Question

Light reaction of photosynthesis occurs in
A. Stroma
B. Thylakoids of granum
C. Matrix
D. Chloroplast membrane

Answer 1

During the first stage of photosynthesis, light energy is converted to chemical energy, which requires a sequence of chemical reactions known as light-dependent reactions.

Complete Answer:
Light-dependent reactions use light energy to create two molecules required for the next photosynthesis stage: the ATP molecule for energy storage and the NADPH reduced electron carrier. Light reactions occur in plants inside the thylakoid membranes of organelles known as chloroplasts.

The photosystems have molecules of pigment. Chlorophyll is one of the primary pigments in plants that is actively involved in the mechanism of light reactions, such as photosynthesis. Carotenoids are used in the accessory pigments. The energy from the sun is absorbed by the chlorophyll in the chloroplasts' thylakoid membrane. The energy which is produced by two-electron transport chains is then transferred to ATP and NADPH. Water is used during the process and oxygen is released.

The light reaction process is described below—
- Sunlight energy is consumed by the chlorophyll pigment in light reactions and is converted into chemical energy in the form of electron charge carrier molecules such as NADPH and ATP.
- In both Photosystems I and II, which are present within the chloroplasts' thylakoid membranes, light energy is used.
- The molecules of carbohydrates are derived from carbon dioxide by using the chemical energy collected during the reactions.
- The energy of light appears to break into water and then removes the electrons from photosystem II; then, in the form of energy, the electrons pass from PSII to b6f (cytochrome) to photosystem I (PSI) and decrease.
- In Photosystems I, the electrons are re-energized and the high-energy electrons reduce $NADP^+$ into NADPH.
- Cytochrome b6f uses electron energy from both Photosystems I and II in the cyclic photophosphorylation process to produce a number of ATPs and stop the production of NADPH, thereby preserving the correct amounts of ATP and NADPH.

The correct Answer is option (D) Chloroplast membrane.

Note: Light reactions harness light energy to drive electron transport and proton pumping, to transform light energy into the biologically useful ATP type, and to create a functional source of NADPH power reduction.