Question

Stomata are the tiny pores that allow gas exchange and water loss. Analyze the diagram below to answer the questions about how they work
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1. Which condition causes the stomata to OPEN?
a) When guard cells lose water and become flaccid
b) When guard cells absorb water and become turgid
c) When the plant is in total darkness
d) When the humidity is extremely low
2. What is the primary function of the guard cells?
a) To absorb sunlight for photosynthesis
b) To transport sugar down to the roots
c) To control the opening and closing of the stoma
d) To protect the leaf from insects

Answer 1

1. b) When guard cells absorb water and become turgid.
- Explanation: Guard cells take up K+ (and other solutes), water follows by osmosis, the cells swell and bow apart, opening the pore. Light usually promotes this; darkness and water stress cause closing.

2. c) To control the opening and closing of the stoma.
- Explanation: Guard cells regulate the stoma size to balance CO2 uptake for photosynthesis with water loss (transpiration). They do not perform photosynthesis for the leaf, transport sugars to roots, or primarily act as insect protection.