Frog and taod dissection


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Frog and taod dissection

  1. 1. Frog Dissection Pictures: Modern Biology, HoltBackground:As members of the class Amphibia, frogs may live some of their adultlives on land, but they must return to water to reproduce. Eggs are laidand fertilized in water. On the outside of the frog’s head are twoexternal nares, or nostrils; two tympani, or eardrums; and two eyes, eachof which has three lids. The third lid, called the nictitating membrane, istransparent. Inside the mouth are two internal nares, or openings into thenostrils; two vomerine teeth in the middle of the roof of the mouth; andtwo maxillary teeth at the sides of the mouth. Also inside the mouthbehind the tongue is the pharynx, or throat.In the pharynx, there are several openings: one into the esophagus, thetube into which food is swallowed; one into the glottis, through which airenters the larynx, or voice box; and two into the Eustachian tubes, whichconnect the pharynx to the ear. The digestive system consists of theorgans of the digestive tract, or food tube, and the digestive glands.From the esophagus, swallowed food moves into the stomach and theninto the small intestine. Bile is a digestive juice made by the liver andstored in the gallbladder. Bile flows into a tube called the common bileduct, into which pancreatic juice, a digestive juice from the pancreas,also flows. The contents of the common bile duct flow into the smallintestine, where most of the digestion and absorption of food into thebloodstream takes place. Indigestible materials pass through the large intestine and then into thecloaca, the common exit chamber of the digestive, excretory, andreproductive systems. The respiratory system consists of the nostrilsand the larynx, which opens into two lungs, hollow sacs with thin walls.
  2. 2. The walls of the lungs are filled with capillaries, which are microscopicblood vessels through which materials pass into and out of the blood. Thecirculatory system consists of the heart, blood vessels, and blood. Theheart has two receiving chambers, or atria, and one sending chamber, orventricle. Blood is carried to the heart in vessels called veins. Veins fromdifferent parts of the body enter the right and left atria. Blood fromboth atria goes into the ventricle and then is pumped into the arteries,which are blood vessels that carry blood away from the heart.The urinary system consists of the frog’s kidneys, ureters, bladder,and cloaca. The kidneys are organs that excrete urine. Connected to eachkidney is a ureter, a tube through which urine passes into the urinarybladder, a sac that stores urine until it passes out of the body throughthe cloaca. The organs of the male reproductive system are the testes,sperm ducts, and cloaca. Those of the female system are the ovaries,oviducts, uteri, and cloaca. The testes produce sperm, or male sex cells,which move through sperm ducts, tubes that carry sperm into the cloaca,from which the sperm move outside the body. The ovaries produce eggs,or female sex cells, which move through oviducts into the uteri, thenthrough the cloaca outside the body.The central nervous system of the frog consists of thebrain, which isenclosed in the skull, and the spinal cord, which is enclosed in thebackbone. Nerves branch out from the spinal cord. The frog’s skeletaland muscular systems consist of its framework of bones and joints, towhich nearly all the voluntary muscles of the body are attached.Voluntary muscles, which are those over which the frog has control, occurin pairs of flexors and extensors. When a flexor of a leg or other bodypart contracts, that part is bent. When the extensor of that body partcontracts, the part straightens.
  3. 3. Objectives:• Describethe appearance of various organs found in the frog.• Namethe organs that make up various systems of the frog.Purpose:In this lab, you will dissect a frog in order to observe the external andinternal structures of frog anatomy.Materials:• safety goggles, gloves, and a lab apron• forceps• preserved frog• dissecting pins (6–10)• dissecting tray and paper towels• plastic storage bag and twist tie• scissors• marking pen• dissecting needleProcedure: 1. Put on safety goggles, gloves, and a lab apron. 2. Place a frog on a dissection tray. To determine the frog’s sex, look at the hand digits, or fingers, on its forelegs. A male frog usually has thick pads on its "thumbs," which is one external difference between the sexes, as shown in the diagram below. Male frogs are also usually smaller than female frogs. Observe several frogs to see the difference between males and females.
