Chapter 13 of 23

57%

Tamil Nadu (TNBSE)Class 10 Science★ 3-6 marks in the TN SSLC Class 10 Science public exam through MCQs and short answers

Structural Organisation of Animals

Samacheer Kalvi (TN State Board) Class 10 Science — Biology Chapter 13, Structural Organisation of Animals. The body organisation of the leech and the rabbit — their digestive, respiratory, circulatory, nervous and reproductive systems — as examples of how animal bodies are organised into organ systems. Notes with comparisons, common mistakes, practice and quick revision.

⏱ 20 min readEasy difficulty✓ Free · NCERT-aligned

Worksheet

Podcast

Listen as a conversation

A teacher & a student talk through the chapter — in your language.

Mind Map

The chapter at a glance

Every concept and exam-favourite branch — revisable in 5 minutes.

…

Study Guide

Night-before notes

Key points, glossary and the questions most likely to show up.

…

VocabularyBuild your vocabularyLexiGenome mines the key words and schedules them with spaced repetition.Mine words →

By the end of this chapter you'll be able to…

1List the levels of organisation in animals
2Describe the body plan and feeding of the leech
3Outline the organ systems of the rabbit
4Explain hirudin and the rabbit's caecum
5Classify the leech and the rabbit

💡

Why this chapter matters

This chapter shows how animal bodies are organised into systems, using the leech and rabbit as models. It builds the comparative understanding needed for the physiology chapters that follow and offers easy recall marks in the TN SSLC exam.

Before you start — revise these

A 5-minute refresher here will save you 30 minutes of confusion below.

🔗

Class 9 Science — Animal tissues

Cells, tissues and organs.

Structural Organisation of Animals — Class 10 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 10 Science, Biology — Chapter 13. How animal bodies are organised, studied through the leech and the rabbit.

1. About this chapter

This chapter studies the body organisation of two animals — the leech (Hirudinaria), an invertebrate, and the rabbit (Oryctolagus), a mammal — looking at their digestive, respiratory, circulatory, nervous and reproductive systems.

2. Levels of organisation

Cells → tissues → organs → organ systems → organism. Different organ systems work together to carry out life processes.

3. The leech (an annelid)

Body: segmented, with anterior and posterior suckers for attachment and movement.
Feeding: a blood-sucking ectoparasite; its saliva contains hirudin, an anticoagulant that prevents blood clotting.
Has digestive, circulatory (blood sinuses), nervous and reproductive systems suited to its parasitic life.

4. The rabbit (a mammal)

A herbivorous mammal with well-developed organ systems:
- Digestive system: mouth, oesophagus, stomach, long intestine with a large caecum (for cellulose digestion).
- Respiratory system: lungs.
- Circulatory system: four-chambered heart, double circulation.
- Nervous system: brain, spinal cord and nerves.
- Reproductive system: separate sexes; internal fertilisation; gives birth to young.

5. Common mistakes

Mistake: Calling the leech an insect. Fix: The leech is an annelid (segmented worm), not an insect.
Mistake: Forgetting why the rabbit has a large caecum. Fix: It helps digest cellulose from its plant diet.
Mistake: Mixing up the levels of organisation. Fix: Cells → tissues → organs → organ systems → organism.

6. Practice (book-back style)

Write the levels of organisation in an animal body.
What is hirudin and why is it useful to the leech?
Why does the rabbit have a large caecum?
Name any three organ systems of the rabbit.
To which group does the leech belong?

7. Answer key

Cells → tissues → organs → organ systems → organism.
An anticoagulant in leech saliva; it prevents the host's blood from clotting while feeding.
To digest cellulose from its herbivorous (plant) diet.
Digestive, respiratory and circulatory systems (any three).
Annelida (segmented worms).

8. Quick revision

Biology Ch 13 · organisation through leech and rabbit.
Levels: cells → tissues → organs → organ systems → organism.
Leech: annelid, blood-sucker; saliva has hirudin (anticoagulant).
Rabbit: herbivorous mammal; large caecum digests cellulose; four-chambered heart.
Organ systems work together for life processes.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Levels of organisation

cells → tissues → organs → organ systems → organism

Increasing complexity.

Leech

annelid; saliva has hirudin (anticoagulant)

Blood-sucking ectoparasite.

Rabbit

herbivorous mammal; large caecum

Caecum digests cellulose.

⚠️

Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Calling the leech an insect

✓ The leech is an annelid (segmented worm), not an insect.

WATCH OUT

✗ Forgetting why the rabbit has a large caecum

✓ It helps digest cellulose from its plant diet.

WATCH OUT

✗ Mixing up the levels of organisation

✓ Cells → tissues → organs → organ systems → organism.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Multiple choice questions

MCQs on leech, rabbit and organ systems.

