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Solve each Samacheer Kalvi exercise question on your own first, then compare your answer with the solutions below. Organ and Organ Systems covers the hierarchy of organisation and the major organ systems — understand how tissues form organs and organs form systems.
Key Concepts (Quick Recap)
Levels of Organisation
| Level | Definition | Example |
|---|
| Cell | Basic unit of life | Neuron, RBC, muscle cell |
| Tissue | Group of similar cells performing a common function | Epithelial, connective, muscular, nervous |
| Organ | Group of tissues working together for a specific function | Stomach, heart, kidney, brain |
| Organ System | Group of organs working together for a major life function | Digestive system, circulatory system |
| Organism | All organ systems working together as a complete living being | Human, frog, earthworm |
The 11 Organ Systems
| System | Major Organs | Primary Function |
|---|
| Integumentary | Skin, hair, nails, glands | Protection, temperature regulation, sensation |
| Skeletal | 206 bones, cartilage, ligaments | Support, protection, movement, mineral storage |
| Muscular | Skeletal, smooth, cardiac muscles | Movement, posture, heat production |
| Digestive | Mouth, oesophagus, stomach, intestines, liver, pancreas | Digestion and absorption of nutrients |
| Circulatory | Heart, blood vessels, blood | Transport of O₂, nutrients, hormones, waste |
| Respiratory | Nose, trachea, lungs | Gas exchange (O₂ in, CO₂ out) |
| Excretory | Kidneys, ureters, urinary bladder, urethra | Removal of metabolic waste (urea, salts, water) |
| Nervous | Brain, spinal cord, nerves | Coordination, impulse conduction, response to stimuli |
| Endocrine | Pituitary, thyroid, adrenal, pancreas, gonads | Chemical coordination via hormones |
| Reproductive | Testes/ovaries, associated ducts and glands | Production of gametes, continuation of species |
| Lymphatic/Immune | Lymph nodes, spleen, thymus, lymph vessels | Immunity, fluid balance, fat absorption |
Organ vs Organ System
| Feature | Organ | Organ System |
|---|
| Composition | Two or more tissues | Two or more organs |
| Example | Stomach (epithelial, muscular, connective, nervous tissues) | Digestive system (stomach, intestines, liver, pancreas) |
| Function | Specific function | Coordinated major life function |
Key Organs and Their Tissue Composition
| Organ | Tissues Present | Function |
|---|
| Heart | Cardiac muscle, epithelial, connective, nervous | Pump blood |
| Stomach | Smooth muscle, epithelial, connective, nervous | Digest food |
| Kidney | Epithelial, connective, nervous | Filter blood, form urine |
| Skin | Epithelial, connective, smooth muscle, nervous | Protection, sensation, temperature regulation |
| Liver | Epithelial, connective, nervous | Metabolism, detoxification, bile production |
Homeostasis
Homeostasis is the maintenance of a stable internal environment despite changes in the external environment. All organ systems contribute:
- Integumentary: Regulates body temperature (sweating, shivering)
- Respiratory: Maintains O₂ and CO₂ levels
- Excretory: Regulates water and electrolyte balance
- Endocrine: Hormonal regulation of blood sugar, calcium, metabolism
- Nervous: Rapid responses to stimuli
I. Choose the Best Answer (MCQs)
Q1. The correct sequence of levels of organisation is (a) Cell → Organ → Tissue → Organ system → Organism (b) Cell → Tissue → Organ → Organ system → Organism (c) Tissue → Cell → Organ → Organ system → Organism (d) Organism → Organ system → Organ → Tissue → Cell
Answer(b) Cell → Tissue → Organ → Organ system → Organism — The hierarchy goes from the simplest (cell) to the most complex (organism). Cells form tissues, tissues form organs, organs form organ systems, and organ systems form the organism.
Q2. The largest organ of the human body is (a) Liver (b) Brain (c) Skin (d) Heart
Answer(c) Skin — The skin is the largest organ of the human body, covering about 1.5-2 m² in adults. It is part of the integumentary system and provides protection, temperature regulation, and sensation.
Q3. The digestive system includes (a) Heart and blood vessels (b) Stomach, intestines, liver, pancreas (c) Kidneys and bladder (d) Brain and spinal cord
Answer(b) Stomach, intestines, liver, pancreas — The digestive system includes the mouth, oesophagus, stomach, small and large intestines, liver, and pancreas. It is responsible for digestion and absorption of food.
Q4. An organ is composed of (a) Only one type of tissue (b) Two or more types of tissues (c) Only cells (d) Only organ systems
Answer(b) Two or more types of tissues — An organ is a structure made of two or more types of tissues working together. For example, the stomach has smooth muscle (for churning), epithelial tissue (for lining), connective tissue (for support), and nervous tissue (for regulation).
Q5. The system responsible for removing metabolic waste is (a) Digestive system (b) Respiratory system (c) Excretory system (d) Reproductive system
Answer(c) Excretory system — The excretory system (kidneys, ureters, bladder, urethra) removes metabolic waste like urea, excess salts, and water from the blood. Note: The digestive system removes undigested waste (faeces), which is different from metabolic waste.
