Biology · Both
Photosynthesis & Respiration
Word and symbol equations, limiting factors for photosynthesis, aerobic and anaerobic respiration.
Photosynthesis makes food in plants; respiration releases energy in all living cells. Know the equations and the factors that affect the rate of photosynthesis.
Photosynthesis
**Word equation:**
carbon dioxide + water → glucose + oxygen
(in the presence of light and chlorophyll)
**Symbol equation:**
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Happens in chloroplasts.
Glucose is used for energy, stored as starch, or used to make cellulose, proteins and lipids.
Worked example
State the two products of photosynthesis.
Solution
**Glucose** and **oxygen**.
Limiting factors
Rate of photosynthesis can be limited by:
• Light intensity
• Carbon dioxide concentration
• Temperature (enzymes denature if too hot)
A limiting factor is the factor in shortest supply that holds back the rate.
Respiration
**Aerobic respiration** (with oxygen):
glucose + oxygen → carbon dioxide + water (+ energy)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy)
**Anaerobic respiration in animals** (without oxygen):
glucose → lactic acid (+ less energy)
**Anaerobic in yeast (fermentation):**
glucose → ethanol + carbon dioxide (+ energy)
Aerobic releases much more energy than anaerobic.
Practice questions
Try these without looking at the answers first.
Q1.Where in the cell does photosynthesis happen?
Show answer
Chloroplasts
Q2.Name three limiting factors for photosynthesis.
Show answer
Light intensity, CO₂ concentration, temperature
Q3.What is the product of anaerobic respiration in muscle cells?
Show answer
Lactic acid