CBSE-2023 PRACTICE PAPER 2
BIOLOGY
Time : 3 hrs Max. Marks : 70
General Instructions
1. All questions are compulsory.
2. The question paper has five sections and 33 questions. All questions are compulsory.
3. Section-A has 16 questions of 1 mark each; Section-B has 5 questions of 2 marks each;
Section-C has 7 questions of 3 marks each; Section-D has 2 case-based questions of 4
marks each and Section—E has 3 questions of 5 marks each.
4. There is no overall choice. However, internal choices have been provided in some questions.
A student has to attempt only one of the alternatives in such questions.
5. Wherever necessary, neat and properly labelled diagrams should be drawn.
Section-A
1. Saheli is a non-steroidal, once a week pill with high contraceptive value. Its mode of action
involves
(a) suppressing the motility of sperms
(b) increasing the hostility of cervix to sperms
(c) inhibiting the oestrogen activity
(d) preventing the implantation of blastocyst in uterus
[1]
2. Given below are four methods of ARTs and their mode of action. Select the correct match.
Methods of ART Modes of action
A. Intra-cytoplasmic sperm 1. External fertilisation followed by embryo
injection transplant in womb
B. Testicular sperm extraction 2, Transfer of zygote into oviducts
C. ZIFT 3. Sperm is injected into the cytoplasm of an ovum
D. IVF 4. Collection of sperm from epididymis or testis
Codes B C D
A
(a) 1 3 2 4
(b) 4 2 1 3
(c) 3 4 2 1
(d) 2 1 4 3
(c) A-3,B-4,C-2,D-1
3. How does the HIV affect the body of a person?
(a) By reducing the number of blood platelets
(b) By reducing the number of WBCs
(c) By increasing the rate of HIV multiplication
(d) By reducing the number of TH cells
[1]
4. A recessive allele in homozygous condition results in dwarfism. Study the two observations
related to this.
(i) In a mainland population, 1 from 1000 individuals has this condition.
(ii) In a tribal population, on nearby island, this condition affects 1 out of 14 individuals. All these
individuals are descendants of 32 migrants from the mainland.
This observation can be related to which of the following phenomenon?
(a) Natural selection (b) Bottle neck effect (c) Founder effect (d) Genetic migration Ans. (c)
Founder effect. [1]
5. The genetic code is defined as the sequence of nitrogenous bases which specifies a
particular amino acid in a polypeptide molecule. Given below are some codons and the amino
acids. Select the correct set of codons and amino acids generated by them.
Genetic Amino acids
codons specified
(a) GUU, GCU Alanine
(b) AUG, ACG Start/Methionine
(c) UUA, UCA Leucine
(d) CGC, AGA Arginine
6. Snake bites are extremely poisonous due to their toxin and can kill a person in absence of
quick reaction. Identify the treatment and the type of immunity generated in patient in
response to it.
Types of immunity
Remedies
generated
(a) Antiserums Artificial active
(b) Toxoids Natural active
Preformed
(c) Artificial passive
antibodies
Inactivated
(d) Natural passive
vaccine
7. Which of the following is a correct combination?
Antibiotics/ Sources Actions
Enzymes
(a) Penicillin P. notatum Antifungal
(b) Statins Monascus perpureus Lowers blood cholesterol
(c) Streptomycin Bacillus polymyxa Eye infections
(d) Ergot Claviceps purpurea Immunosuppressant
[1]
8. The figure below shows the structure of a plasmid.
A foreign DNA was inserted in the lac z gene. The transformants were grown in medium
containing X-gal+ 1 PTG. Select the option which gives correct observation with respect to
transformed cells.
Transformants Types of colonies
(a) Insert within lac z White
(b) Insert outside lacz No colonies
(c) Insert within lac z Blue
(d) Insert outside lac z White
9. A female wasp lays egg in fig fruits, which develops deriving nutrition from its seeds. During
this process, the wasp pollinates the fig inflorescence. This represents a/an
(a) mutualistic association
(b) commensalistic union
(c) antiobiosis
(d) ammensalic interaction
10. On a rotting log, initially the rate of growth of decomposers is very rapid. However, this rate
decline as the utilisation of the available resources increases and no way of replenishment
is present.