II. Fill in the Blanks
1. The basic unit of life is the cell. 2. A group of similar cells performing a common function is a tissue. 3. A group of tissues working together forms an organ. 4. A group of organs working together forms an organ system. 5. All organ systems working together form an organism. 6. The largest organ of the human body is the skin. 7. The circulatory system includes the heart, blood vessels, and blood. 8. The nervous system includes the brain, spinal cord, and nerves. 9. The excretory system includes the kidneys, ureters, urinary bladder, and urethra. 10. The endocrine system uses hormones for chemical coordination. 11. Homeostasis is the maintenance of a stable internal environment. 12. The skeletal system consists of 206 bones in an adult human.
III. True or False (with corrections for false statements)
Q1. An organ is made of only one type of tissue.
AnswerFalse — Correction: An organ is made of two or more types of tissues working together. For example, the stomach has epithelial, muscular, connective, and nervous tissues.
Q2. The skin is the largest organ of the human body.
AnswerTrue — The skin covers about 1.5-2 m² in adults and is part of the integumentary system. It provides protection, sensation, temperature regulation, and vitamin D synthesis.
Q3. The digestive system removes metabolic waste.
AnswerFalse — Correction: The digestive system removes undigested waste (faeces). The excretory system (kidneys) removes metabolic waste (urea, excess salts, water) from the blood.
Q4. All organs in an organ system work independently.
AnswerFalse — Correction: Organs in an organ system work together in a coordinated manner. For example, in the digestive system, the stomach digests food, the small intestine absorbs nutrients, and the liver produces bile — all working together for digestion.
Q5. Homeostasis is maintained by a single organ system.
AnswerFalse — Correction: Homeostasis is maintained by the coordinated action of multiple organ systems. The nervous system provides rapid responses, the endocrine system provides slow, sustained regulation, the excretory system maintains water balance, and the respiratory system maintains gas balance.
IV. Match the Following
| Column A | Column B | Answer |
|---|
| 1. Integumentary system | (a) Kidneys, ureters, bladder | (b) Skin, hair, nails |
| 2. Skeletal system | (b) Skin, hair, nails | (c) Bones, cartilage, ligaments |
| 3. Circulatory system | (c) Bones, cartilage | (d) Heart, blood vessels, blood |
| 4. Excretory system | (d) Heart, blood vessels | (a) Kidneys, ureters, bladder |
| 5. Nervous system | (e) Testes, ovaries | (f) Brain, spinal cord, nerves |
| 6. Reproductive system | (f) Brain, spinal cord | (e) Testes, ovaries, associated ducts |
V. Answer Briefly (2-mark questions)
Q1. Distinguish between an organ and an organ system.
Answer
| Feature | Organ | Organ System | |---|---|---| | Composition | Two or more tissues | Two or more organs | | Example | Stomach (epithelial + muscular + connective + nervous tissues) | Digestive system (stomach + intestines + liver + pancreas) | | Function | Performs a specific function | Performs a major life function | | Complexity | Less complex | More complex |
Q2. Name the organs of the digestive system and state its function.
Answer
Organs: Mouth, oesophagus, stomach, small intestine, large intestine, rectum, anus, liver, pancreas Function: The digestive system breaks down food into simpler substances (digestion) and absorbs nutrients into the blood (absorption).
Q3. What is homeostasis? Give one example.
Answer
Homeostasis is the maintenance of a stable internal environment despite changes in the external environment. Example: When body temperature rises, sweat glands produce sweat (evaporation cools the body). When body temperature falls, shivering generates heat. Both responses maintain a stable body temperature of ~37°C.
Q4. Name any four organ systems and their primary functions.
Answer
1. Circulatory system: Transport of O₂, nutrients, hormones, and waste (heart, blood vessels) 2. Respiratory system: Gas exchange — O₂ in, CO₂ out (lungs, trachea) 3. Nervous system: Coordination and response to stimuli (brain, spinal cord, nerves) 4. Excretory system: Removal of metabolic waste (kidneys, bladder)
VI. Answer in Detail (5-mark questions)
Q1. Explain the levels of organisation in animals with examples.
Answer
1. Cell Level (Basic Unit): The cell is the fundamental unit of life. Each cell performs specific functions. - Examples: Neuron (nerve cell — transmits impulses), RBC (carries oxygen), muscle cell (contracts) 2. Tissue Level: A group of similar cells performing a common function. - Examples: Epithelial tissue (protection, lining), muscular tissue (movement), nervous tissue (impulse conduction) 3. Organ Level: A group of different tissues working together for a specific function. - Examples: Heart (cardiac + epithelial + connective + nervous tissue → pumps blood), Stomach (smooth muscle + epithelial + connective + nervous tissue → digests food) 4. Organ System Level: A group of organs working together for a major life function. - Examples: Digestive system (mouth + oesophagus + stomach + intestines + liver + pancreas → digestion and absorption), Circulatory system (heart + arteries + veins + blood → transport) 5. Organism Level: All organ systems working together form a complete living organism. - Example: Human (all 11 organ systems coordinated → living being)
Q2. Describe the organ systems of the human body with their major organs and functions.
