Cells 7

What is photosynthesis?

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

What is the overall equation for photosynthesis?

6CO2 + 6H2O + light → C6H12O6 + 6O2.

What are the inputs of photosynthesis?

Light, water, and carbon dioxide.

What are the outputs of photosynthesis?

Glucose and oxygen.

Which organisms perform photosynthesis?

Plants.

Which organisms perform cellular respiration?

Both plants and animals.

What is the relationship between photosynthesis and respiration?

Photosynthesis stores energy in glucose while respiration releases energy from glucose.

What organelle carries out photosynthesis?

The chloroplast.

What are the major chloroplast structures?

Outer membrane, inner membrane, thylakoid membrane, stroma, thylakoid space, and intermembrane space.

How many membrane systems does a chloroplast have?

Three.

What are the chloroplast membrane systems?

Outer membrane, inner membrane, and thylakoid membrane.

What are thylakoids?

Flattened membrane sacs where light reactions occur.

Where do light reactions occur?

On the thylakoid membrane.

Where does the Calvin cycle occur?

In the stroma.

What is the stroma?

The fluid-filled region surrounding thylakoids inside the chloroplast.

What is the thylakoid space?

The internal compartment inside thylakoids where protons accumulate.

Why is the thylakoid membrane functionally important?

It contains photosystems, ETC proteins, and ATP synthase.

What important molecules do chloroplasts contain?

Their own DNA and ribosomes.

Can chloroplasts make some of their own proteins?

Yes.

What are the stages of photosynthesis?

Light reactions and Calvin cycle.

What is the main purpose of the light reactions?

Convert light energy into chemical energy.

What is the main purpose of the Calvin cycle?

Use ATP and NADPH to fix CO2 into carbohydrates.

What are photosystems?

Protein complexes containing chlorophyll in the thylakoid membrane.

What pigment absorbs light energy in photosystems?

Chlorophyll.

What happens when chlorophyll absorbs light?

Electrons become energized.

What happens to high-energy electrons after excitation?

They move through the photosynthetic electron transport chain.

What is the photosynthetic electron transport chain?

A series of protein complexes in the thylakoid membrane that transfer high-energy electrons.

What is the electron flow sequence in light reactions?

Photosystem II → ETC → Photosystem I.

What does Photosystem II do?

Absorbs light and provides energized electrons.

What does Photosystem I do?

Re-energizes electrons to produce NADPH.

What molecule is split during light reactions?

Water.

What are the products of water splitting?

Electrons, H+, and oxygen.

Where does the oxygen released in photosynthesis come from?

Water.

What are the outputs of the light reactions?

ATP, NADPH, and oxygen.

What is NADPH?

A high-energy electron carrier used in the Calvin cycle.

What happens to protons during light reactions?

They accumulate in the thylakoid space.

Where is proton concentration highest in chloroplasts during light reactions?

The thylakoid space.

What creates the proton gradient in chloroplasts?

The photosynthetic electron transport chain.

Why is the proton gradient important in photosynthesis?

It drives ATP production.

What is chemiosmosis?

The use of proton movement through ATP synthase to generate ATP.

What enzyme produces ATP in chloroplasts?

ATP synthase.

What reaction does ATP synthase catalyze?

ADP + Pi → ATP.

What powers ATP synthase?

Movement of protons down their concentration gradient.

What happens to ATP and NADPH produced in the light reactions?

They are used in the Calvin cycle.

What does “carbon fixation” mean?

Incorporating CO2 into organic molecules.

What is another name for the Calvin cycle?

Carbon fixation.

What are the 3 stages of the Calvin cycle?

Fixation, reduction, and regeneration.

What happens during Calvin cycle fixation?

CO2 combines with a 5-carbon molecule.

What is the 5-carbon molecule in the Calvin cycle?

Ribulose-1,5-bisphosphate (RuBP).

What is produced during the fixation stage?

6 low-energy 3-carbon molecules.

What happens during the reduction stage?

ATP and NADPH convert low-energy molecules into high-energy G3P.

What high-energy molecule is produced during reduction?

Glyceraldehyde-3-phosphate (G3P).

What is G3P?

A high-energy 3-carbon molecule produced in the Calvin cycle.

How many G3P molecules leave the Calvin cycle?

One.

What happens to the G3P that leaves the cycle?

Two G3P molecules combine to form glucose.

What happens during regeneration?

The 5-carbon RuBP molecules are regenerated.

What is required for regeneration in the Calvin cycle?

ATP.

Which stage of the Calvin cycle regenerates the 5-carbon molecule?

Regeneration.

Does the Calvin cycle directly require light?

No.

What molecules from the light reactions are used in the Calvin cycle?

ATP and NADPH.

What is the purpose of photosynthesis in plants?

To generate glucose.

What do plant cells do with glucose after photosynthesis?

Break it down in respiration to produce ATP.

Why must animals obtain glucose externally?

Animals cannot photosynthesize.

Where does almost all glucose on Earth ultimately come from?

Photosynthesis.

What process breaks down glucose to generate ATP?

Cellular respiration.

What do both photosynthesis and respiration use to generate ATP?

Proton gradients and ATP synthase.

What organelles use ATP synthase?

Chloroplasts and mitochondria.

What do chloroplasts and mitochondria both contain?

DNA and ribosomes.

What major feature do chloroplasts and mitochondria share?

Double membranes.

What theory explains the origin of chloroplasts and mitochondria?

Endosymbiosis.

What does the endosymbiotic theory state?

Ancient cells engulfed bacteria that evolved into organelles.

What evidence supports endosymbiosis?

DNA, ribosomes, double membranes, and independent replication.

Which organelle likely evolved from photosynthetic bacteria?

Chloroplasts.

Which organelle likely evolved from aerobic bacteria?

Mitochondria.

Which chloroplast compartment accumulates protons during light reactions?

The thylakoid space.

Which chloroplast compartment contains the Calvin cycle?

The stroma.

What are the major outputs of the Calvin cycle?

G3P/carbohydrates.

What is the function of ATP in photosynthesis?

Provides energy for the Calvin cycle.

What is the function of NADPH in photosynthesis?

Provides high-energy electrons for the Calvin cycle.

What is the main function of chlorophyll?

Absorb light energy.

What is the overall role of photosynthesis in ecosystems?

It powers almost all life on Earth.

Which stage of photosynthesis produces oxygen?

Light reactions.

Which stage of photosynthesis fixes CO2?

Calvin cycle.

What happens to the oxygen produced during photosynthesis?

It is released into the atmosphere.

What type of energy is stored in glucose?

Chemical energy.