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Biology · 2020 · Set 57/3/1

CBSE Class 12 Biology 2020 — Set 57/3/1

CBSE Class XII Board 2020 · Set 57/3/1

Real board examination⚠ Old pattern · pre-2020 syllabus
Sets

This paper has 6 questions on a topic removed in CBSE’s 2023-24 syllabus update (each marked Not in syllabus). It’s kept for historical accuracy — the exam really asked it that year — but isn’t in the current syllabus and doesn’t count toward a concept’s importance. Switch to to focus on what’s still examinable.

About this paper

The real Class-12 board examination held in 2020. Every question below is solved the concept-first way. Sample papers are labelled honestly — never shown as a past exam.

Total marks
70
Questions
27
Duration
180 min
Sections
5

The marks / questions / duration above are the official exam pattern. We currently have 27 of this paper’s questions (100% of the full paper), with 27 fully solved. Questions we couldn’t yet extract or verify are held — never shown as complete.

Sections & marks

SectionTypeQuestionsMarks eachTotal
ASection AMCQ515
BSection BShort answer I7214
CSection CShort answer II9327
DSection DShort answer III339
ESection ELong answer3515
Total2770

The question paper

The questions we hold for this paper, laid out by section. Solutions are on the Answers tab.

Board Examination

Biology

CBSE Class XII Board 2020 · Set 57/3/1

Series/Set: 57/3/1Roll No. ________
Time Allowed: 3 hoursMaximum Marks: 70

General Instructions

  1. This question paper contains 27 questions divided into 5 sections — A, B, C, D, E.
  2. Section A comprises 5 questions of 1 mark each (MCQ).
  3. Section B comprises 7 questions of 2 marks each (Short answer I).
  4. Section C comprises 9 questions of 3 marks each (Short answer II).
  5. Section D comprises 3 questions of 3 marks each (Short answer III).
  6. Section E comprises 3 questions of 5 marks each (Long answer).

Above is the official exam pattern. The questions printed below are those we currently hold for this paper.

Section A

MCQ · 1 mark each · 5 of 5 shown

Q1.
Introduction of an alien DNA into a plant host cell is achieved by making them (A) Competent with bivalent ions (B) Using microinjections (C) Using gene gun (D) Using lysozymes and chitinase
[1]
Q2.
One of the ex situ conservation methods for endangered species is (A) Biosphere reserves (B) National parks (C) Cryopreservation (D) Wildlife sanctuaries
(OR)
Ozone gas is continuously formed in the stratosphere by (A) Action of UV rays on nascent oxygen (B) Reaction of oxygen with water vapour (C) Action of UV rays on molecular oxygen (D) Action of UV rays on water vapour
⚠ This question is not in the current syllabus — Environmental Issues (removed 2023-24)
[1]
Q3.
Intense lactation in mothers acts as a natural contraceptive due to the (A) Suppression of gonadotropins (B) Hypersecretion of gonadotropins (C) Suppression of gametic transport (D) Suppression of fertilization
[1]
Q4.
The principle of vaccination is based on the property of (A) Specificity (B) Diversity (C) Memory (D) Discrimination between ‘self’ and ‘non-self’
(OR)
Opioids act as (A) Depressants (B) Pain killers (C) Euphoria providers (D) Stimulants
[1]
Q5.
Nematode specific genes were introduced into the tobacco host plant by using the vector (A) Plasmid (B) Bacteriophage (C) pBR 322 (D) Agrobacterium
[1]
Page 1 of 5
Section B

Short answer I · 2 marks each · 7 of 7 shown

Q1.
Spirulina is a rich source of proteins. Mention the two ways by which large scale culturing of these microbes is possible.
⚠ This question is not in the current syllabus — Strategies for Enhancement in Food Production (removed 2023-24)
[2]
Q2.
How does EcoRI specifically act on DNA molecule ? Explain.
[2]
Q3.
(a) Explain the cause responsible in a human to have sex chromosomes as ‘XXY’ instead of ‘XX’ or ‘XY’. (b) List any two ways such individuals are different from the normal being.
[2]
Q4.
Name and explain the technique that can be used in developing improved crop varieties in plants bearing female flowers only. OR When are the non-flowering plants said to be homothallic and monoecious; and heterothallic and dioecious ? Give an example of each.
⚠ This question is not in the current syllabus — Reproduction in Organisms (removed 2023-24)
[2]
Q5.
Mention the kind of interaction mycorrhizae exhibit. How is Glomus in mycorrhizal association beneficial to the plants ?
[2]
Q6.
Given below is the segment of a DNA strand. Write its complementary strand and the RNA strand that can be transcribed from the DNA molecule formed. 5 TAC CGT GAC GTC 3
[2]
Q7.
Name the type of Ecological Pyramid that can exist as upright as well as inverted. Explain how does it happen.
[2]
Page 2 of 5
Section C

