In the context of C3, C4, and CAM photosynthetic pathways, which adaptation would best help a plant survive in a hot desert environment by reducing water loss?

• A. Using CAM photosynthesis, opening stomata mainly at night to take in $C_{2}O$ and storing it as organic acids for use during the day
• B. Relying only on the C3 pathway with no additional mechanisms to reduce photorespiration or water loss
• C. Increasing stomatal density and opening stomata more frequently during daylight to speed gas exchange
• D. Keeping stomata open during the hottest part of the day to maximize $C_{2}O$ uptake

Answer: (A)

Verified step by step guidance

1. Understand the challenge plants face in hot desert environments: high temperatures and low water availability lead to excessive water loss through stomata during the day.
2. Recall the characteristics of the three photosynthetic pathways: C3, C4, and CAM. C3 is the most common but less efficient under heat and drought; C4 minimizes photorespiration and conserves water better; CAM plants open stomata at night to reduce water loss.
3. Analyze how CAM photosynthesis works: stomata open at night when temperatures are cooler and humidity is higher, allowing CO\_2 uptake with minimal water loss. The CO\_2 is stored as organic acids and used during the day for photosynthesis while stomata remain closed.
4. Compare this adaptation to the other options: opening stomata during the hottest part of the day or increasing stomatal density would increase water loss, and relying solely on C3 lacks mechanisms to reduce water loss or photorespiration.
5. Conclude that the best adaptation for survival in hot desert environments is the CAM pathway, which reduces water loss by shifting CO\_2 uptake to nighttime and storing it for daytime use.