Class 11 Biology NCERT Notes- Chapter 7: Structural Organisation in Animals

Detailed Study Notes – Chapter 7: Structural Organisation in Animals (Class 11 Biology, Notes, PDFs, Quizzes, MCQs)

1. The Hierarchy of Animal Organisation

In complex multicellular animals, there is a distinct division of labour facilitated by a hierarchical organisation of the body. This organisation ensures efficient and coordinated activities for the survival of the organism.

• Cells: The basic structural and functional units of the body. In multicellular animals, billions of cells perform various functions.
• Tissues: A group of similar cells, along with intercellular substances, that perform a specific function. All complex animals consist of four basic tissue types: epithelial, connective, muscular, and neural.
• Organs: Structures formed when two or more basic tissue types are organised in a specific proportion and pattern. Examples include the stomach, lung, heart, and kidney. The heart, for instance, is composed of all four tissue types.
• Organ Systems: Formed when two or more organs interact physically and/or chemically to perform a common function. Examples include the digestive system and respiratory system.

This organisational complexity displays an evolutionary trend, where systems become more efficient and coordinated in more evolved organisms.

2. The Frog (Rana tigrina): An Overview

Frogs are vertebrates belonging to the Class Amphibia and Phylum Chordata. They are capable of living both on land and in freshwater. The most common species in India is Rana tigrina.

Key Characteristics and Adaptations:

• Thermoregulation: Frogs are poikilotherms (cold-blooded), meaning their body temperature varies with the surrounding environment.
• Protective Coloration (Mimicry): They can change their skin colour to hide from enemies, a process also known as camouflage.
• Dormancy: To survive extreme temperatures, frogs take shelter in deep burrows.
  • Aestivation (Summer Sleep): Occurs during peak summer to avoid extreme heat.
  • Hibernation (Winter Sleep): Occurs during peak winter to avoid extreme cold.

3. Morphology of the Frog (External Features)

Morphology refers to the study of an organism’s external form and features.

• Skin:
  • Smooth, slippery, and moist due to the presence of mucus.
  • The dorsal (back) side is typically olive green with dark, irregular spots.
  • The ventral (belly) side is a uniform pale yellow.
  • Frogs do not drink water but absorb it directly through their skin.
• Body Structure:
  • Divisible into a head and a trunk.
  • Neck and tail are absent.
  • A pair of nostrils is present above the mouth.
• Sensory Organs on Head:
  • Eyes: Bulged and covered by a nictitating membrane, which protects them underwater.
  • Ear (Tympanum): A membranous tympanum on either side of the eyes receives sound signals.
• Limbs:
  • Forelimbs: Shorter, with four digits.
  • Hind Limbs: Larger and more muscular, with five webbed digits. They are adapted for swimming, walking, leaping, and burrowing.
• Sexual Dimorphism:
  • Male Frogs can be distinguished by:
    • Sound-producing vocal sacs.
    • A copulatory pad on the first digit of the forelimbs.
  • These features are absent in female frogs.

4. Anatomy of the Frog (Internal Systems)

Anatomy is the study of the morphology of internal organs.

4.1. Digestive System

The alimentary canal is short, a characteristic of carnivorous animals.

• Path of Food: Mouth → Buccal Cavity → Pharynx → Oesophagus → Stomach → Intestine → Rectum → Cloaca.
• Mouth: Food is captured by a bilobed tongue.
• Stomach: Secretes HCl and gastric juices to begin digestion. The partially digested food is called chyme.
• Intestine:
  • The duodenum (first part) receives bile from the gall bladder and pancreatic juices from the pancreas via a common bile duct.
  • Bile emulsifies fats.
  • Pancreatic juices digest carbohydrates and proteins.
  • Final digestion and absorption occur in the intestine, facilitated by numerous finger-like folds called villi and microvilli.
• Cloaca: A common chamber that opens to the exterior and is used to pass faecal matter, urine, and gametes.
• Digestive Glands:
  • Liver: Secretes bile, which is stored in the gall bladder.
  • Pancreas: Produces pancreatic juice containing digestive enzymes.

4.2. Respiratory System

Frogs exhibit multiple modes of respiration.

