CBSE Class 12 Biotechnology Question Paper 2025 Solved Code 99

SECTION A

1. The DNA ligase enzyme that is frequently used to ligate different DNA fragments in order to generate rDNA molecules is isolated from: [1 Mark]
(A) T2 Bacteriophage
(B) T4 Bacteriophage
(C) Lambda Bacteriophage
(D) M13 filamentous phage

Answer: (B) T4 Bacteriophage

Teacher's Note:
a) T4 DNA ligase joins DNA fragments by forming phosphodiester bonds.
b) Do not confuse T4 (source of ligase) with M13 (used as a single-stranded cloning vector).

2. Protein Efficiency Ratio (PER) is used as a measure of growth expressed in terms of: [1 Mark]
(A) Weight gain of an adult by consuming 1 g of food protein.
(B) Weight gain of an adult by consuming 100 g of food protein.
(C) Protein nitrogen that is retained by the body by consuming 1 g of food protein.
(D) Protein nitrogen that is retained by the body by consuming 100 g of food protein.

Answer: (A) Weight gain of an adult by consuming 1 g of food protein.

Teacher's Note:
a) PER is a growth-based measure of protein quality, calculated per gram of protein eaten.
b) Protein nitrogen retained by the body describes Net Protein Utilisation or Biological Value, not PER.

3. At the end of one cycle of PCR, two DNA molecules will become _______. [1 Mark]
(A) Eight
(B) Sixteen
(C) Four
(D) Two

Answer: (C) Four

Teacher's Note:
a) In PCR, the number of DNA molecules doubles in every cycle.
b) Use the formula \( N \times 2^{n} \); here \( 2 \times 2^{1} = 4 \).

4. Single base difference in ApoE gene is associated with: [1 Mark]
(A) Resistance to HIV (Human Immunodeficiency Virus)
(B) Migraine
(C) Huntington disease
(D) Alzheimer's disease

Answer: (D) Alzheimer's disease

Teacher's Note:
a) A single base difference (SNP) in the ApoE gene is linked with a higher risk of Alzheimer's disease.
b) Resistance to HIV is linked with a different gene (CCR5), so option (A) is a trap.

5. One of the carbon source used in microbial cell culture is: [1 Mark]
(A) Olive oil
(B) Cereal grains
(C) Ammonium salts
(D) Growth factors

Answer: (B) Cereal grains

Teacher's Note:
a) Cereal grains supply starch, which is a cheap carbon source for microbes.
b) Ammonium salts are a nitrogen source, not a carbon source.

6. A biotechnologist wants to obtain a gene sequence in single stranded form. Which bacteriophage based vector should he choose to obtain the desired result? [1 Mark]
(A) M13 based vector
(B) Bacteriophage Lambda based vector
(C) Plasmid cloning vector of pUC family
(D) Plasmid vector pBR 322

Answer: (A) M13 based vector

Teacher's Note:
a) M13 is a filamentous phage whose genome is single-stranded DNA, so it gives single-stranded copies of the insert.
b) pUC and pBR 322 are plasmids, not bacteriophage vectors.

7. Absence of the enzyme adenosine deaminase in humans causes: [1 Mark]
(A) Thallasemia
(B) Sickle cell anaemia
(C) SCID
(D) Mad cow disease

Answer: (C) SCID

Teacher's Note:
a) SCID stands for Severe Combined Immunodeficiency; ADA deficiency is one of its main causes.
b) ADA deficiency was the first disease treated by gene therapy.

8. The technique to isolate and grow human embryonic stem cells in culture was developed by: [1 Mark]
(A) Ceasar Milstein
(B) James Thomson
(C) George Kohler
(D) George Gay

Answer: (B) James Thomson

Teacher's Note:
a) James Thomson grew human embryonic stem cells in culture in 1998.
b) Kohler and Milstein developed hybridoma technology; George Gay established the HeLa cell line.

9. Gene prediction for bacterial genomes can be done by using the computer program _______. [1 Mark]
(A) GeneMark
(B) GENSCAN
(C) UniProtKB
(D) RefSeq

Answer: (A) GeneMark

Teacher's Note:
a) GeneMark predicts genes in prokaryotic (bacterial) genomes.
b) GENSCAN is used for eukaryotic genomes; UniProtKB and RefSeq are databases, not prediction programs.

