CLASSIFICATION OF PLANTS

Introduction: Plants are included in Kingdom Plantae. These were classified into major groups, each with distinct characters.


(5.1) CLASSIFICATION OF PLANTS:
According to various systems, the classifications of plants are as given below-

(a) Artificial System: - In this system, plants were classified on the basis of one or few convenient superficial characters. Pliny the Elder (79, AD) first of all give artificial system of classification.
- Theophrastus proposed first a kind of artificial system of classification on the basis of habit of plants. He classified them as herbs, shrubs, under shrubs, trees etc.
- C. Linnaeus (1707-1778) used artificial system of classification based only upon floral parts. The plants were classified as Hypogyny, Perigyny and Epigyny. It is also known as Sexual / Numerical System of classification. Linnaeus also classified plants on the basis of number and position of stamens. Plants with one stamen belonged to class Monandria and with 20 or more stamens to class Icosandria.He divided plants into 24 classes. Out of these, 23 classes were of Flowering Plants and 24rth class was of Flowerless plant(Cryptogamia). He published papers like Flora Laponica, Species Plantarum, Critica Botanicaa and Systema Naturae.
This system was inadequate. So, classification according to it was not accepted.

(b) This system is more common and divides plant kingdom into two sub-kingdoms Cryptogamae and Phanerogamae.
Sub-kingdoms were named on the basis of presence or absence of seeds / flowers.
Cryptogamae –(kryptos-concealed gamos-marriage) These included all non-flowering plants without seeds like Algae, Fungi, Lichens, Mosses and Ferns.
Phanerogamae- (Phaneros- visible gamos-marriage) or Spermatophytes (sperma-seed-phyton-plant)-These included all flowering plants with seeds.
Phanerogams can be distinguished from Cryptogams by presence of well-developed vascular tissue for conduction of water, minerals (xylem) and food (phloem). Plants with their vascular tissues resembling trachea (wind pipe) of animals are called Tracheophytes.


(5.2) THALLOPHYTA- ALGAE
1 - It includes both, Algae and fungi.
2 - Algae are usually aquatic, either marine (seaweed) or Fresh water. Few occur in moist soil. Wet rocks, moist tree trunks also. Fungi live in aquatic, sub-aquatic and terrestrial habitats.
3 -Body called ‘Thallus’ is unicellular flagellated (in Chlamydomonas), non-flagellat-ed (in Chlorella),colonial form (in Volvox) or filamentous (Ulothrix,Spirogyra).In some forms, it is flat and leaf like (Laminaria)and attaches to rock by structure called ‘Holdfast’. Fungi has branched Hyphae, which gets interwoven to form Mycelium.
4 -Algae are of different colours because of presence of different pigments in it. Green Algae has green pigments-Chlorophyll-a and Chlorophyll b in girdle /spiral shaped chloroplast. Brown pigment-Fucoxanthin, Red pigment-Phycoerythrin and blue pigment-Phycocyanin impart brown, red and blue colours to algae. Red Algae secretes and deposits calcium carbonate and appears like coral.E.g. of red algae are Polysiphonia,Gelidium, Batrachospermum.
5 - Algae show autotrophic nutrition. Fungi show heterotrophic nutrition.
6 -Algae reproduce vegetatively by fragmentation, budding or tubers. Asexual reproduction occurs by motile and non motile spores. Sexual reproduction occurs by Isogamy,  Anisogamy and Oogamy.
7 -Life Cycle has distinct haploid and diploid phases, which alternate thus exhibiting Alternation of Generations.       On the basis of pigment colours, algae is further sub divided into Chlorophyceae (Green), Phaeophyceae (brown) and Rhodophyceae (red) Algae.


