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Q14:
How does the cork act as a protective tissue?
Solution :
1. Biological Basis of Cork Formation
As plants grow older, the tissues at the periphery of the stem undergo a series of changes. The epidermis is replaced by a secondary meristem called the cork cambium (or phellogen). This meristem divides periclinally to produce cells that mature into cork (phellem) on the outer side and secondary cortex (phelloderm) on the inner side [Per botanical definition of secondary growth].
2. Cellular Characteristics of Cork Cells
Cork cells are characterized by several unique structural adaptations that allow them to serve as a high-performance protective barrier:
- Dead Cells: At maturity, cork cells lose their protoplasts and become dead tissue, rendering them metabolically inert and resistant to decay.
- Suberization: The cell walls are heavily impregnated with a waxy, lipid-based substance known as suberin. [Chemical justification: Suberin is highly hydrophobic, making the tissue impervious to gases and water].
- Tightly Packed Arrangement: The cells are arranged in radial rows without intercellular spaces, forming a continuous, unbroken barrier around the stem [Structural integrity principle].
3. Functional Protective Mechanisms
| Protection Type | Mechanism |
|---|---|
| Desiccation Prevention | The hydrophobic nature of suberin prevents the loss of water through evaporation (transpiration) from the internal tissues. |
| Mechanical Protection | The dense, layered structure protects internal delicate tissues from physical injury, herbivory, and excessive mechanical stress. |
| Pathogen Defense | The chemical composition of suberin acts as a biological deterrent against the entry of fungal spores and bacteria. |
| Thermal Regulation | The air pockets within the tissue structure provide insulation against extreme temperature fluctuations. |
4. Logical Synthesis
The protective efficacy of cork is the direct result of its chemical impregnation ($suberin$) and its physical arrangement ($lack$ $of$ $intercellular$ $spaces$). By creating a hermetic seal, the cork acts as a secondary dermal layer that is far more durable than the primary epidermis, specifically adapted for the rigors of perennial plant life [Per Plant Anatomy and Physiology axioms].
Final Solution: Cork acts as a protective tissue because its cells are dead, compactly arranged without intercellular spaces, and impregnated with a hydrophobic chemical called suberin, which collectively makes the tissue impervious to water, gases, and external pathogens.
More Questions from Class 9 Science Tissues Exercises
- Q1: Define the term “tissue”.
- Q2: How many types of elements together make up the xylem tissue? Name them.
- Q3: How are simple tissues different from complex tissues in plants?
- Q4: Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of their cell wall.
- Q5: What are the functions of the stomata?
- Q6: Diagrammatically show the difference between the three types of muscle fibres.
- Q7: What is the specific function of the cardiac muscle?
- Q8: Differentiate between striated, unstriated and cardiac muscles on the basis of their structure and site/location in the body.
- Q9: Draw a labelled diagram of a neuron.
- Q10(a): Name the following. (a) Tissue that forms the inner lining of our mouth.
- Q10(b): Name the following. (b) Tissue that connects muscle to bone in humans.
- Q10(c): Name the following. (c) Tissue that transports food in plants.
- Q10(d): Name the following. (d) Tissue that stores fat in our body.
- Q10(e): Name the following. (e) Connective tissue with a fluid matrix.
- Q10(f): Name the following. (f) Tissue present in the brain.
- Q11: Identify the type of tissue in the following: skin, bark of tree, bone, lining of kidney tubule, vascular bundle.
- Q12: Name the regions in which parenchyma tissue is present.
- Q13: What is the role of epidermis in plants?
- Q15: Complete the following chart:
CBSE Solutions for Class 9 Science Tissues
Chapters in CBSE - Class 9 Science
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