List of top Biology Questions asked in CBSE CLASS XII

The following information is about drugs and tobacco. Select the correct statement from the options given below.
Identify the incorrect statement regarding PCR.

Answer the following questions:

  • [(i)] Describe the population growth curve applicable in a population of any species in nature that has unlimited resources at its disposal.
  • [(ii)] Explain the equation of this growth curve.
  • [(iii)] Name the growth curve and depict a graphical plot for this type of population growth.
  • [(i)] Explain the conclusion drawn by Alexander von Humboldt during his extensive explorations in the wilderness of South American jungles.
  • [(ii)] Give the equation of the Species-Area relationship.
  • [(iii)] Draw a graphical representation of the relation between species richness and area for a wide variety of taxa such as birds, bats, etc.
Assertion (A): Mode of action of pills and implants/injectables is similar.
Reason (R): The effective period of pills is much longer as compared to implants/injectables.

Student to attempt either option (A) or (B):
(A) Explain what is meant by the term amniocentesis. How is this technique misused in India? 
OR 
(B) Name any two VDs which might occur in a human female. State any two complications in a female if it is left untreated.

Assertion (A): To generate only a part of the plant from a cell is totipotency.
Reason (R): Suitable special nutrient media and sterile conditions are required in in vitro conditions for the division of cells in explants.
Name one commonly occurring genetic disorder in humans which is caused due to monosomy (one chromosome less than the normal number of chromosomes) of sex chromosome. Give its two symptoms.

Answer the following questions:

  • Explain how the process of RNA interference technology is used effectively to prevent infestation of the roots of tobacco plant by the nematode Meloidogyne incognita.
    OR
  • Explain how more than a billion copies of a fragment of DNA are formed using the technique of PCR.

Student to attempt either option (A) or (B):
(A) Explain how the interaction between a fig tree and its tight one-to-one relationship with the pollinator species of wasp is one of the best examples of mutualism. 
OR 
(B) Correctly depict (also indicate the trophic level) and describe the ecological pyramid of number with 32 birds dependent on 20 insects feeding on one banyan tree.

Student to attempt either option (A) or (B):
(A) Give an account of the generalised structure of an antibody molecule produced by B-lymphocytes in response to the pathogen. 
OR 
(B) Other than public awareness and counselling, enlist four measures taken up by NACO, WHO and other NGOs to prevent the spread of HIV infection in the society.

Large scale industrial production of streptokinase for human welfare is done using the microbe:
Isolation of DNA from a plant cell can be achieved by using:
In a pea plant (Pisum sativum), green pod colour is dominant over yellow pod colour. The expected ratio of the phenotypes of the offsprings (F$_1$) in a cross between parents with heterozygous green pod colour and homozygous yellow pod will be:
AGGTATCGCAT is a sequence from the coding strand of a gene. What will be the corresponding sequence of the transcribed mRNA?
Removal of RNA polymerase-III from nucleoplasm of a eukaryotic cell will affect the transcription of which of the following?
Select the following statements that are true for insect pollinated flowers from the given options.
  • Majority of these flowers are large, colourful and rich in nectar.
  • Nectars and seeds are usual floral rewards to attract insects for pollination.
  • Pollen grains of these flowers are generally mucilaginous so as to stick to the body of the insects.
  • A foul odour is emitted by some flowers to attract flies and beetles.
Choose the correct answer:
The approach used in HGP of identifying all the genes that are expressed as RNA is referred to as:

Study the pedigree chart of a family showing the inheritance of myotonic dystrophy:

The trait under study is:

Given below are few statements with reference to the major events in the menstrual cycle of a human female:
  • During the follicular phase, the primary follicles grow to become a Graafian follicle.
  • Gonadotropins FSH and progesterone stimulate follicular development during the follicular phase.
  • LH surge induces rupture of Graafian follicle thereby releasing the corpus luteum.
  • Progesterone released by corpus luteum is essential for maintenance of endometrium.
  • Both LH and progesterone attain a peak level in the middle of the cycle.
Choose the option with all true statements from the given options:
The large bean-shaped organ acting as a filter of the blood in humans is:
In E. coli, a DNA sequence that specifies where RNA polymerase will bind and initiate transcription of a gene is:

Regulation of lac operon by repressor is referred to as:

Explain how the addition of lactose in the medium regulates the switching on of the lac operon in bacteria.

Read the following passage and answer the questions that follow. According to evolutionary theory, every evolutionary change involves the substitution of a new gene for the old one and the new allele arises from the old one. Continuous accumulation of changes in the DNA coding for proteins leads to evolutionary differences. The chemical composition of DNA is basically the same in all living beings, except for differences in the sequence of nitrogenous bases. Given below are percentage relative similarities between human DNA and DNA of other vertebrates:

(a) What is the term used for the substitution of a new gene for the old one and the new allele arising from the old one during evolutionary process?

(b) Which one of the following holds true for the data provided in the above table?

  • [(A)] Greater the evolutionary distance, greater are the differences in the nitrogenous bases.
  • [(B)] Lesser the evolutionary distance, greater are the differences in the nitrogenous bases.
  • [(C)] Greater the evolutionary distance, lesser are the differences in the nitrogenous bases.
  • [(D)] Lesser the evolutionary distance, lesser are the differences in the nitrogenous bases.

(c) [(i)] To which category of evolution (divergent or convergent) does the following relationship belong? Justify your answer.
Human and Rhesus Monkey 
OR

[(ii)] Differentiate between Convergent and Divergent evolution.

Answer the following questions:
    • [(i)] Describe the Species-Area relationship as observed by Alexander von Humboldt, for a wide variety of taxa in nature.
    • [(ii)] Draw the graph showing Species-Area relationship for \( S = CA^Z \). What is the significance of ‘\( Z \)’ in Species-Area relationship?
    OR
    • [(i)] Describe the logistic population growth curve with the help of a suitable graphical representation.
    • [(ii)] Write the equation of Verhulst-Pearl logistic growth curve and explain what ‘\( K \)’ and ‘\( r \)’ suggest in the given equation.