Structural Organisation in Animals - Exercises

Subject: Biology
Chapter: 7 - Structural Organisation in Animals

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Exercises

1. Draw a neat diagram of digestive system of frog. Answer: (Note: The diagram would include the mouth, buccal cavity, oesophagus, stomach, liver, gall bladder, pancreas, duodenum, ileum, rectum, and cloaca.) The alimentary canal of the frog is short, reflecting its carnivorous diet. Food is captured by the bilobed tongue and processed in the stomach with HCl and gastric juices to form chyme. Further digestion occurs in the duodenum with bile and pancreatic juices, and absorption takes place in the intestine via villi and microvilli.

2. Mention the function of the Ureters in frog. Answer: The function of the ureters in a frog varies between sexes:

• In Male Frogs: The ureters function as urinogenital ducts. They emerge from the kidneys and open into the cloaca, serving to transport both urine (excretory waste) and sperms (reproductive cells).
• In Female Frogs: The ureters only transport urine to the cloaca. The oviducts are separate from the ureters and open into the cloaca through distinct openings.

3. Define the terms: Aestivation and Hibernation. Answer:

• Aestivation (Summer Sleep): A period of dormancy during the peak of summer when frogs take shelter in deep burrows to protect themselves from extreme heat and desiccation.
• Hibernation (Winter Sleep): A period of dormancy during the peak of winter when frogs take shelter in deep burrows to protect themselves from extreme cold.

4. How does a frog respire in water? Answer: In water, a frog respires through its skin, a process known as cutaneous respiration. Dissolved oxygen in the water is exchanged directly through the highly vascularized, moist skin by the process of diffusion.

5. Distinguish between male and female frogs (Sexual Dimorphism). Answer: Male frogs can be distinguished from female frogs by the presence of:

1. Vocal Sacs: Sound-producing organs used for calling during the breeding season.
2. Copulatory Pads: Specialized pads on the first digit of the forelimbs that help the male grip the female during amplexus. These features are absent in female frogs.

6. What is a "Portal System"? Name the portal systems found in frogs. Answer: A portal system is a part of the circulatory system where blood from one set of capillaries passes through a large vein to another set of capillaries before returning to the heart. Frogs have two well-developed portal systems:

1. Hepatic Portal System: Connects the liver and the intestine.
2. Renal Portal System: Connects the kidneys and the lower parts of the body.

7. Describe the heart of a frog. Answer: The heart of a frog is a muscular structure located in the upper part of the body cavity and is enclosed by a membrane called the pericardium. It is three-chambered, consisting of two atria and one ventricle. A triangular structure called sinus venosus joins the right atrium, and the ventricle opens into a sac-like conus arteriosus on the ventral side.

8. Why is the alimentary canal of a frog short? Answer: The alimentary canal of a frog is short because frogs are carnivores. Since meat is easier to digest than plant matter (cellulose), a long intestine is not required for nutrient absorption.

9. What is the role of the "Cloaca" in frogs? Answer: The cloaca is a common chamber at the end of the digestive, excretory, and reproductive tracts. It serves as the single exit point for faecal matter, urine, and gametes (sperms or ova) to pass to the exterior.

10. How are frogs beneficial to mankind? Answer: Frogs are beneficial because:

1. They consume insects, thereby protecting crops from pests.
2. They are a vital link in the food chain and food web, maintaining ecological balance in the ecosystem.
3. In some regions, the muscular legs of frogs are used as a source of food.