Overview and explanation I StudySmarter (2023)

Plantare complex multicellular organisms, etcAnimals, also require constant adjustments and adaptations to survive in their environment.In order to survive, plants must respond to external and internal changes in order to surviveHomeostaza.Homeostazait is defined as the ability to maintain the internal environment of the biological system stable through regulatory mechanisms so that it can withstand life-threatening changes, especially external and uncontrolled environmental stresses. Learn more about how these changes affect plant growth factors.

Plants react to stimuli

Plantthey react to various stimuli related to changes in elements important for the survival of plants. This contains:

  • light
  • availability of water
  • weight
  • concentration of carbon dioxide
  • infection bymushroomsIbacteria

The internal regulation required to respond to a stimulus is even more relevant in plants because in contrastAnimals, Plants cannot move. allreactions of plantsthey must be confined to the place where they are rooted. In addition, plants do not havenerve coordinationSystematicallyAnimalsTo. This means that the coordination of reactions between different parts of the plant body depends on chemical communication systems and substances similar to plant hormones, such asplant growth factors,Abscisic acid (ABA), ITo eat.

Plant hormones are therefore crucial in controlling responses to various stimuli. Plant hormone signaling occurs through interactions with the surface or within the membranereceptorsfrom the goalStation. This interaction initiates internal chemical or ionic signaling that amplifies the signal/message and elicits a response.

ABA is an example of a plant hormone that is produced in the plant body and is responsible for controllingreactions of plantsenvironmental pressures such as water scarcity. ABA is therefore known as a stress hormone, the action of which causes the stomata of the plant to close and thus, for example, reduces the loss of water vapor through the leaf or inhibits plant growth.

Stomata are tiny pores on the underside of the leaf through which substances such as oxygen and water vapor can diffuse.

Plant responses to stimuli can be associated with rapid changes in the strength of protective cells.guard cellscontrol themcoup d'étatAn opening through which the leaves interact with the atmosphere and regulate the intake of carbon dioxide, which is essential for controlling the internal environment of the leafphotosynthesis. However, the majorityreactions of plantsIn response to stimuli such as gravity or light, they alter the growth of their roots or shoots using plant growth factors.

plumpnessdescribes that a plant cell stands upright and swells due to the presence of water in the plant cell.

Plant hormones - plant growth factors

plant growth factorsare chemical messengers produced in small amounts by various tissues in the plant body, not specialized cells in glands like animal hormones.

Growth factors are transported throughEqualorXylem Sap can either diffuse directly between cells to target neighboring cells. This leads to a growth-related response, such as cell elongation, which affects the direction of plant growth. There are two main types of plant growth factors: auxins, the most important of which is indoleacetic acid (IAA), and gibberellins.

Equal IXylem synd vascularplant tissuetransportni asimilat (aminokiseline i sucrose) ili voda.


Gibberellins are produced throughout the plant body in high concentrations in young leaves and seeds. These factors play a key role in regulationCollectiveand controllinga continuation of the stem.

Gibberellins are produced by the developing plant embryo in the early stages of germination and stimulate cells to synthesizeamylase,This is crucial for obtaining the energy needed for the growth of the embryo.

Gibberellins are also found in the stems of plants, where they are critically responsible for their growth and plant height through stimulationcell divisionand cell elongation within the stem.

germinationdescribes the process by which a plant develops from a seed.

Amylase is an enzyme that catalyzes the breakdown of starch into sugars that germinating seeds can use for growth.

indole acetic acid

Indoacetic acid (IAA) is the main auxin produced by plants. This growth factor is produced inSharing adviceormeristemroots and shoots and controls their growth by affecting the expansion of plant cells.

meristem cellsare undifferentiated cells in plants that have the ability to undergocell divisionand differentiate into differentplant tissue. They belong to the plantStem cells.

The effect of IAA leads to the elongation of plant cells, because this causes the growth of the young plantStation' Plasticity of the cell wall, which allows them to expand. The acid growth hypothesis offers a possible explanation for this mechanism. According to this hypothesis, IAA increases plant cell wall plasticity by stimulating target cells to increase plasticityactive transportof hydrogen ions from the cell cytoplasm to the cell wall. This acidifies the wall, loosening the bonds in its structure, causing it to stretch and lengthen.


