ANSWER KEYS

CLASS XI SET A

1. The members of phaeophyceae(brown algae) store mannitol. 1

2. It is the reproduction cycle that alternates between cyclic and non-cyclic.Example is life cycle of cnidarians in which one generation is polyp and other is Medusa form.

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3. Phellem or cork is a tissue formed on the outer side of phellogen or cork cambium and is composed of dead cells whereas Phelloderm or secondary cortex is produced on the inner side of phellogen and is made of living cells.

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4. Chromatid is either of the two daughter strands of a duplicated chromosome that are joined by centromere and separate during cell division to become individual chromosome.

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6. Heterospory is reproduction of spores of two different sizes and sexes by the saprophytes of land plants. In evolution of plants Pteridophyta are intermediate between bryophytes and gymnosperms. All bryophytes are homosporous and all gymnosperms are heterosporous. This condition is advanced as sexual dimorphism result in cross fertilization. Primitive or earlier Pteridophyta are homosporous and later are hetersporous.

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7. It is called substrate-level phosphorylation because it involves a direct transfer of a phosphoryl group from a phosphorylated reactive intermediate to ADP or GDP.

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8. Diagram based. 2

9. Casparian strips are found in the endodermal cell walls of plant roots. It prevents water movement from returning to cortex from pericycle, consequently a positive hydrostatic pressure is established in vascular tissue.

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10. Palms have a thickening meristem below their leaf primordia. It adds ground parenchyma and vascular bundles continuously. The ground parenchyma may also further divide even after the completion of elongation. This leads to increase in girth like dicot plants.

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11. a) All mammals except platypus.b) Trygon(sting-ray)c) Torpedo(electric ray).d) Class Osteichthyes (Catia)e) Aurelia or Jelly fishf) Ornithorhynchus(duck-billed platypus)

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12 Cilia is covered with plasma membrane and the core called the axoneme, it possess a number of microtubules running parallel to the long axis. The axoneme usually has nine pairs of doublets of radially arranged peripheral microtubules and a pair of centrally located microtubules. Such an arrangement of axonemal microtubules is referred to as 9+2 array. The central tubules are connected by bridges and is also enclosed by a central sheath which is connected to one of the tubules of each peripheral doublets by a radial spoke. Thus, there are nine radial spokes.

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13. In humans during prophase , a human will have 46 chromosomes, but 92 chromatids.

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14. Digestion starts in the mouth with the mandibles and the maxillae chewing the food. It is also acted upon by the salivary carbohydrases which partially digests the food. The food is then swallowed with the help of lubrication provided by the salivary juice.

The food then enters the oesophagus and then into the crop. Here, the masticated food is temporarily stored.

The food is then passed into the gizzard which acts as the grinding chamber. At the junction of the gizzard and the stomach is a valve called the stomodael valve. It allows the passage of only the thoroughly digested food into the stomach and also, prevents the regurgitation of food from the stomach.

The ground food then enters the stomach. The digestive enzymes secreted by the gastric caecae act upon the food in the stomach. These enzymes include amylase, maltase, invertase, tryptase and lipase. The remaining carbohydrates, proteins and fats are digested here.

The digested food is absorbed through the stomach walls into the surrounding space which is called the haemocoel. The haemocoel consists of a large number of fat bodies which are fat cells having fat globules, protein granules and glycogen. They form storage structures. From here, it is transported to the different body parts.

In the hindgut, absorption of water takes place and the undigested food is formed into almost dry pellets. These are excreted through the anus as faeces.

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15. Primary Metabolites:i.These are the metabolites which have identifiable metabolism functions and play a specific role in the metabolism.ii.These are important in human metabolic processes. e g Amino acids, sugars.

