CBSE Class 12 Biology 2024 question paper (57/2)

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 $An angiosperm embryo sac is located within the :$
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Q.21 mark

\text{F}_2

Column I (Cross)	Column II (Phenotypic Ratio)
1. Mendelian monohybrid	(i) 1 : 2 : 1 ( $\text{F}_2$ )
2. Mendelian dihybrid	(ii) 1 : 1
3. Incomplete dominance	(iii) 3 : 1 ( $\text{F}_2$ )
4. Test cross (monohybrid)	(iv) 9 : 3 : 3 : 1 ( $\text{F}_2$ )

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Q.31 mark $In humans, the secondary oocyte completes meiotic division when :$
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Q.41 mark $Which one of the following statements is not true ?$
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Q.51 mark $0{\cdot}6$
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Q.61 mark $In the double helical structure of DNA molecule, the strands are :$
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Q.71 mark $In a 'transcription unit', the 'terminator' is located towards the :$
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Q.81 mark $A woman with normal vision has a colour blind father. She marries a man with normal vision. The percentage chance of their progeny being colour blind is :$
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Q.91 mark $The vector for dengue fever is :$
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Q.101 mark $Which one of the following pairs is not correctly matched ?$
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Q.111 mark $Which one of the following is not a feature of plasmids ?$
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Q.121 mark $The pyramid of biomass in sea is generally inverted because in sea :$
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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 $Assertion (A) : RNA is unstable and can mutate at a faster rate. Reason (R) : The presence of 2' - OH group in every nucleotide of RNA makes it labile and easily degradable.$
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Q.141 mark $Assertion (A) : Virus-infected cells produce interferons. Reason (R) : Interferons can cause inflammation of virus-infected cells.$
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Q.151 mark $Assertion (A) : Specific enzymes are used to degrade the cell wall in organisms to isolate the DNA from the cell. Reason (R) : Fungal cell wall is degraded by the enzyme cellulase.$
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Q.161 mark $Assertion (A) : Loss of biodiversity can occur due to overexploitation of resources. Reason (R) : Introduction of Clarias gariepinus in Indian rivers has led to a decline in native Indian fishes.$
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Section B

2 marks each

Q.17 (a)2 marks $Name any two copper releasing intra-uterine devices. State two reasons that make them effective contraceptives.$
OR
Q.17 (b)2 marks $Name any two outbreeding devices that flowering plants have developed and explain how they help in encouraging cross-pollination.$
Q.182 marks $Although Haemophilia and sickle cell anemia are two blood related Mendelian disorders, yet, they differ in their pattern of inheritance. State any two differences.$
Q.192 marks $Identify A, B, C and D in the following table : Scientific name of the plant Drug Effect on the human body/human system (a) Papaver somniferum A Depressant/slows down body function (b) Cannabis sativa Cannabinoids B (c) Erythroxylum coca C D$
Q.202 marks $Write the role of 'ori' and restriction site in the cloning vector pBR322.$
Q.212 marks $How is the rate of decomposition affected by the nature of detritus and temperature ?$

Scientific name of the plant	Drug	Effect on the human body/human system
(a) Papaver somniferum	A	Depressant/slows down body function
(b) Cannabis sativa	Cannabinoids	B
(c) Erythroxylum coca	C	D

Section C

3 marks each

Q.223 marks $(a) Why is "in vitro fertilization (IVF)" so named ? State its importance. (b) Distinguish between GIFT and ZIFT.$
Q.23 (a)3 marks $(i) Write the karyotype and the genetic disorder of an individual who has developed from a zygote formed from an 'XX' egg fertilised by a 'Y' sperm. (ii) Mention any two symptoms of this genetic disorder. (iii) Write the possible reason that leads to the formation of this 'XX' egg.$
OR
Q.23 (b)3 marks $In case of any dispute, a very small sample of tissue or even a drop of blood can help us to determine the paternity of a child. Provide a scientific explanation to substantiate the statement.$
Q.243 marks $(a) Explain the process by which amino acid gets attached to the tRNA molecule during translation process. (b) How does the translation process get terminated ? (c) Expand 'UTR'. Where are they located ?$
Q.253 marks $(a) Differentiate between humoral immune response and cell-mediated immune response. (b) Draw a schematic diagram of an antibody molecule and label any four parts.$
Q.263 marks $The picture given below shows : (a) Roots of a typical control tobacco crop plant (infected). (b) Transgenic tobacco plant showing healthy roots even after deliberate infection by nematode. Explain how this transformation was achieved in the tobacco plant.$
Q.273 marks $Given below is a pie chart representing global diversity of vertebrates. (a) Redraw the pie chart identifying the groups 'A', 'B', 'C' and 'D' in their respective positions. (b) Mention two examples of recently extinct animals.$
Q.283 marks $Predation is referred to as a detrimental interaction. Explain any three positive roles, supported by an example each, that a predator plays in an ecosystem.$

