CBSE EXAMINATION PAPER-2023

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.

The diagram shows the life cycle of a pathogenic protozoan

The diagram shows the life cycle of a pathogenic protozoan.

Choose the set of sex determining chromosomes that indicates the correct sex of the respective organism.

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.

Identify the option that gives the correct type of evolution exhibited by the two animals shown, living in the same habitat in Australia.

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?

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.

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.

Identify the option that does not exhibit a parasitic relationship.

Which of the following is commonly known as baker's yeast?

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.

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.

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.

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.

(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?

(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

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.