CBSE 2025, Set 2 Solutions
CBSE Biology (2025)

The number of autosomes present in a human secondary spermatocyte is:

Given below is a diagram of T.S. of a monocot seed with parts I, II & III labelled:

Choose the option where parts I, II and III are identified correctly.

Given below is a heterogeneous RNA formed during Eukaryotic transcription:

How many introns and exons respectively are present in the hnRNA?

If Meselson and Stahl's experiment is continued for 80 minutes (till III generation) then what would be the ratio of DNA containing $N^{15}/N^{15}$ : $N^{15}/N^{14}$ : $N^{14}/N^{14}$ in the medium?

A child with blood group A has a father with blood group B and a mother with blood group AB. Choose the option that gives the correct genotypes of father, mother and the child:

Which one of the following options shows the correct evolutionary order of the plants mentioned below? (i) Ferns (ii) Ginkgo (iii) Zosterophyllum (iv) Gnetales

Study the items of Column-I and those of Column-II:

Choose the option that correctly matches the items of Column-I with those of Column-II:

In a pedigree chart, a square connected to a circle with a double horizontal line represents:

The foetus receives some antibodies from their mother through the placenta during pregnancy. Choose the correct option that shows the type of immunity developed in the foetus.

A diploid organism is heterozygous for three loci, how many types of gametes can be produced by that organism?

During gel electrophoresis migration of DNA fragments leading to their separation takes place on the agarose gel. Choose the correct option:

Identify the organism whose product has been commercialised as a blood cholesterol lowering agent.

Assertion (A): XX-XY type of sex-determination mechanism is an example of male heterogamety. Reason (R): In birds male heterogamety is observed as males produce two different types of gametes.

Select the correct option:

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

Select the correct option:

Assertion (A): Secondary immune response is quicker and stronger than the primary immune response. Reason (R): Our body appears to have the memory of the first encounter therefore response to the subsequent encounter with the same pathogen is quick.

Select the correct option:

Assertion (A): A patient of ADA-deficiency requires periodic or repeated infusion of genetically-engineered lymphocytes. Reason (R): Lymphocytes are not immortal, but have life span.

Select the correct option:

Study the graph showing Ovarian Hormone levels during the menstrual cycle. Identify the hormones 'P' and 'Q' labelled in the diagram.

Study the graph showing Ovarian Hormone levels. Specify the primary source of the hormones 'P' (Estrogen) and 'Q' (Progesterone) marked in the diagram.

Study the graph showing Pituitary Hormone levels during the menstrual cycle. Identify the hormones 'P' and 'Q' labelled in the diagram.

Study the graph showing Pituitary Hormone levels. Write down the role of hormone 'P' (Luteinizing Hormone) in both males and females.

Write the names of two closely linked genes that control $\alpha$-thalassemia.

Differentiate between thalassemia and sickle cell anaemia on the basis of their effect on the globin molecule of Haemoglobin.

Describe any two situations where a medical doctor would recommend the injection of pre-formed antibodies (antitoxins) into the body of a patient.

The symptoms of malaria do not appear immediately after the entry of sporozoites into the human body when bitten by a female Anopheles mosquito. Explain why it happens.

Observe the given sequence of nitrogenous bases on a DNA fragment:

$5^{\prime}\text{-C A G A A T T C T T A-}3^{\prime}$ $3^{\prime}\text{-G T C T T A A G A A T-}5^{\prime}$

Name the restriction enzyme which can recognise this DNA sequence.

Observe the given sequence of nitrogenous bases on a DNA fragment:

$5^{\prime}\text{-C A G A A T T C T T A-}3^{\prime}$ $3^{\prime}\text{-G T C T T A A G A A T-}5^{\prime}$

Write the sequence after the restriction enzyme EcoRI cuts the palindrome.

Why are the ends generated after digestion by a restriction enzyme called 'Sticky Ends'?

Construct a pyramid of biomass starting with phytoplankton, label its three trophic levels. Is the pyramid upright or inverted? Justify your answer.

Draw a pyramid of number where a large population of insects feed upon a very big tree. The insects in turn, are eaten by small birds which in turn are fed upon by big birds.

A bilobed dithecous anther has 200 microspore mother cells per microsporangium. How many male gametophytes can be produced by this anther?

Write the composition of the intine and exine layers of a pollen grain.

Abbreviations used for the different modes of assisted reproductive technology are given below. Expand the abbreviations: (i) ZIFT (ii) ICSI (iii) IUT (iv) GIFT

Why is there a statutory ban on Amniocentesis? Give at least two reasons.

Using a Punnett square, work out the distribution of an autosomal phenotypic feature in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.

How does the process of Natural Selection affect Hardy-Weinberg equilibrium? Explain with the help of graphs.

Samples of blood and urine of a sportsperson are collected before any sports event for drug tests. Why is there a need to conduct such tests?

Samples of blood and urine of a sportsperson are collected before any sports event for drug tests. Name the drugs the authorities usually look for.

Samples of blood and urine of a sportsperson are collected before any sports event for drug tests. Write the generic names of two plants from which commonly tested illicit drugs are obtained.

The insulin synthesised in our body is different from that synthesised by Eli Lilly company using recombinant DNA technology. Differentiate between them.

Why is the insulin extracted from an animal source not in use these days?

Draw a graph for a population whose population density has reached the carrying capacity.

Out of the two population growth curves, which one is considered more realistic for most populations? Why?

Draw a growth curve where resources are not limiting for the growth of a population and give its equation.

Name the two types of specialised cells which carry out the primary and secondary immune response in the human body.

Why is the antibody-mediated immunity also called a humoral immune response?

Organ transplants are often rejected if not taken from suitable compatible persons. (i) Mention the characteristic of our immune system that is responsible for the graft rejection. (ii) Name the type of immune response and the cell involved in it.

How is active immunity different from passive immunity?

Study the complete transcription unit given below:

Name the main enzyme involved in the process of transcription.

Study the complete transcription unit given below:

Identify the coding strand and template strand of DNA in the transcription unit.

Study the complete transcription unit given below:

Identify (C) and (D) in the diagram, and mention their significance in the process of transcription.

Describe the physical location of the Promoter (C) and Terminator (D) in a transcription unit.

Draw a diagrammatic sectional view of a human seminiferous tubule (enlarged) and label the following: (a) Cell that undergoes spermiogenesis. (b) Cell that nourishes male gametes. (c) Cell which undergoes meiosis I and meiosis II.

State what is seminal plasma. Mention two constituents of seminal plasma. How is it different from semen?

Mention the precise event that induces the completion of the meiotic division of the secondary oocyte in humans.

Trace the journey of the zygote until its implantation inside the uterus.

Explain how a bacterial cell is made 'competent' to take up recombinant DNA from the surrounding medium.

Explain the steps of amplification of gene of interest using the PCR technique.

What are transgenic animals?

Why are transgenic animals being produced? Explain any four reasons for their creation.

Explain, giving three specific reasons, why the tropical latitudes show the greatest levels of species diversity compared to temperate regions.

Draw a graph showing the species-area relationship. Name the naturalist who studied such a relationship and write the observation made by him.

The world is facing an accelerated rate of species extinctions due to human activities. Explain any three major causes (The Evil Quartet) of biodiversity losses.

Describe the 'Ex situ' approach for conserving biodiversity. Give any two examples of this approach.