CBSE Class 12 Biology 2026 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 $To separate repetitive DNA from bulk genomic DNA, which of the following method is used ?$
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Q.21 mark $Select the correct option :$
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Q.31 mark $\text{F}_2$
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Q.41 mark $What could be the reason of extinction of Abingdon Tortoise from Galapagos Islands ?$
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Q.51 mark $What conclusion can be drawn if the forelimbs of an aquatic animal and a terrestrial animal have similar anatomical structure ?$
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Q.61 mark $How many of the following features are related to Nirodh - a popular brand of condoms ? (i) Prevention of sexually transmitted infections. (ii) Phagocytosis of sperms. (iii) Male contraceptive device. (iv) Acts as chemical barrier. (v) Physiological changes in cervical mucus.$
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Q.71 mark $A bacterium having radioactive thymidine in its DNA is allowed to multiply in a medium having non-radioactive thymidine for two generations. What percentage of bacteria will have radioactive thymidine in its DNA ?$
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Q.81 mark $What is the role of histamine released by mast cells ?$
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Q.91 mark $Which of the following is used to visualize DNA bands under UV light after gel electrophoresis ?$
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Q.101 mark $\downarrow$
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Q.111 mark $Genetically modified tobacco plants were produced using Agrobacterium vectors. Which property of Agrobacterium helps in carrying nematode specific genes into the host plant ?$
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Q.121 mark $Observe the contents 1, 2, 3 and 4 of soil samples I, II and III shown in the graph. If the temperature and moisture of all soil samples are identical, which soil sample(s) will show faster decomposition ?$
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For Question numbers 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 Code (A), (B), (C) and (D) as given below :
Q.131 mark $Assertion (A) : Apomixis leads to production of genetically identical off-springs. Reason (R) : Apomixis involves fertilization between two genetically similar plants.$
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Q.141 mark $Assertion (A) : Microbes are used for commercial production of alcohol and beverages. Reason (R) : Yeast converts glucose into ethanol and carbon dioxide during fermentation.$
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Q.151 mark $Assertion (A) : IUCN Red List helps in identifying and protecting endangered species worldwide. Reason (R) : The list includes the species facing risk of extinction.$
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Q.161 mark $Assertion (A) : DNA Ligase is used to join DNA fragments. Reason (R) : It catalyses the formation of glycosidic bonds between nucleotides.$
Tap an option to check your answer.

Section B

2 marks each

Q.17 (a)2 marks $\overset{*}{\text{T}}$
OR
Q.17 (b)2 marks $DNA is considered a more stable genetic material than RNA. Justify this statement with suitable reasons.$
Q.182 marks $How do scientists use microinjection and gene gun in biotechnology ?$
Q.192 marks $After significant reduction of BOD during secondary treatment of sewage, what further processes are carried out ? Mention any one important outcome of these processes.$
Q.20 (a)2 marks $In some cases, measuring population density by counting individuals may not be feasible. Mention two other parameters that can be used and justify their use with suitable examples.$
OR
Q.20 (b)2 marks $What factors contribute to the Amazonian rain forests in South America being the most biodiverse regions on Earth ?$
Q.21 (a)2 marks $(i) Name the organ that forms a connection between foetus and the uterus of a pregnant human female. (ii) How does it support both nutrition and hormonal regulation ?$
OR
Q.21 (b)2 marks $Give reasons for : (i) All copulations do not lead to pregnancy. (ii) Meiosis I in spermatogenesis and oogenesis are markedly different.$

haemoglobin chain	Val	His	Leu	Thr	Pro	Glu	Glu
mRNA
DNA	CAT	GTA	AAT	TGA	GGA	C $\overset{*}{\text{T}}$ T	CTC