Section D

Spermatogenesis is an important primary sex characteristic in humans and all other vertebrates. The process is coordinated and controlled under the influence of hormones. It starts with the onset of puberty in humans and thereafter continues. The primordial cells within the embryonic testis which differentiate into spermatogonia are the precursors of the sperms. These are located at the outer walls of the seminiferous tubules where the process of spermatogenesis proceeds.
Q.29 (a)2 marks $State the site of action of FSH in the testes and describe its action thereafter.$
OR
Q.29 (a) OR2 marks $Describe the role of LH in the process of spermatogenesis.$
Q.29 (b)1 mark $Name the cells and their products which undergo : (i) Mitosis and Differentiation (ii) Meiosis I and Meiosis II during the process of spermatogenesis.$
Q.29 (c)1 mark $Name the accessory ducts that the sperms travel through from seminiferous tubules to reach the epididymis.$
In 1981, the health workers of United States of America had become aware of the increased frequency of Kaposi's sarcoma, cancer of the skin and blood vessels and another disease pneumocystis pneumonia, a respiratory infection caused by a protozoan. Both these diseases were very rare in the general population, but occurred frequently in more severely "immunosuppressed" individuals. This led to the recognition of the immune system disorder that was named Acquired Immune Deficiency Syndrome (AIDS). In 1983, virologists working in the USA and France had identified a causative agent for 'AIDS', now known as Human Immunodeficiency Virus (HIV). 'HIV' follows a set path to attack the human body to cause the disease.
Q.30 (a)1 mark $Name the group of cells the HIV attacks after gaining entry into the human body and write the various events that occur within this cell.$
Q.30 (b)1 mark $Write the expanded form of the diagnostic test used for detecting AIDS. Write the possible treatment available for the disease at present.$
Q.30 (c)2 marks $Mention any two steps suggested by WHO for preventing the spread of this disease.$
OR
Q.30 (c) OR2 marks $"A patient suffering from AIDS does not die of this disease but from some other infection." Justify the statement.$

Section E

5 marks each

Q.31 (a)5 marks $(i) Explain the process of double fertilization in an angiosperm starting from the germination of pollen grains on the stigma, mentioning the ploidy of the end products formed at the end. State the role of synergids during the course of the process. (ii) Why does the development of endosperm precede that of the embryo ?$
OR
Q.31 (b)5 marks $(i) Mention the site where fertilisation of the ovum occurs in a human female. Explain the process of fertilization and mention how polyspermy is prevented. (ii) Name the embryonic stage that gets implanted in the uterus. Explain the process of implantation in a human female.$
Q.32 (a)5 marks $\text{F}_1$
OR
Q.32 (b)5 marks $(i) Draw a schematic, self-explanatory labelled diagram of lac operon in a 'switched on condition'. (ii) Why is regulation of lac operon referred to as negative regulation ?$
Q.33 (a)5 marks $(i) Why should a cell be made competent to take up an alien DNA ? How can a bacterial cell be made competent using calcium ions ? Explain. (ii) (1) State the importance of gel electrophoresis in biotechnology. (2) Explain the principle on which this technique works. (3) Mention why ethidium bromide is used in this technique.$
OR
Q.33 (b)5 marks $'Bt cotton', the genetically modified crop, has greatly helped the cotton farmers to increase their crop yield. (i) How was Bt cotton plant made resistant to bollworm ? Explain. (ii) Describe the mechanism that leads to the death of bollworms feeding on Bt cotton plants.$

