CBSE previous Year Solved  Papers  Class 12 Biology Delhi 2012

Time allowed : 3 hours                                                                                           Maximum Marks: 70

General Instructions :

  1.  There are a total of 26 questions and five sections in the question paper, All questions are compulsory.
  2. Section A contains question number 1 to 5, Very Short Answer type questions of one mark each.
  3.  Section B contains question number 6 to 10, Short Answer type I questions of two marks each.
  4.  Section C contains question number 11 to 22, Short Answer type II questions of three marks each.
  5.  Section D contains question number 23, Value Based Question of four marks.
  6. Section E contains question number 24 to 26, Long Answer type questions of five marks each.
  7. There is no overall choice in the question paper, however, an internal choice is provided in one question of two marks, one question of three marks and all three questions of five marks. An examined is to attempt any one of the questions out of two given in the question paper with the same question number.



Question.1. Mention the unique flowering phenomenon exhibited by Strobilanthus kunthiana (neelakuranji).
Answer : The unique flowering phenomenon exhibited by Strobilanthus kunthiana (neelakuranji) is that it flowers once in 12 years.

Question.2. How does smoking tobacco in human lead to oxygen deficiency in their body ?
Answer: Smoking tobacco lead to oxygen deficiency in human body because smoking increases carbon monoxide (CO) content in blood. The greater affinity of CO to haemoglobin/ CO forms a stable bond with haemoglobin. Presence of CO does not allow pxygen to bind with haemoglobin and reduces the concentration of haem-bound oxygen. This causes oxygen deficiency in the body.

Question.3. A garden pea plant (A) produced inflated yellow pod, and another plant (B) of the same species produced constricted
green pods. Identify the dominant traits.
Answer : The trait to produce inflated yellow seeds is dominant over the trait producing constructed green seeds.

Question.4. Why is Eichhomia crassipes nicknamed as “Terror of Bengal” ?
Answer : It grows at an alarming rate and spreads on . the surface of the water body, causes oxygen depletion leading to death of aquatic life of fishes and other aquatic organisms.

Question.5. Write the location and function of the sertoli cells in humans.
Answer : Location of Sertoli cells – In the testis Function of Sertoli cells – Provide nutrition to the developing sperm cells.

Question.6. Name the following:
(a) The semi-dwarf variety of wheat is high-yielding and disease-resistant.
(b) Any one inter-specific hybrid mammal.
Answer : (a) Sonalika and Kalyan Sona are the semi-dwarf.
(b) Mule/Hinny/Liger/Tigon.

Question.7. Write the similarity between the wing of a butterfly and
the wing of a bat. What do you infer from the above with reference to evolution ?
Answer: Analogous organs as their origin is not the same but they perform similar functions. From the above reference we can infer the evolutionary relationship between organisms and show convergent evolution.

Question.8. Write what do phytophagous insects feed on.
Answer : As the name suggest phytophagous insects feed on plants/ Plant sap.


Question.9. Draw a neat labelled sketch of a replicating fork of DNA.

Question.10. Where is sporopollenin present in plants ? State its significance with reference to its chemical nature.
Answer : Present in exine, of pollen or pollen grain Sporopollenin is the most resistant organic polymer hence protects the pollen/gamete and provides protection to pollen from unfavorable conditions.

Question.11. (a) Highlight the role of thymus as a lymphoid organ.
(b) Name the cells that are released from the above mentioned gland. Mention how they help in immunity. .
Answer: (a) Immature lymphocyte differentiate into mature lymphocyte in thymus. T-cells produced in the bone marrow get matured in the thymus and are released from here and migrate to secondary lymphoid organs.
(b) The cells are released from the thymus gland are known as T-lymphocyte. These T-cells help B-cells to produce antibodies and takes part in immunity.

Question.12. Explain the work carried out by Cohen and Boyer that contributed immensely in biotechnology.
Answer : Stanley Cohen and Herbert Boyer constructed the first artificial recombinant DNA. They isolated the antibiotic resistant gene, from the plasmid of a bacterium that was resistant to the antibiotic drug , and then linked this gene with the plasmid of Salmonella typhimurium, construction of artificial recombinant DNA molecule.

