Biology today september

Animal cells lack cell wall while those of plants and fungi possess cell wall.. Cell Cycle and Cell DivisionCELL CYCLE • Cell cycle is a series of events by which a cell duplicates its g

Cell : Structure and Function

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Cell : The Basic Unit of Life

• Cell is a basic membrane-bound unit that contains the fundamental molecules of life and of which all life begins.

• Robert Hooke was the first to observe dead cells in cork and Anton von Leeuwenhoek first saw and described live cells.

• Robert Brown later discovered the nucleus in the cells of orchid roots.

CELL THEORY

• Cell theory was jointly put forward by Matthias Schleiden and Theodor Schwann in 1839 Cell theory includes following

three principles:

– All living organisms are composed of one or more cells

– Cells are the basic units of structure and function in living beings

– All cells are produced from previously existing cells

TYPES OF CELLS

• Cells can be mainly classified into two types on the basis of nuclear organisation: cells that have membrane bound nuclei are

called eukaryotic and cells that lack a membrane bound nucleus are called prokaryotic.

• Cells differ greatly in size, shape and activities Mycoplasma is the smallest cell (0.15 - 0.3 µm in length) while the largest single cell is the egg of ostrich

CELL STRUCTURE

• Cell wall is absent in animal cell A plant cell consists of cell wall and protoplast Protoplasm includes cytoplasm and

nucleus Various cell organelles like mitochondria, Golgi bodies, etc., and many cytoplasmic inclusion bodies are found in

the cytoplasm

• In primitive cells of prokaryotes, genetic material is not organised in the form of nucleus and other membrane bound cell organelles are also absent

• Eukaryotic cells, in general comprise of following main components:

This article covers high yield facts of the given topic

Cell : Structure and Function

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Cell Wall

Structure

• It is the outer rigid, protective covering of plant cells, fungi and some protists

composed of cellulose microfibrils running through a matrix of other complex

polysaccharides

• Bacterial cell wall is made up of peptidoglycan Algae have cell wall made up

of cellulose, galactans, mannas and minerals like calcium carbonate

• In other plants, it consists of cellulose, hemicellulose, pectins and proteins

Cell wall can have three

(i) Middle lamella - Cementing layer between the adjacent cells and is the first layer to be formed during cytokinesis

It is made up of calcium and magnesium pectates

(ii) Primary wall - It is formed inner to middle lamella and is capable of extension It grows by addition of materials

within the existing wall

(iii) Secondary wall - It is produced in mature cells that have stopped growth It is formed by deposition of materials

over surface of existing structure

• Plasmodesmata links the cytoplasm of adjacent plant cells in the cell wall.

Functions

• Provides mechanical support and protection from mechanical injury

• Provides shape and rigidity to the cell

• Counteracts osmotic pressure and prevents bursting of plant cells by inhibiting excessive endosmosis

Table : Differences between prokaryotic and eukaryotic cell

(i) Cell is usually small Cell is comparatively larger

(ii) Cell wall if present possesses muramic acid Cell wall if present, is without muramic acid Animal cells lack cell wall

while those of plants and fungi possess cell wall

(iii) An organised nucleus is absent, instead a nucleoid

and diploid stages are absent

The amount of DNA shows a regular alternation between diploid and haploid stages

(vi) Transcription and translation occur in the cytoplasm Transcription occurs in the nucleus while translation occurs in cytoplasm.(vii) Cell organelles like ER, mitochondria, Golgi

apparatus, lysosomes, centrioles, etc., are absent

ER, mitochondria, Golgi apparatus and lysosomes or their equivalents are present in all the eukaryotic cells Centrioles are usually present in animal cells

(viii) Ribosomes are of 70S type Ribosomes are of 80S type

• The fluid mosaic model is most accepted structural model of cell membrane It was proposed by Singer and Nicolson in

1972 According to this model, there is a bilayer of lipid molecules (phospholipid) with globular protein molecules of two types - integral or transmembrane protein and peripheral or extrinsic protein and sterols which are arranged in different

manner in different regions of the plasma membrane

“I do not have any membrane and my smaller subunit is

40S.”

• It causes compartmentalisation and allows organelles to maintain identity

• Selective permeability of plasma membrane enables it to control the exchange between cell and its environment

• Other specialised functions are - absorption, secretion, fluid transport, electric coupling and other physiological processes

Cytoplasm and Cytoplasmic Matrix

• Matrix is the site of synthesis of a number of biochemicals like fats, nucleotides, carbohydrates, proteins, etc

• Many important pathways such as glycolysis, pentose phosphate pathway and anaerobic respiration occur in the cytoplasmic matrix

• Exchange of materials between cell organelles occurs through cytoplasmic matrix

ENDOMEMBRANE SYSTEM

• It is a grouping of some membrane organelles which function in close coordination with each other, i.e., endoplasmic reticulum, Golgi complex, lysosomes and vacuoles

• Plastids, mitochondria, peroxisomes, glyoxisomes, etc., are not part of this system

Endoplasmic Reticulum (ER)

• ER was discovered by Porter and Thompson in 1945.

Structure

• ER is an interconnected system of membrane lined channels that run through cytoplasm

• It is complicated organelle that exists in three forms - cisternae, vesicles and tubules It is of two types - smooth endoplasmic

reticulum (SER, without ribosomes) and rough endoplasmic reticulum (RER, with ribosomes).

Functions

• RER provides surface for protein synthesis

• The proteins in ER lumen are processed and are packed in membrane bound vesicles for storage

• SER is involved in fat and steroidal hormone synthesis

Golgi Complex

• The Golgi apparatus was discovered by Camillo Golgi in 1898 and was also named after him.

Structure

• It is a parallel arrangement and interconnected system of a cluster of smooth membranous disc-shaped sacs or cisternae

• Golgi complex is made up of four parts: cisternae, tubules, vesicles and Golgian vacuoles.

• One face of Golgi apparatus is convex or forming (cis face) while other is concave side or maturing face (trans face)

Functions

• Golgi apparatus helps in processing, packaging, transport and release of secretory proteins

• Glycosylation of proteins and lipids to form glycoproteins and glycolipids

• They act as primary lysosomes as they store digestive enzymes obtained through ER in the inactive state

• Transformation and recycling of plasma membrane takes place here

Lysosomes

• These were first reported by Christian de Duve in 1955 through fractionation technique They are found in all animal cells

except RBCs In plants and fungi, their function is taken over by vacuoles

Structure

• These are single membrane bound, small vesicular organelles containing hydrolytic enzymes

• The organelle passes through various stages and shows polymorphism There are four types of lysosomes (i) primary lysosome, (ii) secondary lysosome, (iii) residual bodies and (iv) autophagic vacuoles.

Functions

• They help in digestion of food obtained through phagocytosis

• Harmful and unwanted materials are disposed off by lysosomes Thus, lysosomes are called disposal bags or units.

• In injured and dead cells, the lysosome membrane ruptures spontaneously releasing the digestive enzymes or acid hydrolases that

lyse the weakened cells Therefore, these are called as ‘suicide bags’ of the cell.

Vacuoles

• Vacuoles are non-cytoplasmic areas present inside the cytoplasm

Structure

• These are surrounded by single membrane called tonoplast.

• These are formed by expansion and pinching off from endoplasmic reticulum

They are small in animal cells and large in fungal and plant cells

• Depending upon the contents and function, these are of four types - sap

vacuoles, food vacuoles, contractile vacuoles and air vacuoles.

Functions

• Vacuoles maintain osmotic pressure and turgidity and also help in osmoregulation

• They provide buoyancy, mechanical strength and protection

• In plants, the tonoplast facilitates the transport of a number of ions and other materials against concentration gradient

Ribosomes

• Ribosomes were discovered by Robinson and Brown (1953) in plant cells and George Palade (1955) in animal cells

Structure

• They are naked ribonucleoprotein protoplasmic particles (RNP) and are not surrounded by any membrane

• Ribosomes are made up of two subunits; larger and smaller and Mg2+ is required for binding of two subunits

• Eukaryotes have 80S ribosomes with 60S and 40S subunits and prokaryotes have 70S ribosome with 50S and 30S subunits

• Chemically ribosomes are made up of two parts : proteins and rRNA

• It has four sites for specific attachments : mRNAs binding site, aminoacyl site, peptidyl site and exit site.

Functions

• Ribosomes are sites for polypeptide or protein synthesis and therefore, act as protein factories

• Free ribosomes synthesise structural and enzymatic proteins for use inside the cell

• Provide protection to newly synthesised polypeptide by enclosing it in groove of larger subunit of ribosome

Mitochondria

• Mitochondria are semi-autonomous organelles which were first discovered by Kolliker in 1850.

Structure

• Mitochondria are cylindrical, double membranous structure A mitochondrion has two membranes: the outer membrane is smooth

and has porin proteins and the inner mitochondrial membrane produces numerous infoldings called cristae.

• The cristae and the inner face of the inner membrane is studded with mushroom-like projections called F 0 – F 1 particles or oxysomes which are related to ATP synthesis during oxidative phosphorylation.

Functions

• Mitochondria are called power house of cell because they help in cellular respiration and energy generation.

• Mitochondria are the sites of aerobic respiration

• Mitochondria help in synthesis of chlorophyll, cytochromes, pyrimidines, fatty acids, amino acids, etc

Plastids

• The term plastid was given by E.Haeckel in 1866

• Plastids develop from colourless precursors called proplastids Proplastids have ability to divide and differentiate into various types of plastids.

Structure

• Plastids are pigment containing cell organelles found in all plant cell and in euglenoids There are three types of plastids on the

basis of pigments - chloroplasts, chromoplasts and leucoplasts.

• Chloroplasts are chlorophyll containing greenish plastids responsible for trapping light energy during photosynthesis They are semi-autonomous organelles having their own DNA, enzymes and lipids Chromoplasts are non-photosynthetic plastids but are variously coloured because of the presence of carotenoid pigments and leucoplasts are colourless plastids

Functions

• Chloroplasts are the centre of photosynthesis

• Chromoplasts provide colours to the flowers and fruits while leucoplasts store various nutrients like, proteins, fats, etc

Nucleus

• Nucleus is the largest cell organelle, first discovered by Leeuwenhoek in red blood corpuscles of fish.

• Nucleus was first studied by Robert Brown in orchid root cells.

Structure

• The nucleus is a double membrane bound dense body that controls cellular metabolism and transmission to the posterity

• Nuclear envelope consists of two unit membranes separated by perinuclear space.

• Nucleoplasm is transparent, semifluid and colloidal substance which fills the nucleus It contains enzymes required for synthesis and functioning of DNA, RNA and nucleoproteins, etc

• Nuclear matrix contains nucleolus and chromatin Chromatin is the hereditary part of the nucleus and is differentiated into

euchromatin and heterochromatin.

• Nucleolus is a naked, round or slightly irregular structure that is attached to the chromatin at a specific region called nucleolar

organiser region (NOR).

Functions

• It controls cellular activities like - growth, development, reproduction and metabolism Ribosomes are formed in nucleolus part

of the nucleus

• It stores genetic information in DNA and transmits it to the next generation

• It controls the synthesis of RNAs (mRNA, rRNA and tRNA)

Peroxisomes

• They are microbodies, discovered by Christian de Duve and are found in both plant and animal cells.

Structure

• These are spherical, sac-like structures, bounded by a single membrane These contain enzymes for peroxide biosynthesis

• They are in close association with endoplasmic reticulum, mitochondria and chloroplasts

Functions

• Animal peroxisomes metabolise a number of toxic substances like nitrite, phenol, etc

• Plant peroxisomes found in photosynthetic cells perform photorespiration.

