CBSE Class 12 Biology 2026 question paper (57/5)

Maximum marks 70 · Time 3 hours · 3 sets

Try each question first, then open its model answer. Where the paper offers a choice, both questions are shown with OR between them.

Section A

1 mark each

Q.11 mark $Identify the parts P, Q, R, S in the figure given below and select the option in the correct order.$
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Q.21 mark $The foetal ejection reflex in human triggers the release of _________ hormone from __________. Fill in the blanks by choosing right option.$
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Q.31 mark $A DNA molecule is 160 base pairs long. It has 30% Guanine. How many Adenine bases are present in this DNA molecule ?$
Tap an option to check your answer.
Q.41 mark $\times$
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Q.51 mark $In a human female, menstrual cycle of 28 days is represented by the diagram given below. Select the correct statement related with this diagram.$
Tap an option to check your answer.
Q.61 mark $Arrange the following in the correct sequence of their evolution and select the correct option : (i) Seaweed (ii) Invertebrates (iii) Jawless fish$
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Q.71 mark $Monascus purpureus is a yeast used commercially in the production of which one of the following ?$
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Q.81 mark $\downarrow$
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Q.91 mark $Choose a correct option that shows an interaction in which one species benefits while the other is neither harmed nor benefitted.$
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Q.101 mark $Transgenic animals have their genetic material manipulated. Select the correct option in reference to transgenic animals.$
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Q.111 mark $Select the odd option in the context of convergent evolution.$
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Q.121 mark $Which of the following fish led to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in Lake Victoria of East Africa ?$
Tap an option to check your answer.
For Questions number 13 to 16, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below.
Q.131 mark $Assertion (A) : The embryo with 8 to 16 blastomeres is called a morula. Reason (R) : The morula continues to divide and transform into trophoblast.$
Tap an option to check your answer.
Q.141 mark $Assertion (A) : Repetitive sequences make up a very large portion of human genome. Reason (R) : Repetitive sequences do not have direct coding functions in the genome.$
Tap an option to check your answer.
Q.151 mark $Assertion (A) : Trichoderma species are free living fungi that are very common in the root ecosystems. Reason (R) : They are effective bio-control agents of several plant pathogens.$
Tap an option to check your answer.
Q.161 mark $Assertion (A) : The use of chitinase enzyme is necessary for the separation of DNA from yeast cells but not in the case of Spirogyra. Reason (R) : Fungal cell wall is made up of fungal chitin.$
Tap an option to check your answer.

Section B

2 marks each

Q.17 (a)2 marks $Mention the functions of each of the following : (i) Tassels of Corn Cob (ii) Scutellum$
OR
Q.17 (b)2 marks $Farmers prefer apomictic seeds over hybrid seeds. Give any two reasons.$
Q.182 marks $Define the term 'amniocentesis'. Why has the government imposed a statutory ban in spite of its importance in the medical field ?$
Q.192 marks $Name the lymphoid organ that acts as a large reservoir of erythrocytes. Explain its role as a lymphoid organ.$
Q.20 (a)2 marks $Suggest how a virus-free healthy plant can be obtained from a diseased sugarcane plant.$
OR
Q.20 (b)2 marks $In order to force bacteria to take up the recombinant DNA, they must be made competent. Explain how it can be achieved.$
Q.21 (a)2 marks $Differentiate between grazing food chain and detritus food chain.$
OR
Q.21 (b)2 marks $Ecological pyramids are widely accepted but they still have some limitations. Write any two limitations.$

Section C

3 marks each

Q.223 marks $List any three outbreeding devices that flowering plants have developed for cross-pollination and explain how they help to encourage cross-pollination.$
Q.233 marks $Draw a labelled diagram of a 'replicating fork' showing the polarity. Why does DNA replication occur within such 'fork' ?$
Q.243 marks $Study the given chart showing evolution of plants. Answer the following questions : (a) Identify the plant which acts as an immediate ancestor of both ferns and conifers. (b) Name the nearest ancestors of flowering plants. (c) Name the most primitive group of plants. (d) Psilophyton provides common ancestry to which classes ? (e) Name the common ancestor of psilophyton and seed ferns. (f) Name the common ancestor of mosses and tracheophytes.$
Q.253 marks $Mention a product of human welfare obtained with the help of each one of the following : (a) Saccharomyces cerevisiae (b) Propionibacterium shermanni (c) Aspergillus niger (d) Trichoderma polysporum (e) Acetobacter aceti (f) Streptococcus$
Q.263 marks $Transgenic animals are produced by man. Explain any three ways in which such animals can be beneficial to humans.$
Q.273 marks $Explain Gause's 'Competitive Exclusion Principle' with the help of a suitable example.$
Q.283 marks $Explain the level of biodiversity at genetic, species and ecological levels with the help of one example each.$

