Structure–Function in Tissues

• Form follows function — tissue structure suited to its role.
• Xylem dead hollow vessels for water flow; phloem sieve tubes for sap transport.
• Ciliated epithelium moves mucus; adipose stores fat and insulates.
• Blood fluid matrix transports materials; bone rigid for support.

1. Xylem vessels — lignified dead cells, no cytoplasm → uninterrupted water column.
2. Phloem sieve tubes — perforated sieve plates; companion cells provide energy.
3. Root hair cells — large surface area for absorption (epidermal modification).
4. Alveoli — thin squamous epithelium for gas exchange in lungs.
5. Red blood cells — biconcave, no nucleus → more haemoglobin, flexible through capillaries.
6. Neuron long axon — carries impulse over distance.
7. NCERT Ch. 6 — link each tissue diagram to its function.
8. Real world — cartilage cushions joints; fat tissue insulation in polar animals.

Why xylem cells are dead at maturity

Step 1 — Living cytoplasm would block hollow lumen needed for water column.
Step 2 — Lignified walls prevent collapse under tension (transpiration pull).
Step 3 — Dead cells form continuous pipe from root to leaf.
Step 4 — Adjacent living cells (in young xylem) help during development.
Conclusion: loss of protoplast is adaptation for efficient water transport.

• Describing function without linking structure.
• Misconception: all tissues in an organ are same type (organs have multiple tissues).
• Confusing organ and tissue (organ = several tissues).
• Thinking phloem transports water (xylem does).
• Ignoring specialised cell shapes (root hairs, RBCs).

• How does structure of xylem suit its function?
• Why are alveoli thin-walled?
• Relate striations in muscle to function.
• Give one structure–function pair in plants and animals.

Open the Practice tab for graded questions on Structure–Function in Tissues.