chapter8

What are the two stages of photosynthesis?

Light Reactions and Calvin cycle

What happens during the light reactions of photosynthesis?

Light energy is absorbed by chlorophyll and converted into ATP and NADPH

What is the role of the Calvin cycle?

Uses ATP and NADPH to drive carbohydrate synthesis

What is the balanced equation for photosynthesis?

6 CO₂ + 12 H₂O + light energy → C₆H₁₂O₆ + 6 O₂ + 6 H₂O

In photosynthesis, what happens to carbon in CO₂?

It is reduced

In photosynthesis, what happens to oxygen in H₂O?

It is oxidized

What is the free energy change for photosynthesis?

+685 kcal/mol

What is the biosphere?

Regions on Earth and atmosphere where life exists

What do plants produce besides glucose during photosynthesis?

Oxygen (O₂)

What are heterotrophs?

Organisms that must consume organic molecules

What are autotrophs?

Organisms that make organic molecules from inorganic sources

What are photoautotrophs?

Autotrophs that use light and CO₂ to produce organic molecules

What are epidermal cells?

Cells on the outer surface of leaves

What are mesophyll cells?

Leaf cells containing chloroplasts between epidermal layers

What are stomata?

Pores on the underside of leaves for gas exchange

Where does most photosynthesis occur?

In chloroplasts of mesophyll cells

What is a chloroplast?

An organelle where photosynthesis occurs

What pigments in chloroplasts absorb light?

Chlorophyll in thylakoids

What separates the outer and inner chloroplast membranes?

Intermembrane space

What is the thylakoid membrane?

The third chloroplast membrane containing pigments

What do thylakoid membranes enclose?

Thylakoid lumen

What is a granum?

A stack of thylakoids

What is the stroma?

Fluid-filled region between inner membrane and thylakoid membrane

Where does CO₂ enter and O₂ exit the leaf?

Through stomata

What molecules are produced by light reactions?

ATP, NADPH, and O₂

Why is NADPH similar to NADH?

It carries high-energy electrons

How does NADP⁺ become NADPH?

By accepting two electrons and H⁺

What happens to water during light reactions?

It is oxidized and split into O₂ and H⁺

What special pigment accepts electrons in PSII?

P680

What is resonance energy transfer?

Energy transfer between pigment molecules

What happens after electrons leave PSII?

They travel down the electron transport chain

What powers ATP synthase in chloroplasts?

Proton (H⁺) gradient from lumen to stroma

What enzyme produces NADPH?

NADP⁺ reductase

What is the primary role of PSI?

To produce NADPH

What pigment absorbs light in PSI?

P700

Where do electrons go after PSI?

To NADP⁺ reductase

What process describes electron flow from PSII to PSI to NADP⁺?

Linear (noncyclic) electron flow

Which pathway produces both ATP and NADPH?

Noncyclic electron flow

Which pathway produces only ATP?

Cyclic photophosphorylation

Where do cyclic electron flow electrons return?

Back to PSI

What is the role of the cytochrome complex?

Transfers electrons and pumps protons

What protein family is shared by chloroplast and mitochondrial ETC?

Cytochrome b proteins

What does the Z‑scheme represent?

Zigzag energy changes of electrons in PSII & PSI

Where does an electron start its journey in the Z‑scheme?

At lowest energy in PSII

What creates the proton gradient in chloroplasts?

ETC pumping H⁺ into thylakoid lumen

What molecule is the ultimate electron acceptor in photosynthesis?

NADP⁺

How many ATP are used to fix six CO₂?

18 ATP

How many NADPH are used to fix six CO₂?

12 NADPH

What is the main product of the Calvin cycle?

Glyceraldehyde‑3‑phosphate (G3P)

What enzyme fixes CO₂ to RuBP?

Rubisco

What happens during RuBP regeneration?

Remaining G3P molecules regenerate RuBP using ATP

What environmental factors influence photosynthesis efficiency?

Light intensity, temperature, and water availability

What do C4 plants fix CO₂ into initially?

Oxaloacetate (a 4-carbon molecule)

Where does the Calvin cycle occur in C4 plants?

Bundle‑sheath cells

How do CAM plants conserve water?

They open stomata at night and close during day

When do CAM plants take in CO₂?

At night

What compound forms when CAM plants fix CO₂ at night?

Malate

How do C4 and CAM plants differ?

C4 separate by space (cell type), CAM by time (day/night)

Which plant type opens its stomata only at night?

CAM plants

Why have C4 and CAM pathways evolved?

To adapt to environments with high light, temperature, or low water