• In Water: Cutaneous Respiration occurs through the moist skin, where dissolved oxygen is exchanged via diffusion.
• On Land:
  • Buccal Respiration: Through the buccal cavity.
  • Cutaneous Respiration: Through the skin.
  • Pulmonary Respiration: Through a pair of elongated, pink, sac-like lungs located in the thorax. Air enters through the nostrils into the buccal cavity and then into the lungs.
• During Aestivation/Hibernation: Gaseous exchange occurs exclusively through the skin.

4.3. Circulatory System

The frog has a well-developed, closed-type blood vascular system and a lymphatic system.

• Heart: A muscular, three-chambered organ (two atria, one ventricle) covered by a membrane called the pericardium.
  • The sinus venosus, a triangular structure, joins the right atrium and receives deoxygenated blood from the body via major veins (vena cava).
  • The ventricle pumps blood into a sac-like conus arteriosus.
• Blood Vessels: Arteries carry blood away from the heart, and veins carry blood toward the heart.
• Portal Systems:
  • Hepatic Portal System: A special venous connection between the liver and intestine.
  • Renal Portal System: A special venous connection between the kidney and lower parts of the body.
• Blood Composition:
  • Plasma: The fluid matrix.
  • Blood Cells:
    • RBCs (Erythrocytes): Are nucleated and contain the red pigment haemoglobin.
    • WBCs (Leucocytes)
    • Platelets
• Lymphatic System: Consists of lymph, lymph channels, and lymph nodes. Lymph lacks RBCs and some proteins found in blood.

4.4. Excretory System

This well-developed system eliminates nitrogenous wastes.

• Organs: A pair of compact, dark red, bean-like kidneys, ureters, a cloaca, and a urinary bladder.
• Kidneys: Located on either side of the vertebral column. Composed of structural and functional units called nephrons (or uriniferous tubules).
• Excretion: The frog is a ureotelic animal, meaning it excretes urea.
• Urinary Pathways:
  • Male Frogs: The two ureters emerge from the kidneys and act as a urinogenital duct, opening into the cloaca. This duct carries both urine and sperm.
  • Female Frogs: The ureters and oviducts open separately into the cloaca.
• Urinary Bladder: A thin-walled bladder ventral to the rectum also opens into the cloaca.

4.5. Nervous System and Endocrine System

Control and coordination are highly evolved.

• Endocrine System: Glands like the pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenals, and gonads secrete hormones for chemical coordination.
• Nervous System: Organised into three parts:
  1. Central Nervous System (CNS): Brain and spinal cord.
  2. Peripheral Nervous System (PNS): Cranial (10 pairs) and spinal nerves.
  3. Autonomic Nervous System (ANS): Sympathetic and parasympathetic nerves.
• Brain: Enclosed in a bony brain box (cranium) and divided into:
  • Fore-brain: Olfactory lobes, paired cerebral hemispheres, unpaired diencephalon.
  • Mid-brain: A pair of optic lobes.
  • Hind-brain: Cerebellum and medulla oblongata.
  • The medulla oblongata passes through the foramen magnum and continues as the spinal cord, which is enclosed in the vertebral column.

4.6. Sense Organs

• Touch: Sensory papillae.
• Taste: Taste buds.
• Smell: Nasal epithelium.
• Vision: A pair of simple, spherical eyes situated in orbits in the skull.
• Hearing: A tympanum (external ear is absent) and internal ears. The ear serves for both hearing and balancing (equilibrium).

4.7. Reproductive System

Frogs have well-organised male and female reproductive systems.

• Male Reproductive System:
  • A pair of yellowish, ovoid testes attached to the upper part of the kidneys by a double fold of peritoneum called mesorchium.
  • Vasa efferentia (10-12 tubes) arise from the testes, enter the kidneys, and open into Bidder’s canal.
  • The system communicates with the urinogenital duct, which opens into the cloaca.
• Female Reproductive System:
  • A pair of ovaries situated near the kidneys, with no functional connection.
  • A pair of oviducts arises from the ovaries and opens separately into the cloaca.
  • A mature female can lay 2500 to 3000 ova at a time.

5. Reproduction and Development

• Fertilisation: Is external and occurs in water.
• Development: Involves a larval stage.
  • The eggs hatch into a tadpole.
  • The tadpole undergoes metamorphosis to transform into an adult frog.

6. Ecological and Economic Importance

• Frogs are beneficial as they eat insects, thereby protecting crops.
• They are a crucial link in the food chain and food web, helping to maintain ecological balance.
• In some countries, the muscular legs of frogs are consumed as food by humans.