Secondary Metabolites:i.These are the metabolites formed during metabolism, whose role or exact functions in the tissue are not known.ii.These are useful to human .e.g., Alkaloids, flavonoids

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Lipids are esters of higher fatty acid with alcohol such as glycerol. These can be classified as:

a) Simple lipids: they are esters of fatty acid with glycerol and can be Fats-These are esters of fatty acid and glycerol.Waxes- These are esters of higher fatty acids with alcohol other than glycerol.

b) Compound or Conjugated Lipids: They are simple lipids with a prosthetic group. They can be:Glycerophospholipid

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SphingolipidGlycolipid

c) Steroids are compounds with similar chemical structure but similar physical properties.Eg: Cholestrol

d) Prostoglandins which are biologically active lipids.

16. a) Differentiation: The cells are derived from root apical and shoot-apical meristems and cambium differentiate and mature to perform specific functions. This act leading to maturation is termed as differentiation.Example: To form tracheary element, the cells would lose their protoplasm. They also develop a very strong secondary cell wall to carry water.

b) De-differentiation: The living differentiated cells that by now have lost the capacity to divide can regain the capacity of division under certain conditions. This phenomena is de-differentiation. Example: Formation of meristem- interfasicular cambium and cork cambium from fully differentiated parenchyma cells.

c)Re-differentiation: While doing de-differentiation , such meristems/tissues are able to divide and produce cells that once again lose the capacity to divide but mature to perform specific functions i.e get re-differentiatedExample: Secondary xylem and secondary cortex.

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17. The word chemiosmotic means simply that there is osmotic gradient for a chemical in photosynthesis. There is accumulation of H+ ions in the lumen of thylakoids. This gradient is because of many reasons. Firstly, the hydrolysis of water occurring on the inner side of membrane sends its H+ ion to the lumen. Secondly, the H+ ion required for formation of NADPH is taken from stroma. This all cause the gradient accumulating H+ ions which are then send back to the stroma through ATP pump, through its f0 - f1 channel, having ATPase enzyme and so formation of ATP occurs. This all occurs during light reaction and so ATP synthesis is a chemiosmotic phenomenon.

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18. The gradient of increasing hyperosmolarity of medullary interstitium is maintained by a counter current mechanism and the proximity between the Henle’s loop and vasa recta.This gradient is mainly caused by NaCl and urea. The transport of these substances facilitated by the special arrangement of Henle’s loop and vasa

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recta is called the counter current mechanism. NaCl is transported by the ascending limb of Henle’s loop, which is exchanged with the descending limb of vasa-recta. NaCl is returned to the medullary interstitium by the ascending part of vasa recta. But, contrarily, the water diffuses into the blood of ascending limb of vasa recta and is carried away into the general blood circulation.Permeability to urea is found only in the deeper parts of thin ascending limbs of Henle’s loops and collecting ducts. Urea diffuses out of the collecting ducts and enters into the thin ascending limb. A certain amount of urea recycled in this way is trapped in medullary interstitium by the collecting tubule. This mechanism helps in the maintenance of a concentration gradient in the medullary interstitium.Presence of such gradient helps in an easy passage of water from the collecting tubule, resulting in the formation of concentrated urine (filtrate) i.e., nearly four times concentrated than the initial filtrate formed.

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Changes that will take place in food (roti and dal) through the passage of alimentary canal are(i) The food substances are first masticated by the teeth in the mouth, where carbohydrate part of the food is digested by the action of salivary amylase enzyme secreted by the salivary glands.(ii) This partially digested food reaches the stomach, where it receive acidic HCl and mainly the . protein part of the food is digested by the action of proteolytic enzymes.(Hi) The lipid part of the food is digested by the bile secreted by the gall bladder.(iv) In the small intestine, particularly in the duodenum this semidigested food is finally digested by the digestive enzymes present in the intestinal and pancreatic juices.(v) After digestion, the broken down products of food, i.e., amino acids, glycerol, starch, etc., are absorbed mainly in the small intestine.(vi) The undigested remains of food will finally pass through the anus.

