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Plant movements & plant hormones 

Plant movement : The movements in plants are not as apparent as in case of animals. Plants generally show movements at a very slow rate. The higher plants are fixed to the substratum by means of roots. They cannot move from one place to another. Therefore, they show movement of their organs only.

Classification of plant movements :

Plant movements are broadly classified into two types :

 

Coordination in Plants | Biology for Grade 10

 

1. Tropic movements :- Directional movements or orientations of specific part of a plant in response to external stimuli such as light, force of gravity, chemicals, water are called tropisms or tropic movements.

Tropic movements are very slow. The movement of the plant part can be either towards the stimulus (positive tropism) or away from the stimulus (negative tropism).

(i) Phototropism :- Definite direction movement in relation to light.

 

                               Coordination in Plants | Biology for Grade 10

 

Coordination in Plants | Biology for Grade 10

 (ii) Geotropism :- Definite direction movement in relation to gravity.

 

                             Coordination in Plants | Biology for Grade 10

 

     Coordination in Plants | Biology for Grade 10

 (iii) Chemotropism :- Definite direction movement in relation to chemicals.

e.g. - Movement of pollen tubes and fungal hyphae.

 (iv) Hydrotropism :- Definite direction movement in relation to water.

e.g. - Roots of seedlings.

  Coordination in Plants | Biology for Grade 10

(v) Thigmotropism (Haptotropism) :- Definite direction movement in relation to contact or support. The pea plant develops tendrils which help it to climb up other plants or fences or some other support. These tendrils are sensitive to touch.

e.g. - Tendrils, haustoria of Cuscuta 

Coordination in Plants | Biology for Grade 10

Question for Coordination in Plants
Try yourself:
What is the term used to describe the definite direction movement of a plant part in response to light?
View Solution

(2) Nastic movements :- Induced by external stimuli such as light, temperature, touch. However, these are not directional movements. Here, the part of the plant does not respond towards or away from the stimulus. Nastic movements include :-

 (i) Seismonasty :- The turgor changes occur in thin-walled cells of pulvinus, causing folding and drooping of the compound leaves. Such movements occur in response to touch (shock). These movements are very quick and are best seen in 'touch-me-not' plant (Mimosa pudica), also called 'Chhui-mui' or 'Lajwanti' or 'sensitive plant'. If we touch the leaves of the chhui-mui plant with our finger, we find that all its leaves immediately fold up and droop. After sometime, the leaves regain their original status. Here, no growth is involved. Instead, plant cell changes shape by changing the amount of water in them (turgor changes), resulting in folding up and drooping of leaves.

 

  Coordination in Plants | Biology for Grade 10

(ii) Nyctinasty :- Sleep movements - Due to day and night.
e.g. - Daily movement of flowers, leaves, stomata. 

Tropic  Movement

 

Nastic Movement

 

Direction of movement is in the direction of the stimulus.Direction of movement is not determined by the direction of stimulus.
Growth takes place.Growth does not take place.
Movements are slow.Movements are fast.
e.g.Growth movement of the shoot towards lighte.g. The folding up and drooping of leaves in the sensitive plants.

   Chemical Coordination in Plants 

  • A phytohormone can be defined as a chemical substance which is produced naturally in plants and is capable of translocation and regulating one or more physiological processes.
  • Different plant hormones help to coordinate growth development and responses to the environment. They are synthesized at places away from where they act and simply diffuse to the area of action.
  • First plant hormone, discovered by Went was auxin.
  • Main phytohormones are -

 (i) Auxins
 (ii) Gibberellins
 (iii) Cytokinins|
 (iv) Abscisic acid
 (v) Ethylene

(i) Auxins :-

  • When growing plants detect light, a hormone called auxin, synthesized at shoot tip, helps the cells to grow longer.
  • When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot.
  • This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

Functions of Auxins 

  • Promote cell division and elongation
  • Cause apical dominance (terminal or apical bud inhibits the development of lateral buds)
  • Used in parthenocarpy (production of seedless fruits without pollination and fertilization).
  • Help in root initiation in cutting or in callus differentiation. 

