No, bark does not have stomata. Instead, bark contains different structures known as lenticels.
Understanding Gas Exchange in Plants
Plants require structures for gas exchange to facilitate processes like respiration and, in leaves, photosynthesis. These structures vary depending on the plant part.
Stomata vs. Lenticels: A Clear Distinction
According to botanical definitions, stomata are pores in the leaves, primarily responsible for gas exchange and transpiration (water vapor release). In contrast, lenticels are pores in the bark of trees/wood shrubs, serving a similar function for woody stems. This distinction highlights that while both are pores, their location and the specific plant tissues they are found in are different.
| Feature | Stomata | Lenticels |
|---|---|---|
| Location | Primarily on leaves (especially the underside) | On the bark of woody stems, branches, and roots |
| Structure | Tiny pores surrounded by specialized guard cells that regulate opening and closing | Raised, corky pores with loosely arranged cells that allow for gas exchange |
| Function | Regulate gas exchange (CO2 intake, O2 release) and transpiration | Facilitate gas exchange (O2 and CO2) in woody tissues where bark is impermeable to gases |
| Regulation | Open and close in response to environmental cues (light, water availability) | Typically remain open, with less active regulation compared to stomata |
| Appearance | Microscopic, not visible to the naked eye | Often visible as small dots, lines, or raised areas on bark |
What are Stomata?
Stomata (singular: stoma) are microscopic pores found predominantly on the epidermis of leaves, though they can also be present on some stems. Each stoma is flanked by two specialized guard cells that regulate its opening and closing. This control allows the plant to manage the uptake of carbon dioxide for photosynthesis, the release of oxygen, and the loss of water vapor through transpiration. Their ability to open and close is crucial for a plant's survival, balancing the need for gas exchange with the conservation of water.
What are Lenticels?
Lenticels are non-stomatal pores found in the periderm (outer bark) of woody stems, roots, and some fruits. Unlike stomata, lenticels do not have guard cells and therefore cannot actively open and close. They are characterized by a loosely packed mass of cells that facilitate gas exchange between the internal tissues of the woody stem and the atmosphere. This gas exchange is vital for the respiration of living cells within the bark and deeper woody tissues, especially as the bark thickens and becomes impermeable to gases.
Why the Difference?
The presence of different gas exchange structures in leaves and bark is an adaptation to their respective environments and functions:
- Leaves are typically thin, have a high surface area, and are the primary sites of photosynthesis. They require rapid and highly regulated gas exchange, which stomata provide. Their ability to close helps prevent excessive water loss, especially under hot or dry conditions.
- Bark is a protective outer layer of woody stems, often thick and waterproof. As leaves are shed in deciduous trees or as stems mature, the bark takes over the role of protecting the stem and enabling some level of gas exchange for the underlying living cells. Lenticels are well-suited for this, providing continuous aeration through a layer that would otherwise be impermeable.
In summary, while both stomata and lenticels facilitate gas exchange, they are distinct structures located in different parts of the plant and adapted to their specific roles and environments.
