Class 11  >  Plant Growth - Plant Growth & Development, Biology, Class 11

Plant Growth - Plant Growth & Development, Biology, Class 11 - Notes - Class 11

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Phases of Growth - Plant growth and development, Biology, Class 11



  • Growth is a characteristic feature of all living organisms.

  • Growth is a vital process, which brings about permanent and irreversible change in any plant or its part.

  • Growth in plants means increase in shape, size, weight and volume of a plant or plant part.

  • Growth leads to increase in fresh weight, dry weight, length, area, volume and cell number. All these are controlled externally (by environmental factors) and internally (by Genetics).

  • Growth is diffused in animals, but in plants growth is localised & irregular (nail in plant stem, occupies same height till several years of growth).

  • Seed germination is the first step of plant growth. Almost all the plants face a period of suspended growth.

  • If the suspension of growth is due to exogenously controlled factors (environmental factors) then it is called quiescence. Development is a part of growth but growth is

  • When the suspension of growth is due to the endogenously controlled factors (hormonal, genetic) then it is termed as dormancy.

  • Weight increased during growth but exceptions are potato & seed germination, where weight decrease.

(1) Phase of cell division or cell formation :- Number of cells is increases by cell division.

(2) Phase of cell enlargement or cell elongation :- Size of cells increases due to vacuolization & TP (turgor pressure).

(3) Cell maturation or differentiation phase :- (Also called as morphogenetic, organogenic phase) Development or qualitative change is important feature of this phase.

 Pattern or course of plant growth  : (growth curve)

  • The pioneering work on growth was done by Von Sachs.
    He plotted a growth curve between time & growth, which is known as sigmoid curve or S–curve or GP (Grand period)–curve.

  • Growth pattern of cell, organisms is uniform under favourable conditions. Thus following phases of growth are recognized.

(1) Lag phase :- In lag period the growth is slow.

(2) Log phase :- Also called as exponential phase. During this phase growth is maximum & most rapid.

(3) Steady or stationary phase :-. Time taken in growth phases (mainly log phase) is called as "grand period of growth".

 Measurement of growth :

(1) By direct observation

(2) By horizontal microscope

(3) By Crescograph (J.C. Bose) :- It magnifies growth as 10,000 times

PLANT GROWTH,Botany,Class 11

(4) By Auxanometers :-

(i) Arc - auxanometer

(ii) Pfeffer's  auxanometer/pully auxanometer (Permanent graph on smoke paper)

(iii) Micrometer screw - auxanometer  

Factors affecting plant growth :

(1) Light :- Light involves in photosynthesis and determine the direction of shoot and root growth. Light controlled morphogenesis of plant is called photomorphogenesis.

  • Light is not essential during the initial stage of growth or seed germination. In absence of light plant exhibit etiolation.

(2) Temperature :- Optimum temperature for growth is 20 - 35°C. temperature above 45°C damages the protoplasm and growth can be retarded.

Effect of low temperature on flowering is called vernalization.

(3) Water :- Water maintains the turgidity of cell, which is essential for growth. (TP is important for growth.) in order to cell to grow ψw must not be allowed to reach zero.

  • Water is essential for the enzyme activity in protoplasm.

(4) Oxygen :- Necessory for cell respiration.

(5) Mineral nutrients :- All essential elements are compulsory for growth and metabolism.

(6) Genetic factors :- Genotype & Phenotype.


  • First of all idea of plant hormones was given by Von Sachs "organ forming substance"

  • Ist Plant hormone discovered by F.W.Went was auxin but term hormone was given by Starling & phytohormone by Thieman.

  • Chemicals, which act as natural phytohormones are called as synthetic growth hormones. Synthetic auxins – α & β – NAA, 2,4-D, 2,4,5-T, IPA, PAA, IBA, Maleic hydrazide (MH).

N AA – Napthalene acetic acid.

2,4–D – 2, 4-Dichlorophenoxy acetic acid.

2,4,5–T – 2, 4, 5-Trichloro phenoxy acetic acid.