(5.3) BRYOPHYTA (Gk. Bryon-Moss     phyton-Plant)
1 . These occur in damp places, mostly during rainy season growing as green mat on rocks, soil, wall, tree trunks etc.
2 . Thalloid body is flat (Riccia) / liver shaped (Marchantia). So, these are also called as ‘Liverworts’.
3 . Some plants have body differentiated into stem and leaf like structure. Thallus is attached to soil, rocks, wall by root like structures called as ‘ Rhizoids’.
4 . Lack vascular tissues.
5 . Vegetative reproduction is very common and occurs by fragmentation, Gemmae and Tubers. Sexual reproduction involves male sex organs (Antheredium) and female sex organs (Archegonium).
6 . Life cycle has haploid and diploid phases. Haploid (Gametophytic) phase and diploid (Sporophytic) phase alternate with each other exhibiting Alternation of Generations’.
7 . Based on plant body and method of sexual reproduction, Bryophytes are sub-divided into Hepaticae (e.g.Marchantia) ,Anthocerotae (e.g. Anthoceros) and Musci (Funaria) Classes.


(5.4) PTERIDOPHYTA: (Pterido- Pteris    phyton-plant)
1 - Occur in humid and tropical climate on soil, rocks or on other plants. Equisetum grows near water bodies.
2 - Body has underground stem liske Rhizome having roots and aerial shoots with leaves.  Some have simple leaves with single vein and some have compound leaves with several leaflets (pinnules).Compound  leaves in Adiantum are arranged beautifully and look like maiden’s hair. So it is also called as ‘Maiden Hair Fern’.
3 - Sporangia occur on leaves in clusters called ‘Sori’. Spore bearing leaves are called ‘Sporophylls’.
4 - Vegetative reproduction occurs by fragmentation and budding. In ‘Walking fern’-Adiantum, new plant is produced wherever its leaf tip comes in contact with the soil.
5 - Plant body represents Sporophyte and is diploid. Spores are haploid and germinate on moist soil to form thallus like structure called ‘Prothallus’ which represents Gametophyte.
6 - Male sex organs (Antheridium) and female sex organs (Archegonium) help in sexual reproduction.
7 - Alternation of Generations is there. Dominant phase is Sporophytic.
8 - Pteridophyta is divided into 4 sub-classes-Psilopsida, Lycopsida, Sphienopsida and Pteropsida on basis of body organization, leaf structure and location of sporangia.
9 - Examples are-Dryopteris, Pteris, Lycopodium, Selaginella, Adiantum.


(5.5) GYMNOSPERMS: - (Gk. Gymnos-naked    sperma-seed)
1. Found in cool climate of hills. Some occur in warm climate also (Cycas).
2. These are generally tall woody trees. Few are bushes (Ephedra) or climbers    (Gnetum).
3. Have well developed vascular system of xylem and phloem,which helps in absorbing and conducting water in tall trees.
4 . Have no flowers but have seeds.
5. Leaf like structures called Sporophylls bear sporangia. Megasporophyll has Megasporangium (ovule). Microsporophyll has Microsporangium (pollen sac).Microsporophylls   and Megasporophylls form male cones and female cones respectively. Later, these   produce male and female gametes respectively.
6. After fertilization, zygote (2N) is formed in ovule, which ripens to form seed.
7. Alternation of Generation is there. Sporophyte is dominant phase.
8. These are further sub divided into 3 classes- Cycadopsida, Coniferopsida and Gnetopsida on the basis of nature of leaves, wood, vascular system & reproductive structure
9. Examples are Cycas, Araucaria, Ephedra, Gnetum, Pinus, Abies.


(5.6) ANGIOSPERMS: - (Gk. Angion- vessel    sperma-seed)- Flowering Plants.
(i)         Occur in diverse habitats and almost everywhere. These are trees, shrubs and herbs.
(ii)        Body is clearly differentiated into roots, stem and leaves.
(iii)       They have highly developed vascular system of xylem (with vessels) and phloem (With companion cells).
(iv)       Sporophylls are aggregated to form flowers. Stamens in flower represent microspor–ophyll whereas carpel represents megasporophyll.
(v)        Pollination occurs through several agencies like birds, animals, insects etc.
(vi)       After fertilization, ovule remains inside ovary, which later develops into fruit.
(vii)      These show Double Fertilization.
(viii)     Examples are sunflower, Maize, Wheat etc.