10. _______ can be categorized as a food source of nutraceutical proteins. [1 Mark]
(A) Seed storage proteins
(B) Soya protein
(C) Milk proteins
(D) Whey protein concentrates

Answer: (D) Whey protein concentrates

Teacher's Note:
a) Whey protein concentrates are used as health-promoting (nutraceutical) food products.
b) Whey proteins raise glutathione levels in cells, which gives them therapeutic value.

11. Identification of disease specific proteins can be done by using the approach of: [1 Mark]
(A) Functional proteomics
(B) Structural proteomics
(C) Expression proteomics
(D) Proteome mining

Answer: (C) Expression proteomics

Teacher's Note:
a) Expression proteomics compares protein expression in normal and diseased samples to find disease-specific proteins.
b) Structural proteomics deals with 3D structures and functional proteomics with protein interactions.

12. Herceptin is a monoclonal antibody approved for: [1 Mark]
(A) Therapy of early stage breast cancer.
(B) Reversal of acute rejection of transplanted organs.
(C) Stimulation of erythropoiesis.
(D) Use in certain patients having a heart attack.

Answer: (A) Therapy of early stage breast cancer.

Teacher's Note:
a) Herceptin (trastuzumab) targets the HER2 receptor on breast cancer cells.
b) Stimulation of erythropoiesis is done by erythropoietin, which is a hormone, not an antibody.

For Questions 13 to 16, two statements are given - one labelled Assertion (A) and other labelled Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below:
(A) Both Assertion (A) and Reason (R) are true and the Reason (R) is the correct explanation of the Assertion (A).
(B) Both Assertion (A) and Reason (R) are true, but the Reason (R) is not the correct explanation of the Assertion (A).
(C) Assertion (A) is true, but Reason (R) is false.
(D) Assertion (A) is false, but Reason (R) is true.

13. Assertion (A): CO₂ incubators prevent the desiccation of the animal cell culture medium.
Reason (R): A pan of water is kept at all times in a CO₂ incubator chamber to maintain high relative humidity. [1 Mark]
(A) Both Assertion (A) and Reason (R) are true and the Reason (R) is the correct explanation of the Assertion (A).
(B) Both Assertion (A) and Reason (R) are true, but the Reason (R) is not the correct explanation of the Assertion (A).
(C) Assertion (A) is true, but Reason (R) is false.
(D) Assertion (A) is false, but Reason (R) is true.

Answer: (A) Both Assertion (A) and Reason (R) are true and the Reason (R) is the correct explanation of the Assertion (A).

Teacher's Note:
a) The pan of water keeps the humidity high, so the medium does not dry out.
b) This is exactly why desiccation is prevented, so R explains A.

14. Assertion (A): Contact inhibition is absent in cancer cells.
Reason (R): Normal cells stop growing when they reach the walls of the container. [1 Mark]
(A) Both Assertion (A) and Reason (R) are true and the Reason (R) is the correct explanation of the Assertion (A).
(B) Both Assertion (A) and Reason (R) are true, but the Reason (R) is not the correct explanation of the Assertion (A).
(C) Assertion (A) is true, but Reason (R) is false.
(D) Assertion (A) is false, but Reason (R) is true.

Answer: (B) Both Assertion (A) and Reason (R) are true, but the Reason (R) is not the correct explanation of the Assertion (A).

Teacher's Note:
a) Cancer cells keep dividing and pile up in layers because they have lost contact inhibition.
b) R only describes normal cells; it does not explain why cancer cells lack contact inhibition.

15. Assertion (A): Proteins have diverse functions.
Reason (R): All proteins are enzymes. [1 Mark]
(A) Both Assertion (A) and Reason (R) are true and the Reason (R) is the correct explanation of the Assertion (A).
(B) Both Assertion (A) and Reason (R) are true, but the Reason (R) is not the correct explanation of the Assertion (A).
(C) Assertion (A) is true, but Reason (R) is false.
(D) Assertion (A) is false, but Reason (R) is true.

Answer: (C) Assertion (A) is true, but Reason (R) is false.

Teacher's Note:
a) Proteins act as enzymes, hormones, antibodies, transporters and structural components.
b) All enzymes (except ribozymes) are proteins, but all proteins are not enzymes, so R is false.

