technique used for differentiating bacterial cells is Gram staining.
[Note: Murein is similar to peptidoglycan in structure and function. It is present in the cell walls of archaebacteria.

Question 6.
What are mesosomes?
Answer:
Cytoplasm does not show streaming movement. Cytoplasm shows streaming movement.

Question 7.
What are the functions of pili and fimbriae?
Answer:
Respiratory enzymes are present on the infoldings of the plasma membrane called mesosomes. Respiratory enzymes are present within mitochondria.
e-g- Cyanobacteria (Blue green algae) and bacteria. Algae, fungi, plants and animals.

Question 8.
Enlist the organelles present in eukaryotic cells.
Answer:
It also contains various membrane bound cell organelles like endoplasmic reticulum, Golgi complex, mitochondria, plastids, nucleus, microbodies and cytoskeletal elements like microtubules.

Question 9.
Who proposed the fluid-mosaic model?
Answer:
Fluid mosaic model was proposed by Singer and Nicholson (1972).

Question 10.
What are nuclear membrane?
Answer:
Nucleus is known as the master cell organelle as it regulates various metabolic activities through synthesis of various proteins and enzymes.
The nucleus in eukaryotic cell is made up of nuclear envelope, nucleoplasm, nucleolus and chromatin network.
1. Nuclear envelope:
a. Nuclear envelope is a double layered delimiting membrane of nucleus.
b. Two membranes are separated from each other by perinuclear space (10 to 50nm).
c. Outer membrane is connected with endoplasmic reticulum at places and harbours ribosomes on it.
d. The inner membrane is lined by nuclear lamina- a network of protein fibres that helps in maintaining shape of the nucleus.
e. The two membranes along with perinuclear space help in separating nucleoplasm from cytoplasm. However, nuclear membrane is not continuous.
f. There are small openings called nucleopores on the nuclear membrane.
g. The nucleopores are guarded by pore complexes which regulate flow of substances from nucleus to cytoplasm and in reverse direction.

Question 11.
Name two types of chromatin.
Answer:
1. In some regions of chromatin, DNA is more and is genetically active called euchromatin.
2. Some regions that contain more of proteins and less DNA and are genetically inert, are called heterochromatin.

Question 12.
What are lysosomes commonly known as?
Answer:
1. Lysosomes which bring about digestion of cell’s own organic material like a damaged cell organelle are called autophagic vesicle (suicide bags).
2. An autophagic vesicle essentially consists of lysosome fused with membrane bound old cell organelle or organic molecules to be recycled.
3. Thus, lysosomes are capable of destructing all kinds of material in the cell. Therefore, can digest its own cell organelles due to presence of lysosome. Hence, lysosomes are also called as suicide bags.

Question 13.
What are ribosomes?
Answer:
Ribosomes are the protein factories that synthesize proteins using genetic information.

Question 14.
What are glyoxysomes? Where do they occur?
Answer:
Glyoxysomes are membrane bound organelles containing enzymes that convert fatty acids to sugar. They are observed in cells of germinating seeds where the cells utilize sugar (formed by conversion of stored fatty acids) till it starts photosynthesising on its own.

Question 15.
Sketch and label the fluid mosaic model of cell membrane.
Answer:
Fluid mosaic model:

1. Fluid mosaic model was proposed by Singer and Nicholson (1972).
2. This model states that plasma membrane is made up of phospholipid bilayer and proteins.
3. Proteins are embedded in the lipid membrane like icebergs in the sea of lipids.
4. Phospholipid bilayer is fluid in nature.
5. Quasi-fluid nature of lipid enables lateral movement of proteins. This ability to move within the membrane is measured as fluidity.
6. Based on organization of membrane proteins they are of two types, as:

a. The intrinsic proteins occur at different depths of bilayer i.e. they are tightly bound to the phospholipid bilayer and are embedded in it. They span the entire thickness of the membrane. Therefore, they are known as transmembrane proteins. They form channels for passage of water.
b. The extrinsic or peripheral proteins are found on two surfaces of the membrane i.e. are loosely held to the phospholipid layer and can be easily removed.

Question 16.
State the functions of Endoplasmic reticulum.
Answer:
Smooth endoplasmic reticulum (SER):
1. Depending on cell type, it helps in synthesis of lipids for e.g. Steroid secreting cells of cortical region of adrenal gland, testes and ovaries.
2. Smooth endoplasmic reticulum plays a role in detoxification in the liver and storage of calcium ions (muscle cells).

