Molecular BiologyOrganisms do not exist in isolation. When they interact a relationship develops. There are three
main types of relationships between organisms:
A relationship where one of the organisms is helped by the relationship and the other is
unharmed is known as commensalism. For example, barnacles do not harm the whale to
which they attach themselves
A relationship where both organisms benefit from the interaction is known as mutualism. For
example, a certain type of bird catches a ride on a rhinoceros. He eats the bugs off the back
of the rhino all the while cleaning and preening the rhino.

Parasitism is a relationship in which one organism benefits and the other one is harmed or
even killed. An example of parasitism involving microorganisms is how viruses use their
host’s cells to reproduce, often harming and sometimes killings the host as with a
tapeworm inside the human gastrointestinal tract.
Find two additional example organisms for each of the three types of symbiotic relationship.
Explain how each organism enters into the symbiotic relationship and what can be done to aid
and deter their relationship. (12 marks)
The Durham Region began composting initiatives in an attempt to reduce the amount of waste
residents sent to landfills each year. Curb-side “green bins” are collected weekly, and organic
waste is held in a central location where decomposers are added to break down the waste
Adding beneficial microorganisms to compost at large-scale composting facilities aids in the
decomposition or organic waste, and produces high-quality compost in a reduced amount of
time. However, the microorganisms can leach into groundwater and run off into nearby water
systems, where they can harm other organisms.
Do the benefits outweigh the cost? Create a table in which you do a cost-benefit (pros and cons)
analysis of Durham Region’s ‘Green Bin’ initiative. (10 marks)
Once you have completed the analysis write a paragraph in which you argue whether or not
Durham Region should cancel it’s ‘Green Bin’ program. (10 marks) Marking rubric on the
following page