______ is a sessile animal, that relies upon its relationship with plants like algae to build the largest structures of biological origin on earth.

Coral

The correct answer is Option (3) -Coral

• Corals are sessile, meaning they permanently attach themselves to the ocean floor similar to plants. They form a unique partnership known as symbiosis with algae, benefiting both coral and algae. Despite their plant-like appearance, corals are animals because they don't produce their own food.
• Most corals contain algae called zooxanthellae, which provide them with essential nutrients through photosynthesis.