01Variation in energy pathways
Natural selection acts on variation in how organisms capture and use energy. Different molecules and pathways give advantages in different environments.
Plants have multiple pigments (chlorophyll a, chlorophyll b, carotenoids) absorbing different wavelengths, widening the usable light spectrum.
02Examples
C₄ and CAM plants reduce photorespiration in hot, dry climates: C₄ plants (corn) separate carbon fixation spatially; CAM plants (cacti) open stomata at night.
Some organisms use anaerobic pathways where oxygen is scarce. Endotherms burn more energy to hold body temperature but stay active in cold.
03Notebook box
Fitness = reproductive success. Molecular variation (pigments, enzymes, pathways) → different survival in different environments.
Worked example: Why might a population with two versions of an enzyme, one working best at 20 °C and one at 35 °C, survive a climate shift better? → Variation lets some individuals function in the new conditions.