What class of biological agent is produced and dervied from living plants animals or some microorganisms?

Answer 1

The definition of 'biological agent' is pretty much anything that is derived from living plants, animals or microorganisms. The use of harmful agents in warfare is known as "Biological Warfare", and most medicines are initially sourced from various living things, even if they are later synthesized.

Answer 2

Yes, there are many. They are a form of defense for the organism that produces them. They may cause death to the second organism. Bacteria that cause tetanus produces a toxin that causes the muscles to "lock up". Tetanus is often called lock jaw for this reason. No one know why these bacteria do this. Perhaps it prevents competition from other organisms.

Some frogs have very colorful skin and this is a warning that they are dangerous to eat. People use this toxin from the skin of the frog to poison their arrows and darts. They kill game using the darts or arrows.