Section D

The process of copying genetic information from template strand of DNA into RNA is called transcription. It is mediated by RNA polymerase. Transcription takes place in the nucleus of eukaryotic cells. In transcription, only a segment of DNA and only one of the strands is copied into RNA.
Q.29 (a)1 mark $\longrightarrow$
Q.29 (b)(i)1 mark $Why is hnRNA required to undergo splicing ?$
OR
Q.29 (b)(ii)1 mark $Mention the two additional processes which hnRNA needs to undergo after splicing to become functional.$
Q.29 (c)2 marks $Why is only one strand of the DNA transcribed ? Give two reasons.$
We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :
Q.30 (a)1 mark $Why are plasmids and bacteriophages used as cloning vectors ?$
Q.30 (b)(i)1 mark $Identify : (I) The gene in the cloning vector that controls the copy number of the vector. (II) The restriction site - C in the 'rop' gene.$
OR
Q.30 (b)(ii)1 mark $Identify and name two selectable markers shown in the diagram.$
Q.30 (c)2 marks $Name the two restriction sites each in the two genes you have identified as selectable markers.$

Section E

5 marks each

Q.31 (a)5 marks $Briefly explain the events of fertilisation and implantation in an adult human female.$
OR
Q.31 (b)5 marks $(i) Arrange the following hormones in sequence of their secretion in a pregnant woman : hCG; LH; FSH; Relaxin. (ii) Mention the source and the functions of the above mentioned hormones.$
Q.32 (a)5 marks $\text{F}_2$
OR
Q.32 (b)5 marks $Answer the following questions : (i) How does a chromosomal disorder differ from a Mendelian disorder ? Write one example for each. (ii) Name the phenomenon that leads to situations like 'XO' abnormality in humans. Also name this genetic disorder. How are individuals with an XO chromosomal abnormality affected ? Write its symptoms as well as karyotype.$
Q.33 (a)5 marks $(i) Draw the structure of an antibody molecule and label any four of its parts. (ii) Differentiate between active and passive immunity. Write any three differences.$
OR
Q.33 (b)5 marks $(i) (I) Write the scientific names of the two species of filarial worms causing filariasis. (II) How do they affect the body of infected persons ? (III) How does the disease spread ? (ii) Mention the source and the role of the following in providing defence against infection in the human body : (I) Histamine (II) Interferons$

Section A

1 mark each

Q.11 mark $In a human female, menstrual cycle of 28 days is represented by the diagram given below. Select the correct statement related with this diagram.$
Tap an option to check your answer.
Q.21 mark $The cells of endosperm have 24 chromosomes. What will be the number of chromosomes in the gametes ?$
Tap an option to check your answer.
Q.31 mark $During different phases of menstrual cycle, hormones are secreted. Choose the option showing the correct sequence of hormones.$
Tap an option to check your answer.
Q.41 mark $A DNA molecule is 160 base pairs long. It has 30% Guanine. How many Adenine bases are present in this DNA molecule ?$
Tap an option to check your answer.
Q.51 mark $Arrange the following in the correct sequence of their evolution and select the correct option : (i) Seaweed (ii) Invertebrates (iii) Jawless fish$
Tap an option to check your answer.
Q.61 mark $S is the stimulant of central nervous system and interferes with the transport of T, a neurotransmitter. Identify S and T and choose the correct option.$
Tap an option to check your answer.
Q.71 mark $Select the odd option in the context of convergent evolution.$
Tap an option to check your answer.
Q.81 mark $Monascus purpureus is a yeast used commercially in the production of which one of the following ?$
Tap an option to check your answer.
Q.91 mark $\downarrow$
Tap an option to check your answer.
Q.101 mark $Which of the following ecosystem is most productive in terms of net primary productivity ?$
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Q.111 mark $Bt-toxin genes have been expressed in plants in order to provide resistance against : (i) lepidopterans and fungi (ii) animals and bacteria (iii) coleopterans and dipterans (iv) lepidopterans$
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Q.121 mark $According to IUCN, some of the extinctions include : (i) Dodo (ii) Indian gazelle (iii) Thylacine (iv) Steller's Sea Cow$
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For Questions number 13 to 16, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below.
Q.131 mark $Assertion (A) : Genetically modified microbes help in crop protection. Reason (R) : Bacillus thuringiensis (Bt) bacteria control insects by producing prototoxins.$
Tap an option to check your answer.
Q.141 mark $Assertion (A) : Trichoderma species are free living fungi that are very common in the root ecosystems. Reason (R) : They are effective bio-control agents of several plant pathogens.$
Tap an option to check your answer.
Q.151 mark $Assertion (A) : The endometrium undergoes cyclic changes during the menstrual cycle. Reason (R) : Perimetrium contracts strongly during delivery of the baby.$
Tap an option to check your answer.
Q.161 mark $Assertion (A) : Repetitive sequences make up a very large portion of human genome. Reason (R) : Repetitive sequences do not have direct coding functions in the genome.$
Tap an option to check your answer.

