AP Bio Unit 3 Flashcards

What is photosynthesis?

The process that converts light energy into chemical energy stored in sugars.

What are the reactants of photosynthesis?

Carbon dioxide, water, and light energy.

What are the products of photosynthesis?

Sugar and oxygen.

What is the overall photosynthesis equation?

6CO2 + 6H2O + light energy → C6H12O6 + 6O2.

Where does photosynthesis occur?

In chloroplasts.

What are the two stages of photosynthesis?

Light-dependent reactions and the Calvin cycle.

Where do light-dependent reactions occur?

In the thylakoid membranes of chloroplasts.

Where does the Calvin cycle occur?

In the stroma of chloroplasts.

What is the stroma?

The fluid-filled space inside a chloroplast surrounding the thylakoids.

What are thylakoids?

Membrane sacs containing chlorophyll and the photosystems.

What is chlorophyll?

A pigment that absorbs light energy to excite electrons.

What is the purpose of light-dependent reactions?

Convert light energy into chemical energy stored in ATP and NADPH.

What are the products of light-dependent reactions?

ATP, NADPH, and oxygen.

What is Photosystem II (PSII)?

The photosystem that absorbs light and replaces lost electrons by splitting water.

What happens when light hits PSII?

Chlorophyll electrons become excited and enter the electron transport chain.

What is photolysis?

The splitting of water using light energy to produce electrons, H+ ions, and oxygen.

Why is water split during photosynthesis?

To replace electrons lost by PSII and supply H+ ions.

Where does the oxygen released during photosynthesis come from?

From the splitting of water, not carbon dioxide.

What happens to excited electrons in the photosynthetic ETC?

They lose energy that helps pump H+ into the thylakoid interior.

What is the purpose of the photosynthetic electron transport chain?

Transfer electrons and help establish a proton gradient for ATP production.

What is Photosystem I (PSI)?

The photosystem that re-energizes electrons using light to help produce NADPH.

What happens to electrons after PSI absorbs light?

They are transferred to carriers that reduce NADP+ to NADPH.

What is NADP+?

An electron carrier that accepts high-energy electrons and H+ to form NADPH.

What is NADPH used for?

It supplies high-energy electrons for the Calvin cycle.

What is ATP synthase?

A membrane protein that uses H+ flow to produce ATP from ADP and phosphate.

What is chemiosmosis in photosynthesis?

H+ flows through ATP synthase from the thylakoid interior to the stroma, producing ATP.

Where do H+ ions accumulate during light-dependent reactions?

Inside the thylakoid space.

What is the role of light in Photosystems I and II?

Excite electrons to higher energy levels.

What is the Calvin cycle?

The light-independent reactions that use CO2, ATP, and NADPH to produce G3P.

Why is the Calvin cycle called light-independent?

It does not directly require light, but depends on ATP and NADPH from light reactions.

What are the three stages of the Calvin cycle?

Carbon fixation, reduction, and regeneration of RuBP.

Where does carbon fixation occur?

In the stroma of the chloroplast.

What enzyme catalyzes carbon fixation?

Rubisco.

What happens during carbon fixation?

Rubisco attaches CO2 to RuBP, forming an unstable six-carbon intermediate.

What happens to the unstable six-carbon intermediate?

It splits into two molecules of 3-PGA.

What is 3-PGA?

A three-carbon molecule produced during carbon fixation.

What happens during the reduction phase?

ATP and NADPH help convert 3-PGA into G3P.

What is G3P?

A three-carbon sugar that can be used to build glucose and other organic molecules.

What happens during RuBP regeneration?

ATP helps rearrange five G3P molecules to regenerate three RuBP molecules.

How many CO2 molecules enter one Calvin cycle round for one net G3P?

Three CO2 molecules.

How many ATP are used to produce one net G3P?

Nine ATP.

How many NADPH are used to produce one net G3P?

Six NADPH.

How many G3P molecules leave the cycle net after fixing 3 CO2?

One net G3P; the other five regenerate RuBP.

How many net G3P molecules are needed to build one glucose?

Two net G3P molecules.

What supplies energy to the Calvin cycle?

ATP and NADPH from the light-dependent reactions.

What happens to ADP and NADP+ after the Calvin cycle uses ATP and NADPH?

They return to the light-dependent reactions to be recharged.

What is cellular respiration?

The process of breaking down organic molecules to produce ATP.

What is the overall purpose of cellular respiration?

Transfer energy from glucose into ATP that cells can use.

What is the overall equation for aerobic cellular respiration?

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy.

What are the major stages of cellular respiration?

Glycolysis, pyruvate oxidation, Krebs cycle, and oxidative phosphorylation.

Where does glycolysis occur?

In the cytosol, outside the mitochondrion.

What molecule begins glycolysis?

One six-carbon glucose molecule.

What is the main result of glycolysis?

