ATP is the cell's immediate energy carrier. Respiration releases energy from organic molecules, then transfers some of that energy into ATP. Because ATP is small and soluble, it can move to reactions that need energy and deliver it in small, controlled amounts.

ATP, adenosine triphosphate, is the immediate energy currency of cells.

ATP distributes energy from respiration to energy-requiring processes.

Cells use ATP for short-term energy transfer, not long-term energy storage.

Use the visual to explain the process, not to memorize decoration.

Match each ATP feature to why it helps the cell.

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small and soluble

phosphate bond hydrolysis

rapid recycling

not long-term storage

ATP is useful because it is recycled. When ATP is hydrolysed to ADP and phosphate, energy becomes available for cell work. Respiration then phosphorylates ADP back to ATP, so the same molecule system can keep transferring energy again and again. Examples include membrane pumps, macromolecule synthesis, and chromosome movement.

Hydrolysis of ATP to ADP + phosphate releases energy.

Phosphorylation of ADP to ATP stores energy from respiration in a usable form.

ATP powers active transport, anabolic reactions, movement, and other life processes.

Examples include membrane pumps, macromolecule synthesis, and chromosome movement.

Use the visual to explain the process, not to memorize decoration.

Sort each event into ATP hydrolysis or ATP regeneration.

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ATP hydrolysis

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ATP regeneration

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Cell respiration is a system for transferring energy from carbon compounds into ATP. The important idea is control: energy is released in small enzyme-controlled steps. In humans, aerobic respiration uses oxygen and mitochondria for high ATP yield, while anaerobic respiration in cytoplasm allows short-term ATP production without oxygen but produces lactate and much less ATP.

Cell respiration releases energy from organic molecules to make ATP.

Aerobic respiration uses oxygen and mitochondria and produces much more ATP.

Anaerobic respiration in humans happens in cytoplasm, produces lactate, and gives low ATP yield.

Use the visual to explain the process, not to memorize decoration.

Match each respiration route to its correct description.

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aerobic respiration

anaerobic respiration in humans

cell respiration overall

controlled stepwise reactions

Respiration rate is not guessed; it is measured using a change over time, often oxygen uptake. In a respirometer, carbon dioxide is absorbed, so a pressure drop mainly reflects oxygen being used. Rate changes when temperature, substrate type or amount, oxygen availability, activity level, or mass of living tissue changes. Rate depends on metabolic demand, organism size, oxygen, substrate, temperature, and pH.

Variables affecting rate include temperature, substrate, oxygen availability, activity, and organism mass.

A respirometer can measure oxygen uptake per unit time.

Controls are needed for temperature, mass, leaks, and carbon dioxide absorption.

Rate depends on metabolic demand, organism size, oxygen, substrate, temperature, and pH.

Use the visual to explain the process, not to memorize decoration.

A germinating seed respirometer is kept warmer and the fluid moves faster. What is the best interpretation?

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A germinating seed respirometer is kept warmer and the fluid moves faster. What is the best interpretation?

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HL respiration becomes easier when you follow hydrogen. NAD is a coenzyme that accepts hydrogen during oxidation reactions, becoming reduced NAD. Reduced NAD carries electrons and protons to the electron transport chain, where their energy helps make ATP.

NAD accepts hydrogen and becomes reduced NAD.

Reduced NAD carries high-energy electrons and protons.

This carrier links glycolysis/Krebs oxidation to oxidative phosphorylation.

Use the visual to explain the process, not to memorize decoration.

Fill Blanks

Complete the carrier sentence: NAD acceptsand becomes. It carriesto the electron transport chain.

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Complete the carrier sentence: NAD accepts ____ and becomes ____. It carries ____ to the electron transport chain.

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Glycolysis is the cytoplasmic first stage of respiration. One glucose is phosphorylated, split into two three-carbon compounds, oxidized to reduce NAD, and converted to two pyruvate. ATP is used at the start but more ATP is produced later, giving a net gain.