Section B

2 marks each

Q.172 marks $Draw a labelled diagram of the embryonic stage that gets implanted in the human uterus. State the functions of two labelled parts.$
Q.18 (a)2 marks $Mention the functions of each of the following : (i) Tassels of Corn Cob (ii) Scutellum$
OR
Q.18 (b)2 marks $Farmers prefer apomictic seeds over hybrid seeds. Give any two reasons.$
Q.19 (a)2 marks $Suggest how a virus-free healthy plant can be obtained from a diseased sugarcane plant.$
OR
Q.19 (b)2 marks $In order to force bacteria to take up the recombinant DNA, they must be made competent. Explain how it can be achieved.$
Q.20 (a)2 marks $Differentiate between grazing food chain and detritus food chain.$
OR
Q.20 (b)2 marks $Ecological pyramids are widely accepted but they still have some limitations. Write any two limitations.$
Q.212 marks $One of the salient features of the genetic code is that it is nearly universal from bacteria to humans. Mention two exceptions to this rule. Why are some codes said to be degenerates ?$

Section C

3 marks each

Q.223 marks $(a) Draw a sectional view of seminiferous tubule of a human. Label the following cells in the seminiferous tubule : (i) Cells that divide by mitosis to increase their number (ii) Cells that undergo meiosis I (iii) Cells that undergo meiosis II (iv) Cells that help in the process of spermiogenesis (b) Mention the role of Leydig cells.$
Q.233 marks $Explain the polygenic inheritance pattern with the help of a suitable example.$
Q.243 marks $Mention a product of human welfare obtained with the help of each one of the following : (a) Saccharomyces cerevisiae (b) Propionibacterium shermanni (c) Aspergillus niger (d) Trichoderma polysporum (e) Acetobacter aceti (f) Streptococcus$
Q.253 marks $Study the given chart showing evolution of plants. Answer the following questions : (a) Identify the plant which acts as an immediate ancestor of both ferns and conifers. (b) Name the nearest ancestors of flowering plants. (c) Name the most primitive group of plants. (d) Psilophyton provides common ancestry to which classes ? (e) Name the common ancestor of psilophyton and seed ferns. (f) Name the common ancestor of mosses and tracheophytes.$
Q.263 marks $(a) Write the scientific name of the nematode that infects tobacco plants. Also name the part of the plant that it infects. (b) How is Agrobacterium used to protect tobacco plants from attack by this pest ?$
Q.273 marks $Explain the level of biodiversity at genetic, species and ecological levels with the help of one example each.$
Q.283 marks $Explain Gause's 'Competitive Exclusion Principle' with the help of a suitable example.$

Section D

We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :
Q.29 (a)1 mark $Why are plasmids and bacteriophages used as cloning vectors ?$
Q.29 (b)(i)1 mark $Identify : (I) The gene in the cloning vector that controls the copy number of the vector. (II) The restriction site - C in the 'rop' gene.$
OR
Q.29 (b)(ii)1 mark $Identify and name two selectable markers shown in the diagram.$
Q.29 (c)2 marks $Name the two restriction sites each in the two genes you have identified as selectable markers.$
The process of copying genetic information from template strand of DNA into RNA is called transcription. It is mediated by RNA polymerase. Transcription takes place in the nucleus of eukaryotic cells. In transcription, only a segment of DNA and only one of the strands is copied into RNA.
Q.30 (a)1 mark $\longrightarrow$
Q.30 (b)(i)1 mark $Why is hnRNA required to undergo splicing ?$
OR
Q.30 (b)(ii)1 mark $Mention the two additional processes which hnRNA needs to undergo after splicing to become functional.$
Q.30 (c)2 marks $Why is only one strand of the DNA transcribed ? Give two reasons.$

