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Structural Organisation in Animals

Biology · Class 11NCERT pp. 79–842 sets × 25 questions

Key facts and formulas for Structural Organisation in Animals, three worked sample questions, and two full practice sets. Every question has a hint, a reason for every option and a step-by-step solution, with a calculator or animation where one helps. English and Hinglish.

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Key facts for this chapter

IdeaRule or fact
Levels of organisationCell → tissue → organ → organ system → organism. Four basic tissues: epithelial, connective, muscular, neural.
Frog digestive pathMouth → buccal cavity → pharynx → oesophagus → stomach → intestine → rectum → cloaca. Liver makes bile, gall bladder stores it.
Frog skin and restMoist skin absorbs water and breathes. Aestivation = summer rest, hibernation = winter rest. Frog is poikilothermic.
Frog digits and nervesFore limbs 4 digits, hind limbs 5 digits. 10 pairs of cranial nerves. Copulatory pad on first digit of fore limb in males.
Frog heart and bloodThree chambers plus sinus venosus; ventricle opens into conus arteriosus. RBCs are nucleated. Hepatic portal: liver and intestine. Renal portal: kidney and lower body.
Frog brain and sensesForebrain: olfactory lobes. Midbrain: optic lobes. Hindbrain: cerebellum. Eyes and internal ears are organs; others are cell clusters.
Epithelia and junctionsSquamous: vessel lining. Cuboidal brush border: PCT. Ciliated: bronchioles, Fallopian tubes. Tight: seal. Gap: transfer. Adhering: cement.
Connective and muscleAreolar and adipose: loose. Tendon and ligament: dense regular. Cartilage, bone, blood: specialised. Cardiac: intercalated discs. Smooth: involuntary, unstriated.
CockroachMalpighian tubules at midgut-hindgut junction. Foregut: mouth, pharynx, oesophagus, crop, gizzard. Uricotelic, open circulation, tracheae. Anal styles only in males. Tegmina from mesothorax.
Earthworm and human gutClitellum in segments 14–16. Typhlosole increases absorptive area. Dental formula 2123/2123 = 32 teeth. Paneth cells secrete lysozyme.

Three sample questions

Q1. Arrange in order of increasing complexity: (i) organ system (ii) tissue (iii) cell (iv) organ
  1. ii → iii → iv → i
  2. iii → iv → ii → i
  3. iii → ii → iv → i
  4. iii → ii → i → iv
Hint and solution

Hint: Start with the smallest living unit and keep combining: units form groups, groups form working parts, parts form systems.

  1. cell is the basic unit of life — Cells are the smallest structural and functional units, so (iii) is first.
  2. similar cells + matrix → tissue — A group of similar cells with intercellular substance forms a tissue (ii).
  3. tissues → organ → organ system — Different tissues form an organ (iv). Organs working together form an organ system (i).
  4. iii → ii → iv → i — The order is cell, tissue, organ, organ system. Option C.
Answer: C. Cell, tissue, organ, organ system.
Q2. Which statement about tissues is correct?
  1. A tissue is a group of similar cells plus intercellular substances doing a specific function
  2. Complex animals are built from eight basic tissues
  3. A tissue is formed when organ systems combine
  4. Cells of one tissue always do different jobs
Hint and solution

Hint: Recall the definition: what kind of cells, and what lies between them? Also recall how many basic types exist.

  1. Tissue = similar cells + matrix + one function — A tissue is a group of similar cells along with intercellular substances for a specific function.
  2. Basic tissues = 4 — Epithelial, connective, muscular and neural. So 'eight' is wrong.
  3. Cells → tissue → organ — Tissue is made of cells and itself builds organs, so options C and D fail.
  4. Answer: A — The only correct statement is the definition. Option A.
Answer: A. Tissue = similar cells + intercellular substance, one function; there are only four basic types.
Q3. Assertion (A): The heart is an organ that contains all four basic tissues. Reason (R): The heart is built only of muscular tissue.
  1. Both A and R are true and R is the correct explanation of A
  2. Both A and R are true but R is not the correct explanation of A
  3. A is false but R is true
  4. A is true but R is false
Hint and solution

Hint: Judge A and R separately. Does the heart only contain muscle, or also a lining, supporting tissue and nerves?

  1. Heart wall: epithelium, connective, cardiac muscle, nerves — The lining is epithelial, supporting layers are connective, the wall is cardiac muscle and nerves supply it. So A is true.
  2. R says 'only muscular tissue' — The heart has other tissues too, so R is false.
  3. A true, R false — This matches the combination 'A is true but R is false'. Option D.
Answer: D. A is true (epithelial, connective, muscular, neural are all present). R is false.

How to use this chapter

Read the NCERT pages first, then attempt Set 1 without the hints. Note every wrong answer in a mistake list, read the reason for each option, and retry Set 2 two days later. A topic is solid when you can say why each wrong option is wrong.

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