16. Assertion (A): One of the first attempts to study the molecular basis of sickle cell anaemia was to compare the electrophoretic mobility of normal haemoglobin (Hb) and sickle cell haemoglobin (scHb).
Reason (R): Sickle cell haemoglobin (scHb) moved faster than normal haemoglobin (Hb) in electrophoresis. [1 Mark]
(A) Both Assertion (A) and Reason (R) are true and the Reason (R) is the correct explanation of the Assertion (A).
(B) Both Assertion (A) and Reason (R) are true, but the Reason (R) is not the correct explanation of the Assertion (A).
(C) Assertion (A) is true, but Reason (R) is false.
(D) Assertion (A) is false, but Reason (R) is true.

Answer: (C) Assertion (A) is true, but Reason (R) is false.

Teacher's Note:
a) In scHb, negatively charged glutamic acid is replaced by neutral valine, so scHb carries less negative charge.
b) Therefore scHb moves slower, not faster, than normal Hb towards the anode.

SECTION B

17. (a) What is the principle of mass spectrometry? Write its important application. [2 Marks]

Answer:
1. Principle: Mass spectrometry finds the molecular weight of chemical compounds by separating molecular ions according to their mass to charge (m/z) ratio.
2. Application: It is used to obtain structural information about proteins, such as peptide masses and amino acid sequence.

Teacher's Note:
a) The keyword "mass to charge (m/z) ratio" must appear in the principle.
b) Other accepted applications: finding the type and location of amino acid modifications, or the molecular weight of proteins.

OR

(b) Describe briefly, the charge relay system that operates in chymotrypsin enzyme. [2 Marks]

Answer:
1. Chymotrypsin is a chain of 245 amino acids in three peptides that folds into a globular shape, bringing His(57), Asp(102) and Ser(195) close together in space.
2. Negatively charged Asp(102) forms a hydrogen bond with His(57) and partly borrows its hydrogen ion; His(57) makes up this loss by pulling a hydrogen ion from Ser(195), which makes Ser(195) acidic and reactive.

Teacher's Note:
a) Remember the catalytic triad with numbers: His 57, Asp 102 and Ser 195.
b) State the direction of hydrogen ion transfer correctly: Ser to His to Asp.

18. With a suitable example, explain briefly, why the number of predicted genes do not correlate with the genome size and the number of chromosomes in an organism. [2 Marks]

Answer:
1. Example: Humans have 23 chromosomes (haploid) and about 3,000,000,000 base pairs but only 20,000 - 25,000 predicted genes, while the weed Arabidopsis thaliana has only 5 chromosomes and 157,000,000 base pairs but about 25,498 predicted genes.
2. So the number of genes does not match genome size or chromosome number, because of overlapping genes and splice variants (one gene giving many proteins), and because a large part of the genome does not code for protein.

Teacher's Note:
a) Quote numbers from the textbook table (Table 1) to make the example convincing.
b) The keywords "overlapping genes" and "splice variants" carry the reasoning mark.

19. Why is chronic mylogenous leukemia caused? Name the technique used to know the status of this disease. [2 Marks]

Answer:
1. Chronic myelogenous leukemia is caused by a translocation between chromosomes 9 and 22, which produces a shorter chromosome 22 called the Philadelphia chromosome.
2. The status of the disease is found by Fluorescence In Situ Hybridisation (FISH).

Teacher's Note:
a) Karyotype analysis is also accepted as the technique.
b) Name the Philadelphia chromosome; it is the key value point.

For Visually Impaired Candidates (in lieu of Q. 19)

19. What are the uses of the data provided in RefSeq database? [2 Marks]

Answer:
1. The data is used for designing gene chips (DNA microarrays).
2. It is used for describing the sequence features of the human genome.

Teacher's Note:
a) RefSeq is a non-redundant, curated reference sequence database of NCBI.
b) Write the two uses as separate points; each carries one mark.

20. Outline the important steps for isolation of recombinant insulin (Humulin) from Escherichia coli. [2 Marks]

Answer:
1. The fermentation broth is filtered or centrifuged; since insulin is an intracellular product, the clear broth is discarded and the cell mass is kept.
2. The cells are lysed, centrifuged and the proteins solubilised to get crude protein, which is then purified, refolded and finally purified to give pure insulin.

Teacher's Note:
a) The sequence is: broth, filtration/centrifugation, cell mass, cell lysis, crude protein, purification and refolding, pure protein.
b) A common mistake is keeping the clear broth; for an intracellular product the broth is discarded.

