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Solve each Samacheer Kalvi exercise question on your own first, then compare your answer with the solutions below. Tissue Level of Organisation covers the four animal tissue types — master the structural and functional differences.
Key Concepts (Quick Recap)
Four Types of Animal Tissues
| Tissue Type | Function | Key Features |
|---|
| Epithelial | Covering, lining, protection, secretion | Cells tightly packed, no intercellular spaces, basement membrane |
| Connective | Support, binding, transport, insulation | Cells scattered in matrix, most abundant tissue |
| Muscular | Movement, locomotion | Contractile (actin + myosin), elongated cells |
| Nervous | Impulse conduction, coordination | Neurons with dendrites, axon, cell body |
Epithelial Tissue Types
| Type | Shape | Layers | Location | Function |
|---|
| Simple squamous | Flat, flat | Single | Blood vessels, alveoli, Bowman's capsule | Filtration, diffusion |
| Simple cuboidal | Cube-shaped | Single | Kidney tubules, salivary ducts | Absorption, secretion |
| Simple columnar | Tall, pillar-like | Single | Stomach, intestine lining | Absorption, secretion |
| Ciliated columnar | Tall with cilia | Single | Trachea, fallopian tubes | Push mucus/ova |
| Stratified squamous | Flat | Multiple | Skin, oesophagus, mouth | Protection against wear |
| Transitional | Variable | Multiple | Urinary bladder, ureter | Stretching |
Connective Tissue Types
| Type | Matrix | Cells | Location | Function |
|---|
| Areolar (loose) | Gel-like | Fibroblasts, macrophages, mast cells | Below skin, between organs | Binding, support |
| Adipose | Gel-like | Fat cells (adipocytes) | Below skin, around organs | Insulation, fat storage |
| Dense regular | Dense, parallel fibres | Fibroblasts | Tendons, ligaments | Strong attachment |
| Dense irregular | Dense, random fibres | Fibroblasts | Dermis of skin | Strength in multiple directions |
| Cartilage | Solid, flexible | Chondrocytes in lacunae | Nose, ear, trachea, between ribs | Flexibility, support |
| Bone | Solid, rigid (calcium salts) | Osteocytes in lacunae | Skeletal system | Support, protection, locomotion |
| Blood | Fluid (plasma) | RBC, WBC, platelets | Blood vessels | Transport, defence, clotting |
Muscular Tissue Types
| Feature | Skeletal (Striated) | Smooth (Non-striated) | Cardiac |
|---|
| Shape | Long, cylindrical | Spindle-shaped | Branched, cylindrical |
| Striation | Present | Absent | Present (faint) |
| Nuclei | Multinucleate | Uninucleate | Uninucleate |
| Control | Voluntary | Involuntary | Involuntary |
| Location | Attached to bones | Walls of hollow organs | Heart wall |
| Speed | Fast, tires easily | Slow, sustained | Rhythmic, never tires |
| Special feature | — | — | Intercalated discs |
Nervous Tissue — Neuron Structure
| Part | Description |
|---|
| Cell body (cyton/soma) | Contains nucleus and Nissl's granules |
| Dendrites | Short, branched processes — receive impulses |
| Axon | Long, single process — transmits impulse away |
| Myelin sheath | Fatty insulating layer around axon (in myelinated neurons) |
| Nodes of Ranvier | Gaps in the myelin sheath |
| Synapse | Junction between two neurons — neurotransmitters cross here |
Types of Neurons
| Type | Structure | Function | Example |
|---|
| Unipolar | One process from cell body | Sensory | Embryonic neurons |
| Bipolar | Two processes (one dendrite, one axon) | Sensory | Retina, olfactory epithelium |
| Multipolar | Many dendrites, one axon | Motor/interneurons | Most common type in CNS |
I. Choose the Best Answer (MCQs)
Q1. The tissue that forms the inner lining of blood vessels is (a) Simple cuboidal epithelium (b) Simple squamous epithelium (c) Stratified squamous epithelium (d) Simple columnar epithelium
Answer(b) Simple squamous epithelium — Simple squamous epithelium consists of flat, thin cells that form a single layer. It lines blood vessels (endothelium), alveoli, and Bowman's capsule — all sites where diffusion or filtration occurs.