19. Nitrogen fixation in root nodules occurs directly within the bacteroids. The host plat provides bacteroids with carbohydrates, which they oxidize and from which they obtain energy. These carbohydrates are first formed in leaves during photosynthesis and then are translocated through phloem to the root nodules. Sucrose is the most abundant carbohydrate translocated, at

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least in legumes. Some of the electrons and ATP obtained during oxidation by the bacteroids are to reduce N2 to NH4

+.The process requires both a source of electrons and protons and numerous ATP molecules. The original source of electrons and protons is carbohydrate translocated from leaves . Respiration of carbohydrate in bacteroids leads to reduction of NAD+ to NADH+.Fate of Ammonia: Nitrogen assimilation results in the formation of ammonia which is further used for synthesis of amino acids. Most of the plants can assimilate both nitrate and ammonium ions. Thus ,these NH4 are used in the synthesis of amino acids by the following two methods:

a) Reductive aminationb) Transamination

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21. Formation of cross-bridge between the actin and myosin filament help muscle to contract.

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i) An ATP molecule joins the active site on myosin head of myosin myofilament. These heads contains an enzyme, myosin ATPase that along with calcium and magnesium ions catalyses the breakdown of ATP.

ii) The energy is transferred to myosin head which energises and straightens to join an active site on actin myofilament, forming a cross-bridge.

22. The cortex is regulated by neuroendocrine hormones secreted by the pituitary gland, which are under the control of the hypothalamus, as well as by the renin- angiotensin system. The adrenal cortex has three zones or layers:

1. Zona glomerulosa (outer)2. Zona fasciculata3. Zona reticularis

Hormones of the Adrenal Cortex

The different zones of the adrenal cortex produce different hormones.

Mineralocorticoids:These are produced in the zona glomerulosa. The primary mineralocorticoid is aldosterone. Its secretion is regulated by the oligopeptide angiotensin II. Aldosterone is secreted in response to high extracellular potassium levels, low extracellular sodium levels, and low fluid levels and blood volume. Aldosterone secretion affects metabolism in

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different ways: It increases urinary excretion of potassium ions It increases interstitial levels of sodium ions It increases water retention and blood volume.

Glucocorticoids: These are produced in the zona fasciculata. The primary glucocorticoid released by the adrenal gland in humans is cortisol. Its secretion is regulated by the hormone ACTH from the anterior pituitary gland. Upon binding to its target, cortisol enhances metabolism in several ways:

It stimulates the release of amino acids from the body It stimulates lipolysis, the breakdown of fat It stimulates gluconeogenesis, the production of glucose from newly-

released amino acids and lipids It increases water retention It has anti-inflammatory and anti-allergic effects.

Androgens

The zona reticularis produces androgens, the most important of which is DHEA. In general, these hormones do not have an overall effect in the male body, and are converted to more potent androgens such astestosterone and DHT or to estrogens (female sex hormones) in the gonads, acting in this way as a metabolic intermediate.

23. a) Both have 70s ribosomes.b) Because they use pyruvate as a fuelproduced during glycolysis in the cytoplasm.c) Because they undergo only glycolysis and produce 2 molecules of ATP during anaerobic respiration.d) Value based.

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24. a) The major plasma proteins are fibrinogen, globulins and albumins.• Fibrinogen play important role in blood coagulation.• Globulins protects the body against infecting agents

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• Albumins helps inmaintaining the fluid volume within the vascular space.

b) Each peak in the ECG is identified with a letter from P to T that corresponds to a specific electrical activity of the heart.The P-wave represents the electrical excitation or depolarization of the atria. Depolarisation of atria leads to atricular systole.The QRS complex represents the depolarization of the ventricles which initiates ventricular systole.The T-wave represents the return of the ventricles from excited to normal state (repolarisation). The end of T-wave marks the end of systole.

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The cochlea of the inner ear helps in hearing. The cochlea is lined by tiny hair cells and is filled with fluid.

When the middle ear transfers vibrations to the cochlea, the fluid in the cochlea is displaced. This displacement of the fluid makes the hair cells move.