21. What is the most common cause of foaming in microbial culture medium? Which problems are created by foaming in microbiological processes? [2 Marks]

Answer:
1. The most common cause of foaming is the presence of proteins in the culture medium.
2. Foaming denatures proteins and hinders the free diffusion of oxygen in the medium.

Teacher's Note:
a) Both problems (protein denaturation and poor oxygen diffusion) are needed for the full second mark.
b) Foaming is controlled by adding antifoam agents such as silicone oils.

SECTION C

22. Elaborate upon the scientific relevance for therapeutic usefulness of whey with specific examples. [3 Marks]

Answer:
1. Whey proteins raise the level of the tripeptide glutathione (gamma-glutamyl cysteinyl glycine) in cells.
2. Glutathione is a reducing compound that detoxifies xenobiotics and protects cell components from oxygen intermediates and free radicals.
3. Examples: whey is used to treat illnesses such as jaundice and infected skin lesions (also genito-urinary tract infections).

Teacher's Note:
a) Glutathione is the key word; the scientific basis carries 2 marks.
b) Give any two examples of illnesses for the remaining mark.

23. (a) Mention the important features that were incorporated in each of the following vectors: [3 Marks]
(i) COSMIDS
(ii) Shuttle Vectors
(iii) Expression Vectors

Answer:
(i) Cosmids: they carry the COS sites of phage lambda along with plasmid features, that is, an origin of replication, a selectable marker and suitable restriction enzyme sites.
(ii) Shuttle vectors: they have two types of origin of replication and selectable marker genes, one set that works in eukaryotic cells and another that works in Escherichia coli.
(iii) Expression vectors: they carry the signals needed for transcription and translation of the insert, so that the foreign protein is expressed.

Teacher's Note:
a) Cosmid = COS sites of lambda + plasmid; this simple formula helps you remember.
b) Shuttle vectors can "shuttle" between two hosts because they have two sets of replication origins.

OR

(b) Explain the method of Blue-White selection used for screening of recombinant cells containing desired plasmid with gene of interest. [3 Marks]

Answer:
1. The method is based on insertional inactivation of the lac Z gene present on the vector pUC 19.
2. The lac Z gene codes for the enzyme beta-galactosidase, which cleaves a colourless substrate X-Gal into a blue coloured product.
3. If a DNA insert enters the lac Z gene, the gene is inactivated and the enzyme is not made.
4. After transformation, E. coli host cells are plated on a solid medium containing ampicillin and X-Gal.
5. Blue colonies are ampicillin resistant transformed cells that do not have the insert.
6. White colonies are ampicillin resistant and carry the insert (recombinant DNA), so they are selected.

Teacher's Note:
a) Remember: white = recombinant, blue = non-recombinant.
b) The term "insertional inactivation" is an important keyword for this answer.

24. What is the mode of action of tissue Plasminogen Activator (tPA)? Draw a schematic representation to show the method of production of tPA through mammalian cell culture. [3 Marks]

[Figure: Schematic of tPA production: a plasmid containing the t-PA gene insert is introduced into mammalian cells grown in a petri plate; the mammalian cells secrete t-PA; they are then scaled up and transferred to a fermentor.]

Answer:
1. Mode of action: tPA converts the inactive precursor plasminogen into the active enzyme plasmin, which degrades fibrin and dissolves the blood clot (Plasminogen \( \rightarrow \) Plasmin \( \rightarrow \) Fibrin degraded \( \rightarrow \) Dissolution of blood clot).
2. Production: the t-PA gene is inserted into a plasmid, and the plasmid containing the t-PA gene insert is introduced into mammalian cells grown in a petri plate.
3. The mammalian cells that secrete t-PA are scaled up and transferred to a fermentor for large-scale production.

Teacher's Note:
a) The schematic carries 2 marks; label the plasmid, t-PA gene insert, petri plate and fermentor.
b) tPA is used as a clot-dissolving drug in heart attack patients.

For Visually Impaired Candidates (in lieu of Q. 24)

24. What are stem cells? Write the two broad types of mammalian stem cells and an application of each. [3 Marks]

Answer:
1. Stem cells are cells that can renew themselves by mitotic cell division and can differentiate into many different specialised cell types.
2. The two broad types of mammalian stem cells are adult stem cells and embryonic stem cells.
3. Application of adult stem cells: they act as a repair system of the body and maintain the normal turnover of regenerative organs such as blood, skin and intestinal tissues. Application of embryonic stem cells: they can differentiate into cells of all specialised tissues and are used to create mouse models of human diseases.

