Question

1. which example best describes homologous structures?

bird wings and insect wings used for flight
a human arm and a whale flipper sharing similar bones but used differently
a cactus spine and a porcupine quill serving as defenses
shark fins and dolphin fins that look similar because they live in water

Explanation:

Homologous structures are structures in different species that are similar due to common ancestry, even if their functions differ.

• Bird wings and insect wings: These are analogous (similar function, different origin), not homologous.
• Human arm and whale flipper: They have similar bone structures (humerus, radius, ulna, etc.) from a common ancestor, but are used for different tasks (grasping vs. swimming), so this is homologous.
• Cactus spine and porcupine quill: Cactus spines are modified leaves, porcupine quills are modified hairs—different origins, analogous for defense.
• Shark fins (cartilaginous, fish) and dolphin fins (mammalian, modified limbs): Analogous (similar function in water, different origins).

Answer:

B. A human arm and a whale flipper sharing similar bones but used differently