Question

Assertion: CAM plants lack structural compartmentation of leaf, as found in \(\mathrm{C}_{4}\) plants. Reason: Stomata of CAM plants are open during the night.

Short answer

Both the assertion and reason are correct, but the reason does not directly explain the assertion.

Step-by-step solution

- Understanding the Plants

First, understand the difference between C4 plants and CAM plants. C4 plants use a mechanism to concentrate carbon dioxide in a specific space in the leaf to enhance photosynthesis. This mechanism is described as 'structural compartmentation'. On the other hand, CAM plants absorb carbon dioxide at night and store it for use during the day. They do not have structural compartmentation.

- Analyzing the Assertion

The assertion states that CAM plants lack structural compartmentation in the leaf as found in C4 plants. This is indeed true as, unlike C4 plants, CAM plants do not have a specific region in their leaf where they concentrate carbon dioxide for photosynthesis.

- Analyzing the Reason

The Reason provided is that the stomata of CAM plants are open during the night. Well, this is also true. CAM plants open their stomata at night to absorb carbon dioxide.

- Connection between Assertion and Reason

Finally, consider if the Reason accurately explains the Assertion. The assertion is correct, and the reason is also true but there is no direct connection between the two. CAM plants' lack of structural compartmentation isn't because their stomata are open during the night, but their stomata open at night to reduce water loss.

Key concepts

Structural Compartmentation

While both C4 and CAM plants have unique adaptations to thrive in arid conditions, they differ significantly in how they manage carbon dioxide absorption for photosynthesis. In C4 plants, structural compartmentation creates specific regions within the leaf known as "bundle sheath cells." These cells serve as localized areas where carbon dioxide is concentrated, facilitating an efficient space for photosynthesis to occur. This means that C4 plants separate the initial carbon fixation and the Calvin cycle in both time and specific tissues.

In contrast, CAM plants do not exhibit this kind of structural compartmentation. Instead, they keep all photosynthesis processes evenly distributed within their mesophyll cells. This is one of the reasons why CAM plants are distinct—they handle carbon dioxide differently without spatial separation. This feature is vital for CAM plants that operate in harsh conditions where conserving energy and resources is crucial.

• C4 plants have compartmentalized areas for carbon fixation.
• CAM plants maintain an even distribution in photosynthesis processes.
• Structural compartmentation is absent in CAM plants.

Stomata Behavior

Stomata are the tiny openings on the leaves of plants that allow carbon dioxide to enter and oxygen to leave. In most plants, stomata open during the day to absorb sunlight and perform photosynthesis. However, CAM plants exhibit unique stomata behavior as an adaptation to their often dry environments.

CAM plants open their stomata at night, instead of during the day. This nighttime activity is crucial to avoid excessive water loss in the intense heat and light conditions found in their native habitats. By opening at night, CAM plants can minimize water evaporation while still gathering necessary carbon dioxide for photosynthesis.

• CAM stomata open at night to conserve water.
• Daytime closure prevents water loss.
• Stomata behavior is a key adaptation for survival in arid conditions.

Carbon Dioxide Absorption

Carbon dioxide absorption is a critical part of the photosynthesis process. For CAM plants, this process is ingeniously modified to work efficiently in arid environments. During the night, when the stomata are open, CAM plants absorb carbon dioxide and convert it into a four-carbon acid, such as malate.

This acid is stored within their vacuoles until daylight returns. Once the sun rises, the stored carbon dioxide is released internally, allowing the plant to perform photosynthesis without reopening their stomata. This adaptation aids in balancing their need for carbon dioxide intake while also preserving water.

• Nighttime absorption stores CO2 as malate.
• Daylight release of CO2 enables photosynthesis.
• This strategy avoids water loss.

Photosynthesis in CAM Plants

Photosynthesis in CAM plants is distinctive due to the plant's environment-driven adaptation. Instead of the typical continuous process seen in other plants, CAM photosynthesis splits into two distinct phases across night and day.

At night, carbon dioxide absorbed is stored as an acid. During the day, this stored CO2 is released internally to drive the Calvin cycle. This partition not only helps maintain water levels by keeping stomata closed during the day but also efficiently uses the absorbed carbon dioxide.

• CAM photosynthesis is divided into night and day phases.
• Stored CO2 supports the daytime Calvin cycle.
• This efficiency supports survival in dry conditions.