Mangroves are specialised coastal plants that grow in waterlogged, oxygen poor saline soils; which type of modified root helps them breathe in such conditions?

Introduction / Context:
Mangrove forests occupy coastal and estuarine areas where soil is waterlogged, salty and often deficient in oxygen. To survive in these extreme conditions, mangrove plants show several structural adaptations. This question focuses on one key adaptation: the presence of specialised roots that allow the plant to take in oxygen even when the surrounding mud is anaerobic. Understanding these respiratory roots helps you relate plant structure to function in ecology.

Given Data / Assumptions:
- Mangroves grow in saline, marshy, waterlogged soils with poor oxygen availability around the root zone.- Roots normally need oxygen for respiration to generate energy.- The question asks which type of root or stem modification helps mangroves breathe.- Options mention modified roots, modified stems, respiratory roots and respiratory stems, as well as normal roots.

Concept / Approach:
In many mangrove species such as Avicennia, some roots grow upwards out of the mud and water into the air. These erect structures are called pneumatophores or respiratory roots. They have numerous lenticels and air spaces that facilitate gas exchange, allowing oxygen to diffuse into the plant tissues. This is essential because the deeper parts of the soil are often lacking in oxygen. In contrast, storage roots mainly hold food, and modified stems have other functions such as support or photosynthesis. Respiratory stems are not a recognised adaptation in mangroves. Therefore, respiratory roots or pneumatophores are the correct answer.

Step-by-Step Solution:
Step 1: Recall that mangroves grow in anaerobic, waterlogged soils where standard underground roots cannot obtain enough oxygen.Step 2: Remember that many mangroves develop upward growing roots that emerge above the soil and water surface.Step 3: These aerial roots are called pneumatophores and are specially adapted for gas exchange, so they are often called respiratory roots.Step 4: Evaluate the options and identify which one clearly describes respiratory roots projecting above the soil.Step 5: Select option C, which correctly names these as respiratory roots or pneumatophores.

Verification / Alternative check:
Photographs and diagrams of mangrove ecosystems in textbooks show numerous pencil shaped or knee shaped roots sticking out of the mud around the main trunk.Labels on these diagrams usually identify them as pneumatophores or breathing roots.Descriptions emphasise that they have many pores and air passages, confirming that they function as respiratory roots, not as storage roots or stems.

Why Other Options Are Wrong:
Option A is wrong because modified storage roots are adapted mainly to store food, as in carrot or beet, and do not solve the oxygen shortage in mangrove mud.Option B is wrong because modified stems such as cactus stems focus on photosynthesis or water storage, not on breathing in waterlogged soil.Option D is wrong because the term respiratory stems is not standard; stems do not act as primary breathing organs in mangroves.Option E is wrong because normal fibrous roots would suffocate in oxygen poor mud, so specialised structures are required for survival.

Common Pitfalls:
Some students confuse pneumatophores with prop roots or stilt roots seen in other plants and may pick modified stems by mistake.Another pitfall is simply remembering that mangroves have unusual roots but forgetting that these are specifically respiratory or breathing roots.To avoid confusion, connect the term pneumatophore with air in the same way as the word pneumatic, which relates to air pressure, reminding you that these roots handle gas exchange.

Final Answer:
Mangroves possess respiratory roots called pneumatophores that project above the soil and help the plants obtain oxygen in waterlogged, oxygen poor habitats.