Q2. Which of the following is a fluid connective tissue? (a) Bone (b) Cartilage (c) Blood (d) Areolar
Answer(c) Blood — Blood is a fluid connective tissue with cells (RBC, WBC, platelets) suspended in a fluid matrix called plasma. It transports oxygen, nutrients, hormones, and waste throughout the body.
Q3. Ciliated epithelium is found in (a) Skin (b) Trachea (c) Intestine (d) Kidney tubules
Answer(b) Trachea — Ciliated columnar epithelium lines the trachea and fallopian tubes. The cilia beat rhythmically to push mucus (trapping dust and microbes) upward and ova toward the uterus.
Q4. The cells of adipose tissue are called (a) Osteocytes (b) Chondrocytes (c) Adipocytes (d) Fibroblasts
Answer(c) Adipocytes — Adipocytes are fat-storing cells in adipose tissue. Osteocytes are in bone, chondrocytes in cartilage, and fibroblasts in areolar/dense connective tissue.
Q5. Intercalated discs are found in (a) Skeletal muscle (b) Smooth muscle (c) Cardiac muscle (d) Nervous tissue
Answer(c) Cardiac muscle — Intercalated discs are specialised junctions between cardiac muscle cells that allow rapid transmission of electrical impulses, enabling the heart to contract as a unit.
Q6. The functional unit of the nervous system is (a) Axon (b) Dendrite (c) Neuron (d) Synapse
Answer(c) Neuron — The neuron (nerve cell) is the structural and functional unit of the nervous system. It consists of a cell body, dendrites, and an axon, and can transmit electrical impulses.
II. Fill in the Blanks
1. The four types of animal tissues are epithelial, connective, muscular, and nervous. 2. Epithelial tissue rests on a basement membrane. 3. Simple squamous epithelium is found lining blood vessels and alveoli. 4. The cells of bone tissue are called osteocytes. 5. The cells of cartilage are called chondrocytes. 6. Blood has plasma as its matrix. 7. Adipose tissue stores fat and provides insulation. 8. Skeletal muscle is voluntary and striated. 9. Smooth muscle is involuntary and non-striated. 10. Cardiac muscle is involuntary and striated with intercalated discs. 11. The structural and functional unit of the nervous system is the neuron. 12. The gap between two neurons is called the synapse. 13. Nissl's granules are found in the cell body (cyton) of a neuron. 14. Tendons connect muscle to bone, while ligaments connect bone to bone.
III. True or False (with corrections for false statements)
Q1. Epithelial tissue has abundant intercellular spaces.
AnswerFalse — Correction: Epithelial tissue has very little or NO intercellular spaces. Cells are tightly packed and rest on a basement membrane. Connective tissue has abundant intercellular spaces filled with matrix.
Q2. Blood is a connective tissue.
AnswerTrue — Blood is a fluid connective tissue. It has cells (RBC, WBC, platelets) embedded in a fluid matrix (plasma) and connects various body parts by transporting substances.
Q3. Smooth muscle cells are multinucleate.
AnswerFalse — Correction: Smooth muscle cells are uninucleate (single nucleus). Skeletal muscle cells are multinucleate. Cardiac muscle cells are also uninucleate.
Q4. Cartilage is vascular (has blood vessels).
AnswerFalse — Correction: Cartilage is avascular (no blood vessels). Nutrients diffuse through the matrix. Bone is vascular (has blood vessels through Haversian canals).
Q5. Neurons can divide and regenerate throughout life.
AnswerFalse — Correction: Neurons generally do NOT divide after maturity. Once a neuron is destroyed, it cannot be replaced. This is why spinal cord injuries and neurodegenerative diseases are so serious.
IV. Match the Following
| Column A | Column B | Answer |
|---|
| 1. Simple squamous epithelium | (a) Trachea | (b) Blood vessels and alveoli |
| 2. Simple cuboidal epithelium | (b) Blood vessels | (c) Kidney tubules |
| 3. Simple columnar epithelium | (c) Kidney tubules | (d) Intestine lining |
| 4. Ciliated columnar epithelium | (d) Intestine lining | (a) Trachea and fallopian tubes |
| 5. Stratified squamous epithelium | (e) Heart wall | (f) Skin and oesophagus |
| 6. Transitional epithelium | (f) Skin | (g) Urinary bladder |
V. Answer Briefly (2-mark questions)
Q1. What is epithelial tissue? Name its types based on layers.