In this case, the shape of growth curve would become
(a) J-shaped
(b) Z-shaped
(c) S-shaped
(d) A horizontal straight line
11. Study the pyramid of numbers in an ecosystem.
The most probable observation related to this pyramid is
(a) primary consumers are zooplankton, secondary consumers are insect eating birds
(b) primary producers are phytoplanktons, tertiary consumer is whale/dolphin
(c) This pyramid of number is associated with an aquatic ecosystem
(d) Trees acts as a producer which supports a number of consumers, such as birds
12. The diversity of habitats over the total geographical area is called
(a) β-diversity
(b) α-diversity
(c) y-diversity
(d) 8-diversity
13. Assertion (A) In plants, apomixis is a form of asexual reproduction that mimics sexual
reproduction.
Reason (R) Apomixis involves the production of seeds without the fusion of gametes.
.
14. Assertion (A) Prolonged intraspecific competition causes an increase in the size of the niche
of a population.
Reason (R) In such a population, use of a new type of resource will increase through the
generations.
15. Assertion (A) E. coli having pBR322 with DNA insert at BamHl site cannot grow in medium
containing tetracycline.
Reason (R) Recognition site for BamHl is present in tetB region of pBR322.
16. The diagram given depicts the experiment of Meselson and Stahl.
Study the same and comment upon the appropriateness of the Assertion and Reason.
Assertion (A) Egual amount of light DNA and hybrid DNA was observed in E. coli culture
after two generations.
Reason (R) The generation time of E. coli culture was 40 minutes.
Section-B
17. Gametogenesis is the process by which haploid gametes are formed in male and female
gonads. Given below is a flowchart showing hormonal regulation of the process of
gametogenesis. Observe it carefully and answer the questions that follows.
(i) Identify X and Y in the flowchart. Which process is shown under the hormonal control?
(ii) Explain the function of different hormone indicated by Z.
18. A man with colourblind father marries a woman whose father was also colourblind. What are
the chances that their first born girl child would have colour blindness?
19. Second generation vaccines are safer to use. Comment.
20. In the artificially constructed pBR322 vector,
(i) Why the recombinant molecule will not be formed if the 'P' is missing from the above vector?
(ii) In what way does the absence of R and Q will affect the selection of transformed cells.
Discuss.
Sample Paper 2
21. Given below is a diagrammatic representation of trophic levels in an ecosystem.
4. Tertiary consumer
3. Secondary consumer
2. Primary consumer
1. Primary producers
(i) At level 1,80,000 J of energy is received.
Assuming that draw a food chain in a terrestriai ecosystem depicting the transfer of energy
at all 4 trophic levels.
(ii) A food chain cannot be longer than 4-5 trophic levels. Justify the statement giving reason.
Or
(i) Draw a pyramid of number where a tree is supporting a large number of birds,
which inturn are consumed by one or two hawks in the area.
(ii) If the pyramid of energy is drawn for same situation, what will be its shape? Justify your
answer.
Section-C
22. Explain the hormonal control of spermatogenesis in humans regulated by following
hormones.
(i) FSH
(ii) LH
23. Give reason for the following.
(i) Geitonogamy is functionally a cross-pollination, but genetically autogamy.
(ii) Flowering plants need to develop outbreeding devices.
(iii) Banana is parthenocarpic whereas, turkey is parthenogenetic.
24. Observe the diagram below of a DNA showing replication and answer the questions that
follows
(i) Identity the polarity of the strand.
(a) X-X' .
(b) Y-Y'
(ii) In which phase of cell cycle, does the above given process takes place?
(iii) The unwinding of DNA imposes tension on the distal end of DNA molecule. Which protein, P
or O helps to relieve this. Also what is the function of remaining protein?
25. (i) How do you justify that the Archaeopteryx is a connecting link between two specific
groups of organisms?
(ii) Two fossils A and B have been found. Which fossil is older?
