Final answer:
OPTION 4.
Thorns serve a protective function in plants, unlike fur in animals which is for temperature regulation. Thorns are modified branches that can cause physical harm to deter predators.
Step-by-step explanation:
The physical structure in plants that has a different function than fur in animals is the thorn. Thorns are modified branches serving as protective adaptations against herbivores. Unlike fur in animals, which mainly provides insulation and temperature regulation, thorns are rigid, sharp outgrowths that can protect the plant by causing physical damage to potential predators. This defense can deter animals from eating or damaging the plant. Common examples of plants with thorns include roses, Osage orange, and devil's walking stick.