CBSE Class 12 Biology 2023
169 questions · 334 marks · every one with the board’s own marking-scheme answer.
What 2023 actually asked, chapter by chapter
Marks we counted in the 2023 papers themselves. CBSE allocates marks per unit, not per chapter — this is what was observed, not an official CBSE weightage.
| Chapter | Marks | Share |
|---|---|---|
| Molecular Basis of Inheritance19 questions | 48 | 14.4% |
| Principles of Inheritance and Variation15 questions | 32 | 9.6% |
| Human Health and Disease15 questions | 32 | 9.6% |
| Evolution16 questions | 31 | 9.3% |
| Sexual Reproduction in Flowering Plants11 questions | 29 | 8.7% |
| Biotechnology and its Applications14 questions | 27 | 8.1% |
| Human Reproduction14 questions | 26 | 7.8% |
| Biotechnology : Principles and Processes13 questions | 26 | 7.8% |
| Biodiversity and Conservation13 questions | 24 | 7.2% |
| Microbes in Human Welfare12 questions | 20 | 6.0% |
| Reproductive Health10 questions | 16 | 4.8% |
| Organisms and Populations11 questions | 14 | 4.2% |
| Ecosystem6 questions | 9 | 2.7% |
All 169 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 mkasked 3×
- 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 mkasked 2×
- 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 mkasked 3×
- 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 mkasked 2×
- 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 mkasked 3×
- Q4The status of the human population reflected in the human age pyramid given below is:1 mkasked 2×
- 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 mkasked 2×
- 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 mkasked 2×
- Q5A human male decides to adopt a surgical method for contraception. Identify the point in the diagram where a cut would…1 mkasked 3×
- 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 mkasked 2×
- 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 mkasked 3×
- Q7Which one of the following fixes the atmospheric nitrogen but is not an autotroph?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 mkasked 3×
- Q7The primary productivity in an ecosystem is expressed as:1 mkasked 3×
- Q7Select the option that gives the correct description of the process of Natural Selection with respect to the length of…1 mkasked 3×
- 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 mkasked 2×
- Q8Given below is the restriction site of a restriction endonuclease Pst-I and the cleavage sites on a DNA molecule.…1 mkasked 3×
- 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 mkasked 2×
- 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 mkasked 3×
- 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
- 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 mkasked 3×
- Q11The given schematic illustration shows three steps 'P', 'Q' and 'R' of the polymerase chain reaction. Step 'P' Step 'Q'…1 mkasked 3×
- 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 mkasked 3×
- Q13Assertion: Decomposition process is slower if detritus is rich in lignin and cutin. Reason (R): Decomposition is…1 mkasked 3×
- 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 mkasked 3×
- 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 mk
- Q14Assertion: A cattle egret and grazing cattle in close association is a classic example of commensalism. Reason (R): As…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 mkasked 2×
- 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: 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 mkasked 3×
- 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 mkasked 3×
- 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 mkasked 3×
- 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 mkasked 3×
- Q19By using Punnett square depict the genotypes and phenotypes of test crosses (where green pod colour (G) is dominant…2 mkasked 3×
- 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 mkasked 3×
- Q19(i) Identify and name the structures 'A' and 'B' marked in the image given below: (ii) State their importance in…2 mkasked 2×
- 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 mkasked 3×
- Q21India is the seventh largest country in the world in terms of total land area including land and water. Write the value…2 mkasked 2×
- 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 mkasked 3×
- 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 mkasked 3×
- 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 mkasked 3×
- Q22Name and explain a surgical contraceptive method that can be adopted by the male partner of a couple.3 mkasked 3×
- Q23Expand and explain the following techniques used in the 'Test Tube Baby' programme: GIFT ZIFT IUI3 mkasked 3×
- 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 mkasked 3×
- Q24Name the category of drugs represented by the chemical structure given above. If the methyl group is substituted by…3 mkasked 3×
- 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 mkasked 3×
- Q25Darwin's theory of Natural Selection is widely accepted but some limitations have been identified by modern biologists.…3 mkasked 3×
- Q25One of the major approaches of crop improvement programme is Artificial Hybridisation. Explain the steps involved in…3 mkasked 3×
- Q25Differentiate between malignant and benign tumours. Name and explain the most feared property of a malignant tumour.3 mkasked 3×
- 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 mkasked 3×
- 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 mkasked 3×
- 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 mkasked 3×
- 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 mkasked 3×
- Q28(i) Expand the abbreviations given below, used for different modes of assisted reproductive technologies: (1) ZIFT (2)…3 mkasked 3×
- Q28Explain the following population interactions with the help of one example each: Brood Parasitism Co-evolution of…3 mkasked 3×
- Q29The chromosome number is fixed for all normal organisms leading to species specification whereas any abnormality in the…4 mkasked 3×
- Q29Gene expresses itself in a cell system as a protein/enzyme. How does an expression of gene occur in a cell system and…4 mkasked 3×
- Q29When a microorganism invades a host, a definite sequence of events usually occur leading to infection and disease,…4 mkasked 3×
- Q30The following pedigree chart shows the inheritance of a genetic disorder up to three generations of a family. Observe…4 mkasked 3×
- Q30The diagram shows the life cycle of a pathogenic protozoan. (i) Name the parasitic stage that is being transferred from…4 mkasked 3×
- Q30Study the diagrammatic representation given below of the Earth with regions marked 'A' and 'B' respectively. Answer the…4 mkasked 3×
- Q31(i) Explain the monosporic development of embryo sac in the ovule of an angiosperm. (ii) Draw a diagram of the mature…5 mkasked 3×
- 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 mkasked 3×
- 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 mkasked 2×
- Q32Given below is a diagrammatic representation of a human ovum. (i) Identify the parts 'a', 'b' and 'c'. (ii) This ovum…5 mkasked 2×
- Q32A time-bound vaccination programme is followed for the children in our country from their birth up to ten years of age.…5 mkasked 3×
- 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 mkasked 2×
- Q33Bioreactors are the containment vehicles of any biotechnology-based production process. For large scale production and…5 mkasked 3×
- 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 mkasked 2×
- 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.