5B Respiration

Question 1

Where does the energy come from that is used to synthesise ATP?

Answer 1

• solar energy in photosynthesis
• oxidative processes eg. cell respiration breaks down organic molecules to release chemical energy that is stored as ATP

Question 2

What 3 ways does the synthesis of ATP and H2O from ADP and Pi occur?

Answer 2

• occurs in cytoplasm by glycolysis when phosphate groups are transferred from donor molecules (SUBSTRATE-LEVEL PHOSPHORYLATION)
• occurs in mitochondria during aerobic respiration (OXIDATIVE PHOSPHORYLATION)
• occurs in chloroplasts by photosynthesis (PHOTOPHOSPHORYLATION)

Question 3

What is substrate-level phosphorylation?

Answer 3

• the synthesis of ATP and H2O from ADP and Pi in the cytoplasm by glycolysis
• phosphate groups are transferred from donor molecules

Question 4

What is oxidative phosphorylation?

Answer 4

• the synthesis of ATP and H2O from ADP and Pi in the mitochondria during aerobic respiration

Question 5

What is photophosphorylation?

Answer 5

• the synthesis of ATP and H2O from ADP and Pi in the chloroplasts during photosynthesis

Question 6

What are the 2 key functions of ATP within the cell?

Answer 6

• energy: releases energy when hydrolysed
• phosphorylation: it may transfer the released phosphate to other organic molecules (makes them less stable and more reactive)

Question 7

Where does aerobic respiration occur?

Answer 7

in the mitochondria

Question 8

What does aerobic respiration require and produce?

Answer 8

• requires oxygen
• produces CO2, H2O and lots of ATP

Question 9

Where does anaerobic respiration take place?

Answer 9

• in the cytoplasm
• in the absence of oxygen

Question 10

What does anaerobic respiration produce in animals, plants and fungi?

Answer 10

• animals: lactate and a small amount of ATP
• plants and fungi: ethanol, CO2 and a small amount of ATP

Question 11

What are the 4 steps of aerobic respiration?

Answer 11

1. glycolysis
2. link reaction
3. krebs cycle
4. oxidative phosphorylation

Question 12

Describe simply what happens in glycolysis

Answer 12

• the splitting of the 6 carbon glucose into 2x molecules of 3 carbon pyruvate

Question 13

Describe simply what happens in the link reaction

Answer 13

• the 3 carbon pyruvate molecules enter into a series of reactions which lead to the formation of acetylcoenzyme A

Question 14

How many carbons does acetylcoenzyme A consist of?

Answer 14

2

Question 15

Describe simply what happens in the krebs cycle

Answer 15

• the introduction of acetylcoenzyme A into a cycle of redox reactions that yield some ATP and a large quantity of NAD and FAD

Question 16

Describe simply what happens in oxidative phosphorylation

Answer 16

• the use of the electrons associated with reduced NAD and FAD, released from the krebs cycle to synthesise ATP with water produced as a by product

Question 17

Where does glycolysis occur?

Answer 17

in the cytoplasm

Question 18

What are the 4 stages of glycolysis?

Answer 18

1. activation of glucose by phosphorylation
2. splitting of phosphorylated glucose into 2x TP
3. oxidation of 2x TP
4. production of ATP and pyruvate

Question 19

During glycolysis, what is the overall yield from one glucose molecule?

Answer 19

• 2x ATP (NET: 4 produced but 2 used)
• 2x reduced NAD
• 2x pyruvate

Question 20

What is the purpose of the link reaction?

Answer 20

• the pyruvate molecules from glycolysis possess potential energy that can only be released in a process called the krebs cycle
• they must be oxidised before this in the link reaction

Question 21

Where does the link reaction occur?

Answer 21

in mitochondria

Question 22

Describe the stages of the link reaction

Answer 22

1. pyruvate is oxidised to acetate
2. 3 carbon pyruvate loses CO2 and H2
3. H2 is accepted by 2x NAD to form 2x reduced NAD
4. 2 carbon acetate combines with a molecule called coenzyme A to produce acetylcoenzyme A

Question 23

State the equation for the link reaction

Answer 23

pyruvate + NAD + CoA

–>

acetylcoA + reduced NAD + CO2

Question 24

Describe the krebs cycle

Answer 24

• involves a series of redox reactions that take place in the mitochondria
• these redox reactions donate hydrogen atoms to NAD and FAD to reduce them

Question 25

Summarise the steps of the krebs cycle

Answer 25

1. 2 carbon acetylcoA from the link reaction combines with a 4 carbon molecule to form a 6 carbon molecule
2. in a series of reactions, this 6 carbon molecule loses 2 molecules of CO2 and H2 to give a 4 carbon molecule and a single molecule of ATP
3. the 4 carbon molecule can now combine with a new molecule of acetylcoA to begin the cycle again

Question 26

What are NAD and FAD?

Answer 26

• coenzymes
• coenzymes aren’t enzymes, just molecules that some enzymes require in order to function
• coenzymes are needed in photosynthesis and respiration to carry hydrogen atoms from one molecule to another

Question 27

What significance does the krebs cycle have?

Answer 27

• breaks macromolecules into smaller ones
• produces hydrogen that is carried by NAD to the electron transfer chain and provides energy for oxidative phosphorylation (leads to production of ATP)
• regenerates the 4 carbon molecules to combine with acetylcoA which would otherwise accumulate
• source of intermediate compounds used by cells eg. fatty acids, amino acids and chlorophyll