Short answer II · 3 marks each · 9 of 9 shown

Q1.
‘‘Cotton bollworms enjoy feeding on cotton plants, but get killed when feed on Bt cotton plant.’’ Justify the statement. OR (a) Mention the cause of ADA deficiency in humans. (b) How is gene therapy carried out to treat the patients suffering from this disease ? (c) State the possibility of a permanent cure of this disease.
[3]
Q2.
(a) Differentiate between Intrauterine insemination and Intrauterine transfer. (b) Mention one positive and one negative application of amniocentesis.
[3]
Q3.
Explain the solutions found by Ahmed Khan, a Bengaluru based plastic sack manufacturer, after realising the problems created by plastic wastes.
⚠ This question is not in the current syllabus — Environmental Issues (removed 2023-24)
[3]
Q4.
Mention the chemical nature of an antibody and name the type of cells they are produced by. Write the difference between active and passive immune responses on the basis of antibodies. OR Name the cells that act as HIV factory in humans when infected by HIV. Explain the events that occur in these infected cells.
[3]
Q5.
(a) Why is the collection of white winged moths and dark winged moths made in England between 1850 – 1920 considered a good example of natural selection ? (b) ‘‘Evolution is based on chance events in nature and chance mutations in organisms.’’ Justify the statement.
[3]
Q6.
(a) Compare the mechanism of sex determination in humans with that of honey bees, with respect to chromosome number. (b) How is the gamete formation comparable in the above two cases ?
[3]
Page 3 of 5
Q7.
Differentiate between the pattern of inheritance in humans of the blood diseases, haemophilia and thalassemia.
[3]
Q8.
Identify i, ii, iii, iv, v and vi in the following table : | No. | Organism | Bioactive molecules | Use | | --- | --- | --- | --- | | 1 | Monascus purpureus | i | ii | | 2 | iii | iv | Antibiotic | | 3 | v | Cyclosporin A | vi |
[3]
Q9.
(a) Write the scientific name of methanogen bacteria. Where are these bacteria generally found ? Explain their role in biogas production. (b) Name the components of biogas.
[3]
Section D

Short answer III · 3 marks each · 3 of 3 shown

Q1.
Given below is the diagram representing the observations made for separating DNA fragments by Gel electrophoresis technique. Observe the illustration and answer the questions that follow : (a) Why are the DNA fragments seen to be moving in the direction A → B ? (b) Write the medium used on which DNA fragments separate. (c) Mention how the separated DNA fragments can be visualised for further technical use.
[3]
Q2.
Study the transverse section of human ovary given below and answer the questions that follow : (a) Name the hormone that helps in the growth of A → B → C. (b) Name the hormone secreted by A and B. (c) State the role of the hormone produced by D.
[3]
Q3.
Indiscriminate use of chemicals, pesticides and weedicides by humans are polluting our water bodies, which in turn are harming the living organisms. Study the flow chart and answer the questions based on it. (a) Why does the concentration of DDT seem to be considerably high in the top consumer ? (b) How would the organisms at the highest level be affected ? (c) Name the phenomenon observed.
⚠ This question is not in the current syllabus — Environmental Issues (removed 2023-24)
[3]
Page 4 of 5
Section E

Long answer · 5 marks each · 3 of 3 shown

Q1.
(a) According to ecologists, tropical regions in the world account for greater biological diversity. Justify. (b) Why are habitat loss and alien species invasion considered as the causes of biodiversity loss ? Explain with the help of an example of each. OR (a) What is an ecological succession ? (b) Differentiate between primary and secondary succession. Why is secondary succession faster than primary succession ? Explain with suitable examples. (c) What are pioneer species ? Give examples of pioneer species in Xerarch and Hydrarch successions respectively.
⚠ This question is not in the current syllabus — Ecosystem — ecological succession (removed 2023-24)
[5]
Q2.
(a) Name the type of DNA that forms the basis of DNA fingerprinting and mention two features of this DNA. (b) Write the steps carried out in the process of DNA fingerprinting technique, and mention its application. OR Explain the role of different genes in a lac operon, when in a ‘Switched On’ state.
[5]
Q3.
(a) Draw a diagram of a fully developed embryo sac of an angiosperm. Label its chalazal end and any other five parts within the embryo sac. (b) Why does the development of an endosperm precede that of the embryo in angiosperm ? (c) Number of chromosomes in an onion plant cell is 16. Name the cells of the embryo sac having 16 and 24 chromosomes formed after fertilisation. OR Describe the events that occur after fertilisation of an ovum till implantation in a human female.
[5]
Page 5 of 5