Glyoxysomes

• Glyoxysomes appear in germinating oil seeds and cells of some fungi till stored fat is consumed

Structure

• These are microbodies that contain enzymes for b-oxidation of fatty acids and glyoxylate pathway

• These have a single covering membrane and are considered to be special peroxisomes

Functions

• They help in lipid storage

• They also function in photorespiration and nitrogen fixation

• Biomolecules are the naturally occurring carbon containing organic molecules present in living organisms.

• Carbohydrates, lipids, proteins, enzymes, nucleic acids, etc., are the main organic constituents They are large in size, have complex

structures and high molecular weight (usually 10,000 Da) hence, they are called macromolecules.

• Small size having low molecular weight (18-1800 Da) are called micromolecules They include water, gases, minerals, amino

acids, simple sugars, nucleotides, etc

CARBOHYDRATES

• Carbohydrates, containing carbon, hydrogen and oxygen, are the most abundant organic molecules in nature

• They can be generally represented by the empirical formula C n (H 2 O) n or (CH 2 O) n where ‘n’ is an integer

• They are also called saccharides as their basic component is sugar Carbohydrates are of two types: small (monosaccharides, oligosaccharides) and complex (polysaccharides).

Cytoskeleton

• They form structural framework inside the cell and occur only in eukaryotic cells

Structure

• An elaborate network of filamentous proteinaceous structures present in the cytoplasm is called cytoskeleton.

• Microtubules, microfilaments and intermediate filaments collectively form cytoskeleton.

Functions

• Cytoskeleton maintains shape of the cell and its extensions, regulate orientation and distribution of cell organelles

• Microtubules help in the spindle and astral ray formation during cell division They also form cilia and flagella

• Microfilaments are involved in cytoplasmic streaming Intermediate filaments helps in the formation of nuclear matrix

Cilia and Flagella

• They are fine, hair-like movable protoplasmic processes of the cells

Structure

• Cilia and flagella are contractile outgrowths of the cell membrane Cilia are small structures whereas flagella are comparatively longer

• They have a microtubular composition referred to as 9 + 2 arrangement

Functions

• Both are capable of producing a current in fluid medium for locomotion and they also act as sensory organs of the cell

Centrosome and Centrioles

Structure

• Centrosome is an organelle found in animal cells only, containing two cylindrical structures called centrioles They are surrounded

by amorphous pericentriolar materials

• Both the centrioles lie perpendicular to each other and they also possess microtubular structures of 9 + 0 arrangement.

Functions

• They polymerise microtubules for the formation of spindle fibre and astral rays during cell division They also determine poles during the same

• Monosaccharides are simple sugars having a general formula of CnH2nOn, e.g., glucose, fructose and oligosaccharides

contain 2-10 monosaccharides, e.g., sucrose, maltose, lactose, etc

• Polysaccharides have large number of monosaccharides joined together by glycosidic bond, e.g., starch, glycogen, cellulose

• Polysaccharides are of two types, homopolysaccharides that are formed by polymerisation of only one type of monosaccharide

monomers, e.g., starch, cellulose, etc., and heteropolysaccharides are formed by condensation of two or more types of mono- saccharides, e.g., chitin, pectin, etc

TABLE : Comparison of various polysaccharides

Cellulose Found in cell wall of all plants;

wood contains 20% and cotton contains 90% cellulose

Gives mechanical support to plants;

being fibrous, has high tensile strength; fully permeable to water and solutes; source of food for some animals, bacteria and fungi

Linear long chains of 6,000 or more units

1-4 b linkage

of glucose

Starch Present in plants in the form of

starch grains in the chloroplasts

of leaves; stored in storage organs like potato tuber, seeds

of cereals and legumes

Fuel of plants; source of food for animals Has two components:amylose (straight

chain) and amylopectin (branched chain)

1-4 a-glucoseand

1-6 a-glucose

Glycogen Stored in liver and muscles of

animals; found in many fungi

Useful source of glucose in tion; provides energy for metabo-lism

respira-Highly branched chain (resembles amylopectin)

1-4 a-glucose and

1-6 a-glucose

Chitin Exoskeleton of insects, crabs

and prawns Helps animals to retain water; pro-vides strength and elasticity Linear long chain (resembles cellulose) 1-4 b-linkage of N-acetyl

glucosamine

LIPIDS

• Lipids are group of molecules that are insoluble in polar solvents such as water but soluble in non-polar solvents such as benzene

and ether Lipids contain relatively long hydrocarbon chains that are non-polar and thus hydrophobic They are divided into

three types- simple, compound and derived

• Simple lipids are esters of fatty acids with certain alcohols They are further of two types - neutral or true fats and waxes.

• The neutral or true fats are composed of carbon, hydrogen and oxygen A fat molecule consists of two components - one

molecule of glycerol and one to three molecules of long chain fatty acids.

• A glycerol molecule has 3 carbons, each bearing a hydroxyl group (–OH) Fatty acids may be saturated and unsaturated Saturated fatty acids have higher melting points and are solid at normal temperature While unsaturated fatty acids have

lower melting points and are liquid at normal temperature.

• Waxes are lipids composed of long-chain saturated fatty acids and a long chain saturated alcohol of high molecular weight

instead of glycerol, e.g., beewax, lanolin, etc

• Complex lipids are derivatives of simple lipids containing additional groups such as phosphate, nitrogenous base, protein, etc

They are further divided into following types :

– Phospholipids : They contain phosphoric acid and frequently a nitrogenous group, in addition to alcohol and fatty acids.

– Glycolipids : These lipids contain a fatty acid, carbohydrate and nitrogenous base.

– Lipoproteins : These are macromolecular complexes of lipids with proteins.

– Other complex lipids : Sulfolipids, amino lipids and lipopolysaccharides.

• Derived lipids are the derivatives obtained on the hydrolysis of group 1 and group 2 lipids, e.g., steroids, prostaglandins, etc.

Functions of Lipids

• Fats serve as food reserve in both plants and animals

• In seeds and spores, lipids help in thermal insulation, protection from ultraviolet radiations and loss of water

• In animals, fat occurs as droplets inside cells called adipocytes and adipocytes of cold blooded or poikilothermic animals have

higher amount of unsaturated fatty acids as compared to warm blooded or homoeothermic animals

PROTEINS

• Proteins are macromolecules composed of one or more polypeptides (chains of amino acids)

• Chemically a protein is made of carbon, hydrogen, oxygen, nitrogen and sulphur

• The nature of protein is determined by sequence of 20 different amino acids Amino acids are a group of organic compounds

containing two functional groups, a basic amino group (–NH 2 ) and acidic carboxyl group (–COOH).

Structure of Proteins

• Every protein has a three-dimensional structure that can have upto four levels of organisation:

(i) Primary structure is the basic linear sequence of amino acids in a polypeptide chain

(ii) Secondary structure is the development of new stearic relationships of amino acids present in the linear sequence inside

the polypeptides These are of three types: a-helix, b-pleated and collagen helix These are accomplished through

hydrogen bonding between amino acids

(iii) Tertiary structure is the bending and folding of secondary strand of polypeptide to various types of structures It is

stabilised by several types of bonds - hydrogen bonds, ionic bonds, van der Waals interactions, disulphide, hydrophobic bonds, etc

(iv) Quaternary structure is found in multimeric proteins Each polypeptide develops its own tertiary structure and functions

as subunits of protein, e.g., haemoglobin

• On the basis of constitution, proteins are of three types : (i) Simple proteins are made up of amino acids only Additional

non-amino groups are absent, e.g., histones, keratin (ii) Conjugated proteins have non-non-amino prosthetic groups like metals or

ions (iii) Derived proteins are obtained from proteins through denaturation, coagulation and breakdown, e.g., fibrin.

• On the basis of shape, proteins are divided into two categories fibrous and globular proteins Fibrous proteins are elongated,

thread-like structures that have no tertiary structure Globular proteins are rounded or oval in outline obtained by tertiary and quaternary foldings of polypeptides

Functions of Proteins

• Proteins are necessary in building and repairing body tissues

• They transport materials throughout the body

NUCLEOTIDES

• Nucleotides are the basic units of nucleic acids They are composed of a

nitrogen base, a pentose sugar and a phosphate

• There are five types of nitrogenous bases-adenine, guanine (purines),

cytosine, thymine and uracil (pyrimidines).

• Nitrogenous base attached with pentose sugar only is termed as nucleoside.

Table: Formation of nucleosides and nucleotides

Purines

(i) Adenine + Ribose →

or Deoxyribose →

AdenosineDeoxyadenosine

+ H3PO4 + H3PO4

→ Adenylic acid or Adenosine monophosphate (AMP)

→ Deoxyadenylic acid or deoxyadenosine monophosphate (dAMP)

(ii) Guanine + Ribose →

or Deoxyribose →

GuanosineDeoxyguanosine

+ H3PO4 + H3PO4

→ Guanylic acid or guanosine monophosphate (GMP)

→ Deoxyguanylic acid or deoxyguanosine monophosphate (dGMP)

(i) Cytosine + Ribose →

or Deoxyribose →

CytidineDeoxycytidine

+ H3PO4 + H3PO4

→ Cytidylic acid or cytidine monophosphate (CMP)

→ Deoxycytidylic acid or deoxycytidine monophosphate (dCMP)

(ii) Thymine + Deoxyribose only → Deoxythymidine + H3PO4 → Deoxythymidylic acid or deoxythymidine

monophosphate (dTMP)(iii) Uracil + Ribose only → Uridine + H3PO4 → Uridylic acid or uridine monophosphate

(UMP)

NUCLEIC ACIDS

• These are the polynucleotides, i.e., polymers of the nucleotides They contain genetic information determining all the heritable

characters

• There are two types of nucleic acids - deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)

• DNA is the largest macromolecule and is a polymer of deoxyribonucleotides It is composed of monomeric units namely

deoxyadenylate (dAMP), deoxyguanylate (dGMP), deoxycytidylate (dCMP) and deoxythymidylate (dTMP) It does not contain uracil Various forms of DNA are B-DNA, Z-DNA, A-DNA, C-DNA and D-DNA

• The secondary structure exhibited by DNA is the famous Watson-Crick model The two strands of polynucleotides in a DNA double helix are antiparallel to each other and are held together by hydrogen bonds The backbone is formed by the sugar-

phosphate-sugar chain.

• Adenine (A) and Guanine (G) of one strand pairs compulsorily with Thymine (T) and Cytosine (C) respectively on the other strand There are two hydrogen bonds between A and T and three hydrogen bonds between G and C

• RNA is a polymer of ribonucleotides held together by 3′,5′-phosphodiester bridges RNA contains ribose sugar in place of

deoxyribose in DNA RNA contains the pyrimidine uracil in place of thymine found in DNA

PRIMARY AND SECONDARY METABOLITES

• Organic compounds including fats and oils, nucleotides, amino acids, sugars, etc., in living organisms are called primary

metabolites They play important roles in normal physiological processes.

• Analysis of plant, fungal and microbial cells show the presence of thousands of compounds other than these primary metabolites,

e.g., alkaloids, flavonoids, essential oils, antibiotics, pigments, gums, scents, etc., are called secondary metabolites.

• Secondary metabolites attract animals for pollination and seed dispersal They are also used by plants for defense against herbivores and pathogens

ENZYMES

• Enzymes are macromolecular biological catalysts that accelerate chemical reactions without being utilised themselves The term enzyme was coined by W Kuhne (1878).

