Grades 3–5 · Organisms
How does a climbing pea hold onto a support?
A slender pea plant can climb a trellis because leaf parts called tendrils coil around nearby supports. The attachment lets the support carry some of the plant's weight, so its stem and leaves can keep growing upward without a thick trunk.
Contact can start a living response inside a tendril. Touching the responsive side changes activity in its tissues. Early bending is linked with water movement and shortening on one side; later growth also helps maintain the coil. The two sides do not change by the same amount.
That difference in length produces a curve. The shorter side lies inside the bend and the longer side outside it. Continued bending around a suitable thin support makes a coil, so the plant has a physical attachment rather than a straight tendril merely resting against a surface.
First: contact shows the tendril meeting a support; Later: wrapped shows the resulting attachment. Unequal changes on its two sides curve the tissue, with the shorter side inside the bend.
In the diagramContact is followed by a coiling attachmentFirst: contactLater: wrappedTwo snapshots of one living tendril responding to touch.
A pea holds on by changing living tissue, with early water-related bending and later growth helping the coil. It must encounter a support thin enough to wrap around. Other climbers use twining stems, attaching roots or adhesive pads; this tendril is one particular solution.
About this explanation
Starting knowledge: Know that plants grow and that a flexible structure can wrap around a support.
Sources
- Royal Botanic Gardens, Kew — Pea: Plant description
- M. J. Jaffe, Plant Physiology — Physiological Studies on Pea Tendrils: VI. The Characteristics of Sensory Perception and Transduction
- Plant Physiology — Physiological Studies on Pea Tendrils. V. Membrane Changes and Water Movement Associated with Contact Coiling
- Plant Physiology — Physiological Studies on Pea Tendrils. I. Growth and Coiling Following Mechanical Stimulation