Chapter 40 Summary
Core Concepts Summary
40.1 Metabolic rate depends on activity level, body size, and body temperature.
Animals acquire carbohydrates, fats, and protein from their diet for energy to fuel cellular processes and activities. page 852
Carbohydrates are broken down rapidly in the cytosol by anaerobic glycolysis to produce a small amount of ATP in the absence of oxygen. page 852
Carbohydrates and fats produce large amounts of ATP by aerobic respiration through the citric acid cycle and oxidative phosphorylation. page 852
An animal’s metabolic rate is its overall rate of energy use. page 854
Metabolic rate increases with increased physical activity. page 854
Larger animals consume more energy and have higher metabolic rates than smaller ones, but the increase in metabolic rate is less than proportional to mass. page 855
Endothermic animals maintain elevated body temperature by metabolic heat production and have high metabolic rates. page 855
Ectothermic animals depend on external heat sources to warm their bodies. They have lower metabolic rates compared to endothermic animals. page 855
40.2 An animal’s diet supplies the energy the animal 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. page 857
Animals must ingest essential amino acids, minerals, and vitamins, those that cannot be synthesized in their cells. page 857
40.3 Animals have different adaptations for feeding.
Aquatic animals take in food by suspension filter feeding, suction feeding, and active swimming. page 861
Vertebrates have specialized jaws and teeth for biting and mechanically processing food. page 862
Carnivorous animals have enlarged canines and slicing molars for catching prey and eating meat. page 863
Herbivorous animals have molars and premolars with surface ridges that enable them to grind plant matter. page 863
40.4 The digestive tract has regions specialized for different functions, including digestion, absorption, storage, and elimination.
The animal digestive tract is a long tubelike structure that allows different regions to have different functions. page 864
Peristalsis mixes and moves food through the gut by means of smooth muscle contraction and relaxation. page 864
Most animals break down their food into small pieces in the mouth, making it easier to digest. page 864
Initial chemical digestion begins in the mouth. page 865
The stomach stores food and initiates protein digestion through secretions of hydrochloric acid and digestive enzymes, including pepsin. page 865
Proteins, carbohydrates, and lipids are further broken down in the duodenum of the small intestine, facilitated by the secretion of digestive enzymes by the pancreas and of bile, bile salts, and bicarbonate by the liver. page 866
Nutrient absorption takes place in the small intestine. page 866
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Small intestine nutrient absorption is enhanced by an enlarged surface area of villi and smaller microvilli on the surface of cells. page 868
The large intestine absorbs water and inorganic molecules before waste products are eliminated as semisolid feces from the rectum through the anus. page 869
Herbivorous animals have specialized digestive chambers (the rumen and cecum) that enable bacterial fermentation to break down plant cellulose. page 870
Self-Assessment
Discuss how metabolic rate changes with levels of activity, body-
temperature regulation, and size. Self-Assessment 1 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.
Describe how ATP is produced for short and rapid activities versus long and sustained activities.
Self-Assessment 2 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.
Explain how you would measure the metabolic rate of an animal.
Self-Assessment 3 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.
Explain why the world record speed for a 10-
m race is faster than that for a marathon. Self-Assessment 4 Answer
Short bursts of activity are fueled by anaerobic respiration, which provides immediate energy but cannot be sustained. Longer physical activity requires aerobic respiration, which provides energy for sustained exercise and depends on the oxygen delivery to tissues.
Describe what happens in an endotherm and an ectotherm when outside temperature gets cold, and what happens when it gets hot.
Self-Assessment 5 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 increasing the 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.
Describe the order in which energy reserves are used in negative energy balance, such as starvation.
Self-Assessment 6 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.
Name four ways in which animals capture prey and, for each, name an organism that uses it.
Self-Assessment 7 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).
Draw the path of food through the vertebrate digestive tract, naming and describing the major function of each part.
Self-Assessment 8 Answer
Name the principal sites of digestion of proteins, carbohydrates, and fats, and indicate the principal enzymes involved in breaking down each.
Self-Assessment 9 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 by pancreatic amylase. Fats are primarily digested in the small intestine by pancreatic lipases that break down fats into fatty acids and glycerol.
Compare and contrast foregut and hindgut fermentation.
Self-Assessment 10 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 the plant material they ingest.