What is the term for the elongated appendages found in some plants and animals?

The correct term for the elongated appendages found in some plants and animals is "flagella." Flagella are typically whip-like structures used mainly for locomotion. In the context of biology, flagella are most commonly associated with single-celled organisms such as sperm cells and certain protozoa, where they aid in movement through fluid environments. Their structure allows them to propel the organism forward, making them essential for mobility in various aquatic habitats.

While antennae are sensory appendages found predominantly in insects and some crustaceans, and fins are specialized structures used by fish and some other aquatic animals for swimming, these do not encompass the broader definition of elongated appendages seen across different types of organisms in the same way flagella do. Limbs are a general term for appendages in vertebrates, but they aren't specifically elongated in the same manner as flagella. Thus, understanding the unique role and characteristics of flagella is key to appreciating why they represent the correct answer in this context.