Quick Summary
Hormones coordinate growth, development, and body functions. This chapter compares plant hormones with animal hormones and connects each hormone to its source and function.
Key Definitions
- Hormone: Chemical messenger that regulates body activities.
- Endocrine gland: Ductless gland that secretes hormones directly into blood.
- Auxin: Plant hormone involved in cell elongation and tropic movements.
- Gibberellin: Plant hormone that promotes stem elongation and seed germination.
- Insulin: Hormone that regulates blood glucose level.
- Adrenaline: Hormone released during emergency situations.
- Thyroxine: Hormone that regulates metabolism.
Plant Hormones
| Hormone | Main function |
|---|---|
| Auxin | Cell elongation, phototropism |
| Gibberellin | Stem elongation, seed germination |
| Cytokinin | Cell division |
| Abscisic acid | Growth inhibition, dormancy |
| Ethylene | Fruit ripening |
Animal Hormones and Glands
| Gland | Hormone | Function |
|---|---|---|
| Pituitary | Growth hormone | Body growth |
| Thyroid | Thyroxine | Metabolism |
| Pancreas | Insulin | Blood glucose control |
| Adrenal | Adrenaline | Emergency response |
| Testis | Testosterone | Male reproductive functions |
| Ovary | Oestrogen, progesterone | Female reproductive functions |
Tropic Movements in Plants
Plant hormones cause directional growth (tropism) toward or away from a stimulus:
Nervous vs Hormonal Control (deeper comparison)
| Feature | Nervous control | Hormonal control |
|---|---|---|
| Signal | Electrical impulse | Chemical (hormone) |
| Speed | Very fast | Slow |
| Travels via | Neurons | Bloodstream |
| Duration of effect | Short | Long-lasting |
Feedback Regulation
Hormone levels are kept balanced by feedback. For example, when blood sugar rises, the pancreas releases insulin (lowers it); when it falls, it releases glucagon (raises it) — keeping glucose steady.
Hormonal Coordination
Hormones act slowly compared with nerve impulses, but their effects often last longer. They help maintain internal balance and coordinate growth, metabolism, reproduction, and stress responses.
Deficiency and Imbalance
- Lack of insulin can lead to diabetes mellitus.
- Iodine deficiency can affect thyroxine production.
- Abnormal growth hormone levels can affect body growth.
Textbook Solution Strategy
1. For every hormone, learn source and function together. 2. Use tables for gland-hormone-function questions. 3. Compare nervous control and hormonal control when asked. 4. Mention plant examples such as phototropism and fruit ripening. 5. Link deficiency questions to the affected hormone.
Important Questions
One Mark
- What are hormones?
- Name the hormone secreted by pancreas.
- Which plant hormone helps in fruit ripening?
Two Marks
- Differentiate between nervous control and hormonal control.
- Write the functions of auxin and gibberellin.
- What is the role of adrenaline?
Five Marks
- Explain major endocrine glands and their hormones.
- Describe plant hormones and their functions.
- Explain how hormones help in coordination.
Common Mistakes
- Confusing insulin with adrenaline.
- Forgetting that endocrine glands are ductless.
- Writing plant hormones only as animal hormones.
- Missing the source gland in hormone answers.
Revision Checklist
- Plant hormone table revised
- Endocrine gland and hormone table memorised
- Insulin, thyroxine, adrenaline functions revised
- Hormonal vs nervous control comparison practised
- Deficiency examples remembered