Chapter 7: Structural Organisation in Animals Long Questions | biology Class 11 CBSE

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Chapter 7: Structural Organisation in Animals Long Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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Describe the complete digestive system of the frog, including the pathway of food, the role of digestive glands and the process of absorption.

The digestive system consists of the alimentary canal and digestive glands. The canal is short because frogs are carnivores. Food is captured by the bilobed tongue and enters through the mouth into the buccal cavity, then passes to the pharynx, oesophagus, stomach, intestine, rectum and exits via the cloaca.
HCl and gastric juices from the stomach walls act on food to produce partially digested chyme, which is then passed to the duodenum (first part of the small intestine).
The duodenum receives bile from the gall bladder and pancreatic juice from the pancreas through a common bile duct. Bile emulsifies fats while pancreatic juice digests carbohydrates and proteins.
Final digestion occurs in the intestine. Numerous finger-like projections called villi and microvilli on the inner wall of the intestine absorb the digested food, greatly increasing the surface area for absorption.
The liver secretes bile stored in the gall bladder; the pancreas produces pancreatic juice containing digestive enzymes. Both glands play indispensable roles in chemical digestion.
Undigested solid waste passes into the rectum and exits through the cloaca. The digestive system thus efficiently processes food from ingestion to absorption and waste expulsion.

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Question 2

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Compare and contrast the different modes of respiration in frogs, explaining the structural basis and specific conditions under which each mode operates.

Frogs use two different methods of respiration depending on their environment: cutaneous (skin-based) and pulmonary (lung-based) respiration. On land, the buccal cavity and lungs also assist in respiration.
Cutaneous respiration occurs in water: the skin acts as the aquatic respiratory organ. Dissolved oxygen in water diffuses through the moist, vascularised skin. This requires the skin to remain constantly moist.
Pulmonary respiration occurs on land. Air enters through the nostrils into the buccal cavity and then travels to the lungs. The lungs are paired, elongated, pink, sac-like structures in the thorax.
The buccal cavity also functions as a supplementary respiratory surface on land, assisting gas exchange along with the skin and lungs.
During aestivation (summer sleep) and hibernation (winter sleep), frogs are sheltered in burrows and lungs are non-functional; cutaneous respiration through the skin becomes the exclusive mode of gaseous exchange.
Thus frogs have evolved multiple respiratory strategies that allow them to thrive in both aquatic and terrestrial environments, making them true amphibians adapted to a dual lifestyle.

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Question 3

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Describe the blood vascular and lymphatic systems of the frog, explaining the role of each component and any special circulatory pathways.

The vascular system of the frog is a well-developed, closed type consisting of the blood vascular system (heart, blood vessels and blood) and the lymphatic system (lymph, lymph channels and lymph nodes).
The heart is three-chambered with two atria and one ventricle, enclosed in the pericardium. The sinus venosus joins the right atrium and receives blood from the vena cava. The ventricle opens into the conus arteriosus.
Arteries carry blood from the heart to all body parts (arterial system), while veins return blood from body parts to the heart (venous system). The circulation of blood is achieved by the pumping action of the muscular heart.
Two special portal systems exist: the hepatic portal system (venous connection between liver and intestine) and the renal portal system (connection between kidney and lower body parts).
Blood is composed of plasma, nucleated RBCs (erythrocytes) containing haemoglobin, WBCs (leucocytes) and platelets. Blood transports nutrients, gases and water to respective sites during circulation.
Lymph differs from blood in that it lacks a few proteins and RBCs. The lymphatic system, with its lymph channels and nodes, works alongside the blood vascular system to maintain fluid balance and immune function.

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Question 4

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Analyse the nervous system of the frog, covering its organisation, the divisions of the brain and the types of nerves, and explain how the endocrine system complements neural control.

The control and coordination system in the frog is highly evolved and consists of both the neural system and endocrine glands working together to regulate body functions.
The nervous system is organised into three divisions: the central nervous system (CNS — brain and spinal cord), the peripheral nervous system (cranial and spinal nerves) and the autonomic nervous system (sympathetic and parasympathetic).
The brain is enclosed in a bony cranium and is divided into three regions: forebrain (olfactory lobes, paired cerebral hemispheres and unpaired diencephalon), midbrain (characterised by a pair of optic lobes) and 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. There are ten pairs of cranial nerves arising from the brain.
The endocrine system achieves chemical coordination through hormones secreted by glands such as the pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenals and gonads.
Neural control is rapid and specific, while endocrine control through hormones is slower but widespread. Together they ensure complete and efficient coordination of all physiological activities in the frog.

