Students must start practicing the questions from CBSE Sample Papers for Class 12 Biology with Solutions Set 5 are designed as per the revised syllabus.
CBSE Sample Papers for Class 12 Biology Set 5 with Solutions
Time Allowed: 3 Hours
Maximum Marks: 70
General Instructions:
- All questions are compulsory.
- The question paper has five sections and 33 questions. ALL questions are compulsory.
- Section-A has 16 questions of 1 mark each: Section-B has 5 questions of 2 marks each; Section- C has 7 questions of 3 marks each; Section- D has 2 case-based questions of 4 marks each: and Section-E has 3 questions of 5 marks each.
- There is no overall choice. However, internat choices have been provided in some questions. A student has to attempt onty one of the alternatives ¡n such questions.
- Wherever necessary, neat and properly Labeled diagrams should be drawn.
Section – A (16 Marks)
Question 1.
What phenomenon do the flowers shown in the figure exhibit?
(a) Incomplete dominance
(b) Multiple allelism
(c) Co-dominance
(d) Polygenic inheritance 1
Answer:
(a)Incomplete dominance
Explanation:
ncomp1ete dominance is illustrated by the inheritance of flower color in the dog flower (snapdragon or Antirthinum sp. shown in the image). It was discovered that occasionally the F1 had a phenotype that was in between the two parents when experiments on pecs were repeated using the flower colour trait.
Caution:
Students should remember that incomplete dominance in Snapdragon is a result of a monohybrid cross in which one allele is only partially dominant over the other allele in the plant Snapdragon.
Question 2.
Which of the following statement(s) is/are correct?
(I) Few oral contraceptives used are Mala D, Saheli, etc.
(II) Oral administration of small doses of either progestagens or progestagen-estrogen combinations is another contraceptive method used by males.
(III) Oral contraceptives are used in the form of tablets and hence are popularly called ‘pills’.
(IV) Pills have to be taken daily for a period of 22 days Select the correct option:
(a) (I), (II)
(b) (I), (III)
(c) (I), (II). (Ill)
(d) (I), (II), (III). (IV)
Answer:
(a)(I), (II)
Explanation:
New oral contraceptives in use include Mala D and Saheli. Another method of female contraception is the oral administration of small doses of progestagens Ora! contraceptives prevent or delay sperm entry by inhibiting ovulation and implantation as well as changing the cervical mucus quality.
Caution:
Students should know that pills are widely used by females because they are highly effective and have few side effects.
Question 3.
Which of the following is correct for the parts labeled as (i) and (ii)?
| (I) | (II) |
| (a) Cotton balL destroyed by bollworms | A fully mature cotton ball |
| (b) A fuLLy mature cotton ball | Cotton ball destroyed by bollworms |
| (c) Cotton ball destroyed by bollworms | A fully immature cotton ball |
| (d) A fully immature cotton boll | Cotton ball destroyed by bollworms |
Answer:
(I): Cotton ball destroyed by bollworms:
(II): A fully mature cotton ball
Explanation:
From Bacillus thuringiensis, specific Bt toxin genes were isolated and inserted into a variety of crop plants, including cotton as shown in the figure [Cotton balk (i) destroyed by bollworms: (ii) a fully mature cotton ball]. Since the majority of Bt toxins are insect-group specific, the choice of genes depends on the crop and the targeted pest. A gene called crylAc encodes the toxin. There are several of them: for instance, the proteins controlled by the genes crylAc and cryllAb and crylAb control the
Question 4.
Rakesh is a farmer. He is suggested to use biofertilizers instead of chemicals. Why are biological fertilizers and pesticides preferred over chemical ones?
(a) They are safe to use and are non-biological in origin.
(b) They do not spoil the quality of the soil and are target non-specific.
(c) They do not pollute the atmosphere and are non-poisonous.
(d) They are less expensive and are non-biodegradable.
Answer:
(c) They do not pollute the atmosphere and are non-poisonous.
ExpLanation:
Because they are safe to use and’ have a biotogicat origin, biofertilizers and biopesticides are preferred over chemical fertilisers and pesticides. They are target- specific and do not degrade soiL quality. They are not poisonous and do not poLlute the environment. They are biodegradable and less expensive. Related Theory In the case of secondary sewage treatment methane, H2S and CO2 are produced during the microbial digestion of organic compounds. In biogas plants, methane gas ¡s produced from cattle dung.
