Photosynthesis
Definition
Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy (usually from the sun) into chemical energy stored in glucose. This process uses carbon dioxide and water as raw materials and releases oxygen as a byproduct. It occurs in chloroplasts and involves light-dependent and light-independent reactions.
Key Points for NEET
- 1Overall equation: 6CO₂ + 6H₂O + Light → C₆H₁₂O₆ + 6O₂
- 2Occurs in chloroplasts containing chlorophyll
- 3Light reactions occur in thylakoids
- 4Calvin cycle (dark reactions) occurs in stroma
- 5Produces ATP and NADPH in light reactions
Example
A leaf converting sunlight into sugars that the plant uses for energy
Asked in NEET
Common Mistakes to Avoid
- ✗Calling dark reactions "light-independent" does NOT mean they occur at night — they need ATP/NADPH from light reactions
- ✗Confusing C3 (Calvin cycle in all plants) with C4 pathway (only in C4 plants like maize, sugarcane)
- ✗Thinking oxygen comes from CO₂ — it comes from H₂O (proved by Hill reaction with heavy oxygen)
Quick Revision Notes
- ⚡Light reactions: H₂O → O₂ + ATP + NADPH (in thylakoids); Calvin cycle: CO₂ → G3P → glucose (in stroma)
- ⚡PS II (P680) splits water; PS I (P700) reduces NADP⁺ — remember "II before I" in Z-scheme
- ⚡C4 plants fix CO₂ twice: first into OAA (mesophyll), then into Calvin cycle (bundle sheath)
- ⚡Factors affecting rate: light intensity, CO₂ concentration, temperature (Blackman law of limiting factors)
Related Terms
Want to Master Plant Biology?
Join Cerebrum Biology Academy for comprehensive NEET preparation with expert faculty.
More Plant Biology Definitions
Chlorophyll
Chlorophyll is the green pigment found in chloroplasts that is essential for photosynthesis. It absorbs light energy, particularly from red and blue wavelengths, and reflects green light (making plants appear green). Chlorophyll a is the primary pigment, while chlorophyll b is an accessory pigment.
Xylem
Xylem is the vascular tissue in plants that conducts water and dissolved minerals from roots to stems and leaves. It consists of tracheids, vessel elements, xylem fibers, and xylem parenchyma. The movement of water through xylem is driven by transpiration pull and root pressure.
Phloem
Phloem is the vascular tissue that transports organic nutrients (mainly sucrose) from leaves to other parts of the plant. It consists of sieve tubes, companion cells, phloem fibers, and phloem parenchyma. Unlike xylem, phloem can transport in both directions (bidirectional).