what is the means of response in plants
Answers
Answer:
A tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the species. The word tropism comes from the Greek trope (“to turn” or “to change”). Tropisms are usually named for the stimulus involved and may be either positive (towards the stimulus) or negative (away from the stimulus).
Explanation:
As we have studied in our Nervous System study animals respond to stimuli using electrical and chemical signals. We have also learned that chemical messengers in our Endocrine System are used to accomplish life’s needs.
Plants also have the means to respond to their environment in order to successfully live. They use chemicals similar to the endocrine system to accomplish this. This web page will examine these plant responses.
The Regulation of Growth
Plants’ growth is controlled by many factors. Some of the factors are environmental and climatic while others come from within the plants themselves.
External Environmental Factors
Some external factors that regulate the growth of plants are light intensity, day length, gravity, and temperature.
Light- Light, obviously affects the plants ability to grow because light is needed for photosynthesis. Through photosynthesis the plant makes its energy carrying molecules. It is also needed for the production of chlorophyll.
Day Length- Day length causes the plants to flower. Many other roles of day length are being studied such as fruit and seed germination, dormancy, and leaf loss.
Gravity- Gravity causes roots to grow down toward the soil and roots to grow up away from the source of gravity.
Temperature- Temperature affects the rate of enzyme reaction. Higher temperature, to a point, is best for plant growth while low temperatures are needed for some plants to flower.
Tropisms
A tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the species. The word tropism comes from the Greek trope (“to turn” or “to change”). Tropisms are usually named for the stimulus involved and may be either positive (towards the stimulus) or negative (away from the stimulus).
Phototropism
Phototropism is the growth response of a plant in response to light direction. Different parts of a plant exhibit different reactions to light. Stems exhibit positive phototropism while most roots exhibit negative phototropism.

Geotropism
Geotropism is the growth response of a plant in response to gravity. Roots exhibit positive geotropism while stems and leaves exhibit negative geotropism.

Thigmotropism
Thigmotropism is the growth response of a plant to physical contact (touch). Plants that cling to physical structures such as walls exhibit positive thigmotropism.


Hydrotropism
Hydrotropism is the growth response of a plant to water. Roots exhibit positive hydrotropism.

Chemotropism is the growth response of a plant to a particular chemical. Roots grow toward useful minerals in the soil but away from acids.
Growth Regulators
Growth regulators are chemicals that control the growth of a plant. Some of these are growth promoters while others are growth inhibitors.
Growth Promoters
Auxins- Auxins are chemicals that are produced at the meristems, young leaves, and seeds of plants. The most important auxin is indoleacetic acid (IAA). Auxins have a role in the following:
Development of the embryo- From the very first mitotic division of the zygote, auxins guide the patterning of the embryo into the parts that will become the organs of the plant:

Leaf formation- The formation of new leaves in the apical meristem is initiated by the accumulation of auxin. Already-developing leaves deplete the surrounding cells of auxin so that the new leaves do not form too close to them. In this way, the characteristic pattern of leaves in the plant is established.

Phototropism- Plant shoots display positive phototropism: when illuminated from one direction, the shoot proceeds to grow in that direction.
Geotropism- Geotropism is a plant growth response to gravity. Plant shoots display negative geotropism: when placed on its side, a plant shoot will grow up. Roots display positive geotropism: they grow down.
Apical dominance- Growth of the apical bud usually inhibits the development of the lateral buds on the stem beneath. This phenomenon is called apical dominance. If the apical bud of a plant is removed, the inhibition is fruit development by applying IAA to the flowers. Not only does this ensure that all the flowers will “set” fruit, but it also maximizes the likelihood that all the fruits will be ready for harvest at the same time. This process develops seedless fruit.
Root initiation- IAA in epidermal cells of the root initiates the formation of lateral or secondary roots. Auxin also stimulates the formation of adventitious roots in many species. Adventitious roots grow from stems or leaves rather than from the regular root system of the plant. Horticulturists may propagate desirable plants by cutting pieces of stem and placing them base down in moist soil. Eventually adventitious roots grow out