Answer
Epithelial tissue is a sheet of tightly packed cells that covers body surfaces, lines body cavities, and forms glands. It rests on a basement membrane and has no blood vessels (avascular). Based on layers: - Simple epithelium: Single layer of cells — found where absorption or secretion occurs - Stratified (compound) epithelium: Multiple layers — found where protection against wear and tear is needed
Q2. Distinguish between areolar and adipose connective tissue.
Answer
| Feature | Areolar | Adipose | |---|---|---| | Function | Binding and support | Fat storage and insulation | | Cells | Fibroblasts, macrophages, mast cells | Adipocytes (fat cells) | | Matrix | Gel-like with collagen and elastic fibres | Sparse with fat-filled cells | | Location | Below skin, between organs | Below skin, around organs | | Appearance | Loose, translucent | Fatty, yellowish |
Q3. What are the three types of muscle tissue? Give one location for each.
Answer
1. Skeletal muscle (striated, voluntary): Attached to bones — e.g., biceps, triceps 2. Smooth muscle (non-striated, involuntary): Walls of hollow organs — e.g., intestine, blood vessels 3. Cardiac muscle (striated, involuntary): Heart wall (myocardium) — found only in the heart
Q4. Draw and describe the structure of a neuron.
Answer
A neuron has three parts: 1. Cell body (cyton/soma): Contains nucleus and Nissl's granules (clusters of rough ER). It processes incoming signals. 2. Dendrites: Short, branched processes that receive impulses from other neurons and transmit them toward the cell body. 3. Axon: A single, long process that transmits impulses away from the cell body. It may be covered by a myelin sheath (in myelinated neurons) with gaps called Nodes of Ranvier.
VI. Answer in Detail (5-mark questions)
Q1. Describe the types of epithelial tissue with their structure, location, and functions.
Answer
1. Simple Squamous Epithelium: - Structure: Single layer of flat, thin cells - Location: Lining of blood vessels (endothelium), alveoli, Bowman's capsule - Function: Diffusion, filtration, exchange of gases 2. Simple Cuboidal Epithelium: - Structure: Single layer of cube-shaped cells - Location: Kidney tubules, salivary gland ducts, thyroid follicles - Function: Absorption, secretion 3. Simple Columnar Epithelium: - Structure: Single layer of tall, pillar-like cells - Location: Stomach, intestine lining, gallbladder - Function: Absorption, secretion (mucus by goblet cells) 4. Ciliated Columnar Epithelium: - Structure: Columnar cells with cilia on the free surface - Location: Trachea, bronchi, fallopian tubes - Function: Movement of mucus (trachea) and ova (fallopian tubes) 5. Stratified Squamous Epithelium: - Structure: Multiple layers of flat cells; outer layers are dead and keratinised (in skin) - Location: Skin (keratinised), oesophagus, mouth, vagina (non-keratinised) - Function: Protection against wear and tear 6. Transitional Epithelium: - Structure: Multiple layers that can stretch and become thinner - Location: Urinary bladder, ureter, urethra - Function: Allows stretching as the bladder fills
Q2. Describe the types of connective tissue with examples.
