1. What is cork cambium, and how is it formed in plants?
Answer:
Introduction to Cork Cambium:
Cork cambium, also known as phellogen, is a lateral meristem that arises during secondary growth. It forms part of the periderm, which replaces the epidermis in plants as they grow older.
Formation of Cork Cambium:
- Cork cambium originates from the dedifferentiation of parenchyma cells in the cortex or sometimes from the pericycle in roots.
- It becomes active during secondary growth in dicots and gymnosperms, producing cork (phellem) on the outer side and phelloderm on the inner side.
2. Describe the structure and composition of periderm.
Answer:
Components of Periderm:
- Cork (Phellem):
- Outer protective layer of dead, suberized cells.
- Provides waterproofing and prevents desiccation.
- Cork Cambium (Phellogen):
- A thin layer of meristematic cells that produce cork and phelloderm.
- Phelloderm:
- Inner layer of living parenchyma cells, aiding in storage and metabolism.
Significance of Periderm:
The periderm replaces the epidermis and protects the plant against pathogens, mechanical injury, and water loss.
3. What is the role of cork cambium in secondary growth?
Answer:
Role in Secondary Growth:
- Formation of Protective Tissue: Cork cambium produces the cork layer, which acts as a protective barrier against environmental stresses.
- Development of Periderm: It replaces the epidermis, forming a new protective layer that supports growth and durability.
- Contribution to Girth: The activity of cork cambium, along with vascular cambium, increases the girth of the plant during secondary growth.
- Gas Exchange Regulation: Cork cambium forms lenticels, allowing gaseous exchange.
4. Explain the differences between cork, cork cambium, and phelloderm.
Answer:
| Feature | Cork (Phellem) | Cork Cambium (Phellogen) | Phelloderm |
|---|---|---|---|
| Nature | Dead, suberized cells | Meristematic cells | Living parenchyma cells |
| Function | Protection | Production of cork and phelloderm | Storage and metabolism |
| Location | Outer side of cork cambium | Between cork and phelloderm | Inner side of cork cambium |
5. What are lenticels, and how do they form?
Answer:
Definition of Lenticels:
Lenticels are spongy, porous structures formed in the cork layer, facilitating gas exchange between the plant’s internal tissues and the external environment.
Formation:
- Lenticels form due to the localized activity of cork cambium, producing loosely arranged cells with intercellular spaces.
- These structures are visible as small, raised dots on the surface of bark.
6. Discuss the chemical composition of cork and its functional significance.
Answer:
Chemical Composition:
- Suberin: Waxy substance that makes cork cells impermeable to water and gases.
- Lignin: Provides structural rigidity.
- Tannins: Contribute to resistance against pests and decay.
Functional Significance:
- Prevents water loss.
- Protects against pathogens.
- Reduces mechanical damage.
7. How does the cork cambium contribute to wound healing in plants?
Answer:
Role in Wound Healing:
- Activation of Meristematic Cells: After an injury, parenchyma cells near the wound dedifferentiate into cork cambium.
- Formation of Protective Layers: Cork cambium produces cork, sealing the wound and preventing pathogen entry.
- Regeneration: A new periderm is formed to restore protection.
8. Compare and contrast primary and secondary growth.
Answer:
| Aspect | Primary Growth | Secondary Growth |
|---|---|---|
| Tissue Involved | Apical meristems | Lateral meristems (vascular and cork cambium) |
| Direction | Increases length of plant | Increases girth |
| Occurs In | Herbaceous plants and young stems | Woody dicots and gymnosperms |
| Example | Root elongation | Formation of bark |
9. Explain why secondary growth is absent in monocots.
Answer:
- Monocots lack vascular cambium and cork cambium, which are essential for secondary growth.
- Their vascular bundles are scattered, preventing the formation of concentric layers.
- Structural adaptations, such as fibrous roots and flexible stems, reduce the need for secondary growth.
10. Describe the ecological significance of cork.
Answer:
Ecological Importance:
- Protection: Cork shields plants from environmental stress, such as desiccation and pathogen attacks.
- Gas Exchange: Lenticels in cork ensure respiration for internal tissues.
- Resource Use: Cork is harvested sustainably for use in industries, including wine stoppers and insulation.
11. How does the activity of cork cambium differ in stems and roots?
Answer:
- In stems, cork cambium arises from cortical cells and contributes to bark formation.
- In roots, cork cambium originates from the pericycle and develops a protective periderm layer, ensuring durability underground.
12. What are the consequences of excessive cork production?
Answer:
Negative Effects:
- Reduced Gas Exchange: Excessive cork can block lenticels, affecting respiration.
- Cracking of Bark: Overproduction can cause cracks, making plants vulnerable to infections.
13. How is cork used in commercial industries?
Answer:
Uses of Cork:
- Wine Industry: As bottle stoppers due to its impermeable nature.
- Insulation: Thermal and acoustic insulation.
- Crafts: Lightweight material for boards and decorative items.
14. Discuss the differences between vascular cambium and cork cambium.
Answer:
| Feature | Vascular Cambium | Cork Cambium |
|---|---|---|
| Location | Between xylem and phloem | Beneath the epidermis |
| Function | Produces secondary xylem and phloem | Produces cork and phelloderm |
| Contribution | Increases vascular tissue | Forms protective periderm |
15. Why is cork considered eco-friendly?
Answer:
- Cork is a renewable resource harvested without harming the tree.
- Its biodegradability makes it an environmentally friendly material.
16. What is the role of cork cambium in bark formation?
Answer:
Cork cambium, along with vascular cambium, contributes to the formation of bark, which includes both the periderm and secondary phloem.
17. How do environmental factors affect cork cambium activity?
Answer:
- Temperature: High temperatures increase cork cambium activity.
- Water Availability: Drought conditions can lead to reduced cork production.
18. What is the role of cork cambium in preventing water loss?
Answer:
Suberin in cork cells makes them impermeable to water, creating a barrier that prevents transpiration and desiccation.
19. Explain the process of bark shedding.
Answer:
- As the girth increases, the outermost layers of bark are pushed outward.
- They become dead and eventually shed, allowing for the formation of new protective layers.
20. How does secondary growth contribute to plant longevity?
Answer:
- Secondary growth strengthens stems and roots, enabling plants to support greater height and weight.
- It replaces aging tissues, ensuring continued functionality and protection.
These questions and answers provide an in-depth understanding of cork cambium and its critical role in secondary growth.
