List of top Questions asked in CBSE CLASS XII

Assertion (A): Fossils provide direct evidence for evolution.

Reason (R): Fossils help to trace evolutionary relationships among organisms over time.

Which one of the following evidences does not support Darwin's theory of natural selection ?

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

Interferons are most effective in making non-infected cells resistant against the spread of which of the following diseases ?

Perisperm present in seed of black pepper is remnant of

Give the schematic representation of oogenesis in human female. Indicate chromosome number also.

Given below are certain situations related to birth control. Analyse each situation carefully and suggest appropriate contraceptive method that could be used. Also explain its mode of action.

Situation 1 - To prevent entry of sperm into cervix.

Situation 2 - Devices that are inserted by doctors or expert nurses in the vagina.

Situation 3 - Effective emergency contraceptive.

Situation 4 - Permanent method for male partner.

Situation 5 - Surgical method in female to prevent pregnancy.

In angiosperms, the female gametophyte develops from a single cell of megasporangium.

(i) Name that cell of megasporangium and describe the sequential changes it undergoes to form a mature female gametophyte.

(ii) Draw a well labelled diagram of mature female gametophyte. Label any four parts.

Write the importance of following in biotechnology :

(a) Ori (Origin of Replication)

(b) Enzyme Polymerase used in Polymerase Chain Reaction

Name the muscular and glandular layers of female uterus. Mention one function of each.

(a) What is the role of LAB (Lactic Acid Bacteria) in preparation of curd ?

(b) Mention two health benefits of consuming curd.

Assertion (A) : When we see stars, we are apparently peeping into the past.

Reason (R) : What we see today is an object whose emitted light started its journey millions of years back reaching our eyes now.

(i) Why are STI (Sexually Transmitted Infections) not detected in time ? (2 pts.)

(ii) Write two complications caused in later stages.

Exploration of molecular, genetic and species level diversity for gaining products of economic importance is called

Which one of the following is not a component required for Polymerase Chain Reaction (PCR) ?

The features of some structures of human male reproductive system are given below. Choose the correct option that matches the features with the structures.

(i) It opens into the Vasa efferentia through rete testis.

(ii) It carries semen as well as urine.

(iii) It maintains temperature (2 - 2.5\( ^{\circ}\mathrm{C} \)) lower than body temperature for sperm formation.

(iv) It leads to vas deferens that ascends to the abdomen.

Which of the following is not a component of detritus food chain ?

Messelson and Stahl's experiment carried out centrifugation in \( \mathrm{CsCl_2} \) density gradient to separate :

Microbes commonly used in kitchen are

(i) Name the protozoan species that is responsible for causing the most serious and even fatal malarial disease.

(ii) Name the host in which the parasite completes its sexual stages and explain the changes taking place.

(iii) How does the parasite damage the human body after entering the blood stream ?

(iv) Suggest two effective preventive measures to control the spread of this disease in endemic regions.

(i) Watson and Crick's discovery of double helical structure was based on which two findings. Also mention the name of the scientists associated with these findings.

(ii) Write down the salient features of double helix structure of DNA (any three points).