Question 5.
Which Darwin’s finch-eating behavior resulted in the evolution of numerous other varieties?
(a) Fruit eater
(b) Cactus eater
(c) insect eater
(d) Seed eater
Answer:
(d) Seed eater
Explanation:
Many other modified forms of beak emerged from the seed-eating finches, aLlowing them to eat insects, cacti, or fruit As a result, adaptive radiation was found. One of the best illustrations of this process is found in Darwin’s finches.
Question 6.
The figure given below represents a part of plant Michelia.
What part is it?
(a) A dissected flower showing pistil
(b) A multicarpellary, syncarpous pistil
(c) A multicarpellary, apocarpous gynoecium
(d) A typical anatropous ovule
Answer:
(c) A multicarpeiLary, apocarpous gynoecium
ExpLanation:
The given figure represents a multicarpeLtary. apocarpous gynoecium of Michetia. The female reproductive portion of the flower is represented by the gynoecium. A single pistil (monocarpellary) or multiple pistils may be present in the gynoecium (multicarpettary). The pistils may fuse together if there are multiple (syncarpous) or may be free, (apocarpous).
Related Theory:
A dissected flower of Hibiscus showing pistil (other floral parts have been removed):
Question 7.
Which statement is true regarding the process shown in the following figure?
(a) Two short polypeptide chains, chain A and chain C, make up insulin.
(b) Conversion of pro-insulin after removal of C-peptide is shown in the figure.
(c) Insulin is synthesized as active hormone
(d) C-peptide is usually removed much before the maturation of insulin
Answer:
(b) Conversion of pro-insulin after removal of C-peptide is shown in the figure.
Explanation:
Chain A and Chain B, the two brief polypeptide chains that make up insulin, are connected by disulfide bridges. The extra stretch known as C-peptide that is present in pro-hormone insulin, or hormone that needs to be processed before becoming functional, is typically removed during the maturation of insulin.
Question 8.
A complaint was filed against the offspring being exchanged at the hospital. To solve the case, the doctors used blood types. The parents’ genotypes for the blood groups lAi and lAlB. What was the blood type of the child who was mistakenly identified as their child?
(a) A
(b)B
(c) AB
(d) O
Answer:
(d) O
Explanation:
The progeny of these parents can have blood group lAlA, lAlB, lAi, and lBi. The offspring can therefore have blood groups A, B, or AB. The only case that can be resolved solely on the basis of blood groups is the progeny with blood group O.
Question 9.
What is the missing level of the organization? Tertiary consumer→ Secondary consumer→? Primary producer
(a) Carnivore
(b) Primary consumer
(c) Decomposer
(d) Secondary producer
Answer:
(b) Primary consumer
Explanation:
The missing Level of the organization is the primary consumer. These are the organisms that depend on primary producers for their energy requirements. For example cow, goat, deer, buffalo feeding on grass.
Question 10.
Match the columns that fills the missing boxes for the levels in the transformation of mother germ cells into a mature follicle in the given flowchart.
| Column (I) | Column (II) |
| (A) P | Graffan follicle |
| (B) Q | Primary follicle |
| (C) R | Antrum |
(a) (A)-(i), (B)-(ii), (C)-(iii)
(b) (A)-(ii), (B)-(i), (C)-(iii)
(c) (A)-(iii), (B)-(ii), (C)-(i)
(d) (A)-(ii), (B)-(iii), (C)-(i)
Answer:
(d) (A)-(ii), (B)-(iii), (C)-(i) .
Explanation:
The following are the various steps that lead to the development of the mature follicle:
Question 11.
Identity (I) and (II) in the above flow chart.
| (I) | (II) |
| (a) Producers | Chemical evolution |
| (b) Chemical evolution | Producers |
| (c) Consumers | Oxygen Evolution |
| (d) Autotrophs | Chemical evolution |
Answer:
(a) (I): Producers: (II): Chemical evolution
Explanation:
in the history of evolution on earth, chemical evolution is done after organics evolution. Evolution of primary producers in the Sea reference examines how photosynthesis evolved on Earth.
Question 12.
Enzyme used to digest the cell wall of bacteria is.
