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Paper pattern

A · all 16 · 1 mark each · 12 multiple choice and 4 assertion-reason16

B · all 5 · 2 marks each · very short answer, internal choice in 310

C · all 7 · 3 marks each · short answer21

D · all 2 · 4 marks each · case-based, a passage or data then sub-questions8

E · all 3 · 5 marks each · long answer, internal choice in all three15

Board paper total70

CBSE Biology (044) Class XII question paper design and sample question paper, 2026-27: 33 questions, 70 marks, 3 hours, about a third of the questions with an internal choice.

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Likely questions

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2 marks · short answer

Name the four wall layers of a microsporangium in order from outside. Write the role of the innermost layer.Unit I Why are pollen grains of some plants well preserved as fossils? Name the material responsible.Unit I A papaya plant never shows autogamy or geitonogamy, but a castor plant can show geitonogamy. Explain why.Unit I What is a perisperm? How is it different from the endosperm?Unit I Explain why the human testes lie outside the abdominal cavity. Name the cells of the testis that secrete androgens.Unit II Name the three parts of the fallopian tube in order from the ovary. In which part does fertilisation usually take place?Unit II Distinguish between spermiogenesis and spermiation.Unit II How is the sex of a human baby decided at fertilisation? Is it the father or the mother who decides it?Unit II Expand ZIFT and GIFT. Write one difference between them.Unit III List any four features of an ideal contraceptive.Unit III Name two STIs that are not completely curable. Give two ways, other than sexual contact, by which hepatitis-B can spread.Unit III What is lactational amenorrhea? Up to how long after delivery is it effective as a contraceptive method?Unit III What is a test cross? How does it help you find out whether a tall pea plant is homozygous or heterozygous?Unit IV Differentiate between incomplete dominance and co-dominance, giving one example of each.Unit IV Why is haemophilia far more common in men than in women?Unit IV What is pleiotropy? Explain it with the example of phenylketonuria.Unit IV Give two reasons why DNA is a better genetic material than RNA.Unit V A double-stranded DNA has 30% adenine. Calculate the percentages of thymine, guanine and cytosine, and state the rule you used.Unit V Differentiate between the template strand and the coding strand of DNA.Unit V Why is the genetic code said to be degenerate and nearly universal? Give one example of each.Unit V How did Louis Pasteur disprove the theory of spontaneous generation? State the conclusion of his experiment.Unit VI Thorns of Bougainvillea and tendrils of Cucurbita are homologous, while flippers of penguins and dolphins are analogous. Justify both statements.Unit VI In a population at equilibrium, 9% of individuals are homozygous recessive (aa). Calculate the frequencies of alleles A and a, and the percentage of heterozygous individuals.Unit VI Name the hominid whose fossils were found in Java in 1891. Give its brain capacity and one way its diet differed from that of Homo habilis.Unit VI Name the causative organism of typhoid and the test that confirms it. Why is a carrier such as 'Typhoid Mary' a danger to public health?Unit VII What is an allergy? Name the class of antibody produced and two chemicals released by mast cells during an allergic reaction.Unit VII Why is colostrum considered essential for a newborn? Name the antibody it contains and the type of immunity it provides.Unit VII Differentiate between benign and malignant tumours. Why is metastasis the most feared property of malignant tumours?Unit VII Explain how a small amount of curd added to lukewarm milk turns it into curd. How does curd benefit our health?Unit VIII Name the source organisms of streptokinase and cyclosporin A. State one medical use of each.Unit VIII What is mycorrhiza? Name the fungal genus that commonly forms it and give two benefits it gives to plants.Unit VIII Why is it unwise to take antibiotics for a common cold? Why must a prescribed course of antibiotics be completed?Unit VIII Name the two core techniques that enabled modern biotechnology and state what each involves.Unit IX What are sticky ends? How does EcoRI produce them? Write its recognition sequence.Unit IX Why must bacterial cells be made competent before they can take up recombinant DNA? How is this done?Unit IX Name the enzymes used to break open bacterial, plant and fungal cells during DNA isolation. How is the DNA finally precipitated?Unit IX Why does the Bt toxin not kill the Bacillus thuringiensis that produces it, yet kill an insect that eats it?Unit X What is the C peptide? How was the problem of its removal avoided when human insulin was made by recombinant DNA technology?Unit X What is biopiracy? Explain with one example from India.Unit X State the principle of ELISA. Name the two kinds of molecules it can detect to show an infection.Unit X Why is per cent cover or biomass a better measure of population size than the number of individuals in some cases? Give an example.Unit XI A pond had 50 frogs at the start of a year, and 15 young frogs were added by reproduction during the year. Calculate the per capita birth rate and state its unit.Unit XI State Gause's competitive exclusion principle. Under what condition is it true?Unit XI Why is the female mosquito not considered a parasite? Name a plant parasite that has lost its leaves and chlorophyll.Unit XI Distinguish between gross primary productivity and net primary productivity. Write the equation that links them.Unit XII What is humus? Why does decomposition slow down in cold and in waterlogged soils?Unit XII Why is the pyramid of energy always upright, even where the pyramid of biomass is inverted?Unit XII What is stratification? Give an example from a forest.Unit XII Explain the rivet popper hypothesis. What does the loss of rivets on the wings stand for?Unit XIII Distinguish between in situ and ex situ conservation, with two examples of each.Unit XIII What are sacred groves? Name the state where they are the last refuge for many rare and threatened plants.Unit XIII Why are biosphere reserves, national parks and wildlife sanctuaries called in situ methods of conservation? Give your textbook's count of each in India.Unit XIII