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Q&A

Section A: Short-Answer Questions (Answer in 2-3 sentences)

1. Define what a tissue is in the context of multicellular animals.
2. What does it mean for a frog to be a “poikilotherm”?
3. Explain the purpose of camouflage in frogs, and identify the other term used for this adaptation.
4. Distinguish between aestivation and hibernation.
5. Describe the texture and general appearance of a frog’s skin.
6. How do frogs obtain water since they do not drink it?
7. What is the function of the nictitating membrane in a frog’s eye?
8. List two distinct physical features that differentiate a male frog from a female frog.
9. Why is the alimentary canal in a frog relatively short?
10. Trace the path of partially digested food (chyme) from the stomach until it is expelled.
11. What are the two primary digestive glands in a frog, and what do they produce?
12. What is pulmonary respiration, and where do the associated organs reside in the frog’s body?
13. Explain cutaneous respiration and state when it is the primary method of gaseous exchange.
14. Describe the basic three-chambered structure of a frog’s heart.
15. What are the hepatic and renal portal systems found in frogs?
16. Describe a key feature of a frog’s red blood cells (RBCs).
17. What type of nitrogenous waste does a frog excrete, making it a “ureotelic” animal?
18. What is a urinogenital duct, and in which sex of the frog is it found?
19. Name the three main divisions of the frog’s brain.
20. Beyond hearing, what other important function does the ear serve in a frog?
21. What is the function of the mesorchium in the male reproductive system?
22. Approximately how many eggs can a mature female frog lay at once?
23. What type of fertilisation do frogs exhibit, and where does it take place?
24. What is the name of the larval stage in a frog’s life cycle, and what process must it undergo to become an adult?
25. State two reasons why frogs are considered beneficial for both mankind and the ecosystem.

Section B: Multiple-Choice Questions

1. The most common species of frog found in India is: a) Amphibia chordata b) Rana tigrina c) Bufo bufo d) Hyla versicolor
2. The ability of a frog to change its colour to hide from enemies is known as: a) Hibernation b) Aestivation c) Mimicry d) Metamorphosis
3. The body of a frog is divisible into which two parts? a) Head and neck b) Head and trunk c) Trunk and tail d) Head, neck, and trunk
4. Which structure in a frog’s head is a membranous organ that receives sound signals? a) Nictitating membrane b) Olfactory lobe c) Vocal sac d) Tympanum
5. The hind limbs of a frog are larger than the forelimbs and end in: a) Four webbed digits b) Five non-webbed digits c) Five webbed digits d) Four non-webbed digits
6. Partially digested food in the stomach, called chyme, passes next into the: a) Oesophagus b) Duodenum c) Rectum d) Cloaca
7. The liver secretes bile, which is stored in the: a) Pancreas b) Stomach c) Gall bladder d) Duodenum
8. The membrane covering the three-chambered heart of a frog is the: a) Mesorchium b) Peritoneum c) Pleura d) Pericardium
9. Frog red blood cells are distinct because they are: a) Anucleated and biconcave b) Nucleated and contain haemoglobin c) Lacking in haemoglobin d) The same as white blood cells
10. The structural and functional units of the kidney are called: a) Neurons b) Nephrons c) Villi d) Alveoli
11. The brain of a frog is enclosed in a bony structure called the: a) Vertebral column b) Pericardium c) Cranium d) Foramen magnum
12. The hind-brain of a frog consists of the cerebellum and the: a) Optic lobes b) Diencephalon c) Medulla oblongata d) Olfactory lobes
13. Which of the following is a feature found only in male frogs? a) Webbed hind feet b) A copulatory pad c) A nictitating membrane d) A tympanum
14. The vasa efferentia in the male frog emerge from the testes and open into the: a) Oviduct b) Urinogenital duct directly c) Cloaca d) Bidder’s canal
15. The common chamber used to pass faecal matter, urine, and sperm to the exterior is the: a) Rectum b) Urinary bladder c) Cloaca d) Ureter
16. Fertilisation in frogs is: a) Internal and occurs on land b) External and occurs in water c) Internal and occurs in water d) External and occurs on land
17. The transformation of a tadpole into an adult frog is called: a) Aestivation b) Hibernation c) Parthenogenesis d) Metamorphosis
18. Respiration by lungs is referred to as: a) Cutaneous respiration b) Buccal respiration c) Pulmonary respiration d) Aquatic respiration
19. A special venous connection between the liver and intestine is known as the: a) Renal portal system b) Hepatic portal system c) Pulmonary circuit d) Systemic circuit
20. All complex animals, including frogs, consist of how many basic types of tissues? a) One b) Two c) Four d) Six

