For (a): Water is absorbed by the roots and transported to all parts of the plant (e.g. leaves and flowers) through the stem. So we need to draw an arrow from roots to stem, then one arrow from stem to leaves and one arrow from stem to flowers.

For (b)(i): In the presence of sunlight and chlorophyll/chloroplasts, carbon dioxide and water are converted to oxygen and food/sugar through photosynthesis.

For (b)(ii): The insect eats into the tree trunk to obtain the food found in the food-carrying tube of the stem. As a result, roots of the tree are not able to receive sufficient amount of food needed for growth.

For (c): The tiny openings are called stomata. They have 2 main functions:
(1) Allow gaseous exchange to take place.
(2) Allow excess water vapour to escape.

During the day, the temperature of surroundings is high, which may cause too much water vapour to escape. Hence, stomata are closed to prevent excessive water loss.

The temperature of surroundings is lower at night, so the stomata will open to replenish the carbon dioxide used for photosynthesis during the day.