7. Diversity Of Energy Generating Systems In Microbes

Question 1

What carbon sources are available to microbes? 3

Answer 1

1. Needed for growth and reproduction as we are all carbon based life forms
2. Autotrophs fix carbon from atmospheric co2 eg photosynthetic organisms
3. Heterotrophs get carbon from organic molecules eg. Humans

Question 2

Describe aerobic respiration in organoheterotrophs. 6

Answer 2

1. Fatty acids from glycerol, amino acids from proteins and sugars are involved in glycolysis
2. Then, in the Krebs cycle, there is some generation of ATP
3. Also, a 6c compound loses 2c to form co2, producing reducing power in the form of electrons, which are donates to form NADH and FMNH2
4. Electrons are deposited at the electron transport chain, where they are sequentially passed down carrier proteins with reduction of energetic values of electrons as energy is released. This is coupled to atpsynthase
5. Electron passed on to terminal electron acceptor, which is oxygen in aerobes
6. Co2 and h2o are produced

Question 3

How is ATP produced, for example on electron transport chain six, on a bacterial membrane? 3

Answer 3

1. Electrons being pressed down series of electron carriers causes proton motive gradient
2. Moving protons down the gradient via atpsynthase generates ATP
3. As protons move through atpsynthase, there is phosphorylation of ADP and pi to ATP

Question 4

What are microbial fermentations? 6

Answer 4

1. No electron transport chain present or etc not being used
2. Organic electron donor and acceptor, an organic molecule which accumulates over time
3. Anaerobic, ATP yielded through glycolysis
4. Glycolysis and Krebs cycle still over
5. Some commercially important polymers produced including Pyruvate to lactate by lactobacillus
   Pyruvate to co2 And propionate
   Pyruvate to acetone to isopropanol
   Pyruvate to acetate
   Pyruvate to butanol
   Pyruvate to butyrate
6. Pyruvate to co2 and ethanol in yeasts, which are aerobic but can live and grow in partially anaerobic conditions

Question 5

Describe anaerobic respiration in microbes. 6

Answer 5

1. Similar etc as for aerobic respiration
2. Some bacteria can use same etc for aerobic and anaerobic respiration
3. Alternative electron acceptors include organic nitrogen and sulphur, co2 and iron compounds, this varies between species
4. Co2 to organic acids produces very little energy, sulphur a little more and organic acceptors even more
5. Aerobic is more efficient because oxygen releases the most energy, it’s at the bottom of the chain
6. Acceptor used determines energy released, therefore efficiency

Question 6

What the methanogens? 6

Answer 6

1. Members of archaea, and strict anaerobes
2. Mostly use co2 as terminal electron acceptor, producing ch4/methane
3. Most of earth is anaerobic so commonly found, especially in soils, swamps and sediment
4. Marsh gas aka will-o-the-wisp, caused methane gas to bubble in statement water and was investigated by dalton
5. Methane production common in landfill and a lack of control can cause deep seated fired that burn for several years
6. Pipes ensure methane can be directed out to specific points for burning off/hooked up to electricity generators

Question 7

Describe the name, electron donor, acceptor, products and kcal/mol for chemolithotrophs Respiring aerobically. 5

Answer 7

1. Alcaligenes use h2 as a donor, O2 as acceptor, produce h2o and lose 56.6
2. Nitrobacter use no2- as a donor, O2 as acceptor, produce no3- and h2o and lose 17.4
3. Nitrosamines use nh4+ as donor, O2 as acceptor, produce no2- and h2o, and lose 65
4. Thiobacillus ferroxidans uses fe2+ and s as donors, O2 as acceptor, produces fe3+, h2o and h2so4 and loses 223.7
5. They use electrons from inorganic compounds

Question 8

What are iron oxidising bacteria? 6

Answer 8

1. They have a low energy yield, large amounts of iron need to be oxidised
2. Iron is not as good as organic molecules
3. Thiobacillus ferroxidans is found in mines and is one example
4. 2FeS2 + 7O2 + 2H2O -> 2Fe2+ + 4SO42- + 4H+
   This is a purely chemical process of auto oxidation or sulphur oxidisers. Then;
   4Fe2+ + O2 + 2H+ -> 4Fe3+ + 2H2O by T. Ferroxidans
5. The result is an important environmental pollutant
6. Naturally, these bacteria are low in soils but thrive in mines, as there are large amounts of iron oxide and oxygen