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Essay Questions and Model Answers

1. Describe the hierarchy of structural organisation in a complex multicellular animal like a frog. In a complex multicellular animal, there is a clear division of labour supported by a hierarchical structure. The most basic level is the cell, with billions of individual cells performing various functions. A group of similar cells, along with intercellular substances that work together to perform a specific function, is called a tissue. All complex animals have four basic tissue types: epithelial, connective, muscular, and neural. These tissues are then organised in specific proportions and patterns to form organs, such as the heart, lungs, or kidneys. Finally, when two or more organs coordinate through physical or chemical interactions to carry out a common function, they form an organ system, such as the digestive or respiratory system. This entire organisation from cells to organ systems contributes to the survival of the organism as a whole.

2. Explain the various adaptations frogs have for survival, focusing on thermoregulation and predator avoidance. Frogs have several key adaptations for survival. For thermoregulation, they are poikilotherms, or cold-blooded animals, meaning their body temperature fluctuates with the environment. To cope with extreme temperatures, they undergo periods of dormancy in deep burrows: aestivation (summer sleep) to survive intense heat and hibernation (winter sleep) to survive the cold. For predator avoidance, frogs possess an ability called mimicry or camouflage, allowing them to change their skin colour to blend in with their surroundings, such as grass or dry land, making them difficult for enemies to spot.

3. Detail the external morphology of a frog (Rana tigrina). The body of a frog is divided into a head and a trunk, with no neck or tail. Its skin is smooth, slippery, and kept moist by mucus; the dorsal side is olive green with dark spots, while the ventral side is pale yellow. On the head, there is a mouth, a pair of nostrils, and a pair of bulged eyes protected by a nictitating membrane. On either side of the eyes is a membranous tympanum that functions as an ear. The frog has two pairs of limbs: shorter forelimbs with four digits and larger, more muscular hind limbs with five webbed digits, which aid in swimming, leaping, and burrowing.

4. Trace the path of food through the frog’s digestive system, explaining the role of each organ and gland involved. The digestive process begins when a frog captures prey with its bilobed tongue. The food enters the mouth, passes through the buccal cavity and pharynx into a short oesophagus, and then into the stomach. In the stomach, HCl and gastric juices partially digest the food, creating a substance called chyme. The chyme moves to the first part of the intestine, the duodenum, which receives bile from the liver (stored in the gall bladder) and pancreatic juices from the pancreas. Bile emulsifies fats, while pancreatic juices digest proteins and carbohydrates. Final digestion and absorption occur in the intestine, aided by villi and microvilli that increase surface area. Undigested solid waste then moves into the rectum and is passed out through the cloaca.

5. Describe the different modes of respiration in a frog and the conditions under which each is used. Frogs have three main modes of respiration. In water, they rely on cutaneous respiration, where dissolved oxygen is exchanged across the entire surface of their moist, highly vascularised skin via diffusion. On land, they can use buccal respiration (exchanging gases through the lining of the mouth), cutaneous respiration (through the skin), and pulmonary respiration. Pulmonary respiration involves a pair of pink, sac-like lungs; air is drawn in through the nostrils to the buccal cavity and then forced into the lungs. During periods of dormancy (aestivation and hibernation), gaseous exchange occurs exclusively through the skin.

6. Explain the structure and function of the frog’s circulatory system, including the heart, blood composition, and special portal systems. The frog has a closed-type circulatory system. The heart is a three-chambered organ with two atria and one ventricle, covered by a pericardium. The right atrium receives deoxygenated blood from the body, while the single ventricle pumps mixed blood out to the body. The blood consists of plasma, nucleated red blood cells containing haemoglobin, white blood cells, and platelets. The frog also possesses two special portal systems: the hepatic portal system, a venous connection between the intestine and liver, and the renal portal system, a connection between the lower body parts and the kidneys. The entire system is responsible for transporting nutrients, gases, and water throughout the body.

7. Describe the excretory system of a frog, highlighting the differences between male and female systems. The frog’s excretory system consists of a pair of dark red, bean-like kidneys, a pair of ureters, a urinary bladder, and a cloaca. Each kidney contains many functional units called nephrons. As a ureotelic animal, the frog excretes urea, which is separated from the blood in the kidneys. In male frogs, the ureters function as a urinogenital duct, carrying both urine from the kidneys and sperm from the testes to the cloaca. In female frogs, the ureters and the oviducts are separate, and both open independently into the cloaca.