• Enzymes occur in colloidal state and are often produced in inactive form called proenzymes or zymogens and are converted

to active enzymes in the presence of specific factor like pH, substrate, etc

• With few exceptions, all enzymes are proteins Ribozyme, ribonuclease-P and peptidyl transferase are three

non-protein enzymes.

• Enzymes are of two types - simple enzymes and conjugated enzymes Simple enzymes are made of only proteins, e.g., amylase, trypsin, etc Conjugated enzymes or holoenzymes contain a protein part (apoenzyme) and a non-protein part

(prosthetic group) The prosthetic group is firmly attached to apoenzyme.

• Another type of organic co-factors are co-enzymes that are loosely attached to the apoenzyme

• There are six classes of enzymes - (i) Oxidoreductase : Catalyse oxidation and reduction reaction or take part in transfer of electrons (ii) Transferase : They catalyse transfer of a group between a pair of substrates (iii) Hydrolases : Catalyse hydrolysis

of bonds like ester, ether, peptide, etc (iv) Lyases : Catalyse removal of groups from substrates by mechanisms other than hydrolysis (v) Isomerases : Catalyse interconversion of optical, geometrical or positional isomers (vi) Ligases : Catalyse the

linking together of two compounds

Mechanism of Enzyme Action

• There are two modes by which enzymes are supposed to bring about chemical reaction: (i) Formation of enzyme - substrate (ES) complex and (ii) Lowering of activation energy

• Enzymes have a specific three-dimensional structure In the active site of enzyme, substrate fits to proceed chemical reaction The point where substrate is bound on the active site is known as the substrate binding site.

• This is the first step of an enzymatic reaction where, the enzyme forms a temporary association with its substrate, hence the name

enzyme-substrate complex.

• Two models have been proposed to explain the formation of ES complex:

– Lock and key hypothesis : It was proposed by Emil Fischer in 1894

According to this, both enzyme and substrate molecules have specific

geometrical shapes The region of active site of the enzyme is such that

it allows the particular substrate molecule to be held over it This also

explains the specificity of enzyme action

– Induced-fit hypothesis : It is the modification of lock and key hypothesis

and was proposed by Koshland in 1959 According to this theory, when

the substrate binds to an enzyme, it may induce conformational change in enzyme molecule in such a way that it is fit for the substrate-enzyme interaction

• The number of substrate molecules converted to products per minute by enzyme molecule is called turn over number

Activation Energy : All the molecules of substrate possess energy, which is utilised to collide with other molecules to reach that

transition state between the reactant and product This energy is called activation energy It is quite high for the reaction to

proceed and is lowered by the enzyme

Factors Affecting Enzyme Activity

• The conditions which can alter the tertiary structure of protein can affect the activity of an enzyme

• Optimum temperature for enzyme activity is 25°C - 40°C High temperature denatures enzymes due to degradation of

linkages in its polypeptide chains and low temperature inactivates them due to reduction in speed of molecular movement.

• Every enzyme has an optimum pH which is most effective Most enzymes function near neutral pH with the exception of several

digestive enzymes

• With the increase in substrate concentration, the velocity of the enzymatic reaction rises at first The reaction ultimately

reaches a maximum velocity (Vmax) which is not exceeded by any further rise in concentration of the substrate This is because the enzyme molecules are fewer than the substrate molecules and after saturation of these molecules, there are no free enzyme molecules to bind with the additional substrate molecule

• Michaelis-Menten equation : To determine the effect of substrate concentration in enzymatic reaction Leoner Michaelis

and Maud Menten (1913) proposed a mathematical model and derived a relationship which is mathematically expressed as

K +[S ];

max

m

where, K m = Michaelis–Menten constant, i.e., the substrate concentration to produce half maximum velocity,

V = Velocity of reaction, Vmax = Maximum velocity, [S] = Substrate concentration

Inhibition of Enzyme Action

• The reduction of enzyme activity due to presence of certain adverse conditions or chemicals is called enzyme inhibition It can

be classified as :

(i) Reversible inhibition is the type of inhibition that can be overcome by withdrawal of the inhibitor because the effect of

latter is of temporary in nature Reversible inhibitors can bind to enzymes through weak non-covalent interactions such as ionic bonds, etc

(ii) Irreversible inhibition is of permanent type as the enzyme conformation is harmed, e.g., denaturation of enzyme.

(iii) Competitive inhibition is caused by blockage of the active site of enzyme by a chemical which is similar in structure to

the substrate This type of inhibition is usually reversible as the conformational changes do not occur

(iv) Non-competitive inhibition is caused by alteration of conformation of the enzymes by a chemical that binds to a site

other than the active site It is usually irreversible because it cannot be overcome by increasing substrate concentration

Cell Cycle and Cell Division

CELL CYCLE

• Cell cycle is a series of events by which a cell duplicates its genome, synthesises other constituents of the cell and eventually

divides into two daughter cells

• In a typical eukaryotic somatic cell, cell cycle has two main phases- a long non-dividing interphase (I-phase) and a short nucleus dividing mitotic phase (M-phase).

• Interphase is metabolically active phase and is divided into first gap phase or G 1 -phase, synthetic phase or S-phase and second gap phase or G 2 -phase

• G 1 phase : This phase is in between the end of M-phase of previous cell cycle and initiation of S-phase It is the longest phase of

interphase In this phase, cell grows in size and RNA and proteins are synthesised Cell organelles also increase in number From

G1 phase, cells may enter into S-phase or sometimes in G0 phase

• S-phase : During this phase DNA synthesis takes place DNA content becomes double, though the ploidy level remains same Histone proteins are synthesised during S-phase.

• G 2 phase : In this phase, synthesis of DNA stops, however, formation of RNAs and proteins continues which are required for

multiplication of cell organelles, spindle formation, aster formation and cell growth In animal cells, centrosome begins to divide and there is an extensive synthesis of tubulin protein to form microtubules

• M-phase is divided into -karyokinesis or the division of nucleus followed by cytokinesis or the division of cytoplasm Karyokinesis in again divisible into - prophase, metaphase, anaphase and telophase.

• G 0 phase is a period in the cell cycle in which cells exists in a quiescent state G0 phase is viewed either as an extended G1phase, where the cell is neither dividing nor preparing to divide or a distinct quiescent stage that occurs outside the cell cycle

Cell Cycle Checkpoints

• Two key classes of regulatory molecules, cyclins and cyclin dependent protein kinases (CDKs) determine a cell’s progress

through the cell cycle

• Cell cycle checkpoints are the control mechanisms that ensure the fidelity of cell division There are two regulatory mechanisms which takes decision about cell division

– First checkpoint is called G 1 cyclin (CG1 or G1/S) which is present in between G1 and S phase In G1, CDK becomes active

by G1 cyclin and ATP at its activation site It causes transition of G1 to S phase G1 cyclin is destroyed at the end of S-phase and CDK becomes inactive

– Second checkpoint is present between G2 and M-phase During G2 phase, inactive CDK binds to mitotic cyclin (CM

or G2/M) It gets phosphorylated at its both activation and inhibitory sites but still remains inactive On removal of PO4from the inhibitory site, it becomes active and causes transition from G2 to M-phase At the end of M-phase, mitotic cyclin (CM) is degraded, PO4 at activation site is removed and the cell enters into G1 again

CELL DIVISION

• Cell division is the process of formation of new or daughter cells from pre-existing or parent cells It is of three types-amitosis,

mitosis and meiosis.

protein.

Amitosis or Direct Cell Division

• Amitosis is characterised by the splitting of nucleus followed by that of cytoplasm It is a simple method of cell division described

by Flemming (1882).

• In this method, the nucleus elongates and constricts in the middle to form two daughter nuclei without the formation of spindle fibre or the appearance of chromosomes

• It does not divide the nuclear material equitably, e.g., meganucleus of Paramecium, internodal cells of Chara, etc

Mitosis or Equational Division

• Mitosis or mitotic cell division is meant for multiplication of cells It generally takes place in vegetative or somatic cells

• In this process, one parent cell divides into two daughter cells, but the chromosome number remains the same as in parent cell, i.e., daughter cells exactly resemble with parent cell both quantitatively as well as qualitatively hence, it is called equational division Stages of mitosis are as follows:

• Prophase : It is the first stage of mitosis During this stage viscosity of cytoplasm increases, chromatin fibres become shorter

and thicker due to the coiling and get condensed into distinct thread- like chromosomes in late prophase Each chromosome consists of two coiled sister chromatids joined by a centromere that appears

like a ball of wool called spireme stage Spindle fibres form at each side of

the cell and nuclear membrane breaks down Disappearance of nucleolus and

other cellular organelles occur

• Metaphase : The complete disintegration of the nuclear envelope marks

the start of the second phase of mitosis, i.e., metaphase Condensation

of chromosomes is completed by this time At this stage, the number and

morphology of chromosomes can be easily studied and counted under

microscope The chromosomes line up along the centre of the cell and the

spindle fibres attach to each chromosome at the centromere forming the

metaphase plate Small disc-shaped structures at the surface of the centromeres called kinetochores serve at the site of

attachment of spindle fibres

• Anaphase : This is the shortest stage of mitosis Chromosomes divide at the point of centromere and thus, two sister chromatids

get separated Chromatids move to the opposite poles of the cells due to contraction of spindle fibres and appearance of interzonal fibres Nucleolus, Golgi complex and ER re-form

• Telophase : The separated chromatids or newly formed chromosomes reach the opposite pole The nuclear envelop re-form

and the chromatin decondenses In general, the events of prophase occur in reverse sequence during this phase RNA synthesis restarts causing nucleolus to appear

• Cytokinesis : During this, mitosis ends with division of cytoplasm by a process known as cleavage It starts towards the middle

of anaphase and is completed with the telophase It differs in plants and animal cells In plants, it usually occurs by cell plate method wheares in animals it takes place by cleavage

Significance of mitosis

• Growth and development : A full grown organism is developed from a single celled zygote by repeated mitotic divisions.

• Genetic stability : All the daughter cells of a multicellular organism have the same number and type of chromosomes as parent

cells due to equitable distribution of all the chromosomes

• Repairing and healing : The mechanism for replacing old or worn out cells and healing of a wound by new cell production

depend on mitosis

• Regeneration : Some organisms are able to regenerate their missing parts of body or whole organism through mitosis.

Meiosis or Reductional Division

• Meiosis is a kind of cell division that occurs in a diploid cell and reduces the chromosome number by half which results in the production of haploid daughter cells The term was coined by Farmer and Moore.

• It involves two successive nuclear divisions meiosis I and meiosis II but no DNA replication prior to second division There is a short interkinesis between meiosis I and meiosis II.

• Meiosis I is the heterotypic or reductional division because it brings about changes from diploid to haploid state It is studied

under four stages:

• Prophase - I : It is the most complicated and longest phase of meiotic division It is further divided into five stages :

– Leptotene : The size of nucleus is increased, chromosomes become more apparent and show bead -like thickenings called

chromomeres Chromosomes also show a typical arrangement and often referred to as “bouquet” stage.

– Zygotene : Chromosomes become shorter and thicker Pairs of homologous chromosomes called bivalents or tetrad are

seen The process of attachment of the homologous chromosomes due to the development of nucleoprotein is known as

synapsis It produces a complex called synaptonemal complex.

– Pachytene : It is the longest phase of prophase - I, characterised by the appearance of recombination nodules where crossing over (exchange of genetic material) between non-sister chromatids of the homologous pair takes place.