Section C

3 marks each

Q.223 marks $There are limitations of traditional breeding techniques that led to promotion of micro-propagation ? (a) Mention two advantages of micropropagation. (b) Give two examples where it is commercially adopted.$
Q.233 marks $(a) Give the scientific name of the organism used by Morgan to study sex-linked traits. (b) Write any four reasons why this organism made it an ideal experimental model.$
Q.243 marks $Draw a neat diagram of enlarged view of one microsporangium of a Young anther of an angiosperm. Label the different layers of the wall and write the functions of the outermost and innermost layer.$
Q.253 marks $Study the diagram given below : (a) Name and explain the procedure shown in the diagram. Mention one of its advantage and one disadvantage. (b) How is 'Saheli' different from other oral pills in terms of its composition and advantage ?$
Q.263 marks $S.L. Miller conducted an experiment in 1953 to simulate the conditions of early earth in a laboratory setup. Answer the following questions based on the experiment : (a) What was the aim of his experiment ? (b) Name the gases used and the source of energy.$
Q.273 marks $(a) What is a genetic code ? (b) Why did scientists feel the need to propose a genetic code ? (c) Genetic code is said to be 'Universal'. Why ?$
Q.283 marks $(a) A person inhales dust and pathogens but does not always fall sick. Explain how the body protects against such infections. (b) Name and describe any two barriers involved in this protection.$

Section D

Gene manipulation is a fast emerging science. It started with the development of recombinant DNA molecules. This technology which mostly involves cutting and pasting of desired DNA fragments is based on two most important discoveries in bacteria – presence of plasmid and restriction endonucleases. The science of r-DNA technology took birth when Cohen and Boyer (1973) were able to produce a piece of gene containing foreign DNA introduced into plasmid of E.coli.
Q.29 (a)1 mark $Name one core technique of biotechnology that alters the genetic material.$
Q.29 (b)2 marks $What is a plasmid ? Mention its importance in biotechnology.$
Q.29 (c)1 mark $Which gene was isolated by Cohen and Boyer and from which bacteria ?$
OR
Q.29 (c) OR1 mark $How is the action of exonuclease different from that of endonuclease ?$
Below is shown a pond that represents a self-sustaining natural ecosystem with both biotic and abiotic components interacting in a balanced food web. Based on the diagram, answer the questions :
Q.30 (a)1 mark $Mention two abiotic components of a pond ecosystem.$
Q.30 (b)2 marks $Differentiate between the roles of producers and decomposers in such an ecosystem.$
Q.30 (c)1 mark $Draw a simple food chain operating in such an ecosystem and label each trophic level.$
OR
Q.30 (c) OR1 mark $Why is transfer of energy not 100% efficient between trophic levels ?$

Section E

5 marks each

Q.31 (a)5 marks $(i) Explain the role of stigma in pollen pistil interaction. (ii) Describe the post pollination events leading to double fertilization in angiosperms starting with 2-celled pollen grain.$
OR
Q.31 (b)5 marks $(i) Explain menstrual phase in the menstrual cycle of human female. (ii) Why is follicular phase also called proliferative phase ? (iii) Explain the events that occur in Graafian follicle at the time of ovulation and thereafter. (iv) Draw a Graafian follicle and label - Antrum and secondary oocyte.$
Q.32 (a)5 marks $Observe the segment of mRNA given below and answers the questions given below : (i) Explain and illustrate the steps involved to make fully processed hn RNA. (ii) Gene encoding RNA polymerase I and RNA polymerase III have been affected by mutation. Explain its impact on the synthesis of polypeptide giving reasons.$
OR
Q.32 (b)5 marks $\text{F}_2$
Q.33 (a)5 marks $A 30 year old man was admitted to a hospital with recurrent infections, weight loss, prolonged fever. His blood report showed a decline in count of T-Lymphocytes thus affecting immune system. (i) Identify the disease and its causative agent. (ii) How did the pathogen affect the immune system once it entered the body ? Explain. (iii) Mention two major modes of its transmission.$
OR
Q.33 (b)5 marks $(i) Why are microbes considered effective biocontrol agents in sustainable agriculture ? (ii) Explain the role of the following as biocontrol agents naming the pests or diseases they help to control : (1) A Bacterium (2) A Fungus (3) Virus$