Glycolysis occurs in the cytoplasm.

One glucose forms two pyruvate molecules.

There is a net gain of ATP and reduced NAD.

Use the visual to explain the process, not to memorize decoration.

Put the simplified glycolysis story in order.

Order

1

six-carbon sugar is split

2

two pyruvate are produced

3

glucose is phosphorylated

4

ATP is formed by substrate-level phosphorylation

5

three-carbon compounds are oxidized and NAD is reduced

Put the simplified glycolysis story in order.

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glucose is phosphorylated

six-carbon sugar is split

three-carbon compounds are oxidized and NAD is reduced

ATP is formed by substrate-level phosphorylation

two pyruvate are produced

When oxygen is unavailable, pyruvate cannot continue through aerobic respiration. Cells still need glycolysis to make some ATP, so they regenerate NAD. In humans, pyruvate is reduced to lactate. In yeast, pyruvate is converted to ethanol and carbon dioxide. The point is not high ATP yield; the point is keeping glycolysis running. Regenerated NAD allows glycolysis to continue. Fermentation regenerates NAD for glycolysis and is used in baking and brewing.

Humans: pyruvate is reduced to lactate during anaerobic respiration.

Yeast: pyruvate forms ethanol and carbon dioxide.

Both pathways regenerate NAD so glycolysis can continue.

Regenerated NAD allows glycolysis to continue.

Fermentation regenerates NAD for glycolysis and is used in baking and brewing.

Use the visual to explain the process, not to memorize decoration.

Sort each statement into human anaerobic respiration or yeast anaerobic respiration.

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Humans

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Yeast

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Sort each statement into human anaerobic respiration or yeast anaerobic respiration.

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The link reaction prepares pyruvate for the Krebs cycle. Pyruvate enters the mitochondrion, loses carbon dioxide, is oxidized so NAD is reduced, and the remaining two-carbon acetyl group attaches to coenzyme A to form acetyl-CoA.

The link reaction occurs in the mitochondrion.

Pyruvate is decarboxylated and oxidized.

Products include acetyl-CoA, carbon dioxide, and reduced NAD.

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Match each link reaction event to its meaning.

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decarboxylation

oxidation

coenzyme A joins acetyl group

acetyl-CoA enters next stage

The Krebs cycle is not mainly a big ATP factory by itself. Its main value is that it oxidizes acetyl groups and loads energy onto carriers. Acetyl-CoA combines with oxaloacetate to form citrate, carbon dioxide is released, NAD and FAD are reduced, a small amount of ATP is made, and oxaloacetate is regenerated.

Acetyl-CoA combines with oxaloacetate to form citrate.

The cycle releases carbon dioxide and forms reduced NAD and reduced FAD.

Oxaloacetate is regenerated, allowing the cycle to continue.

Use the visual to explain the process, not to memorize decoration.

Fill Blanks

Complete the Krebs sentence: Acetyl-CoA combines withto form citrate. The cycle releasesand forms reducedand reduced.

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Complete the Krebs sentence: Acetyl-CoA combines with ____ to form citrate. The cycle releases ____ and forms reduced ____ and reduced ____.

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Reduced NAD and reduced FAD deliver electrons to the electron transport chain in the inner mitochondrial membrane. As electrons pass along carriers, released energy pumps protons from the matrix into the intermembrane space. This creates a proton gradient, which stores potential energy for ATP synthesis. Electron transfers release energy while coenzymes are reoxidized.

The electron transport chain is in the inner mitochondrial membrane.

Energy from electron transfer pumps protons into the intermembrane space.

The proton gradient is the immediate energy store used for chemiosmosis.

Electron transfers release energy while coenzymes are reoxidized.

Use the visual to explain the process, not to memorize decoration.

Put the proton-gradient story in order.

Order

1

reduced NAD/FAD donate electrons

2

electrons pass along carrier proteins

3

energy is released from electron transfer

4

protons are pumped into the intermembrane space

5

a proton gradient forms across the inner mitochondrial membrane

Put the proton-gradient story in order.

