Photosynthesis:
Photosynthesis is the process by which plants, algae, and some bacteria convert sunlight, carbon dioxide, and water into glucose and oxygen. It is a vital process that sustains life on Earth by producing oxygen and food.

Process:
Photosynthesis occurs in the chloroplasts, which are specialized structures found in the cells of plants. The process can be divided into two stages: the light-dependent reactions and the light-independent reactions.

Light-dependent reactions:
1. Light energy is absorbed by the chlorophyll pigment located in the chloroplasts.
2. This energy is used to split water molecules into hydrogen and oxygen. Oxygen is released as a byproduct.
3. The energy from the absorbed light is also used to convert ADP (adenosine diphosphate) into ATP (adenosine triphosphate), which is the energy currency of cells.
4. The hydrogen atoms produced from the water molecules combine with a molecule called NADP+ (nicotinamide adenine dinucleotide phosphate) to form NADPH.

Light-independent reactions:
1. The ATP and NADPH produced in the light-dependent reactions are used to convert carbon dioxide into glucose.
2. This process is known as the Calvin cycle or the dark reaction.
3. The carbon dioxide molecules are fixed and combined with hydrogen to form glucose.
4. Glucose is then used by the plant for energy or stored for later use.

Importance:
Photosynthesis is crucial for the survival of plants and other organisms that depend on them. Here are some reasons why it is important:

1. Oxygen production: Photosynthesis releases oxygen into the atmosphere, which is essential for the respiration of animals and other organisms.

2. Food production: Plants produce glucose through photosynthesis, which serves as a source of energy for plants themselves and for other organisms that consume plants.

3. Carbon dioxide absorption: Photosynthesis helps remove carbon dioxide from the atmosphere, playing a vital role in regulating the Earth's climate.

4. Energy source: Fossil fuels, such as coal, oil, and natural gas, are formed from ancient plants that underwent photosynthesis. These fuels provide energy for various human activities.

In conclusion, photosynthesis is the process by which plants convert sunlight, carbon dioxide, and water into glucose and oxygen. It is a fundamental process that sustains life on Earth and plays a crucial role in the ecosystem.

Correct answer is b