Section A

1 mark each

Q.11 mark $Genetically modified tobacco plants were produced using Agrobacterium vectors. Which property of Agrobacterium helps in carrying nematode specific genes into the host plant ?$
Tap an option to check your answer.
Q.21 mark $Observe the contents 1, 2, 3 and 4 of soil samples I, II and III shown in the graph. If the temperature and moisture of all soil samples are identical, which soil sample(s) will show faster decomposition ?$
Tap an option to check your answer.
Q.31 mark $A woman having genes for haemophilia on one X chromosome and a gene for colour blindness on another X chromosome marries a normal man. The progeny will show$
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Q.41 mark $Which of the following is an important parameter for assessing the impact of any biotic or abiotic factor on population growth ?$
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Q.51 mark $If a sperm nucleus is injected into an oocyte then all of the following events are bypassed except -$
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Q.61 mark $If A = species richness and B = Endemism then biodiversity hotspots have$
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Q.71 mark $Two plants whose DNA has been sequenced are$
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Q.81 mark $Antivenom injection is an example of$
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Q.91 mark $To separate repetitive DNA from bulk genomic DNA, which of the following method is used ?$
Tap an option to check your answer.
Q.101 mark $What conclusion can be drawn if the forelimbs of an aquatic animal and a terrestrial animal have similar anatomical structure ?$
Tap an option to check your answer.
Q.111 mark $Which of the following is used to visualize DNA bands under UV light after gel electrophoresis ?$
Tap an option to check your answer.
Q.121 mark $\downarrow$
Tap an option to check your answer.
For Question numbers 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 Code (A), (B), (C) and (D) as given below :
Q.131 mark $Assertion (A) : Pollen grains have a mucilaginous covering on them in most of the water pollinating plants. Reason (R) : Mucilaginous covering help pollen grains to be submerged in water.$
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Q.141 mark $Assertion (A) : Microbes are used for commercial production of alcohol and beverages. Reason (R) : Yeast converts glucose into ethanol and carbon dioxide during fermentation.$
Tap an option to check your answer.
Q.151 mark $Assertion (A) : IUCN Red List helps in identifying and protecting endangered species worldwide. Reason (R) : The list includes the species facing risk of extinction.$
Tap an option to check your answer.
Q.161 mark $Assertion (A) : DNA Ligase is used to join DNA fragments. Reason (R) : It catalyses the formation of glycosidic bonds between nucleotides.$
Tap an option to check your answer.

Section B

2 marks each

Q.17 (a)2 marks $Is it possible for a trait to be inherited by an organism but not expressed in its phenotype ? Justify and illustrate your answer with a suitable Mendelian Cross.$
OR
Q.17 (b)2 marks $Explain the two major approaches used while sequencing the total DNA from a cell.$
Q.182 marks $Briefly describe the process of DNA extraction from a fungal cell. Name the chemicals used in the process.$
Q.192 marks $Differentiate between opioids and cannabinoids on the basis of their (a) Receptor site in human body. (b) Mode of action in human body.$
Q.20 (a)2 marks $(i) Name the organ that forms a connection between foetus and the uterus of a pregnant human female. (ii) How does it support both nutrition and hormonal regulation ?$
OR
Q.20 (b)2 marks $Give reasons for : (i) All copulations do not lead to pregnancy. (ii) Meiosis I in spermatogenesis and oogenesis are markedly different.$
Q.21 (a)2 marks $In some cases, measuring population density by counting individuals may not be feasible. Mention two other parameters that can be used and justify their use with suitable examples.$
OR
Q.21 (b)2 marks $What factors contribute to the Amazonian rain forests in South America being the most biodiverse regions on Earth ?$

