AP Biology Unit 3 Topic(s) 6 + 7

What is the main purpose of cellular respiration?

To harvest chemical energy from organic molecules and generate ATP

What is the word equation for cellular respiration?

Organic molecules + O₂ → CO₂ + H₂O + energy

What is the major fuel source for animals and what does it become?

Starch

What is the balanced equation for glucose oxidation in respiration?

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy (ATP + heat)

What kind of process is the breakdown of glucose in respiration?

A catabolic, energy

In cellular respiration, which molecule is oxidized and which is reduced?

Glucose is oxidized to CO₂

What happens to electron energy during glucose oxidation?

Electrons move to a lower energy state, releasing energy for ATP synthesis

What mnemonics help remember oxidation and reduction?

OIL RIG and LEO goes GER

What is the typical downhill path of electrons in respiration?

Glucose → NADH → ETC → O₂

How is glucose broken down to harvest energy?

In steps, removing electrons that are carried to the ETC

What do dehydrogenase enzymes remove from glucose?

2 electrons and 2 protons (2e⁻ and 2H⁺)

Why are dehydrogenases considered oxidizing agents for glucose?

They remove electrons and protons from glucose, oxidizing it

How is NAD⁺ reduced during energy harvest?

It accepts 2e⁻ and 1H⁺ to become NADH (stores energy)

What happens to the extra proton during dehydrogenase action?

It is released to the surrounding solution as H⁺

What is the role of NADH in respiration?

It carries high

What is the electron transport chain (ETC)?

A series of membrane proteins that shuttle electrons through redox reactions

What does the ETC release and how is it used?

Energy, which is used to help make ATP

Who is the final electron acceptor in the ETC and what is formed?

Oxygen

it forms H₂O when combined with electrons and H⁺

What are the three stages of cellular respiration?

Glycolysis

Pyruvate oxidation & the citric acid cycle

Oxidative phosphorylation (ETC + chemiosmosis)

Where does glycolysis occur?

In the cytosol

What does glycolysis do to glucose?

Splits one 6

What are the net products of glycolysis?

2 pyruvate, 2 ATP (net), 2 NADH, and 2 H₂O

What are the two stages of glycolysis?

Energy investment stage and energy payoff stage

How is ATP generated during the payoff stage of glycolysis?

By substrate

What is the net energy yield from glycolysis per glucose?

2 ATP and 2 NADH

How many ATP are invested and produced in glycolysis?

2 ATP invested

4 ATP produced

net 2 ATP

What is the NAD⁺/NADH balance in glycolysis?

2 NAD⁺ are reduced to 2 NADH with 2 H⁺ produced

What happens to pyruvate when oxygen is present?

It enters the mitochondria (in eukaryotic cells)

Into what is pyruvate converted before the citric acid cycle?

Acetyl

What are the products of pyruvate oxidation per glucose?

2 NADH and 2 CO₂ (and 2 acetyl

What are the products of pyruvate oxidation per pyruvate?

1 acetyl

What is another name for the citric acid cycle?

The Krebs cycle

Where does the citric acid cycle occur?

In the mitochondrial matrix

What does the citric acid cycle begin with?

Acetyl

What are the outputs of the citric acid cycle per glucose?

2 ATP, 6 NADH, 2 FADH₂, and 4 CO₂

What happens to electrons during the citric acid cycle?

They are transferred to NADH and FADH₂

What two components make up oxidative phosphorylation?

The electron transport chain and chemiosmosis

Where is the ETC located?

In the inner mitochondrial membrane (cristae)

How do ETC proteins change state as electrons pass?

They alternate between reduced (accepts e⁻) and oxidized (donates e⁻) states

What is the role of cristae for the ETC?

They increase surface area for ETC reactions

Does the ETC directly make ATP?

No

it releases energy in steps and pumps protons to create a gradient

What is formed when oxygen accepts electrons and protons?

Water (H₂O)

What major gradient does the ETC create?

A proton (H⁺) gradient across the inner mitochondrial membrane

Where are protons pumped during ETC activity?

From the matrix to the intermembrane space

What powers proton pumping in the ETC?

The exergonic flow of electrons donated by NADH and FADH₂

What does the proton gradient power?

Chemiosmosis (using H⁺ to do cellular work, chiefly ATP synthesis)

What enzyme makes ATP during chemiosmosis?

ATP synthase

What provides the energy for ATP synthase?

The H⁺ gradient across the inner mitochondrial membrane

How do protons move through ATP synthase?

They flow down their gradient through the enzyme’s channel

What mechanical action does ATP synthase perform?

Its rotor spins when H⁺ binds

What does ATP synthase’s rotation activate?

Catalytic sites that convert ADP + P to ATP

How many ATP are produced by chemiosmosis per glucose?

About 26–28 ATP

What are the inputs to oxidative phosphorylation per glucose?

10 NADH and 2 FADH₂

How many ATP are produced in oxidative phosphorylation per glucose?

About 26–28 ATP

What is the total ATP yield per glucose in aerobic respiration?

About 30–32 ATP

What is oxygen’s role in aerobic respiration?

Final electron acceptor that drives electrons down the ETC

How can cells make ATP without oxygen?

By anaerobic respiration or by fermentation

What is anaerobic respiration?

ATP generation using an ETC without oxygen as the final acceptor

Where does anaerobic respiration typically occur?

In prokaryotes living in oxygen

What are common final electron acceptors in anaerobic respiration?

Sulfates or nitrates

What is fermentation?

ATP generation without an ETC, as an extension of glycolysis

What happens to NAD⁺ in fermentation?

It is recycled (regenerated) from NADH

Where does fermentation occur?

In the cytosol

Does fermentation require oxygen?

No

What are the two main types of fermentation?

Alcohol fermentation and lactic acid fermentation

What happens to pyruvate in alcohol fermentation?

It is converted to ethanol

What intermediate appears in alcohol fermentation?

Acetaldehyde

Which organisms commonly perform alcohol fermentation?

Bacteria and yeast

What are the products of alcohol fermentation per glucose?

2 ethanol, 2 CO₂, 2 ATP, and regenerated NAD⁺

What happens to pyruvate in lactic acid fermentation?

It is reduced by NADH to form lactate

What are the products of lactic acid fermentation per glucose?

2 lactate, 2 ATP, and regenerated NAD⁺

What is a common example of lactic acid fermentation in animals?

Muscle cells ferment when oxygen is limited

What sensation is associated with muscle fermentation?

A burning feeling during strenuous exercise

What happens to lactate after muscles produce it?

It enters the blood, travels to the liver, and is converted back to glucose

How does lactate in blood affect pH?

It lowers blood pH

What condition can result from unprocessed lactate buildup?

Lactic acidosis (dangerously low blood pH)

How do ATP yields compare with and without oxygen?

With O₂: ~30–32 ATP

without O₂ (fermentation): 2 ATP

What are the main pathway options after glycolysis?

With O₂: Pyruvate oxidation → Citric acid cycle → Oxidative phosphorylation

Without O₂: Fermentation (lactic acid or alcohol)