5 (a) Figure 9 shows the effect of light intensity and temperature on the rate of photosynthesis - Edexcel - GCSE Biology Combined Science - Question 5 - 2018 - Paper 1

Temperature has a significant impact on the rate of photosynthesis. As temperature increases, the rate also increases due to higher kinetic energy, which allows enzymes to work more efficiently in catalyzing the reactions involved in photosynthesis. However, if the temperature goes beyond the optimum level, enzyme denaturation occurs, leading to a decrease in the photosynthesis rate.

Transpiration is the process where water is absorbed by the roots from the soil and is then transported through the plant, primarily through the xylem. This movement is driven by evaporation of water from the leaves through the stomata, creating a negative pressure that pulls water up from the roots in a one-directional flow facilitated by capillary action and the cohesion-tension theory.

Translocation, on the other hand, involves the movement of sugars produced during photosynthesis from the leaves to other parts of the plant, mainly through the phloem. This process is bidirectional; sugars can be transported to the roots and sink areas where they are utilized or stored as energy sources.

The result indicates that the rate of photosynthesis is inversely proportional to the distance from a light source, hence the correct answer is D.