  4. 4. 3. Use the diagram below to locate and identify the external features of the head. Find the mouth, external nares, tympani, eyes, and nictitating membranes.4. Turn the frog on its back and pin down the legs. Cut the hinges of the mouth and open it wide. Use the diagram below to locate and identify the structures inside the mouth. Use a probe to help find each part: the vomerine teeth, the maxillary teeth, the internal nares, the tongue, the openings to the Eustachian tubes, the esophagus, the pharynx, and the slit-like glottis.
  5. 5. 5. Look for the opening to the frog’s cloaca, located between the hind legs. Use forceps to lift the skin and use scissors to cut along the center of the body from the cloaca to the lip. Turn back the skin, cut toward the side at each leg, and pin the skin flat. The diagram above shows how to make these cuts6. Lift and cut through the muscles and breast bone to open up the body cavity. If your frog is a female, the abdominal cavity may be filled with dark-colored eggs. If so, remove the eggs on one side so you can see the organs underlying them.7. Use the diagram below to locate and identify the organs of the digestive system: esophagus, stomach, small intestine, large intestine, cloaca, liver, gallbladder, and pancreas.
  6. 6. 8. Again refer to the diagram below to identify the parts of the circulatory and respiratory systems that are in the chest cavity. Find the left atrium, right atrium, and ventricle of the heart. Find an artery attached to the heart and another artery near the backbone. Find a vein near one of the shoulders. Find the two lungs.
  7. 7. 9. Use a probe and scissors to lift and remove the intestines and liver. Use the diagram on the next page to identify the parts of the urinary and reproductive systems. Remove the peritonealmembrane, which is connective tissue that lies on top of the red kidneys. Observe the yellow fatbodiesthat are attached to the kidneys. Find the ureters; the urinary bladder; the testesandsperm ductsin themale;and theovaries, oviducts, and uteriin the female.10. Remove the kidneys and look for threadlike spinal nerves that extend from the spinal cord. Dissect a thigh, and trace one nerve into a leg muscle. Note the size and texture of the leg muscles.
  8. 8. 11. Dispose of your materials according to the directions from your teacher. 12. Clean up your work area and wash your hands before leaving the lab. Frog Dissection Worksheet 1. What do you think is the function of the nictitating membrane, and why? 2. A frog does not chew its food. What do the positions of its teeth suggest about how the frog uses them? 3. Trace the path of food through the digestive tract. 4. Trace the path of blood through the circulatory system, starting at the right atrium. 5. Trace the path of air through the respiratory system. 6. Trace the paths of sperm in a male and eggs in a female. 7. Trace the path of urine in both sexes. 8. Which parts of the frog’s nervous system can be observed in its abdominal cavity and hind leg? 9. Suppose in a living frog the spinal nerve extending to the leg muscle were cut. What ability would the frog lose? Why? 10. The abdominal cavity of a frog at the end of hibernation season would contain very small fat bodies or none at all. What is the function of the fat bodies? 11. Structures of an animal’s body that fit it for its environment are adaptations. How do the frog’s powerful hind legs help it to fit into a life both in water and on land? 12. During one mating of frogs, the female lays some 2,000 to 3,000 eggs in water as the male sheds millions of sperm over them. How do these large numbers relate to the frog’s fitness for life in water?Anatomy of a frog
  9. 9. ogs are amphibians, living both on land and in water. Their anatomy is very unique. Their bodies aresimilar to humans in that they have skin, bones, muscles, and organs. The body of a frog can be dividedinto a head, a short neck, and a trunk. The head contains the brain, mouth, eyes, ears and nose. Thefrogs head movement is limited due to the short, almost rigid neck. The trunk of a frog forms walls for asingle body cavity known as the coelom. The coelom holds all of the frogs internal organs. Frogs havethe same kinds of organs as humans and the same organ systems. For example, frogs have a long, stickytongue which they use to capture food. They also have teeth, which