Comparative Digestive Systems Biology 11 G.Burgess 2006

Digestion The breakdown of nutrient materials into smaller absorbable particles. There are two main forms of digestion –Mechanical Digestion: breaking down of materials physically (ie. Chewing food) –Chemical Digestion: breaking down of materials by adding acids, bases and enzymes (ie. Salivary amylase breaks down starch into maltose in your mouth)

Unicellular organisms Most unicellular organisms do not require digestion because most of their nutrients are already small enough to be absorbed into the cell However, some, like the paramecium are able to bring in solid particles as food vacuoles. These use lysosomes (packed with hydrolytic enzymes) to breakdown the contents of the food vacuoles.

Plants Plants and other autotrophic organisms do not always require digestion. As always, there are exceptions Plants that cannot get nitrogen from the soil (ie. Venus fly trap or pitcher plant), get nitrogen by digesting insects in specialized leaf structures that secrete digestive enzymes.

Multicellular organisms Multicellular organisms have a variety of specialized digestive organs. Annelids (ie. earthworm) have a series of organs for digesting Mouth, pharynx, esophagus, crop, gizzard, intestine Orthopterans (grasshoppers) use the same type of digestive parts as the earthworm, however, they also have an organ called the gastric caeca. Amphibians (frog) also have much the same type of digestive organs, however, they do not have a crop or gizzard. Instead, they have a stomach. Each of these organisms also have specialized mouth parts so that they can eat their natural foods.

Earthworm Digestive System Pharynx Mouth Esophagus Crop Gizzard Intestine Anus

Grasshopper Digestive System MouthCrop EsophagusGizzard Intestine Anus

Frog Digestive System Esophagus Stomach Liver Galbladder Intestine Cloaca Anus

Human Digestive System Mouth Pharynx Esophagus Liver Gallbladder Stomach Small intestine Large intestine Rectum Anus