How Does the Stomata Function in Photosynthesis and Transpiration?
Stomate (plural: stomata) refers to any of the microscopic openings or pores found in the epidermis of leaves and young stems in plants. These tiny pores are essential for the exchange of gases between the plant’s internal tissues and the outside air. The structure and function of stomata make them one of the most important features for plant survival and growth.
Each stomate is surrounded by specialized cells known as guard cells. These guard cells control the opening and closing of the pore, allowing the plant to balance its needs for gas exchange with the need to conserve water. Stomata are usually more abundant on the lower surface of leaves, but they can also be present on young stems and other parts of the plant.
The movement of gases through stomata is vital for processes such as respiration and photosynthesis. Stomata help facilitate the intake of carbon dioxide (CO2) and the release of oxygen (O2). They also allow water vapor to exit the plant during transpiration, which assists in cooling and maintains the plant’s water balance.
Structure of a Stomate
A typical stomate consists of two main parts:
- Stomatal Pore: The microscopic opening or pore in the epidermis that permits gas exchange.
- Guard Cells: Specialized curved cells that flank the pore on either side. These cells swell or shrink to open or close the pore, depending on the plant’s needs and environmental conditions.
The guard cells’ ability to change shape is what regulates the movement of gases and water vapor through each stomate. In many plants, the structure and behavior of these cells directly affect how effectively the plant can adapt to changes in humidity, light, and temperature.
Function of Stomata
Stomata are crucial because they:
- Allow the plant to take in carbon dioxide necessary for photosynthesis.
- Enable the release of oxygen generated during photosynthesis.
- Facilitate water vapor loss (transpiration), which helps move water and minerals up from the roots and assists in cooling the leaf surface.
Stomata and Gas Exchange
The stomate acts as an adjustable gateway, opening wider to permit more gas flow or closing tightly to reduce water loss. This adjustment is vital when there is excess heat or drought, as closing the pores helps the plant conserve water, though it also reduces gas exchange.
Key Terms and Scientific Significance
| Term | Definition | Significance |
|---|---|---|
| Stomate (Stoma) | Microscopic pore in the plant epidermis | Enables exchange of gases (CO2, O2, H2O) between the inner tissues and the external air |
| Guard Cells | Specialized curved cells flanking each stomate | Regulate the opening and closing of the stomatal pore |
Stepwise Summary: How Stomata Function
- Air containing carbon dioxide enters the leaf through the stomatal pore.
- Oxygen, a byproduct of photosynthesis, exits the leaf through the same pore.
- Water vapor is lost to the atmosphere during transpiration, especially when stomata are open.
- Guard cells close the pore during water stress, reducing water vapor loss.
Example for Better Understanding
On a dry, hot day, you might notice that some plants look wilted. This is often because their stomata have mostly closed to prevent further water loss. At the same time, their ability to perform photosynthesis is reduced due to decreased gas exchange.
Practice Questions
- What is the main function of a stomate in the leaf epidermis?
- How do guard cells control the stomatal pore?
- Explain why stomata are mostly found in the epidermis of leaves and young stems.
Explore Related Biology Topics on Vedantu
- Preparing Temporary Mount of Leaf Peel to Show Stomata
- Difference Between Stomata and Lenticels
- Leaf Morphology
- Plant Tissues
- Plant Water Relations
- Transpiration
- Photosynthesis Process
Understanding the role and structure of stomata is foundational in plant biology. This concept helps explain how plants interact with their environment, make their own food, and maintain hydration. Strengthening your grasp of these ideas lays the groundwork for many other biology topics and practical experiments.
FAQs on Stomata in Plants: Structure, Functions, and Importance
1. What is stomata and its function?
Stomata are tiny pores found mainly on the surface of plant leaves and young stems.
Functions of stomata:
- Facilitate gas exchange (carbon dioxide intake for photosynthesis and oxygen release)
- Allow transpiration, helping regulate water loss and temperature
- Support respiration by enabling oxygen entry and carbon dioxide exit
- Play an essential role in photosynthesis and maintaining water balance in plants.
2. What is the difference between stoma and stomata?
Stoma refers to a single microscopic pore, while stomata is the plural form, meaning all such pores present on the plant surface.
Example: One stoma may close at night; thousands of stomata can be found on the underside of a leaf.
3. Where is stomata located?
Stomata are located mainly on the epidermis (surface layer) of leaves, especially the lower side, but can also be found on stems and other soft plant organs.
Key locations:
- Lower epidermis of dicot leaves (most abundant)
- Both sides of monocot leaves
- Young stems and herbaceous parts
4. What controls the opening and closing of stomata?
Guard cells control the opening and closing of stomata.
They adjust their shape due to water pressure (turgor) changes, which are influenced by:
- Light (opens in daylight, closes at night)
- Water availability (closes during water scarcity)
- Internal carbon dioxide concentration
This process helps plants balance gas exchange and water loss.
5. Do humans have stomata?
No, humans do not have stomata. Stomata are specialized structures found only in plants, not in animal or human bodies. Humans exchange gases through their respiratory system, not through microscopic pores like stomata.
6. What do the stomata do in photosynthesis?
Stomata allow carbon dioxide from the atmosphere to enter plant leaves, which is essential for photosynthesis.
- Permit CO2 intake for glucose synthesis
- Enable release of oxygen as a by-product
Without stomata, photosynthesis and plant growth would be severely hindered.
7. State two functions of stomata.
Two main functions of stomata are:
- Enabling exchange of gases (CO2 and O2) for photosynthesis and respiration
- Allowing transpiration, which helps cool the plant and facilitates water and nutrient movement from roots to leaves
8. How do guard cells control the opening and closing of stomata?
Guard cells swell and become turgid when filled with water, opening the stoma. When they lose water and become flaccid, the stoma closes.
This reversible change is regulated by:
- Water availability
- Light
- Internal carbon dioxide levels
This mechanism helps prevent water loss and allows gas exchange as required.
9. What are the types of stomata based on their arrangement?
Stomata types based on subsidiary cells:
- Anomocytic: Surrounded by similar epidermal cells (e.g., Ranunculus)
- Anisocytic: Surrounded by three uneven-sized cells (e.g., Brassica)
- Paracytic: Accompanied by two subsidiary cells parallel to the stoma (e.g., Peach)
- Diacytic: With two subsidiary cells at right angles to the pore (e.g., Coleus)
10. Differentiate between stomata and lenticels.
Stomata are tiny pores found on leaf and stem surfaces mainly responsible for gas exchange and transpiration, while lenticels are small, spongy openings found on the stems of woody plants that facilitate gas exchange in older tissues.
- Stomata open and close actively, lenticels remain open
- Stomata mainly occur on leaves, lenticels are on woody stems
11. Describe the structure of stomata.
Stomata typically consist of:
- A central pore (the stoma)
- Two bean- or kidney-shaped guard cells surrounding the pore
- Sometimes, subsidiary cells supporting the complex
This structure allows controlled opening and closing for optimum gas exchange and water regulation.
12. Why do stomata mostly occur on the lower surface of a leaf?
Stomata are predominantly found on the lower leaf surface to minimize water loss due to direct sunlight.
Advantages:
- Reduces excessive transpiration
- Helps maintain suitable internal moisture
- Ensures efficient gas exchange even in high light conditions