Question.13. Why do clownfish and sea anemone pair up ? What is this relationship called ?
Answer : Clown fish lives in tentacles of sea anemone and gets protection from its predators by moving around the stinging tentacles of the sea anemone.
The sea anemone is neither helped or harmed by the inte-raction with the fish, the relationship is called commensalism.

Question.14. (a) State the difference between meiocyte and gamete with
respect to chromosome number.
(b) Why is a whiptail lizard is referred to as partheno-genetic ?
Answer : (a) Meiocyte – diploid (2n)
Gamete – haploid (n)
(b) Whiptail lizard referred as parthenogenetic because it is a female and gives rise to new female reptile without fertilization and female gamete undergoes development to form new organism from unfertilised egg.

Question.15. Name the plant source of the drug popularly called “smack”. How does it affect the body of the abuser ?
Answer: Plant source of smack: Papaver somniferum (Poppy) which is a stronger analgesic than morphine.
Effect of smack on the body of abuser: It reduces heart rate and increase blood sugar and it is a depressant which slow down body function.
Why is Rhizobium categorized as a ‘symbiotic bacterium’ ? How does it act as a biofertiliser ?
Answer : Rhizobium, a symbiotic bacteria, which live in the . root nodule of leguminous plants, fixes atmospheric nitrogen into organic forms to be used by plants. It is a biofertilizer as it is a living organism that enriches nutrient content of the plant. Bacterium gets food and shelter from the plant.

Question.16. (a) State the role of DNA ligase in biotechnology.
(b) What happens when Meloidegyne incognitia consumes cells with RNAi gene ?
Answer : Role of DNA ligase in biotechnology, (a) Joining of DNA fragment is done by DNA ligase, linking of Okazaki fragments or discontinous synthesis fragments and linking of desired gene with plasmid to form recombinant DNA.
(b) If Meloidegyne incognitia consumes cells with RNAi gene so specific mRNA of the nematode is silenced and prevents the translation of mRNA. Thus causes death of parasites.

Question.17. Some organisms suspend their metabolic activities to survive in unfavourable conditions. Explain with the help of any four examples.
Answer : Some examples with their unfavourable conditions under which they suspend their metabolic activities:

  1.  Polar bear – hibernation during winter
  2.  Snails / fishes – Aestivation during summer
  3.  Species of zooplankton – diapauses
  4.  Higher plants/ spores of bacteria/ fungi — become dormant , and cyst formation as in case of amoeba .

Question.18. (a) Name the Protozoan parasite that causes amoebic dysentery in humans.
(b) Mention two diagnostic symptoms of the disease.
(c) How is this disease transmitted to others?
Answer : (a) The Protozoan parasite that causes amoebic dysentery in humans is Entamoeba histolytica
(b) Symptoms : Constipation, abdominal pain , stools with mucus and blood clot.
(c) This disease is transmitted to others by fecally contaminated food and water.


Question.19. It is established that RNA is the first genetic material. Explain giving three reasons.
Answer : Reason for RNA is the first genetic material:

  1.  Processes like metabolism, translation, splicing evolved around RNA.
  2.  RNA is reactive and catalyses reaction and in some virus it is the hereditary material.
  3.  It is unstable and hence would have mutated to lead to , evolution.

(a) Name the enzyme responsible for the transcription of tRNA and the amino acid the initiator tRNA gets linked with.
(b) Explain the role of initiator tRNA in initiation of protein synthesis.
Answer : (a) Enzyme responsible for the transcription of tRNA: RNA polymerase in prokaryotes and RNA polymerase III in eukaryotes.
The amino acid the initiator tRNA get linked with Formyl methionine in prokaryotes and methionine in eukaryotes.
(b) The role of initiator tRNA in initiation of protein synthesis.

  1.  This tRNA combine with amino acid methionine in presence of amino acyl-tRNA synthetic enzymes resulting in the formation of charged tRNA.
  2.  The mRNA attaches to smaller subunit of ribosome and charged initiator tRNA. After that tRNA joins the initiator codon and signals the start of translation.
  3. The initiator tRNA function on the ability of anticodon sequence mutants of initiator tRNA to initiate, protein synthesis. The anticodon UAC recognizes the mRNA AUG codon and binds by forming complementary base pairs, leaves the amino acid, initiating protein synthesis.

