KENDRIYA VIDYALAYA B.S.F DABLA

CLASS XII SC.    II-TERM UNIT TEST

Duration : 90 Mins                     Sub: Biology                 Max Marks : 40

General Instructions:

(i) All questions are compulsory.

(ii) The question paper consists of two sections A and B. Section A contains 6 questions of 5Marks each and Section B is of 10 questions of 1mark each.

Section  A

  1. a) Explain the observations of Meselson and Stahl when :-

(i) they cultured E. coli in a medium containing  15NH4Cl  for a few generations and centrifuged the content.

(ii) they transferred one such bacterium to the normal medium of  NH4Cl.

(b) What does the above experiment prove?

(c) Which is the first genetic material identified?

  1. (i) How and at what stage does Plasmodium enter into a human body?

(ii) With the help of a flow-chart, only show the stages of asexual reproduction in the life cycle of the parasite in the infected human.

(iii) Why does the victim show symptoms of high fever?

  1. Explain Hershey-Chase experiment. What was proved through this experiment?
  2. (a) A true breeding pea plant, homozygous for inflated green pods is crossed with another pea plant with constricted yellow pods (ffgg). What would be the phenotype and genotype of F1 and F2 generations? Give the phenotype ratio of F2 generation.

(b) State the generalisation proposed by Mendel on the basis of the above mentioned cross.

  1. (a)One of the codons on mRNA is AUG. Draw the structure of tRNA adapter molecule for this codon. Explain the uniqueness of this tRNA.

(b) Explain the process of charging of tRNA. Why is it essential in translation?

  1. Study the given pedigree chart and answer the questions that follow:

DIAGRAM IS NOT AVAILABLE

(a) Is the trait recessive or dominant?

(b) Is the trait sex-linked or autosomal?

(c) Give the genotypes of the parents shown in generation I and their third child shown in generation II and the first grandchild shown in generation III.

Section  B

  1. Name the two types of cells in which the HIV multiplies after gaining entry into the human body.
  2. Why do sports persons often fall victim to cocaine addiction?
  3. What is the economic value of Spirulina?
  4. What was the speciality of the milk produced by the transgenic cow Rosie?
  5. How do neutrophils act as a cellular barrier to pathogens in humans?
  6. Suggest any two techniques which can help in early detection of bacterial viral infections much before the symptoms appear in the body.
  7. Name the type of immunity that is present at the time of birth in humans.
  8. Which of the following is the semi-dwarf wheat that is high yielding and disease resistant?

Pusa Shubra,    Kalyan Sona,     Ratna.

  1. Why are the plants produced by rnicropropagation called somaclones?
  2. Name the technique by which healthy plants can be recovered from the diseased plants.