IPA – Indole Propeonic/Pyruvic acid

PAA – Phenyl/phenoxy acetic acid

PLANT GROWTH,Botany,Class 11



Auxins - Plant growth and development, Biology, Class 11


  • First of all Charles Darwin & F. Darwin (1880) was studying phototropism. They observed coleoptile bending in Canary grass (Phalaris). Wrote, Book "Power of movements in plants" term - “Stimulus” By Darwin

  • Boysen & Jensen 1910 :- Experiments on oat (Avena sativa) Plant. In the first experiment, he removed the coleoptile tip and then replaced it on stump. On providing unilateral light the coleoptile tip gave positive curvature.
    They observed, that if gelatin inserted between the tip & cut stump, then coleoptile bends towards the unilateral light. If mica inserted then coleoptile fail to show phototropism. Material substance term for growth hormone was given by him.

  • Paal :- Demonstrated that, when the cut tip was replaced on cut end (stump) eccentrically (asymmetrically) it causes bending even in dark.
    If coca butter or platinum foil inserted-there is no curvature observed.
    Idea of unequal distribution of growth substance given by Paal. large amount of substance found on shaded side.

  • F.W. Went (1928):- Went isolated the growing tip of Avena sativa on agar plate & performed Agar–block experiment.

  • He give name “auxin” to growth substance, thus credit of auxin discovery goes to F. W. Went

  • He also found that the curvature (bending) in Avena coleoptile is proportional , with in limits to the amount of auxin in Agar - block. This test was named as Avena curvature-test (Bioassay of Auxin).

  • Went found that 27% auxin present on illuminated side & 57 % on the dark side. (About 16% auxin lost on illuminated side & rest transferred to base) 

  • Transport of natural auxin is basipetal & polar type. (Synthetic → auxin = apolar transport) 

  • Kogl & Haagen Smit (1931) :- Isolated an active substance from urine of pellagra patient, which was called as auxin - A or chemically auxenotriolic acid (C18H32O5)
    Later a similar substance was isolated from corn grain oil and was named as auxin-B or auxenolonic acid. (C18H30O4)

  •  Again Kogl, Erxleben & Haagen Smit 1934 - Isolated another substance from human urine and named as heteroauxin (IAA - C10H9O2N) by Thimann. 

  • Auxin from Rhizopus was obtained by Thimann.

  • Auxin biosynthesis occurs by tryptophan amino acid in the presence of Zn++ ion.

  • Plant Growth - Plant Growth & Development, Biology, Class 11 - Notes - Class 11

  • Now IBA (Indole butyric acid) has been also isolated from plants (natural auxin) but IAA, is most widely found auxin in plants.

  • The compounds, which can be converted into auxin are called as auxin precursor, whereas the compound, which inhibit the activity of auxin are called asantiauxins.

The auxin, which can be easily extracted in agar are called free auxins, while auxins, which are not easily extracted practically are calledbound auxins. A dynamic equilibrium is exists between these two forms (free and bound auxins). ​

Physiological effects and applications of auxin

(1) Apical dominance :- The phenomenon, in which apical bud dominates over the growth of lateral buds is called apical dominance. Prunning in gardens promotes densing of hedge.

(2) Cell division & cell enlargement/Callus formation :- Auxin is important in tissue culture & Grafting. It stimulates division of intrafascicular cambium. Also inhealing of wounds.

(3) Shortening of internodes :- a-NAA induces the formation of dwarf shoot or spurs in apple, pear etc., thus number of fruits increases.

(4) Prevention of lodging :- Auxin spray prevents lodging of crops, immature leaves & fruits.

(5) Root initiation :- Rooting on stem cuttings is promoted by IBA & NAA (Root growth inhibited by auxin)

(6) Potato dormancy :- MH (Maleic-Hydrazide), a-NAA, induces dormancy of lateral buds in potato tubers & potato can stored for long duration.

(7) Prevention of abscission :-  IAA, NAA prevents premature abscission of plant organs.

(8) Flower initiation :- Auxin is inhibitor of flowering but it promotes uniform flowering in pine apple & litchiplants.

(9) Parthenocarpy :- Seed less fruits can be produced by spray of IAA. (By Gusteffson)

(10) Selective weed killer :- Dicot broad leave weeds can be eradicated by  PLANT GROWTH,Botany,Class 11

Agent orange is used in biowar. It was used by USA against Vietnam (1966-70)

(11) Femaleness :- Feminising effect in some plants.

(12) Flower & fruit thinning :- Certain trees like mango form less number of fruits in alternate years. But auxins can produced normal fruit crops every year. This is known as fruit thinning.

(13) When antiauxin (TIBA-Tri-Iodo Benzoic Acid) are sprayed on mature cotton field then cotton balls can picked easily.


