CBSE Class 12 Biology 2025 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 $The histone core in a nucleosome of chromatin thread is a/an :$
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Q.21 mark $Given below are few statements with reference to the uterus in the female reproductive system : (i) The myometrium exhibits strong contractions during the delivery of the baby. (ii) The uterus opens into the cervix through a narrow opening called vagina. (iii) The cavity of the cervix and the vagina forms the birth canal. (iv) The outermost layer of uterus is a thin membranous perimetrium. (v) The uterus is supported by tendons attached to the pelvic wall. Choose the option with all true statements from the given options :$
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Q.31 mark $During the process of transcription, after binding to a promoter, RNA polymerase catalyses and makes the bases in the template strand of DNA available for base pairing, with the bases of :$
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Q.41 mark $Which of the following is not an example of aneuploidy ?$
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Q.51 mark $Colostrum secreted by the mother's mammary glands in a human female during the initial days of lactation is rich in antibody :$
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Q.61 mark $Select the statements that are true for pollination mechanism in flowering plants from the given options. (i) In Vallisneria, the female flowers are pollinated by pollen grains inside the water. (ii) In Zostera, pollen grains are released on the surface of water. (iii) In most of the water-pollinated species, pollen grains are covered by a mucilaginous coating. (iv) Pollination by water is quite rare and limited to about 30 genera. Choose the correct answer :$
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Q.71 mark $Which of the following combinations is a correct example of convergent evolution in Australian marsupials and Placental mammals ?$
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Q.81 mark $Isolation of DNA from a fungal cell can be achieved by using :$
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Q.91 mark $During a monohybrid cross involving a tall pea plant with a dwarf pea plant, the offspring populations were tall and dwarf in equal ratio. Find out the genotype of parent pea plants.$
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Q.101 mark $25^{\text{th}}$
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Q.111 mark $Large scale industrial production of Butyric acid for human welfare is done using the microbe :$
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Q.121 mark $The correct depiction of the centrifugation step of the experiment conducted by Alfred Hershey and Martha Chase on using radioactive labelled phages to prove that DNA is the genetic material is :$
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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 $Assertion (A) : To generate only a part of the plant from a cell is totipotency. Reason (R) : Suitable special nutrient media and sterile conditions are required in 'in vitro' conditions for the division of cells in explants.$
Tap an option to check your answer.
Q.141 mark $Assertion (A) : Biogas plants are more often built in rural areas. Reason (R) : The excreta or gobar of cattle is rich in Methanobacterium.$
Tap an option to check your answer.
Q.151 mark $Assertion (A) : Gene pairs present on the same chromosome may be tightly linked or loosely linked. Reason (R) : Frequency of recombination between gene pairs on different chromosomes as a measure of the distance between genes can be used for 'mapping' their position on the chromosomes.$
Tap an option to check your answer.
Q.161 mark $Assertion (A) : Cu-T, Cu-7 and LNG-20 are the most widely used copper-releasing IUDs. Reason (R) : Cu-ions in IUDs effectively suppress sperm motility and the fertilising capacity of sperms.$
Tap an option to check your answer.

Section B

2 marks each

Q.17 (a)2 marks $Give an account of the generalised structure of an antibody molecule produced by B-lymphocytes in response to the pathogen.$
OR
Q.17 (b)2 marks $Other than public awareness and counselling, enlist four measures taken up by NACO, WHO and other NGOs to prevent the spread of HIV infection in the society.$
Q.182 marks $Given below are the diagrammatic representations of the replicating fork of DNA in E. coli. Study the diagrams and answer the questions that follow. (a) Which one of the three diagrams (i), (ii) or (iii) is the correct representation of the replicating fork of DNA replication ? Explain your answer. (b) Name the enzyme used in E. coli to join the newly synthesised fragments of DNA.$
Q.19 (a)2 marks $Explain what is meant by the term amniocentesis. How is this technique misused in India ?$
OR
Q.19 (b)2 marks $Name any two VDs which might occur in a human female. State any two complications in a female if it is left untreated.$
Q.202 marks $\downarrow$
Q.21 (a)2 marks $Explain how the interaction between a fig tree and its tight one-to-one relationship with the pollinator species of wasp is one of the best examples of mutualism.$
OR
Q.21 (b)2 marks $Correctly depict (also indicate the trophic level) and describe the ecological pyramid of number with 32 birds dependent on 20 insects feeding on one banyan tree.$

