1) The document discusses four examples of symbiotic relationships: between rhizobium bacteria and legume plants, termites and protists in their intestines, epiphytic plants and their hosts, and humans and the AIDS virus. 2) In the first two relationships, both organisms benefit through nitrogen fixation by bacteria and cellulose digestion by protists. 3) The third relationship is commensal, where epiphytic plants benefit from nutrients on host plants without affecting them. 4) The fourth relationship of AIDS is parasitic, as the virus benefits by weakening the human immune system at the human's expense.

1. Stephanie Okpara
August 27, 2009
AP Biology- Pd. 1
Free-Response Question 4
The participants in the symbiotic relationship pertaining to plant root nodules are
rhizobium and legumes. The host is the legume and the symbiont is the rhizobuim. This
relationship is a mutual relationship meaning that both organisms benefit from the
relationship. Rhizobium live in the host plant’s root cells and bind nitrogen from the air
in the nodules. In exchange for this service, the bacteria receives high-energy
carbohydrates produced in photosynthesis.
One example of the symbiotic relationship of the digestion of cellulose is the
termite. The participants in this relationship are termites and protists, which reside in the
termite’s intestines. This relationship is also mutual. The protists digest the cellulose
contained in wood which helps the termite digest it otherwise the termite would die from
a lack of nutrition. In return, the termite provides food and refuge for the protist.
The participants in the symbiotic relationship of epiphytic plants are epiphytes
and various mosses, ferns, bromeliads, orchids, and other plants. The relationship is
commensal meaning that one organism benefits and the other is unaffected. Epiphytes
grown on sturdier plants and obtain nutrients from rainwater, decaying leaves, and
sunlight and not from the host.
The two participants in the relationship of AIDS are the human (host) and the
virus (symbiont). This is a parasitic relationship, a relationship where the symbiont
benefits at the expense of the host. This virus reduces the effectiveness of the immune
system and leaves the individual vulnerable to infections and tumors. This causes the
human to slowly deteriorate.