CBSE Half Yearly Sample Paper 2020-21 Biology for class 12


Time: 3:00 hour                                    Sub- Biology                                         M.M.-70

All questions are compulsory.

(Q-1 to Q-8 is of 1 mark each)

  1. How many microspore mother cells would be required to produce 100 pollen grains in a pollen sac? And why?
  2. How do interferons protect us?
  3. Where is acrosome present in human? Write its functions.
  4. Mention the function of trophoblast in human embryo.
  5. Mention the role of codone AUG and UGA during protein synthesis.
  6. Name the cells that nourish the germ cells in the testes.
  7. Differentiate between DNA and RNA.
  8. Expand GIFT and ICSI.


(Q-9 to Q-18 is of 2 marks each)

  1. Why is a person with cuts by any object given Titanus antitoxin?
  2. Name the plant source of Cocain. How does it affect the human body?
  3. Why is ZIFT is a boon to childless couples? Explain the procedure.
  4. List the adaptive features of air pollinated flowers.
  5. Define Lactation.


Differentiate between benign and malignant tumour.

  1. Name the plant source of Ganjha. How does this affect the human?
  2. Where does triple fusion takes place in flowering plants? Why is it so called and mention its significance.
  3. Define the genetic code.
  4. In which organ of female reproductive system are fimbrae present? Write their function.
  5. A woman with blood group O married a man with blood group AB. Show the possible blood groups of the progeny. Mention the genotype of the progeny.


(Q-19 to Q-27 is of 3 marks each)

  1. A girl baby has been reported suffering from Haemophelia. How is it possible? Explain with the help of cross.
  2. Mention the pathogens that causesamoebiosis (dysentry). Give three symptoms and one mode of transmission.
  3. List out the Haploid and Deploid form given below

(a) ovum (b) ovary (c) enther  (d) zygote  (e) sperm   (f) pollen

  1. Describe the process of Megasporogenesisupto 8 nucleate stage in angiosperm plants.
  2. Draw a well labelled diagram of angiospermic ovule.
  3. Trace the events that occur in human body to cause immune deficiency when HIV enters the body.


Explain the sex determination process in human. How it differs from sex determination in insects.

  1. Explain the role of the following in increasing the soil fertility and crop yield.
  • Leguminous plants b-Cyanobacteria c-Mycorrhiza
  1. What is antibody? Draw a labelled diagram of antibody molecule.
  2. The base sequence in one of the strand of DNA is- TGACATGTA-
  • Give base sequence of its complementary strand.
  • How do these base pairs held together in DNA?
  • Explain the base complementarity rule. Name the scientist who frame this rule.


(Q-28 to Q-30 is of 5 marks each)

  1. With the help of Punnet square find the percentage of homozygous tall plant in F2 generation crossing a true tall and dwarf pea plant.
  • Draw a labelled diagram of female reproductive system in human.
  • Draw a double stranded polynucleotide chain with all the four nitrogenous bases. Label its polarity.


Describe the events of spermatogenesis with the help of schematic representation and how it differs from Oogenesis.

  1. Expand the abbreviations given bellow-
  • MALT (b) HIV (c) CMI  (d) NACO  (e) AIDS
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