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Biology Lecture #2 - The Digestive System.docx

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Queen's University
BIOL 103
Virginia K Walker

Biology Lecture #2 – The Digestive System  Topics to be covered, fluid compartments, nutrition, digestion and absorption Fluid Compartments  Intracellular fluid  Extracellular fluid, which includes plasma and interstitial fluid  Movement occurs between compartments  Passive diffusion  Largely non-polar molecules such as lipids  Facilitated transport  Moves down concentration gradient, but cannot pass barrier by themselves, needs aid of transport protein  Active transport  Moves against concentration gradient via an unenergetically favourable way which is what makes it an active process  Osmosis – how water moves through membranes and is dependent on concentration of solute  Isotonic Solution – when concentration of solute inside is same as outside  Hypertonic Solution – lower concentration inside, fluid moves outside  Hypotonic Solution - higher concentration inside, fluid moves in Nutrition  Divided into two main categories  Autotrophs – self nutrition  Organisms that harvest energy from light or chemical energy (eg. Plants)  Heterotrophs – other nutrition  Organisms that must get their nutrients from the environment such as by eating other organisms  Nutrients – organic molecules  Carbohydrates  Proteins  Lipids  Vitamins  Nucleic acids  Inorganic nutrients (not found in body)  Minerals (such as zinc) Phases of the digestive process  Phases of digestion for an animal  Ingestion – where food is consumed (eg. Mouth)  Digestion – where nutrients are broken down (eg. Stomach)  Absorption – ions, water and small molecules (eg. Large and small intestines)  Elimination – waste excretion, anything that wasn’t absorbed (eg. Anus)  Extracellular Digestion –  Allows for cells to digest organisms larger than itself (such as the bacteria hydra)  Digestive enzymes are secreted into the gastrovascular cavity, and the resulting nutrients are absorbed by phagocytosis  Wastes are then excreted outside of the mouth  Intracellular Digestion  Phagocytosis – cellular process of engulfing solid particles by cell membrane  Membrane surrounds particle, forming a small vacuole which then pinches off  Lysosomes fuse with vacuole and empty their enzymes onto the ingested material  Organisms that are more complex have an alimentary canal with openings at both ends  Anterior End (ingestion) – oral cavity, salivary glands, pharynx, esophagus  Middle Portion (storage and initial digestion) – stomach, small intestine and associated organs such as liver, gallbladder and pancrease  Posterior Part (final digestion, absorption and elimination) – reminder of small intestine and the large intestine  Teeth – accessory structures  Teeth of a carnivore that consumes whole pray – long teeth to pull prey in and large jaw to consume prey  Terrestrial carnivore – canines and molars to mechanically break down flesh  Teeth of a terrestrial herbivore – mostly flat molars where they can grind down cellulose in plant material into fine pulp  Cropping teeth of a marine algae eater – grabbing food items to get into mouth  Terrestrial omnivore – balanced approach, some good for grinding whereas some others for ripping apart muscle  Oral Cavi
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