Plant physics · Robotics · Experiments
Biomimetics models to understand plant physics
Plant physics is intruiguing because plants are everywhere in our environment but we do not really pay attention to their functionning. Much efforts are done to improve crop yields with resilience to pathogens and harsh environmental conditions. Most of these efforts are done by biologists and chemists with rewarding but controversial discoveries such as gentically modified organisms (GMO) and pesticides.
Plant physics is concerned by questions related to the fundamental functionning of plants. It tackles fundamental questions such as :
(1) How do plants bring water from roots to leaves?
(2) How do plants bring sugar produced by photosynthesis to the roots?
(3) How do plants become rigid with turgor pressure?
(4) How do plant sense gravity?
(5) How does the Venus fly trap snap?
(6) ...
Each of these questions might have answer in genetics, biochemistry or evolutionary biology. We focus here on the understanding of the physical phenomena at play.
Why biomimetic models for plant physics?
An animal can move when environmental conditions become difficult: swallows spend the winter in the tropics, and camels can travel dozens of kilometers in search of water. A plant, however, cannot. Its roots hold it firmly in the ground. Seeking shelter from the wind or rain, or seeking out light, are not really options. These developmental factors depend almost exclusively on where the plant germinates.
To compensate for their inability to move, plants have a larger genome than animals. For example, a poplar has about 40,000 genes, compared to 25,000 in a human. Thanks to this large genome, plants are the masters of epigenetics, adapting their physical traits to external conditions: a tree growing in a windy location will have smaller leaves and a thicker trunk than another tree of the same species in a calmer location.
Plants cannot move from one place to another, but they can move. Certain flexible plant parts, called pulvini, can change shape to produce movement. There are several iconic examples: the sunflower that follows the sun, the black locust that folds its leaves to avoid the sun, the mimosa pudica—known as the sensitive plant—which folds its leaves as soon as it is touched, and Codariocalyx motorius, the dancing plant! The Samanea saman, which folds its leaves at the slightest passing of a cloud, or, more poetically, the daisy that folds its petals at sunset. In fact, all plants move as they grow, and many retain their motor abilities even when mature.
The Robotic Gallery of Plant Physics invites visitors to explore plant movements through biomimetic robots inspired by research in plant physics. The movements examined include the active movements of flexible organs, as well as passive movements caused by the environment (wind, rain, drought) and internal movements related to fluid flows and growth.
The articles are organized around video resources and a controllable physical model. For further reading, high-quality bibliographic resources on the subject are listed. Biomimetic physical models have unparalleled educational value, though they carry the risk of limiting our understanding of the complexity of the biological world to that of a physical process.
Most of the biomimetic models presented are idealizations of the biological world designed to investigate, under controlled conditions, a single physical phenomenon or a few coupled physical phenomena. Their educational and persuasive power should not make us forget that biology is inherently complex and that the optimality of a trait must always be considered in light of multiple selective pressures.
Questions :
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