CBSE Class 12 Biology 2023
171 questions · 336 marks · 169 with the board’s own marking-scheme answer, 2 with no official answer on the site.
Marks by chapter
Counted from the 171 questions listed below, as the 2023 papers print them. CBSE allocates marks per unit, not per chapter — this is what was observed, not an official CBSE weightage. Every year compared →
| Chapter | Marks | Share |
|---|---|---|
| Molecular Basis of Inheritance20 questions | 49 | 14.6% |
| Principles of Inheritance and Variation15 questions | 32 | 9.5% |
| Human Health and Disease15 questions | 32 | 9.5% |
| Evolution16 questions | 31 | 9.2% |
| Sexual Reproduction in Flowering Plants11 questions | 29 | 8.6% |
| Biotechnology and its Applications14 questions | 27 | 8.0% |
| Human Reproduction14 questions | 26 | 7.7% |
| Biotechnology : Principles and Processes13 questions | 26 | 7.7% |
| Biodiversity and Conservation13 questions | 24 | 7.1% |
| Microbes in Human Welfare13 questions | 21 | 6.3% |
| Reproductive Health10 questions | 16 | 4.8% |
| Organisms and Populations11 questions | 14 | 4.2% |
| Ecosystem6 questions | 9 | 2.7% |
171 questions from 2023
- Q1A human ovum completes its second meiosis:1 mk
- Q1At which stage during evolution did human use hides to protect their bodies and buried their dead?1 mk
- Q1Which one of the following processes results in the production of recombinants in future generations? (i) Mutation (ii)…1 mk
- Q1Three genes R, S and T are located on the same chromosome. If the recombinant percentage between R and S is 20 %, R and…1 mk
- Q1Choose the set of sex determining chromosomes that indicates the correct sex of the respective organism.1 mk
- Q1Interferons are proteins. In humans they are secreted by:1 mk
- Q2Which of the following statements are true about the males in a colony of honey bees? (i) They have 16 chromosomes per…1 mk
- Q2Which of the following structures is well-developed in a mature seed of black pepper?1 mk
- Q2Given below is a list of steps Meselson and Stahl carried out in their experiment to prove that DNA replication is…1 mk
- Q2Given below are Column A with a list of certain Assisted Reproductive Technologies (ART) and in Column B the procedures…1 mk
- Q2Identify the region 'X', the factor 'Y' and the enzyme 'Z' involved in the process of transcription in prokaryote as…1 mk
- Q3Observe the following line diagram depicting the 28 days menstrual cycle of a healthy young woman. Select the option of…1 mk
- Q3Identify the option that gives the correct type of evolution exhibited by the two animals shown, living in the same…1 mk
- Q3The decrease in the T-lymphocytes count in human blood will result in: 11 mk
- Q3Many copepods live on the body surface of marine fish. This relationship is an example of:1 mk
- Q4The first gene-sequenced crop is:1 mk
- Q4Which one of the following was not present during the Mesozoic Era of the geological time scale?1 mk
- Q4Select the option that shows the correctly identified 'U', 'X', 'Y' and 'Z' in a developing dicot embryo.1 mk
- Q4The status of the human population reflected in the human age pyramid given below is:1 mk
- Q4Match the correct Structures given in Column I with the Fruit in Column II in the chart given below:1 mk
- Q4The graph plotted below is based on the data collected by biology students with respect to the levels of oxygen at the…1 mk
- Q5Which of the following options correctly matches the name of the hormone to its site of production in the human body?1 mk
- Q5Which one of the following products was produced as a result of DNA manipulation in the first transgenic cow 'Rosie'?1 mk
- Q5Given below are four aspects of Reproductive Health in Column A and their related information in Column B: Select the…1 mk
- Q5Identify the element used by Hershey and Chase to label the protein in their experiment, from the following options:1 mk
- Q5Given below are two columns. In Column I is the list of four enzymes and in Column II is the list of functions of the…1 mk
- Q5A human male decides to adopt a surgical method for contraception. Identify the point in the diagram where a cut would…1 mk
- Q5A Tight one-to-one relationship between many species of fig tree and certain wasps is an example of -1 mk
- Q6Given below are structural details of a human mammary gland: 1 (i) The glandular tissue in the breast has 15-20…1 mk
