CBSE Class 12 Biology 2023 — Set 57/3/1

Which of the following seeds have remained alive for the longest period ? (a) Phoenix dactylifera (b) Striga asiatica (c) Mangifera indica (d) Yucca gigantea

Select the options which is/are incorrect statement(s) with respect to T-lymphocytes in the human body. (i) They are a type of white blood cells. (ii) They are produced in bone marrow. (iii) They remain active at all times in the body. (iv) They mature in the bone marrow. (a) (i) and (iv) only (b) (iii) only (c) (iv) only (d) (iii) and (iv) only

Human settlement often leads to habitat loss which leads to fragmentation, forming smaller patches of habitats. Select the statements that describe how a small patch differs from a large patch of the same habitat. (i) Invasive species will never be seen here. (ii) Population of large animals decreases. (iii) Biodiversity decreases. (iv) Competition from surrounding habitats increases. (a) (ii), (iii) and (iv) only (b) (ii) and (iv) only (c) (i) and (iii) only (d) (i), (ii) and (iii) only

Identify the option that does not exhibit a parasitic relationship. (a) Head lice in humans (b) Cuscuta on a mango tree (c) Female Anopheles (d) Ticks on dogs

Identify the fungus that ripens the famous 'Roquefort' cheese : (a) Saccharomyces cerevisiae (b) Propionibacterium sharmanii (c) Monascus purpureus (d) Penicillium notatum

The given schematic illustration shows three steps 'P', 'Q' and 'R' of the polymerase chain reaction. [Figure: schematic of PCR steps P, Q, R showing DNA strands with 5' and 3' ends] Which of the following statements are correct with reference to the illustration given above ? (i) Step 'P' is showing denaturation at low temperature. (ii) Step 'Q' is a denaturation of DNA strand at high temperature, followed by annealing. (iii) Step 'R' is an extension of DNA in presence of thermostable DNA polymerase. (iv) Step 'Q' is extension with two sets of primers. (a) (i) and (iii) only (b) (ii) and (iii) only (c) (ii) only (d) (i) only

DNA profiles of the child and three individuals 1, 2 and 3 who claim to be the parents of the child are given below. Select the option that shows the correct actual parent/parents of the child. [Figure: DNA profile gel showing bands for Child X, Individual 1, Individual 2, Individual 3] (a) Individual 1 and 3 (b) Individual 1 and 2 (c) Individual 2 and 3 (d) Individual 1 is the only parent of the child amongst 1, 2 and 3

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 humans the genotype with all the dominant alleles (AABBCC) will have the darkest skin colour. Reason (R) : In a polygenic trait, phenotype reflects the contribution of each allele.

Assertion (A) : The number of white winged moths decreased drastically after industrialisation in England. Reason (R) : Effects of industrialisation were more marked in rural areas of England.

Assertion (A) : More and more children in metro cities of India suffer from allergies and asthma due to sensitivity to the environment. Reason (R) : Modern day lifestyle and a protected environment in early life has resulted in lowering the immunity.

(a) Explain the process of the development of a male gametophyte in an angiosperm. (b) Why is it called a male gametophyte ?

Given below is a food web that involves nine organisms. [Figure: food web with organisms numbered 1 to 9 connected by arrows] (a) Identify two producers and two carnivores shown in the food web. (b) Is it possible to make an ecological pyramid depicting this food web ? Give reason in support of your answer.

Illustrate with the help of an example how introduction of an alien species turns invasive and causes decline of an indigenous species.

(a) 'Insertional inactivation' is a method to detect recombinant DNA. Explain the method. OR (b) Explain how recombinant DNA technology is used to detect a disease even before any clinical symptom appears.

(a) (i) How many types of RNA polymerases are there in a eukaryote cell ? Mention which one of them transcribes hnRNA. (ii) Write the changes that hnRNA undergoes before it leaves the nucleus as mRNA. OR (b) The length of DNA in any cell is far greater than the dimension of its nucleus. Explain how this enormous DNA is packaged in a eukaryotic cell.

Expand and explain the following techniques used in the 'Test Tube Baby' programme : (a) GIFT (b) ZIFT (c) IUI

Given below is a diagrammatic sectional view of a seminiferous tubule. State the developmental process of : [Figure: sectional view of seminiferous tubule with labels a, b, c, d, e] (a) (i) 'b' from 'a'. (ii) 'e' from 'd'. (iii) 'd' from 'b'. (b) Identify 'a', 'b' and 'c'.