– Diplotene : Dissolution of synaptonemal complex occurs partially therefore, the homologous chromosomes separate except

in the region of crossing over The points of attachment between homologous chromosomes after the partial dissolution of

nucleoprotein complex are called chiasmata Lampbrush chromosomes are actually condensed diplotene chromosomes

– Diakinesis : Chiasmata shift towards the ends of the chromosomes It is termed

as terminalisation The nucleolus degenerates, nuclear envelope disappears,

centrioles migrate to poles and spindle fibres begin to form

• Metaphase - I : The bivalents arrange themselves on the equator of the bipolar

spindle forming metaphase plate Chromosomes are in maximum condensed

state and are ready to separate

• Anaphase - I : Bivalent chromosomes get separated, microtubules of the

spindle fibres begin to shorten and each separated chromosome with two

chromatids start moving towards the opposite poles Because of the random

orientation of homologous chromosomes on the metaphase plate, a pole may receive

either the maternal or the paternal homologue from each chromosome pair

• Telophase - I : The haploid set of chromosomes elongate or decondense, nucleolus is formed from a satellite chromosome and

nuclear envelope reappears It is generally followed by cytokinesis

• Interkinesis : It is the metabolic stage between meiosis - I and meiosis - II Protein and RNA synthesis may occur but there is

no DNA synthesis It is short lived and plays important role in bringing true haploidy

• Meiosis - II : It is also called homotypic or equational division as it maintains the number of chromosomes produced at the end

of reduction division Meiosis - II is divisible into prophase - II, metaphase - II, anaphase - II, telophase - II and cytokinesis

All these phases are similar to mitosis But meiosis II is not mitosis, as it always occurs in haploid cells and daughter cells formed after meiosis II are neither similar to each other not to the parent cell

Significance of meiosis - I and meiosis - II

• Meiosis is essential for gamete formation and maintenance of chromosome number in sexually reproducing organisms.

• Paternal and maternal chromosomes assort independently during meiosis, that causes reshuffling of chromosomes and the

traits controlled by them

• Crossing over facilitates new combination of genes thus, helps in producing variations

• Meiosis also provide evidences for the basic similarity and relationship among organisms.

• Meiosis II plays important function in separating the chromatids of univalent chromosomes that differ from each other in their linkage groups due to crossing over

CHAPTER-14 : RESPIRATION IN PLANTS

Multiple Choice Questions

1 In electron transport system within the inner mitochondrial

membrane, complex II and complex III respectively are

(a) NADH-Q reductase and succinate Q-reductase

(b) succinate-Q reductase and QH2-cytochrome c reductase

(c) NADH-Q reductase and succinate - Q reductase

(d) succinate-Q reductase and cytochrome c oxidase.

2 How much amount of energy will be liberated from 2 mole

of glucose through cellular respiration?

(a) 686 kcal (b) 1372 kcal

(c) 870 kcal (d) 2870 kcal

3 Which of the following statement(s) is/are correct?

(i) Toxic products like ammonia are produced by

protoplasmic respiration

(ii) In anaerobic respiration, more substrate is decomposed,

as a result little part of it is left for growth and repair in

plants

(iii) A plant growth is maximum at compensation point

because there is very little loss of organic matter due

to respiration

(iv) The gas exchange demand is very high in plants and

each plant part takes care of its own gas exchange

needs

(a) (i) and (iii) (b) (iii) and (iv)

(c) (i) and (ii) (d) (iv) only

4 In the given experiment, test tube containing potassium hydroxide is suspended so that

(a) oxygen released by germinating seeds is absorbed, creating a partial vacuum that causes the rise of water

in the beaker(b) carbon dioxide released by the germinating seeds is absorbed, creating a partial vacuum that causes the rise of water in bent tube

(c) water vapour is absorbed creating a partial vacuum that causes the rise of water in the beaker

(d) oxygen present in the conical flask is completely absorbed to create anaerobic condition

5 If C4H6O5 is broken down as respiratory substrate under aerobic conditions, the respiratory quotient will be

(a) more than one (b) equal to one(c) less than one (d) zero

UNIT-V : PLANT PHYSIOLOGY (PART-II)

Maximise your chance of success in medical entrance exams by reading this article This section is specially designed to optimise your preparation by practising more and more It is a unitwise series having chapterwise question bank, allowing you to prepare systematically and become more competent.

Recall question or single concept question – indicated by a single finger.

Application question or question which requires 2 or 3 concepts - indicated by 2 fingers.

Application question or question which requires 3 or more concepts - indicated by 3 fingers.

CHECK YOUR ITALS

for NEET, AIIMS and JIPMER

6 The given reaction is completed in the presence of

7 The complete oxidation of pyruvate by the stepwise removal

of all the hydrogen atoms, give rise to

(a) two molecules of NADPH

(b) two molecules of FADH2

(c) two molecules of CO2

(d) four molecules of NADH

8 Select the incorrect pair of statements about the common

process of aerobic and anaerobic respiration

(i) It is the process of complete oxidation of glucose

(ii) Two molecules of pyruvic acid are produced through

the process

(iii) The entire process is mediated by ten enzymes

(iv) Net gain of 3ATP and 2NADH, is achieved during the

process

(a) (i) and (ii) (b) (ii) and (iii)

(c) (i) and (iii) (d) (i) and (iv)

9 Select the correct sequence of formation of intermediates

10 Which of the following steps is associated with NADH

formation during TCA cycle?

(a) Acetyl CoA Citrate

(b) Citrate cis Aconitate

(c) Isocitrate Oxalosuccinate

(d) Succinyl CoA Succinate

11 If both fatty acids and carbohydrates are available to muscles,

which will be consumed first during respiration?

(a) Carbohydrates (b) Fatty acids

(c) Both at the same time (d) None of these

12 (i) is found in aerobic respiration towards the end of the

(ii) process

(i) (ii)

(a) Glycolysis anabolic

(b) Terminal oxidation catabolic

(c) Glycolysis catabolic

(d) Terminal oxidation anabolic

13 Consider the following statements and select the correct option

(i) Acetaldehyde is reduced to ethyl alcohol or ethanol

by alcohol dehydrogenase in yeasts during anaerobic condition

(ii) Succinyl CoA, produced during glycolysis, forms cytochrome and chlorophyll

(iii) Enzyme fumarase helps to convert fumarate into malate by addition of one molecule of water

(iv) Fermentation generally utilises NADH produced during glycolysis

(a) (i) and (ii) are incorrect

(b) (ii), (iii) and (iv) are incorrect

(c) (iii) and (iv) are incorrect

(d) Only (ii) is incorrect

14 Antimycin A is a respiratory poison that inhibits(a) electron transport chain

(b) formation of phosphoenol pyruvate(c) oxidation of glyceraldehyde 3-phosphate(d) formation of acetyl CoA from pyruvic acid

15 How many protons are used up for synthesis of one ATP molecule during electron transport chain?

(a) 2 (b) 3 (c) 5 (d) 10

Match The Columns

16 Match Column I with Column II

A Lactic acid (i) Respiratory quotient

B Respirometer (ii) Oxidative decarboxylation

C Pyruvate (iii) Muscle fatigue dehydrogenase

D Cytochromes (iv) Isomerisation

E Phosphoglycero- (v) Inner mitochondrial mutase membrane

17 Match Column I with Column II (There can be more than one match for items in column I.)

A Fructose (i) Aconitase 1,6-biphosphate

B Fumarate (ii) FADH2

C Fermentation (iii) Zymosis

D Cytochrome c oxidase (iv) Aldolase

E Citrate (v) Succinate (vi) Glyceraldehyde

3-phosphate (vii) Lactic dehydrogenase (viii) Cytochrome a

(ix) cis aconitate

(x) Electron transport chain

Passage Based Questions

18.(A) Complete the given passage with appropriate words or

phrases

Glycolysis is the (i) stage of breakdown of (ii) through a

series of (iii) enzyme mediated reactions Glycolysis has

two phases : (iv) and (v) In glycolysis, (vi) molecules

of ATP are consumed during formation of fructose

1,6-biphosphate from glucose and (vii) molecules of ATP

are produced by substrate level phosphorylation (viii)

molecules of NADH are also formed Oxygen is (ix) for

glycolysis

(B) Read the given passage and correct the errors, wherever

present

In fermentation, the incomplete oxidation of glucose is

achieved under aerobic conditions The two common

products are ethanol and pyruvic acid It is normal

mode of respiration of plants Less quantity of O2 is

evolved and there is no requirement of peroxisomes

686 kcal of energy are formed per gm mole of glucose

NADH produced during Krebs' cycle is used up

Assertion & Reason

In each of the following questions, a statement of Assertion (A)

is given and a corresponding statement of Reason (R) is given

just below it Of the statements, mark the correct answer as :

(a) If both A and R are true and R is the correct explanation of A

(b) If both A and R are true but R is not the correct explanation of A

(c) If A is true but R is false

(d) If both A and R are false

19 Assertion : Yeast produces ethyl alcohol during anaerobic

respiration

Reason : Accumulation of alcohol, produced by fermentation,

beyond a certain limit can kill the microorganism

20 Assertion : About 50% of the energy liberated during

cellular respiration is used for synthesis of biomolecules

and other life activities

Reason : Energy is liberated in controlled fashion in

several steps and is mostly stored in ATP

21 Assertion : An intermediate RQ value is obtained where

an organism is undergoing both aerobic and anaerobic

respiration

Reason : RQ values indicate that living organisms always

use a single respiratory substrate

22 Assertion : 3-phosphoglycerate is changed to

2-phospho-glycerate by isomerisation during glycolysis

Reason : Isomerisation of 3-phosphoglycerate is an

energy spending phase of glycolysis

23 Assertion : F1 particles are present in the inner

mitochondrial membrane

Reason : An electron gradient formed on the inner

mitochondrial membrane forms ATP

24 Assertion : The passage of electrons in electron transport

chain is a downhill journey

Reason : Electron passes from one enzyme to the next with

a loss of energy at each step

25 Assertion : Substrate level phosphorylation is not present

in Krebs' cycle

Reason : Substrate level phosphorylation requires

electrons to move through electron transport chain

26 Assertion : Oxidative phosphorylation is linked to

terminal oxidation of reduced coenzymes NADH and FADH2 in respiration

Reason : The coenzymes release electrons that pass over

a series of carriers in electron transport chain

27 Assertion : Fats are used as respiratory substrates by a

number of organisms

Reason : Fats contain more energy as compared to

carbohydrates

28 Assertion : Glycolysis uses oxygen as terminal oxidant.

Reason : Glycolysis is connected with oxidative

phos-phorylation

Figure Based Questions

29 Study the given figure and answer the following questions

(a) Identify A, B and C in the given figure.

(b) How does a proton gradient develop in the system? (c) At which condition will C produce ATP?

30 Refer to the given figure and answer the following questions

(a) Identify X, Y and Z in the given figure.