Question.20. State the theory of Biogenesis. How does Miller s experiment support this theory ?
Answer : Theory of Biogenesis : The first forih of life could have come , from pre-existing, non-living organic molecules (e.g, RNA, protein etc.) proposed by Oparin and Haldane. This theory suggest that origin of life is first abiogenesis and biogenesis later.

Question.21. Name the two different categories of microbes naturally occurring in sewage water. Explain their role in cleaning sewage water into usable water.
Answer: Different categories of microbes naturally occurring in sewage water, all aerobic and anaerobic bacteria, fungi, filamentous fungi.
Role in cleaning sewage water into Potable water :

  1.  The primary effluent is passed into large aeration tanks where if is constantly agitated.
  2.  This allows abundant growth of aerobic microbes like bacteria and filamentous fungi.
  3. The growth of these microbes reduces BOD of effluents. Once the BOD is reduced significantly, then the effluent is passed into settling tanks where the bacterial floes are allowed to sediment.
  4.  This sediment is called activated sludge. A small part of activated sludge is again introduced into large tanks called anaerpbic sludge digesters.
  5. flere anaerobic bacteria digest the bacterial and fungi in the sludge.
  6.  This digestion produces methane, H2S and COz gas. These gases form biogas.
  7.  The effluent from secondary treatment is them released
    into natural water bodies.

Question.22. Write the function of each one of the following :
(a) (Oviducal) Fimbriae (b) Coleoptile (c) Oxytocin
Answer : (a) (Oviducal) Fimbriae : Collection of ovum released by ovary.
(b) Coleoptile : Protects the plumule of the monocot embryo.
(c) Oxytocin : Causes uterine contraction for partu- rition(child birth) and also promotes milk ejection.

Question.23. Name the genes responsible for making Bt cotton plants resistant to bollworm attack How do such plants attain resistance against bollworm attacks ? Explain.
Answer: The Bt toxin is encoded by the cry gene, crylhC and crylLAb, which produces protein crystals during a particular phase of their growth. This toxin provides resistance to plants against lepidoptern, coleoptern and dipterans pests. Bt cotton, is the variety of cotton in which the gene from the bacterium that encodes for the toxin is incorporated. When boll worm bites the cotton fruits, it consumes the toxic insecticidal protein. The protoxin gets activated by the alkaline pH of the gut of the insect and binds to the surface of the midgut epithelium of the insects and causes swelling and cell lysis, which eventually leads to the death of the insects.

Question.24. Study a part of the life cycle of malarial parasite given below. Answer the questions that follow:
(a) Mention the roles of ‘A’ in the life cycle of the malarial parasite.
(b) Name the event ‘C’ and the organ where this event occurs.
(c) Identify the organ ‘B’ and name the cells being released from it.
Answer: (a) A represents the female mosquito. Gametocytes of Plasmodium enter the mosquito when it bites an infected person and takes the malaria parasite along with the blood meal.
(b) C is the fertilization stage and it takes place in the intestine of the mosquito.
(c) B is the salivary gland of the female anopheles mosquito and the sporozoites escape out of the mosquitos salivary gland.

Question.25. Given below is the representation of amino acid composition not the relevant translated portion of P-chain of haemoglobin, related to the shape of human red blood cells.
(a) Is this representation indicating a normal human or a sufferer from certain related genetic disease ? Give reason in support of your answer.
(b) What difference would be noticed in the phenotype of the normal and the sufferer related to this gene ?
Who are likely to suffer more from the defect related to the gene represented the males, the females or both males and females equally ? And why ?
Answer : (a) Yes, this representation is indicating a normal human. Normal person mRNA contains GAG codon which codes for glutamic acid, at the 6th position.
(b) In a sufferer who exhibit sickle cell trait, the codon GAG is replaced by GUG in the mRNA. Hence, during translation of the defective mRNA, Glutamic acid is replaced by Valine at the 6th position of Beta globin chain of the haemoglobin.
(c) Both the males and females suffer equally because sickle cell anaemia is not a sex linked disease. It is an autosomal recessive disease and sickle shaped RBC will cause equal deficiency of oxygen in both males and females.

Question.26. By the end of 2002 the public transport of Delhi switched over to a new fuel. Name the fuel. Why is this fuel considered better? Explain.
Answer : Delhi Government switched to CNG (Compressed Natural Gas). Delhi had been categorized as the fourth most polluted city of the world in a list of 41 cities. Burning of fossil fuels has added to the pollution of air in Delhi. CNG is considered better due to following reasons :

  1. CNG is a clean fuel that produces very little unburnt particles and thus it is considered as eco-friendly.
  2. CNG burns most efficiently, unlike petrol or diesel, in the automobiles and very little of it is left unburnt.
  3. Moreover, CNG is cheaper than petrol or diesel.

