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In photosynthesis, the light-dependent reactions take place on the thylakoid membranes. The inside of the thylakoid membrane is called the lumen, and outside the thylakoid membrane is the stroma, where the light-independent reactions take place.The thylakoid membrane contains some integral membrane protein complexes that catalyze the light reactions.There are four major protein complexes in the thylakoid membrane: Photosystem II (PSII), Cytochrome b6f complex, Photosystem I (PSI), and ATP synthase.he thylakoid membrane contains some integral membrane protein complexes that catalyze the light reactions. There are four major protein complexes in the thylakoid membrane: Photosystem II (PSII), Cytochrome b6f complex, Photosystem I (PSI), and ATP synthase.
Phototropism (growing towards light) occurs because the tips of growing plant shoots contain a pigment that's sensitive to light, especially blue light. When light shines on the shoot, it gets absorbed by the pigment (called phototropin), and that triggers the release of the plant hormone auxin, which makes cells grow. The direction of the light determines where the auxin acts. If light is coming from the right, auxin gets sent down the left (shady) side of the shoot. That makes the cells on the shady side grow longer, putting a kink in the shoot so it points to the light.