OBSERVATIONS OF A UNICELLULAR ORGANISM
The purpose of this lab is to find, follow and study this organism as if you were
the first person to ever have a look at it. It lives in fresh water. Your lab report should
include words and several sketches to describe as completely as possible this new
living thing, and how it carries out its life functions. In particular, pay attention to: how it
gets food, how it digests food, how it senses its environment, how it moves, how it gets
rid of waste, how it absorbs oxygen and gets rid of carbon dioxide, how it reproduces,
and how it responds to chemical toxins. Some terms mentioned in this sheet may be
found in your text or in other biology books found in the room. Do not get information
from the web for this – in other words, try to draw the creature (a Paramecium) yourself
without being biased by pictures from the web.
All of this information goes in your lab notebook. The things you need to draw
and/or label are listed in red. The questions you need to answer are given in blue.
Some of the things you do in this lab are optional and you should do them only if you
have time. These are indicated in green. You will not be penalized if you don’t do them,
but it would be nice if you have the time to do them.
Work down this list in the order given:
1. Draw a full page creature. Include any detail of cellular structure you see. You
can use the web or textbooks to help you identify and label structures. Write
down the names of things you have identified, with lines connecting the name
and the structure in your picture. Give a brief (one sentence) description of what
the structure does.
2. Label the anterior and posterior ends of the creature.
3. Describe the motion of your organism as it moves in one direction. Use
diagrams for this purpose. (They can be smaller than full page). Explain what it
does when it encounters obstacles in its path. (“Cotton corrals” will help you
here.) What structures does it use for movement? Draw them.
4. Locate and add to your drawing (if you haven’t already) the contractile vacuoles,
a very fancy organelle. These fill up and periodically empty. Count the number
of times a contractile vacuole empties in a two minute time period – in one
sentence, present this information. (These vacuoles are important to your critter--fresh water is continually flooding into the cell. What is the function of these
vacuoles?)
5. Add a drop of yeast suspension stained with Congo Red to your little beast.
Yeast are a type of fungi and are a good food source. You should watch carefully
to see if you can see how the little fella gets the yeast inside itself (SKETCH
THIS in small pictures). Carefully watch a food vacuole and note any changes in
it. Answer the following questions:
a. Describe any color change you see in the vacuole. Congo Red is the
stain used to color the yeast cells. It is also a pH indicator. Explain the
color change – what happens to the yeast particle once it is engulfed by
the organism? This color change should take about 10 minutes.
b. What function do cilia play in getting food?
6. If you observe reproduction and a response to chemical toxins (such as an acid),
describe and sketch these.