- Q6Which of the following hormones are active during the ovulatory phase of menstrual cycle in a normal human female?1 mk
- Q6Study the DNA profiles obtained as a result of DNA fingerprinting of a child 'X' and three individuals 1, 2 and 3.…1 mk
- Q6Which of the following seeds have remained alive for the longest period?1 mk
- Q6Select the pathogen mismatched with the symptoms of disease caused by it from the list given below:1 mk
- Q7Which one of the following fixes the atmospheric nitrogen but is not an autotroph?1 mk
- Q7Given below is a sequence of bases in mRNA of a bacterial cell. Identify the amino acid that would be incorporated at…1 mk
- Q7Select the options which is/are incorrect statement(s) with respect to T-lymphocytes in the human body. (i) They are a…1 mk
- Q7The primary productivity in an ecosystem is expressed as:1 mk
- Q7Select the option that gives the correct description of the process of Natural Selection with respect to the length of…1 mk
- Q8Interaction between clown fish living among the stinging tentacles of sea anemone is an example of -1 mk
- Q8Tetanus antitoxin (Tetanus toxoid) when injected into the human body it immediately provides:1 mk
- Q8Human settlement often leads to habitat loss which leads to fragmentation, forming smaller patches of habitats. Select…1 mk
- Q8Given below is the restriction site of a restriction endonuclease Pst-I and the cleavage sites on a DNA molecule. 5^′…1 mkasked 2×
- Q8Which of the following samples of DNA in the table given below will give the desired result during polymerase chain…1 mk
- Q9Which one of the following is used during 'RNA i' process, to silence the desired gene?1 mk
- Q9Identify the option that does not exhibit a parasitic relationship.1 mk
- Q9Given below are two columns. In Column I the names of four contraceptive devices are given and in Column II the modes…1 mk
- Q9Given below are the steps carried out to construct a recombinant DNA. Which one of the following gives the correct…1 mk
- Q9The IUCN Red Data List (2004) in the last 500 years documents the extinction of nearly 784 species including: 11 mk
- Q10Which one among the following regions is not a hotspot of biodiversity?1 mk
- Q10Given below are the list of the commercially important products and their source organisms. Select the option that…1 mk
- Q10Which one among the following biofertilizers does not fix atmospheric nitrogen?1 mk
- Q10In which one of the following options does the endocrine gland correctly match with its hormonal secretion and its…1 mk
- Q10After the completion of biosynthetic stage in a bioreactor, the product undergoes a series of processes before it is…1 mk
- Q10Identify the fungus that ripens the famous 'Roquefort' cheese:1 mk
- Q10Which one of the following groups faces maximum threat of extinction? 11 mk
- Q11Which of the following hormones is not secreted by the human placenta?1 mk
- Q11The organism used in construction of the first artificial recombinant DNA by Cohen and Boyer in 1972 was:1 mk
- Q11Given below is a diagram of an ecological pyramid of numbers. Choose the correct food chain from the list of food…1 mk
- Q11The sixth extinction in progress currently is different from all previous extinctions on earth as it is:1 mk
- Q11Important attributes belonging to a population but not to an individual are: 1 (i) Birth rate and death rate (ii) Male…1 mk
- Q11The given schematic illustration shows three steps 'P', 'Q' and 'R' of the polymerase chain reaction. Step 'P' Step 'Q'…1 mk
- Q12Examples that show commensalism are: (i) An orchid growing on mango tree (ii) Cuckoo bird and crow (iii) Cuscuta…1 mk
- Q12Who among the following challenged the patent right granted to the University of Mississippi Medical Centre for 'use of…1 mk
- Q12Which of the following sexually transmitted disease is not caused by a virus?1 mk
- Q12DNA profiles of the child and three individuals 1, 2 and 3 who claim to be the parents of the child are given below.…1 mk
- Q13Assertion: In humans the genotype with all the dominant alleles (AABBCC) will have the darkest skin colour. Reason (R):…1 mk
- Q13Assertion: In a monohybrid cross between tall plants and dwarf plants, the F_2 generation showed tall and dwarf plants…1 mk
- Q13Assertion: Determining the sex of an unborn child followed by MTP is an illegal practice. Reason (R): Amniocentesis is…1 mk
