Question

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

Short answer

Option (b) - stomata that are located in pits on the undersides of their leaves, or narrow, needlelike leaves can help limit water loss in plants that occupy dry habitats, as it creates a more humid microclimate and reduces surface area exposed to air, thus reducing water loss through transpiration.

Step-by-step solution

Analyse option (a) - Abundant companion cells and sieve-tube elements

Companion cells and sieve-tube elements are parts of the phloem tissue in plants and are involved in the transport of sugars and other organic molecules, but they do not primarily relate to water conservation. So option (a) is not the right answer.

Analyse option (b) - Stomata located in pits on the undersides of leaves, or narrow, needlelike leaves

Stomata are tiny openings on the surface of leaves that allow for gas exchange, including the release of water vapor from the plant. Stomata being located in pits on the undersides of leaves can create a more humid microclimate, reducing water loss. Narrow, needlelike leaves also help in reducing the surface area exposed to air, which further reduces water loss through transpiration. Therefore, option (b) can help limit water loss in plants that occupy dry habitats.

Analyse option (c) - Extensive networks of xylem and phloem

Xylem and phloem are the two main types of vascular tissues in plants. Xylem mainly transports water and dissolved minerals, while phloem transports organic molecules. Although they are essential for a plant's survival, an extensive network of these tissues does not directly result in water conservation. Option (c) is not the right answer.

Analyse option (d) - Stomata located on the top surface of leaves, or broad leaves

Stomata on the top surface of leaves and broad leaves both increase the surface area exposed to air, which can increase water loss through transpiration. Therefore, this feature does not help to limit water loss in plants that occupy dry habitats. Option (d) is not the right answer.

Identify the correct option

After analyzing all the options, we concluded that option (b) - stomata that are located in pits on the undersides of their leaves or narrow, needlelike leaves can help limit water loss in plants that occupy dry habitats.

Key concepts

Water Conservation in Plants

Plants residing in arid and dry habitats have developed remarkable strategies to conserve water, ensuring their survival in environments where this precious resource is limited. One of the primary strategies is through morphological adaptations, such as having narrow, needle-like leaves, which are observed in plants like pine trees. These needle-like leaves reduce the surface area that is exposed to the sun and wind, minimizing the amount of water lost through evaporation.

Moreover, some plants have a thick, waxy coating on their leaves, known as a cuticle, which serves as an excellent barrier to water loss. In cacti, leaves have evolved into spines, reducing water loss to an even greater extent and offering protection from herbivores. Additionally, plants may have fewer stomata or have stomata that open only at night when the temperatures are cooler and humidity is higher, a process known as 'crassulacean acid metabolism' (CAM) photosynthesis. These features collectively contribute to effective water conservation in plants found in dry habitats.

Stomatal Adaptations

Stomatal adaptations play a pivotal role in plant water conservation. Stomata are small openings on the leaf surface that regulate gas exchange by opening and closing. In dry habitats, plants often possess stomata that are sunk in pits on the undersides of their leaves. This adaptation creates a humid microclimate around the stomata, reducing the gradient between the moist air inside the leaf and the dry air outside. As a result, the rate of transpiration, or water loss, is curbed.

Some plants adjust by having the ability to close their stomata during the hottest parts of the day or during periods of drought. Stomatal density may also vary, with some desert plants having fewer stomata to limit water loss. These adaptations are crucial for maintaining internal water balance and allowing plants to thrive even in challenging dry ecosystems.

Plant Transpiration Mechanisms

Transpiration is the process by which water vapor is lost from a plant's aerial parts, mainly through stomata on the leaves. It is an essential mechanism as it drives the transport of water from the roots to the rest of the plant and contributes to temperature regulation.

In dry habitats, plants have evolved several transpiration mechanisms to minimize water loss. Some adopt a daytime shutdown, where the stomata close during peak sunlight hours to reduce transpiration. Others may utilize deeper root systems to access water from further underground, reducing the need for frequent transpiration. Plants can also control the timing of transpiration by only allowing it during cooler and more humid periods, usually at night. These advanced regulatory mechanisms are indicators of how plants have adapted to control and minimize water loss, ensuring their survival in arid climates.