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Biology · 2020 · Set 57/1/1

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

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

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

This paper has 5 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 57/1/1

Series/Set: 57/1/1Roll 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.
Meselson and Stahl carried out centrifugation in CsCl2 density gradient to separate : (A) DNA from RNA (B) DNA from protein (C) The normal DNA from 15N-DNA (D) DNA from tRNA
[1]
Q2.
Self-pollination is fully ensured if (A) the flower is bisexual. (B) the style is longer than the filament. (C) the flower is cleistogamous. (D) the time of pistil and anther maturity is different.
(OR)
Zoospores are the reproductive units to carry asexual reproduction in (A) Chlamydomonas (B) Spirogyra (C) Yeast (D) Rhizopus
⚠ This question is not in the current syllabus — Reproduction in Organisms (removed 2023-24)
[1]
Q3.
Micropropagation can be achieved by (A) Self-pollination (B) Asexual reproduction (C) Tissue culture (D) Vegetative propagation
(OR)
The microbes commonly used in kitchens are (A) Lactobacillus and Yeast (B) Penicillium and Yeast (C) Microspora and E. coli (D) Rhizopus and Lactobacillus
⚠ This question is not in the current syllabus — Strategies for Enhancement in Food Production (removed 2023-24)
[1]
Q4.
The main barrier that prevents the entry of micro-organisms into our body is (A) Antibodies (B) Macrophages (C) Monocytes (D) Skin
[1]
Q5.
Nematode specific genes were introduced into the tobacco host plant using a vector (A) pBR 322 (B) Plasmid (C) Bacteriophage (D) Agrobacterium
[1]
Page 1 of 5
Section B

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

Q1.
Given below is one of the strands of a DNA segment : 3′ CGTACGTACGTACGTA 5′ (a) Write its complementary strand. (b) Write a possible RNA strand that can be transcribed from the above DNA molecule formed.
[2]
Q2.
Wings of birds and wings of butterflies contribute to locomotion. Explain the type of evolution such organs are a result of.
[2]
Q3.
It is often observed that the chances of a person suffering from measles in his or her lifetime are low if he or she has suffered from the disease in their early childhood. Justify the statement.
[2]
Q4.
List the three hormones produced in women only during pregnancy. What happens to the levels of estrogen and progesterone during pregnancy ?
[2]
Q5.
A student on a field trip suddenly felt breathlessness and started to sneeze very badly. Name this response and explain what it is due to.
[2]
Q6.
With the help of a suitable example, explain how cross-breeding is carried out in developing a new breed in animals.
⚠ This question is not in the current syllabus — Strategies for Enhancement in Food Production (removed 2023-24)
[2]
Q7.
Name the genus of baculovirus that acts as a biological control agent in spite of being a pathogen. Justify by giving three reasons that make it an excellent candidate for the job. OR ‘‘Micro-organisms play an important role for the biological treatment of sewage.’’ Justify.
[2]
Page 2 of 5
Section C

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

Q1.
Draw a schematic transverse section of a mature anther of an angiosperm. Label its epidermis, middle layers, tapetum, endothecium, sporogenous tissue and the connective.
[3]
Q2.
Differentiate between wind pollinated and insect pollinated flowers.
[3]
Q3.
Generally it is observed that human males suffer from hemophilia more than human females, who rarely suffer from it. Explain giving reasons. OR F1 progeny of pea plant bearing violet flowers and snapdragon plant bearing red flowers were selfed to produce their respective F2 progeny. Compare the phenotypes, the genotypes and the pattern of inheritance of their respective F2 progeny.
[3]
Q4.
Explain the changes that milk undergoes when suitable starter/inoculum is added to it. How does the end product formed prove to be beneficial for human health ?
[3]
Q5.
Alien species invasion has been a threat to biodiversity. Justify with the help of a suitable example. List any other three causes responsible for such a loss.
[3]
Q6.
Study the table given below and identify a, b, c, d, e and f : | Crops | Variety | Resistance to disease | | --- | --- | --- | | a | Pusa sadabahar | b | | c | d | White rust | | e | Himgiri | f | OR What is plant breeding ? Explain the two steps involved in classical plant breeding.
⚠ This question is not in the current syllabus — Strategies for Enhancement in Food Production (removed 2023-24)
[3]
Page 3 of 5
Q7.
Explain the three steps carried out in the formation of recombinant DNA using the enzyme EcoRI.
[3]
Q8.
Name any two natural cloning vectors. Give reasons that make them act as cloning vectors. Write the two characteristics the engineered vectors are made to possess.
[3]
Q9.
Explain the difference between commensalism and mutualism types of interactions, with the help of a suitable example of each.
[3]
Section D

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

Q1.
Insulin in the human body is secreted by pancreas as prohormone/proinsulin. The schematic polypeptide structure of proinsulin is given below. This proinsulin needs to undergo processing before it becomes functional in the body. Answer the questions that follow : (a) State the change the proinsulin undergoes at the time of its processing to become functional. (b) Name the technique the American company Eli Lilly used for the commercial production of human insulin. (c) How are the two polypeptides of a functional insulin chemically held together ?
[3]
Q2.
The cytological observations made in a number of insects led to the development of the concept of genetic/chromosomal basis of sex-determination mechanism. Honey bee is an interesting example to study the mechanism of sex-determination. Study the schematic cross between the male and the female honey bees given below and answer the questions that follow : (a) Identify the cell divisions ‘A’ and ‘B’ that lead to gamete formation in female and male honey bees respectively. (b) Name the process ‘C’ that leads to the development of male honey bee (drone).
[3]
Q3.
Study the age pyramids ‘A’, ‘B’ and ‘C’ of the human population given below and answer the questions that follow : (a) Identify pyramids ‘B’ and ‘C’. (b) Write the basis on which the above pyramids are plotted.
[3]
Page 4 of 5
Section E

Long answer · 5 marks each · 3 of 3 shown

Q1.
(a) IVF is a very popular method these days that is helping childless couples to bear a child. Describe the different steps that are carried out in this technique. (b) Would you consider Gamete Intrafallopian Transfer (GIFT) as an IVF ? Give a reason in support of your answer. OR (a) Draw a sectional view of a human ovary and label primary follicle, tertiary follicle, Graafian follicle and corpus luteum in it. (b) Name the gonadotropins and explain their role in oogenesis and the release of ova.
[5]
Q2.
Describe the experiment carried out by Hershey and Chase. Write the conclusion they arrived at. OR (a) Describe the observations made on collection of white winged moths and dark winged moths in England between the years 1850 and 1920. What did these observations lead to ? (b) How is the use of herbicides, pesticides and antibiotics by humans for various purposes, comparable with the observations made on moths in the above question ? What is this type of phenomenon called ?
[5]
Q3.
Describe the model of phosphorus cycle in the terrestrial ecosystem. OR Describe the DDT biomagnification occurring in an aquatic food chain. State the negative effects the process has on the organisms at the last trophic level of the food chain.
⚠ This question is not in the current syllabus — Environmental Issues / Ecosystem - nutrient cycling (removed 2023-24)
[5]
Page 5 of 5