Rough Endoplasmic Reticulum (RER):

1. Rough ER is primarily involved in protein synthesis. For e.g. Pancreatic cells synthesize the protein insulin in the ER.
2. These proteins are secreted by ribosomes attached to rough ER and are called secretory proteins. These proteins get wrapped in membrane that buds off from transitional region of ER. Such membrane bound proteins depart from ER as transport vesicles.
3. Rough ER is also involved in formation of membrane for the cell. The ER membrane grows in place by addition of membrane proteins and phospholipids to its own membrane. Portions of this expanded membrane are transferred to other components of endomembrane system.

Question 17.
Write short note on lysosomes.
Answer:
Lysosomes:

1. Lysosomes are considered as dismantling and restructuring units of a cell.
2. These are membrane bound vesicles containing hydrolytic enzymes. The enzymes in lysosomes are used by most eukaryotic cells to digest (hydrolyse) macromolecules.
3. The lysosomal enzymes show optimal activity in acidic pH.
4. Lysosomes arise from Golgi associated endoplasmic reticulum.
5. Lysosomes are polymorphic in nature and are classified as primary lysosomes, secondary or hybrid lysosomes, residual body and autophagic vesicle.
6. The list of lysosomal enzymes includes:
   All types of hydrolases viz, amylases, proteases and lipases.

Question 18.
Lysosomes are known as suicide bags of the cell. Give reason.
Answer:

1. Lysosomes which bring about digestion of cell’s own organic material like a damaged cell organelle are called autophagic vesicle (suicide bags).
2. An autophagic vesicle essentially consists of lysosome fused with membrane-bound old cell organelle or organic molecules to be recycled.
3. Thus, lysosomes are capable of destructing all kinds of material in the cell. Therefore, can digest its own cell organelles due to presence of lysosome. Hence, lysosomes are also called as suicide bags.

Question 19.
Describe the structure of plant cell wall.
Answer:
In plants, cell wall shows middle lamella, primary wall and secondary wall

1. Middle lamella:
   It is thin and present between two adjacent r cells. It is the first structure formed from cell plate during cytokinesis. It is mainly made up of pectin, calcium and magnesium pectate. Softening of ripe fruit is due to solubilization of pectin.
2. Primary wall:
   In young plant cell, it is capable of growth. It is laid inside to middle lamella.
   It is the only wall seen in meristematic tissue, mesophyll, pith, etc.
3. Secondary wall:
   It is present inner to primary wall. Once the growth of primary wall stops, secondary wall is laid. At some places thickening is absent which leads to formation of pits.

Question 20.
Describe the cell wall of eukaryotic cells and state their function.
Answer:

1. The rigid, protective and supportive covering, outside the cell membrane is called cell wall. It is present in plant cells, fungi and some protists.
2. Algae show presence of cellulose, galactans, mannans and minerals like calcium carbonate in cell wall.
3. In other plants, it is made up of hemicelluloses, pectin, lipids and protein.
4. Microfibrils of plant cell wall show presence of cellulose which is responsible for rigidity.
5. Some of the depositions of cell wall are silica (grass stem), cutin (epidermal walls of land plants), suberin (endodermal cells of root), wax, lignin.
6. Function:
   1. Provides support, rigidity and shape to the cell.
   2. Protects the protoplasm against mechanical injury and infections.

Question 21.
1. Draw neat and labelled diagram of ultrastructure of mitochondria,
2. Explain the structure of mitochondria.
Answer:
Mitochondrion is known as the power house of the cell. It plays significant role in aerobic respiration. Mitochondria are absent in prokaryotic cells and red blood corpuscles (RBCs).

The structure of mitochondrion:

1. Shape of the mitochondria may be oval or spherical or like spiral strip.
2. It is a double membrane bound organelle.
3. Outer membrane is permeable to various metabolites due to presence of a protein-Porin or Parson’s particles.
4. Inner membrane is selectively permeable to few substances only.
5. Both membranes are separated by intermembrane space.
6. Inner membrane shows several finger like or plate like folds called as cristae which bears numerous particles oxysomes and cytochromes / electron carriers.
7. Inner membrane encloses a cavity called inner chamber, containing a fluid-matrix.
8. Matrix contains few coils of circular DNA, RNA, 70S types of ribosomes, lipids and various enzymes of Krebs’ cycle and other pathways.

