The past couple of posts have been about human anatomy and physiology (which is what I’m currently teaching at SJSU) so I decided to branch out just a tiny bit in today’s post–today I’m going to give a brief introduction to viruses. Here’s today’s question:
Members of which of the following groups CANNOT produce their own ATP?
This question is testing two things: your knowledge of vocabulary and your knowledge of organismal groups. First off, the vocab. ATP is the big work in this question. ATP stands for Adenosine Triphospate, and is the energy source for cells (well, it’s quite a bit more complex than that, but I’m not going to go into it here. If you would like a very, very in depth discussion on the chemical basis of ATP and its exact function, do a search on Wikipedia. The ATP article there is fabulous). All cells use ATP to carry out essential functions such as growth, repair, and reproduction. Most organisms produce their own ATP–they have to, or they die. So, which of the above groups doesn’t? Let’s look at the groups and what they are.
Lichens: Lichens are symbiotic associations of (usually) an algae and a fungus. Without getting into the varieties of lichens, or the controversy on their relationship, the particular algae and fungus cannot live alone. However, once together the lichen is able to live, grow, and reproduce all on its own, and therefore produces its own ATP.
Bacteria: Bacteria are microscopic, single celled (for the most part) organisms. These are considered one of the smallest free-living organisms we know about. Bacteria have the ability to function apart from any other organism, although many thrive when in a symbiotic or parasitic relationship with something else. Bacteria produce their own ATP.
Diatoms: Diatoms are algae with cells walls made of silica (ever heard of diatomaceous earth? Yep, that’s these guys). Being algae, these singe celled organisms are able to live freely, and do so in bodies of water. A certain type of diatoms is what is responsible for red tide. Neat! Anyhow, since they are able to live freely, they produce their own ATP.
Protozoa: Protozoa are single celled, eukaryotic (have a membrane bound nucleus) organisms that are, for the most part, motile. They are much larger than bacteria, and differ in many other ways that I won’t get into here. Once again, however, single celled organisms capable of moving/growing/reproducing without other organisms, so they must produce their own ATP.
Viruses: Ah, viruses. Viruses are the bane of many a biologist. There have been whole summits on if a virus is alive or not, and the latest answer to come from the top minds in the field is “um…dunno.” Viruses simple beasts–they consists solely of a protein coat and an inner genome (either DNA or RNA, but not both) and are unable to carry out basic processes such as growth or reproduction without the assistance of another cell. This is where the controversy comes in–if they are unable to grow and reproduce on their own, are they really alive? Well, that’s neither here nor there for the moment. What we’re worried about is how viruses work. Viruses must hijack another cell and take over its ATP producing capabilities in order to do anything. It does this by injecting its genome into the host cell’s genome, and telling the host cell what to do from there. The host cell is sometimes destroyed during this process, and the virus goes on to infect another host.
So, the answer we’re looking for is “C” virus. Viruses must hijack another cell for basic functions, and therfore don’t produce their own ATP.