Higher Order Advance Round Explanations · sponge) and Euspongia (Bath sponge) are the examples of phylum Porifera. 23. (c) NCERT (XI) Ch - 4, Pg. 52 The body of the aschelminthes

Objective NCERT GEAR UP

BIOLOGY

Higher Order Advance Round Explanations

Advance Round Explanations1

The Living World (Questions on Page No. 11)

20. (d) NCERT (XI) Ch - 1, A - Pg. 3; B & C - Pg. 5

All living organisms grow. Increase in mass and increase in number of individuals are twin characteristics of growth. The sum total of all the chemical reactions occurring in our body is metabolism. Metabolic reactions can be demonstrated outside the body in cell-free systems. The most obvious and technically complicated feature of all living organisms is this ability to sense their surroundings or environment and respond to these environmental stimuli which could be physical, chemical or biological.

21. (c) NCERT (XI) Ch - 1, Pg. 7

In Ficus bengalensis L., letter L. signifies the taxonomist Linnaeus. The first word Ficus represents the genus while the second component bengalensis denotes the specific epithet. Both the words in a biological name, when handwritten, are separately underlined, or printed in italics to indicate their Latin origin.

22. (c) Based on characteristics, all living organisms can be classified into different taxa. This process of classification is taxonomy. Classification is the process by which anything is grouped into convenient categories based on some easily observable characters.

23. (b) NCERT (XI) Ch - 1, Pg. 9

Genera are aggregates of closely related species. Each genus may have one or more than one specific epithets representing different organisms, but having morphological similarities. For example, Lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris) with several common features, are all species of the genus Panthera.

24. (d) NCERT (XI) Ch - 1, Pg. 12Biological museums are generally set up in educational institutes such as schools and colleges. Museums have collections of preserved plant and animal specimens for study and reference. Specimens are preserved in the containers or jars in preservative solutions. Museums often have collections of

skeletons of animals too. 25. (b) The plants become dried by transferring

their moisture into the blotting sheets. Blotting papers need to be changed regularly until the plant gets dried. The changing time depends on the weather conditions.

26. (d) NCERT (XI) Ch - 1, A - Pg. 11; C - Pg. 14

The taxonomic hierarchy for Mangifera indica can written as Plantae → Angiospermae → Dicotyledonae → Sapindales → Anacardiaceae → Mangifera indicaTaxonomic keys are generally analytical in nature. Family Fabaceae is divided into three sub-families, i.e., Leguminosae, Mimosaceae and Caesalpiniaceae.

Biological Classification (Questions on Page No. 34-35)

28. (b) NCERT (XI) Ch - 2, Pg. 19

Methanogens are included in group Archaebacteria. They are special since they live in some of the most harsh habitats such as marshy areas. Methanogens are present in the gut of several ruminant animals such as cows and buffaloes and they are responsible for the production of methane (biogas) from the dung of these animals.

29. (c) Archaebacteria differ from other bacteria in having a different cell wall structure. Archaeal membrane lipids have ether bonds instead of ester bonds and this feature is responsible for their survival in extreme conditions.

30. (a,b) Heterotrophs are most abundant bacteria. Streptomyces is a genus of Gram-positive bacteria that grows in various environment and produced nearly two third of the naturally occurring antibiotics.

31. (d) NCERT (XI) Ch - 2, Pg. 21

Euglenoids are fresh water organisms found in stagnant water. Instead of a cell wall, they have a protein rich layer called pellicle which makes their body flexible. They have two flagella, a short and a long one. Though they are photosynthetic in the presence of sunlight, when deprived of sunlight they behave like

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heterotrophs by predating on other smaller organisms. Example: Euglena

32. (d) NCERT (XI) Ch - 2, Pg. 21

Slime moulds are saprophytic protists. The body moves along decaying twigs and leaves engulfing organic material. Under suitable conditions, they form an aggregation called plasmodium which may grow and spread over several feet. The spores formed during unfavourable conditions possess true walls. The spores are dispersed by air currents.

33. (a) NCERT (XI) Ch - 2, Pg. 34

In Ascomycetes, the asexual spores are conidia produced exogenously on the special mycelium called conidiophores. Conidia on germination produce mycelium. Sexual spores are called ascospores which are produced endogenously in sac like asci (singular ascus). These asci are arranged in different types of fruiting bodies called ascocarps. Mycelium is branched and septate. Some examples are Aspergillus, Claviceps and Neurospora.

34. (b) Lichens form the pioneer community in a lithosere whereas plankton stage is the pioneer stage for hydrosere. Lichens are very good pollution indicators – they do not grow in polluted areas.

35. (d) NCERT (XI) Ch - 2, Pg. 21

Euglenoids are photosynthetic in the presence of sunlight, when deprived of sunlight they behave like heterotrophs by predating on other smaller organisms.

36. (c) The antibiotics have no effect on viruses because they use their host cells to perform their activities for them.

37. (a) Chemoheterotrophs are unable to synthe-size their own organic molecules. Instead, these organisms get their energy from the oxidation of inorganic molecules such as car-bohydrates, amino acids, lipids, etc., in their environment.

38. (b) Chemosynthetic autotrophic bacteria ox-idise various inorganic substances such as nitrates, nitrites and ammonia and use the re-leased energy for their ATP production. They

play a great role in recycling nutrients like ni-trogen, phosphorous, iron and sulphur.

39. (c) NCERT (XI) Ch - 2, Pg. 20

Chrysophtes group includes diatoms and golden algae (desmids). In diatoms the cell walls form two thin overlapping shells, which fit together as in a soap box. The walls are embedded with silica and thus the walls are indestructible.Euglenoids have a protein rich layer called pellicle.Flagellated protozoans are the parasitic forms cause diseases such as sleeping sickness. Example: Trypanosoma

40. (c) If food begins to run out, mycelia respond by making spores, which are dispersed by wind or animals. Mycelia reproduce when food is low; spore production allows starving mycelia to disperse offspring to new habitats where more food might be available. Thus, spore production is favoured by natural selection when individuals are under nutritional stress.

41. (b) NCERT (XI) Ch - 2, Pg. 24

In Ascomycetes, sexual spores are called ascospores which are produced endogenously in sac like asci (singular ascus). These asci are arranged in different types of fruiting bodies called ascocarps. Ascocarps contains many structures with eight haploid spores lined up in a row.

42. (d) Prokaryotes are the simple organisms which have primitive nucleus. They do not have no well defined nucleus. This feature is not an adaptation and is common to all prokaryotes.

43. (a) Chemoautotrophic bacteria are able to manufacture their organic food from inorganic raw materials with the help of energy derived from exergonic chemical reactions involving oxidation of an inorganic substance present in the external medium. E.g., Nitrosomonas, Nitrobacter

44. (c) NCERT (XI) Ch - 2, Pg. 20

The slime moulds resemble both protozoa and the true fungi. They are like protozoa in their


amoeboid plasmodial stage and similar to true fungi in abundant spore formation. A spore of slime mould possesses a cell wall of cellulose.

45. (a) NCERT (XI) Ch - 2, Pg. 21

Instead of a cell wall, Euglena have a protein rich layer called pellicle which makes their body flexible.

46. (c) Absorptive heterotroph is an organism which obtains its food by secreting digestive enzymes into the environment to break down large food molecules, then absorbing the breakdown products.

47. (b) An endospore is a dormant, tough, and non-reproductive structure produced by certain bacteria. Endospore can survive environmental assaults that would normally kill the bacterium. These stresses include high temperature, high UV irradiation, desiccation, etc.

Plant Kingdom (Questions on Page No. 61-62)

25. (c) NCERT (XI) Ch - 3, Pg. 30

Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely aquatic (both fresh water and marine) organisms. The algae reproduce by vegetative, asexual and sexual methods. Chlamydomonas is a unicellular alga.

26. (d) NCERT (XI) Ch - 3, Pg. 32-33

The members of phaeophyceae or brown algae are found primarily in marine habitats. They possess chlorophyll a, c, carotenoids and xanthophylls. Vegetative reproduction takes place by fragmentation. Asexual reproduction in most brown algae is by biflagellate zoospores that are pear-shaped and have two unequal laterally attached flagella. In sexual reproduction, the gametes are pyriform (pear-shaped) and bear two laterally attached flagella.

27. (c) NCERT (XI) Ch - 3, Pg. 30

Volvox is colonial alga and forms spherical colony. It reproduces by oogamous in which fusion between one large, non-motile (static) female gamete and a smaller, motile male gamete.

28. (a) NCERT (XI) Ch - 3, Pg. 35

Bryophytes are also called amphibians of the plant kingdom because these plants can live in soil but are dependent on water for sexual reproduction.

29. (a) Bryophytes produce biflagellate antherozoids. The water is essential for fertilization in mosses. The antherozoids are released into water where they come in contact with archegonium. The bryophytes are divided into liverworts and mosses.

30. (c) NCERT (XI) Ch - 3, Pg. 35 & 38

Water is essential to develop a new plant body with respect to sexual reproduction for bryophytes and pteridophytes.

31. (d) NCERT (XI) Ch - 3, Pg. 42

Bryophytes and pteridophytes exhibit an intermediate condition (Haplo-diplontic); both phases are multicellular. However, they differ in their dominant phases.

32. (c) NCERT (XI) Ch - 3, Pg. 32

The vegetative cells of brown algae have a cellulosic wall usually covered on the outside by a gelatinous coating of algin. Dentist use the salts of alginic acid to take the measurement of dentury.

33. (a) NCERT (XI) Ch - 3, Pg. 36

Funaria is a bryophyte which requires water for sexual reproduction.

34. (a) Angiosperms are most diverse and widespread of all plant groups. Their dominance is due to the power of adaptability in diverse habitat. They are well-adapted to terrestrial life and occur in diverse habitats like cold tundra to hot tropical and even desert areas. They also thrive well in the aquatic habitat. Therefore they have dominated the land flora.

35. (a) Cyanophycean starch is similar to glycogen and amylopectin due to the presence of consists of alpha-1,4 linked glucan molecules.

36. (c) NCERT (XI) Ch - 3, Pg. 33

The members of rhodophyceae are commonly called red algae because of the predominance of the red pigment, r-phycoerythrin in their body.

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37. (a) NCERT (XI) Ch - 3, Pg. 36

In pteridophytes, the main plant body is a sporophyte which is differentiated into true root, stem and leaves. These organs possess well-differentiated vascular tissues.

38. (None) NCERT (XI) Ch - 3, Pg. 35

All option shows the ecological importance of moss plants. Some mosses provide food for herbaceous mammals, birds and other animals. Species of Sphagnum, a moss, provide peat that have long been used as fuel, and as packing material for trans-shipment of living material because of their capacity to hold water. Mosses along with lichens are the first organisms to colonise rocks and hence, are of great ecological importance. They decompose rocks making the substrate suitable for the growth of higher plants. Since mosses form dense mats on the soil, they reduce the impact of falling rain and prevent soil erosion.

