photosynthesis (5.1, 5.2, 5.4, 5.6) (simple)

Question 1

What are the two stages of photosynthesis?

Answer 1

Light-dependent reactions
Light-independent reactions (Calvin cycle)

Question 2

What happens in light-dependent reactions?

Answer 2

Light energy splits water
ATP and NADPH are made
A protein gradient forms to power ATP synthesis

Question 3

What happens in light-independent reactions (Calvin cycle)?

Answer 3

Uses ATP & NADPH to convert CO2 into sugar
CO₂ turns into 3-carbon G3P
G3P helps form glucose, lipids, or proteins

Question 4

Where do photosynthesis reactions occur?

Answer 4

In the chloroplasts
Thylakoids: light-dependent reactions
Stroma: Calvin cycle

Question 5

What happens when pigment molecules absorb light?

Answer 5

1. Electron returns to ground state (releases heat or light)
2. Energy transferred to another electron
3. Electron is captured by a primary acceptor

Question 6

What are chlorophyll and carotenoids?

Answer 6

Chlorophyll a: main pigment, donates electrons
Chlorophyll b & carotenoids: accessory pigments
Accessory pigments form antenna complex

Question 7

What light do pigments absorb?

Answer 7

Chlorophyll a: absorbs blue & red, not green/yellow
Carotenoids: do not absorb red to yellow

Question 8

What are photosystems?

Answer 8

Groups of pigment proteins
Photosystem I = P700 (absorbs 700 nm light)
Photosystem II = P680 (absorbs 680 nm light, splits water)

Question 9

What happens in Photosystem II (P680)?

Answer 9

Light excites electrons
Electrons go to acceptor
P680 becomes positive and pulls electrons from water

Question 10

What is linear electron transport?

Answer 10

Electrons move: PSII → plastoquinone → cytochrome → plastocyanin → PSI → NADPH
Creates protein gradient for ATP
Requires light at both PSII and PSI

Question 11

How is ATP made?

Answer 11

High proton concentration in the lumen
Protons flow through ATP synthase
Energy used to form ATP (chemiosmosis)

Question 12

What is cyclic electron transport?

Answer 12

Electrons go back to plastoquinone instead of forming NADPH
More protons pumped → more ATP made
Used when more ATP than NADPH is needed

Question 13

What are the phases of the Calvin cycle?

Answer 13

1. Fixation – CO2 + RuBP → 3-phosphoglycerate (via rubisco)
2. Reduction – ATP & NADPH convert it to G3P
3. Regeneration – G3P regenerates RuBP using ATP

Question 14

Summary of Photosynthesis Outputs

Answer 14

Light-dependent: ATP, NADPH, O2
Calvin cycle: G3P (used to make glucose)