Biology Sample Paper Class 12 CBSE Board Exam 2020

The sample paper is one of the best resources for the student to prepare for the exam. These help the student to get a prior experience before they attempt for the final exam also, they will know if they are prepared for the exam completely or not. They can test their knowledge for all these subjects and get confident about the answer. if any discrepancies occur in the written answer, they can focus more on such a question, so that there are no mistakes happening in the final paper. they can also mark themselves for correct and wrong answers.

Structure of CBSE Class 12th Biology Model Paper 2020

Biology the paper will be of three hours and a total of 70 marks. the paper will consist of 27 questions all divided into five sections.

Section A: Multiple choice questions.

There will be a very multiple choice type question  1 to 5  in this section. each question will have 1 mark.

Section B: Short answer questions.

There will be Short answer questions of 6 to 12, each question will have 2 marks.

Section C: short answer type II questions

There will be short answer type questions of 13 to 21, each question will have 3 marks.

Section D: case-based short answer type question

There will be case-based short answer type question of 22 to 24, each The question will have 3 marks each.

Section E: Long answer type question

There will be also long answer type question of 25 to 27, each The question will have 5 marks each

There is no overall choice in the question paper. However, internal choices are provided in two questions of one mark, one question of two marks, two questions of three marks and all three questions of five marks. An examinee is to attempt any one of the questions out of the two given in the question paper with the same question number.

SECTION – A

1.   Androgens are synthesize by:                                                                

       a.) Sertoli Cells

b.) Leydig cells

c.) Seminal vesicles

d.) Bulbourethral gland

OR

A procedure that finds use in testing for genetic disorders, but is also misused for foeticide is:

a.) Lactational amenorrhea

b.) Amniocentesis

c.) Artificial insemination

d.) Parturition

2.    Transplantation of tissues/organs to save certain patients often fail due to the rejection of such tissues/organs in the patient’s body. Which type of immune response Is it responsible for such rejection?

a.) auto-immune response

b.) humoral immune response

c.) physiological immune response

d.) cell-mediated immune response

OR 

Which of the following are the correct reasons for Rheumatoid arthritis?

   i.) Lymphocytes become more active 

  ii.) Body attacks self cells 

 iii.)  More antibodies are produced in the body

iv.)  The ability to differentiate pathogens or foreign molecules from self cells is lost

Choose the correct answer from the options given below:

 a.) i and ii

 b.) iii and iv

c.) i and iii

d.) ii and iv

3.       Name the enzymes 'P' and 'Q' that carry out the following processes          

a.) Enzyme P-Exonuclease and Enzyme Q-Permease

b.) Enzyme P-Exonuclease and Enzyme Q- Ligase

c.) Enzyme P-Endonuclease and Enzyme Q- Permease

d.) Enzyme P-Endonuclease and Enzyme Q-Ligase

4.   A biotechnologist wanted to create a colony of E.coli possessing the plasmid pBR322, sensitive to Tetracycline. Which one of the following restriction sites would he use to ligate a foreign DNA?

       a.) Sal I

b.) Pvu I

c.) EcoRI

d.) Hind III

5.   Most important cause of biodiversity loss is 

       a.) Overexploitation of economic species

b.) Habitat loss and fragmentation

c.) Invasive species

d.) Breakdown of plant-pollinator relationships

SECTION B

6.   How does an encysted Amoeba reproduce on the return of favorable 2 conditions?

OR

What are gemmules and conidia? Name one organism each in which these are formed?

7.   Name any two copper-related IUD’s. Explain how it acts as a contraceptive?

8.   Why is it not possible to study the inheritance pattern of traits in human beings, the same way as it is done in pea plants? Name the alternate method employed for such an analysis of human traits.

9.  Carefully examine structures A and B of pentose sugar given below. Which one is more reactive? Give reasons.

10.  Name the technology and the procedure involved which can help a scientist recover virus-free sugarcane plants from diseased canes for his crop breeding experiments.

11.  Explain the events that occur in the host cell on the introduction of nematode-resistant gene into the tobacco plant by using Agrobacterium vectors.

12.  Construct a pyramid of biomass starting with phytoplankton. Label three trophic levels. Is the pyramid upright or inverted? Justify your answer.

SECTION C

13.  Draw a well-labeled diagram of L.S of a pistil showing the passage of growing of pollen tube up to its destination.

14.  How does the gain or loss of chromosome(s) take place in humans? Describe one example each of chromosomal disorder along with the symptoms involving an autosome and a sex chromosome.

