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Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 45
Test Yourself Questions
1. The process whereby incoming sensory stimulation is converted to neural signals is
a. an action potential.
b. a threshold potential.
c. perception.
d. sensory transduction.
e. reception.
Answer: d. The process whereby incoming sensory stimulation is converted to neural signals is sensory
transduction.
2. Photoreceptors are examples of
a. nociceptors.
b. baroreceptors.
c. mechanoreceptors.
d. electromagnetic receptors.
e. thermoreceptors.
Answer: d. Photoreceptors are examples of electromagnetic receptors.
3. The sensory receptors for hearing are located in
a. the organ of Corti.
b. the Eustachian tube.
c. the retina.
d. the tympanic membrane.
e. a, b and c.
Answer: a. The sensory receptors for hearing are located in the organ of Corti.
4. Statocysts are sensory organs for
a. hearing found in many invertebrates.
b. equilibrium found in mammals.
c. equilibrium found in many invertebrates.
d. water current changes found in fish.
e. hearing found in amphibians.
Answer: c. Statocysts are sensory organs for equilibrium found in many invertebrates.
5. The eyecups of planaria can
a. focus light to form an image.
b. detect light.
c. detect the direction of light.
d. all of the above.
e. b and c only.
Answer: e. The eye cup of planaria can detect light and its incoming direction.
6. The light detectors of a compound eye are called
a. retinas.
b. opsins.
c. cones.
d. ommatidia.
e. statocysts.
Answer: d. The individual light detectors of a compound eye are called ommatidia.
7. In the mammalian eye, light is focused on the retina when
a. the lens moves forward or backward.
b. the lens changes shape.
c. the eyeball changes shape.
d. the pupil dilates.
e. none of the above.
Answer: b. In the mammalian eye, light is focused on the retina when the lens changes shape.
8. The level of glutamate release from photoreceptors would be highest when
a. a person is standing in full sunlight.
b. a person is in a completely dark room.
c. a person is in a dimly lit room.
d. Na+ channels of the photoreceptor are closed.
e. both a and d.
Answer: b. The level of glutamate release from photoreceptors would be highest when a person is in a
completely dark room.
9. Cone pigments detect different wavelengths of light due to
a. their location in the retina.
b. the amount of light they absorb.
c. the type of retinal that have.
d. the type of opsin protein they have.
e. interactions with bipolar cells.
Answer: b. Cone pigments detect different wavelengths of light due to the type of opsin protein they
have.
10. The stimulation for olfaction involves odorant molecules
a. bending the cilia of olfactory receptor cells.
b. binding to receptors of olfactory receptor cells.
c. entering the cytoplasm of olfactory receptor cells.
d. closing K+ channels of olfactory receptor cells.
e. all of the above.
Answer: b. The stimulation for olfaction involves odorant molecules binding to receptors of olfactory
receptor cells.
Conceptual Questions
1.
Define sensory transduction and perception.
sensory transduction - The process by which incoming stimuli are converted into neural signals.
perception - An awareness of the sensations that are experienced.
2.
Explain how the mammalian ear is adapted to distinguish sounds of different frequencies.
Answer: The organ of Corti contains the hair cells and sensory neurons that initiate signaling. The hair
cells sit on top of the basilar membrane and their cilia are embedded in the tectorial membrane at the
top of the organ of Corti. Pressure waves of particular frequencies cause the basilar membrane to
vibrate at particular sites. This bends the cilia of hair cells back and forth, sending oscillating signals to
the sensory neurons. Consequently, the sensory neurons send intermittent action potentials to the CNS
via the auditory nerve. Hair cells at the end of the basilar membrane closest to the oval window respond
to high-pitched sounds, and lower-pitched sounds trigger hair cell movement further along the basilar
membrane.
3.
Explain how eye placement affects binocular vision.
Answer: Animals that have both eyes located at the front of the head have binocular vision, because the
overlapping images coming into both eyes are processed together to form one perception. Binocular
vision provides excellent depth perception because the images coming into each eye are slightly
different. Predators depend on binocular vision to locate prey precisely. In contrast animals with eyes
toward the side of the head have monocular vision, which allows them to see a wide area at one time,
although binocular vision is reduced. Most prey animals benefit from monocular vision.
Experimental Questions
1. What were the two major hypotheses to explain how animals discriminate between different odors?
How did Buck and Axel test the hypothesis of multiple olfactory receptor proteins?
Answer: One possibility is that many different types of odor molecules might bind to one or just a few
types of receptors proteins, with the brain responding differently depending on the number or
distribution of the activated receptor cells. Alternatively, odors might be distinguished at the level of
receptor proteins. The second hypothesis is that organisms can make a large number of receptor
proteins, each type binding a particular odor molecule or group of odor molecules.
The researchers extracted RNA molecules from the olfactory receptor cells of the nasal epithelium.
They then used this RNA to identify genes that encoded G-protein coupled receptor proteins.
2. What were the results of Buck and Axel’s study?
Answer: In their study, they identified 18 different genes that encoded different G-protein coupled
receptor proteins.
3. Considering the two hypotheses explaining how animals discriminate between different odors (see
Experimental Question 1), which one was supported by the results of this experiment? With the
evidence presented by Buck and Axel, what is the current hypothesis explaining the discrimination of
odors in animals?
Answer: The results of the experiment conducted by Buck and Axel support the hypothesis that animals
discriminate between different odors based on having a variety of receptor proteins that recognize
different odor molecules. Each olfactory receptor cell has a single type of receptor that is specific to
particular odor molecules. Because most odors are due to multiple chemicals that activate many
different types of odor receptor molecules at the same time, the brain detects odors based on the
combination of the activated receptors. Odor seems to be discriminated by many olfactory receptor
proteins which are in the membrane of separate olfactory receptor cells.
Collaborative Questions
1. Discuss two different types of mechanoreceptors.
Answer:
Mechanoreceptors detect physical stimuli such as sound, pressure, touch, and movement. These stimuli
deform the mechanoreceptors, thus sending information to the central nervous system for interpretation.
The lateral line system - These are types of sensory receptors which detect changes in water movement
and are predominantly found in fish. In this sensory system, a series of pores and canals run along the
side of the fish and open up into the water. As water is moved around the fish, cilia which are attached
to hair cells bend due to the moving water. As a result of this bending, sensory information is sent to the
brain for interpretation and response.
Skin receptors - Different types of sensory receptors are located at different depths below the surface of
the skin. Some receptors are designed to detect light pressure while others are deeper and detect much
deeper pressure.
2. Discuss different types of eyes found in animals.
Answer:
Eye cup - This is the simplest of all the photoreceptors found in animals. It consists of a cup containing
photoreceptor cells which send information to be interpreted. This type of eye is able to differentiate
between the presence and absence of light, and its direction, but doesn't form a visual image. An
example of this type of eye is found in the flatworm.
Compound eye - This eye consists of several hundred to several thousand light detectors called
ommatidia. Each ommatidium makes up one facet of the compound eye. By comparing images from
many ommatidia, the invertebrate forms an image which is sent to the brain for interpretation. This type
of eye is found in arthropods such as insects and crustaceans.
Single lens eye - Unlike the compound eye which has hundreds or thousands of lenses, this type of eye
has only one lens. Images are transmitted through a hole in the eye called the pupil and passes through
a single lens. This image is then projected to the back of the eye onto the retina. The retina is
connected to a nerve and the sensory information is then transmitted to the brain for interpretation.