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The body structure, or anatomy, of the frog is very similar to the anatomy of man. Both man and the frog have the same kinds of organs and systems of organs. The frog's anatomy, however, is much simpler.

General Body Features
As in other higher vertebrates, the frog body may be divided into a ___________________
__ ______________.
The flat head contains the brain, mouth, eyes, ears, and nose. A short, almost rigid neck permits only limited head movement. The stubby trunk forms walls for a single body cavity, the coelom. Man's internal organs are housed in one of three distinct hollow cavities--the chest, the abdomen, and the pelvis. The human chest is separated from the abdomen by a powerful muscular partition, the diaphragm. There is no such partition in the frog's coelom. All the frog's internal organs--including the heart, the lungs, and all organs of digestion--are held in this single hollow space.

The Skeleton and Muscles
The frog's body is supported and protected by a bony framework called the skeleton. ____________, except for an expanded area that encases the ____________. Only _________ _____________ make up the frog's backbone, or vertebral column. The human backbone has 24 vertebrae. The frog ____________.The frog does not have a tail. Only a spikelike bone, the urostyle, remains as evidence that primitive frogs probably had tails. The ____________
is a downward extension of the vertebral column. The shoulders and front legs of the frog are somewhat similar to man's shoulders and arms. The frog has one __________
. Man has two forearm bones, the radius and the ulna. Both frog and man have one ___________________________. The hind legs of the frog are highly specialized for leaping. The single ________________________. Man has two lower leg bones, the tibia and the fibula. In man and in the frog, the ____________ is the single upper leg (thigh) bone. A third division of the frog's leg consists of two elongated anklebones, or tarsals. These are the ___________________________. The astragalus corresponds to the human talus. The calcaneusin the human skeleton is the heel bone. As in other vertebrates, the frog skeleton is moved by muscles. Skeleton-moving muscles are made of skeletal, or ___________________. Internal organs contain smooth muscle tissue.

The Circulatory System
The frog heart is the only organ contained within the coelom which has its own protective covering. This is the ____________. There are two upper chambers of the heart, ___________ _________________________. The frog heart, however, has only one lower chamber, _______ ____________ In man, the lower heart chamber is divided into two compartments, the right ventricle and the left ventricle. Oxygen-rich blood and oxygen-poor blood containing waste gases are present together in the frog ventricle at all times. The oxygenated and oxygen-poor bloods, however, do not mix. Such mixing is prevented by a unique arrangement of the frog's heart. Instead of "perching" on top of the ventricle, the right atrium dips downward into the ventricle. This causes oxygen-poor blood entering the right atrium to pass all the way down to the bottom of the ventricle. Meanwhile, oxygenated blood is received by the left atrium and enters the same single ventricle. The pool of oxygen-poor blood at the bottom of the ventricle holds up the oxygenated blood and prevents it from sinking to the bottom. When the oxygen-poor blood flows from the ventricle into vessels leading to the lungs, the oxygenated blood tries to "follow" it. The lung vessels, however, are filled with oxygen-poor blood, blocking the oxygen-laden blood and forcing oxygenated blood to detour into the arteries. These carry the oxygenated blood to the tissues. Frog blood has both a solid and a liquid portion. The liquid plasma carries solid elements such as red blood cells and white blood cells.

The Skin and Respiratory System

The frog is covered by a soft, thin, moist skin composed of two layers, _______________ _________________. The skin does not merely protect the frog but ____________________An extensive network of blood vessels runs throughout the frog's skin. Oxygen can pass through the membranous skin, thereby entering directly into the blood. When a frog submerges beneath the water, all its respiration takes place through the skin. Oxygen is obtained directly from the water. The frog does not breathe through its skin alone. Adult frogs have paired, simple, ___________ As in man, air enters the body through two nostrils, passes through the windpipe, and is received by the lungs. The mechanism of breathing, however, is different in the frog from that in man. In humans breathing is aided by the ribs, the diaphragm, and the chest muscles. The frog has no ribs or diaphragm, and its chest muscles are not involved in breathing. ___________ ____________________________________________________________. However, it may also breathe with its mouth closed. The floor of the mouth is lowered, causing the frog's throat to "puff out." When the nostrils open, air enters the enlarged mouth. Then, with nostrils closed, the air in the mouth is forced into the lungs by contraction of the floor of the mouth.
The Digestive and Excretory Systems
The frog's mouth is where digestion begins. It is equipped with feeble, practically ______ _______These are present only in the upper jaw. The frog's ____________ is highly specialized. Normally, the tip of its tongue is folded backward toward the throat. From this position the frog can flick it out rapidly to grasp any passing prey. To better hold this prey, the tongue is sticky. Food passes from the frog's mouth into the stomach by way of the __________. From the ____________ the food moves into the _____________________, where most of the digestion occurs. Large digestive glands, the liver and the pancreas, are attached to the digestive system by ducts. A gall bladder is also present. Liquid wastes from the kidneys travel by way of the ureters to the urinary bladder. Solid wastes from the ________________ pass into the ____________. Both liquid and solid waste material leave the body by way of the cloaca and the cloacal vent.

