Bacteria: Round, Rod or Spiral?
Dichotomous Key
Introduction: Thousands of different types of bacteria are known and have been observed, and there are
possibly many more that have not yet been observed. How can a scientist tell these organisms apart when
they are so small? One way is the bacteria's characteristic shape or pattern of joining together in groups.
Objective: TLW identify bacteria names by using a dichotomous key and by observing the shape and
pattern of the bacteria.
Procedure: Using the key, name the eleven organisms drawn below
KEY
1.
a. the general shape of the bacterium is round…………………….………………..go to # 2
b. the general shape of the bacterium is rod-like (long & straight)……………..…go to # 5
c. the general shape of the bacterium is spiral……………..Treponema pallidum (syphylis)
2.
a. grouped in pairs………………………………………………..………………….go to # 3
b. grouped in chains…………………………..………………………………….....go to # 4
c. grouped in clumps………………………………………..Staphylococcus aureus (Boils)
3.
a. without a heavy cover……………………..…Diplococcus menigitidis (Spinal meningitis)
b. with a heavy cover………………………..…..… Diplococcus pneumoniae (Pneumonia)
4.
a. large in size………………………………..…….…...Streptococcus pyogenes (Tonsillitis)
b. small in size………………………..…… Streptococcus lactis (Used to make buttermilk)
5.
a. rods are in chains…………………………………….……. Bacillus anthracis (Anthrax)
b. rods are in pairs…………………………….... Bacillus lactis (Used to make sauerkraut)
c. rods are single………………………………………………….….……………..go to # 6
6.
a. rods have hairs (cilia)…………………………….….… Bacillus typhosa (Typhoid fever)
b. rods have a bulge (spore) in middle…………… Bacillus botulinum (Botulism poisoning)
c. rods have a bulge (spore) at end……………….…….……….... Bacillus tetani (Tetanus)
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