Section C

3 marks each

Q.223 marks $Explain the neuroendocrine mechanism involved in the process of parturition in a human female leading to the expulsion of the baby out of the uterus through the birth canal.$
Q.233 marks $During a medical investigation, an infant was found to possess an extra copy of chromosome no. 21. Identify the disorder the child is suffering from. Describe the symptoms the child is likely to develop later in life.$
Q.243 marks $(a) Write the full form of BOD. (b) Define BOD. Explain how it is a measure of the organic matter present in the water body.$
Q.253 marks $Enlist three advantages of genetically modified plants.$

Q.263 marks

\text{I}^{\text{A}}\text{I}^{\text{A}}

Q.273 marks $Explain how the loss of habitat and fragmentation drives plants and animals to extinction with the help of an example of habitat loss in the Tropical Rain Forest. Also write the effect of fragmentation of a habitat on the population decline.$
Q.283 marks $Many of the flowering plants producing hermaphrodite flowers have developed many devices to discourage self-pollination and to encourage cross-pollination. Given below is a picture of one such outbreeding device in a flowering plant. Study the picture and answer the questions that follow : (a) Explain how the given type of pollination is advantageous to the plant. (b) Can this flowering plant show geitonogamy ? Justify your answer.$

Genotype	Phenotype
$\text{I}^{\text{A}}\text{I}^{\text{A}}$	A
$\text{I}^{\text{A}}\text{i}$	A
$\text{I}^{\text{B}}\text{I}^{\text{B}}$	B
$\text{I}^{\text{B}}\text{i}$	B
$\text{I}^{\text{A}}\text{I}^{\text{B}}$	AB
ii	O

Section D

Highly conserved proteins such as Haemoglobin and Cytochrome-C provide the best biochemical evidences to trace evolutionary relationships between different groups. Cytochrome-C is formed of 104 amino acids. Cytochrome-C is the respiratory pigment present in all eukaryotic cells. It has evolved at a constant rate during evolution. In chimpanzees and humans, Cytochrome-C genes are identical. The given data shows the evolution of the Cytochrome-C gene in different mammals from kangaroos, cows, rodents to humans :
Groups Nucleotide substitution in the gene of Cytochrome-C Millions of years ago
Human/Kangaroo 100 125 mya
Human/Cow 75 120 mya
Human/Rodent 60 75 mya
Q.29 (a)1 mark $Select the correct option for the time of separation of two groups and the number of nucleotide substitutions in the gene of Cytochrome-C : Options Time of separation of two groups during evolution Number of nucleotide substitutions (i) Lesser Greater (ii) Greater Lesser (iii) Greater Greater$
Q.29 (b)2 marks $What do you infer about the type of evolution (convergent or divergent) for the given pair of groups and why ? (i) Human and Kangaroo (ii) Human and Rodent$
Q.29 (c) (i)1 mark $Define convergent evolution.$
OR
Q.29 (c) (ii)1 mark $Define divergent evolution.$
In 2021, $5{\cdot}3$ percent of 15 to 16-year-olds worldwide ( $13{\cdot}5$ million individuals) had used Cannabis in the past year according to UNODC. The adolescent brain is still developing and drug use can have long-term negative effects. Early drug use initiation can lead to faster development of dependence than in adults and other problems in adulthood. Parts of the Amazon Basin are at the intersection of multiple forms of organised crimes that are accelerating devastation, with severe implications for the security, health and well-being of the population across the region. The direct impact of coca cultivation on deforestation is minimal, but indirectly it acts as a catalyst for "Narco-deforestation". The laundering of drug trafficking profits into land speculation etc. is posing a growing danger to the world's largest rainforest.
Q.30 (a)1 mark $Which age group or period of growth people are more vulnerable to drug abuse ?$
Q.30 (b)1 mark $Explain the negative impact of coca cultivation on the world's largest rainforest.$
Q.30 (c) (i)2 marks $From which part of the plant are cannabinoids mainly obtained ? Mention any one negative effect of this drug on adolescents.$
OR
Q.30 (c) (ii)2 marks $State the scientific name of the plant from which coca alkaloids are derived and state one negative impact of use of excessive dosage of cocaine.$

