10.2 photosynthesis converts light energy into chemical energy

Question 1

Light as Energy

Answer 1

• Light is electromagnetic radiation that travels in waves.
• Shorter wavelengths have more energy; longer wavelengths have less.
• Light can act as particles called photons.

Question 2

Behavior of Light

Answer 2

Light can be absorbed, reflected, or transmitted when it interacts with molecules.
- Absorbed photons can add energy to molecules, leading to an excited state.
- Different molecules absorb specific wavelengths of light.

Question 3

Pigments in Photosynthesis

Answer 3

• Pigments are molecules that absorb specific wavelengths of visible light.
• Chlorophyll A is the primary pigment in photosynthesis, absorbing blue and red light.
• Other pigments include chlorophyll B, carotenoids, and phycobilins, which broaden the range of absorbed light.

Question 4

Photosystem Structure

Answer 4

• Photosystems consist of light-harvesting complexes and a reaction center.
• Pigments in the complexes absorb photons and transfer energy to the reaction center.
• Chlorophyll A in the reaction center converts light energy into chemical energy.

Question 5

Electron Transport

Answer 5

• Noncyclic electron transport involves two photosystems and electron carriers.
• Electrons move through the chain, releasing energy used to pump protons across the thylakoid membrane.

Question 6

ATP Synthesis

Answer 6

• Protons accumulate in the thylakoid lumen, creating an electrochemical gradient.
• ATP synthase channels allow protons to flow back into the stroma, driving ATP synthesis through chemiosmosis.
• This process, called photophosphorylation, generates ATP from ADP and inorganic phosphate.

Question 7

Redox Reaction in Photosynthesis

Answer 7

• Chlorophyll gets oxidized to Chl+ during photosynthesis, while an acceptor molecule is reduced.
• The final electron acceptor is NADP+, which is reduced to NADPH.

Question 8

Photosystem Absorption Peaks

Answer 8

• Photosystem I absorbs best at 700 nm.
• Photosystem II absorbs best at 680 nm.

Question 9

Cyclic Electron Transport

Answer 9

• Cyclic electron transport uses only photosystem I and electron transport to produce ATP instead of NADPH.
• ATP is formed via photophosphorylation.
• High H+ concentration in the lumen drives H+ back into the stroma through ATP synthase channels.

Question 10

Action Spectrum vs. Absorption Spectrum

Answer 10

• Action spectrum: Plot of photosynthetic rate against wavelengths of light.
• Absorption spectrum: Plot of wavelengths absorbed by a pigment.