NCERT Solutions for Class 12 Biology Chapter 9: Biotechnology: Principles and Processes (NCERT 2026–27)

These Class 12 Biology Chapter 9 solutions cover Biotechnology: Principles and Processes from the latest NCERT textbook (session 2026–27). You get every end-of-chapter Exercise question reproduced verbatim and answered in exam-ready prose, plus a clear explanation of the tools (restriction enzymes, vectors, host) and the processes (isolation of DNA, PCR, bioreactors, downstream processing) of recombinant DNA technology. Extra short and long questions, MCQs and Assertion–Reason practice are added so you can score full marks in your board exam.

Class: 12 Subject: Biology Chapter: 9 Title: Biotechnology: Principles and Processes Unit: Biotechnology Session: 2026–27
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Class 12 Biology Chapter 9 Solutions – Overview

Chapter 9, Biotechnology: Principles and Processes, explains how scientists use living organisms, cells or enzymes to make useful products on a large scale. The two pillars are genetic engineering (altering the chemistry of DNA/RNA and moving it into a host to change its phenotype) and bioprocess engineering (maintaining sterile conditions to grow the desired microbe or cell in large amounts). The chapter develops the principle of recombinant DNA technology — isolating a desired gene, joining it to a vector that carries an origin of replication, transferring it into a competent host such as E. coli, and letting it multiply. You learn the essential tools (restriction enzymes, DNA ligase, vectors like pBR322 and Ti plasmid, and a competent host) and the ordered processes (isolation of DNA, restriction digestion, amplification by PCR, insertion into the host, large-scale culture in bioreactors, and downstream processing).

Key Concepts & Definitions

Recombinant DNA (rDNA): a new combination of DNA created in vitro by joining a desired DNA fragment to a vector using DNA ligase, so the fragment can replicate inside a host.

Restriction endonuclease: a “molecular scissor” that recognises a specific palindromic sequence and cuts both strands a little away from the centre, leaving complementary single-stranded sticky ends (e.g. EcoRI cuts G⇓AATTC).

Cloning vector: a DNA molecule (plasmid such as pBR322, or bacteriophage) that carries foreign DNA into a host. Key features: origin of replication (ori), selectable marker, single cloning sites, and a means of selecting recombinants (e.g. insertional inactivation of tetR or of β-galactosidase).

Competent host: a cell (e.g. E. coli) treated with a divalent cation such as Ca2+ and given a brief heat shock at 42°C so it can take up DNA through its wall.

PCR (Polymerase Chain Reaction): in vitro amplification of a target DNA using two primers and a thermostable DNA polymerase (Taq polymerase from Thermus aquaticus); each cycle has denaturation, primer annealing and extension, and can make about a billion copies.

Gel electrophoresis: separation of DNA fragments on an agarose gel; being negatively charged, fragments move towards the anode and resolve by size — smaller fragments move farther. Bands are stained with ethidium bromide and viewed under UV, then cut out (elution).

Bioreactor: a vessel (100–1000 L) that provides optimum growth conditions (temperature, pH, substrate, salts, vitamins, oxygen) for large-scale culture; commonly a stirred-tank type.

Downstream processing: separation, purification, formulation, quality control and clinical testing carried out after biosynthesis to make a marketable product.

NCERT Exercises — Complete Solutions

All questions below are reproduced verbatim from the NCERT textbook (Exercises, Chapter 9). Answers are original, exam-ready explanations.

1. Can you list 10 recombinant proteins which are used in medical practice? Find out where they are used as therapeutics (use the internet).

