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Gravitropism (also known as geotropism) is a coordinated process of differential growth by a plant in response to gravity pulling on it. It also occurs in fungi. Gravity can be either "artificial gravity" [clarification needed] or natural gravity. It is a general feature of all higher and many lower plants as well as other organisms.
Hydrotropism (hydro- "water"; tropism "involuntary orientation by an organism, that involves turning or curving as a positive or negative response to a stimulus") [1] is a plant's growth response in which the direction of growth is determined by a stimulus or gradient in water concentration. A common example is a plant root growing in humid air ...
Plant tropisms are directional movements of a plant with respect to a directional stimulus. One such tropism is gravitropism, or the growth or movement of a plant with respect to gravity. Plant roots grow towards the pull of gravity and away from sunlight, and shoots and stems grow against the pull of gravity and towards sunlight.
Terrestrial plants have rigid cell walls meant for withstanding harsh weather, as well as keeping the plant upright as the plant resists gravity. Gravitropism, along with phototropism and hydrotropism, are traits believed to have evolved during the transition from an aquatic to terrestrial habitat.
Due to the plants continuous fight against gravity, plants typically mature much more quickly than when grown in soil or other traditional hydroponic growing systems. [55] Because rotary hydroponic systems have a small size, they allow for more plant material to be grown per area of floor space than other traditional hydroponic systems.
Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and matrix effects such as capillary action (which is caused by surface tension). The concept of water potential has proved useful in understanding and computing water movement within plants, animals, and soil.
As a water molecule evaporates from the leaf's surface it pulls on the adjacent water molecule, creating a continuous water flow through the plant. [ 6 ] Two major factors influence the rate of water flow from the soil to the roots: the hydraulic conductivity of the soil and the magnitude of the pressure gradient through the soil.
A plant only reacts to gravity if the gravistimulation is maintained for longer than a critical amount of time, called the minimal presentation time (MPT). For many plant organs the MPT lies somewhere between 10 and 200 seconds, and therefore a clinostat should rotate on a comparable timescale in order to avoid a gravitropic response.