CHAPTER SUMMARY
40.1 METABOLIC RATE DEPENDS ON LEVEL OF ACTIVITY, BODY SIZE, AND BODY TEMPERATURE.
- Animals acquire carbohydrates, fats, and protein from their diet for energy to fuel cellular processes and activities.
- Carbohydrates are broken down rapidly in the cytosol by anaerobic glycolysis to produce a small amount of ATP in the absence of oxygen.
- Carbohydrates and fats produce large amounts of ATP by aerobic respiration through the citric acid cycle and oxidative phosphorylation.
- An animal’s metabolic rate is its overall rate of energy use.
- Metabolic rate increases with increased physical activity.
- As the end product of anaerobic glycolysis, lactic acid decreases cellular pH and limits sustainable exercise.
- Larger animals consume more energy and have higher metabolic rates than smaller ones, but the increase in metabolic rate is not proportional to mass.
- Endothermic animals maintain elevated body temperature by metabolic heat production and have high metabolic rates.
- Ectothermic animals depend on external heat sources to warm their bodies. They have lower metabolic rates compared to endothermic animals.
40.2 AN ANIMAL’S DIET SUPPLIES THE ENERGY IT NEEDS FOR HOMEOSTASIS AND ESSENTIAL NUTRIENTS IT CANNOT SYNTHESIZE ON ITS OWN.
- An animal is in energy balance when the amount of energy that it takes in is equal to the amount it uses to sustain life and perform its functions.
- Animals must ingest essential amino acids, minerals, and vitamins, those that cannot be synthesized in their cells.
40.3 DIFFERENT ANIMALS HAVE DIFFERENT ADAPTATIONS FOR FEEDING.
- Aquatic animals take in food by suspension filter feeding, suction feeding, and active swimming.
- Vertebrates have specialized jaws and teeth for biting and mechanically processing food.
- Carnivorous animals have enlarged canines and slicing molars for catching prey and eating meat.
- Herbivorous animals have molars and premolars with surface ridges that enable them to grind plant matter.
40.4 THE DIGESTIVE TRACT IS A TUBELIKE STRUCTURE WITH REGIONS SPECIALIZED FOR DIFFERENT FUNCTIONS.
- The animal digestive tract consists of a series of compartments linked by a gut tube that allows for spatial and temporal control of digestion and absorption of nutrients.
- Most animals break down their food into small pieces in the mouth, making it easier to digest.
- Peristalsis mixes and moves food and digestion products through the gut by means of smooth muscle contractions.
- The stomach stores food and initiates protein digestion through secretions of hydrochloric acid and digestive enzymes, including pepsin.
- Carbohydrates and lipids are broken down in the duodenum of the vertebrate midgut, facilitated by the secretion of digestive enzymes, bile salts, and bicarbonate.
- Small intestine nutrient absorption is enhanced by an enlarged surface area of villi and smaller microvilli on the surface of cells.
- The colon of the hindgut reabsorbs water before waste products are eliminated as semisolid feces from the rectum through the anus.
- Herbivorous animals have specialized digestive chambers (rumen and cecum) that enable bacterial fermentation to break down plant cellulose.
Self-Assessment Question 1
Discuss how metabolic rate changes with levels of activity, body temperature regulation, and size.
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Model Answer:
When an animal is at rest, its basal metabolic rate produces enough energy to maintain the animal’s essential functions (circulation, respiration, etc). As activity level increases, metabolic rate also increases to meet the demand for additional energy. As the size of an animal increases, the energy requirement also increases so the metabolic rate for larger animals is greater than for smaller animals. Finally, those animals that regulate their body temperature by utilizing the heat produced from metabolism (endotherms) must have a higher metabolic rate than similarly sized animals that are ectotherms, which rely on external heat sources to balance their internal temperature.
Self-Assessment Question 2
Describe how ATP is produced for short and rapid activities versus long and sustained activities.
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Model Answer:
For short and rapid bursts of energy, animals use anaerobic glycolysis and fermentation to generate small amounts of ATP very quickly. For prolonged activities, oxygen is used to drive aerobic respiration to generate more ATP.
Self-Assessment Question 3
Explain how you would measure the metabolic rate of an animal.
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Model Answer:
The metabolic rate of an animal can be measured by determining its rate of oxygen consumption, which can be accomplished by placing the animal in an enclosed space where the amount of oxygen used by the animal can be monitored.
Self-Assessment Question 4
Explain why the world record speed for a 10-m race is faster than that for a marathon.
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Model Answer:
As runners increase their speed, their body must rely more heavily on anaerobic metabolism to generate ATP quickly to meet the energy needs of their muscle cells. However, the lactic acid produced by fermentation builds up in the blood and leads to fatigue, so in order to increase the distance a runner can cover, they must slow down in order to minimize lactic acid buildup and reduce fatigue.
Self-Assessment Question 5
Describe what happens in an endotherm and an ectotherm when outside temperature gets cold, and what happens when it gets hot.
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Model Answer:
Endotherms rely on the heat released during internal metabolic reactions to maintain thermal homeostasis. When the animal’s temperature becomes too high, it releases excess heat to the environment (e.g., by sweating), whereas if the animal’s temperature is too low, heat can be retained by constricting peripheral blood vessels, shivering or by increasing basal metabolic rate. Ectotherms, which use external heat sources in the environment to maintain their internal temperature, use behavioral changes to regulate their temperature. When the outside temperature is cold, ectotherms can increase their body temperature by increasing their exposure to heat sources (e.g. the sun) and moving to surfaces that radiate heat. When the outside temperature is hot, these animals decrease their activity levels, move into the shade and find cool surfaces to rest on in order to regulate their internal temperature.
Self-Assessment Question 6
Describe the order in which energy reserves are used in negative energy balance, such as starvation.
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Model Answer:
If the food supply is inadequate, animals first utilize glycogen and fat reserves to generate energy. But after prolonged periods of undernourishment, protein stores (found mostly in muscles) will be metabolized as a last resort to meet the energy needs of the animal.
Self-Assessment Question 7
Name four ways in which animals capture prey and, for each, name one organism that uses it.
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Model Answer:
Animals capture prey by suspension filter feeding (e.g., baleen whales); suction (e.g., aquatic salamanders); swimming to it (e.g., sharks); or, for carnivorous animals, using their sharp, specialized teeth to catch it (e.g., dogs).
Self-Assessment Question 8
Draw the path of food through the vertebrate digestive tract, naming and describing the major function of each part.
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Model Answer:
Self-Assessment Question 9
Name the principal sites of digestion of proteins, carbohydrates, and fats, and indicate the principal enzymes involved in breaking down each.
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Model Answer:
The main site of protein digestion is the stomach, where the enzyme pepsin works to break down proteins into smaller peptides. Proteins are further digested by trypsin in the small intestine. Digestion of carbohydrates begins in the mouth when food mixes with salivary amylase, which breaks down sugars and starches. Carbohydrates are further digested in the small intestine. Fats are primarily digested in the small intestine by lipases which break down fats into fatty acids and glycerol.
Self-Assessment Question 10
Compare and contrast foregut and hindgut fermentation.
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Model Answer:
Both foregut and hindgut fermenters utilize bacteria in their gut to help break down plant materials into nutrients that can be absorbed. Foregut fermenters maximize nutrient absorption by processing the plant material extensively within several chambers of the stomach (where the bacteria reside) before it reaches the small intestine. In contrast, hindgut fermenters pass the ingested material through the small intestine before it is fermented by the bacteria residing in the colon and cecum, reducing the ability of these animals to extract nutrients from plant material they ingest.