1. Bioenergetics and Digestion

2. 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

3. 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

4. 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

5. 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.

6. 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

7. 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

8. 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

9. 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
gastrovascular

10. 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

11. 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

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

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

14. 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)