Atmospheric CO₂ has been increasing rapidly since the late 1800s, largely due to human activities. Recall that CO₂ enters leaves through stomata and can then be used for photosynthesis. However, transpiration occurs as a result of water evaporating through stomata. How have plants responded to elevated CO₂ levels?
Which of these structural features can help to limit water loss in plants that occupy dry habitats?
a. Abundant companion cells and sieve-tube elements
b. Stomata that are located in pits on the undersides of their leaves, or narrow, needlelike leaves c. extensive networks of xylem and phloem
d. Stomata that are located on the top surface of leaves, or broad leaves

Verified step by step guidance

1. Understand the role of stomata: Stomata are small openings on the surface of leaves that allow for gas exchange. CO2 enters through stomata for photosynthesis, but water vapor also exits through them, leading to transpiration.
2. Consider the impact of elevated CO2 levels: With increased CO2, plants may adjust their stomatal density or opening size to optimize photosynthesis while minimizing water loss.
3. Identify adaptations for dry habitats: Plants in arid environments have evolved structural features to reduce water loss, such as stomata located in pits or narrow, needlelike leaves.
4. Evaluate the options: Option b describes features like stomata in pits and needlelike leaves, which are adaptations to limit water loss by reducing exposure to air and minimizing transpiration.
5. Conclude which features are beneficial: Based on the adaptations for dry habitats, option b is the most relevant choice for limiting water loss in plants exposed to elevated CO2 levels.

Key Concepts

Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy, using carbon dioxide and water to produce glucose and oxygen. This process primarily occurs in the chloroplasts of plant cells and is essential for plant growth and energy production. Elevated CO2 levels can enhance photosynthesis, potentially increasing plant growth and altering water use efficiency.

Transpiration

Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems, and flowers. It occurs mainly through stomata, which are small openings on the leaf surface. Transpiration helps in nutrient transport and temperature regulation but can lead to water loss, especially in dry habitats, making adaptations crucial for survival.

Stomatal Adaptations

Stomatal adaptations are structural changes in plants that help regulate gas exchange and water loss. In dry habitats, plants may have stomata located in pits or on the undersides of leaves, or possess narrow, needle-like leaves to minimize water loss. These adaptations help maintain water balance while allowing CO2 uptake for photosynthesis, crucial for survival in arid environments.