energy and respiration

a level biology 9700

Where does glycolysis occur?

Cytoplasm

What is the overall purpose of glycolysis?

To split one 6C glucose molecule into two 3C pyruvate molecules, producing ATP and reduced NAD

What happens during phosphorylation?

2 ATP transfer phosphate groups to glucose, raising its energy level and making it more reactive.

What happens after the first phosphate is added?

Glucose phosphate is formed, then rearranges to fructose phosphate.

What happens after the second phosphate is added?

Fructose 1,6-bisphosphate is formed.

What happens to fructose 1,6-bisphosphate?

It splits into two 3C triose phosphate molecules.

What happens to triose phosphate?

It is oxidised. Hydrogen is removed and transferred to NAD.

What is oxidation?

Removal of hydrogen.

What is reduction?

Addition of hydrogen.

What happens when NAD accepts hydrogen?

NAD is reduced to reduced NAD.

How many reduced NAD are produced per glucose in glycolysis?

2 reduced NAD.

How is ATP produced during the later stages of glycolysis?

A phosphate group is transferred directly from a substrate to ADP.

What is this type of ATP production called? (glycolysis)

Substrate-linked phosphorylation.

How many ATP are produced during glycolysis?

4 ATP.

What are the products of glycolysis per glucose?

2 pyruvate + 2 reduced NAD + net 2 ATP.

Where does the link reaction occur?

Mitochondrial matrix.

What is decarboxylation?

Removal of CO₂.

What is dehydrogenation?

Removal of hydrogen.

What happens to pyruvate during the link reaction?

Pyruvate is decarboxylated and dehydrogenated, then the remaining molecule combines with CoA.

What is produced from pyruvate?

Acetyl CoA.

What happens to the hydrogen removed from pyruvate?

It is transferred to NAD, producing reduced NAD.

What does CoA do?

Carries and supplies acetyl groups.

What is CoA partly made from?

Pantothenic acid (vitamin B5) and a nucleoside.

What is the link reaction equation?

Pyruvate + CoA + NAD → acetyl CoA + CO₂ + reduced NAD.

What is produced from ONE pyruvate in the link reaction?

1 acetyl CoA + 1 CO₂ + 1 reduced NAD.

Where does the Krebs cycle occur?

Mitochondrial matrix.

What begins each turn of the Krebs cycle?

Acetyl CoA combines with oxaloacetate.

What combines in the first step?

2C acetyl CoA + 4C oxaloacetate → 6C citrate.

What happens to citrate?

It undergoes a series of decarboxylation and dehydrogenation reactions.

What happens during decarboxylation in the Krebs cycle?

Carbon is removed and released as CO₂.

What happens during dehydrogenation in the Krebs cycle?

Hydrogen is removed and accepted by NAD or FAD.

What happens to the carbon skeleton during the cycle?

It loses 2 carbons as CO₂ and eventually becomes 4C oxaloacetate again.

What is produced per ONE turn of the Krebs cycle?

2 CO₂ + 3 reduced NAD + 1 reduced FAD + 1 ATP.

Why does the Krebs cycle turn twice per glucose?

One glucose produces 2 pyruvate, which produce 2 acetyl CoA.

What is produced by the Krebs cycle per glucose?

4 CO₂ + 6 reduced NAD + 2 reduced FAD + 2 ATP.

Where does oxidative phosphorylation occur?

Inner mitochondrial membrane/cristae.

What is the electron transport chain?

A series of electron carriers in the inner mitochondrial membrane.

What happens to reduced NAD and reduced FAD?

They bring hydrogen to the inner mitochondrial membrane.

What happens to the hydrogen?

It splits into H⁺ ions and electrons.

What happens to the electrons?

They enter the electron transport chain and pass between electron carriers.

What happens to electron carriers during electron transfer?

They are reduced when accepting electrons and oxidised when passing them on.

What type of reactions occur in the electron transport chain?

Redox reactions.

What happens as electrons move along the electron transport chain? what is it used for?

They release energy used for Actively pumping H⁺ from the mitochondrial matrix into the intermembrane space.

What does pumping H⁺ create?

A proton concentration gradient, with a higher H⁺ concentration in the intermembrane space.

How do H⁺ ions return to the matrix?

By facilitated diffusion through ATP synthase.

What happens when H⁺ passes through ATP synthase?

Energy from H⁺ movement is used to synthesise ATP from ADP + Pi.

What is chemiosmosis?

The movement of H⁺ down its concentration gradient through ATP synthase, driving ATP synthesis.

What is the final electron acceptor?

Oxygen

What happens when oxygen accepts electrons?

H20 is formed

What is the equation for water formation?

→ O₂ + 4H⁺ + 4e⁻ → 2H₂O.

Where does ethanol fermentation occur?

Yeast, some microorganisms and some plant tissues.

What happens to pyruvate during ethanol fermentation?

Pyruvate is decarboxylated to ethanal, releasing CO₂.

What happens to ethanal?

It accepts hydrogen from reduced NAD and is reduced to ethanol.

Which enzyme converts ethanal to ethanol?

Alcohol dehydrogenase.

What happens to reduced NAD during ethanol fermentation?

It loses hydrogen and becomes oxidised NAD.

Why must NAD be regenerated during fermentation?

NAD is needed to accept hydrogen during glycolysis, allowing glycolysis to continue.

What happens to ethanol?

It cannot be further metabolised and is a waste product.

Where does lactate fermentation occur?

Mammalian muscles when oxygen is insufficient and some microorganisms.

What happens to pyruvate during lactate fermentation?

Pyruvate accepts hydrogen from reduced NAD and is reduced to lactate.

Which enzyme catalyses lactate formation?

Lactate dehydrogenase.

What happens to reduced NAD?

It is oxidised back to NAD.

Why does lactate fermentation allow glycolysis to continue?

It regenerates NAD, allowing NAD to accept more hydrogen during glycolysis.

What can happen to lactate after exercise?

It can be oxidised back to pyruvate or converted to glycogen.

Why are rice paddies flooded?

Rice tolerates flooding while many competing weeds cannot, reducing competition.

How does flooding increase rice yield?

Fewer weeds compete with rice for light and mineral ions.

How do some rice varieties respond to rising water?

They rapidly grow taller so their leaves and flower spikes remain above water.

What is aerenchyma?

Tissue containing loosely packed cells and air spaces through which gases can diffuse.

How does aerenchyma help rice survive flooding?

It allows O₂ to diffuse from above-water parts to submerged tissues, including roots.

What is the chronological sequence of aerobic respiration?

What is the chronological sequence of aerobic respiration?

Glucose
↓
Glycolysis → 2 pyruvate + 2 reduced NAD + 2 ATP net
↓
Link reaction → acetyl CoA + CO₂ + reduced NAD
↓
Krebs cycle → CO₂ + reduced NAD + reduced FAD + ATP
↓
Oxidative phosphorylation
↓
Reduced NAD/FAD donate hydrogen → H⁺ + electrons
↓
Electrons move along ETC → energy released
↓
Energy pumps H⁺ into intermembrane space
↓
H⁺ diffuses through ATP synthase
↓
ATP produced by chemiosmosis
↓
O₂ accepts electrons + H⁺
↓
H₂O

What are the key differences between aerobic respiration and fermentation?

Aerobic: requires O₂, uses mitochondria, completely oxidises glucose, produces much more ATP, CO₂ + H₂O produced.
Fermentation: no O₂ required, occurs in cytoplasm, only glycolysis produces ATP, regenerates NAD so glycolysis continues.