1. What is biological tropism?

    • Answer

      In biology, tropism refers to the growth or movement of an organism in response to environmental stimuli. Biological tropism is most commonly observed in plants.

  2. In addition to phototropism, or an organism’s response to light stimuli, what are at least two other types of tropism that exist in nature? 

    • Answer

      Answers vary but could include the following: chemotropism (response to chemicals), gravitropism/geotropism (response to gravity), hydrotropism (response to water), sonotropism (response to sound), thermotropism (response to temperature), or thigmotropism (response to touch).

  3. How is time-lapse photography different from high-speed, or slow-motion, photography?

    • Answer

      In time-lapse photography, individual frames are captured at a much slower rate than they are viewed. Then, when the frames are combined and played at normal speed (24 frames per second), time appears to be going faster. High-speed, or slow-motion, photography collects frames at a much faster rate (128 or more frames per second) than they are viewed, making time appear to slow down.

  • In positive phototropism, organisms move or grow toward a light source. In negative phototropism, organisms move or grow away from a light source.
  • Auxins are the class of light-sensing hormones responsible for regulating phototropism in plants. 
  • Dr. John Nash Ott’s work with time-lapse photography and plant growth led him to believe that exposure to different wavelengths of light could impact animal and human behavior. Ott discussed these views in his 1973 book, Health & Light
high-speed photography

the science of taking pictures of very fast phenomena.


art and science of producing still or moving images using the chemical reaction of light on a sensitive surface, such as film or an electronic sensor.


growth or movement of a sessile organism toward or away from a source of light.

time-lapse photography

photographing of a slow and continuous process at regular intervals, for projection at a higher speed.


an orientation of an organism to an external stimulus, as light, especially by growth rather than by movement.


This material is based in part upon work supported by the National Science Foundation under Grant No. DRL-0840250. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.


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