(b) Give the reactions and also identify A and B in the

given figure

(c) In the given cycle, how many times oxidative

decarboxylation takes place? Explain

CHAPTER-15 : PLANT GROWTH AND DEVELOPMENT

Multiple Choice Questions

1 The growth curve of meristematic cells at growing tip of a

plant and an embryo will be

(a) linear and Y-shaped respectively

(b) J-shaped and Y-shaped respectively

(c) Y-shaped and J-shaped respectively

(d) linear and J-shaped respectively

2 Naphthalene acetic acid is applied on an apple tree The

tree will produce

(a) more dwarf shoots and more apples

(b) more long branches and more apples

(c) long root for deep penetration within soil

(d) less side branches and more apical growth

3 Which of the following is not true about gibberellins?

(i) Mevalonic acid is a precursor for GA synthesis

(ii) A mixture of GA4 and GA7 is used commercially

(iii) Transport is both basipetal and acropetal

(iv) A single plant possesses only one kind of GA

(a) (i) and (ii) (b) (ii) and (iii)

(c) (iii) and (iv) (d) (iv) only

4 Read to the given statements and identify X, Y and Z

(i) X delays the senescence of leaves and other organs by

mobilisation of nutrients

(ii) Spraying of Y on sugarcane crop increases length of

stem and yield of sugarcane

(iii) Z increases resistance of plants to cold and other types

of stresses

(a) X-Auxin; Y-Gibberellin; Z-Ethylene

(b) X-Cytokinin; Y-Gibberellin; Z-Abscisic acid

(c) X-Gibberellin; Y-Auxin; Z-Cytokinin

(d) X-Ethylene; Y-Cytokinin; Z-Auxin

5 The critical period of a long day plant is 9 hrs Four potted

plants of the same species are exposed with different light

periods

Potted plant Photoperiod

I II III IV

10 hrs.

8 hrs.

11 hrs.

15 hrs.

Which plants would show flowering after exposure?

(a) I and III only (b) I, III and IV only

(c) III and IV only (d) II only

6 Apical bud of a tea plant is plucked and painted with a paste

of auxin at the cut portion It will cause(a) dense bushy growth of the plant(b) less number of lateral buds(c) early flowering of the plant(d) increased number of leaves

7 Chrysanthemum is a short day plant with a critical day length

of 15 hrs Under which of the following condition the plant will flower?

(a) Normal seedling with 16 hrs photoperiod

(b) Defoliated seedling with 12 hrs photoperiod

(c) Seedling with one intact leaf in 12 hrs photoperiod.(d) Defoliated seedling with 15 hrs photoperiod

8 Minimum vegetative growth, required for the plant to

produce flower in Xanthium is represented by

(a) 8-leaved stage (b) 7- leaved stage(c) 5-leaved stage (d) there is no such limit

9 Initial size of a leaf was 50 cm2 In one day time period it is increased upto 55 cm2 What is the absolute growth rate of the leaf?

(a) 5 cm2/day (b) 55 cm2/day(c) 0.5 cm2/day (d) 0.5 cm2/hr

10 Which of the following statements is/are correct related to the compound in the given figure?

(i) It stops mitosis in vascular cambium towards the approach of winter

(ii) It is known to promote flowering in long day plants.(iii) It increases transpiration rate by opening of stomata.(iv) It induces a positive surface potential on cell membrane

(a) (i), (ii) and (iii) (b) (ii) and (iv)(c) (i), (ii) and (iv) (d) (i) and (iv)

11 In Hyoscyamus niger, the low temperature required for

inducing flowering is(a) 0° – 5°C (b) 3° – 17°C (c) 12° – 18°C (d) 0° – 2°C

12 Critical photoperiod of plant X is 12 hrs Now in one set

of plants, the night phase is interrupted by red light and in another set of plants night phase is interrupted first by red light and then by far red light In first condition plants do not produce flower but in second condition plant produce flower X is a

(a) short day plant (b) long day plant(c) day neutral plant (d) short night plant

13 Which of the following growth regulator promotes rapid

elongation of leaf bases and internodes in deep water rice

plant?

(a) GA (b) IAA

(c) Ethylene (d) ABA

14 A set of tomato plants with minimum vegetative growth

are exposed to certain given conditions

(i) Continuous night phase

(ii) Night phase interrupted by red light

(iii) Night phase interrupted first by red light and then by

far red light

In which of the given conditions flowering will occur?

(a) (i) only (b) (i) and (iii)

(c) (ii) only (d) (i), (ii) and (iii)

15 _ inhibits gibberellin mediated amylase formation

during germination of cereal grains

(a) ABA (b) Zeatin (c) NAA (d) 2,4-D

Match The Columns

16 Match Column I with Column II

Column I Column II

A IAA (i) SDP

B Xanthium (ii) Coconut milk

C Cucumber (iii) Tryptophan

D Spinach (iv) LDP

E Cytokinin (v) Day neutral plant

17 Match Column I with Column II (There can be more than

one match for items in Column I)

A Gibberellin (i) Epicotyl hook formation

B Auxin (ii) Phytochrome

C Ethylene (iii) Vernalin

D Photoreceptor (iv) Avena curvature bioassay

E Vernalisation (v) Barley endosperm bioassay

(vi) Low temperature

(vii) NAAM

(viii) Bolting in rosette plants

(ix) Ethephon

(x) Root growth inhibition assay

Passage Based Questions

18.(A) Complete the given passage with appropriate words or

phrases

(i) is the universal natural auxin present in plants Natural

auxin passes from (ii) to the region of (iii) Movement of

auxin is (iv) which is (v) in stem and (vi) in root In higher

concentration, auxin (vii) growth In an old senescent leaf,

an external application of auxin promotes (viii) It is due to

triggering of (ix) biosynthesis Both auxin and (ix) hasten

the (x) formation in senescent leaf

(B) Read the given passage and correct the errors, wherever present

The long day plants come to flower after receiving photoperiod below a critical length These plants also called long night plants because they require darkness above a critical level They can flower under complete darkness Flowering is inhibited if dark period is interrupted

by light Supply of auxins induce flowering in many cases under inductive photoperiods

Assertion & Reason

In each of the following questions, a statement of Assertion (A)

is given and a corresponding statement of Reason (R) is given just below it Of the statements, mark the correct answer as :(a) If both A and R are true and R is the correct explanation of A(b) If both A and R are true but R is not the correct explanation of A(c) If A is true but R is false (d) If both A and R are false

19 Assertion : Abscisic acid is known as dormin.

Reason : Abscisic acid is employed for breaking of seed

and bud dormancy

20 Assertion : Genetically male plants of Cannabis can

be induced to produce female flowers in the presence of gibberellin

Reason : Gibberellin has feminising effect in some plants.

21 Assertion : Defoliated seedlings of Xanthium cannot

flower even with 12 hrs photoperiod

Reason : Photoperiodic stimulus is picked up by the fully

developed leaves causing photoperiodic perception

22 Assertion : TIBA acts as antiauxin by blocking the

transport of auxin

Reason : Bound auxin cannot be extracted easily except

with the help of organic solvents

23 Assertion : Florigen is different in different plant species,

produced in response to specific photoperiodicity typical of

a plant type

Reason : Florigen is produced only when the plant is

under the juvenile stage

24 Assertion : Vernalisation has no role in inducing flowering Reason : The stimulus of vernalisation is perceived only by

meristematic cells

25 Assertion : ABA promotes rooting in stem cuttings of Poinsettia.

Reason : ABA promotes growth by cell division.

AUGUST 2018

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Winner : Saumya Sharma (Navi Mumbai, Maharashtra)

26 Assertion : Maximum synthesis of ethylene occurs during

climacteric ripening of fruits and tissues undergoing

senescence

Reason : Ethylene inhibits transverse growth and

stimulates longitudinal growth

27 Assertion : Response to a PGR may differ from one plant

organ to another

Reason : The site of production and the site of action

of PGRs may be different

28 Assertion : Juvenile conifers sprayed with mixture of GA4

and GA7 reach early maturity

Reason : Gibberellins help in cell growth of stem, leaves

and other aerial parts

Figure Based Questions

29 Refer to the given figure and answer the following questions

(a) Identify A and B in the given figure.

(b) What is the equation and graphical representation of B? (c) How is exponential growth achieved by A?

30 Study the given figure on a short day plant and answer the following questions

Darkness Flash of light

Light

Critical night length

24 hours

(a) Which of the given conditions produce flower?

(b) How does the flash of light in C affect flowering? (c) What would happen if plants are treated with a far

red light before the treatment with flash of light?

SOLUTIONSCHAPTER-14 : RESPIRATION IN PLANTS

1. (b) 2. (b) 3. (c) 4. (b) 5. (a)

6. (b) 7. (c) 8. (d) 9. (c) 10. (c)

11. (a) 12. (b) 13. (d) 14. (a) 15. (b)

16. A-(iii); B-(i); C-(ii);D-(v); E-(iv)

17. A-(iv, vi); B-(ii, v); C-(iii, vii); D-(viii, x); E-(i, ix)

18.(A) (i) first (ii) glucose

(iii) ten (iv) preparatory

(v) pay off (vi) two

(vii) four (viii) Two

(ix) not required

(B) In fermentation, the incomplete oxidation of glucose is achieved

under aerobic anaerobic conditions The two common products

are ethanol and pyruvic lactic acid It is normal mode of respiration

of plants microorganisms Less quantity of O2 CO2 is evolved

and there is no requirement of peroxisomes mitochondria

686 39-59 kcal of energy are formed per gm mole of glucose

NADH produced during Krebs' glycolysis cycle is used up

19. (b) 20. (b) 21. (c) 22. (c) 23. (a)

24. (a) 25. (d) 26. (a) 27. (a) 28. (d)

29 (a) The given figure is showing ATP synthesis by F0 – F1

particle Here, A is 2H+, B is F0 and C is F1

(b) F0 – F1 particles are present in the inner mitochondrial membrane ATP synthase becomes active when there is a proton gradient having higher concentration of H+ on the F0side as compared to F1 side Increased proton concentration

in outer surface of inner mitochondrial membrane is produced by the pushing of protons with the help of energy liberated by passage of electrons from one carrier to another during electron transport chain

GLIMPSE OF NEXT ISSUE

Bio Digest XI

: Transport in Plants and

Mineral Nutrition

Bio Digest XII

: Human Health and

f

Gases, Body Fluids and Circulation, Excretory Products and their Elimination)

Monthly Tune Up (XI)

: Biomolecu

les and Cell Cycle

and Cell Division

Monthly Tune Up (XII)

: Evolution and Human

Health and Diseases

(c) The flow of protons through the F0 channel induces F1

particle to function as ATP synthase The energy of the

proton gradient is used in attaching a phosphate radicle

to ADP by high energy bond and this helps in producing

ATP

30 (a) The given figure is of citric acid cycle Here X is NADH,

Y is FADH2 and Z is GTP

(b) The reactions are as follows:

(i) Acetyl CoA + Oxaloacetate + H2O Citrate

synthase (A)Citric acid + CoA(ii) Succinic acid + FAD dehydrogenase B Succinate ( )

Fumaric acid + FADH2

(c) In the citric acid cycle, oxidative decarboxylation takes place

three times During (i) oxidation of pyruvate to acetyl-CoA, (ii)

formation of a-ketoglutarate and (iii) when a-ketoglutarate

is both dehydrogenated and decarboxylated by an enzyme,

16. A-(iii); B-(i); C-(v);D-(iv); E-(ii)

17. A-(v, viii); B-(iv, vii, x); C-(i, ix); D-(ii); E-(iii, vi)

18.(A) (i) IAA (ii) shoot tip

(iii) elongation (iv) polar

(v) basipetal (vi) acropetal

(vii) inhibits (viii) leaf fall

(ix) ethylene (x) abscission zone

(B) The long day plants come to flower after receiving

photoperiod below above a critical length These plants

also called long short night plants because they require

darkness above below a critical level They can cannot

flower under complete darkness Flowering is inhibited

stimulated if dark period is interrupted by light Supply of

auxins gibberellins induce flowering in many cases under

inductive non-inductive photoperiods

19. (c) 20. (d) 21. (a) 22. (b) 23. (d)

