ap bio concept 7.1: Catabolic pathways yield energy by oxidizing organic fuels

What is the source of energy in an ecosystem, and how does it leave?

• Source: Sunlight (solar energy).

• Exit: Leaves as heat.

What process transfers energy from solar to chemical form?

Photosynthesis converts solar energy into chemical energy by exciting electrons in the chloroplast.

How are photosynthesis and cellular respiration connected?

Photosynthesis produces oxygen and glucose, which are used as fuel in cellular respiration.
Cellular respiration regenerates ATP, needed for work, using these products.

Why is ATP important in cells?

It is the "currency" of energy for cellular processes.

What is the role of the mitochondria?

It is the "powerhouse" of the cell, responsible for ATP production.

Define anabolic reaction with example

Builds molecules (e.g., glucose in photosynthesis).

Define catabolic reaction with example

Breaks down molecules (e.g., glucose in cellular respiration, exergonic reaction releasing energy).

What is fermentation?

Partial sugar degradation without oxygen.

What is aerobic respiration?

Uses oxygen and organic molecules to yield ATP efficiently.

What is anaerobic respiration?

Similar to aerobic but uses compounds other than oxygen.

What catabolic porcess is the most efficient?

Aerobic respiration

Formula for cellular respiration

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP + Heat)

Why are carbohydrates, fats, and proteins used as fuel?

They contain high energy due to abundant hydrogen atoms.Their oxidation releases energy for ATP production.

What is a redox reaction?

A chemical reaction where electrons are transferred, releasing energy for ATP synthesis.

Define oxidation

Loss of electrons (more positive).

Define reduction

Gain of electrons (more negative).

What is the mnemonic for redox reactions?

OIL RIG: Oxidation Is Loss, Reduction Is Gain.

Who are the reducing agents?

Donates electrons

Who are the oxidizing agents?

Accepts electrons

Explain the role of hydrogen in cellular respiration.

Transferring hydrogen to oxygen releases energy used for ATP synthesis.

What is the electron transport chain?

A series of steps that transfer electrons to produce ATP, reducing energy loss as heat.

What is the role of NAD+ in cellular respiration?

It acts as an electron carrier and oxidizing agent.
NAD⁺ → Reduced to NADH → Stores energy for ATP production. (becomes more negative)

Why is the stepwise energy release in the chain important?

It prevents energy loss as heat, enabling efficient ATP synthesis.

How is oxygen involved in the electron transport chain?

Oxygen pulls electrons down the chain, driving energy release.

What are the three stages of cellular respiration?

Glycolysis, Citric Acid Cycle, Oxidative Phosphorylation

What is Glycolysis?

Breaks glucose into two pyruvate molecules.

What is the Citric Acid Cycle?

Completes glucose breakdown, releasing CO_²

What is Oxidative Phosphorylation?

Produces most ATP through redox reactions.

Where does glycolysis occur?

Cytosol

Where do the citric acid cycle and oxidative phosphorylation occur?

Mitochondria

What is substrate-level phosphorylation?

ATP production via direct transfer of a phosphate group to ADP.

Why is oxidative phosphorylation more efficient than substrate-level phosphorylation?

It uses redox reactions to produce 90% of ATP in cellular respiration.

How many ATP molecules are produced per glucose molecule?

30-32 ATP

What is cellular respiration?

The process by which cells break down macromolecules (like glucose) to produce ATP, the energy currency of the cell.

What is the purpose of glycolysis?

To begin extracting energy from glucose by breaking it into two pyruvate molecules.

What does glycolysis require as input?

1 glucose molecule.

2 ATP molecules.

What are the outputs of glycolysis?

4 ATP, 2 NADH, and 2 PYRUVATE MOLECULES

What happens to the pyruvate produced in glycolysis?

It undergoes oxidation to form 2 acetyl-CoA molecules and 2 NADH.

What molecule enters the Krebs cycle, and how many times does it occur per glucose?

Acetyl-CoA, entering twice per glucose (once for each acetyl-CoA).

What are the outputs of the Krebs cycle per acetyl-CoA?

3 NADH, 1 FADH₂, and 1 ATP (or GTP).

What are the total outputs of the Krebs cycle for one glucose molecule? (occurs twice)

6 NADH, 2 FADH₂, and 2 ATP (or GTP).

What role do NADH and FADH2 play after the Krebs cycle?

They carry high-energy electrons to the electron transport chain.

What is oxidative phosphorylation?

A process that uses NADH and FADH₂ to create a hydrogen ion gradient and produce ATP.

What happens in the electron transport chain?

NADH and FADH₂ donate electrons, powering pumps that create an electrochemical gradient of hydrogen ions across the membrane.

What enzyme produces ATP in this step?

ATP synthase, powered by the hydrogen ion gradient.

How much ATP does NADH produce?

2.5 ATP

How much ATP does FADH₂ produce?

1.5 ATP

How many ATP molecules does a single glucose produce in the final step?

30-32 ATP

How many NADH molecules were produced in total?

10 NADH —> 25 ATP

• 2 from glycolysis.

• 2 from pyruvate oxidation.

• 6 from the Krebs cycle.

How many FADH₂ molecules were produced in total?

2 FADH₂ —> 3 ATP

All from the Krebs cycle.

How much regular ATP did we have?

4 ATP

• 2 from glycolysis.

• 2 from the Krebs cycle.