Which of the following statements is/are correct? 1. Viruses lack enzymes necessary for the generation of energy. 2. Viruses can be cultured in any synthetic medium. 3. Viruses are transmitted from one organism to another by biological vectors only. Select the correct answer using the codes given below.

Statement 1 is correct. A virus has no metabolic machinery of its own. It lacks the enzymes of glycolysis and respiration and cannot generate ATP. It borrows the host cell's ribosomes, enzymes and energy to replicate, which is why it is treated as an obligate intracellular parasite.

Statement 2 is wrong. Viruses cannot be grown in cell-free synthetic media. They need living host systems such as embryonated eggs, cell cultures or animals. This is why vaccine viruses were historically grown in chick embryos.

Statement 3 is wrong. Vector transmission is only one route. Viruses also spread through direct contact, respiratory droplets, contaminated water and food, faecal-oral routes, body fluids and mechanical carriage. Dengue and Japanese encephalitis are vector-borne, but influenza and polio are not.

Core concept: the living and non-living boundary of viruses and their dependence on host machinery. Mains link: antiviral drug design targets viral entry and replication, since the virus has no independent metabolism to attack.

Trap: marking statement 2 as correct because viruses are 'grown in labs' and assuming any medium will do. Culture always needs a living host.