Question 22.
1. Draw neat and labelled diagram of structure of plasma membrane proposed by Singer and Nicholson,
2. Write any two functions of plasma membrane.
Answer:
1. Fluid mosaic model:

1. Fluid mosaic model was proposed by Singer and Nicholson (1972).
2. This model states that plasma membrane is made up of phospholipid bilayer and proteins.
3. Proteins are embedded in the lipid membrane like icebergs in the sea of lipids.
4. Phospholipid bilayer is fluid in nature.
5. Quasi-fluid nature of lipid enables lateral movement of proteins. This ability to move within the membrane is measured as fluidity.
vi. Based on organization of membrane proteins they are of two types, as:
a. The intrinsic proteins occur at different depths of bilayer i.e. they are tightly bound to the phospholipid bilayer and are embedded in it. They span the entire thickness of the membrane. Therefore, they are known as transmembrane proteins. They form channels for passage of water.
b. The extrinsic or peripheral proteins are found on two surfaces of the membrane i.e. are loosely held to the phospholipid layer and can be easily removed.

(ii)

1. The significant function of plasma membrane is transport of molecules across it. Plasma membrane is selectively permeable.

2. Passive transport:
a. Many molecules move across the membrane without spending energy.
b. Some molecules move by simple diffusion along the concentration gradient i.e. from higher to lower concentration.
c. Neutral molecules may move across the membrane by the process of simple diffusion.
d. Water may also move by osmosis.

3. Active transport:
a. Few ions or molecules are transported against concentration gradient i.e. from lower to higher concentration.
b. This requires energy, hence ATP is utilized. As such a transport is an energy dependent process in which ATP is utilized, it is called Active transport e.g. Na⁺ /K⁺ pump.
c. Polar molecules cannot pass through non-polar lipid bilayer. Therefore, they require carrier proteins to facilitate their transport across the membrane.

Question 23.
1. Draw neat and labelled diagram of nucleus,
2. Write a short note on nuclear envelope.
Answer:
Nucleus is known as the master cell organelle as it regulates various metabolic activities through synthesis of various proteins and enzymes.
The nucleus in eukaryotic cell is made up of nuclear envelope, nucleoplasm, nucleolus and chromatin network.
1. Nuclear envelope:
a. Nuclear envelope is a double layered delimiting membrane of nucleus.
b. Two membranes are separated from each other by perinuclear space (10 to 50nm).
c. Outer membrane is connected with endoplasmic reticulum at places and harbours ribosomes on it.
d. The inner membrane is lined by nuclear lamina- a network of protein fibres that helps in maintaining shape of the nucleus.
e. The two membranes along with perinuclear space help in separating nucleoplasm from cytoplasm. However, nuclear membrane is not continuous.
f. There are small openings called nucleopores on the nuclear membrane.
g. The nucleopores are guarded by pore complexes which regulate flow of substances from nucleus to cytoplasm and in reverse direction.

2. Nucleoplasm or karyolymph:
a. The nucleoplasm or karyolymph contains various substances like nucleic acids, protein molecules, minerals and salts.
b. It contains chromatin network and nucleolus.

3. Nucleolus:
a. Nucleolus is made up of rRNA and ribosomal proteins and it is known as the site of ribosome biogenesis.
b. The rRNA and ribosomal proteins are transported to cytoplasm and are assembled together to form ribosomes.
c. Depending on synthetic activity of a cell, there are one or more nucleoli present in the nucleoplasm. For e.g. cells of oocyte contain large nucleolus whereas sperm cells contain small inconspicuous one.
d. Nucleolus appear as dense spherical body present near chromatin network.

Question 24.
Which components of a cell help in formation of spindle apparatus formed during cell division?
Answer:
Centrioles and centrosomes play significant role in formation of spindle apparatus during cell division.

Question 25.
Write a note on control unit of a cell.
Answer:
a. Nucleus contains the genetic material of an organism.
b. This genetic material is present in the form of Deoxyribonucleic Acid (DNA) which is responsible for synthesis of various proteins and enzymes.
c. These proteins and enzymes in turn regulate metabolic activities of the cells.
Therefore, nucleus is considered as control unit of a cell.