- Q13Assertion: Decomposition process is slower if detritus is rich in lignin and cutin. Reason (R): Decomposition is…1 mkasked 2×
- Q13Assertion: A patient of ADA deficiency undergoing treatment for gene therapy requires periodic infusion of genetically…1 mk
- Q13Assertion: Crystal protein Bt toxin does not kill the Bacillus but kills the insects. Reason (R): Bt toxin exists in…1 mk
- Q13Assertion: A species of wasp and a fig species cannot complete their life cycle without each other. Reason (R): While…1 mk
- Q13Assertion: The Covid-19 virus has a shorter life-span and evolves into new strains at a fast speed. Reason (R): RNA…1 mk
- Q14Assertion: For sequencing, the total DNA from a cell is isolated and converted into random fragments. Reason (R): DNA…1 mk
- Q14Assertion: Synthetic oligonucleotide polymers are used during Annealing in a PCR. Reason (R): The primers bind to the…1 mk
- Q14Assertion: For DNA sequencing, the total DNA from a cell is isolated and converted into random fragments of relatively…1 mk
- Q14Assertion: The number of white winged moths decreased drastically after industrialisation in England. Reason (R):…1 mkasked 2×
- Q14Assertion (A): A cattle egret and grazing cattle in close association is a classic example of commensalism. Reason (R):…1 mk
- Q14Assertion: Homo sapiens have evolved from chimpanzee-like ancestors. Reason (R): There is no difference between the two…1 mk
- Q15Assertion: In order to cut the DNA with a restriction enzyme, it needs to be released from the membrane which encloses…1 mk
- Q15Assertion: Breast-feeding is advised by the doctor as it is essential for the new borns. Reason (R): Colostrum secreted…1 mk
- Q15Assertion: More and more children in metro cities of India suffer from allergies and asthma due to sensitivity to the…1 mk
- Q15Assertion: Endosperm is completely consumed during the development of embryo in ex-albuminous seeds. Reason (R):…1 mk
- Q15Assertion: In an operon, the regulator and operator genes are not associated with the constitutive genes. Reason (R):…1 mk
- Q15Assertion: Biologists are sure about how many prokaryotic species are living now. Reason (R): The conventional…1 mk
- Q16Assertion: Cattle and goats are never seen browsing on Calotropis growing in abandoned fields. Reason (R): Cattle and…1 mk
- Q16Assertion: The Mediterranean orchid Ophrys uses sexual deceit to get pollinated by a species of bee. Reason (R): The…1 mk
- Q16Assertion: Darwin showed how even a slow growing animal like an elephant could reach enormous numbers. Reason (R): When…1 mk
- Q16Assertion (A): The Monarch butterfly is highly distasteful to the predators. Reason (R): The butterfly has a very rough…1 mk
- Q16Assertion: Mary Mallon continued to spread typhoid for many years. Reason (R): Salmonella typhi generally enters the…1 mk
- Q16Assertion: In Thalassemia an abnormal myoglobin chain is synthesized due to a gene defect. Reason (R): α -Thalassemia…1 mk
- Q16Assertion: Birds like pigeon have heterogametic females whereas the males are homogametic. Reason (R): In pigeons,…1 mk
- Q17Explain the process of the development of a male gametophyte in an angiosperm. Why is it called a male gametophyte?2 mk
- Q17Name (i) a GM cereal crop having enhanced nutritional value, (ii) the nutrient it is rich in. State any two benefits of…2 mk
- Q17State the principle involved in separation of DNA fragments using gel electrophoresis. How are DNA fragments visualised…2 mk
- Q17The graph given below shows the number of primordial follicles per ovary in women at different ages. Study the graph…2 mk
- Q18Write the first step the primary effluent undergoes when it enters the secondary treatment plant and state the purpose.…2 mk
- Q18(i) Give an example of a genus of fungi that forms mycorrhizial association with plants. (ii) How does the plant derive…2 mk
- Q18Name the two institutes which developed the technology of biogas production in India. Explain the main principle used…2 mk
- Q18Mention the main objective of the Ramsar Convention. Name any two sites in India that are important in the Ramsar…2 mk
- Q18"Cattle and goats do not browse the Calotropis plant." Justify the statement giving reasons.2 mk
- Q18From which end of the ovule, and how does the pollen tube gain its entry into the embryo sac of a Hibiscus flower?…2 mk
