CBSE Class 12 Biology 2025 — Set 57/6/1

Select the statements that are true for the seed of angiosperm from the given options : (i) Non-albuminous seeds have no residual endosperm. (ii) Residual, persistent nucellus in wheat is known as perisperm. (iii) Integuments of ovules harden as tough protective seed coat. (iv) Metabolic activity of the embryo slows down in dormancy. Choose the correct option : (A) (i) and (ii) (B) (ii) and (iii) (C) (iii) and (iv) (D) (i) and (iv)

Which of the following do not follow the law of independent assortment ? (A) Genes on non-homologous chromosomes and absence of linkage (B) Two or more genes on homologous chromosomes (C) Linked genes located on the same chromosomes (D) Two or more distant genes present on the same chromosome

A characteristic property that distinguishes a malignant tumor from a benign tumor is : (A) Metamorphosis (B) Metastasis (C) Metabolism (D) Metagenesis

The cloning site present in the tetracycline resistance gene of E. coli cloning vector pBR322 is : (A) EcoR I (B) Pvu II (C) Sal I (D) Pst I

Bottled fruit juices are clearer as compared to those made at home, as they are clarified by the use of : (A) Lipases and pectinases (B) Pectinases and proteases (C) Proteases and cellulases (D) Nucleases and lipases

In his observations of small black birds in the Galapagos Islands, Darwin found that all the finches arose from the original ancestor : (A) Insect-eating finches (B) Seed-eating finches (C) Cactus-eating finches (D) Fruit-eating finches

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. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A) : In dihybrid crosses involving sex-linked genes in Drosophila generation of non-parental gene combinations are observed. Reason (R) : Two genes present on different chromosomes show linkage and recombination in Drosophila.

Assertion (A) : Male contraceptive 'Nirodh' works on the principle of avoiding chances of ovum and sperm meeting. Reason (R) : It is made of thin rubber/latex sheath and is used to cover the penis before coitus.

Assertion (A) : Isolated single cells can be fused to produce somatic hybrids. Reason (R) : Cells selected for somatic hybridisation have desirable characters.

Assertion (A) : In humans, filariasis is characteried by inflammation in the lower limbs. Reason (R) : Filarial worm usually lives in the lymphatic vessels of the lower limbs.

(a) How is the interaction between Ophrys and its specific bee pollinator one of the best examples of co-evolution ? Explain. OR (b) Arrange the given important steps of decomposition in their correct order of occurrence in the breakdown of complex organic matter and explain the fourth step in the process. [Box with terms: Catabolism, Leaching, Fragmentation, Mineralisation, Humification]

The basic scheme of the essential steps involved in the process of recombinant DNA technology is summarised below in the form of a flow diagram. Study the given flow diagram and answer the questions that follow. Step 1: Vector DNA (Plasmid) (cut using Restriction Enzyme) + Alien DNA (cut using Restriction Enzyme) Step 2: Recombinant DNA molecule Step 3: Transfer of recombinant DNA molecule in E. coli (Host) Step 4: Replication of the recombinant DNA molecule in E. coli to form multiple copies of the alien gene (a) What is the technical term used for Step 4 in the above process ? (b) Which of the given two combinations of restriction enzyme should be used in Step 1 ? Justify your answer. (i) EcoR I to cut the plasmid and Hind III to cut the alien DNA. (ii) EcoR I to cut both the plasmid and alien DNA.

(a) (i) Explain why the milk produced by the mother during the initial days of lactation is considered to be very essential for the newborn infant. (ii) What is the term used for the milk produced during the initial days of lactation ? OR (b) Many children in the metro cities are suffering from a very common exaggerated response of the immune system to certain weak antigens in air. (i) What is the term used for the above mentioned disease ? (ii) Name the main type of antibody produced by the immune system in response to this disease. (iii) Which two main inflammation-causing chemicals are produced by the mast cells in such an immune response ?

Study the given molecular structure of double-stranded polynucleotide chain of DNA and answer the questions that follow. [Figure of double-stranded DNA polynucleotide chain with base pairs A-T, T-A, G-C, C-G, showing 5' and 3' ends] (a) How many phosphodiester bonds are present in the given double-stranded polynucleotide chain ? (b) How many base pairs are there in each helical turn of double helix structure of DNA ? Also write the distance between a base pair in a helix. (c) In addition to H-bonds, what confers additional stability to the helical structure of DNA ?

(a) Why are restrictions imposed on MTP in India ? Up to how many weeks or trimesters, is MTP considered relatively safe for a female, if necessary to perform, by a medical practitioner ? OR (b) Expand PID. Name any two common viral infections transmitted through sexual contact in human females.

Flowering plants with hermaphrodite flowers have developed many reproductive strategies to ensure cross-pollination. Study the given outbreeding devices adopted by certain flowering plants and answer the questions that follow. [Table: Stigma vs Pollen grains of Plant A/B/C — Stigma of Plant A: ×, ✓, ✓; Stigma of Plant B: ✓, ×, ✓; Stigma of Plant C: ✓, ✓, ×] Note : All plants belong to the same species. × – No pollen tube growth/inhibition of pollen germination on stigma. ✓ – Pollen germination on stigma. (a) Name and define the outbreeding device described in the above table. (b) Explain what would have been the disadvantage to the plant in the absence of the given strategy.