Question 26.
What are the various types of plastids? ii. Describe the chemical composition and functions of eukaryotic cell wall.
Answer:
(i)

1. Plastids are classified according to the pigments present in it. Three main types of plastids are – leucoplasts, chromoplasts and chloroplasts.
2. Leucoplasts do not contain any photosynthetic pigments they are of various shapes and sizes. These are meant for storage of nutrients:
a. Amyloplasts store starch. b. Elaioplasts store oils. c. Aleuroplasts store proteins.
3. Chromoplasts contain pigments like carotene and xanthophyll etc.
a. They impart yellow, orange or red colour to flowers and fruits.
b. These plastids are found in the coloured parts of flowers and fruits.
iv. Chloroplasts are plastids containing green pigment chlorophyll along with other enzymes that help in production of sugar by photosynthesis. They are present in plants, algae and few protists like Euglena.

(ii)

1. The rigid, protective and supportive covering, outside the cell membrane is called cell wall. It is present in plant cells, fungi and some protists.
2. Algae show presence of cellulose, galactans, mannans and minerals like calcium carbonate in cell wall.
3. In other plants, it is made up of hemicelluloses, pectin, lipids and protein.
4. Microfibrils of plant cell wall show presence of cellulose which is responsible for rigidity.
5. Some of the depositions of cell wall are silica (grass stem), cutin (epidermal walls of land plants), suberin (endodermal cells of root), wax, lignin.
6. Function:
   Provides support, rigidity and shape to the cell.
   Protects the protoplasm against mechanical injury and infections.

Question 27.
1. Explain the structure of ribosomes in detail.
2. What are sphaerosomes?
3. What is totipotency?
Answer:
(i) Ribosomes are the protein factories that synthesize proteins using genetic information.

1. Ribosomes are protein factories of cell and were first observed as dense particles in electron micrograph of a cell by scientist Palade in 1953.
2. Ribosomes lack membranous covering around them and are made up of Ribosomal RNA and proteins.
3. In a eukaryotic cell, ribosomes are present in mitochondria, plastids (in plant cells) and in cytosol.
4. Ribosomes are either found attached to outer surface of Rough Endoplasmic Reticulum and nuclear membrane or freely suspended in cytoplasm.
5. Both are of 80S type. Each ribosome is made up of two subunits- a large (60S) and a small (40S) subunit.
6. Bound ribosomes generally produce proteins that are transported outside the cell after processing in ER and Golgi body. e.g. Bound ribosomes of acinar cells of pancreas produce pancreatic digestive enzymes.
7. Free ribosomes come together and form chains called polyribosomes for protein synthesis.
8. Free ribosomes generally produce enzymatic proteins that are used up in cytoplasm, like enzymes required for breakdown of sugar.
9. Both types of ribosomes (bound and free) can interchange position and function.
10. Number of ribosomes is high in cells actively engaged in protein synthesis.

(ii) Sphaerosomes:
a. These are found mainly in cells involved in synthesis and storage of fats. For e. g. endosperm of oil seeds.
b. The membrane of sphaerosome is half unit membrane i.e. this membrane has only one phospholipid layer.

(iii) 1. Totipotency (totus – entire, potential – power) is the capacity or the potential of living nucleated cell, to differentiate into any other type of cell and thus, can form a complete new organism.
2. A cell is totipotent as it has the entire genetic information of the organism stored in its nucleus.
3. Embryonic animal cells are totipotent and are termed as stem cells.
4. Stem cells are used in curing many diseases. Therefore, they have great potential for medical applications.

Question 28.
1. Give any two functions of each of the following:
a. Golgi complex
b. Lysosomes
2. What are the major differences between eukaryotic and prokaryotic cells? Write any two points.
3. Explain the structure of cilia and flagella.
Answer:
1. a. Functions of Golgi complex:
a. Golgi body carries out two types of functions, modification of secretions of ER and production of its own secretions.
b. Cistemae contain specific enzymes for specific functions.
c. Refining (modification) of product takes place in a sequential manner.
d. For example, certain sugar component is added or removed from glycolipids and glycoproteins that are brought from ER, thus forming a variety of products.
e. Golgi bodies also manufacture their own products. Golgi bodies in many plant cells produce non-cellulose polysaccharides like pectin.
f. Manufactured or modified, all products of Golgi complex leave cistemae from trans face as transport vesicles.
b. i. Lysosomes which bring about digestion of cell’s own organic material like a damaged cell organelle are called autophagic vesicle (suicide bags).
2. An autophagic vesicle essentially consists of lysosome fused with membrane bound old cell organelle or organic molecules to be recycled.
3. Thus, lysosomes are capable of destructing all kinds of material in the cell. Therefore, can digest its own cell organelles due to presence of lysosome. Hence, lysosomes are also called as suicide bags.