unfortunately are very weak andrather useless. Humans have tongues and teeth as well (and a mouth of course).If you closely examine the head of a frog, you will find the following: eye sockets, eyes, mouth, tongue,vomerine teeth, maxillary teeth, gullet teeth, external nostrils, internal nostrils, the glottis opening,eustachian tube openings, the tympanic membranes and the esophagus. The eyes, the mouth and thenostrils are all examples of a frogs external structures. In addition, a frogs external structures alsoinclude the webbed feet and the cloaca opening. The tympanic membranes or eardrums are exposed,but a frog does not have external ears. The internal structures of a frog include: the heart, the lungs, thekidneys, the stomach, the liver, the small intestine, the large intestine, the spleen, the pancreas, the gallbladder, the urinary bladder, the cloaca, the ureter, the oviducts, the testes, the ovaries and fat bodies.Again, the frog has organs that are similar to those of humans. For example, a frog has a brain, kidneys,lungs, eyes, a stomach, intestines and a heart. The one major difference between the anatomy of a frogand that of humans is that the anatomy of a frog is simpler than the anatomy of a man. Frogs dont haveribs or a diaphragm. Humans have both and a diaphragm (thoracic diaphragm) plays an importantfunction in breathing and respiration. Breathing takes oxygen in and carbon dioxide out of the body.Respiration is the process by which our cells are provided with oxygen for metabolism and carbondioxide, which is produced as a waste gas, is removed.A frog uses its tongue for grabbing prey. The vomarine and maxillary teeth are used for holding the prey.The internal nostrils are used by the frog for breathing. The tympanic membrane is the eardrum. It islocated behind the frogs eyes. The eustachian tubes equalize the pressure in the frogs inner ear. Theglottis is a tube, which leads to the lungs, while the esophagus is a tube which leads to the frogsstomach. The stomach helps the frog break down food and the liver also helps with digestion (it makesbile). Bile (also known as gall) is a fluid secreted by hepatocytes from the liver of most vertebrates(humans and frogs are vertebrates). Hepatocytes are cells present in the liver, and they initiate theformation and secretion of bile. In many species, bile is stored in the gall bladder between meals. Wheneating, the bile is discharged into the duodenum. Bile, therefore helps with digestion. The duodenum,which is the first and shortest part of the small intestine, is responsible for the breakdown of food in thesmall intestine. Most chemical digestion takes place in the duodenum. The small intestine absorbsnutrients from food. The large intestine absorbs water. It also collects waste. You can also think of thecloaca as storing waste, as this part of the frog collects eggs, sperm, urine and feces. The cloaca(opening) is also where sperm, eggs, urine, and feces exit the frogs body. The spleen stores blood, while
  10. 10. the kidneys filter the blood. The ureters carry urine from the kidneys to the bladder. The (urinary)bladder stores urine. The testes make sperm, while the ovaries makes eggs and the eggs travel throughthe oviducts.A frogs skin is always moist. It is made up of two layers, an outer epidermis and an inner dermis. Inaddition to protecting the frog, the skin also helps the frog breathe. A frog will take in oxygen from thewater through their skin. The oxygen in the water passes through their skin and goes directly to theirblood. Frogs also have a pair of lungs which allows them to breathe when on land. A frog has very fewbones. They make up the skeleton of the frog. The skull (head bone) is large and flat. The legs are longfor jumping. In addition to being specialized for jumping, the bones in their upper and hind legs are alsospecialized for leaping. The muscles move the skeleton of the frog. The muscles help the frog jump andswim.Frogs have other systems similar to humans that are a part of their bodies. For example, a frog has anervous system (all of the nerves and the spine), a circulatory system (the heart and blood goingthrough the body) and a digestive system (the food going through the mouth to the intestines). Theheart (which is part of the circulatory system) is three-chambered. There are two atria and one ventricle.There is a valve within the