Bioassay means the testing of substance for it's activity in causing a growth response in a living plant or it's parts.

(i) Avena curvature test

(ii) Root growth inhibition test, are bioassays for examining auxinactivity.


Gibberellins - Plant growth and development, Biology, Class 11


  • First of all Japanese farmers observed peculiar symptoms in rice seedlings & called the bakanae disease (foolish seedling disease)

  • Rice plants become thin, tall & pale due to infection of Gibberella (Ascomycetes) or Fusarium (Duteromycetes) confirmed by Kurosawa & Swada. 

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

  • Gibberellin, is an acidic & posses a gibben ring structure, are able to overcome genetic dwarfism in plants.

  • 100 type of Gibberellins (GA1, GA2 GA3 ............ GA100) are known. GA3 [C19H26O6] is representative of all gibberellins.

  • GA found in all groups of plants (algae, to angiosperms, but as a flowering hormone acts only in angiosperms.

  • Biosynthesis of gibberellin takes place by mevalonic acid pathway (Kaurene→GA)

Physiological effects and applications

(1) Stem/internode elongation :- GA induces internode elongation, leaf expansion & used in sugarcane cultivation.

Gibberellins induce stem elongation in rosette plants (Cabbage) this phenomenon known as bolting effect. (Elimination of rossete habit in some plants by gibberellins action is bolting)

(2) Elongation of genetic dwarf plants :- When gibberellin are applied to dwarf maize, Pisum & Vicia faba, then they become tall. The rosset plant of sugarbeet indicate an extreme dwarfism, this habit can be eliminate by GA.

(3) Flowering in LDP, in short light duration :- (Shortning of life cycle)

(4) Parthenocarpy :- Like auxin, exogenous use of GA also induces the formation of seedless fruits.

(5) Substitution of cold treatment or vernalisation :- The biennials plants form their vegetative body in the Ist year. Then they pass through a winter season & produce flower & fruits in IInd year. GA induces flower in first year.

(6) Breaking of dormancy :- GA breaks the dormancy of seeds, buds and tubers

(7) Seed germination :- Gibberellin induce the synthesis of hydrolysing enzymes like a-amylse, lipases, & proteases

(8) Sex expression :- GA induces maleness in Cucumis, Cannabis.

(9) Germination of photoblastic seeds :- Gibberellin treated light sensitive seeds can germinates in dark. Ex.

Lettuce, Tobacco.

(10) Fruit & flower enlarger :- Size of grape fruits & bunch & Geranium flowers increased by GA

PLANT GROWTH,Botany,Class 11

(11) In fermentation :- More growth of yeast cells by GA.

(12) Increase height of Sugarcene plant :- (More sugar contents by IAA )

Bio–assay :–

(1) a-amylase activity test in Barley endosperm

(2) Dwarf Pea & Maize test


Cytokinins - Plant growth and development, Biology, Class 11


  • Cytokinin was discovered by Miller when he was working (in lab. of prof. Skoog) on tobacco pith culture. He added the contents of an old DNA-bottle (Herring fish sperms DNA) to the culture medium & observed that the tobacco pith callus could grow for longer period.

  • Miller isolated an active substance from autoclaved DNA from Herring sperm, which stimulated cell division.

  • He named this substance as kinetin

  • Term cytokinin By Letham, Phytokinin by Osborne and Kinin by Skoog.

  • The first natural cytokinin was identified & crystalized from immature corn grains by Letham & named asZeatin.

  • The most common cytokinin in plants are isopentenyl adenine zeatin .

  • BAP (Benzylamino purine), diphenylurea and thidiazuron are synthetic cytokinins.

  • Cytokinin is a derivative of adenine base.

  • Root tips are major site of synthesis of CK (by mevalonic acid pathway). 

  • Movement of cytokinin is polar & basipetal.

  • Coconut milk factor also performed activity like cytokinin, thus used in tissue culture.

  • Zachau obtained cytokinins from serine-t-RNA of yeast. Physiological effects and applications

(1) Cell division & Cell enlargement :- One of the most important biological effect of CK (cytokinin) on plants is induction of cell division. In tissue culture also.

(2) Formation of interfascicular cambium and induce secondary growth.

(3) Morphogenesis :- Morphogenetic changes induced by CK in presence of IAA.