The Nervous System and Sense Organs
The frog has a __________________ nervous system. It consists of a ____________________ ____________ The important parts of the frog brain correspond to comparable parts in the human brain. The ____________ regulates automatic functions such as digestion and respiration. Body posture and muscular co-ordination are controlled by the ____________. The ____________ is very small in the frog. By comparison the human cerebrum is very large. In man the cerebrum is involved in many important life processes. Only _____________________ originate in the frog's brain. Man has 12. Similarly, the frog has only ______________________. Man has 30 pairs. Two simple holes make up the nostrils for the frog. There are complex valves but no long nasal passages as there are in man. The frog's sense of smell is registered by olfactory lobes. These make up the forward portion of the brain. The eye is crude. Its fixed lens cannot change its focus. Poorly developed eyelids do not move. To close its eye, the frog draws the organ into its socket.________________________________________________________ ____________________ There is no external ear. Both eardrums, or tympanic membranes, are exposed. There is only one bone in the frog's middle ear. The human middle ear contains three bones (ossicles). As in man, semicircular canals help to maintain body balance. Life Cycle of a Frog
True Love? When Frogs mate, the male frog tends to clasp the female underneath in an embrace called ____________ He literally climbs on her back, reaches his arms around her "waist", either just in front of the hind legs, just behind the front legs, or even around the head. Amplexus can last several days! Usually, it occurs in the water, though some species, like the bufos on the right mate on land or even in trees! While in some cases, complicated courting behavior occurs before mating, many species of frogs are known for attempting to mate with anything that moves which isn't small enough to eat!

Spawn (egg-mass)
While in the amplexus position, the male frog fertilizes the eggs as they get are laid. _________ ___________________________, whereas_______________________________________. Some frogs leave after this point, but others stick around to watch over the little ones. Some have very unusual ways of caring for their young.

Frogs and Toads tend to lay many many eggs because there are many hazards between fertalization and full grown frogness! Those eggs that die tend to turn white or opaque. The lucky ones that actually manage to hatch still start out on a journey of many perils. Life starts right as the central yolk splits in two. It then divides into four, then eight, etc.- until it looks a bit like a rasberry inside a jello cup. Soon, the embryo starts to look more and more like a tadpole, getting longer and moving about in it's egg. Usually, about 6-21 days (average!) after being fertilized, the egg will hatch. Most eggs are found in calm or static waters, to prevent getting too rumbled about in infancy! Some frogs, like the Coast foam-nest treefrog, actually mate in treebranches overlooking static bonds and streams. Their egg masses form large cocoon-like foamy masses. The foam sometimes cakes dry in the sun, protecting the inside moisture. When the rain comes along, after developement of 7 to 9 days, the foam drips down, dropping tiny tadpoles into the river or pond below.

Shortly _________________, the tadpole still feeds on the remaining yolk, which is actually in its gut! The tadpole at this point consists of ___________________________________________. It's really fragile at this point. They usually will stick themselves to floating weeds or grasses in the water using little sticky organs between its' mouth and belly area. Then, 7 to 10 days after the tadpole has hatched, it will begin to swim around and feed on algae. After about 4 weeks, the gills start getting grown over by skin, until they eventually disappear. The tadpoles get teeny tiny teeth which help them grate food turning it into soupy oxygenated particles. They have long coiled guts that help them digest as much nutrients from their meadger diets as possible. By the fourth week, tadpoles can actually be fairly social creatures. Some even interact and school like fish!

Tadpole with legs
After about_____________________________ start to sprout. The head becomes more distinct and the body elongates. By now the diet may grow to include larger items like dead insects and even plants. The arms will begin to bulge where they will eventually pop out, elbow first. After about 9 weeks, the tadpole looks more like a teeny frog with a really long tail. It is now well on it's way to being almost full grown!

Young Frog, or Froglet By ____________, the tadpole has only a teeny tail stub and looks like a __________________ _______________. Soon, it will leave the water, only to return again to laymore eggs and start the process all over again!

Frog :
By between ________________, depending on water and food supply, the frog has completed the ____________________. Some frogs that live in higher altitudes or in colder places might take a whole winter to go through the tadpole stage...others may have unique development stages that vary from your "traditional" tadpole-in-the-water type life cycle. Now these frogs will start the whole process again...finding mates and creating new froggies.