Question 9

What is acid mine drainage and why is it important? 6/1

Answer 9

1. Oxygen allows oxidation of FeS2, releases H2SO4
2. Creates acidic conditions, as water comes up acidic. Ferrous ions are stable which causes pollution
3. Ferrous ions are available for oxidation to ferric
4. Precipitates insoluble ferric hydroxide
5. T. Ferroxidans is an acidophile, meaning it evolved to grow in acidic conditions
6. Major pollution problems as sulphuric acid produced causes mine run off to have a pH of 2/3
   - ——
7. Resulting accumulation of iron ions is very toxic and acidity kills plants and trees

Question 10

Describe photosynthesis. 6

Answer 10

1. Anoxygenic means anaerobic, no oxygen in early earth led to evolution of proteins that could be used
2. Use H2, H2S or reduced organic molecule as electron donor eg. Methane
3. Oxygenic photosynthesis generates O2, and uses H2O as electron source
4. They increase O2 levels eg Cyanobacteria
5. Oxygenic bacteria are different colours for capturing different wavelengths of light
6. 400M years until evidence of first photosynthetic bacteria

Question 11

Describe anoxygenic photosynthesis. 5

Answer 11

1. Evolved first.
2. Purple sulphur bacteria and been sulphur bacteria
3. Light excited electrons
4. Sulphur compounds donate electrons eg. H2S
5. Elemental sulphur formed inside cell in purple, outside cell in green

Question 12

Describe the anoxygenic photosynthetic cycle. 5

Answer 12

1. Cyclic electron transfer generates ATP
2. Non cyclic electron transfer generates NADH, reducing power
3. Light moves electron up to more energetic state
4. Electron is passed through carriers
5. Electron donor replaces electrons

Question 13

Describe oxygenic photosynthesis. 6

Answer 13

1. Generates oxygen and began in Cyanobacteria
2. Uses water as electron donor
3. Two photosystems, an oxygenic and a second one, allowing them to take electrons from water to form O2
4. Non cyclic electron flow
5. Stromatolites were prevalent in shallow water and oxygenated the planet
6. They’re made of Cyanobacteria and the O2 bubbles out

Question 14

Describe the oxygenic photosynthetic mechanism. 6

Answer 14

1. This involves two photosystems, which are non cyclical. It is called the z scheme
2. In photosystem I, a phytochrome accepts and electron and a photon of light causes it to enter an energetically high state. The electron is then passed down a series of carriers.
3. Electron forms reducing power (NADPH) in a non cyclical manner. This is anoxygenic.
4. Photosystem II also has phytochrome - energy from a photon of light is needed to remove an electron from water, which is difficult, and generates O2
5. This results in energetically high electrons, which are passed down corners to Lower energy states. Protons are removed and a proton motive gradient is produced, generating ATP.
6. The electron is passed back to photosystem I. Photosystem II evolved to get electrons from water

Question 15

Describe mitochondria and chloroplasts. 5

Answer 15

1. Mitochondria are the same size as bacteria
2. Have their own dna, similar to bacteria
3. Large primitive eukaryote engulfed bacteria and lost its independence over evolutionary time
4. Plants and algae have chloroplasts, the size of Cyanobacteria cells
5. Similar dna to Cyanobacteria, same process

Question 16

Describe some modes of energy production that are available to microbes. 5

Answer 16

1. As earth’s atmosphere changed and different environments were reached, microbes had to develop new systems for energy production
2. In some environments eg hydrothermal vents, microbes used energy derived from chemicals - chemotrophy
3. Those using organic chemicals eg glucose and other sugars, acetate, proteins and fatty acids are chemoorganotrophs
4. Those using inorganic chemicals eg h2, h2s, fe2+ and h4+ are chemolithotrophs and include the earliest archaea.
5. Oxygenise phototrophs then developed and use energy from the sun