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BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 21 Nutrition and Digestion From PowerPoint® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Getting Their Fill of Krill • Animals obtain and process nutrients in a variety of ways • Humpback whales eat small fishes and crustaceans called krill – This painting shows how the whales corral their food using “bubble nets” Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Humpback whales strain their food from seawater using large, brushlike plates called baleen – When they feed, they take in large amounts of seawater in which the fish and krill live – They must filter out the water in order to get a meal Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • In a typical day, a humpback whale’s digestive system will process as much as 2 tons of fish and krill – They store the excess energy they harvest in the form of blubber – In about 4 months, a humpback whale eats, digests, and stores as fat enough food for an entire year Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings OBTAINING AND PROCESSING FOOD 21.1 Animals ingest their food in a variety of ways • Animal diets are highly varied – Herbivores are plant-eaters – Carnivores are meat-eaters – Omnivores eat both plants and other animals Figure 21.1A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Most animals ingest chunks of food Figure 21.1E Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – Some animals are suspension feeders, consuming particles from water – Some are substrate feeders, living in or on their food source Figure 21.1B, C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – Some are fluid feeders, sucking liquids Figure 21.1D Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Flagellated choanocytes filter food from the water passing through the porous body Choanocyte in contact with an amoebocyte Pores WATER FLOW Skeletal fiber Central cavity Choanocyte Flagella Amoebocyte Figure 18.3C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Coiled thread Tentacle Capsule (nematocyst) “Trigger” Discharge of thread Prey CNIDOCYTE Figure 18.4D Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 18.6 Flatworms are the simplest bilateral animals • Phylum Platyhelminthes – Planarians have a simple nervous system consisting of a brain, sense organs, and branching nerves – As in cnidarians, the mouth of a flatworm is the only opening for its gastrovascular cavity Digestive tract (gastrovascular cavity) Mouth Eyespots Nervous tissue clusters Figure 18.6A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nerve cords Bilateral symmetry VISCERAL MASS Coelom Kidney Heart Reproductive organs Digestive tract MANTLE Shell Mantle cavity RADULA Radula Anus Gill Mouth FOOT Nerve cords Mouth Figure 18.9A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Most leeches are free-living carnivores, but some suck blood Figure 18.11C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – The water vascular system has suction-cup-like tube feet used for respiration and locomotion Anus Spines Stomach TUBE FEET CANALS Figure 18.14A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.2 Overview: Food processing occurs in four stages Small molecules Pieces of food Mechanical breakdown Nutrient molecules enter body Chemical breakdown (enzymatic hydrolysis) cells Undigested material Food 1 INGESTION 2 DIGESTION 3 ABSORPTION 4 ELIMINATION Figure 21.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.3 Digestion occurs in specialized compartments • Food is digested in compartments housing hydrolytic enzymes • Most animals have a specialized digestive tract Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Relatively simple animals have a sac with a single opening – This is called a gastrovascular cavity – Example: hydra Mouth Tentacle Flagella Hydrolytic enzymes Food particle Food (Daphnia, a water flea) Engulfment Gastro- of food vascular particle cavity Digestion in food vacuole Figure 21.3A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • In most animals, the digestive compartment is an alimentary canal – This is a tube running from mouth to anus – This tube is divided into specialized regions that process food sequentially Crop Esophagus Pharynx Gizzard Intestine Anus Mouth EARTHWORM Wall of intestine Interior of intestine Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 21.3B Esophagus Stomach Gizzard Anus Esophagus Stomach Gizzard Intestine Crop Gastric pouches Mouth GRASSHOPPER Intestine Mouth Crop Anus BIRD Figure 21.3B (cont) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings HUMAN DIGESTIVE SYSTEM 21.4 The human digestive system consists of an alimentary canal and accessory glands • When food is swallowed, it is moved through the alimentary canal by peristalsis – Peristalsis is rhythmic muscle contraction in the walls of the digestive tract – Ringlike sphincter muscles regulate the passage of food Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Oral cavity Mouth Tongue Salivary glands Pharynx Esophagus Liver Stomach Pyloric sphincter Gallbladder Pancreas Small intestine Stomach Small intestine Large intestine Rectum Anus Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 21.4 21.5 Digestion begins in the oral cavity • The teeth break up food • Saliva moistens it • Salivary enzymes begin the hydrolysis of starch • The tongue pushes the chewed food into the pharynx Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings TEETH Incisors Canine Premolars Molars Tongue “Wisdom” tooth Salivary glands Opening of a salivary gland duct Figure 21.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.6 The food and breathing passages both open into the pharynx • The swallowing reflex moves food from the pharynx into the esophagus – At the same time, food is kept out of the trachea Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Bolus of food Epiglottis up Tongue Pharynx Epiglottis down Larynx Trachea (windpipe) Esophageal sphincter Larynx down Larynx up Esophagus Esophagus Sphincter contracted Sphincter relaxed Sphincter contracted Figure 21.