CBSE Board Biology Class XII | Sample Paper -1 |

CBSE Board Biology Class XII | Sample Paper -1 |


Time: 3 hour

Subject- Biology M.M.-80

All questions are compulsory.

Section – A (1 mark each)

  1. Who was the first to suggest that codons are triplet?
  2. Where is sporopollenin found in plants? Give its significance.
  3. Mention one positive and one negative application of amniocentesis.
  4. A hemophilic son was born to normal parents. Give the genotype of the parents.
  5. Give the polarity of the leading and template strands during DNA replication.
  6. Mention the cause of evolution according Hugo –de-vries.
  7. Why an AIDS patient does suffers from many other infections?

Section –B (2 mark each)

  1. The base sequence in one of DNA strand is –


  • Give the base sequence of its complementary strand.
  • How are these base links to the pentose sugar?
  1. Draw a diagram of nucleosome.
  2. Why rhizobium is called symbiotic ? How does it act as bio fertilizer?
  3. Mention the factors responsible for the success of green revolution.
  4. Divergent evolution leads to homologous structures. Explain it with example.


Name four vestigial organs in human and How the support evolution?

  1. Given above is a lac operon in E.coli. What is the significant role of i gene in switching on or off the operon?
i P O Z Y a
  1. Red flower                                         Red flower

Rr                                                         Rr

R       r                                                  R      r

R r
r C D





Write the genotype of A, B, C, D

Write the phenotype of A, B, C, D

  1. Expend ZIFT. Why is it a boon to childless couple? Explain its procedure.
  2. Draw a labelled diagram of an embryosac of angiospermic flower.

Section—C (3 marks each)

  1. What is triple fusion? Where and how does it take place? Name the product of triple fusion.


  1. Write the name and steps A, B, C, D, E, F in the

process given below.




  1. Name the phenomenon that leads to XO disorder in human. How do human with XO Suffer? Explain .


Explain the Mechanism of sex determination in insect like Drossophila.

  1. Why in RNA regarded as the first genetic material?
  2. Write the name, symptoms and causative agents of two helminthic diseases.
  3. State the views of operin and Haldane on evolution. How does Miller’s experiment support their view?
  4. Describe the structure and function of anti body with a labelled diagram.
  5. How does industrial malanism support Darvin’s theory of natural selection? Explain.


Explain pastver’s   experiment criticising spontaneous theory.

  1. Name two diseases each which are transmitted in the following ways.
  • Through contaminated food and water.
  • Through insect vectors.
  • Through air/droplets inhaled.
  1. Draw a brief sketch of biogas plant with complete labelling.

Long answered    —                                                                               3×5=15

  1. Explain the causes, inheritance pattern and symptoms of any two mandalion genetic disorders.
  2. What is semi conservative DNA replication? How was it experimentally proved and by whom?


Write the function of the following –

  • Corpus leutium iii- endometrium                   v- Frimbrae
  • leydig cells           iv- germinal epithelium of testes.
  1. Write short notes on –
  • DNA finger printing ii- codominance


Name any five hybrid varieties of crop plants which have been developed in India.

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