Signals from these cells are converted into nerve impulses and sent to the brain through the auditory nerve thereby helping in the process of hearing.

b)Two structures of the inner ear help to maintain balance and equilibrium -

the three semicircular canals that are interconnected and positioned at right angles to each other just like a gyroscope.

the vestibule (has the saccule and utricle) that connects the semicircular canals to the cochlea

The semicircular canals and the vestibule of the inner ear together help to maintain the balance and equilibrium of the body.

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b)It occurs in mesophyll cells and bundle sheath cells.

c) C3 Cycle C4 CycleIt operates in all plants. It operates in C4 plants only.The first stable compound is 3 carbon,phosphoglyceric acid.

The first stable product is oxalo acetic acid.

The carboxylase enzyme is Rubisco.

Carboxylase enzyme is PEP carboxylase and Rubisco.

Kranz anatomy is absent. Kranz anatomy is present.Oxygen has inhibitory effect. Oxygen has no inhibitory effect.Single CO2 fixation. Two CO2 fixation.Occurs in plants like Mango,apple etc.

Occurs in plants like maize,sorghum etc.

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a)It takes place in the thyllakoid membrane of the chloroplast.

b)While noncyclic photophosphorylation uses both photosystem I and photosystem II acting in series.  In this, it transports a noncyclic electron. The active reaction center in noncyclic photophosphorylation is P680 and electrons travel in a non-cyclic manner. The electrons from photosystem I is accepted by NADHP. In this process, both NADHP and ATP are produced. The process of photolysis or water splitting is present unlike cyclic photophosphorylation and towards the end, oxygen is evolved as a byproduct. 

26. Enzymes generally lower activation energy by reducing the energy needed for reactants to come together and react. Enzymes bring reactants together so they don’t have to expend energy moving about until they collide at random. Enzymes bind both reactant molecules (called substrates), tightly and specifically, at a site on the enzyme molecule called the active site . This forms an enzyme-substrate complex.

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By binding reactants at the active site, enzymes also position reactants correctly, so they do not have to overcome intermolecular forces that would otherwise push them apart. This allows the molecules to interact with less energy.

Enzymes may also allow reactions to occur by different pathways that have lower activation energy.

Steps of catalytic cycle of an enzyme action are :(a) The substrate binds to the active side of the enzyme.(b) This binding of the substrate induces the enzymes to alter its shape and fit more closely around the substrate.(c)The active site of the enzyme, now is in close proximity of the substrate breaks the chemical bonds of the substrate and an enzyme-product complex is formed.(d) The enzyme releases the products of the reactionand the free enzyme is ready to take up another molecule of the substrate

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The important features of Watson – Crick Model or double helix model of DNA are as follows:1. The DNA molecule consists of two polynucleotide chains or strands that

spirally twisted around each other and coiled around a common axis to form a right-handed double-helix.

2. The two strands are antiparallel i.e. they ran in opposite directions so that the 3′ end of one chain facing the 5′ end of the other.

. The sugar-phosphate backbones remain on the outside, while the core of the helix contains the purine and pyrimidine bases.

The two strands are held together by hydrogen bonds between the purine and pyrimidine bases of the opposite strands.

5. Adenine (A) always pairs with thymine (T) by two hydrogen bonds and guanine (G) always pairs with cytosine (C) by three hydrogen bonds. This complimentarily is known as the base pairing rule. Thus, the two stands are complementary to one another.

6. The base sequence along a polynucleotide chain is variable and a specific sequence of bases carries the genetic information.

7. The base compositions of DNA obey Chargaff s rules (E.E. Chargaff, 1950) according to which A=T and G=C; as a corollary ∑ purines (A+G) = 2 pyrimidines (C+T); also (A+C) = (G+T). It also states that ratio of (A+T) and (G+C) is constant for a species (range 0.4 to 1.9).

8. The diameter of DNA is 20nm or 20 A. Adjacent bases are separated 0.34 nm or by 3.4 A along the axis. The length of a complete turn of helix is 3.4 nm or 34 A i.e. there are 10bp per turn. (B- DNA-Watson rick DNA).