List of top Questions asked in CBSE CLASS XII

Study the following cases :

Case I : A person bitten by a rabid dog is immediately given an injection of antitoxin for rabies.

Case II : A child is given rabies vaccine as a preventive measure.

(a) Identify the type of immunity provided in both the cases.

(b) Differentiate between the two types of immunity.

(c) What is a vaccine ? How does it help in preventing a disease ?

A gene having non-coding introns and coding exons is known as :

(i) Rearrange the following in correct order of their appearance on Earth between 2 million years and 40,000 years ago : Homo Neanderthalensis, Australopithecus, Homo erectus, Homo habilis

(ii) Which one of the above :

(I) had the largest brain size ?

(II) ate fruits ?

A child is born with a genetic disorder due to the deletion of a gene.

(a) Name such a gene studied by you. Explain how gene therapy can help in treating such a condition.

(b) Mention one challenge associated with this therapy.

Assertion (A) : Net Primary Productivity (NPP) is always less than Gross Primary Productivity (GPP).

Reason (R) : A portion of Gross Primary Productivity (GPP) is used by plants for respiration.

(i) What is natural selection ?

(ii) Explain the type of natural selection that promotes evolutionary change. Give an example.

What does I in restriction enzyme Hind \( \mathrm{S_2} \)I indicate?

What would be the minimum possibility of a dominant trait being expressed in an offspring after a monohybrid test cross ?

Match the items given in Column I with Column II and select the correct option.

Which of the following is a carrier for the disease Amoebiasis?

In a human, the average gene consists of ______ (i) bases and the largest known human gene contains ______ (ii) bases.

Select the correct option to fill in the blanks (i) and (ii):

(i) What are multiple alleles? How do they differ from simple dominant-recessive allele pairs?

(ii) Explain the concept of multiple alleles with the help of a human trait studied by you.

(iii) Mention all possible genotypes with their corresponding phenotypes of the human trait as explained by you.

(iv) Comment on the type of inheritance pattern involved in the example explained by you.

(c) To which class of compounds does nicotine belong? Name one other drug from the same class.

The following questions are based on the classic experiment conducted by Hershey and Chase.

(i) Why were bacteriophages chosen by the scientists?

(ii) Name the radioactive isotopes used and state the reason for using them.

(iii) Describe the steps of the experiment.

(iv) Why is this experiment considered a major breakthrough in the field of molecular biology?

(b) How does cigarette smoking result in high blood pressure and increase in heart rate?

(a) (ii) How will this affect the concentration of carbon monoxide and haem-bound oxygen at 10 minutes?

(a) Who discovered Penicillin and how? Explain.

(b) Why is this discovery considered accidental?

(c) In what way did it prove to be a "milestone" in the field of medicine?

A patient reports a high fever, chills and sweating. His blood shows the presence of a toxic substance.

(i) Identify the disease and the causative organism.

(ii) Explain why this disease shows recurring pattern of fever.

State any four reasons why Mendel succeeded in his genetic hybridisation experiments on garden peas.

A foreign company patented the medicinal use of turmeric already known to Indian households.

(a) Name and define this unethical practice.

(b) What has the Indian Government done to check this ?