Correct Option
The correct option isThey facilitate seed dispersal by wind.
Explanation
The fruit of a sunflower is technically known as a cypsela. A characteristic feature of the family Asteraceae (to which sunflowers belong) is the modification of the calyx into a structure called the pappus. In sunflowers, the pappus appears as hairy or plume-like structures attached to the fruit.
Option Analysis
- They protect the seed from predation by insects. is Incorrect: While the fruit wall (pericarp) provides some protection to the seed, the hairy pappus structures are not primarily designed for protection against predation.
- They enable the seed to float on water surfaces. is Incorrect: Adaptations for floating on water (hydrochory) typically involve fibrous or spongy outer coats (e.g., coconut). The fine hairs of a sunflower are not designed for buoyancy in water.
- They facilitate seed dispersal by wind. is Correct: The hairy pappus acts as a parachute mechanism. It increases the surface area of the fruit without significantly increasing its weight, allowing it to be caught by air currents. This facilitates anemochory, or seed dispersal by wind, enabling the seeds to travel far from the parent plant to reduce competition.
- They allow the seed to attach to the fur of animals. is Incorrect: Structures that facilitate attachment to animal fur (zoochory) are typically stiff hooks, barbs, or spines (e.g., Xanthium). The soft, hairy pappus of a sunflower is not adapted for this mode of dispersal.
Key Takeaway: The pappus is a modified calyx found in the Asteraceae family that functions as a parachute to facilitate the wind dispersal of seeds.