List of top Questions asked in CBSE CLASS XII

Assertion (A) : DNA Ligase is used to join DNA fragments.

Reason (R) : It catalyses the formation of glycosidic bonds between nucleotides.

Assertion (A) : Microbes are used for commercial production of alcohol and beverages.

Reason (R) : Yeast converts glucose into ethanol and carbon dioxide during fermentation.

Assertion (A) : Apomixis leads to production of genetically identical off-springs.

Reason (R) : Apomixis involves fertilization between two genetically similar plants.

Genetically modified tobacco plants were produced using Agrobacterium vectors. Which property of Agrobacterium helps in carrying nematode specific genes into the host plant ?

Which of the following is used to visualize DNA bands under UV light after gel electrophoresis ?

What is the role of histamine released by mast cells ?

A bacterium having radioactive thymidine in its DNA is allowed to multiply in a medium having non-radioactive thymidine for two generations. What percentage of bacteria will have radioactive thymidine in its DNA ?

How many of the following features are related to Nirodh - a popular brand of condoms ?

(i) Prevention of sexually transmitted infections.

(ii) Phagocytosis of sperms.

(iii) Male contraceptive device.

(iv) Acts as chemical barrier.

(v) Physiological changes in cervical mucus.

What could be the reason of extinction of Abingdon Tortoise from Galapagos Islands ?

What conclusion can be drawn if the forelimbs of an aquatic animal and a terrestrial animal have similar anatomical structure ?

In a dihybrid cross, 2400 individuals are produced in \( \mathrm{F_2} \) generation. Approximately how many will be phenotypically similar to parents ?

Select the correct option :

To separate repetitive DNA from bulk genomic DNA, which of the following method is used ?

(i) Differentiate between Mendelian and Chromosomal disorders.

(ii) Which disorder is known as "Inborn Error of Metabolism" ? Mention its cause and any one symptom. Name the harmful compounds formed.

Describe how the lac operon operates both in the presence and absence of an inducer in E.coli.

(i) What is primary productivity of an ecosystem and how is it expressed ?

(ii) Explain the equation given below :

NPP = GPP - R

Biodiversity conservation is crucial for maintaining ecological balance and ensuring the survival of future generations.

Describe four advanced ex-situ methods used for conservation of biodiversity.

Write any two advantages of producing plants by micro-propagation.

What is adaptive radiation ? Give one example from any habitat.

Suggest and describe a technique through which a healthy sugarcane plant can be obtained from virus infected sugarcane plant.

Mendel published his work on inheritance in 1865, but it remained unnoticed for over three decades.

State the reasons why his work was not recognised during his life time. (4 points)

A DNA molecule is 140 base pairs long. It has 20% thymine. How many guanine bases are present in the molecule ?

Expression of a particular gene helps to identify transformants. What is this gene known as ?