TwoOldGuys™ Study Guides
BI-122 Biology
Plant Physiology

response to environment



photoperiodism [photomorphogenesis]


Some plants respond to touch by curling tendril toward touch.
Venus flytraps close leaf in response to touch.
Sensitive plant wilts in response to touch (harder touch → more wilt).
Many plant exhibit circadian changes in leaf position, or flower opening.


Many plants become dormant in response to actual adverse conditions (winter, seasonal drought, non-seasonal drought), or even anticipated adverse conditions (photoperiodism).

temperature extremes

Temperate and Boreal Zone species produce 'anti-freeze' during winter.
Some plants which are subject to sudden, large temperature swings produce heat shock proteins.
Seed dormancy allows seeds to survive decades to centuries until dormancy is broken usually by sufficient water present.



For those species with cork under the bark, the cork itself is a cushion to minimize mechanical injury from falling limbs or small rocks. Most plants exude some substance out of any injury which penetrates to the vascular tissue. This substance loses water to the air, and effectively closes the wound [analogous to a animal scab]. Some species exude oils, waxes or resins [pines]; while some [rubber tree, milkweed, dandelion) produce latex [the raw material for natural rubber]. Others exude unidentified chemicals.

biologically induced

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revised 19 aug 2006