26. Antibiotics are regarded as one of the most significant discoveries of the 20th century. These
have greatly contributed towards the welfare of the human society. Analyse and compile a
report on how the discovery of antibiotics has helped mankind in the field of medicine.
Or
(i) Explain why the use of tobacco in any form is considered to be injurious to health.
(ii) Can our friends influence us to start taking alcohol/drugs. If yes, suggest one preventive
measure one can take to overcome this influence?
27. The figure below shows the restriction site for a specific restriction enzyme X.
(i) This restriction site is palindromic. What does this indicate?
(ii) If this sequence is present at 5 places in the given DNA fragment. How many fragments
would we observe when we run an agarose gel electrophoresis?
(iii) To observe these separated DNA fragments, the dye bromophenol blue is added and
visualised under flouroscence microscope. Is this process correct? Elaborate.
28. (i) Why some species are generally at a greater risk of extinction when compared to others?
List any three reasons.
(ii) State the importance of cryopreservation as a strategy of conservation for biodiversity?
Section-D
29. Study the pedigree chart given below.
Answer the following questions following.
(i) On the basis of the inheritance pattern represented by this pedigree chart, what is your
conclusion with respect to the given disease/trait? [1]'
(ii) To a couple where the female is unaffected the female is and the male is affected, what will
be the the genotype of the offsprings they have. Show the same by using a genetic cross.
[1]
(iii) What would happen to the male children of the couple where woman is a carrier for this trait
and man is normal? Explain with the help of a cross. [2]
Or
(iii) What will happen to the female who is homozygous for this trait? [2]
30. The graph shows the relationship between the average age at death and the number of
cigarettes smoked per day.
Cigarettes smoked per day
(i) What conclusion can you draw from the graph? [1]
(ii) How does tobacco smoking relate to oxygen deficiency in the blood. [1]
(iii) Identify the major effect of nicotine present in tobacco smoke on the body
Or
(iii) How does nicotine affects the working of heart? [2]
Section-E
31. Male and female gametes in human beings differ from each other in terms of both structure
and function. Enumerate some major differences between the two, along with their diagrams.
Or (i) Plan an experiment and prepare flowchart of the steps that you would follow to ensure that
the seeds are formed only from the desired sets of pollen grains. Name the type of
experiment that you carried out.
(ii) Write the importance of such experiments.
32. Study the inhertance pattern given below.
(i) A non-haemophilic couple was informed by their doctor that there is the possibility of a
haemophilic child to be born to them. Using the idea shown above elaborate on what bases
did the doctor conveys this information. Give the genotypes and the phenotypes of all the
possible children who could be born to them.
(ii) Human females are rarely haemophilic. Comment.
Or
The above given figure shows a very widely used technique for paternity disputes. Explain
this technique.
33. Almost any disease causing organisms such as bacteria, virus, fungi, prions, etc., or their
toxins can be used as biological weapons. Historical biological weapons programmes have
included efforts to produce aflatoxin, anthrax and many others. In the bioweapon industry,
genetic engineering is used to create new pathogenic strains through increased survivability,
infertility, virulence, etc.
(i) List any two characteristics that make bioweapons attractive to countries and terrorists.
(ii) In their natural state, the organisms or toxins do not have the efficiency to cause the large
scale damage as compared to their bioweapon forms. Explain, how are these natural forms
turned into bioweapons.
(iii) Genetic modification to this extent can have unpredictable or unforeseen risks to the living
forms and the environment. Comment.
Or
The steps involved in formation of recombinant DNA using a plasmid and host bacterial cell
are shown below.
(i) The plasmid vector is cut with an enzyme to create sticky ends. Discuss why was this
necessary?
(ii) The recipient bacterial cell which is the host in this process, had to undergo a treatment at
stage B before it could form the recombinant molecule.
What is this treatment? Give an idea for what purpose was it used?
(iii) What will be your strategy to select the transformed plasmids from those cells who have not
picked up the gene of interest?
