Photosynthesis and the Calvin Cycle

Photosynthesis converts solar energy into chemical energy in plants, algae, and some prokaryotes. It occurs in two stages: light reactions and the Calvin cycle. Light reactions in the thylakoid membrane produce ATP and NADPH, while the Calvin cycle in the stroma uses these products to convert CO2 into glucose. Photopigments like chlorophyll absorb light, initiating electron transport in photosystems. Photosystem II releases oxygen, and Photosystem I produces NADPH. Cyclic electron flow adjusts ATP/NADPH ratios. The Calvin cycle involves carbon fixation, reduction, and regeneration phases, ultimately synthesizing glucose.

What is the primary function of photosynthesis in plants?

• To absorb oxygen

• To convert chemical energy into solar energy

• To convert solar energy into chemical energy

• To produce carbon dioxide

Where does photophosphorylation occur in the chloroplast?

• In the outer membrane

• In the thylakoid membrane

• In the grana

• In the stroma

Which pigment is primarily responsible for absorbing light in photosynthesis?

• Xanthophylls

• Chlorophyll a

• Chlorophyll b

• Carotenoids

What is the role of accessory pigments in photosynthesis?

• To provide photoprotection

• To reflect all light

• To narrow the absorption spectrum

• To absorb only green light

In photosystem II, what molecule donates electrons to replace those lost by P680?

• NADPH

• Carbon dioxide

• Water

• Oxygen

What is the final electron acceptor in the light reactions of photosynthesis?

• NADP+

• ATP

• Water

• Oxygen

How does the electron transport chain in chloroplasts differ from that in mitochondria?

• It generates ATP without a proton gradient

• It uses chemical energy from food

• It pumps protons into the intermembrane space

• It pumps protons into the thylakoid space

During the Calvin cycle, what enzyme is responsible for fixing carbon dioxide?

• Rubisco

• ATP synthase

• NADP+ reductase

• Cytochrome b6f

What is the main product of the Calvin cycle that can be converted into glucose?

• NADPH

• Oxygen

• Glyceraldehyde 3-phosphate

• ATP

How many rounds of the Calvin cycle are required to produce one glucose molecule?

• One

• Four

• Two

• Three