Biology · Biotechnology: Principles and Processes · NEET
Agrobacterium tumefaciens is a soil bacterium that naturally carries a Ti plasmid (Ti = Tumour-inducing plasmid). In nature it transfers a piece of DNA called T-DNA into dicot plant cells and makes them grow tumours. Scientists "disarm" this Ti plasmid (remove the tumour genes, insert the gene of interest), so it becomes a harmless cloning vector that delivers our gene into plants. Memory hook: think of Agrobacterium as "nature's own genetic engineer" that we tamed.
The Ti (Tumour-inducing) plasmid of Agrobacterium carries T-DNA. We disarm it (remove tumour genes) and insert our gene of interest, so the harmless plasmid delivers that gene into a plant cell.
Your doubts, answered
What does 'Ti' in Ti plasmid actually stand for?
Ti stands for Tumour-inducing plasmid. In the wild, this plasmid carries genes that turn a normal plant cell into a tumour (a crown gall). NEET asks this exact full form directly, so remember: Ti = Tumour-inducing, NOT 'temperature independent' or 'tumour inhibiting'.
Is the Ti plasmid used for plants or for animals?
Only for PLANTS (dicot plants). Agrobacterium naturally infects dicots, so its Ti plasmid is the standard vector to deliver genes into plant cells. For animal cells (like human lymphocytes) we use a disarmed RETROVIRUS instead, not the Ti plasmid. Mixing these two is the most common NEET mistake.
Why do we call the Ti plasmid 'disarmed'?
'Disarmed' means the tumour-causing genes have been removed. The natural Ti plasmid makes tumours, which we do not want in a crop plant. So we delete those tumour genes and insert our gene of interest. The disarmed Ti plasmid still delivers T-DNA into the plant cell, but it no longer harms or makes tumours in the plant.
Can Agrobacterium deliver a gene into bacteria or human cells?
No. Agrobacterium tumefaciens delivers genes ONLY into plant (eukaryotic) cells. It is not used for prokaryotic hosts like E. coli, and not for human cells. A NEET 2023 question marked the statement 'used for both prokaryotic and eukaryotic hosts' as INCORRECT for exactly this reason.
What is T-DNA and how is it linked to the Ti plasmid?
T-DNA (Transfer DNA) is the segment of the Ti plasmid that actually moves from the bacterium into the plant cell's genome. In nature, T-DNA carries tumour genes. In genetic engineering, we replace those with our gene of interest, so the T-DNA carries and inserts OUR gene into the plant DNA.
⚠️ The NEET trap ✗ The Ti plasmid can be used as a vector to deliver genes into any host cell, including bacteria and human cells. ✓ The Ti plasmid of Agrobacterium tumefaciens delivers genes only into PLANT (eukaryotic) cells. Animal cells use disarmed retroviruses; bacteria use plasmids like pBR322 or lambda phage. 🧠 Match the vector to its host: Ti plasmid -> plants, retrovirus -> animal/human cells, pBR322 / lambda phage -> bacteria. NEET loves swapping these in match-the-column questions.
Real NEET questions
NEET 2024
The "Ti plasmid" of Agrobacterium tumefaciens stands for
A · Tumor independent plasmid
B · Tumor inducing plasmid ✓
C · Temperature independent plasmid
D · Tumour inhibiting plasmid
Solution: 'Ti' stands for Tumour-inducing plasmid. In nature it delivers T-DNA that induces tumours in dicot plants; it is later disarmed into a harmless cloning vector for delivering genes into plants.
NEET 2023
Which of the following statement is incorrect about Agrobacterium tumefaciens?
A · It transforms normal plant cells into tumorous cells.
B · It delivers 'T-DNA' into plant cell.
C · It is used to deliver gene of interest in both prokaryotic as well as eukaryotic host cells. ✓
D · 'Ti' plasmid from Agrobacterium tumefaciens used for gene transfer is not pathogenic to plant cells.
Solution: Agrobacterium delivers genes only into plant (eukaryotic) cells, NOT into prokaryotic hosts. So the statement that it works for both prokaryotic and eukaryotic hosts is incorrect. The other three statements are all true per NCERT.
NEET 2026
Match List I with List II: A. Genetically modified organism, B. Thermostable DNA polymerase, C. Ti plasmid, D. pBR322 with (I) Agrobacterium tumefaciens, (II) Bt cotton, (III) Thermus aquaticus, (IV) Escherichia coli
A · A-II, B-III, C-I, D-IV ✓
B · A-II, B-I, C-IV, D-III
C · A-I, B-IV, C-III, D-II
D · A-I, B-II, C-IV, D-III
Solution: Bt cotton is the GMO (A-II); Taq polymerase comes from Thermus aquaticus (B-III); the Ti plasmid is from Agrobacterium tumefaciens (C-I); pBR322 is an E. coli cloning vector (D-IV).
Solved Biotechnology: Principles and Processes NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What is Agrobacterium tumefaciens used for in biotechnology?
Its Ti plasmid is used as a natural cloning vector to transfer genes of interest into plant (dicot) cells during plant genetic engineering.
What is the full form of Ti in Ti plasmid?
Ti stands for Tumour-inducing plasmid, because in nature it induces tumours (crown galls) in infected plants.
Why is the Ti plasmid disarmed before use?
The natural tumour-causing genes are removed so the plasmid no longer harms the plant, while it still delivers the inserted gene of interest into the plant genome.
Which vector is used for animal cells instead of the Ti plasmid?
Disarmed retroviruses are used to deliver genes into animal and human cells; the Ti plasmid is only for plants.
What is T-DNA?
T-DNA (Transfer DNA) is the part of the Ti plasmid that integrates into the plant cell genome, carrying either tumour genes (natural) or the gene of interest (engineered).