ANSWER Ten recombinant proteins (made by cloning the human/animal gene in a host such as E. coli, yeast or animal cells) used in medicine, with their therapeutic use:
Recombinant proteinTherapeutic use
Insulin (Humulin)Treatment of diabetes mellitus
Human growth hormone (somatotropin)Treatment of dwarfism / growth deficiency
Erythropoietin (EPO)Stimulates red-blood-cell formation in anaemia / kidney failure
Factor VIIITreatment of haemophilia A (clotting disorder)
Factor IXTreatment of haemophilia B
Tissue plasminogen activator (tPA)Dissolves blood clots in heart attack and stroke
Interferons (α, β, γ)Antiviral, anticancer; multiple sclerosis
Interleukin-2Immune stimulation; certain cancers
Hepatitis B vaccine (recombinant surface antigen)Immunisation against hepatitis B
Streptokinase / DNase (Dornase alfa)Clot dissolution; thinning mucus in cystic fibrosis
(Granulocyte colony-stimulating factor, follicle-stimulating hormone and recombinant clotting factors are further examples.)

2. Make a chart (with diagrammatic representation) showing a restriction enzyme, the substrate DNA on which it acts, the site at which it cuts DNA and the product it produces.

ANSWER Take EcoRI as the example restriction enzyme. It recognises the palindromic sequence GAATTC and cuts each strand between G and A, leaving complementary single-stranded “sticky ends.”
StageRepresentation
Restriction enzymeEcoRI (from Escherichia coli RY13)
Substrate DNA (recognition site)5’—G A A T T C—3′
3’—C T T A A G—5′
Site of cutBetween G and A on both strands (G⇓AATTC):
5’—G      A A T T C—3′
3’—C T T A A      G—5′
ProductTwo fragments, each with a 4-base single-stranded “sticky end” (5′-AATT overhang) able to base-pair with any DNA cut by the same enzyme
Because the cut leaves matching sticky ends, fragments from different sources cut by the same enzyme can be joined end-to-end with DNA ligase to form recombinant DNA.

3. From what you have learnt, can you tell whether enzymes are bigger or DNA is bigger in molecular size? How did you know?

ANSWER DNA is far bigger. Enzymes are proteins built from at most a few thousand amino acids, whereas a single DNA molecule (a chromosome) contains millions to billions of nucleotide base pairs. We can reason it from the chapter: a restriction enzyme acts on the DNA — it “inspects” the length of a long DNA molecule to find a short recognition sequence and then cuts it. An enzyme can move along and recognise a small site only because the DNA substrate is enormously longer than the enzyme itself. The genetic information for making thousands of such enzymes is itself stored in the DNA, so the DNA must be the larger molecule.

4. What would be the molar concentration of human DNA in a human cell? Consult your teacher.

ANSWER A typical diploid human cell contains just two copies of the genome (2 molecules of DNA per gene/locus). Molar concentration = number of moles ÷ volume. Number of moles of DNA = 2 ÷ (6.022 × 1023) ≈ 3.32 × 10−24 mol. Taking the volume of a human cell as roughly 10−12 L (about 1000 µm3), molar concentration ≈ (3.32 × 10−24 mol) ÷ (10−12 L) ≈ 3.3 × 10−12 M (of the order of a few picomolar). The exact figure depends on the assumed cell volume, but the key point is that the molar concentration of human DNA in a single cell is extremely small — in the picomolar range — because there are only two genome copies present.

5. Do eukaryotic cells have restriction endonucleases? Justify your answer.

ANSWER No, eukaryotic cells normally do not have restriction endonucleases. These enzymes are part of the bacterial (prokaryotic) defence system known as the restriction–modification system. In bacteria, restriction endonucleases cut foreign (e.g. bacteriophage) DNA at specific recognition sequences, restricting the growth of the invader, while the cell’s own DNA is protected by methylation at those sites. Eukaryotes do not face the same need to destroy invading phage DNA in this way and rely on other defence mechanisms, so they lack these site-specific cutting enzymes. (This is why the restriction enzymes used in genetic engineering are obtained from bacteria.)

6. Besides better aeration and mixing properties, what other advantages do stirred tank bioreactors have over shake flasks?

