CBSE 2025, Set 1 Solutions
CBSE Biology (2025)

A man whose father was colour-blind marries a woman who had a colour-blind mother and normal father. What percentage of male children of this couple will be colour-blind?

GEAC stands for:

Match the items in Column-A with that of Column-B:

Choose the option that matches the items correctly:

The process of mineralization by microorganisms help in the release of:

Transplantation of tissues/organs to some patients often fails due to rejection of such tissues/organs by the body of the patient. Which type of immune response is responsible for such rejections?

Match the following items of Column-I with that of Column-II:

Choose the option that matches correctly:

The diagram given below shows labelling of four parts of a dicot embryo during its development as P, Q, R and S.

Choose the option that indicates correct labelling of P, Q, R and S of the embryo in different stages of its development:

Amplification of gene of interest by using DNA polymerase may go upto:

The sequence of nitrogenous bases in a segment of a coding strand of DNA is $5^{\prime}\text{-AATGCTAGGCAC-}3^{\prime}$. Choose the option that shows the correct sequence of nitrogenous bases in the mRNA transcribed by the DNA.

How many pollen grains and ovules are likely to be formed in the anther and the ovary of an angiosperm bearing 50 microspore mother cells and 50 megaspore mother cells respectively?

Assertion (A): One of the property of genetic code is degeneracy. Reason (R): Some amino acids can be coded by more than one codon.

Select the correct option:

Assertion (A): When the two genes in a dihybrid cross are situated on the same chromosome, the proportion of parental gene combinations is much higher than non-parental type. Reason (R): Higher parental gene combinations can be attributed to crossing over between two genes.

Select the correct option:

How are morphine and heroin related? Mention their effect on the human body.

Study the cross given below:

Identify the abnormalities '1' and '2' in the offsprings of a cross done between a couple.

Based on the cross identifying abnormalities '1' and '2', distinguish between the physical symptoms of these two disorders.

Study the pedigree chart given below, showing the inheritance pattern of blood group in a family:

(a) Give the possible genotypes of individual 1 and 2.

Study the pedigree chart given below, showing the inheritance pattern of blood group in a family:

(b) Which antigen or antigens will be present on the plasma membranes of the R.B.Cs of individuals '5' and '8'?

Write the palindromic nucleotide sequence for following sequence of DNA segment: $5^{\prime}\text{-GAATTC-}3^{\prime}$

Name the restriction endonuclease that recognizes the palindromic sequence $5^{\prime}\text{-GAATTC-}3^{\prime}$.

Study a part of the life cycle of Plasmodium given below:

Name the infective stage of Plasmodium that is stored in the female Anopheles mosquito.

Study a part of the life cycle of Plasmodium given below:

Where does fertilization and development of the parasite take place?

Study a part of the life cycle of Plasmodium given below:

Identify labels P and Q in the given diagram.

Asexual and sexual phases of the life cycle of the Plasmodium take place in two different hosts. Write their names.

"Indiscriminate human activities such as alien species invasion, fragmentation and habitat loss have accelerated the loss of biodiversity." Justify by taking one example for each.

State the importance of the following in the conservation of biodiversity: (i) IUCN Red data list (ii) Hot spots

Study the diagram given below and answer the questions that follow:

Identify the structure shown in the above figure.

Study the diagram given below and answer the questions that follow:

Identify the labels P and Q.

Write the nature of histone proteins found in a nucleosome.

Distinguish between Euchromatin and Heterochromatin.

Shyam and Radha are expecting their first child with Radha being in her second month of pregnancy with no complications. Shyam's family has a history of cystic fibrosis while Radha's family has a history of Down's syndrome, leading to a concern that the baby may have one of these conditions.

Suggest and explain a way of testing if their baby is at risk for any genetic disorders.

Shyam and Radha underwent testing for potential genetic disorders in their unborn baby. In case of the presence of one or both of the abnormalities posing a severe risk to the child and the mother's health, mention one possible option for them to consider. Is that option safe for Radha at her current gestational age (second month)? Justify.

Under what conditions is Medical Termination of Pregnancy (MTP) considered illegal?

Explain the basis on which the gel electrophoresis technique works. Write any two ways the products obtained through this technique can be utilised.

Compare and contrast convergent and divergent evolution.

Study the graphs given below for Case 1 and Case 2 showing different levels of certain hormones:

Which hormone is responsible for the peak "P" observed in Case 1 and Case 2? Write one function of that hormone.

Write changes that take place in the ovary and uterus during the follicular phase of the menstrual cycle.

Study the graphs given below for Case 1 and Case 2 showing different levels of certain hormones:

Name the hormone Q of Case 2. Write one function of hormone Q.

Study the graphs given below for Case 1 and Case 2 showing different levels of certain hormones:

Which structure in the ovary will remain functional in Case 2 (where HCG is present)? How is it formed?

The Monarch butterfly is highly distasteful to its predator because of a special chemical present in its body. How does the butterfly acquire this chemical?

If population density at a time $t+1$ is 800, Emigration = 100, Immigration = 200, Natality = 200 and Mortality = 150, calculate the population density at time $t$ and comment upon the type of age pyramid that will be formed in this case.

What is the difference in a method of measuring population density in an area if there are 200 carrot grass plants to only single huge banyan tree?

Name two methods to measure the population density of tigers.

State what do you understand by "MALT"? Where it is located inside our body?

Explain cytokine barriers in the context of the human immune system.

Name the diagnostic test for AIDS. On what principle does it work?

Bone marrow and thymus play an important role in the human immune system. Explain how they are able to achieve this.

Study the following table and fill 'H', 'I', 'J', 'K', 'L' and 'M' with suitable words:

Why are baculoviruses used as biological control agents?

Distinguish between the two cells enclosed in a mature male gametophyte of an angiosperm.

The given diagram shows three methods of pollen transfer in plants. Examine them carefully and write the technical terms used for pollen transfer methods '1', '2' and '3'.

How do the following plants achieve pollination successfully? (a) Water lily (b) Vallisneria

Write the advantages of pollen transfer via Xenogamy (Cross-pollination).

Given below is the diagram of a human ovum surrounded by a few sperms. Observe the diagram and answer the questions that follow:

Compare the fate of sperms 'P', 'Q' and 'R' shown in the diagram.

Write the role of Zona pellucida in the process of fertilization.

Analyse the cellular changes occurring in the ovum immediately after the entry of the sperm.

How do the acrosome and middle piece of a human sperm play an important role in human fertilization?

Perform a cross between two sickle cell carriers. What ratio is obtained between carrier, disease free and diseased individuals in $F_1$ progeny? Name the nitrogenous base substituted in the haemoglobin molecule in this disease.

Explain the difference in inheritance pattern of flower colour in garden pea plant and snap-dragon plant with the help of monohybrid crosses.

Explain how the lac operon operates in E. coli in the presence of an inducer.

Explain how the lac operon operates in E. coli in the absence of an inducer.