Question

3. In the search for extraterrestrial life, scientists expect that the most likely candidate would belong to one particular domain.

a.) Which domain would it be: Bacteria, Archaea or Eukarya? Explain why the expectation would be reasonable.

b.)Why are typical bacteria and cyanobacteria classified together in the Domain Bacteria? How do they differ?

c.) Identify three benefits of bacteria to humans.

d.) Describe three benefits of bacteria to the ecosystem.

Answer 1

3 a. Domain would be Archae

• Archaeal organisms do not produce protective outer walls of cellulose and their membranes do not contain the same chemicals as bacteria.
• This molecule might help the species ability to withstand environments where other organisms perish
• Archaea are also thought to play important roles in the carbon and nitrogen cycles.
• That's why Archae bacteria are extremophilic, they can withstand life in extraterrestrial

b.

It's because of the similarities between typical bacteria and cyanobacteria, they are classified together  

• Both bacteria and blue green algae are simple and their DNA is devoid of histone proteins and hence true chromosomes are not organised.
• Both posses saprophytic mode of life.
• In both groups the cells are covered by mucilage sheath.
• True cell organelles like plastids, golgi bodies, mitochondria etc are absent.
• Both possess the ability to fix nitrogen from the atmosphere.
• Formation of resting spores is characteristic in both.
• Motile spores are not seen in both groups.
• Both organisms are capable of withstanding high rate of desiccation and high temperature.

• Both reproduce asexually by binary fission
• Both are prokaryotes.

.	Characters	Bacteria	Cyanobacteria
1	Size	Comparatively smaller.	Comparatively larger.
2	Distribution	Found every possible places in earth.	Only found in presence of sunlight and moisture.
3	Flagella	May bear flagella.	Flagella always absent.
4	Cell wall	1-2 layered.	4 layered.
5	Composition of cell wall	Glycolipids and peptidoglycan.	Cellulose and pectin.
6	Nutrition	May be autotrophic or heterotrophic.	Usually autotrophic.
7	Photosynthetic pigments	Photosynthetic pigment is bacteriochlorophyll.	Photosynthetic pigments is chlorophyll a.
8	Accessory pigment	Absent	Accessory pigment like phycocyanin and phycoerythrin are present in dominating form.
9	Reserve food	Glycogen	Cyanophycean starch
10	Spore formation	Is endogenous.	Is not endogenous.
11	Hydrogen donor	During photosynthesis hydrogen donor is not water; as a result oxygen is not evolved. Thus photosynthesis is anoxygenic.	Hydrogen donor is water, oxygen is evolved. Process is oxygenic.
12	Locomotory organ	Flagella act as locomotory organ.	Lack flagella and other locomotory organ.
13	Heterocyst	Absent	Present

c.

• Bacteria in digestive system help to break down food and keep healthy.
• Bacteria are important in the production of many dietary supplements and pharmaceuticals. For example, Escherichia coli is used for commercial preparation of riboflavin and vitamin K.
• Escherichia coli is an important intermediate for synthesis of the antibiotic amoxicillin.
• Bacteria are used in food production to make yogurt and fermented foods
• Bacteria to break down sewage and to clean up oil spills

d.

• Bacteria help degrade dead animals and plants and bring valuable nutrients back to soil and hence plants can grow.
• Some bacteria help clean harmful pollutants out of the environment in a process called bioremediation.
• Bioremediation uses bacteria that digest toxic substances and convert them into less harmful substances
• By using bioremediation techniques, toxic substances such as heavy metals and petroleum are no longer harmful to the environment.
• Bacteria are necessary part of nutrient, or biogeochemical, cycles in which carbon, nitrogen, sulfur and phosphorus are recycled between living beings and the environment. Without these cycles, there would be no exchange of elements.