Section A

1 mark each

Q.11 mark $Homologous organs indicate :$
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Q.21 mark $0{\cdot}6$
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Q.31 mark $In the double helical structure of DNA molecule, the strands are :$
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Q.41 mark $In a 'transcription unit', the 'terminator' is located towards the :$
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Q.51 mark $Which one of the following option denotes mating between relatives in human pedigree analysis ?$
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Q.61 mark $The vector for dengue fever is :$
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Q.71 mark $Which one of the following pairs is not correctly matched ?$
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Q.81 mark $Which of the following is not required for PCR ?$
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Q.91 mark $The pyramid of biomass in sea is generally inverted because in sea :$
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Q.101 mark $In humans, the secondary oocyte completes meiotic division when :$
Tap an option to check your answer.

Q.111 mark

\text{F}_2

Column I (Cross)	Column II (Phenotypic Ratio)
1. Mendelian monohybrid	(i) 1 : 2 : 1 ( $\text{F}_2$ )
2. Mendelian dihybrid	(ii) 1 : 1
3. Incomplete dominance	(iii) 3 : 1 ( $\text{F}_2$ )
4. Test cross (monohybrid)	(iv) 9 : 3 : 3 : 1 ( $\text{F}_2$ )

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Q.121 mark $The functional megaspore of an angiosperm develops into :$
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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 $Assertion (A) : Loss of biodiversity can occur due to overexploitation of resources. Reason (R) : Introduction of Clarias gariepinus in Indian rivers has led to a decline in native Indian fishes.$
Tap an option to check your answer.
Q.141 mark $Assertion (A) : In genetic engineering, antibiotic genes are used as selectable markers. Reason (R) : Selectable markers help us to identify transformants from non-transformants.$
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Q.151 mark $Assertion (A) : Virus-infected cells produce interferons. Reason (R) : Interferons can cause inflammation of virus-infected cells.$
Tap an option to check your answer.
Q.161 mark $Assertion (A) : RNA is unstable and can mutate at a faster rate. Reason (R) : The presence of 2' - OH group in every nucleotide of RNA makes it labile and easily degradable.$
Tap an option to check your answer.

Section B

2 marks each

Q.172 marks $How is the rate of decomposition affected by the nature of detritus and temperature ?$
Q.182 marks $How is a restriction endonuclease named ? Explain with the help of a suitable example.$
Q.19 (a)2 marks $Name any two copper releasing intra-uterine devices. State two reasons that make them effective contraceptives.$
OR
Q.19 (b)2 marks $Name any two outbreeding devices that flowering plants have developed and explain how they help in encouraging cross-pollination.$
Q.202 marks $Although Haemophilia and sickle cell anemia are two blood related Mendelian disorders, yet, they differ in their pattern of inheritance. State any two differences.$
Q.212 marks $Identify A, B, C and D in the following table : Scientific name of the plant Drug Effect on the human body/human system (a) Papaver somniferum A Depressant/slows down body function (b) Cannabis sativa Cannabinoids B (c) Erythroxylum coca C D$

Scientific name of the plant	Drug	Effect on the human body/human system
(a) Papaver somniferum	A	Depressant/slows down body function
(b) Cannabis sativa	Cannabinoids	B
(c) Erythroxylum coca	C	D

Section C

3 marks each

Q.223 marks $Predation is referred to as a detrimental interaction. Explain any three positive roles, supported by an example each, that a predator plays in an ecosystem.$
Q.233 marks $Given below is a pie chart representing global diversity of vertebrates. (a) Redraw the pie chart identifying the groups 'A', 'B', 'C' and 'D' in their respective positions. (b) Mention two examples of recently extinct animals.$
Q.243 marks $(a) Differentiate between humoral immune response and cell-mediated immune response. (b) Draw a schematic diagram of an antibody molecule and label any four parts.$
Q.25 (a)3 marks $Explain the mechanism of haplo-diploid pattern of sex determination with the help of a suitable example. Why is this pattern so called ?$
OR
Q.25 (b)3 marks $T.S. Morgan and his colleagues worked with Drosophila melanogaster for their experiments. State the findings they arrived at and explain how.$
Q.263 marks $"Human blood group (ABO group) inheritance is a good example of multiple allelism and co-dominance." Justify the statement.$
Q.273 marks $(a) Why is "in vitro fertilization (IVF)" so named ? State its importance. (b) Distinguish between GIFT and ZIFT.$
Q.283 marks $The diagram given below is a biomolecule needed for sugar metabolism in human beings. (a) Name this biomolecule and mention whether it is in active state or inactive state. (b) Identify the parts marked as 'A', 'B', 'C' and 'D'.$