- Q19By using Punnett square depict the genotypes and phenotypes of test crosses (where green pod colour (G) is dominant…2 mk
- Q19Vectors are DNA molecules that can carry a foreign DNA segment into the host cell. (i) Write the significance of 'ori'…2 mk
- Q19Certain specific bacterial spores are mixed in water and sprayed over Brassica crop to control butterfly catterpillars.…2 mk
- Q19List and explain any two factors that lead to a decrease in the population density of an area.2 mk
- Q19Why should antibiotics not be taken indiscriminately? Give any two reasons. "It is advisable to complete the course of…2 mk
- Q19Given below is a food web that involves nine organisms. Identify two producers and two carnivores shown in the food…2 mk
- Q19(i) Identify and name the structures 'A' and 'B' marked in the image given below: (ii) State their importance in…2 mk
- Q20"Abingdon tortoise in Galapagos islands became extinct within a decade on introduction of goats in the island." Explain…2 mk
- Q20Ecological pyramids give important information about the ecological system, but do have some limitations. List any two…2 mk
- Q20Illustrate with the help of an example how introduction of an alien species turns invasive and causes decline of an…2 mk
- Q20Plants capture only 2-10 percent of the photosynthetically active radiation of the Sun and this small amount of energy…2 mk
- Q20(i) Give an example of a genus of virus used as narrow spectrum insecticidal biocontrol agent. (ii) How does its use…2 mk
- Q21Explain the role of microorganisms in the following: Reducing the sugar content in grape juice Production of a fuel2 mk
- Q21"Some species of insects and frogs have evolved with various specific features that help them from being detected."…2 mk
- Q21The diagram given below shows a developmental stage of human embryo. Answer the following questions with reference to…2 mk
- Q21India is the seventh largest country in the world in terms of total land area including land and water. Write the value…2 mk
- Q21Write the scientific name of the source organism of the themostable DNA polymerase used in PCR. State the advantage of…2 mk
- Q21On August 22 in the year 2022, 3358 fires were detected in the Amazon rainforests. Write one short-term and one…2 mk
- Q21'Insertional inactivation' is a method to detect recombinant DNA. Explain the method. OR Explain how recombinant DNA…2 mk
- Q22The diagram given below shows the events occurring in an ovary during Oogenesis in a human female. Identify 'X'.…3 mk
- Q22With the help of a schematic diagram only, show in three steps, the formation of recombinant DNA by the action of…3 mk
- Q22Explain how did the experiment conducted by S.L. Miller substantiate that life evolved from pre-existing non-living…3 mk
- Q22(i) How many types of RNA polymerases are there in a eukaryote cell? Mention which one of them transcribes hnRNA. (ii)…3 mk
- Q22Name and explain a surgical contraceptive method that can be adopted by the male partner of a couple.3 mk
- Q23Expand and explain the following techniques used in the 'Test Tube Baby' programme: GIFT ZIFT IUI3 mk
- Q23Study the given pedigree chart and answer the questions that follow. Is the trait given in the chart dominant or…3 mk
- Q23Human Genome Project (HGP) was a mega project launched in the year 1990 with some important goals. Enlist any four…3 mk
- Q24Name the category of drugs represented by the chemical structure given above. If the methyl group is substituted by…3 mk
- Q24Given below is a diagrammatic sectional view of a seminiferous tubule. State the developmental process of: (i) 'b' from…3 mk
- Q24Industrial melanism in England after 1850 is an excellent example of Natural selection. Explain how?3 mk
- Q24Write the characteristics of 'stem cells'. From where can one obtain 'stem cells' in humans? State any two applications…3 mk
- Q25Darwin's theory of Natural Selection is widely accepted but some limitations have been identified by modern biologists.…3 mk
- Q25One of the major approaches of crop improvement programme is Artificial Hybridisation. Explain the steps involved in…3 mk
- Q25Differentiate between malignant and benign tumours. Name and explain the most feared property of a malignant tumour.3 mk
- Q26"Plasmodium protozoan needs both a mosquito and a human host for its continuity." Explain. OR We all must work towards…3 mk