(ii) Gibberellins (GA) :-

  • Yabuta and Sumiki (1938) were the first to extract a substance from the Gibberella fungus, which they named as Gibberellin.

 Functions of Gibberellins:

  • Stimulate stem elongation.
  • Help in seed germination.
  • Rossette plants show bolting effect when treated with gibberellins.

  (iii) Cytokinins (CK) :- 

  • Cytokinins promote cell division, and it is natural that they are present in greater concentration in areas of rapid cell division such as in fruits and seeds. 

Functions of Cytokinins: 

Promote cell division and elongation 

  • Suppress apical dominance (promotes lateral branches in the presence of apical bud).
  • Help in secondary growth (growth in thickness).
  • Promote production of female flowers.
  • It helps in braking the dormancy of seeds and buds. 

 

(iv) Abscisic Acid (ABA) :- It is also known as stress hormone or dormin. 

 Functions of Abscisic Acid (ABA) 

  • Inhibit growth hence called anti-auxins or anti-gibberellins
  • Reduce transpiration by closing stomata under water stress conditions, hence called stress hormone
  • Stimulate the formation of abscission zone (zone of separation), causes wilting of leaves.

 

Question for Coordination in Plants
Try yourself:
Which hormone is responsible for promoting cell division and elongation in plants?
View Solution

(v) Ethylene (Gaseous hormone) :-  

Functions of Ethylene (Gaseous hormone) 

  • Promote fruit growth and ripening
  • Cause ageing (senescence)  

 

Do you know ?

Photoperiodism :- Effect or requirement of relative length of day (photoperiod) and night (dark phase) on flowering of plants is called as photoperiodism. The phenomenon was first discovered by Garner and Allard on Maryland mammoth (a mutant variety of tobacco) and they classified plants into following groups -

 

 (i) SDP (Short Day Plants) :- They need short day length for flowering.

e.g. - Tobacco, Soybean. Strawberry, Dahlia, Sugarcane.

 

(ii) LDP (Long Day Plants) :- They need long day length for flowering.

e.g. - Potato, Radish, Carrot, Wheat, Spinach.

 

(iii) DNP (Day Neutral Plants) :- They do not need any specific light period for the flowering.

e.g. - Zea, Cotton, Tomato, Sunflowers, Cucumber.

 

Phytochrome :- It is light sensitive pigment responsible for flowering which was discovered by Borthwick and Hendricks.

Vernalization (Yarovization) :- "Acceleration of ability to produce flower by chilling treatment is called vernalisation".

 

The document Coordination in Plants | Biology for Grade 10 is a part of the Grade 10 Course Biology for Grade 10.
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FAQs on Coordination in Plants - Biology for Grade 10

1. What is coordination in plants?
Ans. Coordination in plants refers to the ability of plants to regulate and control various physiological and biochemical processes to respond to internal and external stimuli.
2. How do plants coordinate their growth and development?
Ans. Plants coordinate their growth and development through various mechanisms such as hormonal regulation, cell signaling, and gene expression. These mechanisms allow plants to respond to environmental cues, such as light, gravity, and water availability, to optimize their growth and development.
3. What are some examples of plant hormones involved in coordination?
Ans. Some examples of plant hormones involved in coordination include auxins, cytokinins, gibberellins, abscisic acid, and ethylene. These hormones play important roles in regulating plant growth, development, and responses to environmental stimuli.
4. How do plants respond to external stimuli?
Ans. Plants respond to external stimuli by transducing signals from the environment into intracellular signals, which then trigger specific responses. For example, plants can respond to light by adjusting their growth and development, or to water stress by closing their stomata and reducing water loss.
5. What are some implications of understanding coordination in plants?
Ans. Understanding coordination in plants has important implications for agriculture, environmental management, and biotechnology. By understanding how plants respond to environmental cues, we can develop better strategies for crop management, conservation, and bioremediation. Additionally, this knowledge can be applied to develop new biotechnological tools and approaches for improving plant growth, yield, and stress tolerance.
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