Section D

In 1981, the health workers of United States of America had become aware of the increased frequency of Kaposi's sarcoma, cancer of the skin and blood vessels and another disease pneumocystis pneumonia, a respiratory infection caused by a protozoan. Both these diseases were very rare in the general population, but occurred frequently in more severely "immunosuppressed" individuals. This led to the recognition of the immune system disorder that was named Acquired Immune Deficiency Syndrome (AIDS). In 1983, virologists working in the USA and France had identified a causative agent for 'AIDS', now known as Human Immunodeficiency Virus (HIV). 'HIV' follows a set path to attack the human body to cause the disease.
Q.29 (a)1 mark $Name the group of cells the HIV attacks after gaining entry into the human body and write the various events that occur within this cell.$
Q.29 (b)1 mark $Write the expanded form of the diagnostic test used for detecting AIDS. Write the possible treatment available for the disease at present.$
Q.29 (c)2 marks $Mention any two steps suggested by WHO for preventing the spread of this disease.$
OR
Q.29 (c) OR2 marks $"A patient suffering from AIDS does not die of this disease but from some other infection." Justify the statement.$
Spermatogenesis is an important primary sex characteristic in humans and all other vertebrates. The process is coordinated and controlled under the influence of hormones. It starts with the onset of puberty in humans and thereafter continues. The primordial cells within the embryonic testis which differentiate into spermatogonia are the precursors of the sperms. These are located at the outer walls of the seminiferous tubules where the process of spermatogenesis proceeds.
Q.30 (a)2 marks $State the site of action of FSH in the testes and describe its action thereafter.$
OR
Q.30 (a) OR2 marks $Describe the role of LH in the process of spermatogenesis.$
Q.30 (b)1 mark $Name the cells and their products which undergo : (i) Mitosis and Differentiation (ii) Meiosis I and Meiosis II during the process of spermatogenesis.$
Q.30 (c)1 mark $Name the accessory ducts that the sperms travel through from seminiferous tubules to reach the epididymis.$

Section E

5 marks each

Q.31 (a)5 marks $(i) Why should a cell be made competent to take up an alien DNA ? How can a bacterial cell be made competent using calcium ions ? Explain. (ii) (1) State the importance of gel electrophoresis in biotechnology. (2) Explain the principle on which this technique works. (3) Mention why ethidium bromide is used in this technique.$
OR
Q.31 (b)5 marks $'Bt cotton', the genetically modified crop, has greatly helped the cotton farmers to increase their crop yield. (i) How was Bt cotton plant made resistant to bollworm ? Explain. (ii) Describe the mechanism that leads to the death of bollworms feeding on Bt cotton plants.$
Q.32 (a)5 marks $(i) Explain the process of double fertilization in an angiosperm starting from the germination of pollen grains on the stigma, mentioning the ploidy of the end products formed at the end. State the role of synergids during the course of the process. (ii) Why does the development of endosperm precede that of the embryo ?$
OR
Q.32 (b)5 marks $(i) Mention the site where fertilisation of the ovum occurs in a human female. Explain the process of fertilization and mention how polyspermy is prevented. (ii) Name the embryonic stage that gets implanted in the uterus. Explain the process of implantation in a human female.$
Q.33 (a)5 marks $(i) State Mendel's law of independent assortment. (ii) Explain this law by taking the example of a cross between two heterozygous parents of pea plants with respect to flower colour and flower position using Punnett Square.$
OR
Q.33 (b)5 marks $Explain Griffith's experiment conducted in search of genetic material and write the conclusion he arrived at. How did Avery, MacLeod and McCarty establish the biochemical nature of the "Genetic Material" identified by Griffith ?$

