Part 2: Thermodynamics

Question 1

What is the energy required to start a reaction called?

Answer 1

Activation energy

Question 2

What does ΔG mean?

Answer 2

Gibbs free energy.

Question 3

What type of reaction has ΔG

Answer 3

Exergonic reaction - release of energy

Question 4

What type of reaction has ΔG > 0?

Answer 4

Endergonic reaction - requires energy

Question 5

What value of ΔG is favourable for organisms in the environment, and what conditions are required for this?

Answer 5

ΔG

Question 6

Why must reaction products be removed from the environment?

Answer 6

ΔG must be

Question 7

What are the three mechanisms by which reaction products can be removed from the environment?

Answer 7

1) The product is used as a substrate for another reaction within the organism.
2) The product is used as a substrate for another organism.
3) The product is chemically or physically removed (e.g. precipitation of sulphide as FeS.

Question 8

Which group of organisms can operate under the lowest Threshold Partial Pressure? (TC)

Answer 8

Nitrogen reducers - TC =

Question 9

Why are methanogens low in energy? (EXAM)

Answer 9

They are only able to degrade low-energy compounds including H2, CO2, acetate

Question 10

In what way are anaerobic environments more complex than aerobic? (EXAM)

Answer 10

In anaerobic environments, many organisms are required to work as a system to degrade substrates, whereas in oxic environments, only one organism is needed per substrate (e.g. cellulose).

Question 11

Give examples of environments where the anaerobic carbon cycle is important.

Answer 11

The gut, plant systems.

Question 12

What are the two known methods of energy conservation?

Answer 12

1) Substrate-level phosphorylation

2) Chemiosmotic energy conservation

Question 13

Describe the energy-conserving method of “substrate level phosphylation”.

Answer 13

An inorganic phopshate (Pi) is converted to an organic phosphate that is then transferred to ADP. e.g. pyruvate decarboxylation.

Question 14

Describe the energy-conserving method of “chemiosmotic energy conservation”.

Answer 14

Electrons are carried along the respiratory chain (sequence of proteins with increasing redox potential)

• energy is released on each electron transfer and is used to pump protons across the electrochemical and concentration gradients.
• the energy of the proton gradient is used for ATP production
• the amount of ATP formed depends on the organism’s environment since this affects the strength of the protein gradient.