Question.27. Draw a schematic sketch of pBR 322 plasmid and label the following in it:
(a) Any two restriction sites. (b) Ori and rop genes.
(c) An antibiotic resistant gene.
Answer : Sketch of pBR 322 plasmid :
(b) The Restriction sites mentioned in the figure are Hind III, EcoR I, Bam HI, Sal I, Pvu II, Pst I, Cla I and Antibiotic resistant.
(c) genes: \({ amp }^{ R }\) and \({ tet }^{ R }\)


Question.28. Explain the carbon cycle with the help of a simplified model.
Answer: Key process involved in carbon cycle is photosynthesis and respiration.

  1.  In photosynthesis, carbon-dioxide and water produce carbohydrate and oxygen while respiration oxidizes food to give carbon-dioxide and water.
  2.  71% carbon is found dissolved in oceans. In rock it gets stored as calcium carbonate.
  3. Carbon can either be liberated to atmosphere through respiration or can be passed to. animal when being eaten or remain in plant even after death.
  4.  A considerable amount of COz is fixed annually by process of photosynthesis.
  5.  Excess of carbon-dioxide can cause global warming.

Explain how does:
(a) A primary succession start on a bare rock and reach a climax community ?
(b) The algal bloom eventually choke the water body in an industrial area ?
Answer : (a)

  1.  The species of organisms that first invade a bare area are called pioneer species (lichens).
  2.  Lichens secrete acids which dissolve rocks, thereby leading to weathering and soil formation.
  3. Next serai stage will be bryophytes which can hold in the small amount of soil.
  4.  Bryophytes are then succeeded by grasses.
  5.  They are succeeded by bigger plants, and ultimately, an entire forest gets established. This remains stable as long as the environment remains unchanged.

(b) Effluent from industries contains large amount of nutrients. This causes excessive growth of free-floating algae causing algal bloom. Later, the decomposition of these algae depletes the supply of oxygen, leading to the death of other aquatic animal life thus choking the water body. This ageing process of a lake caused due to nutrient enrichment is called Eutrophication.

Question.29. The following is the illustration of the sequence of ovarian events (a – i) in a human female.
(1) Identify the figure that illustrates ovulation and mention the stage of oogenesis it represents.
(2) Name the ovarian hormone and the pituitary hormone that have caused the above mentioned event.
(3) Explain the changes that occur in the uterus simultaneously in anticipation.
(4) Write the difference between ‘c’ and ‘h’.
(5) Draw a labelled sketch of the structure of a human ovum prior to fertilization.

  1. Figure ‘f’ illustrates stage of ovulation.
  2.  Ovarian hormone = estrogen
    Pituitary hormone = Luetenizing hormone
  3.  Endometrium lining gets thickened and highly vascularised, high regeneration anticipating implantation of the fertilized ovum.
  4.  ‘c’ is developing Graafian follicle while ‘h’ is regressing corpus luteum Human ovum prior to fertilization.

How does the megaspore mother cell develop into 7-celled,-» 8 nucleate embryo sac in an angiosperm ? Draw a labelled diagram of a mature embryo sac.
Answer : The megaspore mother cell undergoes mitosis to form one functional and viable megaspore. The functional megaspore divides mitotically to produce two nuclei which migrate to opposite poles, forming a 2-nucleate embryo sac.

  1. Further mitotic divisions lead to the formation of 4-nucleate followed by 8-nucleate stages of the embryo sac.
  2.  Among the eight nuclei, six are enclosed by cell walls and organised into cells, while the remaining two nuclei (called polar nuclei) are situated above the egg apparatus in a large central cell.
    Out of the six cells, three are grouped at the micropylar end, and constitute the egg apparatus made up of two synergids and one egg cell.
  3. The other three cells are located at the chalazal end, and are called antipodals. Thus, a typical angiosperm embryo sac after maturity is 8-nucleated and 7-celled.