(a) celtutose
(b) Lysozyme
(c) chitinase
(d) zymase
Answer:
(b) lysozyme
Explanation: Lysozyme is used to digest the cell wall so that recombinant DNA can be easily pass through the bacterial cell wall.
Question No. 13 to 16 consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer:
Question 13.
Through the bites of female Anopheles mosquitoes carrying the parasites that cause malaria, people can contract this potentially fatal illness. It can be avoided and treated. nearly half of the world’s population would be at risk from malaria in 2020.
Assertion (A): Plasmodium vi vox has two hosts-femaLe anopheles while the secondary host is man.
Reason (B): Primary host Is where the parasite maintains an amoeboid stage in RBCs.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer:
(c) A is true but R is false
Explanation:
Plasmodium vivax is the cause of malaria. It has two hosts: the primary host, man, where the parasite maintains an amoeboid stage in R.BCS and later produces gametophyte, and the vector of the plasmodium, female anopheles.
Question 14.
Assertion (A): Many varieties were available with observable alternative forms for a trait or a characteristic.
Reason (B): Peas normally cross-pollinate: as their corona does not completely enclose the reproductive organs until pollination is complete.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer:
(c) A is true but R. is false
Explanation:
Mendel selected pea plant (Pisum sativum) for his experiments because:
(i) Many varieties were available with observable alternative forms for a trait or a characteristic.
(ii) Peas normally self-pollinate: as their corolla completely encloses the reproductive organs until pollination is complete.
(iii) it was easily available. It has pure lines for experimental purposes, i.e. they always breed true.
Question 15.
Assertion (A): The female gametophyte is formed from the contents of megaspore.
Reason (B): However it always remains embedded within the membrane of the microspore.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer:
(c) A is true but R is false
Explanation:
From the megaspore’s contents, the female gametophyte develops. But it consistently stays encased in the megaspore membrane. The mature female gametophyte is 7-celled (an egg, two synergids, three antipodals, and a central cell).
Question 16.
Assertion (A): The bacterial cells must be made competent to take up DNA.
Reason (B): This is done by treating them with a specific concentration of magnesium.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer:
(c) A is true but R is false
Explanation:
The bacterial cells must be trained to be able to absorb DNA. This is accomplished by giving them a specific caLcium concentration, which improves the efficiency with which DNA enters the cell through the cell wall pores. Then by first incubating the cells with recombinant DNA on ice, followed by placing them at 42°C, and then putting them back on ice, recombinant DNA can be forced into such cells (heat shock treatment).
Related Theory:
Recombinant DNA is directly injected into the animal ‘ cell’s nucleus using micro-needles or micro-pipettes in the microinjection technique.
Section – B (10 Marks)
Question 17.
From the following table, identify the empty spaces marked (A), (B), (C), and (D):
| Type of microbe | Scientific name | Product | Medical application |
| Fungus | Monascus | Cyclo sporin | (B) |
| (C) | Purpureus | Stotin | (D) |
Answer:
(A) Trichoderma polysporum
(B) Organ transplantation (Immunosuppres-sant)
(C) Yeast
(D) Blood cholesterol-lowering agent
Question 18.
Draw simple diagrams to represent the major plant and invertebrate that make up the world’s biodiversity.
Answer:
Question 19.
Look at the given image. This device is implanted in the female reproductive system by doctors.
Give examples of such more devices used. Explain how this device works.
Answer:
The given image represents copper-releasing lUDs (CuT). The Intra Uterine Devices (lUDs) are currently available as hormone-releasing lUDs (Progestasert, LNG-20), copper-releasing lUDs (Cu 7, Multiload 375), as well as non-medicated lUDs (such as Lippes loop). As a result of the Cu2+ ions released and the increased phagocytosis of sperms within the uterus caused by lUDs, sperm motility and fertility are reduced.
Question 20.
Rashi and her husband wanted to have a child. But their doctor told them that Rashi had a blockage in the fallopian tube. What methods of assisted reproductive techniques will help this couple to have children?
OR
“One way to achieve this goal is by offering sex education in schools.” Give four reasons for why you think this statement is true.
Answer:
Since the female partner’s fallopian tube is blocked, in vitro fertilization and embryo transfer (ET) will help her become pregnant. In this scenario, sperm from the male partner will be gathered and injected into the female partner’s ovum to create a zygote in a lab under simulated conditions, and an embryo with more than 8 blastomeres wilL be transferred into the uterus (LUT – intrauterine transfer) to complete its further development.
