Final answer:
The biome with the most photosynthesis is the Rainforest due to its optimal warm and wet climate, leading to high rates of photosynthesis, efficient enzyme activity, and robust biomass production.
Step-by-step explanation:
The biome in which the most photosynthesis occurs is B) Rainforest. This is due to the warm and wet climate of rainforests that allows photosynthesis to proceed at a high rate. Enzymes in the plants of this biome can work most efficiently, and the plant stomata can remain open for more extended periods without risking excessive transpiration. This results in a maximal amount of carbon dioxide (CO₂) intake, leading to high biomass production and thereby maximum net primary production. Biomes like deserts and tundra have harsher conditions, including extreme temperatures and water scarcity, leading to lower photosynthetic rates and hence lower biomass.