Download 7.7 C notes on Forces that affect life Forces that Affect Plants

7.7 C notes on Forces that affect life
Forces that Affect Plants
A force is a push or a pull that can change the motion of an object. Forces are everywhere.
Forces, including gravity, are constantly acting upon plants and cause them to be in motion.
Plants can be in motion just like we are in motion. Plants move when they grow or respond to
their environment. Work is done when an applied force causes an object to move a distance,
when stored energy in food is used to perform bodily functions in an organism, or when water in
a plant cell forces a wilted plant to return to its upright position.
Upward Force of Seedlings
Friction happens between a moving object and the surface it contacts. This acts as a resister to
prevent the relative motion between the surface and the object. When we move an object, the
direction of this friction force is the opposite of the direction in which the object is being pushed.
Hence, to successfully move an object, this resisting force needs to be overcome. Forces affect
motion. There are many examples you may already notice in your daily life. The process of
seedling growth demonstrates a greater upward force than gravity, which is working in the
opposite direction. This is the reason that the germinating plants can break through the soil.
Turgor Pressure in Cytoplasm Forces Plants Upright
The reason that the plant cells can remain a certain size and shape is found in the cytoplasm.
Water within a plant cell exerts a force, called turgor pressure, which pushes outward on the cell
wall. The ability of a plant to maintain a strong upright position and to return to the upright
position when blown by the wind is the result of this force exerted by water within each plant
cell. The turgor pressure of the water in the cytoplasm must balance the force from outside the
cell. Plants can stand upright due to the effect of this turgor pressure. The combined pressure is
so strong that it could break other hard objects, such as concrete.
Plant Tropisms
Plants use direct environmental stimuli for orientation in growth and movement. This is called
tropism. The responses of the plant may be toward (positive) or away (negative) from the
external stimulus or stimuli. Plants have the ability to sense gravity and grow in the opposite
direction of it. Plants grow upward against the downward force of gravity in a process known as
geotropism. Even when turned, plants will recognize the force of gravity and reorient their stems
upward (negative geotropism) and their roots downward (positive geotropism).
Plants also work to grow toward sunlight in a process known as heliotropism or phototropism.
Some plants’ tendrils can respond to the touch of a nearby limb and grow around the structure
entwining like a vine (thigmotropism).