High auxin + low CK - Root formation

PLANT GROWTH,Botany,Class 11

4) Counteraction of apical dominance :- promotes growth of lateral buds.

(5) Breaking the dormancy of seeds :- Like GA the dormancy of certain seeds can be broken by CK.

(6) Seed germination :- Seeds of parasite plant (Striga) can germinate in the absence of host by CK treatment.

(7) Delay in senescence :- (Richmond Lang Effect) The ageing process of leaves usually accompanies with loss of chlorophyll & rapid catabolism. This is called as senescence. senescence postponed by CK. (increase short life of plant parts)

(8) Lignin biosynthesis.

(9) Parthenocarpy in some fruits.

(10) Pro-plastids modification.

(11) Phloem conduction (nutrients mobilisation)

(12) Femaleness.

(13) Flowring in SDP (also in long days).

(14) Induce stomatal opening :-

Bio–assay :–

(1) Tobacco pith cell division test

(2) Chlorophyll preservation (retension) test (delay in senescence test)

(3) Soyabean and Radish cotyledon cell division test.


Abscisic Acid - Plant growth and development, Biology, Class 11

Abscisic Acid (ABA C15H20O4)

  • First indication of growth inhibitors was given by Osborne.

  • First growth inhibitor was identified by Bennet-Clark and Kefford (1953) from dormant potato tuber and called itb-inhibitor.

  • Addicott & Okhuma (1963) obtained from mature cotton fruits and named as Abscisin II.(C15H20O4)

  •  Waring & Robinson – Isolated a growth inhibitor from old Betula leaves & called as dormin.

  •  Later establised that b-inhibitor, Abscisin-II and dormin are same and called as Abscisic acid.

  •  ABA is the most wide spread growth inhibitor in plants.

  •  ABA synthesized by Mevalonic acid pathway & oxidation of carotenes in chloroplasts.

  • ABA also known as stress hormone, because it protects plants from adverse conditions like water stress. ABA increases tolerance of plants to various type of stresses.

 Physiological effects and applications

(1) Induce abscission – ABA causes ageing and abscission of leaves & fruits (antiauxin) (cellulase & pectinase genes induced by ABA)

(2) Induce bud & seed dormancy – ABA regulates (anti–GA) bud & seed dormancy.

ABA plays a major role in seed maturation enabling seeds to become dormant.

(3) Induce senescence – ABA accelerates senescence of leaves.

(4) Inhibition of cell division & cell elongation – anti CK.

(5) Stomatal closing – ABA causing the stomatal closing under the water stress conditions. Increases resistance to frost injury. (anti transpirant & stress hormone)

(6) Delaying of flowering in LDP.

(7) Tuberisation in potato.

(8) Inhibitor of a–amylase synthesis – Inhibition of seeds germination.

(9) Geotropism in roots.


  •  H.H Cousin first suggested, that ripened oranges are responsible for ripening of unripen bananas.

  •  Ethylene is a gaseous pollutant hydrocarbon, but Burg reported it as a fruit ripening hormone.

  •  Pratt Goeschl – Recognized ethylene as a natural plant growth regulator.

  •  Biosynthesis of ethylene takes place by methionine amino acid. Ethylene is synthesized in large quantity by ripening fruits and senescent organs. *

  • Ethylene also formed in roots in water logged condition.

Physiological effects and applications

(1) Post harvest ripening of fruits – Citrus, oranges, banana, apple, tomato. today ethephon/CEPA (Chloroethyl Phosphonic acid) used at commercial level.

(2) Stimulation of senescence & abscission of leaves. Ethylene is synthesized in large quantity by ripening fruits and senescent organs.

(3) Flowering in pineapple.

(4) Triple response on stem :-

(i) Inhibition of stem elongation

(ii) Stimulation of radial swelling of stem

(iii) Horizontal growth of stem (ageotropism)

(5) Inhibits root growth :- Ethylene is inhibitor of root growth but stimulates the formation of root hairs.

(6) Epinasty of leaves.

(7) Femaleness (Feminising effect) Pineapple (Bromeliaceae).

(8) Tightening of hooks of epicotyl and hypocotyl.

(9) Inhibits the polar movement of auxin.

 Other growth regulating substances

Wound hormone Traumatic Acid :- Induce callus formation on injured parts (healing of wounds) Chemically traumatins are auxin like substance.

Calines (Formative hormones)

(i) Rhizocalines :- Produced by leaves & induce formation of roots.