CLASSIFICATION OF ANGIOSPERMS: -

Most well known system of classification of Angiosperms was given by George Bentham (1800-1864) and Joseph Dalton Hooker (1817-1911). They published it in their book ‘Genra Plantarum’ (1862-1883)

Bentham and Hooker’s System :-It is based on form and relationship of plants. It is handy and accurate and covered about 97,000 species of seed plants. The Phanerogams were divided into classes, which were further sub divided into sub-classes. Sub-classes have ‘series’ which are further categorized into ‘Cohorts’ (equivalent to orders in other systems). Cohorts, further have ‘orders’ (equivalent to Families). There are total 202 orders (families). Few orders could not be placed properly in schematic arrangement and so ,because of their unusual position, these are called ‘Ordines Anomali’.



(Has 6 cohorts, 37 orders)            (Has 3 cohorts, 9 orders)                (7 orders)
Cohort I Ranales (8 orders)          Cohort I Rubiales (2 orders)          order130 Nyctaginaceae

Order1   Ranunculaceae                order 85 Caprifoliaceae                  order131 Illecebraceae
Order 2 Dilleniaceae                       order 86 Rubiaceae                         order132 Amarantaceae
Order 3 Calycanthaceae                Cohort II Asterales (4 orders)        order133 Chenopodiaceae
Order 4 Magnoliaceae                    order 87 Valerianea                           order134 Phytolaccaceae
Order 5 Annonaceae                       order 88 Dipsacaceae                      order135 Batideae
Order 6 Menispermaceae              order 89 Calyceraeae                        order136 Polygonaceae
Order 7 Berberideae                       order 90 Compositae                          Series 2 Multiovulatae-
Order 8 Nymphaeaceae                 Cohort III Campanulales                  (3 orders)    Aquaticeae
Cohort II Parietales (9orders)       Order 91 Stylidieae                            (1 order)
Order 9 Sarraceniaceae                 order 92  Goodeniaceae                   order137 Podostemaceae
Order 10 Papaveraceae                  order 93 Campanulaceae                Series 3 Multiovulatae-
Order11 Cruciferae                          Series 2 Heteromerae                       terrestres
Order 12 Capparidaceae               (has 3 cohorts, 12 orders)                 (3 orders)
Order 13 Resedaceae                    Cohort IV Ericales (6 orders)          order138 Nepenthaceae
Order 14 Cistineae                          order 94 Vaccinaceae                      order 139 Cytinaceae
Order 15 Violaceae                          order 95 Ericaceae                           order140 Aristolochiaceae
Order 16 Canellaceae                     order 96  Monotropeae                    Series 4 Microembryeae
Order 17 Bixineae   order 97           Epacrideae     (4 orders)