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reduced NAD/FAD donate electrons

electrons pass along carrier proteins

energy is released from electron transfer

protons are pumped into the intermembrane space

a proton gradient forms across the inner mitochondrial membrane

Chemiosmosis is how the gradient becomes ATP. Protons diffuse back into the matrix through ATP synthase, and the released energy phosphorylates ADP to ATP. Oxygen is essential at the end because it accepts electrons and protons, forming water and allowing the electron transport chain to continue.

Chemiosmosis is proton diffusion through ATP synthase down a gradient.

ATP synthase phosphorylates ADP to ATP.

Oxygen is the terminal electron acceptor and forms water.

Use the visual to explain the process, not to memorize decoration.

A poison prevents oxygen from accepting electrons in mitochondria. What happens next?

Choose

A poison prevents oxygen from accepting electrons in mitochondria. What happens next?

Choose

Different respiratory substrates suit different needs. Lipids are more reduced, so they release more energy and produce more ATP and metabolic water per gram. But they require more oxygen and are slower to mobilize. Carbohydrates enter glycolysis quickly and are better for rapid ATP supply.

Lipids produce more ATP per gram because they contain more hydrogen and are more reduced.

Lipids also require more oxygen and produce more metabolic water.

Carbohydrates are faster to use and support rapid respiration.

Use the visual to explain the process, not to memorize decoration.

Match each situation to the better substrate logic.

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Reasons

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maximum ATP per gram needed

rapid ATP supply needed

metabolic water is valuable

oxygen is limited

ATP is the immediate energy carrier; hydrolysis powers cell work and phosphorylation reloads ATP. Cell respiration transfers energy from carbon compounds into ATP in controlled steps. Aerobic respiration in humans uses oxygen and mitochondria for high ATP yield, while anaerobic respiration in cytoplasm produces lactate and low ATP. Rate evidence comes from oxygen uptake or carbon dioxide production per unit time. Examples include membrane pumps, macromolecule synthesis, and chromosome movement. Rate depends on metabolic demand, organism size, oxygen, substrate, temperature, and pH.

Use ATP as the link between respiration and life processes such as active transport, biosynthesis, movement, and homeostasis.

Compare aerobic and anaerobic respiration by oxygen use, location, ATP yield, and product in humans.

For rate questions, name the variable, measurement per unit time, and controlled variables.

Examples include membrane pumps, macromolecule synthesis, and chromosome movement.

Rate depends on metabolic demand, organism size, oxygen, substrate, temperature, and pH.

Fill Blanks

Complete the exam skeleton: ATPreleases energy for cell work;of ADP reforms ATP. Aerobic respiration usesand gives high ATP yield; anaerobic respiration in humans forms.

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Use this for questions asking how ATP supplies energy, how ATP is recycled, how aerobic and anaerobic respiration differ in humans, or how respiration rate is measured.

ATP is a small soluble energy currency that distributes energy from respiration to energy-requiring life processes.

ATP hydrolysis to ADP and phosphate releases energy; phosphorylation of ADP reforms ATP using energy from respiration.

Cell respiration transfers energy from organic molecules to ATP through controlled enzyme-catalysed reactions.

Aerobic respiration uses oxygen and mitochondria and gives high ATP yield; anaerobic respiration in human cytoplasm produces lactate and low ATP.

Respiration rate can be measured as oxygen uptake or carbon dioxide production per unit time, with controls such as temperature, mass, and carbon dioxide absorption.

Examples include membrane pumps, macromolecule synthesis, and chromosome movement.

Rate depends on metabolic demand, organism size, oxygen, substrate, temperature, and pH.

Use this for questions asking how ATP supplies energy, how ATP is recycled, how aerobic and anaerobic respiration differ in humans, or how respiration rate is measured.