OR
The importance of sex education in schools is as follows:
- to give the correct information regarding common myths and misconceptions.
- to increase public awareness of reproduction.
- to educate people about sexually transmitted diseases and the development of reproductive organs (STDs)
- educate the students on social vices like sexual assault, sex-related crimes, etc.
Section – C (21 Marks)
Question 21.
(A) Can you determine whether (i) or (ii) have larger molecules based on what you have learned? How did you know?
Substrate
(B) Give the name of the first transgenic cow created and explain how the product quality improved as a result.
(C) Shikha bought some oranges from market to extract juice at home. When she squeezed an orange many embryos of different shapes and sizes were seen. But normally one embryo develops in one seed. Mention how it has happened.
Answer:
(A) (i) is enzymes and (ii) is DNA In comparison to enzyme molecules, the size of DNA molecules is larger. Proteins are enzymes. Genes, a small section of DNA, are used to make proteins.
(B) Human protein-enriched milk (2.4 grammes per liter) was produced by the transgenic cow Rosie.
(C) Several of the nuceLLar cells surrounding the embryo sac in many citrus varieties begin to divide, protrude into the embryo sac, and eventually develop into embryos. Each ovule in these species houses numerous embryos. Polyembryony is the term for when a seed contains multiple embryos.
Question 22.
Differentiate between the functions of floes and anaerobic sludge digesters in the treatment of sewage.
Answer:
Floes are collections of bacteria linked to fungus filaments to create structures resembling meshes. These microbes break down a large amount of organic matter, creating microbial biomass in the process and liberating a large amount of minerals. In a sizable tank known as an anaerobic sludge digester, anaerobic microbes break down the sludge’s aerobic and anaerobic microbes. Methanogens are the producers of biogas. It provides energy and is flammable.
Question 23.
(A) A farmer who lives in village Palampur is advised by his friends to use apomictic seeds. He was told that apomictic seeds are beneficial for farmers. Is that true? Explain your answer.
(B) Do you think apomixis and asexual reproduction are comparable? Give one reason to support your response.
Answer:
(A) It is expensive to produce hybrid seeds, but if desirable hybrids can be transformed into apomicts, there won’t be any character segregation in the hybrid offspring. The farmer doesn’t have to buy new seeds each year if they want to keep using hybrid seeds.
(B) Only a small percentage of flowering plants, including some Asteraceae species and grasses, have developed a unique mechanism to produce seeds without fertilisation. We refer to this as apomixis. Asexual reproduction is what apomixis is, then.
Question 24.
How have transgenic animals proved to be beneficial in production of biological products and chemical safety testing?
Answer:
Production of biological products:
- Medicines required for treating human diseases are obtained by genetic engineering.
- a-l-antitrypsin used to treat emphysema.
- Transgenic cow ‘Rosie’ produces human-protein enriched milk.
Chemical safety (Toxicity/safety testing): Transgenic animals are made that carry genes that make these more sensitive toxic substances than non-transgenic animals.
Question 25.
(A) The principle shown below states that an individual population’s allele frequency never changes. How should you interpret a population’s shift in allele frequency?
| p2: frequency of
homozygous dominant genotype |
2pq: frequency of
heterozygous genotype |
q2: frequency of
homozygous recessive genotype |
(B) Explain how human activities affect organic evolution using appropriate examples.
Answer:
(A) As a result of changes in the frequency of alleles in a population brought on by disturbances in Hardy-Weinberg equilibrium or genetic equilibrium, evolution occurs.
(B) The impact of human behavior on organic evolution are:
- Artificial or selective breeding programs used to create new breeds.
- Rapid selection of resistant varieties has been facilitated by excessive use of pesticides, herbicides, etc., and the selection of bacteria with drug resistance.
- The persistence of dark-winged (melanized) moths in England after industrialization.
Question 26.
(A) The biotechnologist label is allegedly shared by the winemaker and a molecular biologist who created a recombinant vaccine. Which person is right, in your opinion?
(B) List three important biotechnology research areas.
OR
(A) What are the two fundamental methods that made biotechnology possible?
(B) Name two GMO characteristics.