8. Outline the organisation of the frog’s nervous system and its primary sense organs. The frog’s nervous system is highly evolved and organised into a central nervous system (brain and spinal cord), a peripheral nervous system (cranial and spinal nerves), and an autonomic nervous system. The brain, protected by the cranium, is divided into the fore-brain, mid-brain, and hind-brain. The frog possesses several types of sense organs: sensory papillae for touch, taste buds for taste, nasal epithelium for smell, a pair of simple eyes for vision, and a tympanum with internal ears for hearing and equilibrium (balance).

9. Compare and contrast the male and female reproductive systems in a frog. Both male and female frogs have paired gonads. The male system features a pair of yellowish, ovoid testes attached to the kidneys by a mesorchium. Sperm travels from the testes through the vasa efferentia into the kidney’s Bidder’s canal and then exits via the urinogenital duct into the cloaca. The female system has a pair of ovaries located near the kidneys but with no functional connection to them. A pair of oviducts carries ova from the ovaries and opens separately into the cloaca. A key difference is the pathway for gametes: males use a shared urinogenital duct for urine and sperm, while females have separate openings for the ureters and oviducts into the cloaca.

10. Discuss the life cycle of a frog, from fertilisation to adulthood, and explain its ecological importance. The frog’s life cycle begins with external fertilisation in water, where the male releases sperm over the eggs laid by the female. A mature female can lay 2500 to 3000 ova at a time. The fertilised eggs develop and hatch into a larval stage called a tadpole, which is fully aquatic, breathes through gills, and has a tail for swimming. The tadpole then undergoes a process of metamorphosis, during which it gradually develops legs, loses its tail, and develops lungs, transforming into an adult frog. Ecologically, frogs are vital as they consume insects, protecting crops, and serve as an important link in the food chain and food web, contributing to the ecosystem’s balance.

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Answer Keys (Q & A)

Answer Key for Short-Answer Questions

1. A tissue is a group of similar cells along with their intercellular substances that work together to perform a specific function in a multicellular organism.
2. A poikilotherm is a cold-blooded animal, meaning its body temperature is not constant and varies with the temperature of its environment.
3. Camouflage, also called mimicry, allows a frog to change its skin colour to blend in with its surroundings. This protective coloration helps it hide from predators.
4. Aestivation is summer sleep, a period of dormancy to protect the frog from extreme heat. Hibernation is winter sleep, a period of dormancy to protect it from extreme cold.
5. A frog’s skin is smooth, slippery, and always moist due to the presence of mucus. Its dorsal side is olive green with dark spots, and its ventral side is pale yellow.
6. Frogs absorb water directly through their highly vascularised skin. They do not drink water through their mouths.
7. The nictitating membrane is a transparent third eyelid that covers and protects the frog’s eyes when it is underwater.
8. Male frogs are distinguished by the presence of sound-producing vocal sacs and a copulatory pad on the first digit of their forelimbs, both of which are absent in females.
9. The frog’s alimentary canal is short because frogs are carnivores, and carnivorous diets are typically less complex and require a shorter intestine for digestion compared to herbivorous diets.
10. Chyme passes from the stomach into the intestine (starting with the duodenum), where digestion is completed and nutrients are absorbed. Undigested waste then moves into the rectum and is expelled through the cloaca.
11. The two primary digestive glands are the liver and the pancreas. The liver secretes bile (stored in the gall bladder), and the pancreas produces pancreatic juice containing digestive enzymes.
12. Pulmonary respiration is respiration using lungs. In the frog, the lungs are a pair of elongated, pink, sac-like structures located in the upper part of the trunk region (thorax).
13. Cutaneous respiration is the exchange of gases through the skin. It is the sole method of respiration for frogs in water and during aestivation and hibernation.
14. A frog’s heart has three chambers: two atria and one ventricle. The right atrium receives deoxygenated blood from the body, and this blood is then pumped by the single ventricle.
15. The hepatic portal system is a special venous connection between the liver and intestine. The renal portal system is a venous connection between the kidney and the lower parts of the body.
16. A key feature of a frog’s RBCs is that they are nucleated. They also contain the red-coloured pigment haemoglobin.
17. The frog excretes urea as its main nitrogenous waste, which is why it is classified as a ureotelic animal.
18. A urinogenital duct is a tube that carries both urine and gametes (sperm). It is found in the male frog, where the ureters serve this dual function.
19. The three main divisions of the frog’s brain are the fore-brain, mid-brain, and hind-brain.
20. Besides its primary function of hearing, the ear in a frog also serves as an organ of balancing (equilibrium).
21. The mesorchium is a double fold of peritoneum that adheres the testes to the upper part of the kidneys in the male frog.
22. A mature female frog can lay between 2,500 and 3,000 ova at a single time.
23. Frogs exhibit external fertilisation. This process takes place in water, where the female lays her eggs and the male releases sperm over them.
24. The larval stage is called a tadpole. The tadpole must undergo metamorphosis to develop into an adult frog.
25. Frogs are beneficial because they eat insects, which protects crops. They also help maintain ecological balance by serving as an important link in the food chain and food web.