24. (b) 25. (c) 26. (c) 27. (b) 28. (a)

29 (a) Given figure shows embryo development with geometric

and arithmetic phases A represents geometric phase and B

represents arithmetic phase

(b) Arithmetic growth is a type of growth in which the

growth rate is constant and growth occurs in arithmetic

progression Mathematically it is expressed as

30 (a) Flowers will be produced in condition B only Photoperiod is higher than critical night length in A and night phase is interrupted by flash of light in C These conditions will not produce flowers in a short day plant

(b) Short day plants require a continuous critical dark period for flowering If the plant is exposed to a flash of light before achieving a critical dark period, flowering is prevented It is called light break reaction

(c) The effect of light flash (red) can be inhibited by immediately providing far-red light But it does not impart an effect if far-red light exposure is given before red light exposure - because plant response is determined by the last exposure only



Mimic Octopus

Thaumoctopus mimicus, the mimic octopus, was first

discovered in Indonesia The octopus mimics the physical likeness and movement of more than 15 different species depending on the threat it faces If it is threatened by a damselfish, the mimic octopus will imitate a banded sea snake, which is a predator of the damselfish, in order to save its own life Most of the imitations that the mimic octopus makes are that of venomous sea animals such as flat fish,lion fish, sea snake, etc., making it a highly optimised and successful survival strategy Originally it is a small brown octopus with white spots or stripes that grows up to an average length

of about 60 - 70 cm or 2 ft The mimic octopus makes use

of chromatophores present in the pigment sacs on its skin

to transform its appearance These pigment sacs can be expanded or contracted by the octopus to get the desired change of color and appearance

A virus is a small infectious agent that typically consists of a segment of nucleic acid with a protein or lipoprotein coat Viruses replicate only inside the living cells of other organisms as they require host resources for their replication They can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.

STRUCTURE OF VIRUSES

Viruses usually range between 10-400 nm in size while

few are exceptionally large They can be observed only

by electron microscopy and X-ray crystallography A fully

assembled infectious virus is called a virion The simplest

virions consist of two basic components - a core portion

containing nucleic acid (either DNA or RNA) and a protein

coat called capsid Capsid consists of numerous subunits

called capsomeres.

Viruses are grouped on the basis of size and shape,

chemical composition, type of genome and mode of

replication

(i) Helical or Cylindrical Symmetry

Helical morphology is seen in many filamentous and pleomorphic viruses The capsomeres and nucleic

acids are wined together to form helical or spiral tube like structure The rod shaped helical capsid of

these viruses consist of numerous identical capsomeres wrapped around helical filament, e.g., Tobacco

Mosaic Virus (TMV)

(ii) Icosahedral Symmetry

Many viruses appear as spherical, cuboidal or polygonal in shape which are actually icosahedral

An icosahedron is a polyhedron which have 20 equilateral triangular faces and 12 vertices An

icosahedral capsid comprises of both pentamers (pentagonal capsomeres at the vertices) and

hexamers (hexagonal capsomeres at the vertices) The icosahedral capsid is the most efficient way

to enclose a space The total number of capsomeres of different icosahedral viruses varies greatly,

e.g., Turnip Yellow Mosaic Virus (TYMV) have 32 capsomeres, Papilloma Virus have 72 capsomeres,

Adenovirus have 252 capsomeres, etc

Spike

Lipid bilayer envelope Matrix protein Capsid protein

Fig.: Tobacco Mosaic VirusCapsomere

VIRUS

The syllabus for NEET is very vast which

impedes students from acquiring indepth

knowledge and covering the entire syllabus at

the same time An important topic for NEET

is therefore presented here in elaborate form

to enable students grasp the topic, analyse the

type of questions and SCORE HIGH.

(iii) Complex Symmetry

Although most of the viruses have either icosahedral or helical capsids, many viruses do not fit into either of

the two categories, they combine both polygonal and filamentous shapes E.g., Poxviruses, Bacteriophages T4

bacteriophage comprises of polygonal head which contains DNA genome and rod shaped tail of long fibres

Components of Virus

Four components of viruses are :

(a) Nucleoid : Viral genome is made of a single molecule of nucleic acid It may be linear or circular with

various degrees of coiling The nucleic acid is the infective part of virus The nucleic acid is either DNA or RNA but never both Viruses have all four possible nucleic acid types - single stranded DNA, double stranded DNA, single stranded RNA and double stranded RNA

(i) Double stranded or dsDNA occurs in T2 , T4 bacteriophages, Coliphage Lambda, Pox Virus, Adenovirus, etc

(ii) Single stranded or ssDNA occurs in Coliphage f × 174, Coliphage fd, etc The single strand of DNA is called plus strand A

complementary or negative DNA strand is synthesised to produce DNA duplex for replication

(iii) Double stranded or dsRNA is found in Reovirus and Tumour Virus Both are linear type.

(iv) Single stranded or ssRNA is more common in riboviruses The single stranded RNA is generally linear, e.g., Poliomyelitis virus,

influenza virus, etc Retroviruses have two copies of ssRNA, e.g., HIV, Rous Sarcoma Virus of mouse.

(b) Capsid (Sheath, Coat) : It is the proteinaceous covering around the virus which protects the nucleoid from damage by physical and chemical agents The capsid consists of a number of subunits called capsomeres or capsomers The capsid of TMV has 2130

capsomeres In binal bacteriophages, the capsid sheath of tail is contractile

(c) Envelope: Some animal viruses, a few plant and bacterial viruses are bounded by an outer loose membranous layer called an

envelope In contrast to enveloped viruses, the viruses without an envelope are called naked Envelope consists of proteins (from

virus), lipids and carbohydrates (from host) It has subunits called peplomeres or peplomers Surface of envelope can be smooth

or have outgrowths called spikes Common enveloped viruses are HIV, Herpes Virus, Vaccinia Virus, etc.

(d) Enzymes : They are occasional Enzyme lysozyme is present in the region that comes in contact with host cell in bacteriophages

Other enzymes are neuraminidase (in Influenza Virus), RNA polymerase, RNA transcriptase, reverse transcriptase, etc

In some cases, enzymes are associated with the envelope or capsid but most viral enzymes are located within the capsid

• Antibiotics cannot kill viruses because viruses have different mechanisms and machinery to survive and replicate The antibiotic has no ‘target’ to attack in a virus Viruses use their host machinery for replication

Snap Shots

TYPES OF VIRUSES

Viruses are host specific They can be divided into three groups

(i) Plant Viruses

Plant viruses infect plant cells, disturb their metabolism and cause severe diseases in them Like other viruses, plant viruses are obligate intracellular parasites that do not have molecular machinery to replicate without a host Viral diseases result in huge losses

in crop production and quality Infected plants show varied symptoms and most often there is leaf yellowing, leaf distortion, etc The important plant viruses are Tobacco Mosaic Virus (TMV), Potato Virus, Southern Bean Mosaic Virus (SBMV), Turnip Yellow Virus (TYV),

etc Plant viruses are spread mainly by insects, e.g., aphids.

(ii) Animal Viruses

Animal viruses infect the animal cells and cause different fatal diseases in animals including man Generally they have a polyhedron

or spherical shape Animal viruses complete their reproductive cycle in animal cell They enter the host cell through endocytosis or viral penetration, then take over the defence mechanism of the host and hijack the host cellular machinery to synthesise viral components such as nucleic acids and viral proteins The viral components are then assembled into mature viruses which are released through rupturing host cell or budding the cell membrane The released virus then infect other cells in body or remain dormant The protein coat or capsid of animal viruses is surrounded by an envelope Certain common viral infections of human beings are : common cold,

Head

Sheath Tail fibre

Fig.: Bacteriophage

influenza, mumps, measles, rubella (German measles), chicken pox, small pox, polio, viral hepatitis, herpes simplex, viral encephalitis, fever blisters, warts and some types of cancer Among livestock and fowl, viruses cause encephalitis, foot and mouth disease, fowl plague, Newcastle disease, pseudorabis, hog cholera and a variety of warts and other tumors A virus usually displays some specificity for a particular animal group.

(iii) Bacterial Viruses or Bacteriophages

Viruses that infect the bacterial cells are called bacteriophages or simply phages The phages have specific hosts and they are of variable shapes, sizes and structures The most widely studied phages are T-even bacteriophages such as T2,T4, T6, etc., which infect

the colon bacillus, Escherichia coli and are also known as coliphages.

T4 bacteriophage is a large-sized tadpole-shaped complex virus The capsid of the virus consists of an icosahedral head, a short neck with collar and a long helical tail The tail is made up of a thick and hollow mid-piece, a hexagonal base plate or

end plate to which six spikes and six long tail fibres are attached A dsDNA is present inside the head

Viruses are Intermediate Between Living and Non-Living

Viruses are considered as intermediate between living and non-living entities Viruses do not give rise directly to new viruses They are not cellular, although they multiply but their multiplication is very different from cell replication mechanism

They resemble non-living objects in -

(1) lacking protoplast (2) ability to get crystallised, e.g., TMV, Poliomyelitis Virus (3) inability to live independent of a living cell

(4) high specific gravity which is found only in non-living objects (5) absence of respiration (6) absence of energy storing system (7) absence of growth and division Instead different parts of viruses are synthesised separately

They resemble living objects

in-(1) presence of genetic material (2) formed of organic macromolecules (3) ability to multiply or reproduce (4) occurrence of mutation (most mutable virus is HIV) (5) occurrence of enzyme transcriptase in most viruses (6) some viruses contain vitamins like riboflavin

and biotin (e.g., Pox virus) (7) occurrence of antigenic properties (8) infectivity and host specificity (9) they breed true to their type.

LIFE CYCLES OF VIRUSES

Life cycle or reproduction of viruses can be phagic or pinocytic In phagic reproduction, only the viral genome enters into the host

cell whereas in pinocytic reproduction, the whole virus (except envelope, if present) passes into the host cell Phagic reproduction

has two sub-types - lytic and lysogenic.

(i) Lytic Cycle

It is the reproductive cycle of virulent phages, e.g., T4 bacteriophage The phage attaches itself to the host cell through its tail fibres The fibres bend and bring the tip of tail in contact with the host cell wall The tip of the tail produces a hole in the bacterial cell wall

by means of enzyme lysozyme The tail sheath contracts and injects the viral genome into host cell After entering the host cell, the

viral DNA transcribes some early mRNAs to form some enzymes over the host ribosomes Some of these are nucleases They degrade host DNA and mRNAs Phage DNA and mRNA are protected from nucleases due to methylation of their cytosine bases Parent viral

DNA functions as a template and replicates repeatedly with the help of bacterial nucleotides Further, either the normal ability of the host DNA to control the cell is lost, or the host DNA is completely destroyed by early products of the viral genes Thus, phage DNA

is both replicated and transcribed; first the enzymes needed for synthesis of phage DNA are translated, then the capsid proteins are translated Phage particles are assembled around condensed cores of the complete phage nucleic acid At last lytic enzymes which have been coded by phage DNA, break open the bacterium and release the new phage particles which diffuse in the surrounding in search of new host

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August - 2018

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Fig.: Lytic Cycle

Sheath contracted Tail core Phage DNA

Capsid (head)

Plasma membrane

Sheath Tail fibre Baseplate Cell wall Pin

Host bacterial cell

Bacteriophage

Phage DNA Host DNA

Attachment

The phage attaches to

the surface of the host.