Cohort III Polygalineae (4 orders)  order 141 Piperaceae
Order18 Pittosporeae                       order 98 Diapensiaceae         order142 Chloranthaceae
Order 19 Tremandreae                    order 99 Lennoaceae             order143 Myristicaceae
Order 20 Polygaleae                         Cohort V Primulales (3 orders)order144 Monimiaceae
Order 21 Vochysiaceae                    order 100 Plumbagineae
Cohort IV Caryophyllineae (4 orders)                                    Series V Daphnales
Order 22 Frankeniaceae                 order 101 Primulaceae               (5 orders)
Order 23 Caryophyllaceae              order 102 Myrsineae                       order145 Laurineae    
Order 24 Portulaceae                   Cohort VI Ebenales (3 orders)order146 Proteaceae
Order 25 Tamaricaceae               order 103 Sapotaceae                      order 147 Thymelaeaceae
Cohort V Guttiferales  (6 orders)   order 104 Ebenaceae            order148 Penaeaceae
Order 26 Elatineae                      order 105 Styracaceae         order149 Elaeagnaceae
Order 27 Hypericineae                 Series 3 Bicarpellatae        Series VI Achlamydosporae
Order 28 Guttiferae                      (has 4 cohorts, 27 orders)                   (3 orders)
Order 29 Trenstroemiaceae          Cohort VII Gentianales (6 orders)order150 Loranthaceae
Order 30 Dipterocarpaceae        order 106 Oleaceae               order151 Santalaceae
Order 31 Chlaenaceae               order 107 Salvadoraceae      order 152 Balanophoreae
Cohort VI Malvales (3 orders)      order 108 Apocynaceae        Series VII Unisexuales      
Order 32 Malvaceae                    order 109 Asclepiadaceae                      (9 orders)
Order 33 Sterculiaceae                 order 110 Loganiaceae             order 153 Euphorbiaceae
Order 34 Tiliaceae                       order 111 Gentianaceae           order154 Balanopseae
Series 2 Disciflorae (has 4 cohorts                                              order155 Urticaceae
21 orders & 2 anomalous orders) Cohort VIII Polemoniales           order156 Plantanaceae
Cohort VII Geraniales (has 11orders)              (5 orders)                  order157 Leitneriaceae
Order 35 Lineae                            order 112 Polemoniaceae          order158 Juglandeae
Order36 Humiriaceae                    order 113 Hydrophyllaceae       order159 Myricaceae
Order 37 Malpighiaceae                   order 114 Boraginaceae             order160 Casuarinaceae
Order 38 Zygophylleae                 order 115 Convolvulaceae         order161 Cupuliferae
Order 39 Geraniaceae                   order 116 Solanaceae             Series 8 Ordines Anomali
Order 40 Rutaceae                        Cohort IX Personales (8 orders)           (4 orders)
Order 41 Simaroubeae                  order 117 Scrophulariaceae       order162 Salicaceae
Order 42 Ochnaceae                     order118  Orobanchaceae          order163 Lacistemaceae
Order 43 Burseraceae                   order119 Lentibulariaceae      order164 Empetraceae
Order 44 Meliaceae                       order120 Columelliaceae          order165 Ceratophyllaceae
Order 45 Chailletiaceae                 order121 Gesneriaceae
Cohort VIII Olacales(has 3orders)  order122 Bignoniaceae
Order 46 Olacineae                        order123 Pedaliaceae
Order 47 Ilicineae                          order124 Acanthaceae
Order 48 Cyrillae                           Cohort X Lamiales (5 orders)
Cohort IX Celastrales (has 4 orders) order125 Myoporineae
Order 49 Celastrineae                     order 126 Selagineae
Order 50 Stackhousieae                 order 127 Verbenaceae
Order 51 Rhamnaceae                    order 128 Labiatae
Order 52 Ampelideae (Vitaceae)       order 129 Anomalous-Plantagineae
Cohort X Sapindales (has 3 orders)
Order 53 Sapindaceae
Order 54 Sabiaceae
Order 55 Anacardiaceae

2 Anomalous orders

Order 56 Coriarieae
Order 57 Moringeae
Series 3 Calyciflorae                                7 Series of class Monycotyledonae 
(Has 5 cohorts & 27 orders)                       Series 1 Microspermae (3 orders)
Cohort XI Rosales (has 9 orders)              order169 Hydrocharitaceae
Order 58 Connaraceae                                order 170 Burmanniaceae
Order 59 Leguminosae                                order 171 Orchidaceae
Order 60 Rosaceae                                     Series 2 Epigynae (7 orders)
Order 61 Saxifrageae                                  order 172 Scitaminae
Order 62 Crassulaceae                                order 173 Bromiliaceae
Order 63 Droseraceae                                order174 Hoemadoraceae
Order 64 Hamamelideae                             order175 Iridaceae
Order 65 Bruniaceae                                  order176 Amaryllidaceae
Order 66 Haloragaceae                             order177 Taccaceae
Cohort XII Myrtales (has 6 orders)           order178 Dioscoreaceae
Order 67 Rhizophoreae                                Series 3 Coronariae (8 orders)
Order 68 Combretaceae                               order179 Roxburghiaceae
Order 69 Myrtaceae                                     order180 Liliaceae
Order 70 Melastomataceae                            order181 Pontederiaceae
Order 71 Lythraceae                                    order 182 Philydraceae
Order 72 Onagraceae                                   order 183 Xyrideae
Cohort XIII Passiflorales (has 7 orders)          order184 Mayaceae
Order 73 Samydaceae                                   order185 Commelinaceae
Order 74 Loasaceae                                      order186 Rapataceae
Order 75 Turneraceae                                   Series 4 Calycineae (3 orders)
Order 76 Passifloreae                                    order187 Flagellarieae
Order 77 Cucurbitaceae                                order188 Juncaceae
Order 78 Begoniaceae                                   order189 Palmae
Order 79 Datiscaceae                               Series 5 Nudiflorae (5 orders)
Cohort XIV Ficoidales (has 2 orders)         order190 Pandanaceae
Order 80 Cacteae                                     order191 Cyclanthaceae
Order 81 Ficoideae                                  order192 Typhaceae
Cohort XV Umbellales (has 3 orders)         order193 Aroideae
Order 82 Umbelliferae                                 order194 Lemnaceae
Order 83 Araliaceae                                Series 6 Apocarpae (3 orders)
Order 84 Ceraniaceae                             order195 Triurideae
Order196 Alismaceae
Order197 Najadaceae
Series 7 Glumaceae (5 orders)
Order198 Eriocauleae
Order199 Centrolepideae
Order200 Restiaceae
Order201 Cyperaceae
Order202 Gramineae