ANSWER A shake flask handles only a small volume and gives little control, whereas a stirred-tank bioreactor processes large volumes (100–1000 L) and is fully controlled. Besides better aeration and mixing, its added advantages are: • Large-scale processing — far greater biomass and product yield than a flask. • Control systems — built-in temperature-control, pH-control, foam-control and an oxygen-delivery system maintain optimum conditions throughout. • Sampling ports — small volumes can be withdrawn periodically to monitor the culture without contaminating it. • Sterility and continuous operation — conditions can be kept sterile, and a continuous culture system can drain used medium while adding fresh medium to keep cells in the active log phase.

7. Collect 5 examples of palindromic DNA sequences by consulting your teacher. Better try to create a palindromic sequence by following base-pair rules.

ANSWER A DNA palindrome reads the same (5’→3′) on both strands. Five recognition palindromes used by restriction enzymes:
Enzyme5’→3′ top strand
EcoRIGAATTC
BamHIGGATCC
HindIIIAAGCTT
PstICTGCAG
SalIGTCGAC
Creating one: write a sequence and its complement so that reading 5’→3′ on each strand gives the same letters. Example —
5’—G G C C—3′
3’—C C G G—5′
Reading the bottom strand 5’→3′ also gives GGCC, so GGATCC, AGCT and similar even-length symmetric sequences are valid palindromes.

8. Can you recall meiosis and indicate at what stage a recombinant DNA is made?

ANSWER During meiosis, recombination occurs in Pachytene of Prophase I. At this stage, homologous chromosomes are tightly paired (synapsis) as bivalents, and crossing over takes place — non-sister chromatids exchange corresponding segments at the chiasmata. This exchange of DNA segments between homologous chromosomes is mediated by the enzyme recombinase and produces new combinations of alleles, i.e. naturally recombinant DNA. (This is the natural counterpart of the artificial recombinant DNA made in vitro in the laboratory.)

9. Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign DNA in addition to a selectable marker?

ANSWER A reporter enzyme lets us see, directly, whether the foreign DNA has inserted into the vector, through a visible colour change — a method called insertional inactivation. The enzyme β-galactosidase is commonly used. The foreign DNA is inserted within the coding sequence of this enzyme. If a host cell takes up a plasmid without an insert, the gene is intact, β-galactosidase is made, and in the presence of a chromogenic substrate the colony turns blue. If the plasmid carries an insert, the β-galactosidase gene is disrupted (insertional inactivation), no enzyme is made, and the colony stays colourless/white — identifying it as a true recombinant. Thus, while the selectable marker (e.g. antibiotic resistance) only confirms that a cell is transformed, the reporter enzyme distinguishes recombinants from non-recombinants by a simple colour test, avoiding the need to plate on two different antibiotics.

10. Describe briefly the following:

(a) Origin of replication

ANSWER The origin of replication (ori) is a specific DNA sequence from which replication starts. Any piece of DNA linked to this sequence can replicate within host cells. It also controls the copy number of the linked DNA, so a vector with a high-copy ori is chosen when many copies of the target gene are wanted.

(b) Bioreactors

ANSWER Bioreactors are large vessels (100–1000 L) in which raw materials are biologically converted into specific products, enzymes, etc., using microbial, plant, animal or human cells. They provide optimum growth conditions (temperature, pH, substrate, salts, vitamins and oxygen). The common stirred-tank type has an agitator, an oxygen-delivery system, a foam-control system, temperature and pH control, and sampling ports.

(c) Downstream processing

ANSWER Downstream processing is the series of steps a product undergoes after the biosynthetic stage, before it is sold. It includes separation and purification of the product, formulation with suitable preservatives, clinical trials (in the case of drugs) and strict quality-control testing. The exact processing differs from product to product.

11. Explain briefly

(a) PCR

ANSWER PCR (Polymerase Chain Reaction) amplifies a gene/DNA of interest in vitro. It uses two sets of primers (short chemically synthesised oligonucleotides complementary to flanking regions) and a thermostable DNA polymerase (Taq polymerase from Thermus aquaticus). Each cycle has three steps — denaturation (strands separated by heat), primer annealing (primers bind the template), and extension (polymerase synthesises new strands). Repeating many cycles can amplify the segment about a billion times; the product can then be ligated into a vector for cloning.