(ii) Lysogenic Cycle

Bacteriophage such as P1 and l-phage, have

entirely different pattern of life cycle than the

virulent phages Lambda phage (l phage) has

a higher degree of regulation of its genes

The phage is parasitic over Escherichia coli

It does not possess tail fibres for attachment

to bacterial cell The tail directly comes in

contact with bacterial cells, drills a hole in

the wall and injects the phage DNA into the

cell In lysogenic cycle, the phage DNA does

not take over the control of cellular machinery

of the host Instead, it produces a repressor

and undergoes reduction to temperate or

nonvirulent state.

The viral genome becomes integrated with

the chromosomal DNA of the bacterium

at specific site with the help of the enzyme

integrase The viral genome is called

prophage in this stage Prophage replicates

along with bacterial chromosome and gets distributed to the daughter bacteria Prophage does not form virus particles because the genes connected with taking over of host machinery remain repressed due to formation of a repressor At times the synthesis

of repressor is stopped Repressor can also be destroyed by chemicals, high energy radiations and other adverse conditions This

converts the temperate or non virulent virus into virulent or lytic virus Therefore, the bacterial cell carrying prophage is called

lysogenic cell and the phenomenon of existence of virus genome in prophage state along with host DNA is termed as lysogeny.

(i) The viral genome or its complementary DNA gets integrated

with the host DNA It is called prophage or provirus

The viral genome does not integrate with host DNA

(ii) The host DNA is not hydrolysed during lysogenic phase The host DNA is often hydrolysed in the lytic phase

(iii) The prophage or provirus replicates only once along with

the replication of host genome so that a single particle is

transferred to a daughter cell

The viral genome replicates repeatedly and forms a number of copies in the same host cell

Fig.: Lysogenic cycle

Phage infect the host by injecting its DNA into cytoplasm

Phage DNA integrates into the bacterial chromosome, becoming a prophage.

The bacterium reproduces, copying the prophage and transmitting it to daughter cells.

Certain factors determine whether

Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle.

Phage DNA circularises

or

Daughter cell with prophage

Cell divisions produce

a population of bacteria infected with the prophage

(iv) The cellular machinery of the host is only slightly disturbed The cellular machinery of the host is completely taken over by

the viral genome

(v) The virus is non-virulent or temperate The virus is virulent

(vi) The host cell does not get lysed The host cell undergoes lysis

(vii) Virus particles are liberated rarely A number of virus particles are liberated when the host cell

becomes lysed

Human Immunodeficiency Virus

Human Immunodeficiency Virus (HIV) is a virus that attacks

human immune cells and cause acquired immunodeficiency

syndrome (AIDS) It belongs to the retrovirus family The virus is

discovered in 1983 The genome and proteins of HIV have been

the subject of exclusive research Each virion comprises a viral

envelope and associated matrix enclosing a capsid It has two

copies of single stranded RNA genome and several enzymes HIV

is different in structure from other retroviruses HIV virion is ~100 nm

in diameter Its innermost region consists of a cone-shaped core

that includes two copies of the ssRNA genome, enzyme reverse

transcriptase, integrase, protease, some minor proteins and the

major core proteins Inside the virus membrane there is a protein

layer called the matrix made up of matrix protein p17 The capsid

of the virion is composed of molecules of a protein known as

p24

Once HIV binds to the host cell, the viral envelope fuses with the cell membrane and the virus RNA and enzymes enter the cytoplasm With the help of reverse transcriptase dsDNA in produced from ssRNA The enzyme integrase then facilitates the

integration of this viral DNA into the cellular DNA It is called provirus Production of viral proteins and RNA takes place when

the provirus is transcribed The virus eventually buds out of the cell

• Virologists purify viruses in order to study their structures Most widely used four methods of purification are - (i) differential and density gradient centrifugation, (ii) precipitation, (iii) denaturation of contaminants and (iv) enzymatic digestion of host cell constituents

Snap Shots

VIROIDS

Viroids are the smallest self replicating particles discovered by Diener in 1971 Viroids are infectious RNA particles devoid of any

protein coat The circular RNA is only 300 to 400 nucleotides long that lack AUG codon They are replicated autonomously despite the fact that they do not code for any protein Having no protein coat or capsid, they exist as naked RNA molecules and pass from plant to plant only when the surfaces of both donor and recipient cells are damaged so that there is no membrane barrier for the viroid to pass

The first discovered viroid is Potato Spindle Tuber Viroid (PSTV) Viroids form a class of subviral pathogens which cause infections

and diseases in many plants, e.g., Potato spindle tuber disease, Chrysanthemum stunt, etc Animal or human infection is not known

Viroid does not produce a protein as it does not possess an initiation codon The mechanism of disease production is not very clear Viroid particle can multiply by both RNA dependent and DNA dependent replications

PRIONS

Prions are misfolded proteins that are associated with several fatal neurodegenerative diseases in animals and humans The word prion

is derived from ‘proteinaceous infectious particle’ Prions were named by S.B Prusiner in 1983 They are highly resistant glycoprotein

particles which function as infectious agents They are formed due to mutation in gene PRNP Prions can also act as catalyst converting

normal protein into prion state Prions are not affected by proteases, nucleases, temperature upto 800°C, UV radiations and formaldehyde.Prions accumulate in nervous tissue and bring about its degeneration Common diseases caused by them are scrapie of sheep, mad cow disease, Cruetzfeldt-Jakob disease (CJD) and kuru

protein p17 Capsid protein p24

Docking glycoprotein gp120 p10 protease

MHC proteins

Transmembrane glycoprotein gp41

Fig : Human Immunodeficiency Virus (HIV)

Reverse transcriptase (p64) ssRNA

1 In lytic phase of viral reproduction

(i) the viral genome does not integrate with host DNA

(ii) the host DNA is not hydrolysed in the lytic phase

(iii) the virus is virulent

(iv) the host cell does not get lysed

(a) (i) and (ii) are correct (b) (ii) and (iii) are correct

(c) (ii) and (iv) are correct (d) (i) and (iii) are correct

2 Which of the following plant disease is caused by viroid?

(a) Potato mosaic disease

(b) Potato leaf roll disease

(c) Bhendi yellow vein mosaic disease

(d) Potato spindle tuber disease

3 Tobacco mosaic virus have (i) symmetry in capsid and (ii)

4 Read the given statements and select the correct option

Statement A : Viral genome is usually made of a single

molecule of nucleic acid

Statement B : The single molecule of nucleic acid in virus

is only linear form of either DNA or RNA

(a) Both statements A and B are true and B is the correct

explanation of A

(b) Both statements A and B are true but B is not the

correct explanation of A

(c) Statement A is true but B is false

(d) Both statements A and B are false

5 Viroids differ from viruses in having

(a) DNA molecules without protein coat

(b) RNA molecules with protein coat

(c) RNA molecules without protein coat

(d) DNA molecules with protein coat (NEET 2017)

6 Diener discovered

(a) free infectious RNA (b) infectious protein

(c) free infectious DNA (d) infectious glycoprotein

7 Read the given statements related to retroviruses and select

the correct option

(i) These are causative agents for certain kind of cancer in

humans

(ii) They carry gene for DNA dependent RNA polymerase

(iii) DNA is not present at any stage in their life cycle

(iv) The genetic material in mature retrovirus is RNA

(a) (i) and (iii) are incorrect

(b) (ii) and (iii) are incorrect

(c) (iii) and (iv) are incorrect

(d) (i) and (iii) are incorrect

8 Which of the following statements is wrong for viroids?(a) They cause infections

(b) Their RNA is of high molecular weight

(c) They lack a protein coat

(d) They are smaller than viruses (NEET 2016)

9 Which of the following in not true about prions?

(a) These are infectious small sized glycoprotein particles.(b) They are not affected by nuclease but are affected by protease

(c) They are formed due to mutation in gene PRNP.

(d) They accumulate in nervous tissue and cause degeneration

10 Select the mismatched pair

(a) T4 bacteriophage – ds DNA(b) Reo virus – ds RNA

Contributed by : Sukumar Patra (Dhanbad, Jharkhand)

SOLUTIONS TO AUGUST 2018 CROSSWORD

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(c) Pox virus – ss DNA

(d) Retrovirus – ss RNA

11 Select the wrong statement

(a) The term ‘contagium vivum fluidum’ was coined by

M W Beijerinck

(b) Mosaic disease in tobacco and AIDS in human beings

are caused by viruses

(c) The viroids were discovered by D.J Ivanowsky

(d) W.M Stanley showed that viruses could be crystallised

(NEET 2015)

12 Bacteriophage possesses

(a) organelles for its replication mechanism

(b) ribosomes to produce protein and enzymes

(c) DNA as a genetic material

(d) all of these

13 Which of the following is not true about HIV?

(a) These are the most mutable viruses

(b) They attack immune cells and cause immunodeficiency

(c) They contain one copy of non covalently linked, positive

sense ssRNA

(d) The viral genome encodes a small number of viral proteins

14 Which of the following shows coiled RNA strand and

capsomeres?

(a) Polio virus (b) Tobacco mosaic virus

(c) Measles virus (d) Retrovirus (NEET 2014)

15 Coliphages are

(a) bacteriophages of E.coli (b) algal viruses

(c) viruses attacking fungi (d) mycophages of yeast

16 In pinocytic reproduction

(a) only the nucleic acid enters the host cell

(b) the whole virus excluding envelope enters the host cell

(c) the proteinaceous capsid enters the host cell

(d) the proteinaceous envelope enters the host cell

(a) helical symmetry (b) polyhedral symmetry

(c) rounded symmetry (d) complex symmetry

19 Refer to the given figure and select the correct option

(a) ‘A’ contains double stranded RNA particle

(b) ‘C’ is contractile in nature

(c) ‘B’ has the helical symmetry

(d) ‘D’ helps to produce a hole in the bacterial cell wall

20 Which of the following is correct for viruses?

(a) They have the ability to synthesise nucleic acid and protein by their own

(b) They all have helical symmetry

(c) They have ability to get crystallise

(d) They are not host specific

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UTTAR PRADESH at

1 Metabolically active cells are small in size due to

(a) lower nucleocytoplasmic ratio and lower surface

of flagellum of a Gram negative

bacteria The basal body bears

rings-like swellings in the region of plasma

membrane and cell wall

The rings embedded in the plasma

membrane are

(a) A, B, C, D (b) A, B, C

(c) C, D (d) B, C, D

3 Read the following statements and select the correct option

(i) Salivary glands, intestinal glands and most of the sweat

glands are merocrine glands

(ii) Areolar tissues possess macrophages but lack mast cells

(iii) Brown fat occurs in infants and generates more heat

than white fat

(iv) Smooth muscle fibres may have branches and are

bound together in a connective tissue sheath

(a) (i) and (iv) are correct

(b) (ii) and (iii) are correct

(c) (i), (ii), (iii) are incorrect

(d) (ii) and (iv) are incorrect

This specially designed column enables students to self analyse their extent

of understanding of specified chapters Give yourself four marks for correct

answer and deduct one mark for wrong answer Self check table given at the

end will help you to check your readiness

• Cell - The Basic Unit of Life

4 Primary lysosomes are newly pinched off vesicles from(a) convex side of Golgi apparatus

(b) concave side of Golgi apparatus(c) smooth endoplasmic reticulum(d) granular endoplasmic reticulum

5 Identify the given glands A and B and choose the correct option accordingly

Gland type Location Secretion

(a) A- Unicellular Intestine Intestinal juice(b) B-Endocrine Alimentary canal Mucous(c) A-Multicellular Buccal cavity Saliva(d) B-Multicellular Skin Sweat

6 Which among the following statements is incorrect in relation

to difference between euchromatin and heterochromatin?(a) Euchromatin is lightly stained and diffused but hetero-chromatin is darkly stained and condensed

(b) Euchromatin lacks active genes and does not take part

in transcription but heterochromatin contains active genes and takes part in transcription

(c) Crossing over is common in euchromatin but chromatin inhibits crossing over

hetero-(d) Euchromatin forms bulk of chromatin but matin is present at certain places in chromatin

heterochro-7 Select the incorrect match among the given pairs.