Animal Kingdom (Questions on Page No. 87-88)

22. (c) NCERT (XI) Ch - 4, Pg. 50

They are aquatic, mostly marine, sessile or free-swimming, radially symmetrical animals. They have a central gastro-vascular cavity with a single opening, mouth on hypostome. Digestion is extracellular and intracellular. Sycon (Scypha), Spongilla (Fresh water sponge) and Euspongia (Bath sponge) are the examples of phylum Porifera.

23. (c) NCERT (XI) Ch - 4, Pg. 52

The body of the aschelminthes is circular in cross-section, hence, the name roundworms. Alimentary canal is complete with a well developed muscular pharynx. An excretory tube removes body wastes from the body cavity through the excretory pore. Sexes are separate (dioecious), i.e., males and females are distinct. Nephridia, present in phylum Annelida, help in osmoregulation and excretion.

24. (d) NCERT (XI) Ch - 4, Pg. 53

The body of arthropods is covered by

chitinous exoskeleton. The body consists of head, thorax and abdomen. They have jointed appendages (arthros-joint, poda-appendages).

25. (b) NCERT (XI) Ch - 4, Pg. 52

The body surface is distinctly marked out into segments or metameres and, hence, the phylum name Annelida. Neural system consists of paired ganglia (sing. ganglion) connected by lateral nerves to a double ventral nerve cord.

26. (c) NCERT (XI) Ch - 4, Pg. 56-57

Torpedo and Trygon belongs to class Chondrichthyes.

27. (d) In cockroach, corpora allata, an endocrine hormone, secretes juvenile hormone, which plays a crucial role in metamorphosis.

28. (b) The larval stage of the primitive lamprey known as ammocoetes larva. It forms a connecting link between protochordata and vertebrata.

29. (b) NCERT (XI) Ch - 4, Pg. 48

In some animals, the body cavity is not lined by mesoderm, instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called pseudocoelom and the animals possessing them are called pseudocoelomates, e.g., aschelminthes.

30. (d) NCERT (XI) Ch - 4, Pg. 53

Arthropoda is the largest phylum. The body consists of head, thorax and abdomen. They have jointed appendages (arthros-joint, poda-appendages). Excretion takes place through malpighian tubules.

31. (b) Honeybee, crayfish (subphylum Crusta-ceans), and spider (subphylum Chelicerates) belong to phylum Arthropoda.

32. (c) NCERT (XI) Ch - 4, Pg. 53

All insects have six legs (three pairs of jointed legs) and usually four wings (two pairs).

33. (c) NCERT (XI) Ch - 4, Pg. 57

Amphibians can live in aquatic as well as terrestrial habitats. Most of them have two


pairs of limbs. Body is divisible into head and trunk. The amphibian skin is moist (without scales). Respiration is by gills, lungs and through skin. The heart is three-chambered (two auricles and one ventricle).

34. (b) Squirrel and crows are warm-blooded (homoiothermous) animals, i.e., they are able to maintain a constant body temperature. Fishes, amphibians and reptiles are poikilothermous (cold-blooded).

35. (c) Sponges in which the cells are loosely aggregated and do not form tissues or organs are grouped under subkingdom Parazoa.

36. (b) NCERT (XI) Ch - 4, Pg. 51

Tapeworms are parasites and they absorb nutrients from the host directly through their body surface. Hence they do not need a digestive tract.

37. (b) In cockroach, excretion takes place through Malpighian tubules. The Malpighian tubules end blindly in the body cavity and open not directly to the exterior but to the alimentary canal at the junction between midgut and hindgut. When Malpighian tubules of cockroach open directly outside the body, excess water and mineral will lose from the body.

Morphology of Flowering Plants (Questions on Page No. 111)

37. (a) NCERT (XI) Ch - 5, Pg. 67

Tap roots of carrot, turnip and adventitious roots of sweet potato, get swollen and store food. Pneumatophores help to get oxygen for respiration. Prop roots provides mechanical support and help in photosynthesis.

38. (c) NCERT (XI) Ch - 5, Pg. 70The arrangement of veins and the veinlets in the lamina of leaf is termed as venation. When the veinlets form a network, the venation is termed as reticulate. It is found in dicotyledonous plants. When the veins run parallel to each other within a lamina, the venation is termed as parallel. It is the characteristic of most monocotyledons.

39. (c) NCERT (XI) Ch - 5, Pg. 67

Roots in some plants change their shape and structure and become modified to perform functions other than absorption and conduction of water and minerals. They are modified for support, storage of food and respiration.

40. (d) NCERT (XI) Ch - 5, Pg. 67

Leaves are the most important vegetative organs for photosynthesis.

41. (d) NCERT (XI) Ch - 5, Pg. 71

In some plants such as Australian acacia, the leaves are small and short-lived. The petioles in these plants expand, become green and synthesise food.

42. (b) NCERT (XI) Ch - 5, Pg. 79

The floral formula of family Fabaceae is

% + K C A G(5) 1+2+(2) (9)+1 1

43. (a) NCERT (XI) Ch - 5, Pg. 78-79

Zygomorphic flower with vexillary aestivation, diadelphous androecium and marginal placentation occurs in members of family Fabaceae.Examples: Sweet pea (Pisum sativum), Sesbania, Trifolium, etc.

Anatomy of Flowering Plants (Questions on Page No. 132)

23. (d) NCERT (XI) Ch - 6, Pg. 88

The companion cells are specialized parenchymatous cells, which are closely associated with sieve tube elements. The sieve tube elements and companion cells are connected by pit fields present between their common longitudinal walls. The companion cells help in maintaining the pressure gradient in the sieve tubes.

24. (d) In dicot root, vessels of xylem are angular or polygonal in shape, when we cut it in transverse section. In monocot root, vessels of xylem are rounded or oval.

25. (b) NCERT (XI) Ch - 6, Pg. 96

The spring wood is lighter in colour and has a lower density whereas the autumn wood is darker and has a higher density.

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26. (d) In young stems, the tissues are from the outside to the inside: epidermis, periderm, cortex, primary phloem, secondary phloem, vascular cambium, secondary xylem, and primary xylem.

27. (b) NCERT (XI) Ch - 6, Pg. 87

In stems, the protoxylem lies towards the centre (pith) and the metaxylem lies towards the periphery of the organ. This type of primary xylem is called endarch. In roots, the protoxylem lies towards periphery and metaxylem lies towards the centre. Such arrangement of primary xylem is called exarch.

Structural Organization in Animals (Questions on Page No. 156)

24. (b) NCERT (XI) Ch - 7, Pg. 101

The columnar epithelium is composed of a single layer of tall and slender cells. Their nuclei are located at the base. Free surface may have microvilli. They are found in the lining of stomach and intestine and help in secretion and absorption.

25. (a) NCERT (XI) Ch - 7, Pg. 101

The parietal layer of Bowman’s capsule is usually lined by a layer of simple squamous epithelium.

26. (b) NCERT (XI) Ch - 7, Pg. 101

The squamous epithelium is made of a single thin layer of flattened cells with irregular boundaries. They are found in the walls of blood vessels and air sacs of lungs and are involved in functions like forming a diffusion boundary.

27. (d) Transitional epithelium is a type of stratified epithelium. It consists of multiple layers of epithelial cells which can contract and expand as needed. Because of its function in the transition of degree of distension, it is named as transitional epithelium.

28. (c) NCERT (XI) Ch - 7, Pg. 101

The epithelial cells are compactly packed with little intercellular matrix.

29. (d) The basement membrane is formed by epidermis and connective tissue.

Cell: The Unit of Life (Questions on Page No. 177)

22. (c) Mitochondria and chloroplast both are considered as sites of production of cellular energy. They contain circular naked DNA, RNA and 70S ribosomes.

23. (c) NCERT (XI) Ch - 8, Pg. 136

The given figure represents the sectional view of chloroplast. The chloroplasts are also double membrane bound. Of the two, the inner chloroplast membrane is relatively less permeable. The space limited by the inner membrane of the chloroplast is called the stroma. A number of organised flattened membranous sacs called the thylakoids, are present in the stroma. The stroma of the chloroplast contains enzymes required for the synthesis of carbohydrates and proteins.

24. (c) In the absence of ribosomes, ER appears smooth and is called smooth endoplasmic reticulum (SER). The smooth endoplasmic reticulum is the major site for synthesis of lipid. In animal cells lipid-like steroidal hormones are synthesized in SER. It is also associated with the detoxification and metabolism of drugs.

25. (a) The chromosome synapsis is accompanied by the formation of complex structure called synaptonemal complex. Recombination nod-ules are proteinaceous structures found in association with the synaptonemal complex during prophase I of meiosis. They are in-volved in homologous synapsis and early events in recombination.

26. (c) During cell division, the failure of homologous chromosomes or sister chromatids to separate properly is called non-disjunction. It results in change in chromosomal number which leads to either aneuploidy or euploidy.

27. (b) NCERT (XI) Ch - 8, Pg. 134

Lysosomes are membrane bound vesicular structures formed by the process of packaging in the golgi apparatus. The isolated


lysosomal vesicles have been found to be very rich in almost all types of hydrolytic enzymes (hydrolases – lipases, proteases, carbohydrases) optimally active at the acidic pH. These enzymes are capable of digesting carbohydrates, proteins, lipids and nucleic acids.

Biomolecules (Questions on Page No. 197)

22. (d) NCERT (XI) Ch - 9, B - Pg. 155; C - Pg. 160; E - Pg. 154; F - Pg. 156.A - The Gibbs free energy of the product is the same as it would be without the enzyme. Thus, the enzyme does not affect the free energy of the reaction.B - The chemical or metabolic conversion refers to a reaction. The chemical which is converted into a product is called a ‘substrate’. Hence enzymes, i.e., proteins with three dimensional structures including an ‘active site’, convert a substrate (S) into a product (P).C - Enzymes lower activation energy of reactions and enhance greatly the rate of the reactions.D - Enzymes are highly specific both in the reactions that they catalyze and in their choice of reactants, which are called substrates.E - An enzyme like any protein has a primary structure, i.e., amino acid sequence of the protein. An enzyme like any protein has the secondary and the tertiary structure.F - The energy input needed to start a chemical reaction is called activation energy

23. (d) NCERT (XI) Ch - 9, Pg. 160Enzymes speed up reactions by lowering activation energy.

24. (d) Many plants produce nitrogen containing secondary metabolites such as alkaloids that to function as defenses against herbivores, especially mammals, because of their general toxicity and deterrence capability. These chemical defenses can act as repellents or toxins to herbivores, or reduce plant digestibility. Anti-nutritional compounds are not the example of

primary or secondary metabolites. 25. (a) NCERT (XI) Ch - 9, Pg. 157

The correct sequence is as follows:i. The substrate binds to the active site of the

enzyme, fitting into the active site.ii. The binding of the substrate induces the

enzymes to alter its shape, fitting more tightly around the substrate.

iii. The active site of the enzyme, now in close proximity of the substrate, breaks the chemical bonds of the substrate and the new enzyme-product complex is formed.

iv. The enzyme releases the products of the reaction and the free enzyme is ready to bind to another molecule of the substrate and run through the catalytic cycle once again

26. (c) A carbohydrate is a biomolecule consisting of carbon, hydrogen and oxygen atoms. If the carbonyl group is an aldehyde (more common in carbohydrates) then the monosaccharide is an aldose. If the carbonyl group is a ketone then the monosaccharide is a ketose.