(ii)

1. Cilium or flagellum helps in locomotion of unicellular organisms.
2. They consist of basal body, basal plate and shaft.
3. Basal body is placed in outer part of cytoplasm. It is derived from centriole. It has nine peripheral triplets of fibrils.
4. Shaft is exposed part of cilia or flagella. It consists of two parts- sheath and axoneme.
5. Sheath is covering membrane of cilium or flagellum.
6. Core called axoneme possesses 11 fibrils (microtubules) running parallel to long axis.
7. It shows 9 peripheral doublet microtubules and two single central microtubules (9+2).
8. The central tubules are enclosed by central sheath.
9. This sheath is connected to one of the tubules of peripheral doublets by a radial spoke.
10. Central tubules are connected to each other by bridges.
11. The peripheral doublet microtubules are connected to each other through linkers or inter-doublet bridge.
    Cilia act as oars causing movement of cell.

Question 29.
Write a note on glycoprotein molecules found on membranes of RBC.
Answer:
Glycoproteins are protein molecules modified within the Golgi complex by having a short sugar chain (polysaccharide) attached to them.
The polysaccharide part of glycoproteins located on the surfaces of red blood cells acts as the antigen responsible for determining the blood group of an individual.
Different polysaccharide part of glycoproteins act as different type of antigens that determine the blood groups.
Four types of blood groups A, B, AB, and O are recognized on the basis of presence or absence of these antigens.

Question 30.
Describe in detail the structure of nucleus.
Answer:
Nucleus is known as the master cell organelle as it regulates various metabolic activities through synthesis of various proteins and enzymes.
The nucleus in eukaryotic cell is made up of nuclear envelope, nucleoplasm, nucleolus and chromatin network.
1. Nuclear envelope:
a. Nuclear envelope is a double layered delimiting membrane of nucleus.
b. Two membranes are separated from each other by perinuclear space (10 to 50nm).
c. Outer membrane is connected with endoplasmic reticulum at places and harbours ribosomes on it.
d. The inner membrane is lined by nuclear lamina- a network of protein fibres that helps in maintaining shape of the nucleus.
e. The two membranes along with perinuclear space help in separating nucleoplasm from cytoplasm. However, nuclear membrane is not continuous.
f. There are small openings called nucleopores on the nuclear membrane.
g. The nucleopores are guarded by pore complexes which regulate flow of substances from nucleus to cytoplasm and in reverse direction.

2. Nucleoplasm or karyolymph:
a. The nucleoplasm or karyolymph contains various substances like nucleic acids, protein molecules, minerals and salts.
b. It contains chromatin network and nucleolus.

3. Nucleolus:
a. Nucleolus is made up of rRNA and ribosomal proteins and it is known as the site of ribosome biogenesis.
b. The rRNA and ribosomal proteins are transported to cytoplasm and are assembled together to form ribosomes.
c. Depending on synthetic activity of a cell, there are one or more nucleoli present in the nucleoplasm. For e.g. cells of oocyte contain large nucleolus whereas sperm cells contain small inconspicuous one.
d. Nucleolus appear as dense spherical body present near chromatin network.

Question 31.
Observe the diagram given below and answer the questions based on it.
1. Identify the structure labelled as ‘A’.
2. Mention the two types of the given cell organelle.
3. Which type of ribosomes would be seen on the membrane of the given structure.
Answer:
1. Smooth endoplasmic reticulum (SER):

1. Depending on cell type, it helps in synthesis of lipids for e.g. Steroid secreting cells of cortical region of adrenal gland, testes and ovaries.
2. Smooth endoplasmic reticulum plays a role in detoxification in the liver and storage of calcium ions (muscle cells).

Rough Endoplasmic Reticulum (RER):
1. Rough ER is primarily involved in protein synthesis. For e.g. Pancreatic cells synthesize the protein insulin in the ER.
2. These proteins are secreted by ribosomes attached to rough ER and are called secretory proteins. These proteins get wrapped in membrane that buds off from transitional region of ER. Such membrane bound proteins depart from ER as transport vesicles.
3. Rough ER is also involved in formation of membrane for the cell. The ER membrane grows in place by addition of membrane proteins and phospholipids to its own membrane. Portions of this expanded membrane are transferred to other components of endomembrane system.