Groups	Nucleotide substitution in the gene of Cytochrome-C	Millions of years ago
Human/Kangaroo	100	125 mya
Human/Cow	75	120 mya
Human/Rodent	60	75 mya

Options	Time of separation of two groups during evolution	Number of nucleotide substitutions
(i)	Lesser	Greater
(ii)	Greater	Lesser
(iii)	Greater	Greater

Section E

5 marks each

Q.31 (a)5 marks $Define transgenic animals. Explain in detail any four areas where they can be used for human benefit.$
OR
Q.31 (b)5 marks $Describe the structure and working of a sparged stirred-tank bioreactor.$
Q.32 (a)5 marks $(i) Describe the population growth curve applicable in a population of any species in nature that has unlimited resources at its disposal. (ii) Explain the equation of this growth curve. (iii) Name the growth curve and depict a graphical plot for this type of population growth.$
OR
Q.32 (b)5 marks $(i) Explain the conclusion drawn by Alexander von Humboldt during his extensive explorations in the wilderness of South American jungles. (ii) Give the equation of the Species-Area relationship. (iii) Draw a graphical representation of the relation between species richness and area for a wide variety of taxa such as birds, bats, etc.$
Q.33 (a)5 marks $(i) Explain the structure of a typical monocotyledonous embryo of a flowering plant. (ii) How are multiple embryos formed in a citrus fruit ? What is the mechanism known as ?$
OR
Q.33 (b)5 marks $(i) Name and explain the structural organisation of the male sex accessory ducts in the human male reproductive system. (ii) Describe the role of gonadotropin FSH in the regulation of spermatogenesis.$

Section A

1 mark each

Q.11 mark $The region of chromatin that are actively transcribed are thought to be :$
Tap an option to check your answer.
Q.21 mark $Given below are few statements with reference to the ovaries of the human female reproductive system : (i) It is 2 - 4 cm in length and is connected to the pelvic wall by tendons. (ii) It is covered by a thin epithelium which encloses the ovarian stroma. (iii) The stroma is divided into a peripheral medulla and an inner cortex. (iv) The ovaries are the primary female sex organs that produce the female gamete (ovum). (v) Ovaries are located one on each side of the lower abdomen. Choose the option with all true statements from the given options :$
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Q.31 mark $The approach of sequencing the whole set of genome, including all the coding and non-coding sequences in HGP is :$
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Q.41 mark $In the pedigree chart given below, what should be the genotype of the indicated member ?$
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Q.51 mark $The lobed organ located near the heart and beneath the breast bone in humans is :$
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Q.61 mark $Unisexuality of flowers prevents which process ?$
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Q.71 mark $Which of the following combinations is a correct example of convergent evolution in Placental mammals and Australian marsupials ?$
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Q.81 mark $Isolation of DNA from a bacterial cell can be achieved by using :$
Tap an option to check your answer.