One glucose becomes two pyruvate molecules.

What are the net products of glycolysis per glucose?

Two pyruvate, two net ATP, and two NADH.

What is the energy investment phase of glycolysis?

The first phase, where two ATP are used to phosphorylate glucose-derived molecules.

What is the energy payoff phase of glycolysis?

The phase that produces four ATP and two NADH per glucose.

How many ATP are invested during glycolysis?

Two ATP.

How many ATP are produced gross during glycolysis?

Four ATP.

What is the net ATP gain from glycolysis?

Two ATP per glucose.

What is substrate-level phosphorylation?

Direct transfer of a phosphate group to ADP to make ATP.

What does hexokinase do in glycolysis?

Transfers a phosphate from ATP to glucose.

What does phosphofructokinase do?

Uses ATP to phosphorylate fructose-6-phosphate, forming fructose-1,6-bisphosphate.

What does aldolase do in glycolysis?

Splits the six-carbon sugar into two three-carbon molecules.

What happens to DHAP during glycolysis?

It is converted into G3P so both three-carbon molecules continue through the pathway.

What does glyceraldehyde-3-phosphate dehydrogenase produce?

NADH and 1,3-bisphosphoglycerate from G3P.

What is pyruvate?

A three-carbon molecule produced at the end of glycolysis.

What is pyruvate oxidation?

The link reaction that converts pyruvate into acetyl-CoA before the Krebs cycle.

Where does pyruvate oxidation occur in eukaryotes?

In the mitochondrial matrix.

What happens to each pyruvate during pyruvate oxidation?

One CO2 is released, NADH is produced, and the remaining two-carbon group joins CoA.

What is acetyl-CoA?

A two-carbon acetyl group attached to coenzyme A that enters the Krebs cycle.

What are the products of pyruvate oxidation per glucose?

Two acetyl-CoA, two CO2, and two NADH.

What is the Krebs cycle also called?

The citric acid cycle.

Where does the Krebs cycle occur?

In the mitochondrial matrix.

What enters the Krebs cycle?

Acetyl-CoA, which combines with oxaloacetate to form citrate.

What happens when acetyl-CoA joins oxaloacetate?

A six-carbon citrate molecule forms and coenzyme A is released.

What is the role of oxaloacetate?

It combines with acetyl-CoA and is regenerated at the end of the cycle.

What happens during the Krebs cycle?

Acetyl groups are oxidized, CO2 is released, and NADH, FADH2, and ATP or GTP are produced.

What are the products of one Krebs cycle turn?

Three NADH, one FADH2, one ATP or GTP, and two CO2.

How many turns of the Krebs cycle occur per glucose?

Two turns, because one glucose produces two acetyl-CoA.

What are the total Krebs cycle products per glucose?

Six NADH, two FADH2, two ATP or GTP, and four CO2.

What happens to NAD+ in the Krebs cycle?

It accepts electrons and H+ during oxidation reactions to become NADH.

What happens to FAD in the Krebs cycle?

It accepts electrons and H+ to become FADH2.

What is released as waste during pyruvate oxidation and the Krebs cycle?

Carbon dioxide.

What is oxidative phosphorylation?

ATP production powered by the electron transport chain and chemiosmosis.

Where does oxidative phosphorylation occur?

At the inner mitochondrial membrane.

What are the two parts of oxidative phosphorylation?

The electron transport chain and chemiosmosis.

What is the mitochondrial electron transport chain (ETC)?

Membrane protein complexes that transfer electrons and pump H+ across the inner mitochondrial membrane.

Where do NADH and FADH2 deliver electrons?

To the electron transport chain in the inner mitochondrial membrane.

Where does NADH donate its electrons to the mitochondrial ETC?

Complex I.

Where does FADH2 donate its electrons to the mitochondrial ETC?

Complex II.

Why does FADH2 generally produce less ATP than NADH?

FADH2 enters at Complex II, bypassing Complex I and contributing to less H+ pumping.

What happens as electrons move through the mitochondrial ETC?

Energy released pumps H+ from the matrix into the intermembrane space.

What is the final electron acceptor in aerobic respiration?

Oxygen.

What happens when oxygen accepts electrons and H+?

Water forms.

Why is oxygen necessary for aerobic cellular respiration?

It accepts electrons at the end of the ETC, allowing electron flow to continue.

What happens if oxygen is unavailable?

The mitochondrial ETC stops, oxidative phosphorylation ceases, and cells must rely on other pathways for ATP.

What is the mitochondrial intermembrane space?

The region between the outer and inner mitochondrial membranes where H+ accumulates.

What is the mitochondrial matrix?

The innermost compartment where pyruvate oxidation and the Krebs cycle occur.

What are cristae?

Folds of the inner mitochondrial membrane that increase surface area for ATP production.

What is the proton gradient?

A difference in H+ concentration and electrical charge across a membrane.