What is Ti plasmid?

✅Explanation:
Ti plasmid is a large, circular piece of DNA found in the bacterium Agrobacterium tumefaciens. It is responsible for the bacterium's ability to cause crown gall disease in plants by transferring the T-DNA region of the plasmid into the plant cell.

📌Other Options:
(b) Bacterial chromosome: This is the main DNA molecule of the bacterium, which contains essential genes for its survival. Ti plasmid is an extrachromosomal DNA molecule.
(c) An enzyme: Enzymes are proteins that catalyze biochemical reactions. Ti plasmid is a DNA molecule.
(d) Virus DNA: Viruses are infectious agents that contain either DNA or RNA as their genetic material. Ti plasmid is a bacterial plasmid.