Structural Organisation in Animals Class 11 Biology NCERT Solutions

Step-by-step solution

1. 1This is a drawing question, and since the specimen is the frog, the Rana tigrina or the Rana hexadactyla, the diagram should be a labelled dorsal or ventral view of the alimentary canal of the frog with the associated glands. Draw it as a simple tube with the glands attached, because what is examined is the course of the alimentary canal and the ducts that pour into it, and not the external body outline.
2. 2Begin the diagram at the mouth, and label the mouth and the buccal cavity, the latter being the wide chamber behind the mouth which receives the food and which also bears the teeth on its roof. A frog has a small tongue, which is used mainly for capture and not for swallowing, so it can be labelled as a small tongue at the floor of the buccal cavity.
3. 3Behind the buccal cavity label the pharynx, which is the common chamber that receives both the food and the air, since the glottis and the gullet open into it, and this is the point worth annotating because it explains how a frog can breathe while it feeds. Then label the gullet or the oesophagus, the short tube that carries the food from the pharynx to the stomach.
4. 4Then the stomach, which in the frog is a wide sac, and it is drawn wider than the intestine at the junction with the oesophagus, and the pyloric part leads into the small intestine. Label the small intestine or the ileum, which is the coiled part where digestion and absorption occur, and mark the duodenum as the part immediately after the stomach, since it is here that the ducts arrive.
5. 5Now the glands and their ducts, and these carry marks of their own. The liver is the large, dark, three-lobed gland and it is attached to the stomach, and the gall bladder is a small sac on the liver that stores the bile. Draw the bile duct from the gall bladder and the liver, and the pancreatic duct from the pancreas, and show both entering the duodenum at the same region, labelled as the hepatopancreatic or bile duct, since this single common entry point is the standard feature to be shown. The pancreas is the elongated gland lying between the stomach and the duodenum, and mark the mesentery attaching the intestine to the dorsal body wall, which is what holds the coils in place.
6. 6Finally label the end of the alimentary canal: the large intestine or the rectum, which is the short straight terminal part, and then the cloaca, the common chamber into which the digestive tract, the ureters and the reproductive ducts all open. Show the cloaca opening outside by the cloacal aperture, and note that the anus is absent in the frog, so the cloaca serves both functions.
7. 7The caption to write with the figure is that the alimentary canal of the frog shows the buccal cavity, the pharynx, the oesophagus, the stomach, the ileum and the rectum in that order, that the bile and the pancreatic juices reach the duodenum by a common hepatopancreatic duct, and that the canal ends in the cloaca, which receives the faeces, the urine and the gametes.

Step-by-step solution

1. 1The question asks for a single function, so the answer should be one sentence, and the marks come from getting the destination right and not mixing the ureters with the vasa efferentia.
2. 2The function of the ureters is to carry the urine from the kidneys to the cloaca. In the frog the pair of kidneys is opisthonephric, so the ureters arise from the kidneys and run backwards, and they open into the cloaca at its anterior end, and the urine is discharged into the cloaca and then passed out of the body with the faeces, so there is no separate urinary bladder and the cloaca serves for excretion as well as for digestion.
3. 3The two facts that usually earn the second mark, and that must be stated to be safe, are these. First, the ureters are not to be confused with the vasa efferentia, which are the ducts of the testis and carry the sperm, and which in the male open into the same cloaca, so both ducts reach the cloaca but only the ureters carry urine. Second, the frog has no urinary bladder, since the urino-genital duct and the cloaca receive the urine directly, and in the male the ureters join the vasa efferentia to form a common urino-genital duct which also opens into the cloaca.
4. 4So the complete statement to write is that the ureters carry the urine from the opisthonephric kidneys to the cloaca, from which it leaves the body along with the faeces, the frog having no urinary bladder; and they are distinct from the vasa efferentia of the testis, which carry the sperm and in the male join the ureters to form the urino-genital duct.