Question.30.What is the inheritance pattern observed in the size of starch grains and seed shape of Pisum sativunP. Workout the monohybrid cross showing the above traits. How does this pattern of inheritance deviate from that of Mendelian law of dominance?
Answer : In pea plants (Pisum sativum), a single gene controls the expression of a number of traits, namely starch synheiss & size of starch grains. This phenomenon is called pleiotropy & genes are called pleiotropic & genes are called pleiotropic genes. It has two alleles B and b. BB homozygotes produced large starch grains as compared to that produced by bb homozygotes. The cross involved is
Deviation from Mendels law of dominance : If starch grain size is considered as the phenotype, the trait of size of starch grain shows incomplete dominance. Hence in heterozygous condition the starch grain are of intermediate size. The trait of seed shape follows Law of Dominance and the hybrid will show only dominant trait.
State the aim and describe Messelson and Stahl’s experiment. Answer: Messelson and Stahl in 1958 aimed at proving that the DNA replicates in a semi-conservative fashion. The semi-conservative DNA replication suggests that after the completion of replication, each DNA molecule will have one parental and one newly-synthesised strand.
Experiment done by Messlson & stahl:

  1. They grew colonies of E.Coli for several generations on a culture medium haring NH4C1 with heay isotope of Nitrogen, 15N.
  2. This heavy isotope got incorporated in Nitrogen containing compounds, like DNA.
  3. When the whole DNA was found to contain heavy isotope of N2, the bacteria were shifted to culture medium having normal nitrogen, 14N.
  4.  After 20 minutes, 1st generation of E. Coli was obtained. Its DNA was isolated & tested for presence of heavy DNA & normal DNA. This was done for several generations.
  5.  To test the presence of ype of isotope, the isolated DNA was added to tubes having CsCl. The tube were provided with centrifugal force for many hours, till the DNA come to lie at a fixed position in the tube.
  6. DNA of I generation, having completely heavy isotope was heaviest.
  7. When E. Coli Was shifted to normal N2 Containing culture, the DNA of its I generation was slighdy less dense than its parental material.
  8. In the 2nd generation, DNA formed two sedimens, one like the FI generation & second lighter than it.
  9. I generation DNA had intermediate density having both 15N & 14N. 2nd generation was one intermediate with (15N & 14N) & other lighter with only 14N. Their ratio was 50-50 in 2nd generation.
  10.  In 3rd generation, same two types were produced, but ratio of intermediate reduced to 25% & intermediate percentae reduced to 12.5% & lighter one at 8.75%.
  11.  ‘This is possible only when in each generation out of the two stands of DNA, one was obtained from parent double stran & other is formed new. This proves semi-conservative nature of DNA replication.



Question.1. Cucurbits and papaya plants bear staminate and pistillate flowers. Mention the categories they are put under separately on the basis of the type of flowers they bear.
Answer : Papaya is dioecious because the staminate and pistillate flowers are borne in two different plants while cucumber is monoecious because it bears both staminate and pistillate flowers in the same plant.

Question.4. What is the interaction called between Cuscuta and shoe flower bush ?
Answer : The interaction between Cuscuta and shoe fl&wer bush is called parasitism.

Question.5. When do the oogenesis and the spermatogenesis initiate in human females and males respectively ?
Answer: Oogenesis starts in females in their foetal stage while spermatogenesis in males starts at puberty.

Question.7. State the significance of the study of fossils in evolution.
Answer : The significance of the study of fossils in evolution :
(i) Study of fossils indicates the geological period in which various life forms were arisen.
(ii) The calculation of geological period can be done via radioactive dating.
(iii) We can know the morphological details of the organisms in the past and can relate them to the organisms in the present to understand the process of evolution.


Question.13. Draw a schematic diagram of a part of double stranded dinucleotide DNA chain having all the four nitrogenous bases and showing the correct polarity.
Answer: Schematic diagram of a double stranded dinucleotide DNA chain having all the four nitrogenous bases with polarity.

Question.14. Name of parasite the causes filariasis in humans. “Mention its two diagnostic symptoms. How is this transmitted to others?
Answer : Wuchereria (W bancrofti and W. malayi), are the filarial worms that cause filariasis in humans.

Diagnostic symptoms :
1. Chronic inflammation of the organs in which they live for many years. Lymphatic organs are most affected.
2. The genital organs are also often affected resulting in gross deformities.
Transmission: The pathogens are transmitted to a healthy person through the bite by the female mosquito vectors.

