Photosynthesis Quiz

Photosynthesis: Light-Dependent Reactions and the Structure of Chloroplasts

• Photosynthesis involves a series of reactions that use light and are anabolic.
• Light is transduced, meaning it is changed from one type of energy to another, and is converted into chemical energy.
• Chlorophyll and carotenoids are photosensitive pigments that absorb light.
• Photosystems, which contain these pigments and electron transport chains, are fixed in thylakoid membranes for efficiency.
• There are two different photosystems, each linked to different electron transport chains and sensitive to different wavelengths of light.
• A photosystem consists of an antenna complex, which transfers energy to a reaction center molecule where light-dependent reactions begin.
• The light-dependent reactions use light to synthesize ATP and reduced NADP, which provide energy and hydrogen ions for the light-independent reactions.
• Electrons in chlorophyll molecules in photosystem II are excited by light, escape the molecule, and are replaced by electrons from photolysis of water.
• The excited electrons pass through an electron transport chain, losing energy and pumping protons into the thylakoid space, which leads to the chemiosmotic synthesis of ATP.
• Electrons in photosystem I are excited by light and pass through a second electron transport chain, ultimately forming reduced NADP.
• A photosynthetic unit is a collection of pigments, electron carriers, and ATP synthase that can carry out all the reactions in the light-dependent stage of photosynthesis.
• Cyclic photophosphorylation is a process where only photosystem I is used, and electrons lost from the chlorophyll molecule are returned to it, producing ATP when sugars cannot be synthesized due to a lack of carbon dioxide.