Science on the Farm for Kids

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Thigmotropism – When plants are in contact with a touch stimulus or a physical object, they tend to respond to such a stimulus by growing on and within those objects. The most common example is the behavior of tendrils – leaves and petioles of plants, which are used for support and often coil around the object or “climb.” One side of the tendril is exposed to the touch; those stimuli are transferred to the side of the plant that’s not in contact with the object, signaling the plant to “curl.” The side in contact with the object tends to display slower growth, and the side with no contact experiences increased rate of growth – also known as differential growth.

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Phototropism – Plant tropism controls the growth of a plant in response to a light source. Various plants like gymnosperms and angiosperms have their stems growing in the direction of the light, which is known as a positive tropism. When plant hormones such as auxins gather on the shaded part of the plant, it results in the elongation of cells in that area faster than cells on the opposite side of the plant stem. That causes the stem to move in the direction of the light source.

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Gravitropism – Gravitropism, also known as geotropism, is the plant’s response to gravity. It’s the reason why a plant’s roots grow in the opposite direction from its stem. If a plant is laid on its side, the stem will still grow in an upward direction against gravity – negative gravitropism). At the same time the roots will keep a downward direction – positive gravitropism. The process enables a plant to keep an ideal position with the light source as well as provide the roots with access to water and minerals, which the plant needs for its growth.

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Hydrotropism – We all know water is essential for a plant’s well-being; hydrotropism regulates the growth of the plant to a water source. It protects plants from various drought conditions and an excessive degree of water exposure. The part of the plant located closer to the water source tends to grow much slower than the part on the opposite side of the source.

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Thermotropism – This plant movement happens as a response to temperature change in the environment, heat or cold. Plants like Rhododendron curl their leaves when it’s very cold, and Mimosa pudica collapses its leaves and folds them when there’s a decline in temperature. Plants exposed to optimum – best – temperatures on one side, and a too-warm or too-cold temperature on the other display faster growth on the side with optimum temperature.

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Larry Scheckel For Agri-View

QUESTION: How does a corn seed know which way to grow?

Larry Scheckel is the author of “Seneca Seasons: A Farm Boy Remembers.” He grew up on a family farm in the hill country of southwestern Wisconsin, one of nine children. His teaching career stretched to more than 38 years teaching physics and aerospace science to more than 4,000 high school students at Tomah, Wisconsin.