(b) Restriction enzymes and DNA

ANSWER Restriction enzymes are endonucleases (“molecular scissors”) that recognise a specific palindromic sequence in DNA and cut both strands of the double helix in their sugar-phosphate backbone, a little away from the centre of the palindrome but between the same two bases on the opposite strands. This leaves complementary single-stranded sticky ends. DNA cut by the same enzyme has matching sticky ends that can be joined by DNA ligase, which is the basis for making recombinant DNA. They belong to the class of nucleases (exonucleases remove end nucleotides; endonucleases cut within the DNA).

(c) Chitinase

ANSWER Chitinase is an enzyme used during the isolation of DNA from fungal cells. Fungal cell walls are made of chitin, so chitinase breaks open (digests) the fungal cell wall to release the DNA along with other macromolecules, allowing the genetic material to be extracted and purified. (Compare: lysozyme is used for bacteria, cellulase for plant cells.)

12. Discuss with your teacher and find out how to distinguish between

(a) Plasmid DNA and Chromosomal DNA

ANSWER
Plasmid DNAChromosomal DNA
Small, circular, extra-chromosomal DNALarge; the main genome of the cell
Replicates autonomously; copy number can vary (1–100+)Replicates once with the cell; one (or paired) copy
Carries non-essential genes (e.g. antibiotic resistance); used as a vectorCarries genes essential for survival

(b) RNA and DNA

ANSWER
RNADNA
Sugar is riboseSugar is deoxyribose
Bases A, U, G, C (uracil instead of thymine)Bases A, T, G, C (thymine)
Usually single-stranded; less stableUsually double-stranded; more stable; the genetic material in most organisms
Removed during DNA isolation by treatment with ribonucleasePrecipitated and spooled out as fine threads with chilled ethanol

(c) Exonuclease and Endonuclease

ANSWER
ExonucleaseEndonuclease
Removes nucleotides from the ends of DNAMakes cuts at specific internal positions within the DNA
Acts in a sequence-independent way at the terminiRestriction endonucleases recognise specific palindromic sequences
Used for end trimming/degradationUsed in genetic engineering to cut DNA at recognition sites

Extra Practice Questions

Short Answer Type Questions

Q1. Name the two core techniques that gave birth to modern biotechnology.

ANSWERGenetic engineering (altering DNA/RNA and introducing it into a host) and bioprocess engineering (maintaining sterile conditions for large-scale growth of the desired cell).

Q2. How is a bacterial cell made “competent” to take up DNA?

ANSWERThe cells are treated with a specific concentration of a divalent cation such as Ca2+, which increases pore uptake of DNA. The recombinant DNA is then incubated with the cells on ice, given a brief heat shock at 42°C, and placed back on ice, so the DNA enters the cell.

Q3. Why is DNA visualised with ethidium bromide and not in visible light directly?

ANSWERPure DNA is colourless and cannot be seen in visible light. Ethidium bromide binds DNA and, when exposed to UV radiation, shows bright orange bands on the agarose gel, allowing the separated fragments to be located and eluted.

Q4. State the three basic steps in genetically modifying an organism.

ANSWER(i) Identification of DNA with desirable genes; (ii) introduction of the identified DNA into the host; (iii) maintenance of the introduced DNA in the host and its transfer to the progeny.

Q5. Name three methods, other than the heat-shock method, used to introduce alien DNA into host cells.

ANSWERMicro-injection (DNA injected directly into the nucleus of an animal cell); biolistics or “gene gun” (cells bombarded with DNA-coated gold/tungsten particles, used for plants); and the use of “disarmed pathogen” vectors that infect the cell and transfer the recombinant DNA.

Long Answer Type Questions

Q1. Describe, in order, the main steps of recombinant DNA technology.

