Describe the role of the stomata in gas exchange during photosynthesis.

6.1 Plant Nutrition – Photosynthesis

The Role of Stomata in Gas Exchange

Imagine a plant as a busy factory that needs raw materials to build food. The stomata (plural of stomata) are like tiny doors on the leaf surface that open and close to let gases in and out. They are mainly found on the underside of leaves, guarded by two guard cells that control the opening.

During photosynthesis, the plant needs carbon dioxide ($CO_2$) to build sugars and releases oxygen ($O_2$) as a by‑product. The stomata make this possible by:

• Allowing $CO_2$ from the air to enter the leaf.
• Letting $O_2$ produced in the chloroplasts escape into the atmosphere.
• Releasing water vapor ($H_2O$) during transpiration, which also helps pull more air into the leaf.

Think of stomata as the plant’s “breathing system” – just as we inhale air and exhale carbon dioxide, stomata let the plant inhale $CO_2$ and exhale $O_2$.

How Stomata Work (Step‑by‑Step)

1. Guard cells take in water. When they absorb water, they swell and the stomatal pore opens.
2. Air enters. $CO_2$ from the atmosphere diffuses through the open pore into the leaf.
3. Photosynthesis happens. Inside the chloroplasts, $CO_2$ and $H_2O$ are converted into glucose and $O_2$.
4. Products exit. $O_2$ and water vapor exit through the same stomatal pore, while the glucose stays inside the plant.
5. Guard cells release water. When the plant needs to conserve water, guard cells lose water, the pore closes, and the plant reduces gas exchange.

Gas Exchange in Numbers

Key Equation

The overall reaction of photosynthesis can be written as:

$$\text{Photosynthesis: }6CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2$$

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