- Q26Treatment of wastewater is done in a sewage treatment plant to make it less polluting. Explain the following with…3 mk
- Q27On spraying Bacillus thuringiensis on an infected cotton crop field the pests are killed by the toxin, however the…3 mk
- Q27Write the scientific name of the nematode that infests the tobacco plants and the part that it infests. How is…3 mk
- Q27Mention Darwin's observations made on finches during his visit to Galapagos Islands. Write the explanation given by…3 mk
- Q27Eli Lilly's contribution for diabetic patients through r-DNA technology has been overwhelmingly accepted. Explain how?3 mk
- Q27Name the two primate ancestors of the present day humans, who existed approximately about 15 million years ago.…3 mk
- Q28Study the pedigree chart of a family given below and answer the questions that follow: Is the disease in this pedigree…3 mk
- Q28Trace the journey of a zygote from the isthmus of the fallopian tube up to its implantation in the uterus of a human…3 mk
- Q28"RNA interference has been used to produce transgenic tobacco plants to protect them from the infestation by specific…3 mk
- Q28Study the pedigree chart given below and answer the questions that follow: (i) Is this trait recessive or dominant?…3 mk
- Q28"Biodiversity plays a major role in many ecosystem services that nature provides." Describe any two broadly utilatarian…3 mk
- Q28(i) Expand the abbreviations given below, used for different modes of assisted reproductive technologies: (1) ZIFT (2)…3 mk
- Q28Explain the following population interactions with the help of one example each: Brood Parasitism Co-evolution of…3 mk
- Q29The chromosome number is fixed for all normal organisms leading to species specification whereas any abnormality in the…4 mk
- Q29Gene expresses itself in a cell system as a protein/enzyme. How does an expression of gene occur in a cell system and…4 mk
- Q29When a microorganism invades a host, a definite sequence of events usually occur leading to infection and disease,…4 mk
- Q30The following pedigree chart shows the inheritance of a genetic disorder up to three generations of a family. Observe…4 mk
- Q30The diagram shows the life cycle of a pathogenic protozoan. (i) Name the parasitic stage that is being transferred from…4 mk
- Q30Study the diagrammatic representation given below of the Earth with regions marked 'A' and 'B' respectively. Answer the…4 mk
- Q31(i) Explain the monosporic development of embryo sac in the ovule of an angiosperm. (ii) Draw a diagram of the mature…5 mk
- Q31(i) Draw a labelled diagram of a replication fork in a prokaryote indicating the process of DNA replication. (ii)…5 mk
- Q31(i) When and how does foetal ejection reflex begin? (ii) Pituitary gland and uterine muscles play an important role…5 mk
- Q31Answer the following questions with respect to recombinant DNA technology: (i) Why is plasmid considered to be an…5 mk
- Q31(i) How and why is charging of tRNA essential in the process of translation? (ii) State the function of ribosome as a…5 mk
- Q31Meselson and Stahl carried out an experiment to prove the nature of DNA replication. Recall the experiment and answer…5 mk
- Q32Given below is a diagrammatic representation of a human ovum. (i) Identify the parts 'a', 'b' and 'c'. (ii) This ovum…5 mk
- Q32A time-bound vaccination programme is followed for the children in our country from their birth up to ten years of age.…5 mk
- Q32Name and describe the steps involved in the technique widely used in forensics that serves as the basis of paternity…5 mk
- Q32"It is sometimes observed that the F_1 progeny shows a phenotype that resembles both the parents." Explain this type of…5 mk
- Q32Protein synthesis requires the services of all three types of RNAs, namely t-RNA, m-RNA and r-RNA. Explain the role of…5 mk
- Q33Bioreactors are the containment vehicles of any biotechnology-based production process. For large scale production and…5 mk
- Q33(i) Describe the phenomenon of adaptive radiation as explained by Darwin. (ii) Is human evolution an example of…5 mk
- Q33Study the diagram given below showing the modes of pollination. Answer the questions that follow. (i) The given diagram…5 mk
- Q33(i) Describe the arrangement of nuclei and cells in a mature embryo sac of a typical angiosperm. (ii) Explain the…5 mk
Other Biology years
Answers come from CBSE’s own marking schemes. How we source them.