Q.91 mark

Match the terms in Column-I with their description in Column-II and choose the correct option. Column-I (Terms) Column-II (Descriptions) a. Dominance (i) Many genes govern a single character. b. Codominance (ii) In a heterozygote organism, only one allele expresses itself. c. Pleiotropy (iii) In a heterozygous organism, both alleles express themselves fully. d. Polygenic inheritance (iv) A single gene influences many characters.

Column-I (Terms)	Column-II (Descriptions)
a. Dominance	(i) Many genes govern a single character.
b. Codominance	(ii) In a heterozygote organism, only one allele expresses itself.
c. Pleiotropy	(iii) In a heterozygous organism, both alleles express themselves fully.
d. Polygenic inheritance	(iv) A single gene influences many characters.

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Q.101 mark $Which enzyme(s) will be produced in a bacterial cell in which 'UAG' is inserted in the 'lac-y gene' due to mutation ? Choose the correct option :$
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Q.111 mark $Large scale industrial production of citric acid for human welfare is done using the microbe :$
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Q.121 mark $In a DNA, percentage of thymine is 20. What is the percentage of Guanine ?$
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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 $Assertion (A) : Gene pairs present on the same chromosome may be tightly linked or loosely linked. Reason (R) : Frequency of recombination between gene pairs on different chromosomes as a measure of the distance between genes can be used for 'mapping' their position on the chromosomes.$
Tap an option to check your answer.
Q.141 mark $Assertion (A) : Cu-T, Cu-7 and LNG-20 are the most widely used copper-releasing IUDs. Reason (R) : Cu-ions in IUDs effectively suppress sperm motility and the fertilising capacity of sperms.$
Tap an option to check your answer.
Q.151 mark $Assertion (A) : To generate only a part of the plant from a cell is totipotency. Reason (R) : Suitable special nutrient media and sterile conditions are required in 'in vitro' conditions for the division of cells in explants.$
Tap an option to check your answer.
Q.161 mark $Assertion (A) : Lymphocytes arise from bone marrow and present in the blood and lymph and serve as natural killer cells. Reason (R) : Lymphocytes migrate to thymus, where they develop into T-cells and begin to mature.$
Tap an option to check your answer.

Section B

2 marks each

Q.172 marks $\downarrow$
Q.18 (a)2 marks $Explain what is meant by the term amniocentesis. How is this technique misused in India ?$
OR
Q.18 (b)2 marks $Name any two VDs which might occur in a human female. State any two complications in a female if it is left untreated.$
Q.19 (a)2 marks $Explain how the interaction between a fig tree and its tight one-to-one relationship with the pollinator species of wasp is one of the best examples of mutualism.$
OR
Q.19 (b)2 marks $Correctly depict (also indicate the trophic level) and describe the ecological pyramid of number with 32 birds dependent on 20 insects feeding on one banyan tree.$
Q.202 marks $Given below are the diagrammatic representations of the replicating fork of DNA in E. coli. Study the diagrams and answer the questions that follow. (a) Which one of the three diagrams (i), (ii) or (iii) is the correct representation of the replicating fork of DNA replication ? Explain your answer. (b) Name the enzyme used in E. coli to join the newly synthesised fragments of DNA.$
Q.21 (a)2 marks $Give an account of the generalised structure of an antibody molecule produced by B-lymphocytes in response to the pathogen.$
OR
Q.21 (b)2 marks $Other than public awareness and counselling, enlist four measures taken up by NACO, WHO and other NGOs to prevent the spread of HIV infection in the society.$

Section C

3 marks each

Q.223 marks $Explain how the loss of habitat and fragmentation drives plants and animals to extinction with the help of an example of habitat loss in the Tropical Rain Forest. Also write the effect of fragmentation of a habitat on the population decline.$

