CBSE EXAMINATION PAPER-2023
BIOLOGY
(Solved)
General Instructions :
Read the following instructions carefully and follow them :
- This question paper contains 38 questions. All questions are compulsory.
- This question paper is divided into 5 sections.
- Section A – questions number 1 to 4 are case based questions
- Section B – questions number 5 to 18 are multiple choice questions
- Section C – questions number 19 to 24 are very short answer
- Section D – questions number 25 to 32 are short answer
- Section E – questions number 33 to 38 are long answer
- There is no overall choice given in the question paper. However, an internal choice has been provided in few questions.
- Use of calculator is NOT allowed.
Section A
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.
(1) If the mother 'B' is a carrier of the disease, what will be the probability of their daughter being a sufferer of this disease?
(2) (ii) Is it a recessive or a dominant disorder?
(3) Write the genotypes of the individuals 'C', 'D' and 'H'.
(4) If the female 'D' marries a normal man, what will be the probability of their daughter being a sufferer of this disease?
(5) Is the disease sex-linked or autosomal as per the chart ? Give reasons in support of your answer.
The diagram shows the life cycle of a pathogenic protozoan
The diagram shows the life cycle of a pathogenic protozoan.
(1) Name the parasitic stage that is being transfered from host 'X' to host 'Y'.
(2) Write the changes the parasite undergoes in the liver.
(3) Write the changes the parasite undergoes when it enters the RBC.
(4) Trace the changes parasite undergoes when the host 'X' takes the the blood meal from infected host 'Y'.
(5) At which stage during the life cycle of the pathogen does the host 'Y' experience the symptoms of the diseas. e ? Name thedisease and the toxic substance responsible for these symptoms.
Section B
Choose the set of sex determining chromosomes that indicates the correct sex of the respective organism.
The correct option is 'XO type of sex chromosomes determine male sex in grasshoppers.' In grasshoppers, males have an XO chromosome configuration where they have one X chromosome and no second sex chromosome, whereas females have two X chromosomes. The other options provided are incorrect because: homozygous sex chromosomes (ZZ) determine male sex in birds, not female; homozygous sex chromosomes (XX) produce female, not male, in Drosophila; and the XXY condition in humans corresponds to Klinefelter syndrome, not Turner Syndrome, which is characterized by a single X chromosome (monosomy).
Given below is a list of steps Meselson and Stahl carried out in their experiment to prove that DNA replication is semi-conservative. Select the option that gives the correct sequence of steps followed by them.
(i) Bacteria transferred to a N14 medium and sampled every 20 minutes.
(ii) All bacteria contain hybrid DNA (N14 DNA and N15 DNA).
(iii) Bacteria grown in N15 medium for many generations.
(iv) All bacteria contain N15 DNA.
(v) Bacteria contain either all N14 DNA or all hybrid DNA.
The correct sequence is (iii) (iv) (ii) (i) (v). First, they grew bacteria in N15 medium (iii) until all DNA was N15 (iv). After that, they transferred them to N14 medium, where they observed that the DNA became hybrid (ii) and later concluded that the bacteria contain either all N14 DNA or all hybrid DNA (v). This progression confirms the semi-conservative nature of DNA replication.
Identify the option that gives the correct type of evolution exhibited by the two animals shown, living in the same habitat in Australia.
The correct answer is Convergent Evolution. This type of evolution occurs when unrelated species develop similar traits due to adapting to similar environments or ecological niches, which is common when two animals live in the same habitat.
Which of the following options correctly matches the name of the hormone to its site of production in the human body?
Which of the following seeds have remained alive for the longest period?
Phoenix dactylifera, commonly known as date palm seeds, have been reported to remain viable for over 2,000 years, making them the seeds that have remained alive for the longest period compared to the other options.
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.
The incorrect statements are (iii) and (iv) only. T-lymphocytes do not remain active at all times in the body; they are activated in response to specific antigens. Additionally, while T-lymphocytes originate in the bone marrow, they mature in the thymus gland, not in the bone marrow.
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.
The correct option is (ii), (iii) and (iv) only. In smaller patches, the population of large animals declines due to insufficient space and resources. Biodiversity is lower in smaller habitats because they can support fewer species. Additionally, competition with surrounding habitats increases, as species are forced into a smaller area and compete for limited resources.
Identify the option that does not exhibit a parasitic relationship.
The correct answer is 'Female Anopheles' because while it is a blood-feeding mosquito, it is not a parasite in the same way the other options are. Head lice, Cuscuta, and ticks are all true parasites that depend on their hosts for survival, whereas Female Anopheles primarily seek blood meals for reproduction but do not necessarily harm the host in a parasitic sense.
Which of the following is commonly known as baker's yeast?
The correct answer is Saccharomyces cerevisiae, as this species of yeast is widely used in baking due to its ability to ferment sugars, producing carbon dioxide and alcohol, which helps in the rising of dough.
The given schematic illustration shows three steps 'P', 'Q' and 'R' of the I polymerase chain reaction.
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.
The correct statements are (ii) and (iii) only. In the polymerase chain reaction, step 'Q' involves the denaturation of DNA strands which occurs at a high temperature (around 94-98°C), while step 'R' is correctly identified as the extension phase where DNA polymerase synthesizes a new DNA strand. Statement (i) is incorrect because denaturation occurs at high temperature, not low. Statement (iv) is also incorrect because the extension does not involve two sets of primers.
Assertion (A): In humans the genotype with all the dominant alleles (AABBCC) will have the darkest skin color.
Reason (R): In a polygenic trait, phenotype reflects the contribution of each allele.
Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). While the genotype AABBCC is associated with darker skin color due to having all dominant alleles, the reason provided explains the nature of polygenic inheritance, which does not specifically justify why this particular genotype results in the darkest skin color.
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.
Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). The decrease in the number of white-winged moths was primarily due to pollution caused by industrialisation, such as soot from factories, rather than being directly linked to the effects of industrialisation being more prominent in rural areas.
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.
Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A) because the protective environment often limits exposure to common allergens and pathogens, which can lead to a weaker immune system, making children more susceptible to allergies and asthma.
Assertion (A): The Mediterranean orchid Ophrys uses sexual deceit to get pollinated by a species of bee. Reason (R): The female bee changes its colour depending on the temperature of the area.
Assertion (A) is true because the Ophrys orchid mimics the appearance and scent of female bees to attract male bees for pollination. Reason (R) is false because the female bee's coloration does not depend on the temperature of the area. Therefore, the correct answer is: Assertion (A) is true, but Reason (R) is false.
Section C
(a) Explain the process of the development of a male gametophyte in an angiosperm.
(b) Why is it called a male gametophyte ?
(a) Write the first step the primary effluent undergoes when it enters the secondary treatment plant and state the purpose.
(b) What is the level of B.O.D indicative of in the secondary treatment plant ? Mention its significance.
Given below is a food web that involves nine organisms.
(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.
Explain how recombinant DNA technology is used to detect a disease even before any clinical symptom appears.
'Insertion inactivation' is metjod to detect recombinant DNA . Explain the method?
Section D
(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.
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 :
(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.
(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
Section E
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.
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.
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.
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.
Given below is a diagrammatic representation of a human ovum.
(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?
(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.
Other Years — BIOLOGY