27. (b) Lipids are generally water insoluble because they have long hydrocarbon chains. Therefore, when water and the other liquid containing lipids shake vigorously, after a few minutes they separate into two layers, e.g., oil in water.

28. (a) The constant flow of materials in and out of the cell keeps the metabolic pathways from ever reaching equilibrium, and the cell continues to do work throughout its life only when a continuous supply of energy is provided.

29. (d) NCERT (XI) Ch - 9, C & D - Pg. 152Anabolic pathways require energy to synthesize larger molecules. Catabolic pathways generate energy by breaking down larger molecules. The substrate for cholesterol synthesis is acetic acid.All biomolecules have a turn over. This means that they are constantly being changed into some other biomolecules and also made from some other biomolecules. This breaking and making is through chemical reactions constantly occurring in living organisms.

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Flow of metabolites through metabolic pathway has a definite rate and direction like automobile traffic. This metabolite flow is called the dynamic state of body constituents.

30. (d) NCERT (XI) Ch - 9, Pg. 158

The enzyme involved is hexokinase. It catalyzes the transfer of phosphate group.

31. (d) When steroid hormones cross plasma membrane they does not require ATP, i.e, they perform simple diffusion because these hormones are cholesterol derivative.

Cell Cycle and Cell Division (Questions on Page No. 218)

21. (b) The diagram depicts the anaphase stage. In the anaphase cell, there are 8 chromosomes and DNA content is 20 pg.At G1 stage, the number of chromosomes will be 4 and amount of DNA will be 10 pg.

22. (d) NCERT (XI) Ch - 10, A, C, D, E and H - Pg. 168

B - Pg. 167F, G - Pg. 166 The sequence of events that occur during meiosis are:B (DNA replication) →A (Compaction of chromosomes start) →E (Action of recombinase enzyme) →D (Dissolution of synaptonemal complex) →C (Meiotic spindle assembled) → G (Segregation of homologous chromosomes) →F (Separation of sister chromatids) →H (Formation of tetrad of cells)

23. (a) The DNA content is 2C after M-phase. G1 phase is the interval phase between mitosis and initiation of DNA replication. In G1 phase, the initial amount of DNA was 2C. In S phase, DNA replicates and the amount of DNA doubles. So now, the amount will be 4C. In G2 phase, there will be no change in the amount of DNA. It remains 4C. The number of chromosomes after M phase is 14. At G1 phase, there will be 14 chromosomes. After S phase, the DNA content doubles but chromosome number still remains same here, i.e., 14. After completion of M phase,

the number of chromosomes will be 28 with each daughter cell having same number of chromosomes as that of parent, i.e., 14.

24. (b) The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids.Centromeres are required for accurate segre-gation of chromosomes. Chromosomes that lack centromeres segregate randomly during mitosis and are eventually lost from cells.

25. (b) Crossing over occurs between the non - sister chromatid of homologous chromosomes.

26. (a) During the pachytene, chromosomes get crossed with each other and form a four stranded or tetrad appearance. Tetrad is two chromosomes or four chromatids. If n=8; then in pachytene, there are 8 tetrad; 2 pair centriole; 16 pair sister chromatid.

Transport in Plants (Questions on Page No. 239)

20. (b) NCERT (XI) Ch - 11, Pg. 181

When a cell is placed in a solution, there is no net gradient and no net flow of water towards the inside or outside to balance the osmotic pressure of the cytoplasm. This is referred to isotonic solution.

21. (b) NCERT (XI) Ch - 11, Pg. 186

As various ions from the soil are actively transported into the vascular tissues of the roots, water follows (its potential gradient) and increases the pressure inside the xylem. This positive pressure is called root pressure, and can be responsible for pushing up water to small heights in the stem. Choose a small soft-stemmed plant and on a day, when there is plenty of atmospheric moisture, cut the stem horizontally near the base with a sharp blade, early in the morning. You will soon see drops of solution ooze out of the cut stem; this comes out due to the positive root pressure.

22. (c) Nitrogen is deposited into the soil by a number of different methods or ways such as nitrogen fertilizer, nitrogen fixation by leguminous crops, manure additions, and crop


residues. There are fewer ways that results in the nitrogen lost from the soil such as leaching, denitrification and volatilization.

23. (c) NCERT (XI) Ch - 11, Pg. 189

Transport proteins of endodermal cells are control points, where a plant adjusts the quantity and types of solutes that reach the xylem.

24. (a) In the cell walls of higher plants, the tensile fibers are made from the polysaccharide cellulose, the most abundant organic macromolecule on Earth, tightly linked into a network by cross-linking glycans.

25. (a) In meristematic cells, intercellular space is absent.

26. (b) Nonpolar molecules diffuse through more rapidly because much of the bilayer is nonpolar.

27. (a) NCERT (XI) Ch - 11, Pg. 190

The chief sinks for the mineral elements are the growing regions of the plant, such as the apical and lateral meristems, young leaves, developing flowers, fruits and seeds, and the storage organs. Unloading of mineral ions occurs at the fine vein endings through diffusion and active uptake by these cells.

Mineral Nutrition (Questions on Page No. 259)

23. (b) NCERT (XI) Ch - 12, Pg. 198

Boron is required for uptake and utilization of Ca2+ , membrane functioning, pollen germination, cell elongation, cell differentiation and carbohydrate translocation.

24. (b) NCERT (XI) Ch - 12, Pg. 195

In 1860, Julius von Sachs, a prominent German botanist, demonstrated, for the first time, that plants could be grown to maturity in a defined nutrient solution in complete absence of soil. This technique of growing plants in a nutrient solution is known as hydroponics. Hydroponics has been successfully employed as a technique for the commercial production of vegetables such as tomato, seedless cucumber and lettuce.

25. (d) NCERT (XI) Ch - 12, Pg. 197

Potassium: Potassium helps to maintain an anion-cation balance in cells and is involved in protein synthesis, opening and closing of stomata, activation of enzymes and in the maintenance of the turgidity of cells.Chlorine: It helps in determining the solute concentration and the anion-cation balance in cells. It is essential for the water-splitting reaction in photosynthesis, a reaction that leads to oxygen evolution.Phosphorus: It is a constituent of cell membranes, certain proteins, all nucleic acids and nucleotides, and is required for all phosphorylation reactions.Sodium: Principal cation of interstitial fluid.Calcium: Needed for normal blood clotting.

26. (d) NCERT (XI) Ch - 12, Pg. 202-203

The enzyme nitrogenase is a Mo-Fe protein and catalyzes the conversion of atmospheric nitrogen to ammonia, the first stable product of nitrogen fixation. The enzyme nitrogenase is highly sensitive to the molecular oxygen; it requires anaerobic conditions. The nodules have adaptations that ensure that the enzyme is protected from oxygen. To protect these enzymes, the nodule contains an oxygen scavenger called leg-haemoglobin. The nitrogenase enzyme requires a very high input of energy (8 ATP for each NH3 produced). The energy required, thus, is obtained from the respiration of the host cells.

27. (a) NCERT (XI) Ch - 12, Pg. 204

The two most important amides – asparagine and glutamine – found in plants are a structural part of proteins. Since amides contain more nitrogen than the amino acids, they are transported to other parts of the plant via xylem vessels.

28. (c) NCERT (XI) Ch - 12, Pg. 197-198

Copper is associated with certain enzymes involved in redox reactions and is reversibly oxidised from Cu+ to Cu2+. Iron is an important constituent of proteins involved in the transfer of electrons like ferredoxin and cytochromes.

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Photosynthesis in Higher Plants (Questions on Page No. 281-282)

24. (c) NCERT (XI) Ch - 13, Pg. 212-214

The main steps of chemosynthetic ATP synthesis in the light reaction are as follows:Light excites electrons in PSII → Electrons from PS II pass along electron transport chain → Carriers use energy from electrons to move H+ across the membrane → H+

concentration gradient generates → H+

diffuses through ATP synthetase → Energy of H+

flow is used by ATP synthetase to make ATP

25. (d) If the interior of the thylakoid is no longer separated from the stroma, the chemiosmotic process for synthesis of ATP ceases since protons need to flow from the interior of the thylakoid to the stroma to make ATP.

26. (c) If the same experiment is performed without passing light through a prism then the bacteria would be relatively evenly distributed. This is because bacteria congregated to where the most photosynthesis happens. In the absence of light, there is no photosynthesis and thus the bacteria will spread out evenly.

27. (d) Photosynthesis is a process in which green plants manufacture their own food with help of CO2,H2O in presence of sunlight and it takes place in chloroplast. In the above question, no photosynthesis takes place because the chloroplast is not intact. The soda water causes destruction of membranes of chloroplast.

28. (b) NCERT (XI) Ch - 13, Pg. 215

The products of light reaction are ATP, NADPH and O2 . Of these O2 diffuses out of the chloroplast while ATP and NADPH are used to drive the processes leading to the synthesis of food, more accurately, sugars. This is the biosynthetic phase of photosynthesis. This process does not directly depend on the presence of light but is dependent on the products of the light reaction, i.e., ATP and NADPH, besides CO2 and H2O. This can be verified by the following observation that immediately after light becomes unavailable,

the biosynthetic process continues for some time, and then stops. If then, light is made available, the synthesis starts again.

29. (d) NCERT (XI) Ch - 13, Pg. 214The proton gradient is important because it is the breakdown of this gradient that leads to release of energy. The gradient is broken down due to the movement of protons across the membrane to the stroma through the transmembrane channel of the F0 of the ATPase.

30. (c) At higher light intensities, gradually the rate does not show further increase as other factors become limiting. Carbon dioxide is the major limiting factor for photosynthesis therefore when CO2 concentration was increased, the rate of photosynthesis also increased.

31. (a) Statement C and D are not related to photorespiration. In the photorespiratory pathway, there is neither synthesis of sugars, nor of ATP. Rather it results in the release of CO2 with the utilization of ATP. In the photorespiratory pathway there is no synthesis of ATP or NADPH. Therefore, photorespiration is a wasteful process. In C4 plants photorespiration does not occur.

32. (a) A permeable membrane does not allow the proton gradient formation therefore it is not required for ATP synthesis through chemiosmotic hypothesis.

33. (b) Carotenoids are accessory pigments which absorb light and transfer the energy to chlorophyll a. They absorb light in the blue-green and violet region and reflect the longer yellow, red, and orange wavelengths.

34. (a) If the interior of the thylakoid is no longer separated from the stroma, the chemiosmotic process for synthesis of ATP ceases since protons need to flow from the interior of the thylakoid to the stroma to make ATP.

Respiration in Plants (Questions on Page No. 303)

27. (c) Precursor of auxin is tryptophan amino acid. Oxaloacetate is also involved in gluconeogenesis, urea cycle, glyoxylate cycle, amino acid synthesis, and fatty acid synthesis.


