Download Bacteria Bafflement

Science 7
Unit 2
Earth & Life History
Name: ______________________________
Date: ______________ Period: __________
Bacteria Bafflement
Part A: Bacterial Growth by Reproduction
Bacteria reproduce asexually by dividing the cell in half; each bacterium splits itself to make
two new bacteria (the original bacterium cease to exist). Bacteria reproduce every 20 minutes if they
are in goo, optimum conditions such as warm temperature, moisture and sufficient food.
When one bacterium divides in two, the two new bacteria grow to full size in a few minutes.
When conditions are favorable, these bacteria divide in two again, forming four bacteria. Eventually
these four will each divide, forming a total of eight. If optimum conditions continue, millions of bacteria
will be produced in a very short time.
Find out how many bacteria will be produced from one original bacterium, if the bacteria divide
every 20 minutes.
1. Hypothesize the number of bacteria there will be: ______________
2. Bacterial Growth: Complete the table of data.
Time
1:00 pm
1:20 pm
1:40 pm
2:00 pm
2:20 pm
2:40 pm
3:00 pm
Number of
bacteria
1
2
4
8
Time
3:20 pm
3:40 pm
4:00 pm
4:20 pm
4:40 pm
5:00 pm
5:20 pm
Number of
bacteria
3. Graph: Make a line graph of the data above. Label the y-axis “Number of Bacteria” and
number each line by 500’s. Label the x-axis “Time” and label each line with the times from the
table.
4. How close was your hypothesis to the actual number of bacteria?
___________________________
5. If the bacteria continued to divide every 20 minutes for 24 hours, there would be so many
bacteria that their mass would be 2000 Kg (44,000 pounds). Fortunately, this doesn’t happen.
What are two possible reasons why the bacteria fail to produce these huge numbers?
a. ________________________________________________________________________
b. ________________________________________________________________________
Part B: Identifying Bacteria
Use the Dichotomous Key to help identify each bacterium pictured. What is its morphology? Read
steps 1 and 1b. Choose the step that best describes the pictured bacterium. Do what the statement
says to do. Continue until you arrive at the bacterium’s scientific name Write the scientific name next
to its picture, Repeat this process for each bacterium picture. No bacterium have the same name.
1a. If the bacterium is round, go to #2.
1b. If the bacterium is not round, go to #5.
2a. If the bacterium is paired with another one, go to #3.
2b. If the bacterium is not paired, go to #4.
3a. If the bacterium has a thick cell membrane, it is Diplococcus pneumoniae which causes
the disease pneumonia.
3b. If the bacterium has a thin cell membrane, it is Diplococcus meningitides which causes
the disease spinal meningitis.
4a. If the bacterium is in a chain with many others, it is Streptococcus lactis which helps
people make buttermilk.
4b. If the bacterium is in a clump with many others, it is Staphylococcus aureus which causes
acne and Toxic Shock Syndrome.
5a. If the bacterium is long and spiral shaped, it is Treponema pallidum which causes the
disease syphilis.
5b. If the bacterium is long and rod-shaped, go to #6.
6a. If the bacterium has a bulge, go to #7.
6b. If the bacterium is a single, straight rod, it is Bacillus lactis which makes yogurt.
7a. If the bacterium has a bulge in the middle of the rod, it is Bacillus botulinum which causes
botulism poisoning.
7b. If the bacterium has a small bulge at the end of a narrow rod, it is Bacillus tetani
which causes tetanus.
Imagine that while looking through your microscope you find all the bacteria in the pictures below. You must
use the Key to identify the eight bacteria and decide which ones are helpful and which ones are harmful. When
you have identified each bacterium, write its scientific name and whether it is helpful or harmful next to it.
Bacterium Picture
Bacterium Name
Helpful or Harmful?