The correct answer is option B. Water exits through a stoma by transpiration and helps pull up the water in the stem.
In the model of a plant's shoot system and root system, the top section typically represents the shoot system, including the leaves and stems. To determine what is happening in the top section, let's analyze the options:
A. Water made by photosynthesis is stored in a vacuole for later use in the leaf.
- This statement is incorrect. Water is not made by photosynthesis; rather, photosynthesis produces glucose using water, carbon dioxide, and sunlight.
B. Water exits through a stoma by transpiration and helps pull up the water in the stem.
- This is a correct description of what happens in the top section. Transpiration is the process by which water vapor exits through stomata (tiny pores on leaves), creating a negative pressure that aids in pulling water up from the roots through the stem.
C. Water flows in through a stoma to xylem in the leaf, where it is used for photosynthesis.
- This statement is not accurate. Water is primarily absorbed by the roots and transported through the xylem to the leaves, where it is used in various processes, including photosynthesis.
D. Water flows between the xylem and ground tissue and in and out of a stoma.
- This option is not an accurate representation. Water primarily moves through the xylem, and stomata are the main sites for transpiration, not for direct water intake.
**Correct Option:**
B. Water exits through a stoma by transpiration and helps pull up the water in the stem.