Name: ______Date: ______
Prokaryotes:
Eubacteria and Archaebacteria
SOLUTIONS
Eubacteria (Section 12.2 – pgs. 419-431)
1. Most people think that all bacteria are pathogenic (disease-causing). List four examples where this is not the case.
· Different stages of the nitrogen cycle require the work of bacteria to make the soil fertile and to fix nitrogen from the atmosphere (Nitrogen important in DNA, proteins).
· We use bacteria to make edible products like vinegar, butter, cheese and yogurt.
· Bacteria that are decomposers are important because they recycle nutrients from the dead to the living.
· Some animals (e.g. cows) require bacteria to digest plant materials such as cellulose. Humans need some bacteria to aid in absorption of vitamins in the gut (e.g. Vitamin K and B12).
2. Bacteria show incredible diversity. How are bacteria classified?
· Shape
· Structure of cell wall
· Sources of food (carbon) and energy
· Analysis of RNA sequences
3. What are the three main shapes exhibited by bacteria? Provide an example for each.
Shape / Name / ExampleRound / Cocci / Streptococcus mutans
Rod / Bacilli / Clostridium botulinum
Spiral / Spirilli / Treponema pallidum
4. Bacteria are also classified according to the structure of their cell walls. Gram-staining is a procedure that uses crystal violet and iodine in order to identify a Gram-positive vs. a Gram-negative bacterium. What is the difference between a Gram-positive bacterium and a Gram-negative bacterium? What colour do each appear when stained?
·
· Gram-positive bacteria have a thick protein layer on their cell walls and stain purple. The thick protein layer is caused by the presence of a larger amount of a compound called peptidoglycan.
· Gram–negative bacteria have a thin protein layer on their cell walls and stain pink. Gram-negative bacteria have a thinner protein layer because they have less peptidoglycan than gram-positive bacteria. Also, they have an outer membrane that prevents some antibacterial agents from entering the cell. This would explain why most Gram-negative bacteria are pathogenic (disease-causing). (See Figure 12.14)
5. Most pathogenic bacteria (disease-causing) are Gram-negative because of the different amino acids and sugars that are on their cell walls. Why is it important that your doctor has knowledge of this?
· Doctors use the knowledge of which type of cell is present in order to choose which antibiotics or other antibacterial agents to prescribe for a particular bacterial infection.
6. Bacteria live EVERYWHERE, including: on and inside plants and animals, on the living, on the dead, in the soil, in the depths of the oceans, in extreme cold and hot, and in salty waters. Why are bacteria found in almost every kind of environment?
· Bacteria can use widely different sources of energy and materials that other organisms cannot.
7. Study figure 12.8 and the “Word Link” box. Define the following terms:
Bacteria can be classified according to their source for carbon:
a. AUTOTROPHS – organisms whose principle carbon source is CO2. This compound is then used to create other carbon compounds like glucose. Also known as producers.
b. HETEROTROPHS – organisms whose principle carbon sources are other carbon compounds like glucose. They cannot make these compounds from CO2, so they need to feed on others. Also known as consumers.
Bacteria can be classified according to their source of energy:
· PHOTOTROPHS – organisms whose energy source is from light (Sun)
· CHEMOTROPHS – organisms whose energy source is from chemicals
Bacteria can be classified according to their energy source and source of carbon:
f. PHOTOAUTOTROPHS – organisms whose energy source is light and whose principle carbon source is CO2.
· Bacteria examples: cyanobacteria
· Other examples: trees, grass, some protists like algae
g. PHOTOHETEROTROPHS – organisms whose energy source is light and uses organic compounds (e.g. glucose) as its principle source of carbon.
· Bacteria examples: Certain marine prokaryotes like Rhodobacter, Chloroflexus
h. CHEMOAUTOTROPHS – organisms whose principle carbon source is CO2 and uses inorganic chemical compounds (e.g. hydrogen sulfide, ammonia and Iron ions) as an energy source.
· Unique to certain prokaryotes
i. CHEMOHETEROTROPHS – organisms who must consume organic molecules (e.g. glucose) for both energy and as a carbon source.
· Many prokaryotes and protists, fungi, animals and some plants
Bacteria can be classified according to their dependence/lack of dependence on Oxygen:
c. AEROBIC BACTERIA – require oxygen gas for growth and metabolism
d. OBLIGATE ANAEROBIC BACTERIA – do not require oxygen for growth, die when exposed to oxygen
e. FACULTATIVE ANAEROBIC BACTERIA – can grow either in the presence or absence of oxygen
8. Based upon your definitions in 8 above and from studying figure 12.8, place the following types of bacteria in order from oldest to youngest.
a. Photoautotrophs (SECOND OLDEST)
b. Photoheterotrophs (THIRD OLDEST)
c. Chemoautotrophs (OLDEST – rely on material in “primitive” atmosphere)
d. Chemoheterotrophs (FOURTH OLDEST)
9. Describe the organization of the bacterial genome.
· Have a bacterial chromosome (without nuclear membrane) and plasmids (small circular molecules of DNA that contain “accessory genes”).
10. Why can’t bacteria reproduce by mitosis or meiosis? They lack nuclei
11. What is the name of the process by which bacteria reproduce under ideal conditions? Why type of reproduction is this?
· Binary Fission (asexual reproduction)
12. Bacteria, given the right environmental conditions, can reproduce at an exponential rate. Why isn’t the entire Earth’s surface covered with bacteria?
