Growth | Jamb Biology

Meaning of Growth

1. Definition: Growth is the irreversible increase in size, volume, or number of cells in an organism.
2. Cell Division: Growth begins with mitotic cell division, increasing the number of cells.
3. Cell Expansion: Cells enlarge after division, contributing to growth.
4. Cell Differentiation: Specialized tissues and organs form as cells take on specific roles.
5. In Plants: Growth is localized to meristematic regions, such as root and shoot tips.
6. In Animals: Growth is uniform and occurs throughout the body.
7. Measurement: Growth can be measured in terms of height, weight, or biomass.
8. Types: Includes primary growth (length) and secondary growth (girth).
9. Continuous Process: In plants, growth is continuous as long as conditions are favorable.
10. Significance: Growth is vital for reproduction, survival, and adaptation.
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Germination of Seeds

11. Definition: Germination is the process by which a seed develops into a seedling under favorable conditions.
12. Stages of Germination:
    • Imbibition: Seed absorbs water and swells.
    • Activation: Metabolic processes restart in the seed.
    • Emergence: The radicle (root) and plumule (shoot) break through the seed coat.
13. Radicle Growth: First to emerge, establishing the plant’s root system.
14. Plumule Growth: Develops into the shoot, producing leaves.
15. Energy Source: Stored food in the endosperm or cotyledons is utilized during early growth.
16. Photosynthesis: Begins once leaves emerge and the seedling can produce its own food.
17. Viable Seed: Germination occurs only if the seed is viable (alive and capable of growth).
18. Seed Dormancy: Some seeds undergo dormancy, delaying germination until conditions are optimal.
19. Enzyme Activation: Enzymes like amylase convert stored starch into sugars for energy.
20. Growth Continuation: Germination transitions into growth as the seedling develops.
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Conditions Necessary for Germination

21. Water: Essential for seed imbibition, enzyme activation, and metabolic processes.
22. Oxygen: Required for aerobic respiration to produce energy.
23. Temperature: A specific range is needed for enzyme activity (varies by species).
24. Light: Some seeds require light (e.g., lettuce) or darkness (e.g., onion) for germination.
25. Hormones: Growth hormones like gibberellins promote seed germination.
26. Seed Coat Permeability: Must allow water and gases to enter.
27. Absence of Inhibitors: Germination may be inhibited by chemical compounds in the seed.
28. Nutrients: Stored nutrients in the seed support early growth.
29. Soil pH: The soil environment must be conducive to root growth.
30. Time: Germination requires sufficient time for metabolic processes to take place.
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Epigeal and Hypogeal Germination

31. Definition of Epigeal Germination: The cotyledons are pushed above the soil surface as the seedling grows.
32. Example of Epigeal Germination: Beans and castor seeds.
33. Process in Epigeal Germination: The elongation of the hypocotyl lifts the cotyledons above the soil.
34. Advantage: Cotyledons are exposed to light and may assist in photosynthesis.
35. Disadvantage: Cotyledons are vulnerable to environmental damage.
    
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36. Definition of Hypogeal Germination: The cotyledons remain underground as the seedling grows.
37. Example of Hypogeal Germination: Maize and pea seeds.
38. Process in Hypogeal Germination: The epicotyl elongates, leaving the cotyledons below the soil.
39. Advantage: Cotyledons are protected from environmental stress.
40. Disadvantage: Seedlings depend entirely on stored nutrients until leaves develop.
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Applying Knowledge of Germination Conditions to Plant Growth

41. Optimal Watering: Provide adequate but not excessive water to prevent seed rot.
42. Soil Aeration: Ensure soil is well-aerated to facilitate oxygen availability for respiration.
43. Temperature Management: Maintain appropriate temperature ranges for specific plant species.
44. Light Regulation: Identify whether seeds require light or darkness for germination and act accordingly.
45. Seed Treatment: Break dormancy through scarification or soaking if necessary.
46. Nutrient Supply: Enrich soil with essential nutrients for early root and shoot development.
47. Weed Control: Remove weeds to minimize competition for resources.
48. Disease Prevention: Use treated seeds or fungicides to protect against pathogens.
49. Spacing: Plant seeds at appropriate distances to ensure adequate growth space.
50. Monitoring: Regularly check for pests, diseases, and environmental stressors affecting germination and growth.

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