Abstract
An investigation of how roots grow when the direction of gravity changes.
Hypothesis
Roots will grow according to how the gravity direction chenges.
Introduction
A process called geotropism (also called gravitropism) is the response of plant roots to gravity. There are two types of geotropism: positive geotropism and negative geotropism. Positive geotropism is observed in plants when their roots grow downward, while on the contrary, when shoots grow, negative geotropism is observed. Many different explanations have been proposed for why plant shoots grow “up” and roots grow “down.” Other plant parts, such as root hairs and leaves, may exhibit transversal gravitropism, growing perpendicular to the main up-down axis of the plant. To this day, we know that plants growing on earth have evolved to respond to many different stimulations to help them orient themselves to their best advantage. As you can discover in the phototropism activity, light is a crucial factor in determining the direction of plant growth. But gravity, the force that causes bodies to fall to the earth and holds the planets in their orbits about the sun, is also critically important. The effect of light on plant growth is called phototropism. Phototropism is understood as a secondary process, usually in the same direction as the negative geotropism. Transversal geotropismis is a direction of growth that is vertical to the shoot axis. The direction of many lateral shoots, side roots, leaves, etc. is described by this term. All directions diverting from that of the shoot axis are called plagiotropic. Orthotropic organs (shoot axis, main root) are usually of radial symmetry, plagiotropic organs (leaves, side roots, etc.) are mostly of dorsiventral organisation (having different dorsal and ventral surfaces).
Bibliography:
http://www.nasa.gov/pdf/562190main_LS4_Gravitropism_C4.pdf Retreived on 9 July 2013, (Web PDF file, from National Aeronautics and Space Administration (NASA), Aerospace Education Services Project.
http://www.biologie.uni-hamburg.de/b-online/e32/32c.htm Retrieved on 9 July 2013, (Web) 1996-2004, from University of Hamburg, Faculty of Mathematics, Computer Science and Natural Sciences
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