Transpiration Is A Necessary Trade-Off for Gas Exchange in Leaves
Definition
Transpiration
Transpiration is the loss of water vapor from the aerial parts of a plant, primarily through tiny pores in the leaves called stomata.
- Transpiration is a consequence of gas exchange, driven by the need for moist surfaces for diffusion.
- Environmental factors like temperature, humidity, wind, and light intensity greatly influence transpiration rates.
- Stomatal regulation by guard cells allows plants to adapt to changing conditions, balancing water conservation with photosynthetic needs.
How Transpiration Works
- It happens as a side effect of gas exchange, plants open stomata to take in carbon dioxide for photosynthesis, and water vapor slips out.
- Essential functions of transpiration:
- Cools the plant (like sweating for humans).
- Pulls water up from the roots to the leaves via the xylem.
- Maintains cell turgor, keeping plants firm and upright.
Transpiration is a passive process driven by environmental factors, but plants actively regulate it by controlling the opening and closing of their stomata.
How Transpiration Happens
- Inside the leaf: Spongy mesophyll cells have moist walls where gases dissolve for exchange.
- Water evaporation: Some of this water evaporates into the air spaces inside the leaf.
- Water vapor escape: The vapor diffuses out of the leaf through open stomata.
Factors Affecting Transpiration Rates
Temperature
- Hotter = Faster transpiration.
- Warm air increases evaporation and holds more water vapor, speeding up water loss.
On a hot summer day, a plant exposed to direct sunlight loses water more rapidly due to increased evaporation and diffusion rates.
Humidity
- Dry air = Faster transpiration.
- Humid air slows it down since the difference in water vapor concentration (inside vs. outside the leaf) isn’t as steep.
