Question

Read the given statements and select the correct option. Statement 1 : Crassulacean acid metabolism occurs in succulent plants which grow in xeric conditions. Statement \(2:\) Stomata are generally sunken in succulent plants. (a) Both statements 1 and 2 are correct and statement 2 is the correct explanation of statement 1 . (b) Both statements 1 and 2 are correct but statement 2 is not the correct explanation of statement 1 . (c) Statement 1 is correct and statement 2 is incorrect. (d) Both statements 1 and 2 are incorrect.

Short answer

Both statements 1 and 2 are correct, but statement 2 is not the correct explanation of statement 1.

Step-by-step solution

Examining Statement 1

Review Statement 1: 'Crassulacean acid metabolism occurs in succulent plants which grow in xeric conditions.' Check this statement against known facts about Crassulacean acid metabolism (CAM). It is known that CAM is a photosynthetic adaptation in some plants living in arid conditions to limit water loss. CAM plants, including many succulents, open their stomata at night (when evaporation rates are lower) to fix CO2, which is stored as an acid and then used during the day for photosynthesis. Therefore, Statement 1 is correct.

Examining Statement 2

Review Statement 2: 'Stomata are generally sunken in succulent plants.' Verify this statement by examining the typical adaptations in succulent plants, which often have structural modifications to reduce water loss. Sunken stomata are one such adaptation, as they help create a boundary layer of still air that reduces the rate of transpiration. This adaptation is common among succulent plants that grow in xeric (dry) environments. Therefore, Statement 2 is also correct.

Evaluating the Relationship

Determine if Statement 2 is the correct explanation for Statement 1. Crassulacean acid metabolism (CAM) is an adaptation to arid conditions that involves opening stomata at night, not necessarily due to the stomata being sunken. Although both statements are true, the fact that stomata are sunken does not explain why CAM occurs. CAM is an adaptation to reduce water loss, and having sunken stomata is another independent adaptation towards the same goal. Therefore, they do not have a cause-and-effect relationship as implied by option (a).

Key concepts

Succulent Plants

Succulent plants are fascinating and resilient flora that thrive in environments where water is scarce. Their name itself, 'succulent,' comes from the Latin 'sucus,' which means juice or sap, reflecting their ability to store water.

These plants have thick, fleshy parts that are designed to retain moisture, which is a lifesaver in arid conditions. The leaves, stems, or roots of succulents can appear swollen, a characteristic called 'succulence.' It's this unique adaptation that allows succulents to survive prolonged dry periods. They can endure where rain is infrequent and conserve water to sustain vital processes.

Some common examples include the jade plant, aloe vera, and agave—all of which have thick leaves that store moisture. This internal reserve helps them withstand drought and makes them a popular choice for xeriscaping and water-efficient gardening.

Xeric Conditions

Xeric conditions refer to environments defined by very low water availability, often associated with deserts or places where the evaporation rate in the soil and air is much higher than precipitation. Plants and animals living in these regions must adapt to survive with minimal moisture.

For plants, this could mean developing extensive root systems to access deep water sources or reduced leaf surface area to minimize water loss. Behavioral adaptations are also observed in animals that become nocturnal to avoid the daytime heat. Succulent plants fit particularly well into xeric ecosystems due to their water-retentive tissues, a protective waxy cuticle on their surfaces, and other physiological adaptations such as the Crassulacean acid metabolism (CAM) which allows them to minimize water loss while maintaining photosynthesis.

Stomatal Adaptations

Stomatal adaptations are crucial for plants to survive in harsh environments, like those with xeric conditions. The stomata are tiny openings on the surface of leaves that allow for the exchange of gases—carbon dioxide (CO2) entering for photosynthesis, and oxygen (O2) and water vapor exiting as waste products.

In succulent plants, stomata are typically sunken below the leaf surface, creating a microclimate that reduces evaporation rate. This is vital for water conservation. Additionally, succulents can control the opening and closing of their stomata, only opening them at night through the Crassulacean acid metabolism (CAM) pathway. At night, temperatures are cooler, and humidity is often higher, which reduces water loss. The CO2 gathered at night is then used for photosynthesis during the day when the stomata are closed, further conserving water.