frogs heart known as the spiral valve. It directs the flow of blood to preventoxygenated and de-oxygenated blood from mixing. A frogs sense of hearing (which is part of thenervous system) is highly developed. Frogs can detect high-pitched sounds with their ears. In addition tobreathing oxygen through their skin when in water, frogs can also detect low-pitched sounds throughtheir skin. Another highly developed system is a frogs sense of sight and smell (which again are bothpart of the nervous system). Frogs detect predators and prey using their large eyes. Their eyes howeverhave poorly developed eyelids, which do not close. In order to close its eye, a frog has to draw the eyeinto its socket. There is a third eyelid, known as the nictitating membrane. It can be drawn over thepulled in eye (eyeball). Frogs also use their sense of smell to detect chemical signals. These signals helpthem to identify potential food.Now that we know the basics of frog anatomy, lets move onto the Activities and Extended Learning.ActivitiesPrint
  11. 11. Extended LearningWrite some of the things you have learned about frogs from the Study Guide. Your answer should be inshort essay format, 3-5 paragraphs. As you write the essay, answer the following questions in completesentences, using your own words:1. How are frogs adapted for aquatic life?2. How are frogs adapted for terrestrial life?3. If frogs have lungs, why do they also breathe through their skin?Get a book or search the web for the human body. See if you can find the similarities and differencesbetween a frogs anatomy and a humans anatomy. You should be able find some of the information inthe Study Guide. You can also use the links provided in the Resources.How are frogs and humans alike?How are frogs and humans different?Diffrences and similarities of frog and a toadBoth the frog and the toad are amphibians that live in both land and water. The word amphibian comesfrom the Greek words amphi and bios, which mean "double life". They both have long life spans of thirtyto forty years. The similarities between the two are many, right from the way their eggs look and hatchto the time taken for a tadpole to become a frog or a toad.Most of us confuse frogs and toads because they look very similar. If only we cared to take a closer look,we can see there are some differences between the two.
  12. 12. A midwife toad carrying eggsPicture of a leopard frogA midwife toad carrying eggsA Leopard FrogSome differencesCommon frogs are a light brownish green color, which helps them to stay camouflaged at the bottom ofa muddy pond, or in a pile of damp leaves. Toads that live in temperate regions are usually brown andolive in color, while those in the tropics are brighter in color.Frogs have smooth, moist skins, whilst toads are dry and warty-skinned. Secondly, frogs have longpowerful hind legs, which they use for swimming and jumping. Toads, on the other hand, have shorterlegs and can only crawl along.A third difference, you might not be able to see easily is that while most frogs have teeth, most toadshave none. Also toads lay lesser number of eggs than frogs. A toad lays between 4,000 and 12,000 eggsevery year, while a female bullfrog may lay anywhere between 18,000 and 20,000 in a year.A frog spawn (mass of eggs laid in still water) is quite easy to spot as it settles near the surface of thewater in large round clumps, while a toad spawn is laid in long strings.The two tadpoles:As we have mentioned earlier, similarities between the two, which are perhaps more in number thandissimilarities, begin right at the egg laying stage (except, of course, the number of eggs laid). The eggs
  13. 13. of both look like specks of dust floating on top of the water in a jelly-like substance. After one or twoweeks, tadpoles begin to emerge from the jelly-like spawn, which they feed on during their first fewdays before moving on to nibble at algae with their rasping teeth. At this stage, the tadpoles look morelike fish, with gills and a long swimming tail, than frog or toads. They breathe through the gills like a fish.It takes around twelve to fourteen weeks for tadpoles to develop further and the process of change isknown as metamorphosis’. At the end of this stage, the tadpoles drop their gills and tail and developlegs and lungs. The last stage, after which the tadpole becomes a frog or toad could take up to one year!