REVISION SUMMARY: Structural Organisation in Animals (Class 11 NCERT)
1. Chapter at a Glance
- In multicellular animals, a group of similar cells along with intercellular substances performs a specific function; such an organisation is called tissue.
- All complex animals consist of only four basic types of tissues organised in specific proportion and pattern to form organs; organs associate to form organ systems.
- Cells, tissues, organs and organ systems split up the work exhibiting division of labour and contribute to the survival of the body as a whole.
- Frog (Rana tigrina) belongs to class Amphibia of phylum Chordata; it is poikilotherm (cold-blooded) and shows camouflage (mimicry).
- Frog exhibits aestivation (summer sleep) and hibernation (winter sleep); skin is moist, mucus-covered and used for cutaneous respiration.
- Body is divisible into head and trunk (no neck or tail); sexual dimorphism present (vocal sacs and copulatory pads in males).
- Alimentary canal is short (carnivorous habit); respiration occurs by skin (aquatic), buccal cavity, skin and lungs (terrestrial).
- Closed circulatory system with 3-chambered heart; excretion is ureotelic; nervous system has 10 pairs of cranial nerves; fertilisation and development are external (tadpole larva).
2. Definitions and Laws
- Tissue: “a group of similar cells alongwith intercellular substances perform a specific function. Such an organisation is called tissue.”
- Morphology: “study of form or externally visible features.”
- Anatomy: “study of morphology of internal organs in the animals.”
- Poikilotherms (cold blooded): animals whose “body temperature varies with the temperature of the environment.”
- Mimicry (protective coloration): ability “to change the colour to hide them from their enemies.”
- Aestivation: “summer sleep.”
- Hibernation: “winter sleep.”
- Hepatic portal system: “Special venous connection between liver and intestine.”
- Renal portal system: “Special venous connection between the kidney and lower parts of the body.”
- Uriniferous tubules or nephrons: “structural and functional units” of kidney.
- Ureotelic animal: frog “excretes urea.”
(No laws or numerical formulae present in the chapter.)
3. Important Diagrams and Activities
- Figure 7.1 External features of frog — demonstrates head-trunk division, nostrils, eyes with nictitating membrane, tympanum, forelimbs (4 digits) and hind limbs (5 webbed digits).
- Figure 7.2 Diagrammatic representation of internal organs of frog showing complete digestive system — shows alimentary canal (mouth to cloaca), liver, gall bladder, pancreas and associated organs.
- Figure 7.3 Male reproductive system — shows testes, vasa efferentia, Bidder’s canal, urinogenital duct and cloaca.
- Figure 7.4 Female reproductive system — shows ovaries, oviducts opening separately into cloaca.
- Activity: Draw a neat diagram of digestive system of frog (Exercise 1) — required to label alimentary canal and digestive glands.
4. Common Misconceptions and Exam Pitfalls
- Students often write that frogs “drink water”; text states “The frog never drinks water but absorb it through the skin.”
- Confusion between mimicry and camouflage: NCERT uses “mimicry” for protective colour change.
- Mistaking heart chambers or circulation: frog has 3-chambered heart (2 atria + 1 ventricle) with closed type single circulation and hepatic & renal portal systems.
- Ureters in males act as urinogenital duct; in females ureters and oviducts open separately into cloaca.
- RBCs are nucleated in frogs (unlike mammals).
- External ear absent; only tympanum visible; ear functions for both hearing and equilibrium.
- Number of ova: 2500–3000 at a time; development involves tadpole metamorphosis.
5. Formula Sheet
No formulas, equations or numerical data are given in the chapter.