Answer:
(A) They both qualify as biotechnologists, to be sure. A yeast strain is used in winemakers to ferment grape juice to make wine. A cloned gene is used by the molecular biologist as the antigen. Utilizing the antigen as a vaccine. Antigen can form in significant amounts thanks to this. Both use living things to produce goods and f services that benefit people.
(B) (1) Supplying the best catalyst in the form of a better organism, typically a ” microbe or pure enzyme.
(2) Engineering the best conditions for a catalyst to function
(3) Purifying the protein or organic compound using downstream processing techniques.
OR
(A) The two main methods that made modern biotechnology possible are as follows:
(1) The chemistry of genetic material (DNA and RNA) can be changed using genetic engineering techniques, which can then be introduced into hosts to ‘ change the phenotype of the host organism.
(2) in chemical engineering processes, maintaining sterile (microbial contamination-free) environments allows for the large-scale growth of only the desired microbe/eukaryotic cell for the production of biotechnological products like antibiotics, vaccines, enzymes, etc
(B) (1) They are able to produce proteins with medicinal value.
(2) They have the capacity to create enhanced, altered, or novel metabolites.
Question 27.
(A) Comment on the phrase “Migration may increase or lessen the impact of selection.”
(B) What are the factors responsible for the evolution of synthetic theory? 3
Answer:
(A) Migration is the act of people moving from one location to another. Either a different group or a specific population may accept the individuals. When people transfer to another population some alleles that provide better adaptations may be lost Movement into a population may introduce specific alleles that distort the results of selection. Therefore, we might conclude that migration can alter the results of selection.
(B) The factors are:
- Changes in chromosome number and the structure.
- Gene mutations.
- Reproductive isolation
- Genetic recombination
- Natural selection
Question 28.
The following graph shows the species-area relationship. Answer the following questions as directed.
(A) Name the naturalist who studied the relationship shown in the graph. What were his observations?
(B) Write the situations as discovered by the ecologists when the value of‘Z’ (slope of the line) lies between
- 0.1 and 0.2
- 0.6 and 1.2
What does ‘Z’ stand for?
(C) When would the slope of the line ‘(b)’ become steeper?
Answer:
(A) German naturalist and geographer Alexander von Humboldt He observed that within a region species richness increased with increasing explored area, but only up to a limit. In fact, the relation between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) turns out to be a rectangular hyperbola.
(B) (i) When the value of Z is between 0.1 and 0.2 the slope of regression is similar when unaffected distribution in an areas is analyzed.
(ii) When the value of Z is between 0.6 and 1.2 the slope of regression is steeper when we analyze the species-area relationship among very large areas like entire continent. Z stands for the regression coefficient, icient.
(C) The slope will become steeper when species richness increases.
Related Theory:
On a logarithmic scale, the relationship is a straight line described by the equation
log S = log C+Z log A
where
S = Species richness, A = Area, Z = slope of the line (regression coefficient), C = Y-intercept
Section – D (8 Marks)
(Q. No. 29 and 30 are case based questions. Each question has subparts with internal choice in one subpart.)
Question 29.
in her kitchen garden, Preksha had a pea plant with purple flowers that she was trying to identify the genotype of. She crossed a purple-flowered plant with a white-flowered plant to achieve this. As a result, the only flower found on every plant that was produced was purple. These plants selfed, producing 25 white flower plants and 75 purple flower plants. She can now cross a purple flowering plant with a white flowering plant to determine its genotype.
(A) Which law of inheritance cannot be derived from the crosses done by Preksha? 1
(B) What do we call the character, i.e., purple colour of the flowers that appeared in the first filial generation?
(C) To determine the genotype of a purple-flowered plant, Preksha crossed this plant with a white-flowered plant. Which cross is represented by this?
OR
(C) What do we call a pair of genes that is unable to express its effect in the presence of its contrasting component in a heterozygote?
Answer:
(A) Mendel’s law of independent assortment Although Praksha has only used monohybrid cross, or one pair of traits, this law can also be derived from dihybrid crosses.
(B) Dominant character: The heterozygous person does not experience the effects of the other factor or allele because it is a recessive trait.