· Predators, unfavourable environmental conditions, and varied availability of resources
13. Describe the process of conjugation. What type of reproduction is this? What is the advantage to of this type of reproduction?
· Bacterial cells become linked to one another through bridging structures called pili (sex pili).
· One bacterium transfers all or part of its chromosome and/or certain plasmids to the other across this structure
· Receiving cell undergoes binary fission to produce more cells with the same genetic makeup
· Sexual reproduction
· Advantage: produces cells with new genetic combinations (more variability) à provides a chance that some may be better adapted to changing environmental conditions (better adaptability) à Natural Selection à Evolution!
14. What is a bacterial plasmid? One amazing fact about plasmids is that they carry “accessory genes” or genes that are not responsible for the normal functioning of bacteria. Examples of “accessory genes” are those genes that confer antibiotic resistance. Plasmids can do two amazing things with their plasmids. Describe them.
· Plasmids are small circular DNA that are separate from the main chromosome.
· Plasmids can split from the main bacterial chromosome and rejoin it.
· Plasmids can move from one bacterial cell to another through conjugation.
15. Study figure 12.11. What type of enzyme is used in order to remove the insulin gene from the E.coli plasmid?
· Restriction enzymes
16. What are bacterial endospores?
· Bacteria develop a tough outer coating that surrounds their DNA and a small amount of cytoplasm. This structure is an endospore. It prevents the bacterial cell from growing and reproducing when the cell is in extreme heat or cold, enabling the cell to survive in unfavourable conditions.
· When unfavourable conditions return, the endospore loses its coat and begins to grow and divide like a normal cell.
17. How do antibiotics work? Describe two ways.
· Stop bacteria from growing by interfering with processes that are essential for bacterial growth and reproduction.
· Prevent bacteria from building or repairing cell walls and membranes or from making more RNA and DNA.
· Some antibiotics kill bacteria.
18. How are some bacteria resistant to the effects of certain antibiotics? Describe two possibilities.
· reduce the amount of the drug entering the cell (alter the molecular structure of drug or changing the target site of drug)
19. How do bacteria develop antibiotic resistance? Describe two ways.
· Mutation
· Transmission of extra genes through conjugation
20. What has greatly reduced the effectiveness of many antibiotics?
· The ability of plasmids to readily transfer genes for drug resistance among different bacteria
Analyzing Data
Bacteria and other microbes are considerably difficult to identify. Bacteria are extremely small and show only a few variations in appearance. Testing for chemical characteristics is often needed to distinguish between bacteria that are similar in appearance. The table below gives characteristics for a variety of bacteria that often need to be identified in medical laboratories.
Familiarize yourself with the table. A “+” in the table indicates that an organism does have the listed characteristic. A "-" in the table indicates that the bacterium does NOT have the characteristic A blank means that the information is not available. Use the information in the table to identify the two unknown organisms described below.
Organism / Shape or Form / Type of Cell Wall / Capsule / Flagella / Endospores / Aerobic / Causes Lysis of Red Blood Cells / Grows Well At 20oC / SugarsFermented
Glucose / Maltose / Lactose
1. Bacillus anthracis / Bacillus / A / + / - / + / + / - / - / + / + / +
2. Bacillus subtilis / Bacillus / A / - / - / + / + / - / + / + / + / +
3. Clostridium botulinum / Bacillus / A / - / + / + / - / + / - / + / -
4. Clostridium tetani / Bacillus / A / - / + / + / - / + / - / - / -
5. Diplococcus pneumoniae / Diplococcus / A / + / - / - / + / + / -
6. Escherichia coli / Bacillus / B / - / - / - / + / - / - / + / + / +
7. Klebsiella pneumoniae / Bacillus / B / + / - / - / + / - / - / + / + / +
8. Neisseria catarrhalis / Diplococcus / B / - / - / - / + / - / + / + / + / -
9. Neisseria gonorrheae / Diplococcus / B / - / - / - / + / - / - / + / - / -
10. Neisseria meningitidis / Diplococcus / B / - / - / - / + / - / - / - / - / -
11. Pseudomonas aeruginosa / Bacillus / B / - / + / - / + / - / + / - / - / -
12. Salmonella typhi / Bacillus / B / - / + / - / + / - / + / + / -
13. Serratia marcescens / Bacillus / B / - / + / - / + / + / + / + / -
14, Staphylococcus aureus / Staphylococcus / A / - / - / - / + / + / - / +
15. Staphylococcus epidermidis / Staphylococcus / A / - / - / - / + / - / - / +
16. Streptococcus fecalis / Streptococcus / A / - / - / - / + / - / - / +
17. Streptococcus hemolyticus / Streptococcus / A / - / - / - / + / + / - / +
1. Unknown A is examined under a microscope and observed to be a diplococcus. A test is done that shows that the diplococcus has cell wall type B and has no capsule. Samples of unknown A are placed in incubator at 20oC and at 37oC. The sample at 37oC grows well, but the one at 20oC does not. The unknown organism is tested for the ability to ferment the sugars glucose, maltose, and lactose. It can only ferment glucose.
The identity of unknown A is ______
2. Unknown B is a bacillus with cell wall type A. It is anaerobic and causes lysis (bursting) of red blood cells. This organism is tested for the ability to ferment the sugars glucose and lactose. It cannot ferment either of these sugars.
The identity of unknown B is ______