Answer
A. Loose Connective Tissue: 1. Areolar tissue: - Gel-like matrix with collagen and elastic fibres - Cells: Fibroblasts, macrophages, mast cells - Location: Below skin, between organs - Function: Binding, support, defence (macrophages engulf bacteria) 2. Adipose tissue: - Cells filled with fat globules (adipocytes), pushing nucleus to periphery - Location: Below skin, around kidneys and heart - Function: Insulation (heat regulation), fat storage, shock absorption B. Dense Connective Tissue: 3. Dense regular: - Parallel collagen fibres with fibroblasts in rows - Location: Tendons (muscle to bone), ligaments (bone to bone) - Function: Strong attachment, resists pulling force in one direction 4. Dense irregular: - Randomly arranged collagen fibres - Location: Dermis of skin, pericardium - Function: Strength in multiple directions C. Specialised Connective Tissue: 5. Cartilage: - Solid but flexible matrix (chondrin) - Cells: Chondrocytes in lacunae - Avascular (no blood vessels) - Types: Hyaline (nose, trachea), Elastic (ear, epiglottis), Fibrocartilage (intervertebral discs) 6. Bone: - Hard, rigid matrix with calcium salts (calcium phosphate) - Cells: Osteocytes in lacunae, arranged in Haversian systems - Vascular (has blood vessels through Haversian canals) - Function: Support, protection, mineral storage, blood cell formation (in marrow) 7. Blood: - Fluid matrix (plasma: 55%, cells: 45%) - RBC (erythrocytes): Transport O₂ (contain haemoglobin) - WBC (leucocytes): Defence (5 types — neutrophils, eosinophils, basophils, lymphocytes, monocytes) - Platelets (thrombocytes): Blood clotting - Function: Transport, defence, clotting, thermoregulation
Q3. Describe the structure and types of muscle tissue.
Answer
1. Skeletal (Striated) Muscle: - Long, cylindrical fibres with multiple nuclei (multinucleate) - Striated (striped) appearance due to alternating actin and myosin bands - Voluntary control (controlled by will) - Attached to bones by tendons - Contracts quickly but tires easily - Location: Arms, legs, face, trunk muscles - Function: Body movement, posture maintenance 2. Smooth (Non-striated) Muscle: - Spindle-shaped cells with a single nucleus (uninucleate) - No striations (no regular arrangement of actin and myosin) - Involuntary control (not controlled by will) - Found in walls of hollow organs - Contracts slowly but can sustain contraction - Location: Stomach, intestine, blood vessels, urinary bladder, uterus - Function: Peristalsis, blood pressure regulation, pupil constriction 3. Cardiac Muscle: - Branched, cylindrical cells with a single nucleus (uninucleate) - Faintly striated (has actin and myosin, but arrangement differs from skeletal) - Involuntary control (beats automatically) - Intercalated discs — unique feature allowing rapid impulse transmission - Found ONLY in the heart wall (myocardium) - Contracts rhythmically and never tires - Function: Pumping blood through the heart
Common Mistakes to Avoid
- Confusing simple and stratified epithelium: Simple = single layer (absorption/secretion). Stratified = multiple layers (protection). Remember: more layers = more protection.
- Calling blood a muscle tissue: Blood is a CONNECTIVE tissue (fluid connective tissue). It has cells in a matrix, like other connective tissues.
- Mixing up osteocytes, chondrocytes, and adipocytes: Osteocytes = bone cells. Chondrocytes = cartilage cells. Adipocytes = fat cells. Remember the pattern: osteo = bone, chondro = cartilage, adipo = fat.
- Saying smooth muscle is striated: Smooth muscle is NON-STRIATED. Only skeletal and cardiac muscles are striated.
- Confusing tendons and ligaments: Tendons connect MUSCLE to BONE. Ligaments connect BONE to BONE. Both are dense regular connective tissue.
- Saying cartilage has blood vessels: Cartilage is AVASCULAR — nutrients diffuse through the matrix. This is why cartilage heals slowly.
- Forgetting that neurons cannot divide: Neurons are post-mitotic — once destroyed, they cannot regenerate (generally). This is different from most other body cells.
Exam Checklist
- [ ] Can you list the four types of animal tissues with their functions?
- [ ] Can you classify epithelial tissue by shape (squamous, cuboidal, columnar) and layers (simple, stratified)?
- [ ] Can you give the location and function of each epithelial type?
- [ ] Can you distinguish between areolar, adipose, dense, cartilage, bone, and blood connective tissues?
- [ ] Can you name the cells of each connective tissue (fibroblasts, adipocytes, chondrocytes, osteocytes)?
- [ ] Can you compare skeletal, smooth, and cardiac muscle (shape, nuclei, striation, control, location)?
- [ ] Can you describe the structure of a neuron (cell body, dendrites, axon)?
- [ ] Can you explain the synapse and how impulses cross it?
- [ ] Can you explain why blood is called a connective tissue?
- [ ] Can you distinguish between tendons and ligaments?