Question.15. Name the source of streptokinase. How does this bio molecule function in our body ?
Answer : Streptokinase enzyme is produced by the bacterium Streptococcus. It is modified by genetic engineering and is used as a clot buster for removing clots from the blood vessels of patients who have suffered from myocardial infraction leading to hqart attack.
How do mycorrhizae act as biofertilizers? Explain. Name a genus of fungi that forms a mycorrhizal association with plants.
Answer : Mycorrhizae act as biofertilizers : The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant. The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the fungi with energy yielding carbohydrates.
The fungi belonging to the genus Glomus form mycorrhizal associations with plants.


Question.19. Write the function of each of the following :
(a) Middle piece in human sperm.
(b) Tapetum in anthers.
(c) Luteinizing hormone in human males.
(a) Middle piece in human sperm : It possesses numerous mitochondria, which produces energy for the movement of tail that facilitate sperm motility essential for fertilization.
(b) Tapetum in anthers : Tapetum is the inner most layer in the main function of tapetum is to provide nourishment to the developing pollen grains.
(c) Luteinizing hormones in human males : It stimulates the leydig cells to produce androgen like testosterone.

Question.26. How does an algal bloom cause eutrophication of a water body? Name the weed that can grow in such a eutrophic lake.
Answer : Algaes are the major producers of any aquatic ecosystem. Presence of large amount of nutrients in water. also causes excessive growth of planktonic algae called an algal bloom which imparts a distinct colour to the waste bodies. Later, the decomposition of these algae depletes the supply of oxygen, leading to the death of other aquatic animal life. This phenomenon is called eutrophication.
Water hyacinth (Eichhornia crassipes) is a weed that can grow in such an eutrophic lake.


Question.28. (a) Draw a ‘pyramid of numbers’ of a situation where a large population of insects feed upon a very big tree. The insects in turn, are eaten by small birds which in turn are fed upon by big birds.
(b) Differentiate giving reason, between the pyramid of biomass of the above situation and the pyramid of numbers that you have drawn.
Answer : (a) Pyramid of numbers showing interaction between trees, insects, birds and big birds.
(b) (i) ‘Pyramid of number’ is spindle shaped as the number of insects is maximum. The number of trees and birds are less than the insects. The numbers is gradually decreasing at each trophic level.
(ii) The Pyramid of Biomass in this ecosystem is erect because the biomass decreases at each tropic level.
(a) What are the two types of desirable approaches to conserve biodiversity? Explain with examples bringing out the difference between the two types.
(b) What is the association between the bumblebee and its favourite orchid Ophrys ? How would extinction or change of one affect the other ?
Answer : (a) Two approaches to conserve biodiversity are :
(i) In situ conservation
(ii) Ex situ conservation
(b) Mutualism is the type of association seen between the bumblebee and the orchid Ophrys. In this type of association, Orchids show a bewildering diversity of floral patterns many of which have evolved to attract the right pollinator insect (bees and bumblebees) and ensure guaranteed pollination by it. The petals of ophrys recemble the female bundle. If the female bee’s colour patterns change even slightly for any reason during evolution, pollination success will be reduced unless the orchid flower co-evolves to maintain the resemblance of its petal to the female bee.
-Extinction of bumble bee will definitely affect the orchid flower because these bees are the means of pollination for the flower and if they get extinct then the pollination percentage will be reduced. But the extinction of the orchid will not affect the bumble bee population.



Question.1. Mention the difference between spermiogenesis and spermiation.
Answer: Difference between spermiogenesis and spermiation:- Spermiogenesis : It is the process of transforming spermatids into matured spermatozoa or sperms. Spermiation : It is the process when mature spermatozoa are released from the Sertoli cells into the cavity of seminiferous tubules.

Question.3. What is an interaction called when an orchid grows on a mango plant ?
Answer : The relationship between a mango tree and an orchid is an example of commensalism.

Question.4. Write the names of the semi-dwarf and high yielding rice varieties developed in India after 1966.
Answer: Jaya and Ratna are two semi-dwarf and high yielding rice varieties developed in India after 1966,

Question.6. Mention the unique feature with respect to flowering and fruiting in bamboo species.
Answer : Bamboo species flowers only once in their life time, generally after 50-100 years, bamboo species produce large number of fruits and then die.