3 marks · short answer

Differentiate between wind-pollinated and insect-pollinated flowers, giving three points and one example of each.Unit I What is double fertilisation? Name its two products and give the ploidy of each.Unit I What is apomixis? How could it help farmers who grow hybrid crops?Unit I Give three differences between spermatogenesis and oogenesis.Unit II What is the placenta? Write two of its exchange functions and name two hormones it secretes.Unit II Describe the changes in the human zygote from fertilisation until implantation.Unit II Explain how copper-releasing IUDs, hormone-releasing IUDs and oral pills prevent pregnancy.Unit III What is amniocentesis? Why has the government placed a statutory ban on its use for sex determination?Unit III What does WHO mean by reproductive health? List four indicators of improved reproductive health in a society.Unit III A man with blood group A and a woman with blood group B have a child with blood group O. Work out the genotypes of all three and the other blood groups possible among their children.Unit IV Explain sex determination in honey bees. Why does a drone have a grandfather but no father?Unit IV Explain the molecular basis of sickle-cell anaemia. How is it different from thalassemia?Unit IV Name the chromosomal disorder in each case and give its karyotype: (i) a sterile male with breast development, (ii) a sterile female with rudimentary ovaries, (iii) a child with a furrowed tongue and a broad palm with a characteristic crease.Unit IV Describe Meselson and Stahl's experiment. What did it prove about DNA replication?Unit V How is hnRNA processed into mature mRNA in eukaryotes? Why is this not needed in bacteria?Unit V What is a nucleosome? Describe how DNA is packaged in a eukaryotic nucleus.Unit V List any six salient features of the human genome revealed by the Human Genome Project.Unit V What is genetic drift? Explain the founder effect. How is gene flow different from genetic drift?Unit VI With the help of labelled graphs, explain stabilising, directional and disruptive selection.Unit VI Explain adaptive radiation with the example of Australian marsupials. How do placental mammals in Australia show convergent evolution?Unit VI How do fossils in rock layers provide evidence for evolution? Why was Haeckel's embryological evidence disapproved?Unit VI Draw a labelled diagram of an antibody molecule. Distinguish between the humoral and cell-mediated immune responses, and state which one causes graft rejection.Unit VII Name the pathogens that cause amoebiasis, ascariasis and ringworm. Give one symptom and one mode of spread for each.Unit VII Distinguish between addiction and dependence. List four warning signs that may show drug or alcohol abuse in an adolescent.Unit VII Why is a macrophage called an 'HIV factory'? Explain how HIV infection leads to a fall in the number of helper T-lymphocytes.Unit VII Differentiate between primary and secondary treatment of sewage. Why is a small part of the activated sludge pumped back into the aeration tank?Unit VIII What are methanogens? Explain how biogas is produced in a biogas plant, with a labelled diagram.Unit VIII Explain the role of Bacillus thuringiensis, Trichoderma and baculoviruses as biocontrol agents.Unit VIII Describe the three steps of a PCR cycle. Why is Taq polymerase used in PCR?Unit IX Explain how DNA fragments are separated by agarose gel electrophoresis, and how a desired fragment is seen and recovered.Unit IX What is downstream processing? List the systems in a stirred-tank bioreactor that maintain optimal growth conditions.Unit IX How has RNA interference been used to make tobacco plants resistant to the nematode Meloidogyne incognita?Unit X Describe the gene therapy given to a patient with ADA deficiency. Why is this not a permanent cure?Unit X How has recombinant DNA technology helped in producing vaccines such as the hepatitis B vaccine? What are stem cells, where are they found in the early human embryo, and what can they form?Unit X List three advantages of genetically modified crops. What is Golden rice, and why was it developed?Unit X Draw age pyramids to show expanding, stable and declining populations. Label the age groups and state what each shape shows.Unit XI Explain three roles of predators in nature, with one example of each.Unit XI Explain the mutualism between fig trees and wasps, and the 'sexual deceit' of the orchid Ophrys. How do these show co-evolution?Unit XI Distinguish between grazing and detritus food chains. In which type of ecosystem does each dominate? Why is a sparrow said to occupy more than one trophic level?Unit XII Why is the flow of energy in an ecosystem unidirectional? What share of incident sunlight is PAR, and how much of it do plants capture?Unit XII Draw pyramids of number for a grassland and for a large tree with insects and birds. Why are they different?Unit XII Explain genetic, species and ecological diversity with one Indian example of each.Unit XIII Give three reasons why the tropics show greater species diversity than temperate regions.Unit XIII What is the Red Data Book? Using the IUCN Red List figures in your textbook, state how many species became extinct in the last 500 years and which groups face the greatest threat of extinction.Unit XIII