28. (d)

Glycolysis2 ATP 2 NADH X 3 = 6 ATP

Link Reaction 2 NADH X 3 = 6 ATP

Krebs cycle 2 ATP6 NADH × 3 = 18 ATP2 FADH2 × 2 = 4 ATP

Total number of ATPs formed in electron transport chain

38 ATPs

Out of 38 ATPs, 2 ATPs are consumed in active transport of NADH from cytoplasm to mitochondria and 2 ATPs are consumed in glycerol phosphate shuttle. Thus, 34 ATPs are formed inside mitochondria including the use of NADH + H+ produced in glycolysis considering glycerol-P shuttle with respect to each glucose molecule.

29. (a) Plants could use light energy to make carbohydrates from CO2 and water. Hence, when oxygen of CO2 is radiolabelled and provided to the plant, then carbohydrates (hexose) will show radioactivity in the cells exposed to sunlight.

CO2 + H2O → [CH2O] + O2

30. (d) NCERT (XI) Ch - 14, Pg. 231

For aerobic respiration to take place within the mitochondria, the final product of glycolysis, pyruvate is transported from the cytoplasm into the mitochondria. The crucial events in aerobic respiration are:

i) The complete oxidation of pyruvate by the stepwise removal of all the hydrogen atoms, leaving three molecules of CO2

ii) The passing on of the electrons removed as part of the hydrogen atoms to molecular O2 with simultaneous synthesis of ATP.

31. (d) NCERT (XI) Ch - 14, Pg. 229 & 232

A- Glycolysis

In this process, glucose (6C) undergoes partial oxidation to form two molecules of pyruvic

acid (3C).

B – Link reaction

In link reaction, pyruvate (3C) is converted to acetyl coenzyme A (2C). During this process, two molecules of NADH are produced from the metabolism of two molecules of pyruvic acid (produced from one glucose molecule during glycolysis). The acetyl CoA then enters a cyclic pathway, tricarboxylic acid cycle, more commonly called as Krebs’ cycle.

C – Citric acid cycle

The TCA cycle starts with the condensation of acetyl group with oxaloacetic acid (OAA) and water to yield citric acid.

D – Electron transport chain

The following steps in the respiratory process are to release and utilise the energy stored in NADH+H+ and FADH2. This is accomplished when they are oxidised through the electron transport system and the electrons are passed on to O2 resulting in the formation of H2O.

32. (c) NCERT (XI) Ch - 14, Pg. 233

During electron transport chain, electrons from NADH produced in the mitochondrial matrix during citric acid cycle are oxidised by an NADH dehydrogenase (complex I), and electrons are then transferred to ubiquinone located within the inner membrane. Ubiquinone receives reducing equivalents via FADH2 (complex II) that is generated during oxidation of succinate in the citric acid cycle.

The reduced ubiquinone (ubiquinol) is then oxidised with the transfer of electrons to cytochrome c via cytochrome bc 1 complex (complex III). Cytochrome c is a small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for transfer of electrons between complex III and IV. Complex IV refers to cytochrome c oxidase complex containing cytochromes a and a3, and two copper centres. The electrons then moves to cytochrome b, cytochrome c

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and then finally move to cytochrome aa3. So ultimately these electrons are accepted by O2 and H2O is formed.

33. (c) Fermentation accounts for only a partial breakdown of glucose whereas in aerobic respiration, it is completely degraded to CO2 and H2O.

34. (b) During respiration, a mole of glucose (180 g) is oxidized by six moles of oxygen (192 g) to produce six moles of carbon dioxide (264 g), six moles of water (108 grams), and over 686 kcal of useful free energy.

C6H12O6 + 6O2 → 6CO2 + 6H2O + 673 kcal/mole

180g 192 g 264 g 108 g

Calculations:

C6H12O6 = 6 × 12 +12 × 1 + 6 × 16 = 180 g

Now we consider products of this reaction, i.e., 6CO2 = 6 (12 + 32) = 264 g

6H2O= 6 (2 + 16) = 108 g

Plant Growth and Development (Questions on Page No. 322)

20. (c) NCERT (XI) Ch - 15, Pg. 250

Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called respiratory climactic. Ethephon hastens fruit ripening in tomatoes and apples and accelerates abscission in flowers and fruits (thinning of cotton, cherry, walnut).

21. (c) NCERT (XI) Ch - 15, Pg. 247

The major precursor of auxin is the amino acid tryptophan. Spraying juvenile conifers with GAs hastens the maturity period, thus leading to early seed production.

22. (c) NCERT (XI) Ch - 15, Pg. 250

Horizontal growth of seedling, swelling of axis and apical hook formation in dicot seedling are associated with ethylene.

23. (d) NCERT (XI) Ch - 15, Pg. 251

There are a number of events in the life of a plant where more than one PGR interact to affect that event, e.g., dormancy in seeds/ buds, abscission, senescence, apical dominance, etc.

24. (d) NCERT (XI) Ch - 15, Pg. 249

Gibberellin promotes bolting (internode elongation just prior to flowering) in beet, cabbages and many plants with rosette habit.

25. (d) A flash of red light followed by a flash of far-red light given during the middle of the night to a short-day plant will likely have no effect upon flowering.

26. (b) Gibberellins stimulate the production of some mRNAs and then hydrolytic enzymes such as amylase, lipase, ribonuclease, proteases, etc. The enzymes solubilize the reserve food of the seeds and are transferred to embryo axis for its growth.

27. (c) NCERT (XI) Ch - 15, Pg. 249

Auxins are widely used as herbicides. 2, 4-D, widely used to kill dicotyledonous weeds, does not affect mature monocotyledonous plants. It is used to prepare weed-free lawns by gardeners.

Digestion and Absorption (Questions on Page No. 347)

38. (b) NCERT (XI) Ch - 16, A - Pg. 260; B - Pg. 262; C - Pg. 263; D - Pg. 260

Mucosa forms glands in the stomach (gastric glands) and crypts in between the bases of villi in the intestine (crypts of Lieberkuhn). Mucus present in the gastric juice play an important role in protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid. HCl provides the acidic pH (pH 1.8) optimal for pepsins. Villi are


supplied with a network of capillaries and a large lymph vessel called the lacteal.

39. (c) Parietal or oxyntic cells which secrete HCl and intrinsic factor (factor essential for absorption of vitamin B12). Trypsinogen is activated by an enzyme, enterokinase, secreted by the intestinal mucosa into active trypsin, which in turn activates the other enzymes in the pancreatic juice. Rennin is produced in the form of inactive prorennin. After consumption of milk, HCl seceted by oxyntic cells activates prorennin, and converts it into its active form (rennin).

40. (None) NCERT (XI) Ch - 16, Pg. 265

All statements are correct.

Triglycerides are coated with phospholipids, cholesterol, and proteins to form chylomicrons

41. (d) NCERT (XI) Ch - 16, Pg. 265-266

The abnormal frequency of bowel movement and increased liquidity of the faecal discharge is known as diarrhoea. It reduces the absorption of food. Vomiting is the ejection of stomach contents through the mouth. This reflex action is controlled by the vomit centre in the medulla. The digestive wastes, solidified into coherent faeces in the rectum initiate a neural reflex causing an urge or desire for its removal.

42. (b) Pellagra is a disease that occurs due to deficiency of vitamin nicotinamide. Its symptoms are swollen lips, diarrhoea, thick pigmented skin of hands and legs and nervous disorder (irritability).

43. (c) NCERT (XI) Ch - 16, Pg. 263

The intestinal mucosal epithelium has goblet cells which secrete mucus. The secretions of the brush border cells of the mucosa along with the secretions of the goblet cells constitute the intestinal juice or succus entericus. This juice contains a variety of enzymes like disaccharidases (e.g., maltase), dipeptidases, lipases, nucleosidases, etc. Thus, due to

certain abnormality, if brush-bordered cells of intestine not developed, complete digestion of proteins and carbohydrates does not occur.

44. (b) In alimentary canal, serosa is the outermost layer and is made up of a thin mesothelium (epithelium of visceral organs) with some connective tissues. In esophagus, instead of serosa, a dense sheath of collagen fibers called the adventitia is present which lacks mesothelium.

45. (d) Excretion of waste is the function of the excretory system of the body. The excretory system consists of one pair of kidneys, a pair of ureters, a urinary bladder and a urethra.

46. (b) Myenteric plexuses are located between the inner and outer layers of the muscularis externa.

Breathing and Exchange of Gases (Questions on Page No. 368)

23. (d) NCERT (XI) Ch - 17, Pg. 274

Blood is the medium of transport for O2 and CO2. About 97 per cent of O2 is transported by RBCs in the blood. The remaining 3 per cent of O2 is carried in a dissolved state through the plasma. Nearly 20-25 per cent of CO2 is transported by RBCs whereas 70 per cent of it is carried as bicarbonate. About 7 per cent of CO2 is carried in a dissolved state through plasma.

24. (a) Small animals have a larger surface area to volume ratio than large animals. That is why respiratory rate is higher in them.

25. (d) Normal partial pressure of carbon dioxide of deoxygenated blood is 45 mmHg. A decrease in CO2 shifts the curve to the left, while an increase in CO2 shifts the curve to the right. Thus, when pCO2 of deoxygenated blood of a person becomes 48 mm Hg, his O2 dissociation curve remains shifted towards right. The increase in pCO2 reduces the affinity of oxygen to haemoglobin in two ways:

i. Accumulation of CO2 causes formation of carbamino compounds, which bind to

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oxygen and form carbamino-haemoglobin.

ii. Accumulation of CO2 causes an increase in H+ ion concentration and a decrease in the pH, which will shift the curve to the right.

NOTE: A right shift indicates decreased oxygen affinity of haemoglobin allowing more oxygen to be available to the tissues.

26. (d) NCERT (XI) Ch - 17, Pg. 272

Inspiratory Capacity (IC): Total volume of air a person can inspire after a normal expiration. This includes tidal volume and inspiratory reserve volume ( TV+IRV).

Functional Residual Capacity (FRC): Volume of air that will remain in the lungs after a normal expiration. This includes ERV+RV.

Vital Capacity (VC): The maximum volume of air a person can breathe in after a forced expiration. This includes ERV, TV and IRV or the maximum volume of air a person can breathe out after a forced inspiration.

According to the question,

IC + FRC – RV = TV + IRV + ERV + RV – RV = TV + ERV+ IRV = VC

27. (d) The movement of air into and out of lungs is due to development of pressure gradient between the lungs and the atmosphere. Punctures in a person’s chest may lead to loss of pressure gradient, and thus resulting in cessation of breathing.

Body Fluids and Circulation (Questions on Page No. 391)

28. (a) If person had two-chambered heart (one atrium and one ventricle), the oxygenated blood and deoxygenated blood get mixed, then blood would circulate through the body without being fully oxygenated and the tissues will receive less or no oxygen.

29. (b) NCERT (XI) Ch - 18, Pg. 283

Atrioventricular septum is a fibrous tissue

of the membranous septum of the heart just above the septal cusp of the tricuspid valve. It separates the atrium and the ventricle of the same side.

30. (b) Thrombocytopenia is a condition character-ized by abnormally low levels of thrombocytes or blood platelets in the blood. Platelets can re-lease a variety of substances most of which are involved in the coagulation or clotting of blood. A reduction in their number can lead to clotting disorders which will lead to excessive loss of blood from the body.

