Bioenergetics and Digestion

Bioenergetics of an animal – the big picture Food: fuel, carbon skeletons, essential nutrients ATP powers basal or resting metabolism, as well as activity, and temperature regulation Excess calories can be used for biosynthesis 85-90% of energy from food is lost as heat

Do plants have digestive systems? Sundew– Drosera capensis Venus fly trap– Dionaea muscipula Pitcher plant – Heliamphora nutans Carnivorous plants in marshlands have primitive digestive systems Habitats with N-poor soils Adaptation: occasionally feed on animals CH2O  Photosynthesis N+ minerals  insects, etc. Insect traps Glands in trap secrete digestive enzymes Nutrients absorbed by leaf Flypaper trap – Pinguicula gigantea Images from wikipedia.org

Evolution of digestion Different types depending on diet and lifestyle All must accomplish Ingestion Digestion Mechanical breakdown Chemical breakdown Absorption Elimination Digestion occurs in specialized compartments

Digestion in lower forms Incomplete vs. Complete Invertebrate vs. Vertebrate Simple Complex Unicellular vs. Multicellular Intracellular vs. Extracellular Autotroph vs. Heterotroph Evolutionary perspective is manifested by the various digestive processes occurring from the most simple to the most complex forms.

Intracellular digestion (1) (evolved in single-celled protists, retained in simplest animals) Protozoan Ex. Paramecium Endocytosis of food particle Fusion with lysosome Digestion by enzymes Expulsion of waste by exocytosis

Intracellular digestion (2) (evolved in single-celled protists, retained in simplest animals) Food obtained by filtering microorganisms from water Food is phagocytized by choanocytes (collar cells) and amebocytes Waste egested into water circulated in the sponge body SPONGES

Extracellular digestion (by fungi) Sedentary heterotrophs living in or on food supply Saprophytes/parasites No internal cavity  release digestive enzymes Food Enzymatic hydrolysis outside cells Absorption by cells across body surface Image from http://www.aber.ac.uk/fungi/graffeg/decomp/digestion-by-hypha.jpg

Extracellular digestion 1 Extracellular digestion 1. In animals with incomplete digestive systems (1) Cnidarians Ex. Hydra Extracellular digestion Cnidocytes and tentacles Mouth Gastrovascular cavity (GVC) Endocytized into food vacuoles Intracellular digestion Image from http://www.anselm.edu/homepage/jpitocch/genbio/digesthydra.jpg gastrovascular

Extracellular digestion 1 Extracellular digestion 1. In animals with incomplete digestive systems (2) Food phagocytized by intestinal cells Digestion complete within food vacuole Waste egested through mouth Pharynx Mouth Ingestion Branched intestine Secretion of digestive enzymes by intestinal cells Extracellular digestion Intracellular digestion Flatworms Ex. Planaria and tapeworms

Extracellular digestion 2 Extracellular digestion 2. In animals with complete digestive systems (1) Earthworms Food swallowed through muscular pharynx Esophagus Stomach: 1 – Crop, 2 - Gizzard Long, straight intestine Waste: anus 2o cm long with ~ 100 segments 1st – mouth Last – anus Eats its way through soil

Comparison of vertebrate digestive systems (More specialized compartments) Can you name the function of each specialized compartment of the GI tract?

Mammalian digestion (General plan) Organs of the GI tract Accessory digestive organs

Comparison of mammalian digestive systems (Diet plays an important role in the length and structure) Esophagus – no sphincter valve, two-way contraction of esophagus muscles Rumen and reticulum – low partition, intermix, main fermentation <synthesis of vitamins and proteins, breakdown of fibrous feeds> vat teeming with microorganisms (before exposing to gastric juices) Omasum – filter pump to sort food (absorption) Abomasum – true stomach (gastric juices)