(C) Test cross: Instead of self-crossing, a test cross is made between an organism (in this case, a pea plant) exhibiting a dominant phenotype whose genotype needs to be determined and the recessive parent. It is simple to analyse the offspring of such a cross and determine the genotype of the test organism. For a monohybrid cross, the normal test cross ratio is 1, and for a dihybrid cross, it is 1:1:1:1.
OR
(C) Recessive factor or allele refers to the component of an allelic or allelomorphic , pair that is unable to express its effect in the presence of its contrasting component in a heterozygote, such as the allele in the hybrid tall pea plant it. Only when a recessive factor is pure or homozygous, as in the case of the tt gene in dwarf pea plants, is its effect known.
Question 30.
During a lesson on various environmental factors, a teacher draws a diagram that shows the historical strategies for three plant species (X, Y, and Z) along three axes: the intensity of interspecies competition, the degree of habitat disturbance, and the intensity of environmental stress. In habitats with high interspecies competition but low disturbance and stress, species X thrives. In environments with high environmental stress but low intraspecies competition, species Y thrives. In environments with little environmental stress, species Z can grow.
(A) What are the environmental stresses that restrict production?
(B) Comment on the plant growth rate of different areas.
(C) In what kind of environment plant ‘X’ can be found?
OR
identify what type plants are ‘X’, ‘Y’ and ‘Z’.
Answer:
(A) External factors that restrict production, such as shakiness, drought, nutrient scarcity, or extremely low temperatures, cause environmental stress.
(B) In areas with high stress and high disturbance, plant growth is slow. High levels of stress and disturbance cannot help plants reproduce.
(C) ‘X’ type of plants are competitors that thrive in low-stress and low-disturbance environments and have strong competitive ability at high population densities close to the carrying capacity. Such plants grow slowly and are common in non-seasonal tropical regions with little chance of drastic environmental changes.
OR
‘X’ type of plants are likely to be trees. Y type of plants could be desert plants. ‘Z’ type of plants could be herbaceous plant
Section – E (15 Marks)
Question 31.
A virus that uses RNA as its genomic material is referred to as a retrovirus. When a cell becomes infected with a retrovirus, the retroviral RNA is converted to retroviral DNA, which is then inserted into the DNA of the host cell. More retroviruses are then produced by the cell, infecting additional cells. Many diseases, including AIDS and some types of cancer, are linked to retroviruses. The figure given below shows replication of retrovirus.
(A) Step ‘Y’ occurs in presence of which enzyme? What happens with the viral DNA formed in this step?
(B) What happens during the step ‘Z’?
(C) What kind of infections can develop due to decrease in number of T-lymphocytes?
(D) A specialist made the diagnosis that the patient’s immune system had been suppressed. Name the infection.
OR
Look at the given figure and answer the following questions:
(A) What is the role of parts labelled in the following figure?
(B) What kind of lymphoid organ is thymus?
(C) What kind of lymphoid is lymph node?
(D) Name one secondary lymphoid organ
which is not mentioned in the figure. State its role.
Answer:
(A) After entering the host’s body, the virus enters macrophages where, with the aid of the enzyme reverse transcriptase, its RNA genome replicates to produce viral DNA. This viral DNA is incorporated into the DNA of the host cell, instructing it to produce virus particles. In this way, the ‘ macrophages function like an HIV factory as they continue to produce virus.
(B) Viral DNA incorporates in to the host genome during step Z.
(C) The person experiences episodes of fever, diarrhoea, and weight loss during this time. The person begins to develop infections that could have been treated otherwise, including those caused by viruses, fungi, bacteria, notably Mycobacterium, and even parasites Like Toxoplasma, as a result of a decrease in the number of helper T lymphocytes.
(D) The patient is diagnosed with human immunodeficiency virus (HIV) if his immune system is found to be suppressed. Helper T cells allow the HIV virus to replicate and produce offspring viruses.
OR
(A) Lymph nodes are small, solid structures that are positioned along the lymphatic system at various locations. It serves to capture antigen that accidentally enters lymph and tissue fluid. The activation of lymphocytes is caused by antigen trapped in lymph nodes. Thymus is situated close to the heart beneath the collar bone. It offers a micro-environment for the T-lymphocytes’ growth and maturation.
(B) It is a primary lymphoid organ where immature lymphocytes differentiate into antigen-sensitive lymphocytes.
(C) It is a secondary lymphoid organ that serves as the site of lymphocyte-antigen interaction before effector cells are produced.
