--- title: "Light-Dependent Reactions in the Thylakoid Membrane" description: "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 reduci" canonical: https://lightmysky.com/learn/science/light-dependent-reactions-in-the-thylakoid-membrane-mt_3Ooq3BfmpX source: https://lightmysky.com/learn/science/light-dependent-reactions-in-the-thylakoid-membrane-mt_3Ooq3BfmpX.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # 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. Subject: Science · Area: Organisms & Life Processes · Ages 16 to 17 Page: https://lightmysky.com/learn/science/light-dependent-reactions-in-the-thylakoid-membrane-mt_3Ooq3BfmpX ## Ready when they can - 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. ## Lesson: Catching light in the thylakoid 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. **Example.** 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. *(drawing: The sequence shows what the light-dependent reactions supply to the next stage.)* **Tip.** 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. **Recap.** 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.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Photosynthesis and Limiting Factors](https://lightmysky.com/learn/science/photosynthesis-and-limiting-factors-mt_PDn831oIih) ## Opens up - [The Calvin Cycle and Carbon Fixation](https://lightmysky.com/learn/science/the-calvin-cycle-and-carbon-fixation-mt_zGOCx9mNrx)