31. (b) The Na+ level in the blood is controlled by aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP). Aldosterone increases renal reabsorption of Na+.

32. (c) NCERT (XI) Ch - 18, Pg. 287

The conducting system of the heart consists of cardiac muscle cells and conducting fibres that are specialized for initiating impulses and conducting them rapidly through the heart. They initiate the normal cardiac cycle and coordinate the contractions of cardiac chambers. If the neuromuscular conduction pathway in heart is broken between S.A. node and A.V. node, auricles will contract at the rate set by the S.A. node while venticles will contract at the rate of impulse generated by the A.V. node.

Excretory Products and Their Elimination

(Questions on Page No. 416-417) 25. (a) The urinary bladder is lined throughout

by transitional epithelial tissue. This allows urinary bladder to stretch significantly to accommodate large volumes of urine. It also provides protection to the underlying tissues from acidic or alkaline urine.

26. (c) NCERT (XI) Ch - 19, A - Pg. 297; B - Pg. 298; C - Pg. 298; D - Pg. 294

A – True; Atrial natriuretic factor can causes vasodilation (dilation of blood vessels) and


thereby decreases the blood pressure.

B – False; On an average, 25-30 gm of urea is excreted out per day.

C – False; The sweat and sebaceous glands in the skin can eliminate certain substances through their secretions. Sweat produced by the sweat glands is a watery fluid containing NaCl, small amounts of urea, lactic acid, etc. Sebaceous glands eliminate certain substances like sterols, hydrocarbons and waxes through sebum.

D – True; PCT is lined by simple cuboidal brush border epithelium which increases the surface area for reabsorption.

27. (b) A. Annelids have nephridia and insects have malpighian tubules for excretion

B. Blood enters the glomerulus via afferent arteriole and leaves via efferent arteriole.

C. During micturition, the urinary bladder contracts and the urethral sphincters relaxes.

28. (c) NCERT (XI) Ch - 19, Pg. 294-295

Water reabsorption in descending limb of loop of Henle and collecting duct occur under different conditions.

29. (a) The final reabsorption of water from the urine into the blood occurs through the collecting duct of a mammalian nephron resulting in the production of hyperosmotic urine because the loop of Henle creates a sodium gradient in the interstitial fluid.

30. (a) The ascending limb is impermeable to water but permeable ions such as Na+ and some urea into surrounding medullary tissue. So it makes urine dilute or hypotonic.

The descending limb is impermeable to Na+ but permeable to water. Thus, the urine becomes hypertonic.

31. (b) An elevated or increased level of glucose in urine is referred to renal glycosuria.

32. (b) Nephridia is the excretory organ in annelids. Green glands are the excretory organs of arthropoda. The cortex extends in between the medullary pyramids as renal columns called Columns of Bertini.

33. (b) The rate of ultrafiltration of glucose is higher than anions due to negative charge on glomerular basement membrane. The glomerular basement membrane (GBM) present in the glomerular capillary wall determines the size- and charge-selective properties of the glomerular barrier to macromolecules.

34. (c) Sharks, electric ray and sting ray can retain a large amount of urea in the blood and tissue fluid.

Locomotion and Movement (Questions on Page No. 437)

23. (a) NCERT (XI) Ch - 20, Pg. 312

The vertebral column has 12 thoracic vertebrae. The joint between the adjacent vertebrae is cartilaginous joint. The decreased level of estrogen causes osteoporosis in old people.

24. (b) NCERT (XI) Ch - 20, Pg. 307

A neural signal reaching this junction releases a neurotransmitter (Acetylcholine) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm. Increase in Ca2+ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin. Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge.

25. (c) NCERT (XI) Ch - 20, Pg. 308

Upon muscle contraction, the A-bands do not change their length whereas the I-bands and the H-zone shorten.

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26. (d) NCERT (XI) Ch - 20, Pg. 304

The light bands contain actin and is called I-band or isotropic band, whereas the dark band called ‘A’ or anisotropic band contains myosin.

27. (d) Tarsals, femur, metatarsals and tibia are parts of hind limb bones that mainly take part during chasing a ball in the field by a cricket player. Malleus is an ear bone, ulna is a forelimb bone and sternum is a breast bone, all these three does not take part during chasing a ball in the field by a cricket player.

28. (c) Even if a stimulus, several times greater than the threshold stimulus is provided to a muscle fibre, it will contract with same force.

Neural Control and Coordination (Questions on Page No. 461)

27. (a) The parasympathetic division is also called the craniosacral division because its preganglionic neurons arise from brain stem and the spinal cord segments. The sympathetic system is also called the thoracolumbar division.

28. (d) NCERT (XI) Ch - 21, Pg. 317

At a chemical synapse, the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called synaptic cleft. The myelinated nerve fibres are enveloped with Schwann cells, which form a myelin sheath around the axon. Myelinated nerve fibres are found in spinal and cranial nerves. Unmyelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath around the axon, and is commonly found in autonomous and the somatic neural systems.

29. (c) NCERT (XI) Ch - 21, Pg. 319

At electrical synapses, the membranes of pre- and post-synaptic neurons are in very close proximity. Electrical current can flow directly from one neuron into the other across these synapses. Transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse. Electrical synapses are

rare in our system.

30. (c) All the statements are true. Acetylcholine is the primary neurotransmitter at the neuromuscular junction. Parasympathetic pre-ganglionic cell bodies are located in the brain stem and in the spinal cord and post-ganglionic cell bodies are located in or near the organ innervated.

31. (c) NCERT (XI) Ch - 21, Pg. 325

The order of reception and transmission of sound wave from external auditory canal is: Ear drum, malleus, incus, stapes, cochlea, cochlear nerve.

The outer ear consists of the pinna and external auditory meatus (canal). The pinna collects the vibrations in the air which produce sound. The external auditory meatus leads inwards and extends up to the tympanic membrane (the ear drum). There are very fine hairs and wax-secreting glands in the skin of the pinna and the meatus. The tympanic membrane is composed of connective tissues covered with skin outside and with mucus membrane inside. The middle ear contains three ossicles called malleus, incus and stapes which are attached to one another in a chainlike fashion. The malleus is attached to the tympanic membrane and the stapes is attached to the oval window of the cochlea.

32. (b) NCERT (XI) Ch - 21, Pg. 321

The cerebral cortex contains motor areas, sensory areas and large regions that are neither clearly sensory nor motor in function. These regions called as the association areas are responsible for complex functions like intersensory associations, memory and communication.

33. (d) Nissl’s granules are the granular bodies consist of rough endoplasmic reticulum. Rough endoplasmic have ribosomes in its walls. The main function of these ribosomes is


protein synthesis and therefore Nissl granules help in protein synthesis.

34. (b) NCERT (XI) Ch - 21, Pg. 327

The base of canals is swollen and is called ampulla, which contains a projecting ridge called crista ampullaris which has hair cells. The saccule and utricle contain a projecting ridge called macula. The crista and macula are the specific receptors of the vestibular apparatus responsible for maintenance of balance of the body and posture.

35. (d) The sequence of events of muscle contraction is as follows:

Release a acetylcholine neurotransmitter → Generate an action potential in the sarcolemma → Release of calcium ions → Remove the masking of active sites for myosin → Form a cross bridge → Pulls the attached actin filaments towards the centre of A band

36. (c) In chemical synapse, the released neurotransmitters bind to their specific receptors, present on the post-synaptic membrane. If these receptors are removed, chemical synaptic transmission will not occur.

Chemical Coordination and Integration (Questions on Page No. 482)

29. (a) NCERT (XI) Ch - 22, Pg. 338

Hormones produce their effect on target tissue by binding to specific proteins called hormone receptors located in the target tissues only. Water soluble hormones usually need membrane bound receptor that generate secondary messenger for regulating cellular metabolism lipid soluble hormones can pass through cell membrane.

The hormone which interact with intracellular receptor mostly regulate gene expression or chromosome function by interaction of hormone receptor complex with the genome.

30. (c) NCERT (XI) Ch - 22, Pg. 335

The adrenal medulla secretes two hormones called adrenaline or epinephrine and noradrenaline or norepinephrine. Adrenaline and noradrenaline are rapidly secreted in response to stress of any kind and during emergency situations and are called emergency hormones or hormones of Fight or Flight.

These hormones increase alertness, pupilary dilation, piloerection (raising of hairs), sweating, etc. Both the hormones increase the heart beat, the strength of heart contraction and the rate of respiration.

31. (d) NCERT (XI) Ch - 22, Pg. 335

Exopthalmic goitre is a form of hyperthy-roidism, characterised by enlargement of the thyroid gland, protrusion of the eye-balls, increased basal metabolic rate, and weight loss, also called Graves’ disease.

In this, the person produces antibodies that mimic the action of TSH and is not regulated by normal negative feedback control.

32. (b) NCERT (XI) Ch - 22, Pg. 334

An impairment affecting synthesis or release of ADH results in a diminished ability of the kidney to conserve water leading to water loss and dehydration. This condition is known as Diabetes insipidus.

33. (c) NCERT (XI) Ch - 22, Pg. 333

The pars distalis region of pituitary, common-ly called anterior pituitary, produces growth hormone (GH), prolactin (PRL), thyroid stim-ulating hormone (TSH), adrenocorticotrophic hormone (ACTH), luteinizing hormone (LH) and follicle stimulating hormone (FSH). Low secretion of GH results in stunted growth re-sulting in pituitary dwarfism.

34. (b) Apocrine glands: Glandular secretion accumulates in the terminal part of the cell which is pinched off, e.g., mammary glands

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Reproduction in Organisms (Questions on Page No. 13)

27. (b) NCERT (XII) Ch - 1, Pg. 8

The aquatic plant water hyacinth, also known as terror of Bengal, is one of the most invasive weeds found growing wherever there is standing water. It drains oxygen from the water, which leads to death of fishes.

28. (a) Morphallaxis is defined as the regeneration of the whole organism from a small fragment by reorganizing the existing cells, e.g., Hydra, Amoeba. Epimorphosis is defined as the regeneration of the whole organism by cellular differentiation, e.g., limb regeneration in amphibians.

29. (b) In some organisms like rotifers, honeybees and even some lizards and birds (turkey), the female gamete undergoes development to form new organisms without fertilization. This phenomenon is called parthenogenesis. Cucurbits and coconuts are monoecious plants. Peacock have internal fertilization. Ornithorhynchus,i.e., platypus is oviparous.

30. (c) Bee-keeping or apiculture is the maintenance of hives of honeybees for the production of honey. Guava, sunflower, strawberry are the plants which are pollinated by bees.

31. (c) The chromosome complement of Triticum aestivum (2n=26) is similar to that of Gossypium whose ploidy level is also 2n=26. Zea mays has ploidy level of 2n=20. Secale and Aegilops both have the similar ploidy level of 2n=14.

32. (c) Euglena → Longitudinal binary fissionParamoecium → Transverse binary fissionAmoeba → Multiple fissionPlasmodium → Multiple fission

33. (d) Bryophyllum plants bear several adventitious foliar buds on their margins. These leaf buds have the ability to grow and develop into tiny plants.

