Experiments were carried out on plants living in different environments to measure the size of the leaf stomata at different times of the day - HSC - SSCE Biology - Question 11 - 2009 - Paper 1

In a dry environment, plants typically exhibit adaptations to minimize water loss. This often results in smaller and less variable stomata size throughout the day compared to plants in a more humid environment. Graph D is the most appropriate choice as it shows a more consistent stomata size with less fluctuation between light and dark conditions, indicating the plant's adaptation to conserve water in a dry environment.