What is Photosynthesis?
Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose, releasing oxygen as a byproduct. It's the foundation of nearly all life on Earth's food chains.
Photosynthesis converts carbon dioxide and water into glucose and oxygen using light energy captured by chlorophyll, following the equation 6CO2 + 6H2O + light → C6H12O6 + 6O2.
- 1↓Light absorptionChlorophyll in the thylakoid membranes absorbs sunlight.
- 2↓Light-dependent reactionsWater is split, releasing O2 and producing ATP and NADPH.
- 3↓Calvin cycle (light-independent)ATP and NADPH power carbon fixation, converting CO2 into G3P in the stroma.
- 4Glucose synthesisG3P molecules combine to form glucose (C6H12O6) for energy and growth.
Step-by-step worked examples
A plant is given radioactively labeled CO2 (containing carbon-14). Where does the labeled carbon end up first?
CO2 enters the Calvin cycle in the stroma of the chloroplast Carbon fixation attaches CO2 to a 5-carbon molecule (RuBP) The labeled carbon appears first in G3P, and later in glucose
A plant is placed in complete darkness for 24 hours. What happens to its rate of photosynthesis?
Light-dependent reactions require light to split water and generate ATP/NADPH Without light, no ATP or NADPH is produced The Calvin cycle stalls without these inputs, so photosynthesis rate drops to zero
If a plant produces 6 molecules of O2, how many molecules of CO2 and H2O did it use, and how much glucose did it make (per the balanced equation)?
The balanced equation is 6CO2 + 6H2O → C6H12O6 + 6O2 6 O2 produced matches the equation's coefficient exactly So it used 6 CO2 and 6 H2O molecules and made 1 glucose molecule (C6H12O6)
Flashcards
Quick quiz
Q1.What are the reactants of photosynthesis?
Q2.Where does the Calvin cycle take place?
Q3.What gas is released as a byproduct of photosynthesis?
Q4.What molecule stores the chemical energy produced by photosynthesis?
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Common mistakes
Thinking photosynthesis only happens in leaves. — Correct: It occurs in any chlorophyll-containing cell — stems, and even some fruits can photosynthesize.
Believing plants don't respire. — Correct: Plants both photosynthesize and respire; respiration happens all the time, photosynthesis only in light.
Mixing up the light and Calvin cycle locations. — Correct: Light reactions happen in the thylakoid membrane; the Calvin cycle happens in the stroma.
Thinking CO2 is released during photosynthesis. — Correct: CO2 is absorbed (a reactant); oxygen is released as the byproduct.
FAQ
What is photosynthesis?
Photosynthesis is the process plants use to convert light energy, CO2, and water into glucose and oxygen.
What is the formula for photosynthesis?
6CO2 + 6H2O + light energy → C6H12O6 + 6O2.
What are examples of photosynthesis in action?
A green leaf absorbing sunlight, aquatic algae releasing oxygen bubbles, and cacti performing a modified version (CAM) at night are all examples.
How is the rate of photosynthesis affected by light intensity?
Higher light intensity increases the rate up to a saturation point, after which other factors like CO2 or temperature become limiting.