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LAB 2
BACTERIA, PROTISTA, AND FUNGI
Answers to questions in the lab exercise:
Examine Spirillum volutans.
 What is the bacterium’s shape?
The spirillum type. You see spirally-curved rods.
 Can you find the cell wall or the nucleus?
Yes, almost all bacteria have cell walls. It is the outermost layer, outside of the plasma
membrane. No, there is no nucleus. A nucleus is an organelle and bacteria do not
contain organelles.
 How many flagella are visible at each end?
You can see either 2 or 3 flagella.
 Explain how a lake overpopulated with oxygen producing algal growth could experience low
levels of oxygen. At certain times of the year, such lakes experience fish kills. That is, large
numbers of fish die and the lake is said to be “polluted” or “dying”.
When algae grow very abundantly and reach very high population levels, they will
eventually begin to run out of food. When this occurs, they start to die in great
numbers and the decomposition of the dead algae uses up the oxygen. The water can
then become ‘anoxic’, that is, without oxygen and therefore lethal to fish. The situation
clears up when water is less polluted and algae never reach such high population levels.
Examine representative species of algae in the demonstration room.
 How do you account for the differences in colour among the various algae?
The differences in colour are due to the different pigments that they have in their
chloroplasts. For example, the red algae contain phycoerythrin and phycocyanin, the
brown algae contain fucoxanthin, and the green algae contain the same pigments as
plants, that is, xanthophylls and chlorophyll a and b. These different pigments absorb
light of different wave lengths so the pigments and therefore the algae are not the same
colour.
Examine the Amoeba.
 Why is the nucleus in no constant position in the cell?
Because of amoeboid movement and the way in which Amoebas continuously change
shape, the position of the nucleus will change. The organism has an indefinite shape
and the nucleus no fixed location. Also, even when the amoeba is still, the nucleus may
continue to chance position because of cytoplasmic streaming, the flowing movement of
the cytoplasm.
Observe a Paramecium.
 Which end is anterior? Describe the shape differences between the anterior and posterior
end.
The anterior end is rounded and the oral groove faces forward, able to capture food
particles. The posterior end is more pointed.
 How does the Paramecium respond in relation to obstacles?
The Paramecium reverses, rotates, then continues forward. It repeats this process until
a clear path is found.
 How do you think it is capable of reversing direction?
The cilia beat in reverse.
 Why are contractile vacuoles a common organelle in freshwater protozoans and not marine
ones?
Because of the differences in osmotic pressure between fresh and marine water, more
water enters into freshwater organisms. Freshwater protozoans therefore have more
need of contractile vacuoles which discharge excess water. (Contractile vacuoles
regulate water content in a cell by regularly moving to the surface of the cell and
discharging the fluids in their interiors.)