- Quiz: Why are deposit feeders important in marine environment?o Convert a nonusable form of food into a form that can be used by the rest of the food web, aerate the sediment via bioturbation, stabilize the sediments- Quiz: Main function of digestive systemo Break down food mechanically, break down food chemically, absorption of nutrients, expel undigested materials from the body- Quiz: Main benefit of a complete digestive systemo Regional specialization of the digestive processDigestion, Absorption, and Energy Budgets- Digestion: process of splitting up ingested food molecules into smaller chemical components that an animal is capable of distributing to the tissues of its body- Extracellular digestion: digestion in an extracellular body cavity, such as the lumen of the stomach or intestineso Vertebrates, arthropods- Intracellular digestion: food particles are taken into specialized cells prior to digestion and digestion occurs w/in the cello Sponges, cnidarians, flatworms- 3 types of stomachso Batch reactor (least efficient): food ingested first, then digested, then egested, one batch of food at a time (cnidarians, sharks) Cnidarians: polyps and medusa have gastrovascular cavity usedfor feeding (gastro) and circulation (vascular), only one openingo Complete digestive system: tube within a tube, unidirectional passage of food,  Advantages: specialized feeding structures (teeth), regional specialization (food breakdown, nutrient absorption, storage, elimination of indigestible) 2 body plans among those with complete digestive system: pseudocoelomate, (eu)coelomateo Continuous-flow stirred-tank reactor: food ingested continually, newlyingested food mixes with previously ingested food, efficiency varies strongly by configuration of stomach and with feeding speed (speed that food moves through stomach), crabs, food is sometimes not digested completely b/c they’re consistently eating food=low in efficiencyo Plug-flow reactor: food continually ingested, unidirectional flow of food through gut (no mixing), higher concentration of digestive enzymes towards the front so digestion fastest in anterior portion, very high digestion efficiency (sperm whales, humans), very high in efficiency- Variation in digestive systems: depends on evolutionary adaptations, structure varies strongly with diet, function generally the same- Vertebrates vs. arthropods vs. molluscso Vertebrates: headgut (mouth, tongue, pharynx), foregut (esophagus, stomach, crop/gizzard), midgut (small intestine), hindgut (large intestines) Peristalsis (muscle contractions of intestines moves food)o Arthropods: foregut (esophagus, cardiac stomach, pyloric stomach), midgut Contraction of muscles attached to stomach moves food (no muscles in stomach)o Molluscs: cilliary food movement, intracellular digestion  Cilliary tracts: bring food particles into each digestive diverticulum, help move things along Digestion happens inside the cells- Intracellular digestiono Food brought into cell by phagocytosis or pinocytosis Produces food vacuole (endosome)o Lysosome produced by endomembrane system Contains digestive enzymeso Two merge and digestion occurso Indigestible material expelled by exocytosis- Extracellular Digestiono Digestive enzymes releasedo Food particles broken downo Food particles engulfed and digested - Quiz: efficiency of digestion- Digestive system taskso Mechanical Breakdown Depends on type of organism (whale sharks=swallow food whole, polar bear=tears off chunks of food, crabs=shred food completely)o (Secretion of digestive enzymes) Digestive function of the stomach Mixes food…. Digestive enzymes are secreted at all different steps of this process Diet-specific enzyme activity- Physiological adaptations for specific foods- Consequences for trying to eat the wrong food (not enough digestions and nutrition)- Process of breaking down large molecules into smaller molecules that can be absorbed by cells (occurs by hydrolysis using the digestive enzymes)o Absorption Occurs in different locations for different animals, many in the intestine Occurs at molecular level, across membranes, so organisms maximize membrane SA- Villi and microvilli on intestine (brush border cells), break down bacteria, nutrient absorption (max SA for absorption)o Questions- Quiz Questionso Final step of process takes place in the cello Given this location, what is the benefit of increasing the SA with villi? Greater uptake by cells and enhanced endocytosis (same thing)o Other than increasing SA, what else can an organism alter in order to increase absorption of digested food? The time the food is in the stomach (increasing volume doesn’t increase efficiency)- Digestion takes time, the longer food is in the gut, the more gets digested=increases efficiency- Quiz: increasing temperature increases digestion rate of sharks- Environmental Moment: trash in the oceano Leatherback turtles classified as critically endangered worldwideo Wanted to see if plastic really is responsible for turtle mortality o Partial or complete obstruction of digestive tracto Plastic covers microvilli that absorb nutrients from foodo Many marine mammals eat trash- Elimination of Waste- Ambergriso Protective substance that protects whale intestine from sharp objects, like squid beakso Passes out intestine or vomitedo Washes onto beacho Collected and sold to make perfumes- Sperm Whales fight global warming with carbon-neutral feceso Have very highly concentrated amounts of Feo Huge phytoplankton blooms where sperm whales feed, more nutrients low chlorophyllo Phytoplankton sink to bottom and take carbon with them - Digestion facilitation with body heato Stomach warms to a max of 10-15 C above water temperature over a period of 12-2- hourso Heat comes from digestive process itself (metabolic heat) and from muscle contractiono Heat loss reduced by overlying gas bladder and by thick fatty muscle of the body wall, as well as by heat exchanges in the circulationo Speeds digestion, allowing animals to feed frequently when food is abundanto Also increases swimming speedso Cold blooded fish/sharks acting warm bloodedo Counter-current exchange mechanism, shunt warm blood to cold blood back into digestive system so the core of the fish is warmer=increases efficiency/speed of digestion- Energy Budgets- Food consumed and assimilated=provides energy that’s necessary for growth,