Do not confuse cellular respiration with breathing, or anaerobic respiration in humans with ethanol fermentation.

In HL respiration, carbon and hydrogen are followed separately. Glycolysis turns glucose into pyruvate, net ATP, and reduced NAD. Without oxygen, pyruvate becomes lactate in humans or ethanol and carbon dioxide in yeast to regenerate NAD. With oxygen, pyruvate enters the link reaction, forming acetyl-CoA, carbon dioxide, and reduced NAD. The Krebs cycle releases more carbon dioxide and reduced coenzymes. Electron transport uses reduced NAD/FAD to pump protons, chemiosmosis through ATP synthase makes ATP, and oxygen accepts electrons and protons to form water. Substrate comparisons depend on ATP yield, oxygen demand, water production, and speed. Regenerated NAD allows glycolysis to continue. Fermentation regenerates NAD for glycolysis and is used in baking and brewing. Electron transfers release energy while coenzymes are reoxidized.

Trace carbon: glucose -> pyruvate -> acetyl-CoA -> carbon dioxide, or anaerobic products.

Trace hydrogen/electrons: NAD/FAD become reduced and feed the electron transport chain.

Trace protons: electron transport builds the gradient; ATP synthase uses it for chemiosmosis.

Compare substrates by yield, oxygen demand, metabolic water, and speed.

Regenerated NAD allows glycolysis to continue.

Fermentation regenerates NAD for glycolysis and is used in baking and brewing.

Electron transfers release energy while coenzymes are reoxidized.

Put the high-yield aerobic pathway in order.

Order

1

glycolysis forms pyruvate and reduced NAD

2

oxygen accepts electrons and protons to form water

3

Krebs cycle releases carbon dioxide and reduces NAD/FAD

4

protons diffuse through ATP synthase by chemiosmosis

5

link reaction forms acetyl-CoA, carbon dioxide, and reduced NAD

6

electron transport pumps protons across the inner mitochondrial membrane

Use this for HL structured questions asking for the sequence, products, locations, oxygen role, fermentation comparison, or substrate comparison.

NAD accepts hydrogen and becomes reduced NAD, carrying electrons and protons to the electron transport chain.

Glycolysis occurs in cytoplasm and converts glucose to two pyruvate, with net ATP and reduced NAD.

Anaerobic respiration regenerates NAD: pyruvate becomes lactate in humans, or ethanol and carbon dioxide in yeast.

The link reaction converts pyruvate to acetyl-CoA, releases carbon dioxide, and reduces NAD.

The Krebs cycle combines acetyl-CoA with oxaloacetate, regenerates oxaloacetate, releases carbon dioxide, and forms reduced NAD/FAD plus a little ATP.

Electron transport in the inner mitochondrial membrane uses reduced coenzymes to pump protons and generate a proton gradient.

Chemiosmosis occurs when protons flow through ATP synthase, phosphorylating ADP to ATP.

Oxygen is the terminal electron acceptor and forms water, allowing electron transport to continue.

Lipids generally yield more ATP and metabolic water per gram but need more oxygen and are slower than carbohydrates.

Regenerated NAD allows glycolysis to continue.

Fermentation regenerates NAD for glycolysis and is used in baking and brewing.

Electron transfers release energy while coenzymes are reoxidized.

Use this for HL structured questions asking for the sequence, products, locations, oxygen role, fermentation comparison, or substrate comparison.

Do not describe the pathway as disconnected stages; marks often come from linking products of one stage to the next.

IB Biology HL C1.2 Cell respiration Notes

ATP Moves Usable Energy

Use And Recycle ATP

Map The Respiration System

Predict Respiration Rate

Carry Hydrogen With NAD

Trace Glycolysis

Choose The Pyruvate Fate

Enter The Krebs Cycle

Run The Krebs Cycle

Build The Proton Gradient

Make ATP With Oxygen

Choose The Best Fuel

SL Transfer: Explain Core Respiration

HL Transfer: Trace The Respiration Pathway