SOLUTIONS OF PRACTICE PAPER 2
BIOLOGY
Ans.1 (c) Saheli is a non-steroidal, once a week contraceptive pill. It has high contraceptive
value with few side effects. It acts by inhibiting oestrogen activity thus, inhibiting the process of
ovulation and implantation.
Ans.3 (d) HIV that causes Acquired Immuno Deficiency Syndrome (AIDS) in a person reduces
the number of helper-T (TH) cells, which are responsible for the development of immunity in
human body.
Ans.5 (d) Both codons CGC, AGA code for arginine. [1]
Ans.6 (c) In the case of snake bites, the antivenom given to patient contains preformed antibodies,
against snake venom. This helps to generate a quick response and provides passive
immunisation to the patient. [1]
Ans.7 (b) The correct combination is indicated by option
(b) . For others, the correct combination are
Penicillin P. notatum Sore throat, gonorrhea, etc
Streptomycin Streptomyces griseus Pneumonia, TB, etc.
Ergot Claviceps purpurea In parturition, BP, control uterine
haemorrhage, etc.
Ans.8 (a) In blue white screening, the recombinant or transformed cells are differentiated from
others on the basis of their ability to produce colour in the presence of a chromogenic
substrate. In transformed cells, the presence of foreign gene insert, inactivates lac z gene,
due to which colourless or white colonies are formed. [1]
Ans.9 (a) Some plants need help of animals for pollinating their flowers and also for the dispersal
of their seeds. In the above interaction, both the partners, i.e. the plant and animals are
beneficial for each other. Thus, represents a mutualistic association. [1]
Ans.10 (c) According to the above given case, initially due to ample supply of nutrients, the rate
of growth of decomposers is exponential. But at later stages, the population reaches nears
its carrying capacity, due to depletion in the nutrients thus, the growth rate decline. This forms
a S-shaped growth curve which represents the logistic growth of an organism. [1]
Ans.11 (d) This is a spindle-shaped pyramid, wherein a single large-sized tree (producer)
provides food to the large number of herbivore (consumers) which supports a small number
of carnivores that are inturn eaten by the top carnivores. [1]
Ans.12 (c) y-diversity represents the regional diversity, i.e. it is the diversity that represents the
total number of species (or species richness) in all the habitats within a geographical region.
[1]
Question No. 13 to 16 consist of two statements, Assertion (A) and Reason (R). Answer
these questions selecting the appropriate option given below.
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion
(b) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
(c) Assertion is true, but Reason is false
(d) Assertion is false, but Reason is true
Ans.13 (a) Both Assertion and Reason are true and Reason is the correct explanation of
Assertion
Apomixis is a special mode of asexual reproduction that mimics sexual reproduction that
occurs in some plants which results in the formation of seeds without gametic fusion (or
fertilisation), e.g. in some species of Asteraceae. [1]
Ans.14 (a) Both Assertion and Reason are true and Reason is the correct explanation of
Assertion.
A population at its carrying capacity does not have enough limiting resources to go around
and any individual utilising new resources will experience less competition. Use of new
resources will increase through generations and niche will become larger. [1]
Ans.15 (a) Both Assertion and Reason are true and Reason is the correct explanation of
Assertion. pBR322 has recognition sites for several commonly used restriction enzymes. The
recognition site for BamHl is present in tetR region, (i.e. responsible for tetracycline
resistance). When an insert is added at the BamHl recognition site, the gene for tetracycline
resistance becomes non-functional and the recombinant bacteria with plasmid pBR322 that
has DNA insert at BamHl loses tetracycline resistance. [1]
Ans.16 (c) Assertion is true, but Reason is false.
In the experiment done by Meselson and Stahl.
The DNA obtained from the culture, one generation after the transfer from 15Nto 13 14N
medium (i.e. after 20 minutes, because E. coli divides in 20 minutes) had a hybrid and
intermediate DNA. And after generation II, (i.e. after 40 minutes) DNA obtained was
composed of equal amounts of hybrid DNA and light DNA. [1]
Ans.17 (i) In the flowchart given X-Ovary and Y-Uterus.