Q.233 marks

\text{I}^{\text{A}}\text{I}^{\text{A}}

Q.243 marks $Explain the neuroendocrine mechanism involved in the process of parturition in a human female leading to the expulsion of the baby out of the uterus through the birth canal.$
Q.253 marks $Many of the flowering plants producing hermaphrodite flowers have developed many devices to discourage self-pollination and to encourage cross-pollination. Given below is a picture of one such outbreeding device in a flowering plant. Study the picture and answer the questions that follow : (a) Explain how the given type of pollination is advantageous to the plant. (b) Can this flowering plant show geitonogamy ? Justify your answer.$
Q.263 marks $Name a blood related autosomal Mendelian disorder. Why is it called as Mendelian disorder ? How is the disorder transmitted from parents to offspring ?$
Q.273 marks $(a) Write the full form of BOD. (b) Define BOD. Explain how it is a measure of the organic matter present in the water body.$
Q.283 marks $Enlist three advantages of genetically modified plants.$

Genotype	Phenotype
$\text{I}^{\text{A}}\text{I}^{\text{A}}$	A
$\text{I}^{\text{A}}\text{i}$	A
$\text{I}^{\text{B}}\text{I}^{\text{B}}$	B
$\text{I}^{\text{B}}\text{i}$	B
$\text{I}^{\text{A}}\text{I}^{\text{B}}$	AB
ii	O

Section D

In 2021, $5{\cdot}3$ percent of 15 to 16-year-olds worldwide ( $13{\cdot}5$ million individuals) had used Cannabis in the past year according to UNODC. The adolescent brain is still developing and drug use can have long-term negative effects. Early drug use initiation can lead to faster development of dependence than in adults and other problems in adulthood. Parts of the Amazon Basin are at the intersection of multiple forms of organised crimes that are accelerating devastation, with severe implications for the security, health and well-being of the population across the region. The direct impact of coca cultivation on deforestation is minimal, but indirectly it acts as a catalyst for "Narco-deforestation". The laundering of drug trafficking profits into land speculation etc. is posing a growing danger to the world's largest rainforest.
Q.29 (a)1 mark $Which age group or period of growth people are more vulnerable to drug abuse ?$
Q.29 (b)1 mark $Explain the negative impact of coca cultivation on the world's largest rainforest.$
Q.29 (c) (i)2 marks $From which part of the plant are cannabinoids mainly obtained ? Mention any one negative effect of this drug on adolescents.$
OR
Q.29 (c) (ii)2 marks $State the scientific name of the plant from which coca alkaloids are derived and state one negative impact of use of excessive dosage of cocaine.$
Highly conserved proteins such as Haemoglobin and Cytochrome-C provide the best biochemical evidences to trace evolutionary relationships between different groups. Cytochrome-C is formed of 104 amino acids. Cytochrome-C is the respiratory pigment present in all eukaryotic cells. It has evolved at a constant rate during evolution. In chimpanzees and humans, Cytochrome-C genes are identical. The given data shows the evolution of the Cytochrome-C gene in different mammals from kangaroos, cows, rodents to humans :
Groups Nucleotide substitution in the gene of Cytochrome-C Millions of years ago
Human/Kangaroo 100 125 mya
Human/Cow 75 120 mya
Human/Rodent 60 75 mya
Q.30 (a)1 mark $Select the correct option for the time of separation of two groups and the number of nucleotide substitutions in the gene of Cytochrome-C : Options Time of separation of two groups during evolution Number of nucleotide substitutions (i) Lesser Greater (ii) Greater Lesser (iii) Greater Greater$
Q.30 (b)2 marks $What do you infer about the type of evolution (convergent or divergent) for the given pair of groups and why ? (i) Human and Kangaroo (ii) Human and Rodent$
Q.30 (c) (i)1 mark $Define convergent evolution.$
OR
Q.30 (c) (ii)1 mark $Define divergent evolution.$

Groups	Nucleotide substitution in the gene of Cytochrome-C	Millions of years ago
Human/Kangaroo	100	125 mya
Human/Cow	75	120 mya
Human/Rodent	60	75 mya

Options	Time of separation of two groups during evolution	Number of nucleotide substitutions
(i)	Lesser	Greater
(ii)	Greater	Lesser
(iii)	Greater	Greater