Answer
1. Integumentary System: Organs: Skin, hair, nails, sweat glands, sebaceous glands Function: Protection from injury and infection, temperature regulation, sensation, vitamin D synthesis 2. Skeletal System: Organs: 206 bones, cartilage, ligaments, joints Function: Support, protection (skull protects brain, rib cage protects heart and lungs), movement (attachment for muscles), mineral storage (calcium, phosphorus), blood cell formation (red marrow) 3. Muscular System: Organs: Skeletal muscles, smooth muscles, cardiac muscle Function: Movement, posture maintenance, heat production, organ function (peristalsis, heartbeat) 4. Digestive System: Organs: Mouth, oesophagus, stomach, small intestine, large intestine, liver, pancreas Function: Ingestion, digestion, absorption of nutrients, elimination of undigested waste 5. Circulatory System: Organs: Heart, arteries, veins, capillaries, blood Function: Transport of oxygen, nutrients, hormones, CO₂, and waste; temperature regulation; defence (WBC) 6. Respiratory System: Organs: Nose, pharynx, larynx, trachea, bronchi, lungs Function: Gas exchange (O₂ in, CO₂ out), maintaining blood pH 7. Excretory System: Organs: Kidneys, ureters, urinary bladder, urethra Function: Removal of metabolic waste (urea, uric acid), regulation of water and electrolyte balance, blood pressure regulation 8. Nervous System: Organs: Brain, spinal cord, nerves, sense organs Function: Coordination, impulse conduction, response to stimuli, learning, memory 9. Endocrine System: Organs: Pituitary, thyroid, parathyroid, adrenal, pancreas, gonads Function: Chemical coordination via hormones, regulation of growth, metabolism, reproduction 10. Reproductive System: Organs: Testes/ovaries, associated ducts and glands Function: Production of gametes, fertilisation, continuation of species
Q3. Explain how different organ systems work together to maintain homeostasis.
Answer
Homeostasis is the maintenance of a stable internal environment. Multiple organ systems work together: 1. Temperature Regulation: - Integumentary system: Sweat glands produce sweat (cooling); blood vessels dilate (heat loss) or constrict (heat conservation) - Muscular system: Shivering generates heat when cold - Endocrine system: Thyroid hormones regulate metabolic rate and heat production 2. Oxygen and Carbon Dioxide Balance: - Respiratory system: Lungs exchange O₂ and CO₂ with blood - Circulatory system: Blood transports O₂ to tissues and CO₂ to lungs - Nervous system: Respiratory centre in medulla adjusts breathing rate 3. Blood Sugar Regulation: - Endocrine system: Insulin (β-cells of pancreas) lowers blood sugar; Glucagon (α-cells) raises it - Digestive system: Absorbs glucose from food - Circulatory system: Transports glucose and hormones 4. Water and Electrolyte Balance: - Excretory system: Kidneys filter blood, reabsorb water and useful substances, excrete waste - Endocrine system: ADH (antidiuretic hormone) regulates water reabsorption in kidneys - Integumentary system: Sweating removes water and salts 5. Defence Against Disease: - Lymphatic/Immune system: Lymphocytes produce antibodies - Integumentary system: Skin is a physical barrier - Circulatory system: WBCs in blood fight infection
Common Mistakes to Avoid
- Confusing the levels of organisation: The correct order is Cell → Tissue → Organ → Organ System → Organism. Never skip a level.
- Saying an organ is made of one tissue: An organ is made of TWO or more tissues. The stomach, for example, has epithelial, muscular, connective, and nervous tissues.
- Confusing digestive waste and metabolic waste: The digestive system removes undigested food (faeces). The excretory system removes metabolic waste (urea, excess water, salts) from blood. These are different.
- Calling the kidney a digestive organ: The kidney is part of the EXCRETORY system, not the digestive system. It filters blood to remove metabolic waste.
- Forgetting homeostasis involves multiple systems: No single organ system maintains homeostasis alone. Temperature, blood sugar, water balance, and gas exchange all require coordination between systems.
- Mixing up endocrine and exocrine glands: Endocrine glands are ductless and secrete hormones into blood (pituitary, thyroid). Exocrine glands have ducts and secrete into a surface (sweat glands, salivary glands).
Exam Checklist
- [ ] Can you list the levels of organisation in correct order with examples?
- [ ] Can you define cell, tissue, organ, organ system, and organism?
- [ ] Can you name all 11 organ systems with their major organs and functions?
- [ ] Can you explain how tissues combine to form an organ (e.g., stomach)?
- [ ] Can you distinguish between an organ and an organ system?
- [ ] Can you explain homeostasis with examples of how different systems work together?
- [ ] Can you explain why the skin is called the largest organ?
- [ ] Can you describe how the circulatory and respiratory systems work together for gas exchange?
- [ ] Can you explain blood sugar regulation by the endocrine system?
- [ ] Can you distinguish between metabolic waste (excretory) and undigested waste (digestive)?