34. (a) Grafting is generally not successful in monocots as they lack cambium.

35. (c) NCERT (XII) Ch - 1, Pg. 8

The aquatic plant water hyacinth, also known as terror of Bengal, is one of the most invasive weeds found growing wherever there is standing water.

Sexual Reproduction in Flowering Plants (Questions on Page No. 40-41)

25. (b) Both statements A and C are correct. As a rule, only one ovule combines with one pollen grain. Backward flow of cytoplasm from the tip of the pollen tube towards the pollen grain is prevented by the formation of callose plugs at intervals.

26. (b) NCERT (XII) Ch - 2, Pg. 24

Pollen consumption has been claimed to increase the performance of athletes and race horses because pollen grains are rich in nutrients. In western countries, a large number of pollen products in the form of tablets and syrups are available in the market.

27. (b) All unisexual flowers and a large number of bisexual flowers are naturally cross pollinated. Cross pollination occurs in both monoecious and dioecious plants.

28. (b) The endosperm of gymnosperms and pteridophytes is simple haploid (n) tissue of the gametophyte.

29. (c) The biological species concept defines a species as members of populations that can interbreed in nature and produce sterile offsprings. After the mating of plants, progeny formation was absent. Thus the two plants must be considered as different biological species.

30. (d) Floral character can be used to group plants into their various families because these show a wide range of variations in different species.

31. (a) NCERT (XII) Ch - 2, Pg. 38-39

In Citrus and mango, some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into embryos.

32. (a) NCERT (XII) Ch - 2, Pg. 29


Pollination by water (hydrophily) is quite rare in flowering plants and is limited only to about 30 genera, mostly monocots.

33. (b) NCERT (XII) Ch - 2, P.g 38-39

In Citrus and mango varieties some of the nucellar cells surrounding embryo sac start dividing, protrude into the embryo sac and develop into the embryo.

34. (b) NCERT (XII) Ch - 2, Pg. 28

The transfer of pollen grains from the anther of a flower to the stigma of the same flower or another flower of the same plant is known as geitonogamy. It is functionally cross pollination by involving pollinating agent but genetically it is autogamy.

35. (c) When anthers dehisce in the flower buds, pollen grains come in contact with the stigma to effect pollination. Thus, cleistogamous flowers are invariably autogamous as there is no chance of cross-pollen landing on the stigma. Hence, cleistogamous flowers produce assured seed-set even in the absence of pollinators.

36. (c) NCERT (XII) Ch - 2, Pg. 34

Since two types of fusion, syngamy and triple fusion take place in an embryo sac the phenomenon is termed double fertilization. It is an event unique to flowering plants.

Human Reproduction (Questions on Page No. 69)

30. (c) Intentional or voluntary termination of pregnancy before full term is called medical termination of pregnancy (MTP) or induced abortion. MTPs are considered relatively safe during the first trimester, i.e., upto 12 weeks of pregnancy.

31. (b) NCERT (XII) Ch - 3, Pg. 85

Each fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the uterus, the part closer to the ovary is the funnel-shaped infundibulum. The edges of the infundibulum possess finger-like projections called fimbriae, which help in collection of the ovum after ovulation.

32. (d) The mesoderm of the allantois is called the extraembryonic splanchnic mesoderm because it is associated with the endoderm. Ectoderm is also called trophoblast.

33. (b) The primary secretion products from Sertoli cells include androgen binding protein (ABP) and inhibin.

34. (b) NCERT (XII) Ch - 3, Pg. 50

The ovulation (ovulatory phase) is followed by the luteal phase during which the remaining parts of the Graafian follicle transform as the corpus luteum. The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium. Such an endometrium is necessary for implantation of the fertilised ovum and other events of pregnancy.

35. (c) Estrogen is a major factor in the increased size of the uterus and thickening of the uterine wall. During the pregnancy, the uterus increases in size to accommodate the developing pregnancy. This occurs through hyperplasia (increase in the number of cells), hypertrophy (increase in the size of cells) of muscle cells, and stretching of the uterus.

36. (d) Paraurethral gland in females is homologous to prostate in males.

37. (d) NCERT (XII) Ch - 3, Fig 3.9One ovum is released (ovulation) during the middle of each menstrual cycle. Follicular phase (proliferative phase) begins on the first day of menstruation and lasts till the 13th day of the menstrual cycle. Ovulation phase occurs on 14th day. Luteal phase (secretory phase) occurs from 15 to 28 days.

Reproductive Health (Questions on Page No. 89)

23. (d) NCERT (XII) Ch - 4, Pg. 60Lactational amenorrhea (absence of menstruation) method is based on the fact that ovulation and therefore the cycle do not occur during the period of intense lactation following parturition. This method has been reported to be effective only upto a maximum

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period of six months following parturition. 24. (b) Chorionic villi sampling is a test made in early

pregnancy to detect congenital abnormalities in the foetus, in which the physician inserts a narrow flexible tube through the mother’s vagina and cervix into the uterus and a tissue sample is taken from the villi of the chorion.

25. (c) NCERT (XII) Ch - 4, Pg. 64Transfer of an ovum collected from a donor into the fallopian tube (GIFT – gamete intra fallopian transfer) of another female who cannot produce one, but can provide suitable environment for fertilization and further development.

26. (b) NCERT (XII) Ch - 4, Pg. 64Infertility cases either due to inability of the male partner to inseminate the female or due to very low sperm counts in the ejaculates, could be corrected by artificial insemination (AI) technique. In this technique, the semen collected either from the husband or a healthy donor is artificially introduced either into the vagina or into the uterus (IUI – intra-uterine insemination) of the female.

27. (d) IUDs can cause excessive menstrual bleedings, pain and inflammation of uterine wall.

28. (c) NCERT (XII) Ch - 4, Pg. 60Lactational amenorrhoea is effective only upto a maximum period of six months following parturition.

Principles of Inheritance and Variation (Questions on Page No. 115)

33. (d) NCERT (XII) Ch - 5, Pg. 80Based upon the observations on dihybrid crosses (crosses between plants differing in two traits) Mendel proposed a second set of generalizations known as Mendel’s Law of Independent Assortment. The law states that ‘when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters’.

34. (c) Let us suppose RR as cow with red coat and WW as bull having white coat. Then the cross

between them will produce RW offsprings with roan coat in F1 generation. Roan means that their coat is red with a liberal sprinkling of white hairs. In cattle, the alleles producing coat color are co-dominant. Co-dominance is the phenomenon in which both the alleles of a contrasting character are expressed in heterozygous condition.

35. (b) Let us suppose, BB represents broad leaf and bb represents narrow leaf. RR represents red flower colour and rr represents ivory. According to the question, red flower colour is incompletely dominant to ivory, therefore Rr will be pink coloured flowers.A cross between a plant which is heterozygous for both genes and true-breeding broad -leaved red - flowered plant is as follows:Parents: BbRr × BBRRGametes: BR Br bR rr BR F1 generation:

BRBR BBRR

Broad-leaved red flowersBr BBRr

Broad-leaved pink flowersbR BbRR

Broad-leaved Red flowersrr BbRr

Broad-leaved pink flowers

From the above Punnett square, it is cleared that the expected proportion of broad - leaved plants with pink flowers amongst the offspring would be 2 in 4.

36. (d) It is given that the dominant allele (P) produces a purple colour and the recessive allele (p) produces a yellow colour. Thus, the phenotype of purple colour kernels will be PP (homozygous dominant) and Pp (heterozygous dominant). The phenotype of yellow colour kernels will be pp (homozygous recessive).

37. (b) NCERT (XII) Ch - 5, Pg. 77Given that,Blood type of Sita is A, thus the genotype


could be IAIA or IAIO

The blood type of mother and father is B, thus the genotype could be IBIB or IBIO. From this we can conclude that the blood type of Ram could be B or O having genotype IBIB or IOIO

The blood type of their children, Kush, has type O blood only when Sita’s genotype is IAIO and Ram’s genotype is IOIO

38. (d) Because all of the daughters have the same disease as their father, but none of the sons is affected, the gene responsible for the genetic disease is located on the X chromosome of Mr. Verma. In X-linked dominant inheritance, only one copy of the allele is sufficient to cause the disorder.

39. (b) In the given cross, AaBbCcDD x aabbccDD, the genotypic ratio would be 1 : 1 : 1 : 1 : 1 : 1 : 1 : 1

40. (c) The minimum weight of tomatoes obtained from a plant is 40 g. The maximum weight of tomatoes obtained is 140 g.

Minimum weight of tomatoes would have recessive genes means aabb = 40 g

4 recessive genes = 40 g

1 recessive gene = 10 g

Maximum weight of tomatoes would have dominant genes means AABB = 140 g

4 dominant genes = 140 g

1 dominant gene = 35 g

A cross between plants with genotype AABB and aabb will yield AaBb offsprings in F1 generation. AaBb has 2 dominant and 2 recessive alleles, this means that the weight of tomatoes in F1 generation will be

[(2 X 10) + (2 X 35)] = 20 + 70 = 90 g 41. (a) Let us suppose BB are the alleles for

brown eye and bb are the alleles for blue eyes.The genotype of boy must be BB or Bb, his mother and sister must be bb. For brown eye children, the father must be heterozygous dominant.

Parents: Mother × Father bb Bb (blue eye) (brown eye)Offsprings: Bb BB bb

42. (c) In a trihybrid plant (AaBbCc), there are 8 gametes namely ABC, ABc, AbC, Abc, aBC, abC, aBc, abc. The probability of gamete which contain at least one dominant allele is 7/8.

43. (a) NCERT (XII) Ch - 5, Pg. 70

Dominant alleles expresses itself in the homozygous as well as heterozygous condition. The dominant contrasting traits selected by Mendel were smooth and yellow seeds, inflated and green pods, axial flower position and tall plants can express in both homozygous as well as in heterozygous condition.

44. (b) Given that 4 alleles are present at a locus.Number of genotypes = n(n+1)/2 = 4 (4 + 1) /2 = 10Number of phenotypes = 4

45. (b) When F1 progeny is crossed with the recessive parents called test cross. When F1 progeny is crossed with the dominant parent called out cross. Both crosses show similar genotypic ratio, i.e, 1:1.

46. (a) Mendel studied seven traits in pea plants and pea plants have 14 chromosomes, i.e., seven in haploid. This means Mendel studied one gene on a chromosome. However if there would have been 12 chromosomes, i.e., six in haploid then any two of the genes would have been on a single chromosome. In this case, Mendel would have discovered linkage instead of independent assortment.

Molecular Basis of Inheritance (Questions on Page No. 148-149)

26. (a) After uncoiling of DNA molecule, one strand acts as a template for the formation of mRNA. This step occurs in the transcription. The process of protein synthesis is called translation.