Section A

1 mark each

Q.11 mark $The pyramid of biomass in sea is generally inverted because in sea :$
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Q.21 mark $Which one of the following is not used as a vector for rDNA technology ?$
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Q.31 mark $Which one of the following pairs is not correctly matched ?$
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Q.41 mark $Allergic reactions are countered by the administration of :$
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Q.51 mark

\text{F}_2

Column I (Cross)	Column II (Phenotypic Ratio)
1. Mendelian monohybrid	(i) 1 : 2 : 1 ( $\text{F}_2$ )
2. Mendelian dihybrid	(ii) 1 : 1
3. Incomplete dominance	(iii) 3 : 1 ( $\text{F}_2$ )
4. Test cross (monohybrid)	(iv) 9 : 3 : 3 : 1 ( $\text{F}_2$ )

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Q.61 mark $The expected phenotypic ratio amongst the progeny of 60 individuals, obtained from a cross between heterozygous tall pea plant and dwarf pea plant is :$
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Q.71 mark $In humans, the secondary oocyte completes meiotic division when :$
Tap an option to check your answer.
Q.81 mark $0{\cdot}6$
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Q.91 mark $Which one of the following statements is not true ?$
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Q.101 mark $In the absence of fertilization, corpus luteum :$
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Q.111 mark $In the double helical structure of DNA molecule, the strands are :$
Tap an option to check your answer.
Q.121 mark $In a 'transcription unit', the 'terminator' is located towards the :$
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 $Assertion (A) : Virus-infected cells produce interferons. Reason (R) : Interferons can cause inflammation of virus-infected cells.$
Tap an option to check your answer.
Q.141 mark $Assertion (A) : Loss of biodiversity can occur due to overexploitation of resources. Reason (R) : Introduction of Clarias gariepinus in Indian rivers has led to a decline in native Indian fishes.$
Tap an option to check your answer.
Q.151 mark $Assertion (A) : RNA is unstable and can mutate at a faster rate. Reason (R) : The presence of 2' - OH group in every nucleotide of RNA makes it labile and easily degradable.$
Tap an option to check your answer.
Q.161 mark $\beta$
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Section B

2 marks each

Q.172 marks $Although Haemophilia and sickle cell anemia are two blood related Mendelian disorders, yet, they differ in their pattern of inheritance. State any two differences.$
Q.182 marks $Identify A, B, C and D in the following table : Scientific name of the plant Drug Effect on the human body/human system (a) Papaver somniferum A Depressant/slows down body function (b) Cannabis sativa Cannabinoids B (c) Erythroxylum coca C D$
Q.192 marks $How is the rate of decomposition affected by the nature of detritus and temperature ?$
Q.20 (a)2 marks $Name any two copper releasing intra-uterine devices. State two reasons that make them effective contraceptives.$
OR
Q.20 (b)2 marks $Name any two outbreeding devices that flowering plants have developed and explain how they help in encouraging cross-pollination.$
Q.212 marks $How is Ti plasmid of Agrobacterium tumefaciens modified to act as a cloning vector ?$

Scientific name of the plant	Drug	Effect on the human body/human system
(a) Papaver somniferum	A	Depressant/slows down body function
(b) Cannabis sativa	Cannabinoids	B
(c) Erythroxylum coca	C	D

Section C

3 marks each

Q.223 marks $Given below is a pie chart representing global diversity of vertebrates. (a) Redraw the pie chart identifying the groups 'A', 'B', 'C' and 'D' in their respective positions. (b) Mention two examples of recently extinct animals.$
Q.233 marks $Predation is referred to as a detrimental interaction. Explain any three positive roles, supported by an example each, that a predator plays in an ecosystem.$
Q.243 marks $The first clinical gene therapy was given in 1990 to a 4-year-old girl with ADA deficiency. (a) Mention the cause of this disorder. (b) List the possible treatments available for this disorder. (c) How can this disorder be cured permanently ?$
Q.253 marks $Describe any three assisted reproductive techniques practised to treat infertility.$
Q.26 (a)3 marks $(i) Write the karyotype and the genetic disorder of an individual who has developed from a zygote formed from an 'XX' egg fertilised by a 'Y' sperm. (ii) Mention any two symptoms of this genetic disorder. (iii) Write the possible reason that leads to the formation of this 'XX' egg.$
OR
Q.26 (b)3 marks $In case of any dispute, a very small sample of tissue or even a drop of blood can help us to determine the paternity of a child. Provide a scientific explanation to substantiate the statement.$
Q.273 marks $(a) List the salient features of Darwin's theory of natural selection. (b) Microbes have proved to be suitable examples to study evolution by natural selection. Justify giving reasons.$
Q.283 marks $(a) Differentiate between humoral immune response and cell-mediated immune response. (b) Draw a schematic diagram of an antibody molecule and label any four parts.$

