Comprehensive Comparison Table
| Feature | C3 Plants | C4 Plants | CAM Plants |
|---|---|---|---|
| First acceptor | RuBP (5C) | PEP (3C) | PEP (3C) at night |
| First stable product | 3-PGA (3C) | OAA (4C) | OAA → Malic acid (4C) |
| fixing enzyme | RuBisCO | PEP carboxylase (mesophyll) + RuBisCO (bundle sheath) | PEP carboxylase (night) + RuBisCO (day) |
| Kranz anatomy | Absent | Present | Absent |
| Photorespiration | Present (high at >25°C) | Absent | Absent/minimal |
| Separation type | None | Spatial (two cell types) | Temporal (night vs. day) |
| Bundle sheath cells | Not prominent | Large, prominent (Calvin cycle) | Not prominent |
| Stomata pattern | Open day, closed night | Open day, closed night | Closed day, open night |
| Optimum temperature | 20–25°C | 30–40°C | Variable |
| Water use efficiency | Low | High | Very high |
| Light saturation point | ~Half sunlight | Full sunlight | Variable |
| ATP cost per | ~3 ATP | ~5 ATP (extra for PEP regen) | ~6.5 ATP |
| Examples | Wheat, rice, potato, soybean, sunflower | Maize, sugarcane, sorghum, Amaranthus | Cacti, Bryophyllum, Opuntia, pineapple, Agave |
| Dominant habitat | Temperate, cool | Tropical, high-light | Arid, desert |
Key Memory Hook
- C3 = "Three-carbon first product" = Normal, single-cell, RuBisCO only
- C4 = "Four-carbon first product" = Spatial split: PEP (mesophyll) → Malate → Calvin (bundle sheath)
- CAM = "Nocturnal collector" = PEP at night + Calvin during day = same cell, different times