Questions

Short answer questions

Hirudin, caecum, organ systems and classification.

Questions

Diagram labelling

Label parts of the leech / rabbit systems.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· Recall

Write the levels of organisation in an animal body.

▶ Show solution

Cells → tissues → organs → organ systems → organism.

Q2MEDIUM· Concept

What is hirudin and why is it useful to the leech?

▶ Show solution

Hirudin is an anticoagulant in leech saliva that prevents the host's blood from clotting while the leech feeds.

Q3EASY· Concept

Why does the rabbit have a large caecum?

▶ Show solution

To help digest cellulose from its herbivorous (plant) diet.

Q4EASY· Recall

Name any three organ systems of the rabbit.

▶ Show solution

Digestive, respiratory and circulatory systems (any three).

Q5EASY· Recall

To which group does the leech belong?

▶ Show solution

Annelida (segmented worms).

Q6MEDIUM· Reasoning

Why are organ systems necessary in animals?

▶ Show solution

Different organ systems perform specialised functions and work together so the body can carry out all life processes efficiently.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Biology Chapter 13 of Samacheer Kalvi Class 10 Science.
•Levels: cells → tissues → organs → organ systems → organism.
•Leech: annelid, blood-sucker; saliva contains hirudin (anticoagulant).
•Rabbit: herbivorous mammal; large caecum digests cellulose.
•Rabbit has a four-chambered heart and double circulation.
•Organ systems cooperate for life processes.

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 3-6 marks across MCQ and short-answer questions

Question type	Marks each	Typical count	What it tests
MCQ	1	1-2	Classification and facts
Short Answer	2-3	1-2	Hirudin, caecum, organ systems
Diagram	2	0-1	Labelling body systems

Prep strategy

Memorise the levels of organisation
Note the special features of the leech (hirudin)
List the rabbit's organ systems
Remember the caecum's role in cellulose digestion

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Medicine

Hirudin from leeches is studied as a natural anticoagulant.

Comparative biology

Comparing animals reveals how body plans adapt to lifestyles.

Animal husbandry

Understanding rabbit digestion aids in proper feeding.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

State classification precisely (annelid, mammal)
Link each special feature to its function
Use the correct sequence for levels of organisation
Label diagrams where asked

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Compare the circulatory systems of the leech and the rabbit.
Explain the adaptations of the leech to ectoparasitism.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN SSLC Class 10 Public ExamHigh

Foundation / NTSE BiologyMedium

School unit testsHigh

AI helpers for this chapter

Generate more practice on the fly, or have the chapter explained at a different level.

⚡

Generate 5 more questions

Fresh MCQs + short-answer items based on this chapter, plus answer keys.

🧠

Explain at a different level

Re-explain the chapter at the level you actually want.

📝 My notes

Saved on this device — sign in to sync · how this works

0/600

Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

Its simple, segmented body with clear organ systems makes it a good model to understand invertebrate organisation and adaptations to a parasitic life.

It has continuously growing teeth for grinding plants and a large caecum housing microbes that help digest cellulose.

Practice more, ask doubts, find a tutor

Tamil Nadu (TNBSE) Class 10 mock tests

Tamil Nadu (TNBSE) Class 10 PYQs

Ask in Q&A

Science flashcards

Related chapters

Students who read Structural Organisation of Animals usually read these next.

Laws of Motion

Samacheer Kalvi (TN State Board) Class 10 Science — Physics Chapter 1, Laws of Motion. Newton's three laws, inertia, momentum, force and impulse, the law of conservation of linear momentum, and Newton's universal law of gravitation (g, mass vs weight, apparent weight). Notes with formulas, worked numericals, common mistakes, book-back style practice and quick revision.

Optics

Samacheer Kalvi (TN State Board) Class 10 Science — Physics Chapter 2, Optics. Refraction of light, refractive index and Snell's law, refraction through a glass slab, total internal reflection and its applications, lenses and the lens formula, magnification and power of a lens, the human eye and defects of vision. Notes with formulas, worked numericals, common mistakes, practice and quick revision.

Thermal Physics

Samacheer Kalvi (TN State Board) Class 10 Science — Physics Chapter 3, Thermal Physics. Heat and temperature, specific heat capacity and latent heat, thermal expansion of solids (linear, areal, cubical coefficients with β = 2α, γ = 3α), and the gas laws (Boyle, Charles, Avogadro). Notes with formulas, worked numericals, common mistakes, practice and quick revision.

Electricity

Samacheer Kalvi (TN State Board) Class 10 Science — Physics Chapter 4, Electricity. Electric current and potential difference, Ohm's law, resistance and resistivity, resistors in series and parallel, electric power and energy, and the heating effect of current (Joule's law). Notes with formulas, worked numericals, common mistakes, practice and quick revision.