Question

Light reaction photosynthesis is also called
A. Calvin cycle
B. Hill reaction
C. TCA cycle
D. All of the above

Answer 1

Photosynthesis, the method by which green plants and certain other organisms transform light energy into energy. During photosynthesis in green plants, light energy is captured and accustomed to convert water, greenhouse gas, and minerals into oxygen and energy-rich organic compounds.

Complete Answer:
All living organisms need energy to perform various life processes and plants also. To perform various metabolic activities plants need food for energy. With the assistance of the method of photosynthesis plants prepare their own food. The process of using the energy in sunlight to make food (glucose) is known as photosynthesis. It occurs in the chloroplast, and organelle-specific to plant cells. The light reaction is also known as photolysis in which a water molecule breaks down to hydrogen, oxygen, and electrons.

On the surface of the leaves of the plants there are an oversized number of little pores referred to as stomata or stoma. For photosynthesis green plants take greenhouse gas from the air. The CO2 enters the leaves of the plant through the stomata present on their surface. Each stomatal pore is surrounded by a pair of guard cells. The opening and shutting of the pores of stomata is controlled by the guard cells only. When water flows into the guard cells, they swell, become curved and cause the pore to open. On the opposite hand, the guard cells lose water; they shrink, become straight and shut the stomatal pore. an oversized amount of water is additionally lost from the cells of the plant leaves through open stomatal pores. So, when the plant doesn't need dioxide and desires to conserve water, the stomatal pores are closed.

During photosynthesis, the oxygen gas produced goes out through the leaves of the stomatal pores. In most broad-leaved plants, the stomata occur only within the lower surface of the leaf but in narrow-leaved plants, the stomata are equally distributed on both the perimeters of the leaf. In aquatic plants or plants that board water use greenhouse gas dissolved in water for affecting photosynthesis. The stomatal pores allow movement of gases in and out of plant cells. The gaseous exchange in plants takes place through the stomata in leaves and other green parts. Light energy absorbed by pigments in leaves gets converted to chemical energy during the first stage of photosynthesis that involves a series of chemical reactions known as the light-dependent reactions.

Steps:
- Energy from the sunlight is absorbed by the pigment chlorophyll and is converted into chemical energy in the form of electron charge carrier molecules such as NADPH and ATP.
- Light energy is utilized in both the Photosystems I and II, present inside thylakoid membranes of the chloroplasts.
- Carbohydrate molecules are obtained from carbon dioxide through the use of chemical energy.
- The light energy splits into the water and extracts electrons from PS II; then the electrons move from PSII to cytochrome and PSI.
- The electrons are re-energized in the Photosystems I and the electrons of high energy reduce $NADP^+$ into NADPH.
- The transfers of electrons from PSII to PSI, and from PSI to NADPH, are energy-releasing steps since electrons in P680 and P700 are boosted to very high energy levels by the absorption of energy from light.
- In cyclic photophosphorylation, electrons follow a circular path, and only ATP is produced.

Therefore, the correct option is B, Hill reaction.

Note: The ATP and NADPH from the light-dependent reactions are used to make sugars in the Calvin cycle. It takes place in the stroma. The Calvin cycle adds carbon to a simple five-carbon molecule known as RuBP. The end product of Calvin cycle is glucose. 9 ATP are converted to 9 ADP. 6 NADPH are converted to 6 $NADP^+$.