Section E

5 marks each

Q.31 (a)5 marks $\text{F}_2$
OR
Q.31 (b)5 marks $Answer the following questions : (i) How does a chromosomal disorder differ from a Mendelian disorder ? Write one example for each. (ii) Name the phenomenon that leads to situations like 'XO' abnormality in humans. Also name this genetic disorder. How are individuals with an XO chromosomal abnormality affected ? Write its symptoms as well as karyotype.$
Q.32 (a)5 marks $(i) Draw the structure of an antibody molecule and label any four of its parts. (ii) Differentiate between active and passive immunity. Write any three differences.$
OR
Q.32 (b)5 marks $(i) (I) Write the scientific names of the two species of filarial worms causing filariasis. (II) How do they affect the body of infected persons ? (III) How does the disease spread ? (ii) Mention the source and the role of the following in providing defence against infection in the human body : (I) Histamine (II) Interferons$
Q.33 (a)5 marks $Briefly explain the events of fertilisation and implantation in an adult human female.$
OR
Q.33 (b)5 marks $(i) Arrange the following hormones in sequence of their secretion in a pregnant woman : hCG; LH; FSH; Relaxin. (ii) Mention the source and the functions of the above mentioned hormones.$

Section A

1 mark each

Q.11 mark $The foetal ejection reflex in human triggers the release of _________ hormone from __________. Fill in the blanks by choosing right option.$
Tap an option to check your answer.
Q.21 mark $Match the IUDs in Column I with suitable example in Column II. Column I Column II a. Non-medicated i. Lippes loop b. Copper releasing ii. LNG-20 c. Hormone releasing iii. Multiload 375$
Tap an option to check your answer.
Q.31 mark $\times$
Tap an option to check your answer.
Q.41 mark $Arrange the following in the correct sequence of their evolution and select the correct option : (i) Seaweed (ii) Invertebrates (iii) Jawless fish$
Tap an option to check your answer.
Q.51 mark $If a genetic disease is transferred from a phenotypically normal but carrier female to only some of the male progeny, the disease is :$
Tap an option to check your answer.
Q.61 mark $A DNA molecule is 160 base pairs long. It has 30% Guanine. How many Adenine bases are present in this DNA molecule ?$
Tap an option to check your answer.
Q.71 mark $A doctor identifies symptoms of nasal congestion, headache, sore throat, hoarseness and cough in a patient. The conclusion is that the patient is infected by a pathogen :$
Tap an option to check your answer.
Q.81 mark $Which type of selection is industrial melanism observed in moth, Biston betularia ?$
Tap an option to check your answer.
Q.91 mark $C-peptide of human insulin is :$
Tap an option to check your answer.
Q.101 mark $\downarrow$
Tap an option to check your answer.
Q.111 mark $Which of the following fish led to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in Lake Victoria of East Africa ?$
Tap an option to check your answer.
Q.121 mark $Cattle or goats are never seen browsing on the weed, Calotropis. Select the correct option for the reason.$
Tap an option to check your answer.
For Questions number 13 to 16, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below.
Q.131 mark $Assertion (A) : Repetitive sequences make up a very large portion of human genome. Reason (R) : Repetitive sequences do not have direct coding functions in the genome.$
Tap an option to check your answer.
Q.141 mark $Assertion (A) : The embryo with 8 to 16 blastomeres is called a morula. Reason (R) : The morula continues to divide and transform into trophoblast.$
Tap an option to check your answer.
Q.151 mark $Assertion (A) : The use of chitinase enzyme is necessary for the separation of DNA from yeast cells but not in the case of Spirogyra. Reason (R) : Fungal cell wall is made up of fungal chitin.$
Tap an option to check your answer.
Q.161 mark $Assertion (A) : Besides curdling of milk, LAB also improves its nutritional quality by increasing Vitamin B12. Reason (R) : LAB, when present in the stomach checks disease-causing microbes.$
Tap an option to check your answer.