(a) Alien species are highly invasive and are a threat to indigenous species. Substantiate this statement with the help of any two examples. OR (b) State any two criteria for determining biodiversity hotspots.

Answer the following questions with respect to the sex determining mechanism observed in honey bee. (a) Name the type of sex determination system observed in honey bee. (b) Fill in the blanks (i), (ii) and (iii) in the given question. [Table — Parent | Male: • Type of cell division involved during gamete formation in males — (i) _____ • Number of chromosomes in the gametes — (ii) _____ • Number of chromosomes in the diploid cell of the progeny — (iii) _____ ] (c) What will be the sex and chromosome number of the progeny formed from the unfertilised eggs of honey bee ?

Explain how the addition of lactose in the medium regulates the switching on of the lac operon in bacteria.

(a) Name and explain the role of inner and middle walls of the human female uterus. (b) Write the location and function of fimbriae in human female.

(a) What do you mean by activated sludge in an STP ? (b) Explain the biological treatment of the major part of the sludge transferred from the large aeration tank into the anaerobic sludge digesters before its final release into the natural water bodies.

Explain the beneficial role of the following, produced as a result of the processes of biotechnology, to mankind : (a) Cow named Rosie (b) α-1-antitrypsin

Read the following passage and answer the questions that follow. According to evolutionary theory, every evolutionary change involves the substitution of a new gene for the old one and the new allele arises from the old one. Continuous accumulation of changes in the DNA coding for proteins leads to evolutionary differences. The chemical composition of DNA is basically the same in all living beings, except for differences in the sequence of nitrogenous bases. Given below are percentage relative similarities between human DNA and DNA of other vertebrates : [Table — S.No. | Vertebrates | Percentage similarities: 1. Chimpanzee 100; 2. Gibbon 94; 3. Rhesus Monkey 88; 4. Lemur 47; 5. Treeshrew 28; 6. Mouse 21; 7. Hedgehog 19; 8. Chicken 10] (a) What is the term used for the substitution of a new gene for the old one and the new allele arising from the old one during evolutionary process ? (b) Which one of the following holds true for the data provided in the above table ? (A) Greater the evolutionary distance, greater are the differences in the nitrogenous bases. (B) Lesser the evolutionary distance, greater are the differences in the nitrogenous bases. (C) Greater the evolutionary distance, lesser are the differences in the nitrogenous bases. (D) Lesser the evolutionary distance, lesser are the differences in the nitrogenous bases. (c) (i) To which category of evolution (divergent or convergent) does the following relationship belong to ? Justify your answer. Human and Rhesus Monkey OR (c) (ii) Differentiate between Convergent and Divergent evolution.

Read the following passage and answer the questions that follow. Prevention is the frontline response to drug use. Effective interventions address the underlying conditions contributing to drug use, such as a lack of connection to family or community, instability, insecurity, trauma, mental health issues, etc. When addressed, these factors can effectively prevent the initiation of drug use and the progression to drug use disorders. Study the few key figures of drug use given below and answer the questions that follow. [Infographic — People who use drugs 2022: 292 million people; 20% over 10 years; 3% (over 5 years 2018 – 2022). People with drug use disorders, 2022 (in millions). Table No. 1: 1 in 11 in treatment; 1 in 18 (among women in treatment); 1 in 7 (among men in treatment); (p) and (q) figures. Table No. 2: 13·9 million people who inject drugs; 1·6 million living with HIV; 1·4 million living with HIV Hepatitis C] (a) What do you infer from the figures in Table No. 1 about the people with drug use disorders, 2022 (in million) ? State any two of your observations. (b) How are Hepatitis C and HIV related to drug use disorders by people, as shown in Table No. 2 ? State the correlation between the two. (c) (i) Give the scientific name of (p) shown in Table No. 1. OR (c) (ii) Give the scientific name of (q) shown in Table No. 1.

(a) (i) Explain how some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans but do not kill the Bacillus. (ii) How is the above mechanism exploited for the production of Bt cotton plant by biotechnologists ? OR (b) (i) Explain how the amplification of gene of interest is done using PCR. (ii) State two applications of the desired amplified fragment of DNA.

(a) (i) Explain the structure of a mature embryo sac of a typical flowering plant. (ii) How is triple fusion achieved in these plants ? OR (b) Describe the changes in the ovary and the uterus as induced by the changes in the level of pituitary and ovarian hormones during menstrual cycle in a human female.

(a) (i) Describe the Species-Area relationship as observed by Alexander von Humboldt, for a wide variety of taxa in nature. (ii) Draw the graph showing Species-Area relationship for S = CAZ. What is the significance of 'Z' in Species-Area relationship ? OR (b) (i) Describe the logistic population growth curve with the help of a suitable graphical representation. (ii) Write the equation of Verhulst-Pearl logistic growth curve and explain what 'K' and 'r' suggest in the given equation.