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.7 The esophagus squeezes food along to the stomach • Peristalsis in the esophagus moves food boluses into the stomach Circular muscle layer Bolus of food Longitudinal muscles contract, shortening passageway ahead of bolus Longitudinal muscle layer Relaxed muscles Circular muscles contract, constricting passageway and pushing bolus down Relaxed muscles Stomach Figure 21.7 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.8 The stomach stores food and breaks it down with acid and enzymes • The stomach mixes food with gastric juice – The gastric juice contains pepsin, which begins the hydrolysis of protein Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Interior surface of stomach Food particle Pits Gastric juice (mucus, HCI, and pepsinogen) 3 Epithelium Gastric juice Pepsinogen 2 Mucous HCI cells Pepsin (active enzyme) Pyloric sphincter STOMACH Gastric gland 1 Chief cells Pariental cells Figure 21.8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.9 Connection: Bacterial infections can cause ulcers • New evidence suggests that a spiral-shaped prokaryote causes gastric ulcers – Helicobacter pylori growth erodes protective mucus and damages the stomach lining Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.10 The small intestine is the major organ of chemical digestion and nutrient absorption • Alkaline pancreatic juice neutralizes stomach acids – Its enzymes digest polysaccharides, proteins, nucleic acids, and fats • Bile emulsifies fat droplets for attack by pancreatic enzymes – It is made in the liver and stored in the gall bladder Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Bile Liver Stomach Gallbladder Bile Duodenum of small intestine Acid chyme Pancreas Figure 21.10A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Enzymes from the walls of the small intestine complete the digestion of many nutrients Table 21.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The lining of the small intestine is folded and covered with tiny, fingerlike villi – Villi increase the absorptive surface • Nutrients pass through the epithelium of the villi and into the blood – The blood flows to the liver – The liver can store nutrients and convert them to other substances the body can use Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings INTERIOR OF INTESTINE Blood vessel with blood en route to the liver Nutrient absorption Nutrient absorption Microvilli Epithelial cells Lumen Muscle layers Circular folds Villi Blood capillaries Lymph vessel EPITHELIAL CELLS Nutrient absorption INTESTINAL WALL VILLI Figure 21.10B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.11 The large intestine reclaims water • Undigested material passes to the large intestine, or colon Large intestine (colon) End of small intestine – Water is absorbed – Feces are produced Small intestine Rectum Anus Nutrient flow Appendix Cecum Figure 21.11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings DIETS AND DIGESTIVE ADAPTATIONS 21.12 Adaptations of vertebrate digestive systems reflect diet • Herbivores and omnivores generally have longer alimentary canals than carnivores – Plant matter is more difficult to digest than meat – Nutrients in vegetation are less concentrated than in meat Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Small intestine Small intestine Stomach Cecum Colon (large intestine) CARNIVORE Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings HERBIVORE Figure 21.12A • Some mammals house cellulose-digesting microbes in the colon or cecum – The cecum is a pouch where the large and small intestines connect – Examples: horses and elephants • Other mammals re-ingest their feces to recover nutrients – Examples: rabbits and some rodents Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Ruminants such as cows process cellulose in a four-chambered stomach Intestine 3 Omasum 1 Rumen Esophagus Rumen 4 Abomasum 2 Reticulum Figure 21.12B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings NUTRITION 21.13 Overview: A healthful diet satisfies three needs • An animal’s diet provides – fuel for its activities – raw materials for making the body’s own molecules – essential nutrients that the body cannot make Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.14 Chemical energy powers the body • Once nutrients are inside cells, they can be oxidized by cellular metabolism to generate energy – This energy is in the form of ATP Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The energy a resting animal requires each day to stay alive is its basal metabolic rate (BMR) Figure 21.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • More energy is required for an active life – Excess energy is stored as glycogen or fat Table 21.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.15 Connection: Body fat and fad diets • The human body tends to store excess fat molecules instead of using them for fuel • A balanced diet includes adequate amounts of all nutrients Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Fad diets are often ineffective and can be harmful Table 21.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.16 Connection: Vegetarians must be sure to obtain all eight essential amino acids • The eight essential amino acids that adults require must be obtained from food – They are easily obtained from animal protein ESSENTIAL AMINO ACIDS Methionine Valine – They can also be obtained from the proper combination of plant foods (Histidine) Threonine Phenylalanine Corn Leucine Isoleucine Tryptophan Lysine Figure 21.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Beans and other legumes 21.17 Connection: A healthful diet includes 13 vitamins • Most of these vitamins function as coenzymes Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Table 21.17 (Water-soluble vitamins) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Table 21.17 (Fat-soluble vitamins) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.18 Connection: Essential minerals are required for many body functions • Minerals are elements other than carbon, hydrogen, oxygen, and nitrogen – They play a variety of roles in the body Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Table 21.18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.19 Connection: What do food labels tell us? • Food labels provide important nutritional information about packaged foods Figure 21.19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 21.20 Connection: Diet can influence cardiovascular disease and cancer • Choice of diet may reduce the risk of cardiovascular disease and cancer BEHAVIORAL RISK FACTORS Fatty diet UNAVOIDABLE RISK FACTORS High blood cholesterol High blood pressure Lack of exercise Aging Family history CARDIOVASCULAR DISEASE Smoking Being male Figure 21.20 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Table 21.20 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • A sound diet supplies – enough raw materials to make all the macromolecules we need – the proper amounts of prefabricated essential nutrients – enough kilocalories to satisfy our energy needs Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings