B17 instructions for 227. April 15, 2011

Transcription

1 Microviewer 227: Comparative Digestive Systems Introduction This set is one of a series of lessons examining comparative life function systems. In these sets, you will examine slides of different animals, and see the way each organism is adapted to perform its vital life functions. The function of digestive systems is to break down foods. Finally all nutrients, liquid or solid, are dissolved into individual molecules that pass through membranes. As you study this lesson, you will learn about various adaptations for digestion. The magnification given, for example the left side of slide 1 (200X) means that the microscope lenses were set at that power when the photograph was taken. To view a larger version of the image, simply click on the image. Use the back button of your browser to return to the text. Slide 1: Protozoan (Paramecium) left side Ingestion (200X) right side Digestion (100X) The left side of this slide shows a Paramecium ingesting food. Food is pushed into the mouth (M) by cilia around the oral groove (O) and mouth. The food passes into the gullet (G). As the food accumulates at the end of the gullet (2) it bulges into a droplet, breaks off, and forms a food vacuole (1). Thus, as seen on the right side of the slide, many vacuoles (V) form. This Paramecium was fed yeast cells stained orange. Some of the food vacuoles have turned blue! That is evidence that a digestive chemical was secreted into the vacuole. As the vacuoles move around the cell, food is digested. The dissolved nutrients diffuse through the food vacuole membranes (VM) and pass into the cytoplasm (C). Solid indigestible wastes are discharged at a posterior cytopyge (pronounced site oh pije) or anal pore (anal spot). A Paramecium is one celled, but as organisms become multicellular, a division of labour occurs. Cells become specialized. See slide 2. Slide 2: Hydra wet mount (11X) This slide shows a Hydra that swallowed a worm (W) and a water flea, or Daphnia (D). The body of a Hydra is made up of two cell layers. It is a tube with one opening, the hypostome (H) (pronounced high po stome). The inner layer has specialized cells. One group secretes digestive juices that break the food into particles. Most of the particles are then dissolved into nutrients. The nutrients are absorbed by all the inner cells as the fluid is whipped around the body cavity. The movement is caused by special "muscle" cells and by cells with flagella. Many of the particles are swallowed by cells with pseudopods, and digestion takes place inside the cells (see Paramecium). Thus a Hydra has extra cellular digestion in the body cavity and intracellular digestion inside cells. Indigestible solids are eliminated through the hypostome which serves both as a mouth and anus. Slide 3: Planaria wet mount (3X) Planaria is a soft aquatic flatworm. It extrudes its pharynx (P) and sucks in small particles of food through its mouth (M). The movements of the animal pushes food into a digestive tract with three main branches (labels 1, 2, and 3). Digestion, as in a Hydra, is extra cellular and intracellular. Nutrients are absorbed from the tiny branches around the body. Indigestible wastes are extruded through the mouth, which serves as a mouth and anus. Planaria like Hydra, is primitive. It has only one opening to its digestive system. One opening, a mouth anus, is inefficient. Matter has to move in two opposing directions. In higher animals, a one way digestive system evolved with a mouth at the head end, and an anus at the other end. This allows animals to feed continuously while foods are moved on, for digestion, and absorption, and elimination at the anus. Slide 4: Earthworm Longitudinal Section (7X) Earthworms have the basic body plan of a tube within a tube, with a head, mouth and anus. When an earthworm moves, it sucks food into its body with strong muscles on the pharynx (not visible on this slide). The food, organic material in the soil, enters the crop (C) for storage. The food then passes into the muscular gizzard (G) where it is ground by being churned with sand grains. The ground food passes into the intestine where gland cells secrete enzymes that digest all nutrients including cellulose. (*Note: An earthworm gets nourishment from cellulose which we eliminate as "roughage" or "fibre".) Absorptive surface is increased by a ridge, a typhlosole (pronounced tye flow sole), in the intestinal wall. Each day earthworms come to the surface and eliminate solid waste in the form of moist pellets of soil. They conserve their water by eliminating pellets with little water. 1

2 Slide 5: Grasshopper Mouth Parts (1X) A grasshopper is an insect that lives on land. Grasshoppers have special mouth parts that slice and grind plant material. Study the slide. The mandibles (M) slice chunks of food from leaves. The labium (1) (pronounced lay bee um) and the labrum (2) hold the food between the grinding parts, the mandibles and the maxillae (3). The palps (P) are sense organs used to taste food. Saliva moistens the ground up food as it passes into a storage crop. It then passes into a grinding gizzard. When it reaches the stomach, six pairs of gastric glands secrete juices that digest the food. The nutrients are then absorbed by the epithelial (pronounced ep uh theel ee ul) lining of the intestine. Wastes are stored in the rectum where water is absorbed. The solid waste is eliminated as moist pellets via the anus. Thus, a grasshopper conserves water. Digestive systems of insects are variable. Mouth parts of thousands of different insects are modified from the simple grasshopper type. Therefore, different insects are adapted for solid food or liquid food. Slide 6: Frog Intestine Cross Section (20X) When we consider larger animals, like fish, frogs and snakes, we discover similarities to lower animals. Since some larger animals swallow their prey, without chewing, they resemble a Hydra. Let us see how an animal like a frog has adaptations to handle the digestion of a whole insect or a smaller frog. Swallowed food is digested by enzymes in the stomach and intestines. Absorption rate is increased by folds (F) in the intestine. Epithelial (pronounced ep uh theel ee ul) cells (E) perform this function. A frog's food is concentrated animal protein. Therefore, the short intestine absorbs enough nourishment. The small amount of waste is passed into the rectum, the cloaca (pronounced klo ay kuh) and out through the anus. Frogs eliminate wastes that are wet. How can they survive if they do not conserve water? Slide 7: Villi Intestinal Glands left side Cross Section (50X) right side Cross Section (125X) In this discussion of digestion in humans, you will find words in parenthesis. Study them so that you can compare adaptations in humans with those present in lower animals. Humans grind food in their mouths (grasshopper). In the stomach the food is mixed with acid and enzymes and is churned into a semi liquid state. In the intestine, juices (grasshopper, frog) from the liver, pancreas, and intestinal glands (K) digest nutrients. The surface for absorption is enlarged by adaptations (frog). The human intestine is 23 feet long and coiled (frog). Remember, humans eat a great deal of plant food which is not concentrated nourishment (frog). The food must be in the intestine relatively longer than in intestines that receive only animal tissue! The intestine has wrinkles on its lining (frog). On the wrinkles the surface is increased by villi (V). On the villi are microvilli seen only with the electron microscope. Therefore, length, wrinkles, villi, and microvilli increase the absorptive surface. Semi liquid wastes now pass into the large intestine. Slide 8: Human Large Intestine Cross Section (400X) This shows tubular glands (T) in the lining of a human large intestine. The goblet cells (G) are epithelium cells. These cells secrete large quantities of mucus. This mucus lubricates the passage of solid wastes through the intestine. During digestion in a human, seven litres of water pour into the digestive system, per day, from food and secretions. The large intestine must absorb most of this water. Bacteria in the large intestine, act on undigested matter. The bacteria manufacture important amino acids and vitamins that are absorbed along with the water. Pellets of solid waste called feces (pronounced fee seez) pass into the rectum and are dehydrated. Finally it is eliminated via the anus. This slide shows epithelial cells (C). Epithelium tissues are vital in all digestive systems. Different types of epithelium are adapted for the following functions: protection, secretion and absorption. Diarrhea is a disease that reverses the water process in the large intestine. Large quantities of water are secreted into the intestine. If diarrhea persists too long, a person may suffer from loss of water. This is particularly dangerous in infants. Summary All foods must be digested, by enzymes, into small nutrient molecules that can be absorbed. Digestive systems must have large surfaces (relative to the size of the animal) for absorption. Land animals conserve water by absorbing water, from solid wastes, before they are eliminated. Epithelial tissue cells have many different functions in different parts of all digestive systems. They perform the functions of secretion, digestion, absorption, and protection. 2

3 3

4 B17 instructions for 227 4

5 5