ANSWERRecombinant DNA technology proceeds in a fixed sequence. First, the genetic material (DNA) is isolated in pure form: cells are broken open using lysozyme (bacteria), cellulase (plant) or chitinase (fungus); RNA is removed with ribonuclease and proteins with protease; and purified DNA is precipitated with chilled ethanol and spooled out. Second, the DNA is cut at specific sites using restriction endonucleases, and the progress is checked by agarose gel electrophoresis; the vector is cut with the same enzyme. Third, the gene of interest is amplified by PCR using primers and Taq polymerase. Fourth, the cut gene and cut vector are mixed with DNA ligase to form recombinant DNA. Fifth, this rDNA is introduced into a competent host (e.g. E. coli made competent with Ca2+ and heat shock), and transformants are selected using a selectable marker. Sixth, the host is cultured on a large scale in bioreactors to obtain the foreign gene product. Finally, the product is recovered through downstream processing — separation, purification, formulation and quality control — before marketing.

Q2. Explain the features that a good cloning vector must have, using pBR322 as an example.

ANSWERA cloning vector needs four features. (i) An origin of replication (ori) so the linked DNA replicates inside the host, and which also fixes the copy number. (ii) A selectable marker — usually an antibiotic-resistance gene (ampicillin, tetracycline, kanamycin, etc.) — that lets transformed cells be identified and untransformed cells eliminated. (iii) Cloning sites — preferably single recognition sites for common restriction enzymes, so the vector is cut cleanly. (iv) A way to select recombinants. In pBR322, foreign DNA is ligated at the BamHI site inside the tetR (tetracycline-resistance) gene. Recombinants lose tetracycline resistance (insertional inactivation) but retain ampicillin resistance, so they grow on ampicillin medium but not on tetracycline medium, while non-recombinants grow on both. Alternatively, a reporter enzyme such as β-galactosidase gives blue (non-recombinant) versus white (recombinant) colonies, making selection simpler.

Q3. How are genes delivered into plant and animal cells using “disarmed” natural vectors?

ANSWERSome pathogens naturally transfer genes into eukaryotic cells, and scientists have modified these into safe vectors. In plants, Agrobacterium tumefaciens normally delivers a piece of DNA called T-DNA (carried on its tumour-inducing or Ti plasmid) into plant cells, turning them into tumours that make chemicals for the pathogen. The Ti plasmid has now been disarmed — made non-pathogenic — while keeping its gene-delivery machinery, so it can ferry genes of our interest into many plants. In animals, retroviruses can transform normal cells into cancerous cells; they too have been disarmed and are now used to deliver desirable genes into animal cells. Thus a gene ligated into such a vector is transferred into a bacterial, plant or animal host, where it multiplies.

MCQs

1. The first restriction endonuclease isolated and characterised was:

(a) EcoRI    (b) Hind II    (c) BamHI    (d) DNA ligase

2. The “molecular scissors” used in genetic engineering are:

(a) DNA ligases    (b) DNA polymerases    (c) restriction endonucleases    (d) primases

3. Taq polymerase used in PCR is obtained from:

(a) Escherichia coli    (b) Thermus aquaticus    (c) Agrobacterium tumefaciens    (d) Salmonella typhimurium

4. During gel electrophoresis, DNA fragments move towards the:

(a) cathode (negative)    (b) anode (positive)    (c) either electrode    (d) they do not move

5. In recombinant DNA technology, fragments cut by restriction enzymes are joined by:

(a) DNA polymerase    (b) helicase    (c) DNA ligase    (d) exonuclease

6. The recognition sequence of a restriction enzyme is described as a:

(a) random sequence    (b) palindromic sequence    (c) single-stranded loop    (d) tandem repeat

7. Bacterial cells are made “competent” to take up DNA by treatment with:

(a) chilled ethanol    (b) ethidium bromide    (c) a divalent cation such as Ca2+    (d) agarose

