Biology | Answers to Review Questions

Author Dr. George B. Johnson, Washington University
Author Dr. Peter H. Raven, Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer, Carleton College
Contributor Dr. Jonathan Losos, Washington University

Answers to Review Questions

Chapter 55 (p. 1124)

1. The function of a sensory receptor is to receive stimuli and send a corresponding impulse to the CNS. If viable and adequately stimulated, it will do so.

2. Muscle spindle receptors respond to stretching in muscles; Golgi tendon organs respond to tension in tendons when they are being stretched.

3. Otoliths in the saccule and utricle of the inner ear respond to changes in body position relative to gravity. The semicircular canals in the inner ear detect changes in angular acceleration. There are three to detect changes in all three dimensions perpendicular to one another. This works as long cilia of sensory cells move against short cilia in the same direction as fluid moves, altering firing of neurons of short cilia.

4. Sound waves vibrate the tympanic membrane; the hammer, anvil, and stirrup vibrate correspondingly; the stirrup vibrates the oval window. The sense of hearing actually takes place in the basilar membrane of the cochlea. Recognition of pitch is accomplished as the basilar membrane, which is differentially flexible, vibrates in a portion according to the frequency of the sound wave, stimulating hair cells in that region.

5. The lens focuses light rays. Amphibians and fish use muscles to move the lens position relative to the retina, whereas other vertebrates use muscles to alter the shape of the lens and the amount of light entering the eye.

6. When a photoreceptor absorbs light, a chain reaction occurs that is ultimately responsible for slamming shut the sodium channels, at a rate of about 1000/second. This causes the membrane to hyperpolarize.

7. A lighted lightbulb produces heat. The pit organs sense that heat. If the source moves, the snake feels threatened and will strike.

8. Sharks and other fish possess electrical receptors called ampullae of Lorinzini in pores along the body surface. They detect the electrical fields produced by muscle contractions of other animals. Electricity is not a good tool for terrestrial animals since air does not conduct electricity nearly as well as water does.