Topic 10: Nutrition & Digestion Ch. 41. Nutritional Requirements pp Essential Amino Acids p.939. Essential Fatty Acids p.

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1 Topic 10: Nutrition & Digestion Ch. 41 Nutritional Requirements pp Diets for animals must satisfy three needs : 1. Metabolic fuel Energy needed to do cellular work. E.g. glucose 2. Materials for biosynthesis Needed to make components of the organism. E.g. amino acids to make enzymes 3. Essential nutrients Materials that animals need but can not biosynthesize and so must come from their diet. E.g. Essential amino acids, essential fatty acids, vitamins and minerals Essential Amino Acids p.939 Proteins are essential to animal survival. Proteins are made up of combinations of 20 different amino acids. Eight amino acids can only be obtained from the diet (i.e. meat, eggs, cheese). Deficiencies restricts protein synthesis and limits use of other amino acids Essential Fatty Acids p. 939 Fatty acids are needed for making cellular membranes and steroids. Some can not be made by animals. E.g. linoleic acid is necessary for the production of phospholipids in humans. Vitamins pp Vitamins Essential organic molecules required in small amounts which often serve as co-enzymes. Co-enzyme A non-protein part of an enzyme which aids in its function. E.g. A Aids in the function of the eye. E.g. B 12 Aids in the production of red blood cells and nucleic acids. 1

2 Minerals pp.940 Mineral - Essential inorganic ions required in small amounts for proper functioning of cellular processes. E.g. Ca for maintenance of bone, functioning of muscles and nerves. E.g. P for maintenance of bone and ATP. E.g. Fe for component of hemoglobin. E.g. Na for nerve function, osmotic balance of cells. Feeding Mechanisms p.944 Animals have four main feeding mechanisms: 1. Suspension-feeders - Sift small food particles from the water. They have structures that filter water. E.g. Baleen whales Baleen Feeding Mechanisms 2. Substrate-feeders - Live in or on their food, eating their way through. Mouthparts are relatively simple. E.g. Earthworms eat soil containing organic material. 3. Fluid-feeders - Remove nutrient rich fluids from a living organism. They have mouthparts specialized for sucking. E.g. mosquitoes Feeding Mechanisms 4. Bulk-feeders - Eat relatively large pieces of food. E.g. grasshopper Adaptations for bulk feeding include diverse structures such as tentacles (Hydra), pincers, claws, jaws and teeth (mammals, grasshopper, fish). Fig Food Processing pp Food processing consists of four stages: 1. Ingestion Eating. 2. Digestion - Breaking food down into molecules small enough for the body to absorb. A) Intracellular digestion - Breakdown of food within the cell, usually in food vacuoles E.g. Sponges. Food Processing B) Extracellular digestion - Breakdown of food outside cells, within compartments that connect with the outside. This allows for digestion of larger pieces. E.g. Hydra. 3. Absorption - Uptake of monomers from the digestive compartment. 4. Elimination - Undigested material passes out of the digestive compartment. 2

3 Fig Phylum Porifera pp Intracellular digestion example. - Special cells called choanocytes line the interior of the sponge and beat flagella to keep the water moving. - These cells contain collars that trap food particles from the water. - Food is ingested by phagocytosis and the food vacuoles fuse with lysosomes to complete digestion. Fig Phylum Cnidaria pp Extracellular digestion example. Have a gastrovascular cavity (GVC) which has only one opening and digests food as well as transport materials. Tentacles capture prey and stuff into the GVC through its mouth. Cells within gastrodermis secrete digestive enzymes breaking the prey into tiny pieces and then absorb them. Undigested materials are eliminated through the single opening. Extracellular digestion allows it to eat larger prey than if it only used intracellular digestion. Fig Phylum Arthropoda pp The gut takes the form of an alimentary canal, which is a one way tube used for digestion. One way flow of food means that each section of the gut can be specialized which allows for greater efficiency in digestion. I.e. the front part of the gut can be specialized to take food in; another part specialized for digestion; another part for absorption; and another for elimination of undigested food. Phylum Arthropoda In arthropods the alimentary canal is specialized into three sections: 1. Foregut - Ingestion and storage of food. 2. Midgut Digestion and absorption. Gastric caeca - Outpocketings that increase surface area for digestion and absorption, found at the junction of the foregut and midgut. 3. Hindgut - Water absorption and waste storage. 3

4 Fig Phylum Chordata pp Fig Phylum Chordata In mammals food enters the mouth. Salivary glands begin the breakdown of carbohydrates. Food passes to the pharynx (shared by the digestive and respiratory systems) then down the esophagus to the stomach. The stomach stores food and continues digestion of proteins. Food is then passed to the small intestine where most digestion and absorption occurs. Phylum Chordata The liver makes bile that is held and concentrated by the gall baldder. Bile along with enzymes made by the pancreas are added to the food in the small intestine. The small intestine is long (6 m) to increase surface area for digestion and absorption. It also contains folds called villi and smaller finger-like projections called microvilli to further increase surface area. Fig Phylum Chordata The remainder of a meal travels to the large intestine (colon) where water and minerals are absorbed. Next the rectum absorbs more water and compacts the feces. Feces exits through the anus. 4

5 Digestion in Birds p.946 The digestive system of birds is similar to that of mammals with some modifications. Birds have a crop anterior to their stomachs. It is an enlarged part of the esophagus and is used to store food. Food is then passed to a stomach that secretes enzymes and acid for digestion. Then food enters the muscular gizzard, which often contains small stones to break food up. This compensates for lack of teeth. Food then enters the intestine like in mammals. Fig Digestive Enzymes p.950 Digestive enzymes break down polymers into monomers by hydrolysis (addition of water). There are four main groups: 1. Carbohydrases Break down carbohydrates into monosaccharides. It begins in the mouth and continues in the small intestine. 2. Proteases Break down proteins into amino acids. Begins in the stomach and continues in the small intestine. Digestive Enzymes 3. Nucleases Break down nucleic acids into nucleotides. Only in the small intestine. 4. Lipases Break down lipids into glycerol and fatty acids. Only in the small intestine. pp Herbivores Animals that eat plants. Carnivores Animals that eat other animals. Here we focus on mammalian herbivores and carnivores To breakdown tough plant material, herbivores need teeth specialized for grinding. Carnivores need teeth for cutting and tearing. Most of the nutrition from a herbivore s diet comes from breaking down cellulose by the enzyme cellulase. No animal can make cellulase. Herbivores therefore have a symbiotic relationship with bacteria that can breakdown cellulose. These bacteria are either kept in their stomach (ruminants) or in a pouch off where their small intestine (non-ruminant) meets the large intestine called a caecum. Fig

6 Ruminants have large stomachs were pant material is mixed with bacteria, regurgitated, chewed, and swallowed repeatedly. This breaks up the plants into small pieces so it can be easily broken down by bacteria. Eventually this mixture of plants and bacteria is passed to the small intestine, where sugar is absorbed. Fig In non-ruminants, the position of the caecum after the small intestine means that cellulose will be broken down and then eliminated before it is absorbed. This results in coprophageous behaviour in some mammals. Coprophage - Organism that eats feces. E.g. rabbits eat plants and produce green poop. This poop is then eaten and the broken down cellulose is absorbed by the small intestine. A second dark brown poop is then produced, which is not eaten. Carnivores don t eat plants so they lack a rumen and the caecum is reduced (e.g. our appendix). In addition, carnivores tend to have a shorter digestive tract because meat is easier to break down than plants. Fig