(D) Spleen: It is a large organ with a bean-like shape and primarily contains lymphocytes and phagocytes. By capturing blood¬hound microorganisms, it serves as a filter for blood.
Question 32.
The following figure shows diagrammatic sectional view of a seminiferous tubule:
(A) Name and define the process by which structure ‘X’ produces sperms in the testis.
(B) How the structure ‘Y’ do produces the structure ‘Z’?
(C) Name and define the process by which structure ‘Z’ develops into spermatids.
(D) Name and explain the process by which structure ‘Q’ is released from the seminiferous tubules.
OR
(A) Study the figure given below and answer the questions that follow:
- Identify the human embryonic stage that the illustration represents.
- Mention the fate of the inner cell mass after implantation in the uter¬us,
- Where are the stem cells located in this embryo?
- Point out the function of ‘a’ in the figure and identify it.
(B) Chromosome number (2n) in the gametes is reduced to half (n) during reproduction, and it is restored to its original number (2n) in the progeny. What are the procedures that these events go through?
Answer:
(A) Spermatogenesis, which starts at puberty, is a process by which the immature maLe germ cells (spermatogonia) i.e. structure labelled as ‘X’ in the testis produce sperms.
(B) Periodically, meiosis occurs in a subset of spermatogonia called primary spermatocytes. A primary spermatocyte (structure Y) completes the first meiotic division (reduction division), which produces secondary spermatocytes (structure ‘Z’), which are two identical, hapLoid cells with only 23 chromosomes each.
(C) To create four identical, haploid spermatids, the secondary spermatocytes (structure ‘Z’) go through a second meiotic division. Spermiogenesis is the process by which the spermatids develop into spermatozoa (sperms).
(D) After spermiogenesis, sperm heads become embedded in Sertoli cells (structure ‘Q’) and undergo a process known as spermiation in which they are eventually freed from the seminiferous tubules.
OR
(A) (i) Blastocyst (Blastula).
(ii) inner cell mass gets differentiated as embryo after implantation.
(iii) Stem cells are located in the inner cell mass.
(iv) ‘a’ is trophoblast: The blastocyst’s tro- phoblast serves as its outer Layer. Thus, their primary function is to nourish the growing embryo. They also aid in the implantation of the embryo.
(B) During gametogenesis, the number of chromosomes is cut in half or to (n). During fertilisation, the number of chromosomes is restored to the diploid (2n) stage.
Question 33.
(A) Why does replication take place in small replication forks rather than entire lengths?
(B) Why does DNA replication in a replication fork occur both continuously and discontinuously?
(C) What are the exceptions to the generalization that DNA is the genetic material in all organisms? Give evidence that supports these exceptions.
OR
(A) Name the parts ‘P’ and !Q’ of the transcription unit given below.
(B) What does this diagram illustrate? Name the components P, Q, and R.
(C) DNA molecules are arranged in the nucleus of eukaryotes, in the absence of a nucleus, how is the DNA molecule arranged in a bacterial cell?
(D) What will happen to a eukaryotic cell if DNA replication is not followed by cell division?
Answer:
(A) For extremely Long DNA molecules, replication takes place in a small opening of a DNA helix called a replication fork. The two strands of DNA cannot be completely separated along the length of long DNA molecules because doing so would require an enormous amount of energy.
(B) DNA-deperident DNA polymerase only catalyses DNA polymerization in the 5′ →3′ direction. The polarity and anti-parallel orientation of DNA strands are the opposite. Thus, DNA replication is continuous on the template strand with polarity 3’→ 5′ while it is discontinuous on the template strand with polarity 5’→ 3
(C) All plant viruses and some animal viruses have RNA as their genetic makeup.
OR
(A) P-Promoter Q-Coding strand
(B) Nucleosome
(C) DNA is not scattered in prokaryotes, such as bacteria, which lack a nucleus, in a region known as a nucleoid, negatively charged DNA binds with positively charged proteins.
(D) Chromosomes (DNA) that have undergone replication would not be distributed to daughter nuclei if cell division was not carried out afterward. The accumulation of DNA inside the celL is the result of repeated DNA replication without cell division. The cell would expand as a result of the nucleus’ volume being increased. Additionally, it will cause polyploidy.