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Question 5

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Compare the male and female reproductive systems of the frog, highlighting structural differences and the process of reproduction from gamete formation to larval development.

Male reproductive organs consist of a pair of yellowish ovoid testes attached to the kidneys by the mesorchium (double fold of peritoneum). The testes produce sperms which travel through 10–12 vasa efferentia into the kidneys.
In males, the vasa efferentia enter the kidneys and open into Bidder's canal, which communicates with the urinogenital duct. This duct carries both urine and sperms and opens into the cloaca.
Female reproductive organs include a pair of ovaries situated near the kidneys with no functional connection to them. A pair of oviducts arising from the ovaries open separately into the cloaca.
A mature female lays 2500–3000 ova at a time. In females, the ureters and oviducts open separately into the cloaca, unlike males where a single urinogenital duct serves both reproductive and excretory functions.
Fertilisation is external and takes place in water. The fertilised eggs develop into a larval stage called the tadpole.
The tadpole undergoes metamorphosis to transform into the adult frog. This external fertilisation and larval development are characteristic amphibian features of Rana tigrina.

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Question 6

Long Form

Describe the excretory system of the frog in detail, explaining the structural organisation of the kidney, the path of urine and the role of the cloaca.

The excretory system of the frog consists of a pair of kidneys, ureters, urinary bladder and cloaca, and it eliminates nitrogenous wastes from the body.
The kidneys are compact, dark red, bean-shaped structures located posteriorly in the body cavity on both sides of the vertebral column. Each kidney is composed of several nephrons (uriniferous tubules), which are the structural and functional units.
Excretory wastes are carried by blood into the kidneys where they are separated. The frog excretes urea and is therefore classified as a ureotelic animal.
In male frogs, the ureters function as urinogenital ducts, carrying both urine and sperms, and open into the cloaca. In females, the ureters and oviducts open separately into the cloaca.
The thin-walled urinary bladder is present ventral to the rectum and also opens into the cloaca. It serves as a temporary storage for urine.
The cloaca is the common chamber that receives faecal matter from the rectum, urine from the urinary bladder and reproductive products. All these waste products and gametes exit through the cloacal aperture to the exterior.

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Question 7

Long Form

Explain the external morphological features of the frog systematically, relating each feature to its adaptive function.

The body of a frog is divisible into head and trunk; neck and tail are absent. The streamlined, compact body aids both terrestrial and aquatic locomotion.
The skin is smooth, slippery and moist due to mucus. The frog absorbs water directly through this vascularised skin, also using it for cutaneous respiration. The dorsal olive-green colour with dark spots provides camouflage.
Bulging eyes covered by a nictitating membrane provide wide-angle vision and protection in water. The tympanum on either side of the eyes receives sound signals, serving as an ear.
Forelimbs end in four digits and hind limbs in five digits. Hind limbs are larger and more muscular than forelimbs, suited for leaping, swimming and burrowing. Webbed digits on the feet aid in swimming.
Male frogs possess vocal sacs for sound production during mating calls and a copulatory pad on the first digit of the forelimb for gripping the female during mating. These features are absent in females.
A pair of nostrils above the mouth allows air entry during buccal respiration. The bilobed tongue can be projected outward rapidly to capture prey. All these features collectively make the frog well-adapted for its amphibious lifestyle.

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Question 8

Long Form

Discuss the concept of division of labour in multicellular animals, tracing the hierarchy from cell to organ system and illustrating with examples from the frog.