Section C

3 marks each

Q.223 marks $(a) A person inhales dust and pathogens but does not always fall sick. Explain how the body protects against such infections. (b) Name and describe any two barriers involved in this protection.$
Q.233 marks $Study the diagram given below : (a) Name and explain the procedure shown in the diagram. Mention one of its advantage and one disadvantage. (b) How is 'Saheli' different from other oral pills in terms of its composition and advantage ?$
Q.243 marks $Chasmogamous flowers remain open and expose their reproductive parts. Explain how this structural feature supports different types of pollination.$
Q.253 marks $(a) What is a genetic code ? (b) Why did scientists feel the need to propose a genetic code ? (c) Genetic code is said to be 'Universal'. Why ?$
Q.263 marks $There are limitations of traditional breeding techniques that led to promotion of micro-propagation ? (a) Mention two advantages of micropropagation. (b) Give two examples where it is commercially adopted.$
Q.273 marks $(a) Give the scientific name of the organism used by Morgan to study sex-linked traits. (b) Write any four reasons why this organism made it an ideal experimental model.$
Q.283 marks $S.L. Miller conducted an experiment in 1953 to simulate the conditions of early earth in a laboratory setup. Answer the following questions based on the experiment : (a) What was the aim of his experiment ? (b) Name the gases used and the source of energy.$

Section D

Below is shown a pond that represents a self-sustaining natural ecosystem with both biotic and abiotic components interacting in a balanced food web. Based on the diagram, answer the questions :
Q.29 (a)1 mark $Mention two abiotic components of a pond ecosystem.$
Q.29 (b)2 marks $Differentiate between the roles of producers and decomposers in such an ecosystem.$
Q.29 (c)1 mark $Draw a simple food chain operating in such an ecosystem and label each trophic level.$
OR
Q.29 (c) OR1 mark $Why is transfer of energy not 100% efficient between trophic levels ?$
Gene manipulation is a fast emerging science. It started with the development of recombinant DNA molecules. This technology which mostly involves cutting and pasting of desired DNA fragments is based on two most important discoveries in bacteria – presence of plasmid and restriction endonucleases. The science of r-DNA technology took birth when Cohen and Boyer (1973) were able to produce a piece of gene containing foreign DNA introduced into plasmid of E.coli.
Q.30 (a)1 mark $Name one core technique of biotechnology that alters the genetic material.$
Q.30 (b)2 marks $What is a plasmid ? Mention its importance in biotechnology.$
Q.30 (c)1 mark $Which gene was isolated by Cohen and Boyer and from which bacteria ?$
OR
Q.30 (c) OR1 mark $How is the action of exonuclease different from that of endonuclease ?$

Section E

5 marks each

Q.31 (a)5 marks $A 30 year old man was admitted to a hospital with recurrent infections, weight loss, prolonged fever. His blood report showed a decline in count of T-Lymphocytes thus affecting immune system. (i) Identify the disease and its causative agent. (ii) How did the pathogen affect the immune system once it entered the body ? Explain. (iii) Mention two major modes of its transmission.$
OR
Q.31 (b)5 marks $(i) Why are microbes considered effective biocontrol agents in sustainable agriculture ? (ii) Explain the role of the following as biocontrol agents naming the pests or diseases they help to control : (1) A Bacterium (2) A Fungus (3) Virus$
Q.32 (a)5 marks $(i) Identify the structure shown above and name the process taking place. (ii) Write the source of energy for the process and list the enzymes involved. (iii) Mention the difference in the process based on polarity. What terms are used for such synthesis ? (iv) Redraw the structure after completion of the process and label the newly synthesised parts.$
OR
Q.32 (b)5 marks $\text{F}_2$
Q.33 (a)5 marks $(i) Explain the role of stigma in pollen pistil interaction. (ii) Describe the post pollination events leading to double fertilization in angiosperms starting with 2-celled pollen grain.$
OR
Q.33 (b)5 marks $(i) Explain menstrual phase in the menstrual cycle of human female. (ii) Why is follicular phase also called proliferative phase ? (iii) Explain the events that occur in Graafian follicle at the time of ovulation and thereafter. (iv) Draw a Graafian follicle and label - Antrum and secondary oocyte.$