Question.8. State the significance of biochemical similarities among diverse organisms in evolution ?
Answer : The significance of biochemicals similarities in bio-chemicals such as DNA, help in deriving the line of evolution.


Question.15. Mention the importance of Lactic acid bacteria to humans other than setting milk into curd.
Answer : (i) Lactic acid bacteria play a very beneficial role in checking disease causing microbes.
(ii) It also used to produce acid called lactic acid which is an important industrial product. It is used in bakery products, beverages, meat products, confectionery, dairy products, etc.
How do methanogens help in producing biogas ?
Answer : Methanogens such as Methanobacterium act on excreta of cattle and anaerobic sludge and grow anaerobically, producing large amount of methane along with C02 and H2. Methanogens do not use oxygen to respire. In fact, oxygen inhibits the growth of methanogens.

Question.19. (a) Construct a complete transcription unit with promoter and terminator on the basis of the hypothetical template strand given below:
(b) Write the RNA strand transcribed from the above transcription unit along with its polarity.
How are the structural genes inactivated in lac operon in E. coli ? Explain.
Answer : The structural gene in the lac operon consists of three genes, lac z, y and a. The structural gene is inactivated in the presence of repressor and absence of inducer (lactose). The repressor of the operon produced by the i gene. The repressor protein when produced binds to the operator region of the operon and prevents RNA polymerase firom transcribing the operon.


Question.20. Write the function of each of the following:
(a) Seminal vesicle (b) Scutellum (c) Acrosome of human sperm.
Answer: (a) Seminal vesicle : It secretes an alkaline fluid that helps in neutralizing the acidity of the vaginal tract and thereby increasing the life-span of sperms.
(b) Scutellum : Scutellum is the tissue present in seed. It is the papery cotyledon of the monocot seed and acts as a passage for movement of nutrients from the endosperm to the developing embryo.
(c) Acrosome of human sperm : It is present at the tip of sperm. It is a cap-like structure which contains hydrolytic enzymes that help in penetration of egg during fertilization.

Question.25. (a) Why are the colourful polystyrene and plastic packagings used for protecting the food, considered an environmental menace ?
(b) Write about the remedy found for. the efficient use of plastic waste by Ahmed khan of Bangalore. [3]
Answer : (a) Polysterene and plastic packaging used for protecting food cause environmental pollution as these are non-biodegradable substances and its recycling process is very costly and includes manual participation thus exposing workers to toxic substances produced during recycling process.These polybags cause harm to aquatic life, choke the water pipes, etc.
(b) The efficient use of plastic waste by Ahmed Khan in Bangalore. He developed polyblend, a fine powder of recycled modified plastic. This mixture is mixed with the bitumen that is used to lay roads. Ahmed Khan proved that blends of – Polyblend and bitumen, when used to lay roads, enhanced the bitumens water repellant properties, and helped to increase road life by a factor of three.


Question.30. Name the scientists who proved experimentally that DNA is the genetic material ? Describe their experiment.
Answer : Hershey and Chase worked with bacteriophage, E.coli and they proved that DNA is the genetic material. They worked on different radioactive isotopes to label DNA and protein coat of the bacteriophage.
Both of them grew some bacteriophages on a medium containing radioactive phosphorus (P32) to identify DNA and some on a medium containing sulphur (S35) to identify protein. These radioactive labelled phages were allowed’ to infect E.coli bacteria. After infecting, the protein coat of bacteriophage was separated from the bacterial cell by blending and then subjected to the process of centrifugation. Since, the protein coat was lighter, it was found in the
whereas the infected bacteria got settled at the bottom of the centrifuge tube. Hence, it was proved that DNA is the genetic material as it was transferred from virus to bacteria.
(a) List the three different allelic forms of gene T in humans. Explain the different phenotypic expressions, controlled by these three forms,
(b) A woman with blood group A’ marries a man with blood group ‘O’. Discuss the possibilities of the inheritance of the blood groups in the folllowing starting with yes’ or ‘no’ for each :
(i) They produce children with blood group ‘A’ only.
(ii) They produce children some with ‘O’ blood group and some with ‘A’ blood group.
Answer : (a) In humans, the ABO blood groups are controlled by a gene called gene ‘I’. It has three alleles, namely IA, IB and i.
Table showing the Genetic Basis of Blood Groups in Human population.