3. Both are of 80S type. Each ribosome is made up of two subunits- a large (60S) and a small (40S) subunit.

Multiple Choice Questions:

Question 1.
Which of the following is the smallest cell?
(A) Red Blood Cell
(B) Plant cell
(C) Mycoplasma
(D) Euglena
Answer:
(C) Mycoplasma

Question 2.
From the following identify the CORRECT range of size of the bacteria.
(A) 0.3 pm to 1 mm
(B) 1 pm to 1mm
(C) 1 nm to 1 pm
(D) 3 pm to 5 pm
[Note: Prokaryotic cells generally range between 1 to 10 pm in size.]
Answer:
(D) 3 pm to 5 pm

Question 3.
Identify the CORRECT statements.
1. Nerve cells are the longest cells.
2. The concept ‘Omnis cellula-e-cellulla’ was explained by Rudolf Virchow.
3. The cell theory was proposed by Nicolson and Singer.
(A) Statements i and ii are correct.
(B) Statements ii and iii are correct.
(C) Statements i and iii are correct.
(D) Statements i, ii and iii are correct.
Answer:
(A) Statements i and ii are correct.

Question 4.
New cells generate from
(A) bacterial fermentation
(B) regeneration of old cells
(C) pre-existing cells
(D) abiotic materials
Answer:
(C) pre-existing cells

Question 5.
Mesosonle is produced by the infoldings of
(A) mitochondria
(B) chloroplast
(C) golgi complex
(D) plasma membrane
Answer:
(D) plasma membrane

Question 6.
The ribosomes present in prokaryotic cells is of type.
(A) 30S
(B) 80S
(C) 70S
(D) 50S
Answer:
(C) 70S

Question 7.
Complete the analogy.
F-plasmid: Reproduction :: R-plasmid: ________
(A) Respiration
(B) Resistance against antibiotics
(C) Packaging and transportation
(D) Apposition
Answer:
(B) Resistance against antibiotics

Question 8.
A rigid, supportive and protective outer covering of plasma membrane of fungi is called
(A) cell wall
(B) lamella
(C) plasmodesmata
(D) cell membrane
Answer:
(A) cell wall

Question 9.
The cytoplasmic connections from cell to cell are known as
(A) middle lamella
(B) plasmodesmata
(C) cell membrane system
(D) endoplasmic reticulum
Answer:
(B) plasmodesmata

Question 10.
Due to presence of ________, endoplasmic reticulum is termed as rough endoplasmic reticulum.
(A) cistemae
(B) RNA
(C) ribosomes
(D) tubules
Answer:
(C) ribosomes

Question 11.
Golgi body is absent in
(A) Prokaryotes
(B) Mature mammalian RBC
(C) Akaryotes
(D) All of the above
Answer:
(D) All of the above

Question 12.
Lysosomes are not helpful in
(A) Osteogenesis
(B) Cellular digestion
(C) Metamorphosis
(D) Lipogenesis
Answer:
(D) Lipogenesis

Question 13.
Identify the INCORRECT statements from the following.
1. Lysosomal enzymes do not digest their own membrane proteins.
2. Accidental release of lysosomal enzymes in limited amount does not harm the cell because pH of cytosol is near neutral.
3. Any insufficiency in secretion of lysosomal enzymes leads to disorders e.g. in genetic disorder- Klinefelter syndrome.
iv. Due to insufficiency of protease brain gets impaired resulting from accumulation of fats.
(A) Statements i and ii are incorrect.
(B) Statements i, ii and iii are incorrect.
(C) Statements iii and iv are incorrect.
(D) Statements i, ii and iv are incorrect.
Answer:
(C) Statements iii and iv are incorrect.

