Download Stomata and Gas Exchange

Name _____________________________________
Period __________
Stomata and Gas Exchange
Stomata are features that are located on the underside of the leaves of plants that live on
land. These structures, which are the 'pores' of the plant's skin, provide openings for the
exchange of water, oxygen, and carbon dioxide. Stomata are opened and closed with structures
called guard cells. These cells swell by the process of osmosis, water moving from an area of
high concentration to an area of low concentration. When there is an excess of water in the
lower epidermis water will flood into the guard cell causing it to buckle. This swelling causes the
stomata to open, allowing water to evaporate. When the amount of water within the lower
epidermis decreases, the guard cells shrink. The stomata close, and water is conserved.
In addition to the correct level of water, a plant requires carbon dioxide for the process of
photosynthesis. The plant must also be able to release the oxygen, which is an end product of
the photosynthesis process. Stomata offer the plant both a means of entry and exit as gas
transfer takes place. When the stomata are open, the plant can take in carbon dioxide from the
air for photosynthesis and release oxygen back into the environment. While doing so, the plant
also loses an enormous amount of water by evaporation. This process is called transpiration. To
make up for this water loss, additional water is drawn in from the soil by the roots and passed
upward through the plant by the xylem.
Template for Stomatal Unit Drawing
Add the following labels to the diagrams below: guard cell, chloroplast,
stoma, lower epidermis
Name _____________________________________
Period __________
1. Define osmosis [think about the high to low dance] –
2. When do guard cells swell? When do they deflate?
4. What gases pass through stoma when they are open?
5. When stomata are open, what substance is lost in large amounts due to
transpiration?
6. How does a plant make up for large amounts of water lost during transpiration?
What property of water allows this to occur?
7. Thinking required! When would guard cells be open during the day or at
night? Why?