Which type of permanent plant tissue helps aquatic plants to float by enclosing large air spaces?

Introduction / Context:
Aquatic plants often need to float on the water surface or maintain buoyancy to survive and perform photosynthesis efficiently. Their tissues show special adaptations that help them remain light and stable in water. One such adaptation is the presence of a specific type of permanent tissue with large air filled spaces. This question asks you to identify that tissue type, which is particularly associated with buoyancy in aquatic plants.

Given Data / Assumptions:
• The focus is on permanent tissue in aquatic plants that helps them float. • Options include aerenchyma, collenchyma, sclerenchyma, and a distractor stating that no option is correct. • Standard plant anatomical adaptations are assumed.

Concept / Approach:
Aerenchyma is a specialized type of parenchyma tissue characterized by large intercellular air spaces. These spaces reduce the density of plant organs and allow aquatic plants to float or remain buoyant. Collenchyma is a supporting tissue with thickened cell walls found mainly in young stems and petioles, and sclerenchyma is a rigid tissue with thick, lignified walls that provides mechanical strength. Neither collenchyma nor sclerenchyma is primarily responsible for buoyancy. Therefore, aerenchyma is the correct answer because its air filled spaces are directly related to floatation in aquatic plants.

Step-by-Step Solution:
Step 1: Identify that the key function mentioned is helping aquatic plants float. Step 2: Recall that aerenchyma consists of parenchyma cells with large air spaces. Step 3: Recognize that these air spaces make plant tissues less dense and increase buoyancy. Step 4: Note that collenchyma provides flexible support and sclerenchyma provides rigidity, not buoyancy. Step 5: Reject the option stating no correct answer since a well known tissue, aerenchyma, fits the description.

Verification / Alternative check:
Examples such as water hyacinth and lotus have spongy tissues with visible air chambers that allow them to float. Botanical descriptions specifically refer to these tissues as aerenchyma. Cross sections of petioles and stems of aquatic plants frequently show extensive aerenchyma compared to terrestrial plants. These consistent observations support the role of aerenchyma in buoyancy and confirm it as the correct option.

Why Other Options Are Wrong:
Option B (Collenchyma) is incorrect because it functions mainly as a supporting tissue in growing parts of plants and is not specialized for floatation. Option C (Sclerenchyma) is incorrect because it provides mechanical strength with thick, lignified walls and would make tissues heavier, not lighter. Option D (No option is correct) is incorrect because aerenchyma is a well established tissue type responsible for buoyancy in many aquatic plants.

Common Pitfalls:
Some students confuse various supportive tissues and may think that any specialized tissue can help in floatation. It is critical to associate aerenchyma specifically with large intercellular air spaces and buoyancy, while collenchyma and sclerenchyma are more about mechanical support. Recalling that aerenchyma is abundant in hydrophytes is a helpful memory aid.

Final Answer:
The type of permanent tissue that helps aquatic plants to float is aerenchyma.