Column I	Column II
a. Non-medicated	i. Lippes loop
b. Copper releasing	ii. LNG-20
c. Hormone releasing	iii. Multiload 375

Section B

2 marks each

Q.172 marks $State the role of thymus as a lymphoid organ. Name the cells that are released from it and mention their functions.$
Q.18 (a)2 marks $Explain the mutually rewarding relationship between Yucca plant and species of moth.$
OR
Q.18 (b)2 marks $Pollination success will be reduced unless the orchid flower co-evolves with the pollinator. Explain.$
Q.19 (a)2 marks $Differentiate between grazing food chain and detritus food chain.$
OR
Q.19 (b)2 marks $Ecological pyramids are widely accepted but they still have some limitations. Write any two limitations.$
Q.202 marks $How do 'implants' act as an effective method of contraception in human females ? Mention one advantage of implants over contraceptive pills.$
Q.21 (a)2 marks $Explain any two methods of vectorless gene transfer.$
OR
Q.21 (b)2 marks $Name the most commonly used bioreactor. List the advantages of the bioreactor. Also write the importance of sampling ports.$

Section C

3 marks each

Q.223 marks $Draw a labelled diagram of a 'replicating fork' showing the polarity. Why does DNA replication occur within such 'fork' ?$
Q.233 marks $List any three outbreeding devices that flowering plants have developed for cross-pollination and explain how they help to encourage cross-pollination.$
Q.243 marks $Explain how the following microbes act as biocontrol agents : (a) Bacillus thuringiensis (b) Nucleopolyhedrovirus$
Q.253 marks $Transgenic animals are produced by man. Explain any three ways in which such animals can be beneficial to humans.$
Q.263 marks $Explain the level of biodiversity at genetic, species and ecological levels with the help of one example each.$
Q.273 marks $Study the given chart showing evolution of plants. Answer the following questions : (a) Identify the plant which acts as an immediate ancestor of both ferns and conifers. (b) Name the nearest ancestors of flowering plants. (c) Name the most primitive group of plants. (d) Psilophyton provides common ancestry to which classes ? (e) Name the common ancestor of psilophyton and seed ferns. (f) Name the common ancestor of mosses and tracheophytes.$
Q.283 marks $dN/dt = rN$

Section D

The process of copying genetic information from template strand of DNA into RNA is called transcription. It is mediated by RNA polymerase. Transcription takes place in the nucleus of eukaryotic cells. In transcription, only a segment of DNA and only one of the strands is copied into RNA.
Q.29 (a)1 mark $\longrightarrow$
Q.29 (b)(i)1 mark $Why is hnRNA required to undergo splicing ?$
OR
Q.29 (b)(ii)1 mark $Mention the two additional processes which hnRNA needs to undergo after splicing to become functional.$
Q.29 (c)2 marks $Why is only one strand of the DNA transcribed ? Give two reasons.$
We know that plasmids and bacteriophages are the most commonly used vectors in biotechnology experiments. If we can link an alien piece of DNA to the plasmid DNA, the alien DNA can be multiplied equal to the copy number of the plasmid. Engineered vectors are used these days. Study the diagram of the E. coli cloning vector pBR322 and answer the questions that follow :
Q.30 (a)1 mark $Why are plasmids and bacteriophages used as cloning vectors ?$
Q.30 (b)(i)1 mark $Identify : (I) The gene in the cloning vector that controls the copy number of the vector. (II) The restriction site - C in the 'rop' gene.$
OR
Q.30 (b)(ii)1 mark $Identify and name two selectable markers shown in the diagram.$
Q.30 (c)2 marks $Name the two restriction sites each in the two genes you have identified as selectable markers.$

Section E

5 marks each

Q.31 (a)5 marks $\text{F}_2$
OR
Q.31 (b)5 marks $Answer the following questions : (i) How does a chromosomal disorder differ from a Mendelian disorder ? Write one example for each. (ii) Name the phenomenon that leads to situations like 'XO' abnormality in humans. Also name this genetic disorder. How are individuals with an XO chromosomal abnormality affected ? Write its symptoms as well as karyotype.$
Q.32 (a)5 marks $(i) Draw the structure of an antibody molecule and label any four of its parts. (ii) Differentiate between active and passive immunity. Write any three differences.$
OR
Q.32 (b)5 marks $(i) (I) Write the scientific names of the two species of filarial worms causing filariasis. (II) How do they affect the body of infected persons ? (III) How does the disease spread ? (ii) Mention the source and the role of the following in providing defence against infection in the human body : (I) Histamine (II) Interferons$
Q.33 (a)5 marks $Briefly explain the events of fertilisation and implantation in an adult human female.$
OR
Q.33 (b)5 marks $(i) Arrange the following hormones in sequence of their secretion in a pregnant woman : hCG; LH; FSH; Relaxin. (ii) Mention the source and the functions of the above mentioned hormones.$