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27. (d) NCERT (XII) Ch - 6, A - Pg. 106; B - Pg. 112Use of radioactive thymidine to detect distribution of newly synthesized DNA in the chromosomes was performed on Vicia faba (faba beans) by Taylor and colleagues in 1958. The experiments proved that the DNA in chromosomes also replicate semiconservatively.The chemical method developed by Har Gobind Khorana was instrumental in synthesizing RNA molecules with defined combinations of bases (homopolymers and copolymers). Marshall Nirenberg’s cell-free system for protein synthesis finally helped the code to be deciphered. Severo Ochoa enzyme (polynucleotide phosphorylase) was also helpful in polymerizing RNA with defined sequences in a template independent manner (enzymatic synthesis of RNA).

28. (d) Given that, 2Q = R; 2Z = S and R = 0.12 Since it is DNA-like moleculeQ + R + Z + S = 1 ....... Eq. (1)From R, we find Q: Q = R/2 = 0.06 Putting all the values in equation 1, we get0.06 + 0.12 + Z + S = 1 Z + S = 0.82 Z + 2Z = 0.82 Z = 0.82/3 = 27.33 %

29. (b) In double-stranded DNA molecule, amount of purines and amount of pyrimidines is equal. But here, the amount of all 4 bases is different; therefore, DNA is single-stranded. 5-methyl uracil is thymine.

30. (c) Length of 10 base pairs = 3.4 nmLet total number of base pairs be B, thenB base pairs = 136 nmTotal no. of base pairs = 136 × 10 = 3.4 × B⇒ B = 1360 / 3.4 = 400 basesAccording to Chargaff’s rule, A = T ; G = CAdenine = 25% = 0.25

Thus, total number of adenine molecules = 400 × 0.25 = 100Total number of adenine and thymine molecules = 200Similarly, guanine = 0.25Thus, total number of guanine and cytosine molecules = 200We know that, A-T = double bondG-C = triple bondNumber of hydrogen bonds= (200 × 2) + (200 × 3) = 1000

31. (d) During southern blotting, transfer of DNA molecules from gel to nitrocellulose membrane is carried out in the presence of alkaline solution.

32. (c) Male honeybee produces gamete by mitosis. The sex chromosomes in birds are designated as Z and W, and the male is the homomorphic sex (ZZ) and the female heteromorphic (ZW). Y-chromosome of human male has TDF gene.

33. (d) NCERT (XII) Ch - 6, Pg 105

In the semiconservative model, each hybrid DNA molecule from the second generation would be expected to give rise to hybrid molecule and a light molecule in 3rd generation while each light DNA molecule would only yield more light molecules. Thus, the third generation of bacteria contained two types of DNA, 25%intermediate (N15 N14) and 75% light (N14 N14) in 1:3 ratio. Similarly, the fourth generation contains 12.5% N15 N14 and 87.5% N14N14 DNA in 1:7 ratio.

34. (c) If genetic code is overlapping it means that nucleobases from previous codon can be a part of next codon. In the sequence, there are 12 possible codons.AUG, UGU, GUG, UGC, GCC, CCG, CGU, GUA, UAC, ACG, CGG, GGU


35. (d) NCERT (XII) Ch - 6, Pg. 114

Formation of a peptide bond requires energy. Therefore, in the first phase itself amino acids are activated in the presence of ATP and linked to their cognate tRNA – a process commonly called as charging of tRNA or aminoacylation of tRNA.

36. (c) NCERT (XII) Ch - 6, Pg. 121Depending on base composition ( A:T rich or G:C rich), length of segment, and number of repetitive units, the satellite DNA is classified into many categories, such as micro-satellites, mini-satellites etc. These sequences normally do not code for any proteins, but they form a large portion of human genome. These sequence show high degree of polymorphism and form the basis of DNA fingerprinting.

37. (c) NCERT (XII) Ch - 6, Pg. 110

During transcription, RNA polymerase associates transiently with the termination-factor (ρ) to terminate the transcription.

38. (c) During translation initiation in prokaryotes, a GTP molecule is needed in association of formyl-met-tRNA with initiation codon on mRNA.

39. (c) Restriction Fragment Length Polymorphism (RFLP) is a molecular technique that exploits difference in homologous DNA sequences that can be detected by the presence of fragments of different lengths after digestion of the DNA samples in question with specific restriction endonucleases. RFLP, as a molecular marker, is specific to a single restriction enzyme.

Evolution (Questions on Page No. 175-176)

28. (d) NCERT (XII) Ch - 7, Pg. 127Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing non-living organic molecules (e.g. RNA, protein, etc.) and that formation of life was preceded by chemical evolution, i.e., formation of diverse organic molecules from inorganic constituents. The conditions on earth were – high temperature,

volcanic storms, reducing atmosphere containing CH4 , NH3 , etc.

29. (d) Variations due to mutation or recombination during gametogenesis, or due to gene flow or genetic drift results in changed frequency of genes and causes genetic variability.

30. (c) Molecular homology is an important concept in modern evolutionary biology. It is used to test the relationships between modern taxa and to examine the evolutionary processes driving evolution at a molecular level.

31. (b) When populations of a species are separated by a physical or geographical barrier, e.g., river, mountains, etc., allopatric speciation (formation of new species) occurs. Only organisms belong to the same species can interbreed to produce viable, fertile offspring. An inter-breeding population of finches became separated geographically, forming two isolated groups, i.e., different species therefore they are unable to produce fertile offsprings.

32. (a) The theory of recapitulation or Biogenetic law was given by Ernst Haeckal. It states that an individual organism in its development (ontogeny) tends to repeat the stages passed through by its ancestors (phylogeny), i.e., ontogeny recapitulates phylogeny.

33. (c) Fossils are remains of hard parts of life-forms found in rocks. Rocks form sediments and a cross-section of earth’s crust indicates the arrangement of sediments one over the other during the long history of earth. Different-aged rock sediments contain fossils of different life-forms who probably died during the formation of the particular sediment.

34. (d) According to Darwinism, the correct sequence of events in the origin of a new species is D (struggle for existence) →B (variations and their inheritance) →C (survival of the fittest) →A (natural selection)

35. (c) NCERT (XII) Ch - 7, Pg. 136

When more individuals acquire peripheral character value at both ends of the distribution

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curve then it is called disruptive natural selection.

36. (d) Charles Darwin, a British naturalist, proposed the theory of biological evolution by natural selection. Retention of characters of no use or vestigial organs could not be explained by Darwin’s theory. According to his theory, species keep on evolving or changing with time and almost all organisms share common ancestry with some organism. He also studied that the birds of Galapagos Island (Darwin’s finches) developed different beaks as per the availability of the food. This proved adaptive radiation.

37. (d) NCERT (XII) Ch - 7, Pg. 130

In these animals, the same structure developed along different directions due to adaptations to different needs. This is divergent evolution and these structures are homologous. Homology indicates common ancestry.

38. (a) On the basis of above traits the Asians, African and europeans are the members of one species. The biological species concept defines a species as members of populations that can interbreed in nature and produce sterile offsprings.

39. (b) The primitive atmosphere was of a reducing nature. It was transformed into an oxidizing atmosphere due to the emergence of cyanobacteria (oxygenic photoautotrophs).They used water to get hydrogen and released oxygen into the atmosphere.

Human Health and disease (Questions on Page No. 201)

26. (c) Filariasis is caused by W. bancrofti and W. malayi. The major vectors of W. bancrofti are mosquitoes of the genus Culex (in urban and semi-urban areas), Anopheles (in rural areas of Africa and elsewhere) and Aedes (in islands of the Pacific).

27. (b) Antibodies, also called immunoglobulins, are glycoprotein molecules that constitute the gamma globulin part of blood proteins. These are secreted by activated B-cells or plasma cells (WBCs).

28. (a) NCERT (XII) Ch - 8, Pg. 152

Cell-mediated immunity is an immune response that does not secrete antibodies but activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to a foreign antigen, virus or parasite cells. The body is able to differentiate ‘self’ and ‘non-self’ and the cell-mediated immune response is responsible for the graft rejection.

29. (d) NCERT (XII) Ch - 8, Pg. 153

Memory-based acquired immunity evolved in higher vertebrates based on the ability to differentiate foreign organisms (e.g., pathogens) from self cells. Sometimes, due to genetic and other unknown reasons, the body attack self-cells. This results in damage to the body and is called auto-immune disease, e.g., rheumatoid arthritis.

30. (b) Acquired immunity is pathogen specific and is characterized by memory. This means that our body when it encounters a pathogen for the first time produces a response called primary response which is of low intensity. Subsequent encounter with the same pathogen elicits a highly intensified secondary or an amnestic response.

Strategies for Enhancement in Food Production

(Questions on Page No. 225) 24. (b) NCERT (XII) Ch - 9, Pg. 176

More than 25 per cent of human population is suffering from hunger and malnutrition. One of the alternate sources of proteins for animal and human nutrition is Single Cell Protein (SCP). Microbes are being grown on an industrial scale as good source of protein, minerals, fats, carbohydrate and vitamins. Incidentally such utilisation also reduces environmental pollution. It has been calculated that a 250 Kg cow produces 200 g of protein per day. In the same period, 250g of a micro-organism like Methylophilus methylotrophus, because of its high rate of biomass production and growth, can be expected to produce 25 tonnes of protein.


25. (d) NCERT (XII) Ch - 9, Pg. 169 & 170Bee-keeping or apiculture is the maintenance of hives of honeybees for the production of honey. The most common species is Apis indica. Keeping beehives in crop fields during flowering period increases pollination efficiency and improves the yield–beneficial both from the point of view of crop yield and honey yield. Some of the marine fishes that are eaten include – Hilsa, Sardines, Mackerel and Pomfrets. Green revolution was dependent to a large extent on plant breeding techniques for development of high-yielding and disease resistant varieties in wheat, rice, maize, etc.

26. (a) NCERT (XII) Ch - 9, Pg. 169In Multiple Ovulation Embryo Transfer Technology (MOET), a programme for herd improvement, a cow is administered hormones, with FSH-like activity, to induce follicular maturation and super ovulation – instead of one egg, which they normally yield per cycle, they produce 6-8 eggs. The animal is either mated with an elite bull or artificially inseminated. The fertilised eggs at 8–32 cells stages, are recovered non-surgically and transferred to surrogate mothers.

27. (b) NCERT (XII) Ch - 9, A, C and D - Pg. 176; B - Pg. 177

Microbes like Spirulina can be grown easily on materials like waste water from potato processing plants (containing starch), straw, molasses, animal manure and even sewage, to produce large quantities and can serve as food rich in protein, minerals, fats, carbohydrate and vitamins.By somatic hybridization, when a protoplast of tomato is fused with that of potato, and then they are grown to form new hybrid plants combining tomato and potato characteristics. This results in the formation of pomato; unfortunately this plant did not have all the desired combination of characteristics for its commercial utilization.An iron-fortified rice variety has been developed by fortification that contains over

five times as much iron as in commonly consumed varieties.

28. (d) Plant tissue culture is the technique of maintaining and growing plant cells, tissues or organs especially on artificial medium in suitable containers under controlled environmental conditions. Sterilization means complete destruction or killing of microorganisms so that complete aseptic conditions are created for in vitro culturing. Cells/tissues are regularly transferred into new culture vessels containing fresh media. This process is called sub culturing.

