Materi PJJ Biologi Kelas 12 Senin 01 September 2025

Summary

This lesson explores the internal factors that influence plant growth and development, focusing on genes and plant hormones. Genes regulate growth patterns and control vital cellular processes such as protein synthesis. The video highlights key plant hormones, including auxin, cytokinin, gibberellin, traumatic acid, calline hormones, abscisic acid, and ethylene, explaining their production sites and diverse roles in growth, root and stem development, flowering, fruiting, and stress responses. Practical examples, such as the effects of auxin on cuttings and gibberellin on dwarf corn, illustrate hormone functions. The lesson concludes with encouragement for students to ask questions and engage further with the material.

Takeaways

• 🌱 Internal factors in plant growth include genes and hormones, both crucial for plant development.
• 🧬 GenesGenerate key takeaways are hereditary factors that regulate chemical reactions in cells, such as protein synthesis, influencing growth patterns.
• 🌿 Auxin is the first discovered plant hormone, synthesized in apical meristems, and promotes stem elongation, root growth, branch differentiation, and fruit growth.
• 🌊 Auxin also supports root formation in cuttings by being transported from shoots to the base of the cutting.
• 🧪 Cytokinin works with auxin to stimulate cell division, root growth, germination, and delay aging; it can be extracted from coconut milk, yeast, and actively dividing tissues.
• 🌾 Gibberellin, discovered from the fungus *Gibberella fujikuroi*, promotes stem elongation, seed and shoot germination, leaf growth, flowering, fruit development, and root differentiation, especially in dwarf plants.
• 🩹 Traumatic acid, or wound hormone, enables plants to repair damaged tissues through regeneration near injured areas.
• 🌳 Calline hormones stimulate specific organ formation: rhizocaline for roots, caulocalin for stems, phyllolocalin for leaves, and antokalin for flowers.
• 💧 AbscisPlant growth takeawaysic acid inhibits growth, closes stomata during water stress, and induces dormancy, synthesized in leaves, stems, fruits, and seeds.
• 🍎 Ethylene promotes fruit ripening and thickening of stems, produced in ripe fruits, stem segments, and old leaves.
• 📌 Understanding plant hormones and genes is essential for regulating growth, improving propagation, and enhancing crop development.

Q & A

What are the two main internal factors affecting plant growth?

The two main internal factors are genes and hormones.

What role do genes play in plant growth?

Genes control hereditary traits and regulate chemical reactions in cells, such as protein synthesis, which directly influences growth patterns.

What is the definition of plant hormones?

Plant hormones, or phytohormones, are essential growth regulators produced in one part of the plant, while the growth response occurs in other parts.

Where is auxin synthesized in plants, and what are its main functions?

Auxin is synthesized in the apical meristem, shoot tips, young leaves, and flower buds. Its functions include stimulating stem elongation, root growth, branch differentiation, fruit growth, and controlling apical dominance, phototropism, and geotropism.

How does cytokinin interact with auxin, and what is its main function?

Cytokinin works with auxin to promote cell division (cytokinesis). It also supports root growth, root differentiation, germination, flowering, and slows down aging.

What is gibberellin, and how does it affect plant growth?

Gibberellin is a hormone discovered from the fungus Gibberella fujikuroi. It stimulates stem elongation, seed and shoot germination, leaf growth, flowering, fruit development, and root growth, particularly in dwarf varieties.

What is the role of traumatic acid in plants?

Traumatic acid, or wound hormone, helps plants repair damaged tissue through regeneration by forming new tissue near the wound site.

What are calline hormones, and what specific plant organs do they affect?

Calline hormones stimulate the formation of specific plant organs: rhizocaline for roots, caulocalin for stems, phyllolocalin for leaves, and antokalin for flowers.

What is the function of abscisic acid in plants?

Abscisic acid inhibits growth, closes stomata during water shortages, and induces dormancy. It is synthesized in leaves, stems, fruits, and seeds.

How does ethylene influence plant growth and development?

Ethylene promotes fruit ripening and causes the stem to grow thicker. It is produced in ripe fruit tissue, stem segments, and old leaves.

Why is auxin important for root formation in plant cuttings?

Auxin produced in shoots is transported to the base of cuttings, promoting root formation, which is essential for vegetative propagation.

Which plant hormone was first discovered and who discovered it?

Auxin was the first plant hormone discovered, identified by Dutch botanist Brit Wen in 1863.