Teacher's Note:
a) "Self-renewal" and "differentiation" are the two keywords in the definition.
b) Other accepted uses: treating leukemia or spinal cord injury (adult), making chimeric or knock-out mice (embryonic).

25. Although not required for cell growth, antibiotics are added in animal cell culture medium. Give reason. Name two such antibiotics. [3 Marks]

Answer:
1. Antibiotics are added to control the growth of bacterial and fungal contaminants, which can enter the medium easily and grow much faster than animal cells.
2. One such antibiotic is Penicillin, which acts mainly against bacteria.
3. Another such antibiotic is Streptomycin, which is also used against bacterial contamination.

Teacher's Note:
a) Each antibiotic named correctly carries 1 mark.
b) Animal cells grow slowly, so fast-growing microbes can easily take over the culture without antibiotics.

26. It is very difficult to produce hybrids in case of interspecific and intergeneric crosses. Why? Briefly describe the technique to obtain such novel hybrids. [3 Marks]

Answer:
1. In such crosses, the endosperm develops abnormally, which causes early death of the hybrid embryo and leads to sterile seeds.
2. Technique - Embryo rescue: the young hybrid embryo is taken out of the seed before it aborts and is cultured on a suitable nutrient medium in the laboratory.
3. In culture, the embryo gets the nutrition that the faulty endosperm cannot supply, so it grows into a complete hybrid plant.

Teacher's Note:
a) The reason "abnormal endosperm development" carries 1 mark.
b) Protoplast fusion (somatic hybrids and cybrids) or organelle transfer can also be described for the technique.

27. Transgenic plants can be used as factories to produce polyhydroxybutyrate (PHB) on a large scale. How was Arabidopisis plant engineered for the same?
State the drawback of producing PHB by fermentation using bacterium Alcaligenes eutrophus. [3 Marks]

Answer:
1. Three genes involved in PHB synthesis were taken from the bacterium Alcaligenes eutrophus and transferred into Arabidopsis.
2. These genes were expressed only in the chloroplasts of the plant, which produced PHB globules without affecting plant growth and development.
3. Drawback: producing PHB by fermentation using Alcaligenes eutrophus has a high production cost.

Teacher's Note:
a) The words "three genes" and "chloroplasts" are the key value points.
b) PHB is a biodegradable plastic, which is why its cheap production matters.

28. A comparative microarray hybridization experiment was performed between normal and cancerous cells. How will you interpret the result obtained on a microarray, if red and green coloured fluors were used for labelling the cDNA probes of normal and cancerous cells respectively? [3 Marks]

Answer:
1. Red spots show genes expressed in high amounts in normal cells.
2. Green spots show genes expressed in high amounts in cancerous cells.
3. Yellow spots show genes expressed in about equal amounts in both normal and cancerous cells.

Teacher's Note:
a) Yellow is the mixture of red and green, meaning equal binding of both probes.
b) Match colours to samples carefully; the question gives red for normal and green for cancerous.

SECTION D

Instructions: Q. Nos. 29 and 30 are case-based questions. Each of these questions have sub-parts [(i), (ii) and (iii)] with internal choice in one sub-part.

29. Sanger's method of DNA sequencing is a widely used technique to determine the nucleotide sequence of a DNA fragment. Primers are extended using the single strand DNA template as a guide, where the normal substrates i.e. deoxynucleotide 5' triphosphates (dNTPs) are incorporated in the growing DNA chain. This method is based upon the principle of chain termination by ddNTPs (2', 3' dideoxynucleotide tri phosphates) which, if incorporated into each extending chain (instead of the required dNTP) cause termination. Radioactive primers may be used to visualize separated strands in the gel by autoradiography. Nowadays, DNA sequencing have become automated, where ddNTPs are conjugated with fluorescent molecules and the gels obtained are scanned by laser.

(i) Why are primers required in Sanger's method of DNA sequencing? [1 Mark]

Answer: Primers are required because only primers can be extended by DNA polymerase using the single strand DNA template as a guide; the enzyme cannot start a new chain on its own.