Section A

1 mark each

Q.11 mark $Caenorhabditis elegans is a nematode which is$
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Q.21 mark $Self-incompatibility in some flowering plants is a _____ mechanism that prevents self-fertilization. Fill in the blank with the appropriate option :$
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Q.31 mark $Which of the following traits studied by Mendel in pea plant is a recessive trait ?$
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Q.41 mark $Genetically modified tobacco plants were produced using Agrobacterium vectors. Which property of Agrobacterium helps in carrying nematode specific genes into the host plant ?$
Tap an option to check your answer.
Q.51 mark $Observe the contents 1, 2, 3 and 4 of soil samples I, II and III shown in the graph. If the temperature and moisture of all soil samples are identical, which soil sample(s) will show faster decomposition ?$
Tap an option to check your answer.
Q.61 mark $Current percentage of tropical rainforests covering the Earth's land surface is$
Tap an option to check your answer.
Q.71 mark $Study the given pedigree and identify the disease represented.$
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Q.81 mark $\downarrow$
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Q.91 mark $What could be the reason of extinction of Abingdon Tortoise from Galapagos Islands ?$
Tap an option to check your answer.
Q.101 mark $What conclusion can be drawn if the forelimbs of an aquatic animal and a terrestrial animal have similar anatomical structure ?$
Tap an option to check your answer.
Q.111 mark $If any organ fails to function satisfactorily, transplantation is the only remedy to enable the patient to live a normal life. All of the following are true w.r.t. transplantation except -$
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Q.121 mark $Which of the following is used to visualize DNA bands under UV light after gel electrophoresis ?$
Tap an option to check your answer.
For Question numbers 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 Code (A), (B), (C) and (D) as given below :
Q.131 mark $Assertion (A) : DNA Ligase is used to join DNA fragments. Reason (R) : It catalyses the formation of glycosidic bonds between nucleotides.$
Tap an option to check your answer.
Q.141 mark $Assertion (A) : Apomixis leads to production of genetically identical off-springs. Reason (R) : Apomixis involves fertilization between two genetically similar plants.$
Tap an option to check your answer.
Q.151 mark $Assertion (A) : Under a particular set of selection pressure, organisms evolve towards the most efficient reproductive strategy. Reason (R) : Populations evolve to maximise their reproductive fitness in the habitat where they live.$
Tap an option to check your answer.
Q.161 mark $Assertion (A) : Microbes are used for commercial production of alcohol and beverages. Reason (R) : Yeast converts glucose into ethanol and carbon dioxide during fermentation.$
Tap an option to check your answer.

Section B

2 marks each

Q.17 (a)2 marks $(i) Name the organ that forms a connection between foetus and the uterus of a pregnant human female. (ii) How does it support both nutrition and hormonal regulation ?$
OR
Q.17 (b)2 marks $Give reasons for : (i) All copulations do not lead to pregnancy. (ii) Meiosis I in spermatogenesis and oogenesis are markedly different.$
Q.182 marks $A patent with Type I diabetes is unable to produce sufficient insulin. (a) How has recombinant DNA technology helped in addressing this problem ? (b) Mention its advantage over animal derived insulin.$
Q.192 marks $\downarrow$
Q.20 (a)2 marks $Explain the type of interaction between : (i) Egret and Cattle (ii) Cuckoo and Crow$
OR
Q.20 (b)2 marks $Biodiversity exists at various levels within an ecosystem. Explain biodiversity at genetic and ecological level.$
Q.21 (a)2 marks $\overset{*}{\text{T}}$
OR
Q.21 (b)2 marks $DNA is considered a more stable genetic material than RNA. Justify this statement with suitable reasons.$

A	B	C
e.g. Glomus	e.g. Azospirillum	e.g. Rhizobium

haemoglobin chain	Val	His	Leu	Thr	Pro	Glu	Glu
mRNA
DNA	CAT	GTA	AAT	TGA	GGA	C $\overset{*}{\text{T}}$ T	CTC