Section E

5 marks each

Q.31 (a)5 marks $(i) Explain the structure of a typical monocotyledonous embryo of a flowering plant. (ii) How are multiple embryos formed in a citrus fruit ? What is the mechanism known as ?$
OR
Q.31 (b)5 marks $(i) Name and explain the structural organisation of the male sex accessory ducts in the human male reproductive system. (ii) Describe the role of gonadotropin FSH in the regulation of spermatogenesis.$
Q.32 (a)5 marks $(i) Explain why the insecticidal protein producing by Bacillus thuringiensis does not kill the bacteria itself. (ii) How has man exploited this protein to produce cotton bollworm resistant Bt cotton plant ?$
OR
Q.32 (b)5 marks $\beta$
Q.33 (a)5 marks $(i) Describe the population growth curve applicable in a population of any species in nature that has unlimited resources at its disposal. (ii) Explain the equation of this growth curve. (iii) Name the growth curve and depict a graphical plot for this type of population growth.$
OR
Q.33 (b)5 marks $(i) Explain the conclusion drawn by Alexander von Humboldt during his extensive explorations in the wilderness of South American jungles. (ii) Give the equation of the Species-Area relationship. (iii) Draw a graphical representation of the relation between species richness and area for a wide variety of taxa such as birds, bats, etc.$

Section A

1 mark each

Q.11 mark $In E. coli, a DNA sequence that specifies where RNA polymerase will bind and initiate transcription of a gene is :$
Tap an option to check your answer.
Q.21 mark $Given below are few statements with reference to the major events in the menstrual cycle of a human female : (i) During the follicular phase, the primary follicles grow to become a Graafian follicle. (ii) Gonadotropins FSH and progesterone stimulate follicular development during the follicular phase. (iii) LH surge induces rupture of Graafian follicle thereby releasing the corpus luteum. (iv) Progesterone released by corpus luteum is essential for maintenance of endometrium. (v) Both LH and progesterone attain a peak level in the middle of the cycle. Choose the option with all true statements from the given options :$
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Q.31 mark $The approach used in HGP of identifying all the genes that are expressed as RNA is referred to as :$
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Q.41 mark $Study the pedigree chart of a family showing the inheritance of myotonic dystrophy : The trait under study is :$
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Q.51 mark $The large bean-shaped organ acting as a filter of the blood in humans is :$
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Q.61 mark $Select the following statements that are true for insect pollinated flowers from the given options. (i) Majority of these flowers are large, colourful and rich in nectar. (ii) Nectars and seeds are usual floral rewards to attract insects for pollination. (iii) Pollen grains of these flowers are generally mucilaginous so as to stick to the body of the insects. (iv) A foul odour is emitted by some flowers to attract flies and beetles. Choose the correct answer :$
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Q.71 mark $Which of the following combinations is a correct example of convergent evolution in Australian marsupials and Placental mammals ?$
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Q.81 mark $'AGGTATCGCAT' is a sequence from the coding strand of a gene. What will be the corresponding sequence of the transcribed mRNA ?$
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Q.91 mark $Removal of RNA polymerase-III from nucleoplasm of a eukaryotic cell will affect the transcription of which of the following ?$
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Q.101 mark $Large scale industrial production of streptokinase for human welfare is done using the microbe :$
Tap an option to check your answer.
Q.111 mark $Isolation of DNA from a plant cell can be achieved by using :$
Tap an option to check your answer.
Q.121 mark $\text{F}_1$
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 $Assertion (A) : Biogas plants are more often built in rural areas. Reason (R) : The excreta or gobar of cattle is rich in Methanobacterium.$
Tap an option to check your answer.
Q.141 mark $Assertion (A) : Mode of action of pills and implants/injectables is similar. Reason (R) : The effective period of pills is much longer as compared to implants/injectables.$
Tap an option to check your answer.
Q.151 mark $Assertion (A) : To generate only a part of the plant from a cell is totipotency. Reason (R) : Suitable special nutrient media and sterile conditions are required in 'in vitro' conditions for the division of cells in explants.$
Tap an option to check your answer.
Q.161 mark $Assertion (A) : Gene pairs present on the same chromosome may be tightly linked or loosely linked. Reason (R) : Frequency of recombination between gene pairs on different chromosomes as a measure of the distance between genes can be used for 'mapping' their position on the chromosomes.$
Tap an option to check your answer.