5 marks · long answer

Describe the development of the female gametophyte from the megaspore mother cell. Draw a labelled diagram of a mature embryo sac.Unit I Describe the development of endosperm. Draw labelled diagrams of a typical dicot embryo and a grass embryo, and write two differences between them.Unit I Describe the events of the menstrual cycle and the hormones that control each phase. What happens to the corpus luteum if fertilisation does not take place?Unit II Describe spermatogenesis with a flow chart and explain its hormonal control. Draw a labelled diagram of a human sperm.Unit II Describe the natural, barrier, intra-uterine, hormonal and surgical methods of contraception, with one example and the mode of action of each.Unit III What are sexually transmitted infections? Name four. Describe how they spread, the complications they cause if untreated, and three ways to prevent them.Unit III State the law of independent assortment. Explain it with a dihybrid cross between pea plants with round yellow seeds and wrinkled green seeds, using a Punnett square.Unit IV What is the chromosome theory of inheritance? Describe how Morgan's experiments on Drosophila led to the ideas of linkage and recombination.Unit IV Explain the working of the lac operon in E. coli when lactose is (a) absent and (b) present. Draw labelled diagrams.Unit V Describe the experiment of Hershey and Chase. Explain how it showed that DNA, and not protein, is the genetic material.Unit V Explain Darwin's theory of natural selection, stating the observations it was based on. How does industrial melanism in England support it? How did Hugo de Vries' view of evolution differ from Darwin's?Unit VI Describe the theory of chemical evolution proposed by Oparin and Haldane. Explain Miller's experiment with a labelled diagram of his apparatus, and state what it showed.Unit VI Describe the life cycle of Plasmodium in the human and the mosquito, with a labelled diagram. What causes the recurring chills and fever in malaria?Unit VII What is AIDS? Describe how HIV is transmitted and how it multiplies in the body. List the steps taken to prevent the spread of HIV.Unit VII Describe the stages of sewage treatment in a sewage treatment plant and the role of microbes in each. What is BOD, and why is it measured?Unit VIII Explain with examples how microbes are used in the industrial production of fermented beverages, organic acids, enzymes and bioactive molecules.Unit VIII Draw a labelled diagram of the E. coli cloning vector pBR322. Explain the roles of ori, selectable markers and cloning sites, and how insertional inactivation helps to select recombinants.Unit IX List the steps of recombinant DNA technology in the correct order. Explain any three of them, naming the enzyme or tool used at each step.Unit IX What are transgenic animals? Explain any five reasons for producing them, with an example of each.Unit X Describe how Bt cotton protects itself from bollworms. Name the genes involved and explain why the toxin does not harm the bacterium. How does this strategy differ from RNAi-based pest resistance?Unit X Describe exponential and logistic growth with their equations. Draw both growth curves on one graph and explain why logistic growth is more realistic. What is meant by life history variation?Unit XI What is competition? Explain Gause's competitive exclusion principle, competitive release and resource partitioning, with an example of each.Unit XI What is decomposition? Describe its steps in order and explain the factors that control its rate.Unit XII Describe a pond as an ecosystem. Name its abiotic and biotic components and explain how it performs the functions of an ecosystem.Unit XII What are the major causes of biodiversity loss? Explain the evil quartet with one example of each, and name the most important cause.Unit XIII Why should we conserve biodiversity? Explain the narrowly utilitarian, broadly utilitarian and ethical arguments, and describe the rivet popper hypothesis.Unit XIII

4 marks · case-based

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