Section D

In 1981, the health workers of United States of America had become aware of the increased frequency of Kaposi's sarcoma, cancer of the skin and blood vessels and another disease pneumocystis pneumonia, a respiratory infection caused by a protozoan. Both these diseases were very rare in the general population, but occurred frequently in more severely "immunosuppressed" individuals. This led to the recognition of the immune system disorder that was named Acquired Immune Deficiency Syndrome (AIDS). In 1983, virologists working in the USA and France had identified a causative agent for 'AIDS', now known as Human Immunodeficiency Virus (HIV). 'HIV' follows a set path to attack the human body to cause the disease.
Q.29 (a)1 mark $Name the group of cells the HIV attacks after gaining entry into the human body and write the various events that occur within this cell.$
Q.29 (b)1 mark $Write the expanded form of the diagnostic test used for detecting AIDS. Write the possible treatment available for the disease at present.$
Q.29 (c)2 marks $Mention any two steps suggested by WHO for preventing the spread of this disease.$
OR
Q.29 (c) OR2 marks $"A patient suffering from AIDS does not die of this disease but from some other infection." Justify the statement.$
Spermatogenesis is an important primary sex characteristic in humans and all other vertebrates. The process is coordinated and controlled under the influence of hormones. It starts with the onset of puberty in humans and thereafter continues. The primordial cells within the embryonic testis which differentiate into spermatogonia are the precursors of the sperms. These are located at the outer walls of the seminiferous tubules where the process of spermatogenesis proceeds.
Q.30 (a)2 marks $State the site of action of FSH in the testes and describe its action thereafter.$
OR
Q.30 (a) OR2 marks $Describe the role of LH in the process of spermatogenesis.$
Q.30 (b)1 mark $Name the cells and their products which undergo : (i) Mitosis and Differentiation (ii) Meiosis I and Meiosis II during the process of spermatogenesis.$
Q.30 (c)1 mark $Name the accessory ducts that the sperms travel through from seminiferous tubules to reach the epididymis.$

Section E

5 marks each

Q.31 (a)5 marks $^{35}\text{S}$
OR
Q.31 (b)5 marks $(i) Describe the process of transcription in prokaryotes with respect to initiation, elongation and termination. (ii) Write how many types of RNA polymerases are used in transcription in (1) Prokaryotes, (2) Eukaryotes.$
Q.32 (a)5 marks $(i) Why should a cell be made competent to take up an alien DNA ? How can a bacterial cell be made competent using calcium ions ? Explain. (ii) (1) State the importance of gel electrophoresis in biotechnology. (2) Explain the principle on which this technique works. (3) Mention why ethidium bromide is used in this technique.$
OR
Q.32 (b)5 marks $'Bt cotton', the genetically modified crop, has greatly helped the cotton farmers to increase their crop yield. (i) How was Bt cotton plant made resistant to bollworm ? Explain. (ii) Describe the mechanism that leads to the death of bollworms feeding on Bt cotton plants.$
Q.33 (a)5 marks $(i) Explain the process of double fertilization in an angiosperm starting from the germination of pollen grains on the stigma, mentioning the ploidy of the end products formed at the end. State the role of synergids during the course of the process. (ii) Why does the development of endosperm precede that of the embryo ?$
OR
Q.33 (b)5 marks $(i) Mention the site where fertilisation of the ovum occurs in a human female. Explain the process of fertilization and mention how polyspermy is prevented. (ii) Name the embryonic stage that gets implanted in the uterus. Explain the process of implantation in a human female.$