Section C

3 marks each

Q.223 marks $(a) A person inhales dust and pathogens but does not always fall sick. Explain how the body protects against such infections. (b) Name and describe any two barriers involved in this protection.$
Q.233 marks $(a) What is a genetic code ? (b) Why did scientists feel the need to propose a genetic code ? (c) Genetic code is said to be 'Universal'. Why ?$
Q.243 marks $There are limitations of traditional breeding techniques that led to promotion of micro-propagation ? (a) Mention two advantages of micropropagation. (b) Give two examples where it is commercially adopted.$
Q.253 marks $(a) Give the scientific name of the organism used by Morgan to study sex-linked traits. (b) Write any four reasons why this organism made it an ideal experimental model.$
Q.263 marks $(a) Compare homologous and analogous organs by giving any one point of difference. (b) Mention the type of evolution each represents and give one example of each from plants and animals.$
Q.273 marks $Draw a neat diagram of enlarged view of one microsporangium of a Young anther of an angiosperm. Label the different layers of the wall and write the functions of the outermost and innermost layer.$
Q.283 marks $Study the diagram given below : (a) Name and explain the procedure shown in the diagram. Mention one of its advantage and one disadvantage. (b) How is 'Saheli' different from other oral pills in terms of its composition and advantage ?$

Section D

Gene manipulation is a fast emerging science. It started with the development of recombinant DNA molecules. This technology which mostly involves cutting and pasting of desired DNA fragments is based on two most important discoveries in bacteria – presence of plasmid and restriction endonucleases. The science of r-DNA technology took birth when Cohen and Boyer (1973) were able to produce a piece of gene containing foreign DNA introduced into plasmid of E.coli.
Q.29 (a)1 mark $Name one core technique of biotechnology that alters the genetic material.$
Q.29 (b)2 marks $What is a plasmid ? Mention its importance in biotechnology.$
Q.29 (c)1 mark $Which gene was isolated by Cohen and Boyer and from which bacteria ?$
OR
Q.29 (c) OR1 mark $How is the action of exonuclease different from that of endonuclease ?$
Below is shown a pond that represents a self-sustaining natural ecosystem with both biotic and abiotic components interacting in a balanced food web. Based on the diagram, answer the questions :
Q.30 (a)1 mark $Mention two abiotic components of a pond ecosystem.$
Q.30 (b)2 marks $Differentiate between the roles of producers and decomposers in such an ecosystem.$
Q.30 (c)1 mark $Draw a simple food chain operating in such an ecosystem and label each trophic level.$
OR
Q.30 (c) OR1 mark $Why is transfer of energy not 100% efficient between trophic levels ?$

Section E

5 marks each

Q.31 (a)5 marks $In the given diagram - 'A' is an embryonic stage that gets transformed into 'B', which in turn gets implanted in the endometrium of human female. (i) (1) Identify A, B, C and D. (2) State the fate of 'C' immediately after implantation. (3) Name the special cells found in 'C' and their function. (ii) What is the role of oxytocin during parturition ? Where is it released from ?$
OR
Q.31 (b)5 marks $Sexually transmitted infections are a major threat to our society. So it is said that "Prevention is better than cure". (i) Write the three simple principles to be followed to prevent such infections. (ii) How can sex education programs in schools help in improving reproductive health ? (4 points)$
Q.32 (a)5 marks $A 30 year old man was admitted to a hospital with recurrent infections, weight loss, prolonged fever. His blood report showed a decline in count of T-Lymphocytes thus affecting immune system. (i) Identify the disease and its causative agent. (ii) How did the pathogen affect the immune system once it entered the body ? Explain. (iii) Mention two major modes of its transmission.$
OR
Q.32 (b)5 marks $(i) Why are microbes considered effective biocontrol agents in sustainable agriculture ? (ii) Explain the role of the following as biocontrol agents naming the pests or diseases they help to control : (1) A Bacterium (2) A Fungus (3) Virus$
Q.33 (a)5 marks $Observe the segment of mRNA given below and answers the questions given below : (i) Explain and illustrate the steps involved to make fully processed hn RNA. (ii) Gene encoding RNA polymerase I and RNA polymerase III have been affected by mutation. Explain its impact on the synthesis of polypeptide giving reasons.$
OR
Q.33 (b)5 marks $\text{F}_2$