For a plant, those are called environmental stimuli.
Although plants with no sense organs can also sense things and react to them, plants respond to matters such as sun, gravity, pressure, water etc. For a plant, those are called environmental stimuli. Plants regulate their actions using their hormones and respond to changes in the environment. They do it by affecting plant growth Plants are rooted in one place, and cannot move from one place to another physically. But plants still exhibit motion by using hormones under stimuli influence. This movement is found when the two regions of a plant expand unequally. For example: Some plants, such as the pea plant, use tendrils to climb up other plants or fences. Those tendrils are touch-sensitive. The part of the tendril in interaction with the object does not grow as quickly as the part of the tendril away from the object when they come in contact with any supports. This instigates the tendril to circle around and therefore cling to the object. More generally, by rising in a particular direction, the plants respond to stimuli gradually. Because this development is lateral, it appears as though the plant is growing. Depending on their growth there are two types of movement in plants. They are Tropic and Nastic movements Tropic Movement: When the external stimulus path determines the direction of the response in the form of growing it is called tropism. Thus, tropism is a part of a plant’s directional growth motion. It can be either in the stimulus direction, or away from the stimulus. So, if a plant ‘s growth is in the direction of stimulus, it’s called positive tropism. If a plant ‘s growth is in the opposite direction, or away from stimulus production, it is called negative stimulus. Types of Tropic movements: There are five stimuli like light, gravity, chemical, water and touch in the environment. There are five types of movement like phototropism, geotropism, chemotropism, hydrotropism and thigmotropism based on five stimuli. Phototropism: When a part of a plant shifts towards light, it is called phototropism. If a developing plant’s stem moves or bends towards light, it is a positive phototropism and if a plant’s root turns away from light, this means a plant’s roots show negative phototropism. Geotropism: When a section of a plant falls in reaction to gravity, geotropism is called that. For examples, a plant’s roots move downward, so they show positive geotropism and stem moves upward, so it shows negative geotropism. Chemotropism: It is called chemotropism when a plant part moves in response to chemical stimulus. The stimulus here is chemical in nature. For example, during fertilization in a flora, the growth of pollen tube towards the ovule is called positive chemotropism. Hydrotropism: It is called hydrotropism, when a plant element moves in response to water. The trigger here is Water. A plant’s roots move towards water, so that they show positive hydrotropism. Thigmotropism When a part of a plant shows directional motion in response to an object’s touch it is called thigmotropism. For instance, a plant’s tendrils climb towards any support that they touch. Nastic movement: If the direction of response in a plant isn’t determined by stimulus direction, it’s called nastic motion. Nastic movement is not plant part directional movement. Whatever the direction of the stimulus, all the parts of the plant move equally in the same direction in nastic motion. This type of movement usually occurs in leaves, flower petals etc. There are two types of Nasty movements. They are
Thigmonasty: The movement of a part of a plant in response to an object’s touch is called thigmonasty. In this case the motion of a part of a plant is non – directional. An example of thigmonasty is the responsive plant mimosa pudica which is also known as touch-me-not. If we touch this plant’s leaves they immediately fold up and droop down. Photomonasty: The motion of a part of a plant, usually flower petals, is called photonasty in response to light. Non-directional movement. In photonasty the stimulus is light. Examples of photonasty include dandelion and moonflower. Growth movements are the opening and closing of flower petals as a response to light. This is because when the outer surface of the petals grows and when their outer surface grows, the petals close. Examples of Tropic movements:
Examples of Nasty movements: Diurnal leaf movement and insectivorous plant response to prey, such as the Venus fly trap. Key points: Despite of their static nature, plants move due to their growth, accordingly they are divided in to two types they are Tropic movements and Nasty movements. Tropic movements: growth dependent movement in plants is seen Nasty movements: Growth independent movement in plants is seen. Types of tropic movements are phototropism, geotropism, thigmotropism, hydrotropism, chemotropism, which are based on five stimuli present in the environment. Types of Nasty moments are thigmonasty and Photonasty.
In simple words, in response to stimuli, tropism can be described as the movement of plants. The various tropical movements within plants help them adapt and survive to different situations. So, when a plant shows a certain growth movement in response to a stimulus, it’s called tropism
Plants move and respond diverse ways to a variety of different stimuli. Without external stimulus, plants can exhibit spontaneous movement, such as spiraling tendrils seeking a place to fasten and continue growth. They may also show induced movement when responding to external stimuli.
Through their roots in the earth, the plants are rooted at a place, so they cannot move from one place to another.
There are two types of movement. They are tropic movement and nastic movement.
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