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Photosynthesis is the process plants use to capture light energy and store it as chemical energy in glucose. It is one of the most important reactions on Earth because it provides food for plants and releases oxygen into the atmosphere. This process supports food webs, helps regulate carbon dioxide levels, and makes life possible for many organisms. Understanding photosynthesis connects biology, chemistry, and environmental science.
In photosynthesis, plants take in carbon dioxide from the air and water from the soil, then use light absorbed by chlorophyll to drive chemical reactions in chloroplasts. The light-dependent reactions capture energy and help split water, releasing oxygen. The Calvin cycle uses that stored energy to build glucose from carbon dioxide. The glucose can be used immediately for energy or stored for later growth and repair.
Key Facts
- Overall equation: 6CO2 + 6H2O + light energy -> C6H12O6 + 6O2
- Photosynthesis occurs mainly in chloroplasts, especially in leaf cells.
- Chlorophyll absorbs mostly red and blue light and reflects green light.
- Carbon dioxide enters the leaf through stomata, while oxygen exits through stomata.
- Water is transported from roots to leaves through xylem tissue.
- Glucose made in photosynthesis can be used in respiration: C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy
Vocabulary
- Photosynthesis
- The process by which plants use light energy to make glucose from carbon dioxide and water.
- Chlorophyll
- A green pigment in chloroplasts that absorbs light energy for photosynthesis.
- Chloroplast
- A cell organelle in plants where photosynthesis takes place.
- Stomata
- Tiny openings in leaves that allow carbon dioxide to enter and oxygen and water vapor to leave.
- Glucose
- A simple sugar produced by photosynthesis that stores chemical energy.
Common Mistakes to Avoid
- Saying plants only take in carbon dioxide and give off oxygen all the time, which is wrong because plants also carry out respiration and use oxygen continuously.
- Thinking sunlight becomes matter in the plant, which is wrong because light provides energy while the atoms in glucose come mainly from carbon dioxide and water.
- Forgetting that water is a reactant in photosynthesis, which is wrong because the reaction needs both CO2 and H2O to produce glucose and oxygen.
- Assuming oxygen released in photosynthesis comes from carbon dioxide, which is wrong because the released O2 comes from the splitting of water molecules.
Practice Questions
- 1 Write the balanced photosynthesis equation and identify which substances are reactants and which are products.
- 2 If a plant uses 12 molecules of CO2 in photosynthesis, how many molecules of glucose and O2 can it produce according to the balanced equation?
- 3 A plant is placed in bright light but sealed in a container with no carbon dioxide available. Explain why photosynthesis will not continue for long even though light is present.