In unicellular organisms, all life functions are performed by a single cell. In multicellular animals, the same functions are distributed among groups of specialised cells, demonstrating division of labour.
The hierarchy of organisation is: cells → tissues → organs → organ systems. A tissue is a group of similar cells with intercellular substances performing a specific function. There are four basic tissue types in animals.
Tissues organise into organs; for example, the frog's heart contains all four tissue types. Organs collaborate in organ systems: the digestive system, respiratory system, circulatory system, etc.
In the frog, the digestive system handles nutrient absorption; the respiratory system (skin, lungs, buccal cavity) manages gas exchange; the circulatory system distributes materials; and the excretory system removes wastes.
This specialisation ensures greater efficiency: each organ system performs its function optimally without interfering with others, allowing the organism to maintain homeostasis and survive.
The complexity of organ systems in animals shows a discernible evolutionary trend. Division of labour at the cellular, tissue, organ and organ system levels is therefore the organisational principle that makes the survival of complex multicellular animals like frogs possible.

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Question 9

Long Form

Describe the sense organs of frogs in detail, explaining their structure, location and function, and comment on the level of organisation of each.

Frogs possess five types of sense organs corresponding to the five senses: touch (sensory papillae), taste (taste buds), smell (nasal epithelium), vision (eyes) and hearing/balance (tympanum with internal ears).
The eyes are a pair of spherical structures situated in orbits in the skull. They are simple eyes (possessing only one unit) and are covered by the nictitating membrane for protection in water.
The tympanum is the only visible external ear structure in frogs as there is no external ear. The ear serves as an organ of both hearing and balance (equilibrium). Internally, a well-organised ear structure processes sound.
Eyes and internal ears are well-organised, complex sensory structures capable of processing detailed sensory information, while the organs of touch, taste and smell are simpler cellular aggregations around nerve endings.
The nasal epithelium detects odour molecules, while taste buds on the tongue and buccal cavity detect chemical stimuli. Sensory papillae distributed over the body surface detect mechanical (touch) stimuli.
These sense organs together provide frogs with comprehensive information about their environment, enabling them to detect prey, avoid predators, navigate between water and land, and locate mates during breeding season.

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Question 10

Long Form

Analyse how the frog's anatomy reflects its dual adaptation to both terrestrial and aquatic life, providing evidence from at least four organ systems.

The frog is an amphibian adapted to life both on land and in water. Its anatomy provides multiple adaptations across organ systems that support this dual lifestyle.
In the respiratory system: frogs use cutaneous respiration (skin-based) in water, and pulmonary plus buccal respiration on land. The skin must remain moist at all times to enable gas diffusion in aquatic conditions.
In the circulatory system: the well-developed, closed circulatory system efficiently distributes oxygen obtained through both skin and lungs, supporting metabolic demands in both environments.
In the locomotory system: hind limbs are large and muscular with webbed digits for swimming in water, while all four limbs support walking, leaping and burrowing on land. The forelimbs provide stability on land.
In the excretory and reproductive systems: fertilisation is external in water, and tadpole development is aquatic. However, adult frogs can survive on land, excreting urea through their kidneys.
In the integumentary (skin) system: the moist, vascular skin facilitates water absorption (replacing the need to drink) and cutaneous respiration, while dorsal pigmentation provides camouflage in both terrestrial and aquatic habitats. These adaptations collectively make the frog a successful amphibian.

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Chapter 7: Structural Organisation in Animals | Long Questions

Describe the complete digestive system of the frog, including the pathway of food, the role of digestive glands and the process of absorption.

Compare and contrast the different modes of respiration in frogs, explaining the structural basis and specific conditions under which each mode operates.

Describe the blood vascular and lymphatic systems of the frog, explaining the role of each component and any special circulatory pathways.

Analyse the nervous system of the frog, covering its organisation, the divisions of the brain and the types of nerves, and explain how the endocrine system complements neural control.

Compare the male and female reproductive systems of the frog, highlighting structural differences and the process of reproduction from gamete formation to larval development.

Describe the excretory system of the frog in detail, explaining the structural organisation of the kidney, the path of urine and the role of the cloaca.

Explain the external morphological features of the frog systematically, relating each feature to its adaptive function.

Discuss the concept of division of labour in multicellular animals, tracing the hierarchy from cell to organ system and illustrating with examples from the frog.

Describe the sense organs of frogs in detail, explaining their structure, location and function, and comment on the level of organisation of each.

Analyse how the frog's anatomy reflects its dual adaptation to both terrestrial and aquatic life, providing evidence from at least four organ systems.

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