Tropism is a type of different plant growthresponse to stimuliThis allows plants to maximize the conditions of their environment.

Depending on the nature of the provoking stimulus, there are different types of tropisms, but they all cause tropismdirected growthpart of a plant's body, such as shoots or roots. Types of tropisms include:

  • Phototropism (travel of light)
  • GEotropize/Gravitropism(gravity stimuli)
  • CHemotropism (chemical stimuli)
  • THygmotropism (touch stimuli)

This growth can be towards the stimulus (positive response) or away from the stimulus (negative response), which means that the direction of the response (growth) depends on the direction of the stimulus. Below are two examples of the main tropism responses in plants: phototropism andGravitropism.


Phototropism is the directional growth of plant parts such as shoots or roots depending on the directionEasy trip.

When plants grow in ambient light, either in bright or low light and under normal gravity conditions, they tend to grow straight up; Plants tend to grow taller and faster in low light conditions than in bright conditions. However, phototropism occurs when plants are exposed to this radiationone-sided lightor shines brighter on one side than on the other. When plants are exposed to these light levels, phototropism causes shoots to grow toward the light source (or the brighter side) and roots to grow. Since shoots grow in the direction of the stimulus, they have onepositive phototropizam,while it has roots that grownegative phototropizam. This onereactions of plantsHelp ensure survival by making sure the saplings get as much light as possible to function properlyphotosynthesis, and the roots remain buried in the ground moving away from the light as they emerge from the soil.

Negative and positive phototropism is the result of exposure of a part of the plant's body to light, tilted towards or away from the light source. This bending response is due to the uneven distribution of IAA throughout the plant body, in this case caused by light stimuli.

Positive phototropismdescribes growth in the direction of light stimuli.Negative phototropismdescribes growth in the opposite direction to light stimuli.

As previously mentioned, IAA is an auxin that is produced in the growing tips of shoots and roots and is evenly distributed throughout the plant body under normal light. However, non-uniform light distribution stimuli also lead to IAA accumulationshaded sideexposed part of the plant body. in shoots,Stationon the shady side with more IAA it will start to elongate more and bend the whole structure towards the light. However, the opposite occurs with roots, as higher concentrations of IAA inhibit cell elongation, meaning that the light side of the root will expand faster than the shaded side, causing the root to bend into the soil.


next to the lightPlantthey are also sensitive to gravity which affects their direction of growth through gravitropism. Like everything else on Earth, plants receive the same one-way gravitational pull that pulls us toward the Earth's core.

Responses to gravitational stimuli are important for the control of plant growth. For example, there are shoots that grow from the force of attraction into lightnegative gravitrope, while the roots of the plant grow into the soil by gravity and thus growpositive gravitrop.

Positive gravitropismdescribes growth in the direction of attraction.Negative gravitropismdescribes growth against the direction of gravity.

GravitropismThe effects may be more visible with horizontal growthPlant. In horizontally growing plants, roots still show positive gravitropism and shoots show negative gravitropism. Similar to phototropism, gravity affects the distribution of IAA in plants. During lateral growth, IAA accumulates on the underside of the body part (root or shoot), which is closer to the ground. In shoots, the accumulation of IAA promotes cell elongation, i.e. the lower side of the cellStationelongated, and the structure bends and grows upwards like a vertical plant. In roots, the accumulation of IAA inhibits cell elongation, i.e. HStationon the opposite side, it will elongate more, and the structure will bend and grow downward.

Growth factors in plants - important discoveries

  • Mostreactions of plantsThis involves altering their growth using plant growth factors. There are two types of plant growth factors: auxins (IAA) and gibberellins.
  • IAA growth factor is the main auxin that regulates plant growth. This happens because cell elongation is specifically made possible by the increased plasticity of the cell wallStation.
  • Tropism is a type of differential plant growthresponse to stimuliThis allows plants to maximize the conditions of their environment.
  • Phototropism is the response of plant growth to light stimuli.Gravitropismis the response of plant growth to gravitational stimuli. A negative tropic response means that the plant grows in the opposite direction to the stimulus, while a positive tropic response means that the plant grows in the direction of the stimulus.
  • Roots are positively gravitrophic and negatively phototrophic, while shoots are positively phototrophic and negatively gravitrophic. Gravity and light influence the distribution of IAA in plantsStation, enabling plant growth reactions.
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