Question

Roots with negative geotropism for the purpose of oxygen is found in the following

• A. Pillar roots
• B. Stilt roots
• C. Pneumatophores
• D. Velamen roots

Hint:

Pneumatophores are “breathing roots” of mangrove plants and always show negative geotropism to access atmospheric oxygen.

Answer 1

The Correct Option is C

Step 1: Understanding the concept of geotropism.
Geotropism refers to the directional growth of plant parts in response to gravity. Roots generally show positive geotropism (grow downward), but in certain specialized conditions, some roots show negative geotropism (grow upward) to fulfill specific physiological functions like respiration in waterlogged soils.

Step 2: Understanding oxygen requirement in plants.
In marshy, swampy, or waterlogged soils, oxygen availability is extremely low due to saturation of water in soil pores. Therefore, certain plants develop specialized aerial respiratory roots to absorb oxygen directly from the atmosphere.

Step 3: Identification of specialized respiratory roots.
Pneumatophores are specialized breathing roots that grow upward against gravity (negative geotropism). These roots emerge above the soil or water surface and help in gaseous exchange through small pores called lenticels.

Step 4: Analysis of other options.
Pillar roots provide mechanical support (e.g., banyan tree), stilt roots also provide support (e.g., maize, sugarcane), and velamen roots are aerial absorptive roots found in orchids. None of these primarily function as oxygen-absorbing negative geotropic roots.

Step 5: Functional adaptation reasoning.
Pneumatophores are an adaptation to anaerobic environments. Their upward growth ensures exposure to air, enabling efficient respiration in otherwise oxygen-deficient conditions, making them essential for mangrove plants.

Step 6: Final conclusion.
Thus, the correct answer is pneumatophores.