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4.2: Environmental Responses

  • Page ID
    31995
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    Animals can respond to environmental factors by moving to a new location. Plants, however, are rooted in place and must respond to the surrounding environmental factors. Plants have sophisticated systems to detect and respond to light, gravity, temperature, and physical touch (Figure \(\PageIndex{1}\)). Plants may grow towards or away from environmental stimuli, and these growth responses are called tropisms. Environmental factors, particularly temperature and the hours of light and dark each day, also control flowering in many species. Plants detect the latter through photoperiodism. In the absence of light, plants respond physiologically to increase the chance of accessing light. Finally, plants rely on environmental cues to break dormancy in seeds and buds on winter twigs.

    A composite flower under red lights at the International Space Station
    Figure \(\PageIndex{1}\): The first flower to bloom in space. The International Space Station provides a unique opportunity to study the growth of plants under microgravity. Image by NASA (CC-BY-NC).

    Attributions

    Curated and authored by Melissa Ha using 30.6: Plant Sensory Systems and Responses from General Biology by OpenStax (licensed CC-BY). Access for free at openstax.org.

    • 4.2.1: Tropisms
      A tropism is a growth movement whose direction is determined by the direction from which the stimulus strikes the plant. There are two forms:  Positive = the plant, or a part of it, grows in the direction from which the stimulus originates. and Negative = growth away from the stimulus.
    • 4.2.2: Flowering
      The flowering plants (angiosperms) go through a phase of vegetative growth producing more stems and leaves and a flowering phase where they produce the organs for sexual reproduction. In "annuals", like the snapdragon, the vegetative phase begins with germination of the seed. Flowering follows and ends with the senescence and death of the plant. In biennials, the vegetative phase takes up the first year; flowering followed by death occurs the second year.
    • 4.2.3: Photoperiodism
      Many angiosperms flower at about the same time every year. This occurs even though they may have started growing at different times. Their flowering is a response to the changing length of day and night as the season progresses. The phenomenon is called photoperiodism. It helps promote cross pollination.
    • 4.2.4: Etiolation and Shade Avoidance
      The stems of plants raised in the dark elongate much more rapidly than normal, a phenomenon called etiolation. It is a mechanism that increases the probability of the plant reaching the light.
    • 4.2.5: Dormancy
      Dormancy refers to periods when a plant is not actively growing, and it is advantageous when environmental conditions are not favorable. Seeds and winter buds undergo dormancy.
    • 4.2.6: Chapter Summary

    Thumbnail image: Sensitive plant (Mimosa pudica) exhibits a thigmonastic movement. The leaflets and leaves retract when it is touched. Image by piqsels (public domain)


    This page titled 4.2: Environmental Responses is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Melissa Ha, Maria Morrow, & Kammy Algiers (ASCCC Open Educational Resources Initiative) .