Teacher's Note:
a) DNA polymerase needs a free 3'-OH end, which the primer provides.
b) Link your answer to the case text: primers are "extended using the single strand DNA template".

(ii) Write the difference between dNTPs and ddNTPs. What is the function of ddNTPs in Sanger's method of DNA sequencing? [2 Marks]

Answer:
1. Difference: dNTPs have a 3'-OH group on the sugar, whereas ddNTPs lack the 3'-OH group.
2. Function: ddNTPs terminate the growing DNA chain at the point where they are incorporated.

Teacher's Note:
a) Without a 3'-OH, the next nucleotide cannot form a phosphodiester bond, so the chain stops.
b) Structures showing the correct 3' positions of dNTP and ddNTP are also accepted.

(iii) What is the advantage of using ddNTPs conjugated with fluorescent molecules in automated method of DNA sequencing? [1 Mark]

Answer: The danger of using radioisotopes is avoided, and the gels can be scanned by laser.

Teacher's Note:
a) Another accepted advantage: a single lane gel can be run instead of four lanes.
b) Any one advantage is enough for the 1 mark.

OR

(iii) Which enzyme is used in Sanger's method of DNA sequencing? [1 Mark]

Answer: DNA Polymerase.

Teacher's Note:
a) DNA polymerase extends the primer by adding dNTPs or ddNTPs.
b) Do not write DNA ligase or restriction enzyme; they are not used in chain extension.

30. Genetically modified or transgenic crops with improved agronomic traits have been developed by introduction of foreign genes into crop plants, using cell and tissue culture systems. The explants are cultured on a suitable nutrient medium which provides macro-nutrients, micronutrients, carbon source, vitamins, amino acids alongwith plant hormones required for growth, cell division and development of plant cells in culture. Plant cell culture and applications deal with various types of cultures such as organ culture, explant culture, callus culture, cell suspension culture, protoplast culture, mass cell culture and each of these have widespread uses in plant regeneration, genetic transformation studies, and many more applications of plant cell and tissue culture.

(i) What is meant by explant culture? [1 Mark]

Answer: The culture of any piece or part of a plant (called an explant) on a nutrient medium is known as explant culture.

Teacher's Note:
a) An explant can be a piece of leaf, stem, root or any other plant part.
b) Define the term "explant" within your answer for full credit.

(ii) Mention hormones that are used for promoting growth and cell division of plant cells in culture. [2 Marks]

Answer:
1. Auxins, which promote growth (cell elongation) of plant cells.
2. Cytokinins, which promote cell division.

Teacher's Note:
a) Gibberellin is also accepted; any two hormones earn full marks.
b) The ratio of auxin to cytokinin decides whether roots or shoots form in culture.

(iii) What is meant by "Protoplast"? [1 Mark]

Answer: Plant cells without a cell wall are known as protoplasts.

Teacher's Note:
a) Protoplasts are obtained by removing the cell wall with enzymes such as cellulase and pectinase.
b) The phrase "without cell wall" is the key value point.

OR

(iii) Write an application of callus culture. [1 Mark]

Answer: Callus culture is used for micropropagation, that is, regeneration of a large number of plants.

Teacher's Note:
a) Other accepted applications: preparing single cell suspensions or protoplasts, and genetic transformation studies.
b) Only one application is needed.

SECTION E

31. (a) Explain the technique of peptide mapping used to compare normal haemoglobin with sickle cell haemoglobin. [5 Marks]

Answer:
1. Pure Hb and scHb are taken separately in test tubes and digested with the proteolytic enzyme trypsin.
2. The tryptic peptides of Hb and scHb are spotted on two separate strips of Whatman filter paper and separated by paper electrophoresis at pH 2.0.
3. The strips are dried and then chromatographed at right angles to the direction of electrophoresis, using the solvent system Butanol : Water : Acetic acid.
4. The chromatograms are dried and stained with a reagent such as ninhydrin, so that peptide regions appear as orange-yellow spots.
5. The peptide maps (fingerprints) of Hb and scHb are compared, and the amino acid sequence of the peptide placed differently in the scHb map is determined.

Teacher's Note:
a) Peptide mapping combines electrophoresis in one direction with chromatography in the other.
b) Mention trypsin, pH 2.0 and ninhydrin; these are the examiner's keywords.
c) The differing peptide showed that glutamic acid is replaced by valine in scHb.

