Normally stomata are (A)____ in the day time and (B)____ during the night.

Answer

**Step-by-Step Solution:**

1. **Understanding Stomata**: Stomata are small openings found on the surface of leaves that facilitate gas exchange. They play a crucial role in the process of photosynthesis and transpiration.

2. **Stomata During Daytime**: During the daytime, stomata are typically open. This is because photosynthesis occurs when there is sunlight, and the mesophyll cells in the leaves need to take in carbon dioxide (CO2) from the atmosphere. The process of photosynthesis also leads to the release of oxygen (O2).

3. **Transpiration and Guard Cells**: As stomata open, water vapor exits the leaf through transpiration. This loss of water causes the solute concentration in the guard cells (the cells that surround the stomata) to increase. The increase in solute concentration leads to a decrease in water potential in the guard cells.

4. **Turgor Pressure**: The decrease in water potential causes water to enter the guard cells, increasing their turgor pressure. This turgor pressure is what ultimately causes the stomata to open.

5. **Stomata During Nighttime**: In contrast, during the night when there is no sunlight, photosynthesis does not occur. As a result, the stomata typically close to minimize water loss and conserve resources.

6. **Final Answer**: Therefore, we can fill in the blanks: (A) open in the daytime and (B) closed during the night.

**Final Answer**: Normally stomata are (A) open in the daytime and (B) closed during the night.

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