2. Under the same concentration gradient and environmental conditions, glucose diffuses faster than ammonia because glucose is a larger and more polar molecule. (1pt) 3. A marine environment with a C:N ratio of 20 suggests the area is limited by N source, and the imbalance can be restored by promoting nitrogen fixation. (1pt) 4. Phototrophic sulfide oxidizers like purple sulfur bacteria are often found in lake surface which provide light irradiation and oxygen supply. (1pt)