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POSSIBLE ANSWERS FOR HOMEWORK ASSIGNMENT # 3

VERTEBRATE ZOOLOGY SPRING 2000

Dr. W. Crone Topics: Birds, Mammals, and Digestive System

"You Are What You Eat"

  1. What types of sensory information do birds use to capture food? What would be the major sensory inputs for an eagle, an owl, and a vulture, and why?

    2. As flying vertebrates, birds have to be able to identify prey from far away. Sight, hearing, and to lesser extents, touch and smell are involved in this process. A bird's eye contains a retinal (nervous) layer of many vision cells, including cone cells for color vision and rod cells for dim light, black and white vision. The inner ear or cochlea of a bird is sensitive to slight sounds that may be missed by human beings. Three examples of birds, eagles, owls, and vultures, demonstrate slight variations on use of these senses during hunting. Soaring eagles are daytime hunters, and so rely on keen vision to spot prey. Owls hunt at night. With a high proportion of rod cells in their retinas, owls have good night vision, but hearing prey scampering in the dark and feeling for them with talons also assists in capturing a meal. As with eagles, vultures are also daytime feeders. While sight would be the first line of localizing prey, vultures have a reasonably good sense of smell (for a bird). As a result, the smell of carrion (dead flesh) can assist vultures in finding food. In summary, sight is the major sense used by birds to help find prey, but other senses may be of benefit.

    (Sources: Week 8 lecture notes and handout; Hickman et al., 7th ed., Ch. 11, pp. 260-262 and Ch. 30, pp. 650-652)

  2. You come across the skull of a mammal previously unknown to science. Describe the features that you would look for in determining its omnivore (as vs. carnivore or herbivore) diet. Be sure to explain your reasoning.

    3. Given that the mouth is the site of food intake, jaw and teeth structures of a skull gives clues to the diet of a vertebrate, even if it is a mammal unknown to science. Carnivores (meat eaters) and herbivores (plant eaters) represent two extremes of skulls, while omnivores (combined meat and plant diet) should have intermediate structures represented. The jaw of a carnivore may be specialized for stabbing or tearing, while the teeth, especially canines, are sharp for piercing and tearing. Even the premolars and molars may be termed carnassial teeth, given their sharpness for shearing and tearing meat. A herbivore may have pronounced incisors to nip off plant material, a jaw gap or diastema, chisel-shaped premolars for shearing, and large, multicusped molars for grinding the tough cellulose. An omnivore jaw represents a compromise, with all four teeth types present in functional form, but without such extreme modifications.

    (Sources: Week 9 lecture notes and handout; Hickman et al., 7th ed., Ch. 10, pp. 225-226, and Ch. 31, pp. 674-676)

  3. You've been abducted by aliens and are about to become an unwilling participant in their nefarious experiments. Members of this particular spaceship want to study the human digestive tract by removing one organ and studying it. They offer you a choice of removing your stomach, your liver, or your pancreas. Stalling for time in the hopes that someone will come to the rescue, you hem and haw and finally tell the aliens to remove your …… Which organ did you choose for them to remove? Which of these three organs is the one that you can most likely live without, given that the odds of rescue are growing increasingly thin? You will need to defend your reasoning (for the top-secret debriefing that follows your return to the planet!).

A review of the functions of the stomach, liver, and pancreas highlights the difficulty in choosing the most expendable one in a forced selection. The stomach is a site for large meal storage, acid secretion, and the beginning of protein digestion with pepsin enzymes. A strong pyloric sphincter muscle at its distal end allows the parceling out of the acidic chyme mixture into the duodenum of the small intestine. The liver is a site for bile production, material synthesis (e.g., blood proteins, vitamins, and glycogen), and metabolism of drugs such as alcohol. The pancreas has dual exocrine and endocrine functions. Exocrine secretions into the duodenum include buffering juices and protein, carbohydrate, and fat-digesting enzymes. The endocrine pancreas regulates blood sugar (necessary fuel for the brain) via production of the hormones insulin and glucagon. The protein digestion that is typically started in the stomach is completed with the pancreatic enzymes. As a result, the loss of the stomach is the most"replaceable" of the three organs highlighted. A factor that such an afflicted individual would have to consider is to change the diet to small, frequent meals to not overwhelm the digestive and absorptive capacity of the small intestine.

(Sources: Week 10 lecture notes and handout; Hickman et al., 7th ed., Ch. 10, pp. 228-234)

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Please send comments and questions to: cronewil@hvcc.edu

 

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