Final answer:
Desert plants, or xerophytes like the pear cactus, are associated with having spines and being rootless. They have adapted to arid environments with morphological changes that help minimize water loss and are distinct from aquatic plants that have adaptations for water-rich environments.
Therefore the correct answer is option is 4) Desert plants
Step-by-step explanation:
Types of plants that are typically associated with being rootless and having spines are desert plants. These plants, known as xerophytes, have adapted to arid environments by reducing water loss through anatomical modifications. One prime example of a xerophyte is the pear cactus (Opuntia sp.), which has leaves modified into spines to lower the surface-to-volume ratio, thus minimizing water loss. These spines also function as a defense mechanism. Photosynthesis in these plants primarily occurs in the stem, which also has the function of water storage.
Aquatic plants, on the other hand, such as the fragrant water lily (Nymphaea odorata), have adaptations for thriving in water-rich environments, unlike xerophytes. Therefore, the correct answer to the student's question is option 4) Desert plants. To survive in extreme dryness, many desert plants develop deep roots, likely to tap into deep water sources, and have fleshy leaves with sunken stomata for reduced transpiration.