Section B

2 marks each

Q.172 marks $Given below are the diagrammatic representations of the replicating fork of DNA in E. coli. Study the diagrams and answer the questions that follow. (a) Which one of the three diagrams (i), (ii) or (iii) is the correct representation of the replicating fork of DNA replication ? Explain your answer. (b) Name the enzyme used in E. coli to join the newly synthesised fragments of DNA.$
Q.182 marks $\downarrow$
Q.19 (a)2 marks $Explain how the interaction between a fig tree and its tight one-to-one relationship with the pollinator species of wasp is one of the best examples of mutualism.$
OR
Q.19 (b)2 marks $Correctly depict (also indicate the trophic level) and describe the ecological pyramid of number with 32 birds dependent on 20 insects feeding on one banyan tree.$
Q.20 (a)2 marks $Explain what is meant by the term amniocentesis. How is this technique misused in India ?$
OR
Q.20 (b)2 marks $Name any two VDs which might occur in a human female. State any two complications in a female if it is left untreated.$
Q.21 (a)2 marks $Give an account of the generalised structure of an antibody molecule produced by B-lymphocytes in response to the pathogen.$
OR
Q.21 (b)2 marks $Other than public awareness and counselling, enlist four measures taken up by NACO, WHO and other NGOs to prevent the spread of HIV infection in the society.$

Section C

3 marks each

Q.223 marks $Many of the flowering plants producing hermaphrodite flowers have developed many devices to discourage self-pollination and to encourage cross-pollination. Given below is a picture of one such outbreeding device in a flowering plant. Study the picture and answer the questions that follow : (a) Explain how the given type of pollination is advantageous to the plant. (b) Can this flowering plant show geitonogamy ? Justify your answer.$
Q.233 marks $Enlist three advantages of genetically modified plants.$
Q.243 marks $Explain the neuroendocrine mechanism involved in the process of parturition in a human female leading to the expulsion of the baby out of the uterus through the birth canal.$
Q.253 marks $Name one commonly occurring genetic disorder in humans which is caused due to monosomy (one chromosome less than the normal number of chromosomes) of sex chromosome. Give its two symptoms.$
Q.263 marks $Explain how the loss of habitat and fragmentation drives plants and animals to extinction with the help of an example of habitat loss in the Tropical Rain Forest. Also write the effect of fragmentation of a habitat on the population decline.$
Q.273 marks $(a) Write the full form of BOD. (b) Define BOD. Explain how it is a measure of the organic matter present in the water body.$

Q.283 marks

\text{I}^{\text{A}}\text{I}^{\text{A}}

Genotype	Phenotype
$\text{I}^{\text{A}}\text{I}^{\text{A}}$	A
$\text{I}^{\text{A}}\text{i}$	A
$\text{I}^{\text{B}}\text{I}^{\text{B}}$	B
$\text{I}^{\text{B}}\text{i}$	B
$\text{I}^{\text{A}}\text{I}^{\text{B}}$	AB
ii	O