Microbes in Human Welfare (Questions on Page No. 245)

24. (a) During ethanol production a yeast culture tank, which is provided with nutrition supply of ammonium and magnesium phosphate or sulphate, is used as nutrient to the yeast. The acidic condition favours the yeast to produce catalytic enzymes, invertase and zymase. The reactions involved are C12H22O11 + H2O → 2C6H12O6 , with enzyme invertase. C6H12O6 → 2C2H5OH + 2CO2 , with enzyme zymase.

25. (c) NCERT (XII) Ch - 10, Pg. 182Yeast (Saccharomyces cerevisiae) is used for commercial production of ethanol.

26. (d) NCERT (XII) Ch - 10, Pg. 181The large holes in ‘Swiss cheese’ are due to production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii.

27. (a) NCERT (XII) Ch - 10, Pg. 184Treatment of waste water is done by heterotrophic microbes naturally present in the sewage. This treatment is carried out in two stages: i. Primary treatment: These treatment steps

basically involve physical removal of particles – large and small – from the sewage through filtration and sedimentation. All

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solids that settle form the primary sludge, and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.

ii. Secondary treatment: The primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs. While growing, these microbes consume the major part of the organic matter in the effluent. This significantly reduces the BOD (biochemical oxygen demand) of the effluent. In anaerobic sludge digesters, other kinds of bacteria grow anaerobically which digest the bacteria and the fungi in the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as source of energy as it is inflammable.

28. (b) NCERT (XII) Ch - 10, Pg. 183

Bottled fruit juices bought from the market are clearer as compared to those made at home. This is because the bottled juices are clarified by the use of pectinases and proteases.

Biotechnology: Principles and Processes (Questions on Page No. 267)

25. (a) NCERT (XII) Ch - 11, Pg. 200

The selectable markers are used to differentiate recombinants from non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate. In this, a recombinant DNA is inserted within the coding sequence of an enzyme, β-galactosidase. This results into inactivation of the enzyme, which is referred to as insertional inactivation. The presence of a chromogenic substrate gives blue coloured colonies if the plasmid in the bacteria does not have an insert. Presence of insert results into insertional inactivation of the â-galactosidase and the colonies do not produce any colour, these are identified as recombinant colonies.

26. (c) NCERT (XII) Ch - 11, Pg. 197

Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome sites, but between the same two bases on the opposite strands. This leaves single stranded portions at the ends. There are overhanging stretches called sticky ends on each strand. This stickiness of the ends facilitates the action of the enzyme DNA ligase. In the given question, option A and C will produce sticky ends while option B and D will produce blunt ends.

27. (d) Continuous culture system provides regular drainage of the medium and culture cells from one side and fresh medium from the other side leading to higher yield of desired product.

28. (c) NCERT (XII) Ch - 11, Pg. 198

The cutting of DNA by restriction endonucleases results in the fragments of DNA. These fragments can be separated by a technique known as gel electrophoresis. Since DNA fragments are negatively charged molecules they can be separated by forcing them to move towards the anode under an electric field through a medium/matrix.

The separated DNA fragments can be visualized only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation. Bright orange coloured bands of DNA can be visualized in a ethidium bromide stained gel when exposed to UV light.

29. (a) The stirred tank bioreactor has been designed for the availability of oxygen throughout the processes. The most common type of aerobic bioreactor in use today is the stirred tank reactors, which may feature a specific internal configuration designed to provide a specific circulation pattern.

30. (c) A multiple cloning site (MCS), also called a polylinker, is a short segment of DNA which contains many restriction sites. Thus, it allows flexibility in the choice of restriction enzymes.


Biotechnology and its Applications (Questions on Page No. 289)

25. (b) NCERT (XII) Ch - 12, Pg. 212

PCR is used to detect HIV in suspected AIDS patients. It is being used to detect mutations in genes in suspected cancer patients too. It is a powerful technique to identify many other genetic disorders.

26. (d) Bt brinjal provides resistance against lepidopteron insects and bt corn provides resistance against corn borer.

27. (c) Polygalacturonase protein is found most abundantly in ripe tomato and is responsible for softening in ripe tomatoes. In the development of Flavr savr tomato, antisense RNA is used to regulate the expression of the enzyme polygalacturonase.

28. (c) The insulin isolated from other animals may elicit an immune response in the human body. Insulin from an animal source caused some patients to develop allergy or other types of reactions to the foreign protein. Therefore, genetically engineered insulin considered better for human diabetic patients.

29. (c) RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA (silencing). The RNAi pathway is initiated by the enzyme Dicer, which cleaves long double-stranded RNA (dsRNA) molecules into short double-stranded fragments of 21 nucleotide siRNAs.

Organisms and Populations (Questions on Page No. 315)

34. (a) Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP).

35. (c) NCERT (XII) Ch - 13, Pg. 237

Examples given in statement A and B exhibits mutualism. Mutualism interaction confers benefits on both the interacting species. The mycorrhizae (Boletus) are associations between fungi and the roots of higher plants. The fig (e.g., Ficus) shows one-to-one relationship with the pollinator species of wasp (e.g., Blastophaga).

36. (d) Lotus plants in pond = 20New plants by reproduction = 8Birth rate of population

New plants 8100 100Old plants 20

= × = ×

= 0.4 offspring per lotus per year 37. (d) In arithmetic growth, the population

increases by a constant number of individuals with time. If the numbers of individuals are plotted against time it shows a linear curve.

38. (c) When a foreign species is introduced into a geographical area, it become invasive and starts spreading fast because the invaded land does not have its natural predators. The invasive species also have the ability to out-compete native species.

39. (c) NCERT (XII) Ch - 13, Pg. 231

In logistic growth, no population of any species in nature has at its disposal unlimited resources to permit exponential growth. This leads to competition between individuals for limited resources. This type of growth in population is described by the following equation: dN K NrNdt K

− = Where N = Population density at time t r = Intrinsic rate of natural increase K = Carrying capacity

40. (a) NCERT (XII) Ch - 13, Pg. 232

Interspecific interactions arise from the interaction of populations of two different species. They could be beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both.

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41. (b) NCERT (XII) Ch - 13, Pg. 236

Majority of the parasites harms the host; they may reduce the survival, growth and reproduction of the host and reduce its population density. They might render the host more vulnerable to predation by making it physically weak.

42. (b) Ascending trophic level in grazing (grassland) food chain pyramid represents gradual decrease in biomass from producers to the tertiary consumer. This is because pyramid of biomass shows a sharp decrease in biomass at higher trophic levels.

43. (a) NCERT (XII) Ch - 13, Pg. 225

In the absence of an external source of water, the kangaroo rat in North American deserts is capable of meeting all its water requirements through its internal fat oxidation (in which water is a byproduct). It also has the ability to concentrate its urine so that minimal volume of water is used to remove excretory products.

44. (a) Due to conventional practices of animal breeding and care, the contribution to the world farm produce is only 25 per cent, i.e., the productivity per unit is very low.

45. (b) NCERT (XII) Ch - 13, Pg. 226

Some organisms show behavioural responses to cope with variations in their environment. Desert lizards lack the physiological ability that mammals have to deal with the high temperatures of their habitat, but manage to keep their body temperature fairly constant by behavioural means. They bask in the sun and absorb heat when their body temperature drops below the comfort zone, but move into shade when the ambient temperature starts increasing.

46. (c) Rainforests are an asset to the entire world. The destruction of rainforests worldwide is a problem because it eliminates habitat for wild life and depletes the earth of vital environmental services. By vanishing tropical rain forest for agriculture, the fertility of soil is reduced and does not support agriculture.

Ecosystem (Questions on Page No. 339)

27. (b) When any organism dies, it is converted to detritus or dead biomass that serves as an energy source for decomposers. Organisms at each trophic level depend on those at the lower trophic level for their energy demands.

28. (d) NCERT (XII) Ch - 14, Pg. 242

The components of the ecosystem are seen to function as a unit when you consider the following aspects:

(i) Productivity;

(ii) Decomposition;

(iii) Energy flow; and

(iv) Nutrient cycling

29. (d) Because decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients which is used as a substrate for other living being (producer).

30. (d) NCERT (XII) Ch - 14, Pg. 248

Pyramid of biomass shows a sharp decrease in biomass at higher trophic levels.

31. (c) Mr X should be considered as occupying third trophic level, i.e., secondary consumer. Producer (grass) – First trophic level Primary consumer (cow) – Second trophic level Secondary consumer ( man ) – Third trophic level Here cow is eating grass (1st level), grass transfers energy to the cow (2nd level). The cow is producing milk from which curd is prepared. The person, Mr X (3rd level) is eating the curd. This means the energy is getting transferred from cow to man through curd (byproduct of cow).


Biodiversity and Conservation (Questions on Page No. 361)

20. (c) Interspecific interactions arise from the interaction of populations of two different species. They could be beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both.Example: In a field experiment, when all the starfish were removed from an enclosed intertidal area, more 10 species of invertebrates became extinct within a year.

21. (d) NCERT (XII) Ch - 15, Pg. 267In ex situ conservation, gametes of threatened species can be preserved in viable and fertile condition for long periods using cryopreservation techniques.

22. (d) A keystone species have an extremely high impact on a particular ecosystem relative to its population. They play an important role in supporting other species. E.g., Red mangrove grows along the shoreline in the tropics and its roots protect the soil from erosion. The roots also offer protection to small animals, including reef fish.

23. (c) Gene pool is the collection of all the genes of a particular population. If the Bengal Tiger becomes extinct, its gene pool will be lost forever.

Environmental Issues (Questions on Page No. 387)

26. (a) The BOD test measures the rate of uptake of oxygen by micro-organisms in a sample of water and thus, indirectly, BOD is a measure of the organic matter present in the water. The greater the BOD of waste water more is its polluting potential.

Out of the above three samples, sample C is the most polluted, i.e., untreated sewage water, since it has the maximum BOD value of 400 mg/L. After untreated sewage water, secondary effluent discharge from a sewage treatment plant is most polluted. Thus, sample A is secondary effluent discharge from a sewage treatment plant and has the BOD value of 20 mg/L, while sample B is drinking water and has the BOD value of 2 mg/L

27. (b) After secondary treatment of sewage, the effluent is passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge. A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.

28. (c) Ozone, secondary pollutant, is formed when hydrocarbons (HCs) and nitrogen oxides (NOx) combine in the presence of sunlight.

29. (b) NCERT (XII) Ch - 16, Pg. 275

Presence of large amounts of nutrients in waters also causes excessive growth of planktonic (free-floating) algae, called an algal bloom which imparts a distinct colour to the water bodies. Algal blooms cause deterioration of the water quality and fish mortality due to oxygen deficiency.

30. (d) NCERT (XII) Ch - 16, Pg. 283

Exposure to ozone hole lead to extreme sensitivity in some persons and develop a condition such as cataracts, xeroderma pigmentosum, etc.

31. (b) In seasons of lesser solar radiation or areas, smog formation is incomplete and the air is referred to as grey air.

Documents

Higher Order Advance Round Explanations · sponge) and Euspongia (Bath sponge) are the examples of phylum Porifera. 23. (c) NCERT (XI) Ch - 4, Pg. 52 The body of the aschelminthes