Answer Key for Multiple-Choice Questions

1. b) Rana tigrina
2. c) Mimicry
3. b) Head and trunk
4. d) Tympanum
5. c) Five webbed digits
6. b) Duodenum
7. c) Gall bladder
8. d) Pericardium
9. b) Nucleated and contain haemoglobin
10. b) Nephrons
11. c) Cranium
12. c) Medulla oblongata
13. b) A copulatory pad
14. d) Bidder’s canal
15. c) Cloaca
16. b) External and occurs in water
17. d) Metamorphosis
18. c) Pulmonary respiration
19. b) Hepatic portal system
20. c) Four

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Glossary of Key Terms

• Aestivation: Summer sleep; a period of dormancy undertaken by frogs in deep burrows to protect them from extreme heat.
• Anatomy: The study of the morphology of internal organs in animals.
• Bidder’s canal: A canal within the kidney of a male frog into which the vasa efferentia open.
• Camouflage: The ability to change colour to hide from enemies.
• Chyme: Partially digested food that is passed from the stomach to the small intestine.
• Cloaca: A small, median chamber used to pass faecal matter, urine, and gametes (sperms or ova) to the exterior.
• Conus arteriosus: A sac-like structure into which the ventricle of the heart opens.
• Copulatory pad: A pad on the first digit of the forelimbs of male frogs, absent in females.
• Cranium: The bony structure or brain box that encloses the brain.
• Cutaneous respiration: Respiration through the skin.
• Haemoglobin: The red-coloured pigment contained in red blood cells.
• Hepatic portal system: A special venous connection between the liver and intestine.
• Hibernation: Winter sleep; a period of dormancy undertaken by frogs in deep burrows to protect them from extreme cold.
• Mesorchium: A double fold of peritoneum that adheres the testes to the upper part of the kidneys.
• Metamorphosis: The process of development where a larva (tadpole) transforms into an adult.
• Mimicry: Protective coloration used by frogs to hide from their enemies.
• Morphology: The study of form or externally visible features of an organism.
• Nephrons: Structural and functional units of the kidney, also called uriniferous tubules.
• Nictitating membrane: A membrane that covers and protects the eyes of a frog while in water.
• Organ: A structure formed by the organisation of two or more basic tissue types to perform a specific function (e.g., stomach, heart).
• Organ system: A group of two or more organs that perform a common function through physical and/or chemical interaction (e.g., digestive system).
• Pericardium: The membrane that covers the heart.
• Poikilotherms: Cold-blooded animals whose body temperature varies with the temperature of the environment.
• Pulmonary respiration: Respiration by means of lungs.
• Renal portal system: A special venous connection between the kidney and the lower parts of the body.
• Sinus venosus: A triangular structure that joins the right atrium of the heart and receives blood from the vena cava.
• Tadpole: The larval stage in the development of a frog.
• Tissue: A group of similar cells along with intercellular substances that perform a specific function.
• Tympanum: A membranous structure on either side of a frog’s eyes that receives sound signals; the eardrum.
• Ureotelic: An animal that excretes urea as its primary nitrogenous waste.
• Urinogenital duct: A duct in male frogs, formed by the ureters, which carries both urine and sperms to the cloaca.
• Vasa efferentia: 10-12 tubes that arise from the testes in the male frog.
• Villi and microvilli: Numerous finger-like folds in the inner wall of the intestine that absorb digested food.
• Vocal sacs: Sound-producing structures present in male frogs.