Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892



Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

The eyes of vertebrates and cephalopods are similar in structure and function. A difference between the vertebrate eye and the cephalopod eye is that the vertebrate eye has:

a. an iris surrounding the pupil, whereas in cephalopods the pupil surrounds the iris.

b. a lens that changes shape when focusing, whereas in cephalopods the lens moves back and forth to focus.

c. a retina that moves in the socket when recording the image, whereas in cephalopods the retina changes shape when stimulated.

d. a pupil that shrinks in size in bright light, whereas cephalopods have a pupil that enlarges in bright light.

e. retinal synthesized from vitamin A, whereas cephalopods lack retinal.

Summary Introduction


Eyes are the structures that receive visual stimuli with the help of photoreceptors. The photoreceptors in a human eye are present in the form of rods and cone cells, which are located in the retina of the eye. The eyes of vertebrates and cephalopods are somewhat similar as both operate like a camera. Photons are received by the cornea of the eyes, which transmits the light to the rods and cones present in the retina, which generates an image and transfers the signals to the visual cortex of the brain via the optic nerve fibers.


Explanation/justification for the correct answer:

Option (b) states that cephalopods belong to the phylum mollusca and have a single lens eye, like that of vertebrates. The difference between the eyes of cephalopods and those of vertebrates is in the accommodation of the lens. Cephalopods move their lens back and forth with respect to the retina to adjust the image on it. Vertebrates change the shape of their lens in order to adjust the image on the retina. If a vertebrate looks at a distant object, the lens in its eye becomes thin, and if it looks at an object that is nearby, the lens thickens. Hence, option (b) is the correct answer.

Explanation for incorrect answer:

Option (a) states that both cephalopods and vertebrates have an iris, which surrounds the pupil. The pupil allows light to enter the eye while the iris adjusts the muscles of the pupil to regulate the amount of light entering the eyes. In the presence of very bright light, the size of the pupil decreases, while in dim light, the size of pupil increases to allow maximum amount of light to enter the eyes...

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