Section D

Highly conserved proteins such as Haemoglobin and Cytochrome-C provide the best biochemical evidences to trace evolutionary relationships between different groups. Cytochrome-C is formed of 104 amino acids. Cytochrome-C is the respiratory pigment present in all eukaryotic cells. It has evolved at a constant rate during evolution. In chimpanzees and humans, Cytochrome-C genes are identical. The given data shows the evolution of the Cytochrome-C gene in different mammals from kangaroos, cows, rodents to humans :
Groups Nucleotide substitution in the gene of Cytochrome-C Millions of years ago
Human/Kangaroo 100 125 mya
Human/Cow 75 120 mya
Human/Rodent 60 75 mya
Q.29 (a)1 mark $Select the correct option for the time of separation of two groups and the number of nucleotide substitutions in the gene of Cytochrome-C : Options Time of separation of two groups during evolution Number of nucleotide substitutions (i) Lesser Greater (ii) Greater Lesser (iii) Greater Greater$
Q.29 (b)2 marks $What do you infer about the type of evolution (convergent or divergent) for the given pair of groups and why ? (i) Human and Kangaroo (ii) Human and Rodent$
Q.29 (c) (i)1 mark $Define convergent evolution.$
OR
Q.29 (c) (ii)1 mark $Define divergent evolution.$
In 2021, $5{\cdot}3$ percent of 15 to 16-year-olds worldwide ( $13{\cdot}5$ million individuals) had used Cannabis in the past year according to UNODC. The adolescent brain is still developing and drug use can have long-term negative effects. Early drug use initiation can lead to faster development of dependence than in adults and other problems in adulthood. Parts of the Amazon Basin are at the intersection of multiple forms of organised crimes that are accelerating devastation, with severe implications for the security, health and well-being of the population across the region. The direct impact of coca cultivation on deforestation is minimal, but indirectly it acts as a catalyst for "Narco-deforestation". The laundering of drug trafficking profits into land speculation etc. is posing a growing danger to the world's largest rainforest.
Q.30 (a)1 mark $Which age group or period of growth people are more vulnerable to drug abuse ?$
Q.30 (b)1 mark $Explain the negative impact of coca cultivation on the world's largest rainforest.$
Q.30 (c) (i)2 marks $From which part of the plant are cannabinoids mainly obtained ? Mention any one negative effect of this drug on adolescents.$
OR
Q.30 (c) (ii)2 marks $State the scientific name of the plant from which coca alkaloids are derived and state one negative impact of use of excessive dosage of cocaine.$

Groups	Nucleotide substitution in the gene of Cytochrome-C	Millions of years ago
Human/Kangaroo	100	125 mya
Human/Cow	75	120 mya
Human/Rodent	60	75 mya

Options	Time of separation of two groups during evolution	Number of nucleotide substitutions
(i)	Lesser	Greater
(ii)	Greater	Lesser
(iii)	Greater	Greater

Section E

5 marks each

Q.31 (a)5 marks $(i) Describe the population growth curve applicable in a population of any species in nature that has unlimited resources at its disposal. (ii) Explain the equation of this growth curve. (iii) Name the growth curve and depict a graphical plot for this type of population growth.$
OR
Q.31 (b)5 marks $(i) Explain the conclusion drawn by Alexander von Humboldt during his extensive explorations in the wilderness of South American jungles. (ii) Give the equation of the Species-Area relationship. (iii) Draw a graphical representation of the relation between species richness and area for a wide variety of taxa such as birds, bats, etc.$
Q.32 (a)5 marks $Explain how the process of RNA interference technology is used effectively to prevent infestation of the roots of tobacco plant by the nematode Meloidegyne incognitia.$
OR
Q.32 (b)5 marks $Explain how more than a billion copies of a fragment of DNA are formed using the technique of PCR.$
Q.33 (a)5 marks $(i) Explain the structure of a typical monocotyledonous embryo of a flowering plant. (ii) How are multiple embryos formed in a citrus fruit ? What is the mechanism known as ?$
OR
Q.33 (b)5 marks $(i) Name and explain the structural organisation of the male sex accessory ducts in the human male reproductive system. (ii) Describe the role of gonadotropin FSH in the regulation of spermatogenesis.$