8. In pBR322, foreign DNA ligated at the BamHI site causes insertional inactivation of:

(a) the ori    (b) ampicillin resistance (ampR)    (c) tetracycline resistance (tetR)    (d) the rop gene

9. The enzyme used to break open fungal cells during DNA isolation is:

(a) lysozyme    (b) cellulase    (c) chitinase    (d) protease

10. The Ti plasmid used as a cloning vector for plants is obtained from:

(a) a retrovirus    (b) Agrobacterium tumefaciens    (c) E. coli    (d) Bacillus thuringiensis

Answer key: 1-(b), 2-(c), 3-(b), 4-(b), 5-(c), 6-(b), 7-(c), 8-(c), 9-(c), 10-(b).

Assertion–Reason Questions

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: Restriction enzymes leave “sticky ends” after cutting DNA.

Reason: They cut the two strands a little away from the centre of the palindrome, leaving complementary single-stranded overhangs.

A-R 2. Assertion: An alien DNA must be linked to an origin of replication to multiply in a host.

Reason: The origin of replication is the sequence responsible for initiating replication.

A-R 3. Assertion: Eukaryotic cells contain abundant restriction endonucleases.

Reason: Restriction enzymes are part of the bacterial restriction–modification defence system.

A-R 4. Assertion: Taq polymerase is preferred for PCR.

Reason: It is thermostable and remains active during the high-temperature denaturation step.

A-R 5. Assertion: Recombinant colonies of bacteria appear white while non-recombinant colonies appear blue.

Reason: Insertion of foreign DNA inactivates the β-galactosidase gene, so no colour is produced with the chromogenic substrate.

Answer key: 1-(A), 2-(A), 3-(D), 4-(A), 5-(A).

Common Mistakes to Avoid

Watch out for these

  • Confusing exonuclease (cuts from ends) with endonuclease (cuts within the DNA at specific sites).
  • Writing that DNA moves to the cathode — DNA is negatively charged, so it moves to the anode (positive electrode).
  • Mixing up the wall-digesting enzymes: lysozyme for bacteria, cellulase for plant cells, chitinase for fungi.
  • Saying recombinants are blue — recombinants (with insert) are white/colourless; non-recombinants are blue.
  • Forgetting that the source DNA and vector must be cut with the same restriction enzyme so the sticky ends match.
  • Stating that PCR uses an ordinary DNA polymerase — it needs a thermostable polymerase (Taq).

How to score full marks in this chapter

Learn the tools (restriction enzyme, ligase, vector, host) and the ordered processes as separate lists — examiners often ask for “steps of rDNA technology in sequence.” Always mention the example enzyme EcoRI cutting at G⇓AATTC and leaving sticky ends. For selection questions, clearly explain insertional inactivation (both the tetR/ampicillin method and the blue–white β-galactosidase method). Define ori, selectable marker and competent cells precisely, and remember the three PCR steps and that Taq polymerase is thermostable.

Frequently Asked Questions

What is Class 12 Biology Chapter 9 about?

Chapter 9, Biotechnology: Principles and Processes, explains genetic engineering and bioprocess engineering — how recombinant DNA is made using restriction enzymes, ligase, vectors and a competent host, and how the gene product is obtained through PCR, large-scale bioreactor culture and downstream processing.

What are restriction enzymes and why are they called molecular scissors?

Restriction enzymes are endonucleases that recognise specific palindromic DNA sequences and cut both strands at fixed points, leaving complementary sticky ends. They are called “molecular scissors” because they cut DNA precisely, allowing fragments from different sources to be joined into recombinant DNA.

Why is PCR important in recombinant DNA technology?

PCR amplifies the gene of interest about a billion times in vitro using two primers and the thermostable Taq polymerase. The large number of copies makes it easy to ligate the gene into a vector and proceed with cloning.

Are these Class 12 Biology Chapter 9 solutions free?

Yes. All ClearStudy NCERT Solutions for Class 12 Biology are free and follow the official NCERT textbook for session 2026–27.

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