Cellular Respiration

Question 1

What do all living cells need to work

Answer 1

Energy from an outside source

Question 2

Where does energy from organic molecules come from

Answer 2

The sun

Question 3

How is energy from photosynthesis recycled

Answer 3

Photosynthesis = oxygen and organic materials -> used for cellular respiration -> breaks down fuel = generates ATP, carbon dioxide and water = used for photosynthesis

Question 4

Why are catabolic pathways useful in cellular respiration

Answer 4

Transfer of electrons from fuel plays a major role.
Linked to work by drive of ATP.
Regenerates ATP from ADP + Pi

Question 5

What is aerobic respiration

Answer 5

Form of cellular respiration.
Oxygen is consumed as reactant.
Carried out by most eukaryotes and prokaryotes.
Organic compounds + oxygen —> carbon dioxide + water + energy

Question 6

Main sources of fuel

Answer 6

Carbohydrates, fats and protein

Question 7

How can a substance be reduced but not actually lose an electron

Answer 7

Some reactions change the degree of electron sharing in covalent bonds eg methane combustion

Question 8

Why is hydrogen a good fuel for oxidation

Answer 8

Bonds are an excellent source of hilltop electrons.

Energy released when electrons fall down the electron gradient during oxygen transfer.

Question 9

Why is the activation energy barrier important in carbohydrates and fats

Answer 9

Without, glucose would combine almost instantly with oxygen

Question 10

How is glucose stored as energy as NADH

Answer 10

Glucose + NAD+ —dehydrogenase—> C=O + NADH + H+
Electrons are oxidised from glucose and passed through the electron carrier.
Then dehydrogenased.
Coenzymes deliver electrons and protons to NAD+.
Releasing NADH + H+

Question 11

Why is NADH a neutral molecule

Answer 11

2 negative electrons are added and 1 proton is added

Question 12

State the stages of aerobic cellular respiration

Answer 12

Glycolysis
Pyruvate oxidation
Citric acid cycle
Oxidative phosphorylation

Question 13

Where does glycolysis occur

Answer 13

In the cytosol

Question 14

Where does the Krebs cycle and oxidative phosphorylation occur

Answer 14

In the mitochondrial membrane

Question 15

Where are the proteins built into in eukaryotes and prokaryotes

Answer 15

Eukaryotes: the inner membrane of the mitochondria
Prokaryotes: the plasma membrane

Question 16

Roughly, how does the electron transport chain work

Answer 16

Electrons removed from glucose move to the top high-energy tier via NADH.
At the bottom low-energy tier, oxygen captures electrons.
Electrons move from one carrier to the other in redox reactions.

Question 17

Why isn’t oxygen and hydrogen explosive in cellular respiration

Answer 17

Hydrogen is derived from organic materials instead of H2.

Steps in ETC break the fall of electrons to oxygen, releasing energy in the steps.

Question 18

What is the energy investment and payoff phase

Answer 18

Investment - spends ATP
Payoff - pays off ATP from substrate level phosphorylation and NAD+ is reduced to NADH by electrons from oxidation of glucose

Question 19

Steps of glycolysis

Answer 19

Phosphorylation of glucose to glucose phosphate.
Splitting the glucose = triose-phosphate.
Oxidation of triode-phosphate.
Production of ATP.

Question 20

Why do you phosphorylise glucose

Answer 20

To make glucose more reactive.
Provide energy to activate glucose.
Lower the activation energy.

Question 21

How is triose-phosphate made

Answer 21

Phosphorylised glucose is split into 2 3-carbon molecules.

Question 22

How is triose-phosphate oxidised

Answer 22

Hydrogen is removed from each TP molecule and transferred to a hydrogen-carrier molecule
NAD+ —> NADH

Question 23

How is pyruvate made

Answer 23

From triose-phosphate

Question 24

How does pyruvate enter the mitochondria from the cytosol and why

Answer 24

Via active transport when oxygen is present because pyruvate is a charged molecule, so needs a transport protein.

Question 25

What main 3 reactions occur in the Krebs cycle

Answer 25

Pyruvate carboxyl fully oxidises, gives off CO2 when entering mitochondria.
2-carbon fragment is oxidised to store energy - NAD+ —> NADH.
Coenzyme A is attached via a sulphur atom to 2-carbon intermediate = acetyl-CoA, which enters the citric acid cycle.

Question 26

Roughly describe the 8 steps of the citric acid cycle

Answer 26

1. Acetyl CoA adds acetyl group to oxaloacetate = citrate
2. Citrate is converted to isocitrate
3. Isocitrate is oxidised, NAD+ —> NADH, loss of CO2
4. Loss of CO2, NAD+ —> NADH
5. CoA is displaced by a phosphate group, GDP —> GTP
6. 2 hydrogens are transferred, FAD —> FADH2
7. Addition of water rearranges bonds in substrate
8. Substrate is oxidised, NAD+ —> NADH and regenerates oxaloacetate

Question 27

How many molecules of ATP do you have after the citric acid cycle is complete

Answer 27

4 ATP molecules

Question 28

what advantages does the folding of the cristae have on the electron transport chain

Answer 28

Provides space for thousands of copies.

Well suited for sequential redox reactions.

Question 29

What is tightly bound to proteins in the ETC that are essential for catalytic functions

Answer 29

Prosthetic groups eg coenzymes and cofactors

Question 30

What occurs down the ETC

Answer 30

Electrons drop in free energy.
Carriers alternate between oxidised and reduced states.
Last carrier passes electrons to oxygen.