OR

A small stretch of DNA that codes for a polypeptide is given below

3'--- --- --- --- CAT CAT AGA TGA AAC--- --- --- --- 5'

a.) Which type of mutation could have occurred in each type resulting in the following mistakes during replication of the above original sequence?

 i.       3`… … … …CAT CAT AGA TGA ATC… … …5` ii.       3`… … … …CAT ATA GAT GAA AC… … … 5`

b.) How many amino acids will be translated in each of the above two cases?

15.     “Apomixes is a form of asexual reproduction that mimics sexual reproduction

16.

a.) State the hypothesis which S.L. Miller tried to prove in the laboratory with the help of the set up given above.

b.) Name the organic compound observed by him in the liquid water after running the above experiment.

c.) A scientist simulated a similar setup and added CH4, NH3 and water vapor at 800 ℃. Which important component is missing in his experiment?

17.   a.)                                                                                                           

FILL IN THE BLANKS PROVIDED

Amino acid          Phe      Val

DNA Code in Gene            AAA                             CAC

Codon in mRNA   (i)         (ii)

Anticodon in tRNA           (iii) (iv)

b.) A polypeptide consists of 14 different amino acids.

  i)  How many base pairs must be there in the processed    mRNA that codes for this polypeptide?

      ii) How many different types of tRNA are needed for the          synthesis of this polypeptide?

18.  How can inbreeding be both advantageous and disadvantageous in cattle breeding program? (Mention any two advantages and two disadvantages )

19.  “Specific Bt Toxin gene is incorporated into the cotton plant so as to control the infestation of Bollworm”. Mention the organism from which the gene was isolated and explain its mode of action.

20.  State any two criteria for determining biodiversity hotspots. Name any two hotspots designated in India.

OR

Differentiate between in-situ and ex-situ approaches for conserving biodiversity. Give an example for each.

21.  When the gene product is required in large amounts, so transformed bacteria with the plasmid inside the bacteria are cultured on a large scale in an industrial fermenter which then synthesizes its protein. This product is extracted from the fermenter for commercial use.

       a.) Why is the used medium drained out from one side while fresh medium is added from the other?

b.) List any four optimum conditions for achieving the desired product in a bioreactor.

SECTION D

22.

 With reference to the above schematic diagram of Spermatogenesis (a) and Oogenesis(b), answer the following questions

a.) About 300 million spermatozoa may be present in a human male  ejaculation at one time. Calculate how many spermatocytes will be involved to produce this number of spermatozoa.

b.) How many spermatids will be formed?

c.) How many chromatids are found during Oogenesis in Primary oocyte and First polar body in a human female?

23.   Large quantities of sewage are generated every day in cities and towns, which is treated in Sewage Treatment Plants (STPs) to make it less polluting. Given below is the flow diagram of one of the stages of STP.

Observe the given flow diagram and answer the questions accordingly. 

a.) Why primary effluent is passed into large aeration tanks?

b.)  What is the scientific term used for the sediment formed? Mention its significance.

c.) Explain the final step resulting in the formation of biogas in the large tank before the treated effluent is released into water bodies.

24. 

Observe the diagram of the catalytic converter and answer the questions which follow.

a.) Name any two metals used as a catalyst in the catalytic converter.

b.) Name the gases released after passing the exhaust   hydrocarbons through the catalytic converter.

c.) Which other poisonous gas is missing in the exhaust pollutant of   an automobile in the above diagram?

SECTION E

25.   Certain phenotypes in the human population are spread over a gradient and reflect the contribution of more than two genes. What is the term used for the types of inheritance? Describe it with the help of an example in the human population.

OR

Summarize the process by which the sequence of DNA bases in the Human Genome Project was determined using the method developed by Frederick Sanger. Name a free-living non-pathogenic nematode who’s DNA has been sequenced.

26.     a.) What is mutation breeding? Give an example of a crop and disease to which resistance was induced by mutation.

b.) Differentiate between pisciculture and aquaculture.

                                             OR

a.)  If a patient is advised anti-retroviral drugs, which infection is he suffering from? Name the causative organism.

b.) How do vaccines prevent subsequent microbial infections?

c.) How a cancerous cell differs from the normal cell?

d.) Many microbial pathogens enter the gut of humans along with food. Name the physiological barrier that protects the body from such pathogens.

27.   “Indiscriminate human activities have strengthened the greenhouse effect resulting in Global Warming.” Give the relative contribution of various Green House Gases in the form of a pie chart and explain the fate of the energy of sunlight reaching the earth’s surface contributing to Global Warming.

OR

Given below is a table depicting population interactions between species A and species B.

Type of interaction	Species A	Species B
(a)	(-)	(+)
(b)	(+)	(-)

Name the two types of population interactions (a) and (b) depicted in the above table.

Justify giving three reasons, how the type of interaction (b) is important in an ecological context.