(ii) Caulocalines :- Produced by roots & induce formation of stem.

(iii) Phyllocalines :- (Self forming hormone) produced in cotyledons & leaves, induce division of leaf mesophylls.

Morphactins or (HFCA) These are, synthetic growth inhibitors, which are polyvalent (wide range) in action

(i) Inhibition of internode elongation

(ii) Reduction of apical dominance & promotion of lateral branching

(iii) Reduces the laminar area of leaf.

(iv) Abolition of phototropism

  •  Chlormequat (CCC or Cycocel):- Growth inhibitor, which is used in bonsai.

  •  Alar - 85 (B-Nine):- in floriculture

  •  Agent orange :- Mixure of 2,4-D & 2,4,5-T used in bio–war. (Used by U.S.A. in Vieatnam war)

  • Amo - 1618 :- in biowar.

  •  Phosphon-D, Cycocel, Amo-1618, Alar-85, Ancymidol (A-REST) are antigibberellins and cause inhibition to stem growth.


Phyotochromes and Photoperiodicity - Plant growth and development, Biology, Class 11


  •  The relative length of day & night is called as photoperiod.

  •  The response of plants to the photoperiod, expressed in the form of flowering is called as photoperiodism. “Effect or requirement of relative length of day (photoperiod) & night (dark phase) on flowering of plants is called as photoperiodism”

  •  The phenomenon of photoperiodism was first discovered by Garner & Allard on Maryland mammoth (a mutant variety of tobacco) and biloxy soyabean. 

  •  Garner & Allard classified the plants in following groups.

(1) SDP (Short Day Plants) :- “These plants give flowers on exposure to photoperiod equal or shorter than their critical day length”. . They need a continuous (uninterrupted) dark period for flowering. Thus SDP also called as LNP (Long Night Plants).

  • Ex. of SDP :- Tobacco, Soyabean , Viola, Xanthium (Cocklebur), Chrysanthemum, Cannabis, Coleus, Chenopodium, Mustard, Dahlia, Sugarcane , Strawberry, Cosmos, Rice etc.

  •  In SDP the dark period is critical and must be continuous. If this dark period is breaks by a brief exposure to red light, then SDP will not flowers. 

  •  Maximum inhibition of flowering with red light occur at about the middle of critical dark period.

  •  Prolongation of the continuous dark period, initiates early & good flowering in SDP.

(2) LDP (Long Day Plants) :- These plants flowers only when they exposed to critical photoperiod or photoperiod longer than their critical day length”. . The light period is critical for LDP. Ex. :- Henbane (Hyoscyamus) Spinach, Sugarbeets, Radish, Carrot, Wheat, Larkspur, Barley, Avena, Potato.

  •  A brief exposure in the dark period stimulates flowering in LDP

(3) DNP (Day Neutral Plants) or Intermediate plants :- These plants do not need specific light period for the flowering. Ex. Zea, Cotton, Tomato, Sunflower, Cucumber 

  •  L-SDP :- These are SDP but must be exposed to long days during early stage of their growth. Ex. Bryophyllum

  •  S-LDP :- These are LDP but must be exposed to short photoperiod during early stage of growth. Ex. Wheat & Rye sps.

  • Cajlachjan :- Reported that stimulation of critical photoperiod is percepted by leaves. 

  • Chailakhyan :– Discovered “Florigen”, it has been not isolated, thus called as hypothetical hormone.


  •  Borthwick & Hendricks :- Discovered a light sensitive pigment responsible for flowering

  • Butler :- Give term “phytochrome” for this pigment & isolated it.

  •  Pigment phytochrome is a chromophore billiprotein, which is an open tetrapyrrolic related to phycobilin.

  •  Phytochrome mainly located on cell membrane of all type of plants.

  •  Phytochrome :- exists in two different forms Pr (Phytochrome red). – Red light absorbing form, induce flowering in SDP.

  • Absorption range- 630-670 nm. absorption peak-667 nm.

Pfr (Phytochrome far red) – This is far -red light absorbing form, induce flowering in LDP.
Absorption range - 720-740 nm. absorption peak-735 nm.

  •  Both forms of phytochromes are photobiochemically inter-convertible into each other and are stable.

  •  The Pfr (Yellowish) form, gradually changed in to Pr (bluish) form in dark.