(a) Protoplasmic astrocytes – White matter of CNS

(b) Bipolar neurons – Cochlear ganglia

(c) Lymphocytes – Secrete antibodies

(d) Mucoid connective tissue – Umbilical cord

8 The larger subunit of ribosome in Chlamydomonas is

(a) 50 S (b) 60 S (c) 40 S (d) 80 S

9 Read the following statements and select the correct option

Statement A : The medullated nerve fibres of brain and

spinal cord lack neurilemma

Statement B : The medullated fibres of brain and spinal

cord do not regenerate after injury due to lack of neurilemma

(a) Both statements A and B are correct and B is the correct

explanation of A

(b) Both statements A and B are correct but B is not the

correct explanation of A

(c) Statement A is correct but B is incorrect

(d) Both statements A and B are incorrect

10 Match the column I with column II

Column I Column II

A Simple ciliated epithelium (i) Urinary bladder

B Pseudostratified epithelium (ii) Ventricles of brain

C Transitional epithelium (iii) Iris of eyes

D Simple cuboidal epithelium (iv) Human male urethra

(a) A-(ii), B-(iv), C-(iii), D-(i)

(b) A-(ii), B-(iv), C-(i), D-(iii)

(c) A-(iii), B-(iv),C-(i), D-(ii)

(d) A-(iii), B-(i), C-(iv), D-(ii)

11 Which of the following is correct for frog?

(a) Inner finger of female frogs contains amplexusory pads

(b) Frogs have acrodont teeth fixed in socket like humans

(c) Buccopharyngeal respiration in male frog is performed

by sternohyal and petrohyal muscles

(d) Both male and female frogs have a pair of vocal sacs

12 Identify the given blood corpuscles and choose the correct

option

(a) ‘A’ transports oxygen and some amount of carbon

dioxide

(b) ‘B’ is a granulocyte secreting heparin and histamine

(c) ‘C’ is largest of all types of leucocytes

(d) ‘A’ is a granulocyte with phagocytic activity

13 Lysosomes show polymorphism Identify the type of

lysosome from given characters

(i) Formed by fusion of phagosome with lysosome

(ii) Digestion occurs in this lysosome

(iii) Also known as digestive vacuole

(a) Primary lysosome (b) Secondary lysosome(c) Residual lysosome (d) Autolysosome

14 Which of the following is not an example of multi-unit smooth muscles?

(a) Muscles of the walls of large blood vessels(b) Ciliary muscles in the eye

(c) Muscles of urinary bladder (d) Arrector pili muscles of skin dermis

15 Which of the following statements are correct?

(i) Dedifferentiated cells are post-mitotic cells specialised

to perform specific functions

(ii) Outermost mucilage layer of bacterial cell provides protection from toxic chemicals, viruses and phagocytes.(iii) Bacterial plasma membrane is selectively permeable and metabolically active

(iv) Plasmids permanently associated with nucleoid are called episomes

(v) Activities of an organism are sum total of activities and interactions of its constituent cells

(a) (i), (ii) and (v) (b) (ii), (iii) and (iv)(c) (ii), (iii) and (v) (d) (i), (iii) and (iv)

16 present in cell wall of Gram +ve bacteria forms surface antigens and receptor sites

(a) Teichoic acid (b) Mycolic acid(c) Mucopeptide (d) Lysine

17 Identify the mis-matched pair in relation to cockroach.(a) Labium – Responds to taste and smell(b) Pulvillus – Firmly grasps substratum(c) Stomodeal valve – Present between mid gut and

ileum(d) Uricose glands – Discharge uric acid over

spermatophore during copulation

18 Which of the following is not a common feature between mitochondria and plastid?

(a) Presence of double membrane envelope(b) Possess their own DNA, RNA and 80S ribosomes(c) Presence of naked DNA

(d) Production of ATP and taking part in energy transduction

19 Match the organelle given in column I with their functions

in column II

Column I Column II

A Lysosomes (i) Vitellogenesis

B Golgi apparatus (ii) Carbohydrate synthesis

C Mitochondria (iii) Sperm lysins

D Glyoxysomes (iv) Amino acid synthesis(a) A-(ii); B-(i); C-(iv); D-(iii)

(b) A-(iii); B-(ii); C-(iv); D-(i)(c) A-(i); B-(iv); C-(ii); D-(iii)(d) A-(iii); B-(i); C-(iv); D-(ii)

20 Read the given statements and select which ones are true

(T) or false (F)

(i) Change of colour from green to red during ripening

of tomato is due to transformation of chromoplast to

chloroplast

( ii) Flagella present in choanocytes of porifers help in

movement of water

(iii) Enzymes for detoxification of toxic chemicals are

present in rough endoplasmic reticulum

(iv) Astrocytes communicate with one another through

calcium channels

(v) Simple ciliated epithelium is also called urothelium

(i) (ii) (iii) (iv) (v)

(a) T T F T F

(b) F T F T F

(c) F T T F T

(d) T F T F T

21 Select the incorrect option for the type of epithelium shown

in the given figure

(a) Epithelium contains mucus secreting cells

(b) In intestine, epithelium has microvilli to increase

absorptive surface area

(c) It has secretory role in gastric glands and pancreatic

lobules

(d) The cells of deepest layer are columnar and in outer

few layers, cells replace cytoplasm with keratin

22 Which type of neurons are present in dorsal root ganglia of

spinal nerves in adult vertebrates?

(a) Pseudounipolar (b) Unipolar

(c) Multipolar (d) Bipolar

23 Read the given statements about earthworm and select the

option which correctly fills the blanks

(i) nephridia are ectonephric and keep the skin

moist for cutaneous respiration

(ii) Part of digestive system that helps in grinding food is

present in segment(s)

(iii) The secretion of _ keep two earthworms close

together during copulation

(i) (ii) (iii)

(a) Septal 4th seminal vesicle

(b) Pharyngeal 5th – 7th prostate gland

(c) Integumentary 8th accessory glands

(d) Pharyngeal 7th – 9th vasa deferentia

24 Read the following statements and state them as true (T) or false (F)

A Tonofibrils are microfilaments made up of actin and keratin proteins

B Reticular connective tissues are present in the liver, spleen, thymus, lymph nodes

C Cilia and microvilli may be covered by glycocalyx

D Hyaline cartilage is present in the pubic symphysis and intervertebral discs

A B C D

(a) F T T F(b) T T F F(c) F T F F(d) F F F T

25 Endomembrane system comprises of(a) endoplasmic reticulum, Golgi complex, mitochondria and plastids

(b) lysosomes, vacuoles, peroxisomes and Golgi complex.(c) mitochondria, Golgi complex, lysosomes and endoplasmic reticulum

(d) Golgi complex, lysosomes, vacuoles and endoplasmic reticulum

26 Which part of nucleus is the principal site for the development of ribosomal RNAs?

(a) Nucleoplasm (b) Nucleolus(c) Nuclear matrix (d) Nuclear envelope

27 Plastids present in aleurone cells of maize grain are(a) proteoplast (b) amyloplast(c) elaioplast (d) phaeoplast

28 Read the following statements and select the correct option

Statement A : Centrioles are capable of replication Statement B : Centrioles contain DNA, RNA and proteins.

(a) Both statements A and B are correct and B is the correct explanation of A

(b) Both statements A and B are correct but B is not the correct explanation of A

(c) Statement A is correct but B is incorrect

(d) Both statements A and B are incorrect

29 _ secreted by mast cells of connective tissue act as

vasoconstrictor to arrest bleeding and increase blood pressure

(a) Serotonin (b) Histamine

(c) Reticulin (d) Heparin

30 Joints between skull bones are immovable due to the

presence of

(a) yellow elastic connective tissue

(b) white fibrous connective tissue

(c) calcified cartilage

(d) white fibrocartilage

31 Identify the incorrect statement in context of fluid mosaic

model of biomembrane

(a) Tunnel proteins are integral proteins that run

throughout the length of lipid bilayer

(b) Extrinsic proteins form covalent bonds with hydrophobic

tail of lipid molecules

(c) External surface of proteins of a biomembrane have

oligosaccharides

(d) Biomembrane being quasifluid can grow during cell

growth and cell division

32 Read the given statements and select the option which

correctly fill the blanks

(i) Ca2+ ions required during muscle contraction is stored

in _

(ii) _ synthesises acrosome of spermatocytes

(iii) Water soluble pigment anthocyanin is present in _

(iv) New mitochondria develops from pre-existing

mitochondria by _

(i) (ii) (iii) (iv)

(a) Endoplasmic Mitochondria air vacuole division

(d) Golgi apparatus Mitochondria plastids budding

33 Study the given table and identify P, Q, R and S

(i) Loose

connective

tissue

P Forms shock absorbing cushion around eyeballs

(ii) Skeletal tissue Hyaline

cartilage

Q

(iii) Bones R Formed in soft

organs, such as heart of ruminants

(iv) S Ligament Connects bone to

another bone

(a) Areolar tissue

Hyoid apparatus

Sesamoid bones

Yellow fibrous sheets (b) Adipose

tissue

Nasal septum

Replacing bones

Dense irregular connective tissue (c) Areolar

tissue

Tracheal rings

Investing bones

White fibrous cords

(d) Adipose tissue

Sternal parts of ribs

Visceral bones

Yellow elastic connective tissue

34 Lampbrush chromosomes were first observed by(a) Flemming (b) Kollar

(c) Ruckert (d) Balbiani

35 Match the following

Column I Column II

A Periplaneta americana (i) Chloragogen cells

B Rana tigrina (ii) Cannibalism

C Pheretima (iii) Paurometabolous

(iv) 10 pairs of cranial nerves (v) Porphyrin pigment (vi) Corpora cardiaca (vii) Bidder’s canal(a) A-(ii), (vi); B-(iii), (iv); C-(i), (v)

(b) A-(ii), (iii), (vi); B-(iv), (vii); C-(i), (v)(c) A-(iii), (vi); B-(ii), (v), (vii); C-(i), (iv)(d) A-(i), (v); B-(iii), (iv), (vii); D-(ii), (vi)

36 How many of the given statements are correct?

(i) Non-keratinised stratified squamous epithelium is impermeable to water

(ii) Connective tissue develops from embryonic mesoderm.(iii) Areolar tissue is present under the skin as subcutaneous tissue in between and around muscles

(iv) Erythrocytosis causes oxygen shortage in blood and tissues and stimulate secretion of hormone erythropoietin

(v) Both skeletal and smooth muscle fibres are syncytial in nature

(iii) Tubular appendage present in Gram –ve bacteria which helps in forming conjugation tube

(a) Microfilaments Auditory nerve Pili(b) Intermediate filaments Vagus nerve Fimbriae(c) Microtubule Glossopharyngeal Flagella

(d) Cilia Abducens nerve Pili