Which three of the following six statements about feathers are TRUE? (Choose all three correct options.)
The main function of contour feathers is to provide insulation, minimizing heat loss to the environment, while the main function of down feathers is to keep the body surface smooth, producing an aerodynamic shape that minimizes drag during flight.
Feathers are composed of keratin. Epidermal cells of the feather follicle divide, pushing older epidermal cells in the feather follicle distally. These older cells self destruct in the process of keratinization, producing a large amount of keratin.
In down feathers, the barbs are held together by interlocking barbules, forming a uniform and continuous surface that presses against the body for insulation.
Flight feathers are asymmetrical: the barbs on one side of the rachis are longer than the barbs on the other side of the rachis.
In flight, during the downstroke of the wing, the flight feathers overlap such that they form a uniform and continuous surface to press against the air, which generates lift. During the upstroke, the flight feathers rotate such that air can pass between them, minimizing resistance to wing movement.
Feathers are a synapomorphy for sauropsida.
