1Food and FuelChapter 4Why Do Animals Need Food?• Energy needed to maintain homeostasis– Energy to drive otherwise unfavorable chemical reactions– Need to maintain order and complexity in a universe that moves towards disorder• Raw materials needed to assemble and maintain cellular structure and metabolic machinery– maintenance, growth, and reproductionSources of Energy• Ultimate sources–Sun– Inorganic chemicals• Energy must be in the form of high-energy organic molecules for animals to use it– producers • plants (capture light energy)• chemosynthetic bacteria (oxidize inorganic chemicals)– other consumers (animals, fungi, bacteria, protozoans)– detritusObtaining Food• Feeding - acquisition and ingestion of food• Digestion - breakdown of food into simple molecules and release of energy from those molecules• Nutrition - need for particular types of moleculesFeeding• Food absorption through body surfaces• Endocytosis• Suspension Feeding• Fluid Feeding• Seizing of Prey• Grazing• Symbiosis with ProducerAbsorption Through Body Surfaces• Protozoans, endoparasites, aquatic invertebrates• e.g. Tapeworms– surrounded by high-nutrient media– lack digestive tracts and digestive enzymes– absorb nutrients through the integument• e.g. soft-bodied aquatic invertebrates (polycheates, echinoderms, bivalves, etc.)– absorb amino acids from sea water via active transport2Endocytosis• Protozoa, radiolarians, alimentary canal cells– active engulfing of food particles by cells– formation of food vacuoles inside cells– merge with lysosomes to digest food.Suspension Feeding• Bivalves, sponges, small crustacea, fish, birds, mammals – Food items captured out of suspension– Often employ mucus to catch small particles• Enable “short” food chainsFluid Feeding• Piercing and Sucking – platyhelminths, nematodes, annelids, arthropods, humming birds• Cutting and licking– biting flies, cyclostomes, vampire bats, vampire finches• Nursing animals– mammals, some birds, some fishSeizing of Prey•Limbs– arthropods, birds, mammals• Mouth– insect mandibles, fangs, beaks, tongues, pointed teeth• Toxins (venom)– coelenterates, arachnids, insects, snakesGrazing• Scraping or cropping food (plants)• e.g. Gastropods – radula• e.g. Grazing vertebrates– bony plates, molars, or continuously growing teethSymbiotic Relationships• Form symbiotic relationship with producer– obtain needed energy substrates from the producer• e.g. photosynthetic bacteria or algae– sponges, coelentrates, platyhelminths, bivalves– produce sugars, glycerol, etc. for host• e.g. chemosynthetic bacteria– tubeworms from hydrothermal vents– located in organs called trophosomes– produce ATP via oxidation of H2S3Digestion• Food typically consists of protein, carbohydrates and fats– very large molecules– need to be broken down into subunits• amino acids, monosaccharides, fatty acids• Digestion – breakdown of large, complex molecules/structures into smaller, simpler onesDigestion• Mechanical digestion – breaking of large clumps of food into smaller ones– Teeth, gizzard, stomach• Chemical digestion– Breakdown of complex molecules into simpler moleculesDigestive (Alimentary) Systems• Internal cavity for intracellular digestion and absorption of nutrients• Tube-like canal in more advanced organismsDigestive System Types• Batch– Single opening– Food processed in batches• enters, is digested, then is expelled• Continuous flow, stirred-tank–Two openings– Food continuously enters and is mixed into a homogenous mass– Overflow continuously enters remainder of tract• Plug-flow– Bolus of food progressively digested as it moves through tube-like reactor– Composition changes with position in the tubeGeneralized Alimentary Canal• Headgut– Receiving ingested material– Oral cavity, pharynx• Foregut– Conduction, storage and digestion– Esophagus and stomach• Midgut– Chemical digestion and nutrient absorption– Small intestine• Hindgut– Water and ion absorption, waste storage, defecation– Large intestineHeadgut• Mouth and Pharynx– tongue • chemosensory organs (taste buds)• mechanical digestion and swallowing– teeth• mechanical digestion (mastication)– salivary glands • secrete saliva• moistens and lubricates food• contains enzymes4Foregut• Esophagus– conducts food from headgut to stomach– movement by peristalsis• Crop– Sac-like expansion for storage of food– Common in animals that feed infrequentlyForegut• Gizzard– Muscular organ for grinding• Stomach– Primary site of mechanical and chemical digestion• Secretes digestive enzymes and hydrochloric acid• Muscular activity mixes food– Storage of foodTypes of Stomachs• Gastric Ceca (insects, crustaceans)– Tube like outpouchings from foregut– Extracellular digestion and phagocytotic uptake of nutrientsTypes of Stomachs• Monogastric stomachs(most vertebrates)– Single, muscular tube or pouch– Epithelium secretes gastric juices (enzymes and HCl)Types of Stomachs• Digastric stomachs (ruminant mammals)– Multi-chambered stomachs• Rumen – large chamber for fermentation of food by microorganisms• Abomasum – secretes digestive fluidsMidgut• Small Intestine– Chemical digestion– Nutrient absorption• various membrane transport mechanisms– Long tube– Greatly enhanced surface area• Intestinal folds• Finger-like villi• Microvilli on cells5Hindgut• Large intestine and rectum– Absorption of water and ions– Storage of waste materials until defecation– Hindgut fermentation• Microorganisms break down cellulose and other materials• Storage in cecaDigestion of Proteins• Proteins are polymers of amino acids• Digestion of proteins involves hydrolysis of peptide bonds linking amino acidsDigestion of Proteins• Endopeptidases– break up proteins from the middle of the chain– e.g. pepsin -stomach• activated by low pH (inert form = pepsinogen)• cleaves proteins at specific amino acids sequences– between acidic amino acid and an aromatic one–e.g. trypsin - small intestine• produced by pancreas (trypsinogen)• activated by enterokinase (small intestine)• cleaves proteins at basic amino acidsDigestion of Proteins• Exopeptidases– break up proteins from ends of the proteins– e.g. carboxypeptidase (pancreas)• hydrolyzes peptide bonds from the