Given flowchart represents the hormonal control of oogenesis, i.e. the process of formation
of female gametes. [1]
(ii) The hormone Z is the gonadotropin releasing hormone. The function of GnRH is to stimulate
the anterior lobe of pituitary to secrete the hormones called LH and FSH. [1]
Ans.18 Colour blindness is a sex-linked recessive disease which shows criss cross pattern of
inheritance thus, the disease is passed on the daughter from her father and from mother to
son. Now, here the women’s father is affected therefore the women will be the carrier.
Similarly, the man’s father is also affected but he will remain unaffected. Thus, their offspring
will show the following genotype
Ans.19 The second generation vaccines consists of few antigens present on the surface of
infecting agents rather than the whole inactivated organisms. The genotype surface antigens
produced in large quantities by recombinant DNA techniques are injected in safer dose for
the development of immunity. Thus, they are simpler, safer and more potent than its
contemporaries. [2]
Ans.20 (i) P in the above vector determines the ori sequence from where the replication begins.
So, if this is found missing, the vector DNA would not be able to link with the foreign DNA
and replicate. Thus, a recombinant molecule will not be formed. [1]
(ii) Q and R are the selectable marker genes which helps in the identification and selection of
transformed cells. They selectively permit the growth of the transformed cells on the media.
In their absence, we will not be able to identify which host cell carrying the foreign gene
segment. [l]
Ans.21
[1]
(ii) A food chain cannot be longer than 4-5 trophic levels because only 10% energy gets passed
on to next trophic level. Thus, very less energy and biomass remains on reaching 4-5th trophic
levels, which cannot support any further levels. [1] Or
(i)
Thus, a spindle-shaped pyramid of numbers is formed. [1]
(ii) The pyramid of energy will have an upright pyramid shape. This is because producers always
have more energy than the consumers. [1]
Ans.22 The hormonal control of spermatogenesis in humans is explained below
The secretion of Gonadotropin Releasing Hormone (GnRH) by the hypothalamus increases
significantly during puberty. The GnRH further acts on the anterior pituitary and stimulates
the secretion of two gonadotropins, namely
(i) Follicle Stimulating Hormone (FSH) It acts on the Sertoli cells and stimulates them to
secrete certain factors which are necessary for the process of sperrniogenesis.
(ii) Luteinizing Hormone (LH) It acts on the Leydig cells of testes and stimulates them to
secrete testosterone, which further stimulates the process of spermatogenesis. [3]
Ans.23 (i) Transfer of pollen grains from the anther to the stigma of another flower of the same
plant is called geitonogamy. It is functionally cross-pollination (as it involves a pollinating
agent), but genetically similar to autogamy, because the pollen grains come from the same
plant (i.e. genetically same parent). [1]
(ii) Continued self-pollination results in inbreeding depression because majority of flowering
plants produces hermaphrodite flowers and pollen grains generally came in contact with the
stigma of the same flower. To discourage this, flowering plants developed many outbreeding
devices to discourage self-pollination and to encourage cross-pollination. [1]
(iii) Banana fruit is said to be parthenocarpic because it is formed without fertilisation. Such fruits
are called parthenocarpic fruits.
On the other side, turkey is said to be parthenogenetic in nature because in this the female
gamete undergoes development to form new organisms without fertilisation. [1]
Ans.24 (i) (i)5'-3' (ii)3'-5' [1]
(ii) S-phase of interphase [1]
(iii) DNA gyrase or topoisomerase (Q). The other protein/enzyme (P) is helicase which unwinds
the double helix. [1]
Ans25. (i) Archaeopteryx is a connecting link between reptiles and birds. This can be verified by
studying its features which are similar to both these groups of organisms.
Reptilian characters of Archaeopteryx
(a) Non-pneumatic bones.
(b) Jaws with homodont teeth.
(c) Long, lizard-like tail along with body scales. Avian characters of Archaeopteryx
(a) Feathers and beak are present.
(b) Forelimbs modified as wings. [2]
(ii) The fossil which was found in more deeper sedimentary layers is older. [1]
Ans.26 Antibiotics (a Greek word, where anf/'-against and bio-life, i.e. against life in the context
of pathogenic microorganisms) are the chemical substances produced by some microbes
that can kill or retard the growth of other disease causing microbes.
Penicillin was the first antibiotic to be discovered that inhibited the growth of Staphylococcus
bacteria.
After discovering its full potential as an antibiotic, it was extensively used to treat wounded
American soldiers during World War-ll.
After that, many more antibiotics have been identified and purified from other microbes to
conquer the various diseases and their causative agents. Antibiotics have thus, greatly
improved our capacity to treat deadly diseases such as plague, whooping cough (kali khansi),
diphtheria (gal ghotu) and leprosy (kusht rog), which had killed millions all over the globe.
[3]
Or
(i) Tobacco consumption in any form is injurious to health as smoking tobacco can cause
cancer, respiratory disorders, ulcers, etc. It can also increase the level of carbon monoxide
in blood, leading to oxygen deficiency. [2]
(ii) Yes, we can get influenced by our friends due to peer pressure. Thus, a preventive measure
can be to seek help from teachers or parents. Their advice can help us to overcome such
pressure from friends. [1]
Ans.27 (i) The site is a palindrome, which means that the base sequence in one DNA strand (5’-
3’) reads the same in complementary strand when read in 3’-5’ direction. [1]
(ii) We will observe 6 fragments of DNA. [1]
(iii) No, this is incorrect. Because ethidium bromide is used to stain the gel. By doing this, the
DNA bands appears orange in colour when exposed to UV rays. [1]
Ans.28 (i) The three important reasons for some species to be at a greater risk of extinction are
given below
(a) Large body size which makes the organisms feeding for food, space, etc.
(b) Low genetic variability which makes the organism more vulnerable to diseases and unable
to withstand environmental changes.
(c) Narrow range of geographical distribution or endemism. [2]
(ii) The gametes of threatened species can be preserved in a viable and fertile conditions for
long periods by the method of cryopreservation. [1]
Ans.29 (i) This pedigree chart represents the inheritance of a sex-linked disease, e.g.
haemophilia. [1] (ii) The genotype of the offspring can be derived as
The genotypes will be XXh, XY XXh, XY [i]
(iii) If a carrier woman and normal man are married, half of their sons will be haemophilic and
half of . their daughters will be carrier.
Or
(iii) The female who is homozygous for the respective trait will not be able to survive, because
this condition is lethal for females.
Ans.30 (i) People smoking less than 5 cigarettes a day will live longer than those who smoke
more. [2]
(ii) Tobacco contains carbon monoxide which binds irreversible with haemoglobin. This
decreases the oxygen supply to body parts creating 02 deficiency. [1]
(iii) As nicotine is addictive, so it creates urges for smoking at all times of the day. [2]
Or
(iii) Nicotine increases the heart rate by increasing the secretion of adrenaline’ hormone in our
body. [2]
Ans.31 Differences between male gamete (sperm) and female gamete (ovum) of human beings
are given below
Male gamete (Sperm) Female gamete (Ovum)
Male gametes (sperms) are produced inside Female gametes (ova) are produced inside
the testes. the ovary.
Millions of sperms are produced per day. Only one ovum is produced every 28 days.
Sperms are motile in nature. Ovum is non-motile in nature.
The smallest cell in the human body. The largest cell in the human body.
Reserve food material is less. Reserve food material is sufficient.
A sperm is differentiated into four parts, i.e. Ovum is not externally differentiated into
head, neck, middle piece and tail. parts.
Or
(i) Artificial hybridisation is carried out to ensure that the seeds are formed from the desired
set of pollen grains. This is done by emasculation and bagging.
The flowchart below shows the steps involved in it.
In emasculation, the stamens are removed in bud condition from a bisexual flower.
↓
Female flower is obtained.
↓
Emasculated flower is enclosed in a bag made up of butter paper or plastic (Bagging).
↓
Mature and viable pollen grains are collected from male plant.
↓
Bag opened, pollen grains dusted on the stigma.
↓
Bag replaced immediately.
↓
Artificial pollination takes place. [3]
(ii) Importance of such experiments are
(a) Creation of new genetic recombination with better qualities.
(b) Incorporation of a large number of desirable characters into a single variety. [2]
Ans.32
(i) The possibility of one of their child being haemophilic can be predicted by performing the
following cross
Father Genotype - XY (normal)
Mother Genotype - XXh (carrier/non- haemophilic)
(ii) Haemophilia is an X-linked recessive disease. Therefore, the female having haemophilic
allele on single X-chromosome does not produce haemophilic phenotype. So, for the female
being affected by haemophilia should have a mother who is carrier for the disease and her
father should be haemophilic (unavailable in entire life). Therefore, human females are rarely
haemophilic. [2]
Or
The technique given in the question which helps in solving paternity disputes is called DNA
fingerprinting.
Procedure of DNA Fingerprinting
(i) Extraction DNA is extracted from cells by using high-speed, refrigerated centrifuge.
(ii) Amplification Several copies of extracted DNA containing Variable Number Tandem
Repeats (VNTRs) are made by Polymerase Chain Reaction (PCR).
(iii) Restriction Digestion DNA is cut into fragments with restriction. enzymes into precise
reproducible sequences.
(iv) Separation of DNA Sequences Cut DNA fragments are introduced and passed through
electrophoresis set-up containing agarose polymer gel.
(v) Southern Blotting Separated DNA sequences are transferred on to a nitrocellulose or nylon
membrane sheet placed over gel.
(vj) Radioactive DNA probes with base sequences complementary to the possible VNTRs are
introduced/poured over the membrane. .
(vii) VNTR form the basis of DNA fingerprinting. The repeats of it show high degree of
polymorphism.
(viii) After hybridisation with the radiolabelled VNTR probe and autoradiography, bands of various
sizes are formed.
(ix) Bands form a characteristic pattern, which varies from person to person. [5]
Ans.33 (i) Two characteristics are
(a) Cost Efficiency They are low cost weapons.
(b) Large Scale Casualities These weapons can cause more damage than conventional
methods of terrorism. [1]
(ii) The bioweapons industry, technique of genetic, engineering is utilised to manipulate, i.e.
enhance the natural palthogenicity of organisms or toxins.
At first, the genetic material of interest is isolated from the subject organisms.
• The DNA is fragmented by restriction enzymes,
• Desired fragments of DNA are isolated.
• Amplification is done using PCR.
• Ligation of DNA fragments into vector transfer of /•DNA into host.
• Culturing on large scale, extraction and final processing of the product, [2]
(iii) Genetic modification is unethical. Such manipulations of living beings can have
unpredictable effects on other living beings and also the environment
(a) The modified genes can enter the natural forms and cause them to die. .
(b) Appearance of new and unexplained mutations.
Or
(i) The plasmid is cut with a restriction enzyme that makes cut in dsDNA at two different sites.
Few nucleotides away from each other. This creates strands with protruding ends called
sticky ends.
They can associate with gene insert, by forming hydrogen bond among complementary base
pairs. [1
(ii) At stage B, the host bacterial cell is treated with a solution containing calcium ions at 0°C;
followed by a heat shock (raising temperature to 40°C). This treatment creates transient
pores in bacterial cell membrane which allows them to take up the foreign DNA present in
their surroundings. This process is done to facilitate gene transfer by making the recipient
host cell competent. [2]
(iii) Plasmids contain selectable marker genes. Usually the genes encoding resistance to
antibiotics, e.g. ampicillin, tetracycline, etc., are used as selectable markers.
The selectable marker site would be disrupted by the insertion of the foreign gene. The
bacterial cell with recombinant plasmids would be unable to grow in the particular antibiotic
medium that corresponded with original resistance, e.g. If gene is inserted in tet is tetracycline
‘sensitivity would become inactivated and the. recombinant cells would be able to grow in
presence of tetracycline, i.e. become tetr. [2]
