Plant Responses Quiz

External Factors Regulating Plant Growth

• Light intensity and day length impact photosynthesis and growth patterns.
• Gravity directs root and shoot orientation, essential for nutrient and water uptake.
• Temperature influences metabolic rates and seasonal growth cycles.

Tropisms

• Tropism refers to directional growth responses of plants to external stimuli.
• Phototropism: growth towards light to enhance photosynthesis.
• Geotropism: roots grow downward in response to gravity, while shoots grow upward.
• Hydrotropism: roots grow towards areas of higher water availability.
• Thigmotropism: plants like vines respond to touch, enabling support through wrapping.
• Chemotropism: growth in response to chemical signals in the environment.

Plant Growth Regulators (PGRs)

• PGRs are chemicals that influence plant growth processes.
• They are produced in meristematic tissues, the regions of active cell division.
• The combined effect of different PGRs alters growth patterns efficiently.
• Promoters stimulate various growth processes within plants.

Applications of Plant Growth Regulators

• Ethene is used to ripen fruit, enhancing marketability and shelf life.
• Auxin is effective in weed control, disrupting the normal growth of unwanted plants.

Plant Defensive Mechanisms

• Plants must protect against water loss, overheating, infection, and herbivore attacks.
• Structural defenses: Bark acts as a barrier against pathogens, while stinging cells deter herbivores.
• Chemical defenses: Tannins render leaves unpalatable, and toxic chemicals prevent larval development.