Question

How does photosynthesis store energy?

Answer 1

Hint: Green plants and some organisms can prepare their food in the presence of light, this process is called photosynthesis. The food (glucose) is produced from water and carbon dioxide in the presence of light. The pigment chlorophyll plays a significant role in this process. This pigment is responsible for the green colour of the plants.

Complete answer:
 -A cell organelle i.e. chloroplast possess the pigment chlorophyll. It is this organelle that enables photosynthesis.
-A chloroplast is a membrane-bound organelle filled with stroma (a jelly-like material). Stacks of thylakoid membrane called grana are present in the stroma. The grana are connected and the inner membrane of the organelle by stroma lamellae. The chlorophyll pigments are present in the thylakoid membrane.
-The thylakoid membrane contained the photosynthetic light-capturing system (photosystems), ATP synthase, and the electron transport chain. The different chlorophyll pigments will absorb different wavelengths of light and convert it to chemical energy. This occurs in the photosystems (multiprotein complex) present in the thylakoid membrane. In $C3$ plants, photosynthesis has a light-dependent phase and a light-independent phase. The light-dependent phase takes place in the chloroplast thylakoid and the light-independent phase takes place in the chloroplast stroma.
-Water (raw material for the process) is split to generate electrons. The chloroplast electron transport chain (proteins that can transport electrons) carries the electron from photosystem two to photosystem one. The electron transport chain also carries protons formed due to the splitting of water to the lumen of the thylakoid. This creates an electrochemical gradient, low pH in thylakoid lumen, and high pH in the stroma. ATP synthase, an enzyme, utilizes this gradient to make ATP. ATP as we know is an energy-rich molecule.
-Along with ATP, NADPH is also produced. These two molecules are utilized in the Calvin cycle. Carbon dioxide (raw material) is used to make sugar (carbohydrate). This reaction occurs in the stroma. The sugar produced at the end of photosynthesis can be stored as starch granules in the stroma.

Note: In $C3$ plants, the sugar synthesized in the chloroplast is often utilized during respiration. It is also transported to the phloem. The phloem transports the sugar molecules to other parts of the plant. However, the entire starch granule in the chloroplast is not consumed.
-Organisms such as red algae do not store starch in their chloroplast. Instead, starch is stored in the cytoplasm.