Energy transfers in and between organisms

Question 1

What are the stages of aerobic respiration?

Answer 1

Glycolysis, Link reaction, Krebs cycle, and Oxidative Phosphorylation

Question 2

What happens in glycolysis

Answer 2

• Glucose is activated by phosphorylation
• using 2 ATP molecules
• and becomes glucose phosphate (bisphosphate but we only say phosphate)
• Glucose phosphate is hydrolysed into 2 triose phosphate molecules
• each TP is oxidised using NAD + -> reduced NAD by DEHYDROGENATION of TP
• 2 ATP molecules are formed by substrate level phosphorylation
• this leaves pyruvate, a 3 carbon molecule
• pyruvate is then transported to the mitochondria

Question 3

where does glycolysis take place

Answer 3

The cytoplasm

Question 4

Where does the link reaction take place

Answer 4

Matrix of mitochondria

Question 5

Where does the krebs cycle take place

Answer 5

Matrix of mitochondria

Question 6

Where does oxidative phosphorylation take place

Answer 6

Matrix, cristae and intermembrane space of the mitochondria

Question 7

Outline the steps of the link reaction

Answer 7

• pyruvate undergoes decarboxylation (removal of 1 CO2 molecule)
• and dehydrogenation (using NAD + -> reduced NAD)
• this forms acetate (2C)
• acetate combines with coenzyme A to form acetyl coenzyme A (2C)
• coenzyme A transports the acetate to the krebs cycle.

Question 8

What is the purpose of coenzyme A

Answer 8

To carry acetate to the krebs cycle

Question 9

What happens to coenzyme A after carrying out its purpose

Answer 9

It travels back to the link reaction and can be used again to transport more acetate to the krebs cycle

Question 10

What are the products of anaerobic respiration in PLANTS (and yeast)

Answer 10

ethanol and CO2

Question 11

What are the products of anaerobic respiration in ANIMALS

Answer 11

lactic acid and CO2

Question 12

Outline the stages of the krebs cycle

Answer 12

• acetate binds with a 4 carbon molecule and forms a citric acid (6C)
• 6C undergoes decarboxylation and dehydrogenation to form 1 molecule of CO2 and 1 NADH (reduced NAD)
• this leaves a 5C molecule, which then undergoes decarboxylation and dehydrogenation again to form 1 CO2 and 1 NADH
• a 4C molecule is left, which undergoes dehydrogenation to form NAD+ -> NADH, FAD -> FAH2 (reduced), and uses ADP +Pi to form ATP (substrate level phosphorylation).
• this leaves the 4C molecule that is needed in the beginning to combine with acetate, so regeneration

Question 13

outline the stages of oxidative phosphorylation

Answer 13

• hydrogen carriers from the matrix emit the hydrogen they are carrying and release 2e-s
  -this ionises the proteins in the ETC chain, and set off a series of redox reactions along the chain as the 2e-s are carried along.
• as they are passed along, they release energy to the protein carriers, which use this energy to actively pump H+ ions out of the matrix to the intermembrane space, against their concentration gradient
• via chemiosmosis, ATP synthase (embedded in the intermembrane) allows the facillitated diffusion of H+ ions back into the matrix from the intermembrane space, down their concentration gradient.
• ATP synthase uses this energy to synthesis 1 molecule of ATP using ADP and Pi
• 2H+ pick up the 2e-s from the end of the ETC and 1/2 O2 to make 1 molecule of H2O

Question 14

describe the role of saprobionts in the nitrogen cycle.

Answer 14

• They decompose proteins
• to produce ammonium compounds

Question 15

What is nitrification?

Answer 15

ammonium ions are oxidised into nitrite ions and then into nitrate ions. Each stage of nitrification is carried out by different species of nitrifying bacteria.

Question 16

what is ammonification

Answer 16

protein/DNA in dead material (e.g. dead organisms; faeces) decomposed by saprobionts to release ammonium ions.

Question 17

What is nitrogen fixation

Answer 17

nitrogen fixing bacteria convert atmospheric nitrogen gas to ammonium ions.

Question 18

What are denitrifying bacteria?

Answer 18

• bacteria that take nitrates away from the soil that COULD be used in assimilation and turn it back into gas for the atmosphere

Question 19

How does ploughing encourage the growth of aerobic respiring nitrifying bacteria?

Answer 19

creates more air pockets and soil is turned over, allows for more bacteria to have a higher access to concentration of O2 rather than just in the soil

Question 20

Outline the nitrogen cycle

Answer 20

• Nitrogen from the atmosphere enters the soil and some will fixate onto the nodules of roots of plants by nitrogen fixing bacteria.
• Nitrogen fixing bacteria in the soil will undergo nitrification, turning ammonium into nitrites (NO2-)
• nitrifying bacteria will turn these nitrites into nitrates (NO3-), which can then be assimilated into plants for production of proteins/DNA/amino acids
• decomposers/saprobionts will turn decomposed material from animals and plants into ammonium, which then enters the nitrification of nitrogen compounds