OR

(b) Mention any five protein based products with an example of each. [5 Marks]

Answer:
1. Blood products and vaccines - for example, Factor VIII (blood clotting factor) or Hepatitis B vaccine.
2. Therapeutic antibodies and enzymes - for example, Herceptin (monoclonal antibody) or tissue plasminogen activator (tPA).
3. Therapeutic hormones and growth factors - for example, insulin or erythropoietin.
4. Industrial enzymes - for example, proteases used in detergents.
5. Nutraceutical proteins - for example, whey protein concentrates.

Teacher's Note:
a) Each category carries half a mark and its example carries half a mark.
b) Regulatory factors, analytical applications and functional non-catalytic proteins are also accepted categories.
c) Give one clear, correct example for each category; do not repeat the same example.

32. (a) Describe the basic steps of Recombinant DNA Technology. [5 Marks]

Answer:
1. A DNA fragment containing the gene of interest (called the insert) is isolated.
2. A recombinant DNA (rDNA) molecule is made by inserting this fragment into a carrier DNA molecule called a vector (for example, a plasmid) that can replicate by itself inside a host cell.
3. The rDNA is transferred into an E. coli host cell; this process is called transformation.
4. Only those host cells that carry the rDNA are selected.
5. The recombinant cells are allowed to multiply, which multiplies the rDNA molecules (cloning).

Teacher's Note:
a) Write the steps in the correct order: isolate, join, transfer, select, multiply.
b) A labelled flowchart with explanation of these steps is also accepted.
c) Use the terms "insert", "vector" and "transformation" correctly.

OR

(b) Describe the procedure involved in Restriction Fragment Length Polymorphism (RFLP) technique. Why is this technique used in forensic sciences? [5 Marks]

Answer:
1. The test DNA samples are isolated.
2. All the test DNA samples are digested with the same restriction enzyme.
3. The DNA fragments are separated according to size by agarose gel electrophoresis.
4. The gel pattern (band pattern) of the samples is analysed and compared.
5. Use in forensic science: RFLP band patterns differ from person to person, so the technique is used to identify individuals and to find how individuals are related.

Teacher's Note:
a) The four procedure steps carry 4 marks and the forensic application carries 1 mark.
b) Stress that the same restriction enzyme must be used for all samples.
c) A flowchart with explanation of the steps is also accepted.

33. (a) What is a "metagenome"? Describe the metagenomics approach and write its importance to study microorganisms. [5 Marks]

Answer:
1. Metagenome: the genomes of both the culturable and the non-culturable microbes of an environment taken together are called the metagenome.
2. In the metagenomics approach, the collective DNA is extracted from a sample of soil, water or any other environmental niche.
3. The collective DNA is digested with restriction endonucleases, and the DNA fragments obtained are cloned in suitable vectors.
4. The clones are then screened for a variety of molecules with improved characteristics.
5. Importance: it allows us to study the genomes of microbes without culturing them in the laboratory, including those that are difficult or have never been cultured, and to find genes that can be used for human benefit.

Teacher's Note:
a) Include both "culturable and non-culturable" in the definition of metagenome.
b) The approach (extract, digest, clone, screen) carries 3 marks.
c) Most microbes cannot be grown in the laboratory; this is the main reason metagenomics is useful.

OR

(b) How is a continuous culture system maintained in microbial culture? What are its advantages over Fed-batch culture? [5 Marks]

Answer:
1. The growth medium is designed so that one nutrient is present in limited quantity; during exponential growth, just before this nutrient is exhausted, fresh medium containing it is added, and this is repeated every time it is about to run out.
2. The system has an overflow device, so the added volume pushes out an equal volume of culture from the vessel.
3. In a chemostat a constant chemical environment is maintained, whereas in a turbidostat a constant cell concentration is maintained.
4. Advantage: a steady state is achieved and kept for an extended period of time.
5. Advantage: it gives higher productivity.

Teacher's Note:
a) Other accepted advantages: a continuous supply of microbial growth and easier control of constant growth conditions.
b) Do not confuse the chemostat (constant chemical environment) with the turbidostat (constant cell density).
c) The overflow device keeps the culture volume constant; mention it clearly.

Please click the link below to download pdf file of CBSE Class 12 Biotechnology Question Paper 2025 Solved Code 99