1Herbivores – such as cattle, gorillas, sea urchins, and snails, eat mainly autotrophs (plants and algae)and algae)Carnivores - such as lions, hawks, spiders, and whales, mostly eat other animalsOmnivores – ingest both plants and animalsSuspension Feeders – Extract food particles suspended in the surrounding waterSubstrate feeders – live in or on their food source eat their way out of itFluid feeders - obtain food by sucking nutrient-rich fluids from a living host, either a plant or an animalBulk feeders - ingest large pieces of food2Digestion in an animal break the polymers in food into monomers as shown in Figure 5•Protiensamino acids•Protiensamino acids•Carbohydrates  monosaccharides•Nucleic acids  nucleotides•Fats  glycerol and fatty acids3Diagram 1: The four main stages of food processing1.Ingestion –The act of eating 1.Ingestion –The act of eating 2. Digestion – the breaking down of food into molecules small enough for the body to absorb. Digestion typically occurs in two phases:i. Food may be mechanically broken into smaller pieces with chewing or tearing, breaking large chunks of food into smaller onesii. Digestion is the chemical breakdown process called hydrolysis. Catalyzed by specific enzymes, hydrolysis breaks chemical bonds in food molecules by adding water to them3. Absorption – the cells lining the digestive tract take up (absorb) the products of digestion – small molecules such as amino acids and simple sugars. From the digestive tract, these nutrients travel in the blood to body cells, where they are joined together to make the macromolecules of the cells or broken down further to provide energy4. Elimination - undigested material passes out of the digestive tract4The simplest of all digestive compartments are food vacuoles within a cellMost animals, however, uses other specialized compartments to break down larger foods•Gastrovascular cavity – a digestive tract compartment with a single opening, the mouth•Diagram 2:1. Gland cells lining the gastrovascular cavity secrete digestive enzymes that2. Break down the soft tissues of the prey3. Other cells engulf small food particles which4. Are broken down in food vacuoles5Most animals have an alimentary canal, a digestive tract with two openings, a mouth and an anus.an anus.Food entering the mouth usually passes into a pharynx, or throat. Depending on the species, the esophagus may channel food to a crop, gizzard, or a stomach. A crop is a pouch-like organ in which food is softened and stored. Stomachs and gizzards may also store food temporarily, but they are more muscular and they churn and grind the food. Chemical digestion and nutrient absorption occur mainly in the intestine. Undigested material are expelled through the anus.6Diagram 3: •Food enters the mouth, is chewed in the oral cavity, and then pushed by the •Food enters the mouth, is chewed in the oral cavity, and then pushed by the tongue into the pharynx. Once food is swallowed, muscles propel it through the alimentary canal by peristalsis, alternating waves of contraction and relaxation of the smooth muscles lining the canal. Sphincters regulate the passage of food into and out of the stomach. The final steps of digestion and nutrient absorption occur in the small intestine over a period of 5-6 hours. Undigested material moves slowly through the large intestine (taking 12-24 hours), and feces are stored in the rectum and then expelled through the anus.7Figure 7: Digestion begins in the oral cavity in the form of chemical and mechanical digestion. Digestion begins in the oral cavity in the form of chemical and mechanical digestion. The saliva excreted by the salivary glands contains the digestive enzyme, amylase, which begins to break down the starch in your food. This is a chemical digestion. Mechanical digestion occurs by the chewing and smashing of food performed by the teeth.As you anticipate your apple, cheese, and crackers, your salivary glands may start delivering saliva through ducts to the oral cavity even before you take a bite. This is a response to the sight or smell (or even thought) of food. The presence of food in the oral cavity continues to stimulate salivation. In a typical day, your salivary glands excrete more than a liter of saliva. You can see the duct opening and salivary glands in this figure.8Diagram 4: Most of the time the esophageal opening is closed off by a sphincter (blue arrows). Air enters the larynx, the voice box containing the vocal cords, and flows the arrows). Air enters the larynx, the voice box containing the vocal cords, and flows the through trachea to the lungs (black arrows). This situation changes when you start to swallow. The tongue pushes the bolus of food into the pharynx, triggering the swallowing reflex; the esophageal sphincter relaxes and allows the bolus to enter the esophagus (green arrow). At the same time, the larynx moves upward and tips the epiglottis (a flap of cartilage and fibrous connective tissue) down over the opening to the larynx. In this position, the epiglottis prevents food from passing into the trachea. You can see this motion in the bobbing of your larynx (also called your Adam’s apple) during your swallowing. After the bolus enters the esophagus, the larynx moves back downwards, the epiglottis tips up again, and the breath passage reopens (right side of the figure). The esophageal sphincter contracts above the bolus9The esophagus is a muscular tube that conveys food boluses from the pharynx to the stomach. The muscles at the very top of the esophagus are under voluntary control; thus, stomach. The muscles at the very top of the esophagus are under voluntary control; thus, the act of swallowing begins voluntarily. But then involuntary waves of contraction by smooth muscles in the rest of the esophagus take over. Figure 8 shows how waves of muscles contraction – peristalsis – squeeze a bolus toward the stomach. As food is swallowed, muscles above the bolus contract (blue arrows), pushing the bolus downwards. At the same time, muscles around the bolus relax, allowing the passageway to open. Muscles around the bolus relax, allowing the passageway to open. Muscles contractions continue in waves until the bolus enters the stomach.10The Heimlich maneuver was invented by Dr. Henry Heimlich in the 1970’s. It allows people with little medical training to step in and aid a choking victim. The maneuver is often with little