PLANT GROWTH,Botany,Class 11

  • During the day the Pfr form is accumulated in the plants, which is inhibited to flowering in SDP but stimulates in LDP.

  • Phytochrome - Pfr (P730) is active form, which controls many photophysiological processes in plants.

  •  Control of morphogenesis by light & phytochrome is called photomorphogenesis.

  •  Now phytochrome is considered as universal distribution in plant kingdom.

Photomorphogenesis in higher plants appear to be under control of one of three photoreceptors.

(a) Phytochrome – which absorbs red and far red region of light.

(b) Cryptochrome – which absorbs blue and UV-A (380 nm) light.

(c) UV-B-Receptors – which absorb UV-B (290 nm) light.


  •  Effect of low temperature on the initiation and development of flower, was first realised by Klippart 1857

PLANT GROWTH,Botany,Class 11

  •  Detail study and term – ‘‘Vernalisation’’ by Lysenko (Credit of discovery).

  •  Chourad defined as 'acceleration of ability to produce flower by chilling treatment is called vernalisation'.

  •  Mainly embryo tip, shoot apex & leaves perceps induction of low temperature on plants.

  •  Concept of hormone ‘vernalin’ in vernalisation was given by Melcher et. al. This is a hypothetical plant hormone,because not has been isolated till today.

  •  Vernalisation of seeds or plant propagule in laboratory can be induced at 1°C to 10°C in presence of O2 & H2O.

  •  If vernalized plant prapagules are kept in high temperature, just after the low temp. treatment  then effect of vernalisation is reverse, this effect is called asdevernalization.


Significance :–

(i) Better & early flowering.

(ii) Vernalisation increases the resistance to fungal diseases.



  •  Period from complete maturity to degredative changes during the death of an organ or plant is known as senescence.

  •  During senescence a gradual destruction occurs in protoplasm, cell, tissue, organ or plant and functioning of the plant and plant parts.

  •  During the senescence, higher rate of catabolism starts, under the control of growth hormones like ABA, ethylene. Senescence occurs as a result of ageing and leads to death of plant parts or whole plant. (Senescence and ageing - studied in phyto-gerontology)

  •  Senescence may be of following types :-

(a) Whole plant senescence : ex. Tomato, Wheat, Mustard, Rice, Beans.

(b) Organ senescence : When plant part above ground dies (shoot) each year and root & rhizome system alive. Ex. Alfa-alfa, Sugarcane, Banana, Ginger.

(c) Sequential or progressive senescence : Evergreen perennials show progressive or sequential senescence of older leaves, lateral organs, branches, flowers, fruits and shoot.

Ex. Eucalyptus, Mango.

(d) Simultaneous or Synchronous leaf senescence : In perennial deciduous plants, all the leaves undergo senescence and abscission sp.

Ex. Dalbergia sisso, Azadirachta indica, Ficus religeosa.



  •  Detachment of senescent or mature plant organs like leaves, fruits, flowers due to change in hormonal activity.

  •  There is a separation layer (abscission layer) is formed within the region of attatchment of these parts. Cell wall layers and middle lamella are dissolved by the activity ofcellulaseandpectinases (Polysaccharide hydrolysing enzymes) during the abscission.

  •   Hormone ABA is main controllar of abscission process.



(A) Movement of locomotion :- When the whole plant, plant part or organs of plant move from one place to another place.

(I) Autonomous :- (by internal stimulus )

(1) Amoeboid :- Ex : Gametes of Spirogyra

(2) Ciliary movement :- Ex : Chlamydomonas, Euglena, Zoospores

(3) Cyclosis :-

(i) Rotation – Whole protoplasm moves around the one central vacuole, in one direction. Ex :Hydrilla, Vallisneria cells.

(ii) Circulation :- Protoplasm moves, around the different vacuoles in different directions. Ex : Stamenal hairs of Tradescantia.

(II) Induced/paratonic/tactic movement :-  (Due to external stimulus)

(i) Phototactic :- Due to stimulus of light . Ex : Algae - by (Eye spot/Stigma).

(ii) Chemotactic :- Due to stimulus of chemicals. Ex : Male gametes of lower plants (antherozoids). By Chemical gradient sensing mechanism.

(iii) Thermotactic :- Due to stimulus of temperature. Ex : Chlamydomonas , Euglena (B) Movement of curvature :- Movement of plant organs only.

