The cells on the upper side of the root continue to elongate, and, as a result, the root bends downward as it grows. Part of the grass family, wheat is known as a cereal crop and typically used in making bread. The roots do not exhibit phototropism, and they tend to grow whichever way they please. It is not clear whether this failure to complete a life cycle is due to the weightless environment of space or other complicating factors. In microgravity, fluids do not have density because fluid and air convection is absent.
Water moves only by capillary action and air moves very slowly by molecular diffusion.
These factors prove to be extremely detrimental to the plant during flowering and seed-set, as the stagnant air is lacking in oxygen. This state is called carbon dioxide narcosis. To prevent these situations, it is necessary to have a forced convection at both the roots and the shoots during all stages of a plant's life. This can be accomplished with plant-growth units that attend to the light, atmosphere, temperature, mineral nutrient, and water conditions essential for a successful plant life. The light-sensing hormone responsible for the curvature of plant shoots towards light is auxin.