(a) Darwin's theory of Natural Selection is widely accepted but some limitations have been identified by modern biologists. Mention the limitations identified. (b) Name and state the most accepted theory of evolution in modern times. (c) Mention any two ways the limitations identified in Darwin's theory of evolution are explained in modern biology.

[Figure: chemical structure of a drug (morphine-type) showing two HO groups, an O bridge, and N-CH3] (a) Name the category of drugs represented by the chemical structure given above. (b) If the methyl group is substituted by acetyl group we get a bitter crystalline compound. Name the compound. (c) Name the natural source of these compounds. (d) State the harmful effects of this class of drugs on the human body.

(a) Write the scientific name of the nematode that infests the tobacco plants and the part that it infests. (b) How is Agrobacterium used to protect tobacco plant from this attack ?

Explain the following population interactions with the help of one example each : (a) Brood Parasitism (b) Co-evolution of mutualists

The following pedigree chart shows the inheritance of a genetic disorder up to three generations of a family. Observe the chart and answer the questions that follow. [Figure: pedigree chart — Generation I: 'B' (unaffected female) × 'A' (affected male); Generation II: 'C' (female), 'D' (female), 'E' (affected male) × 'F' (female); Generation III: 'G' (female), 'H' (female), 'I' (affected male)] (i) Is the disease sex-linked or autosomal as per the chart ? Give reasons in support of your answer. (ii) Is it a recessive or a dominant disorder ? (iii) Write the genotypes of the individuals 'C', 'D' and 'H'. (iv) (a) If the female 'D' marries a normal man, what will be the probability of their daughter being a sufferer of this disease ? OR (iv) (b) If the mother 'B' is a carrier of the disease, what will be the probability of their daughter being a sufferer of this disease ?

The diagram shows the life cycle of a pathogenic protozoan. [Figure: life cycle showing Host 'X', Host 'Y', stages 'A', 'B', 'C', 'D', female Anopheles mosquito bites, female mosquito bites, infects the liver, RBC] (i) Name the parasitic stage that is being transferred from host 'X' to host 'Y'. (ii) Write the changes the parasite undergoes in the liver. (iii) Write the changes the parasite undergoes when it enters the RBC. (iv) (a) Trace the changes the parasite undergoes when the host 'X' takes its blood meal from infected host 'Y'. OR (iv) (b) At which stage during the life cycle of the pathogen does the host 'Y' experience the symptoms of the disease ? Name the disease and the toxic substance responsible for these symptoms.

(a) Answer the following questions with respect to recombinant DNA technology : (i) Why is plasmid considered to be an important tool in rDNA technology ? From where can plasmids be isolated ? (Any two sources) (ii) Explain the role of 'ori' and selectable marker in a cloning vector. (iii) "r-DNA technology cannot proceed without restriction endonuclease." Justify. OR (b) Answer the following questions based on Bt-crops : (i) Why do farmers prefer to grow Bt cotton crop than genetically unmodified cotton crops ? (ii) Name any two insects that are killed by Bt toxin. (iii) Explain the mechanism by which Bt toxin kills the insects but not the bacterium which possesses the toxin.

(a) Protein synthesis requires the services of all three types of RNAs, namely t-RNA, m-RNA and r-RNA. Explain the role of each of them during the process of protein synthesis in prokaryotes. OR (b) A homozygous tall pea plant with green seeds is crossed with a homozygous dwarf pea plant with yellow seeds. (i) Write the possible phenotype and genotype of F1 generation. (ii) State the laws of Mendel that are proved true by the F1 generation. (iii) Mention the F2 phenotypic ratio along with their possible phenotypes. (iv) Write the genotypes of the male and female gametes produced by F1 progeny.

(a) Given below is a diagrammatic representation of a human ovum. [Figure: human ovum with labels a, b, c, d] (i) Identify the parts 'a', 'b' and 'c'. (ii) This ovum is released from the ovary with incomplete meiotic division. When, where and how is the meiotic division completed ? (iii) How does an ovum ensure the entry of a single sperm during fertilisation ? OR (b) (i) Double fertilisation is an event unique to all flowering plants. Explain the process. (ii) Give a reason for the following : (1) A seed of an orange has many embryos. (2) Cashew is a false fruit but Guava is a true fruit.