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 significantly affects the rate of photosynthesis. As temperature increases, the rate tends to rise due to higher enzyme activity, which facilitates biochemical reactions involved in photosynthesis. However, this effect only continues up to an optimum temperature. Beyond this optimum range, enzymes may become denatured, which decreases the rate of photosynthesis.

Transpiration involves the movement of water from the roots through the plant, primarily taking place through the xylem. Water evaporates from the leaves, creating a negative pressure that draws more water upward from the roots. This process is often described by the cohesion-tension theory, where water molecules stick together and move through the plant in one direction.

Translocation, on the other hand, refers to the movement of sugars produced in the leaves through the phloem. Sugars are transported as sucrose to areas of the plant where they are needed, and this movement is bidirectional, allowing for nutrients to sink to plant parts that require energy, such as the roots.

The results indicate that the rate of photosynthesis is inversely proportional to light intensity, which implies that as the distance from the light source increases, the intensity of light decreases, leading to a reduction in the rate of photosynthesis. Therefore, the correct answer is D.