Question 14.
Tonoplast is a differentially permeable membrane surrounding the
(A) cytoplasm
(B) vacuole
(C) nucleus
(D) mitochondria
Answer:
(B) vacuole

Question 15.
Which organelle is surrounded by two membranes?
(A) Ribosomes
(B) Peroxisomes
(C) Vacuoles
(D) Mitochondria
Answer:
(D) Mitochondria

Question 16.
F₁ particles are present in
(A) plasmids
(B) mitochondria
(C) chloroplast
(D) ribosomes
Answer:
(B) mitochondria

Question 17.
_______ are green plastids containing green pigment chlorophyll.
(A) Chloroplasts
(B) Leucoplast
(C) Chromoplasts
(D) Xanthophyll
Answer:
(A) Chloroplasts

Question 18.
Select the INCORRECT statement about ribosome.
(A) Each ribosome consists of two sub- units-large and small subunit.
(B) Ribosomes are double membrane bound cell organelles.
(C) Ribosomes are made up of ribosomal RNA and protein.
(D) Ribosomes are involved in protein synthesis.
Answer:
(B) Ribosomes are double membrane bound cell organelles.

Question 19.
The space between the two nuclear membranes is known as
(A) peritonial space
(B) periplasmic space
(C) perinuclear space
(D) none of the above
Answer:
(C) perinuclear space

Question 20.
In eukaryotic cells, the chromosomes are located in
(A) nucleus
(B) nucleolus
(C) golgi complex
(D) lysosomes
Answer:
(A) nucleus

Question 21.
What is the normal chromosome number in humans?
(A) 23
(B) 46
(C) 48
(D) 16
Answer:
(B) 46

Question 22.
During which stage of cell division chromosomes become distinct and can be clearly identified?
(A) Interphase
(B) Prophase
(C) Pachytene
(D) Metaphase
Answer:
(D) Metaphase

Question 23.
Microtubules are made up of protein.
(A) tubulin
(B) fibrion
(C) collagen
(D) myosin
Answer:
(A) tubulin

Competitive Corner:

Question 1.
Match the column I with column II.

Column I	Column II
(a) Golgi apparatus	(i) Synthesis of protein
(b) Lysosomes	(ii) Trap waste and excretory products
(c) Vacuoles	(iii) Formation of glycoproteins and glycolipids
(d) Ribosomes	(iv) Digesting  biomolecules

Choose the right match from options given below:
(A) a-i, b-ii, c-iv, d-iii
(B) a-iii, b-iv, c-ii, d-i
(C) a-iv, b-iii, c-i, d-ii
(D) a-iii, b-ii, c-iv, d-i
Answer:
(B) a-iii, b-iv, c-ii, d-i

Question 2.
The concept of “Omnis cellula – e- cellula” regarding cell division was first proposed by:
(A) Schleiden
(B) Aristotle
(C) Rudolf Virchow
(D) Theodore Schwann
Answer:
(C) Rudolf Virchow

Question 3.
The Golgi complex participates in
(A) respiration in bacteria
(B) formation of secretory vesicles
(C) fatty acid breakdown
(D) activation of amino acid
Answer:
(B) formation of secretory vesicles

Question 4.
Which of the following is true for nucleolus?
(A) It takes part in spindle formation.
(B) It is a membrane-bound structure.
(C) Larger nucleoli are present in dividing cells.
(D) It is a site for active ribosomal RNA synthesis.
Hint: Large nucleoli are found in cells that are actively engaged in protein synthesis. Nucleolus is non-membranous structure.
Answer:
(D) It is a site for active ribosomal RNA synthesis.

Question 5.
Given below are cell organelles and their functions. Select the INCORRECT match.
(A) Lysosome – Phagocytosis
(B) Centriole – Spindle formation
(C) Sphaerosomes – Storage and synthesis of fats
(D) Leucoplast – Photosynthesis
Hint: Leucoplasts store food material.
Answer:
(D) Leucoplast – Photosynthesis

Question 6.
Which of the following cell organelles is responsible for extracting energy from carbohydrates to form ATP?
(A) Lysosome
(B) Ribosome
(C) Chloroplast
(D) Mitochondria
Hint: Glucose (carbohydrate) on complete oxidation from ATP during respiration. The ATP synthesis during carbohydrate oxidation takes place in the Mitochondria (site of aerobic respiration). Mitochondria produce cellular energy in the form of ATP.
Answer:
(D) Mitochondria

Question 7.
Which of the following components provides sticky character to the bacterial cell?
(A) Cell wall
(B) Nuclear membrane
(C) Plasma membrane
(D) Glycocalyx
Hint: In some bacteria, glycocalyx is rich in glycoproteins and could be a loose sheath called as slime layer. This slime layer or glycocalyx imparts sticky character to bacterial cell wall or bacteria.
Answer:
(D) Glycocalyx