Coordination in Life Processes — Telangana (SSC) Class 10 Science Solutions (Free)

Tropism is the growth response of plants toward or away from a stimulus. - Phototropism: growth toward light (stems grow toward light, roots away) - Geotropism: growth response to gravity (roots grow downward, stems upward) - Hydrotropism: growth toward water - Chemotropism: growth response to chemicals

Plant hormones are chemical messengers that regulate growth and responses to stimuli. - Auxin: promotes cell elongation, controls phototropism - Gibberellin: promotes stem elongation and seed germination - Cytokinin: promotes cell division and delays aging - Ethylene: promotes fruit ripening and leaf abscission - Abscisic acid: inhibits growth, promotes dormancy, closes stomata during drought

When a plant is exposed to unidirectional light: - Auxin (growth hormone) accumulates on the shaded side - Higher auxin concentration causes cells on shaded side to elongate more - Cells on illuminated side elongate less - Result: stem bends toward light (positive phototropism) Auxin is distributed by the plant tip sensor detecting light direction

Nastic movements are growth responses independent of stimulus direction. - Movement direction is determined by plant structure, not stimulus direction - Example: Nyctinastic movements - opening and closing of leaves/flowers with time of day (sleep movements in Mimosa, tulip flowers) - These movements do not involve growth, just cell turgor changes

Stomatal opening is controlled by guard cells: - Light: triggers photosynthesis, increases K+ in guard cells, water enters by osmosis, guards swell, stoma opens - ABA hormone: released during drought, causes K+ to exit guard cells, water leaves, stoma closes - This prevents water loss during stress while allowing gas exchange