Light-Dependent Reactions in the Thylakoid Membrane
Thylakoid membranes hold pigments that trap light. The light-dependent reactions split water, make ATP, and reduce NADP+ to NADPH, also called reduced NADP. ATP and NADPH then supply energy and reducing power to carbon-fixing reactions.
What a learner can do afterwards
- Places the light-dependent reactions in the thylakoid membrane and says why they happen there.
- Names what water is split into and where each product goes.
- Lists the two products that carry energy and reducing power onward.
1 · Read
An earlier topic showed that light can limit photosynthesis. The light is used inside a chloroplast, where stacks of thylakoid membranes sit in a fluid called the stroma. The light-dependent reactions run in the thylakoid membranes, where chlorophyll in photosystems absorbs photons. This stage makes ATP and reduces NADP+ to NADPH, also called reduced NADP. The next stage uses those two products in the stroma to build carbohydrates. Without light, their supplies run down.
Light energy drives the splitting of water. The products are oxygen, hydrogen ions called protons, and electrons. Oxygen is released as a gas. Protons collect in the thylakoid space, while electrons move through an electron transport chain.
The electron transport chain pumps more protons into the thylakoid space. The thylakoid membrane separates that space from the stroma, so protons build up on one side and form a concentration gradient. Protons then flow back through ATP synthase, which makes ATP. At the end of the chain, NADP+ gains electrons and a hydrogen ion to become NADPH. ATP carries usable energy, while NADPH carries high-energy electrons for the carbon-fixing reactions.
Sugar is built in the stroma during carbon-fixing reactions, not in the thylakoid membrane. The light-dependent reactions supply ATP and NADPH for that work.
In the thylakoid membrane, light splits water and drives the formation of ATP and NADPH for carbon-fixing reactions.
Original light-dependent-reactions lesson and assessment text authored for the Hoofer taxonomy.
The rewritten reading was written for this dataset. Other readings summarise Khan Academy articles on photosynthesis and chloroplasts. Videos are linked from Khan Academy. The light-reaction flashcards were written for the Hoofer taxonomy. License terms for the imported sources are not recorded.
2 · Watch
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