(I) Autonomous :-  Movement of variation - Dance movement by Desmodium. (Indian telegraph plant) due to turgor pressure change.

Epinasty & hyponasty, the growth movements in flower & leaves.

(II)Induced/Paratonic movement :- (By external stimulus, but directional)

 (i) Tropic movement :- Definite direction towards stimulus.

PLANT GROWTH,Botany,Class 11

Chemotropism  :- Ex.Pollen tubes & fungal hyphae

  •  Definite direction in relation to chemicals.

(d) Thigmotropism (haptotropism) :- Ex : Tendrils, haustoria of Cuscuta.

  •  Definite direction in response to contact or support.

(e) Hydrotropism :- Ex : Roots of seedlings

(ii) Nastic movement (External stimulus but diffused type or nondirectional) :-

(a) Nyctinasty :- Ex : Flowers, leaves, stomata, daily movement (Sleep movements)

  •  Due to rhythemicity of day and night.

(b) Thigmonasty or haptonasty :- Tentacles of insectivorous plants

(c) Chemonasty :- Ex : Tentacles of insectivorous plants

(d) Seismonasty :- Ex : Mimosa (touch me not plant) turgor change in pulvinus leaf base K+ ion also involved in this movement.



  •  Many plant parts specially leaves exhibits nastic movement and involves differential growth, this type of movement is known as movement of gwowth.  This movement, is caused due to unequal growth in plant organs. Ex : Epinasty, hyponasty, Nutation.

  •  Epinasty & hyponasty :- Ex : Leaves, flower (petal) opening & closing respectively. Epinasty - More growth on upper surface of plant parts.

Hyponasty - More growth on lower surface of plant parts.
Both epinasty & hyponasty are example of autonomic growth movements.

  • Nutation :- Zig zag growth of plant organ mainly shoot, is called as nutation

  • Circumnutation :- Spiral growth of plants in tendrils

  • Portulaca is known as compas plant.

  • Rhizomes diageotropic (90° to gravitation force) 

  • Clinostat :- used for nullifying geotropism

PLANT GROWTH,Botany,Class 11

  • Traumatropism :- Injury induced plant movement

  •  Plageotropism :-  Shown by stem & root branches growing at an angle of 45° from axis of plant.

  •  Climacteric fruits (Banana, Apple, Avocados):- Fruits, in which rate of respiration increases (climacteric respiration)during their ripening(ethylene). Citrus is non climacteric fruits.

  •  The flower stalk of the poppy is +vely geotropic but after the opening of flower, this stalk change as  negative geotropic.

  •  Formation of nodule is a combined activity of cytokinin (By bacteria) and auxin.(By leguminous plant)

  •  Blue light has more effects on most of physiological and growth processess in plants except photosynthesis and photoperiodism.

  •  Arabidopsis thaliana (Brassicaceae) is the most widely used plant tool for the studies of devlopmental genetics and growth physiology of plants. 

  •  Betacyanin or Betalains :- Pigment mainly found in valcoule of beet roots and flower of Bougainvellia are differ from anthocyanin due to the presence of nitrogen (N). These pigments do not show reversibility of colour change due to pH change.

  •  Anthocyanin is water soluble vacuolar pigment, which does not involve in photosynthesis.

Anthocyanin exhibits different colour like purple, pink, blue, scarlet etc.
The colour of anthocyanin is sensitive to pH change for Ex. colour of anthocyanin changes from Red (acidic pH) to Violet (neutral pH) to blue (in alkaline pH).
Turgorin-a newly discovered hormone found in pulvinous leaf base regulates turgor pressure changing movements.

Growth rate : Increased growth per unit time.

Plants growth is of two types :

(a) Arithmetec growth : From dividing cell two new cells are formed (by mitotic division) out of them one daughter cell continues to divide while other differentiate and mature (stop dividing).

(b) Geometric / Exponential growth : From dividing cell (bymitotic division) both daughter cells retains the ability to divide and continue to do so.

(c) Absolute and relative growth rates : Absolute growth rate : Measurement and the comparision of total growth per unit time in plant or plant parts.
or Total growth occurs in unit time in plant or plant parts.

PLANT GROWTH,Botany,Class 11

Relative growth Rate : The growth of the given system per unit time expressed on a common basis i.e. per unit initial parameter in plant parts. or Total growth occurs in unit time in comparision to initial growth in plant or plant parts. Relative growth rate is generally high in young developing plant parts.

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