Final answer:
The most important factors in determining major terrestrial biomes are temperature and water, as they directly affect plant growth and the structure of plant and animal communities within biomes.
Step-by-step explanation:
The two factors that are most important in determining major terrestrial biomes are temperature and water, specifically precipitation levels. These abiotic factors are crucial because they influence the availability of moisture and the warmth necessary for plant growth, which in turn supports the entire food web within a biome. In terrestrial biomes, these two factors shape the composition of animal and plant communities, and lead to the development of the various biomes found around the world, such as tropical rainforests, savannas, and tundras. In contrast, while aquatic biomes also rely on abiotic factors, they are more influenced by light, temperature, water movement, and dissolved solids such as salinity.