Tag: biology

The free type of movements induced by some external stimuli like light, temperature, chemicals, etc are called as tactic movements. They are of three types: Phototactic, chemotactic and thermotactic.

The movement of chloroplasts in palisade cells in response to light is called as phototactic movement. Phototaxis is the movement of an organism in response to light; that is, the response to variation in light intensity and direction.

Desmodium gyrans is also called as 'Indian telegraph plant' which is a dancing plant. The movement in this plant is called as movement of variation. It is not categorized into nastic or curvature movements.

If the movement of curvature exhibited by plant organs is due to some external stimuli (caused by light, temperature, gravity, foreign bodies, etc), it is called induced movement of curvature. There are several spontaneous movements of curvature like Nastic movements, nutation, etc. Opening of sunflower is due to the light radiation of the sun. So it is an example of photonastic movement. Seismonasty is induced by movement by touch, shock, rain, wind, etc. Example: the leaves of plants Mimosa pudica and M.spegazzinii. All these are included in movement of curvature.

Growth movements are brought about by the unequal growth in different regions of the same organ. If shoot growth occurs at a faster rate alternately on right and left sides of the axis, resulting in a zig-zag axis, the movement is said to be nutation. When the leaves mature in growth and the flower buds open, more rapid growth occurs on the upper surface. This results in unfolding of coiled leaves and opening of the flowers. These are categorised under autonomic movement of growth.

Etiolation is a process in flowering plants grown in partial or complete absence of light. It is characterized by long, weak stems, smaller, sparser leaves due to longer internodes and a pale yellow colour called as chlorosis.  It increases the likelihood that a plant will reach a light source, often from under leaf litter, or shade from competing plants. The growing tips are strongly attracted to light and will elongate towards it.

Vernation is the formation of new leaves or fronds. Circinate vernation is the manner in which a fern frond emerges. As the fern frond is formed, it is tightly curled so that the tender growing tip of the frond is protected within a coil. At this stage it is called a crozier or fiddlehead. As the lower parts of  the frond expand and toughen up, they begin to photosynthesize, supporting the further growth and expansion of the frond. In case of many fronds, long hairs or scales provide additional protection to the growing tips before they are fully uncoiled. Circinate vernation may also be observed in the extension of leaflets, in the compound leaves of Cycads.

Daily movements of plants are a part of circadian rhythms. A circadian rhythm is a biological process that displays an endogenous entrainable oscillation of about 24 hours. These 24-hour rhythms are driven by a circadian clock, and they have been widely observed in plants, animals, fungi and cyanobacteria.

Rapid rotational movement of cytoplasm is due to increase in water content. Cytoplasmic streaming also called as protoplasmic streaming, the movement of the fluid substance within a plant or animal cell. The motion transports nutrients, proteins and organelles within cells. First discovered in the 1830s, the presence of cytoplasmic streaming helped convince biologists that cells were fundamental units of life.

Siesmonasty means a response to shaking. The best example is Mimosa pudica (Touch-me-not plant) which is the sensitive plant. Such, plants respond to stimuli such as touch, blow or mechanical shock by folding their leaflets and lowering their leaves. This effect is caused by a change in the turgidity of the leaflets brought about by the movement of water into and out of the parenchymatous cells of the pulvinus or swollen leaf base.