CLASS I: Dicotyledons
- Seeds are with 2 cotyledons.
-Leaves have reticulate venation with alternate, spiral or whorled arrangement.
-Flowers are tetramerous or pentamerous (i.e. have four or five members in floral whorls).
-Vascular bundle is open type i.e. cambium present between xylem and phloem.
Class was further sub-divided into sub-classes on basis of no. and nature of floral whorls. On basis of position of ovary, sub-classes were further sub divided into series, which were further categorized into ‘cohorts’ (equivalent to order) and ‘orders’ (equivalent to Families).

(a) Sub-class: Polypetalae  (poly-free      petalae-petals)
-Corolla has whorl of 4-5 petals, which are free from one another. Calyx present.
-Sepals and petals are distinct and form two whorls.

Series (i) Thalamiflorae
-Many stamens, sepals and petals arising from thalamus above ovary.
-Ovary superior without any disc.
-Sepals are free from ovary.
-It has 6 cohorts and 34 orders. (See chart)

Series (ii) Disciflorae
-Flowers hypogynous, definite stamens.
-Ovary superior with nectariferous disc at the base.
-Sepals are either free (polysepalous) or fused (gamosepalous).
-It has 4 cohorts and 23 orders. (See chart).

Series (iii) Calyciflorae
-Flowers are perigynous or epigynous
-Inferior ovary.
-Sepals are fused and calyx forms a tube around ovary.
-Includes 5 cohorts and 27 orders. (See chart).

(b) Sub-class: Gamopetalae ( gamo-fused  petalae-petals)
-Corolla has 4-5 petals, which are either partially or completely fused with one another.
-Sepals and petals are distinct.
-Stamens are attached to petals (Epipetalous).

Series (i) Inferae
-Stamens equal to the number of corolla lobes.
-Epigynous flowers.
-Inferior ovary.
-Has 3 cohorts and 9 orders. (See chart).

Series (ii) Heteromerae
-Stamens either equal to or twice the number of lobes of corolla.
-Stamens free from corolla.
-Hypogynous flower with more than two carpels.
-Superior ovary.
-Has 3 cohorts and 12 orders. (See chart).

Series (iii) Bicarpellatae
-Stamens less in number than corolla lobes.
-Two or more carpels with superior ovary.
-Hypogynous flower.
-Includes 4 cohorts and 24 orders.

(c ) Sub-class : Monochlamydae (Incompletae / Apetalae)
( mono-one    chlamydae-whorl)
-Incomplete flowers.
-Sepals and Petals are not distinct.
-Flowers have only one whorl with no petals. (Sepaloid).
-No cohorts.

Series (i) Curvembryae
-Embryo curved around the endosperm.
-One ovule.
-It has 7orders. (See chart).

Series (ii) Multiovulatae Aquaticeae
-Many ovules.
-Are submerged aquatic plants.
-It has 1 order.(see chart)

Series (iii) Multiovulatae Terrestres
-Many ovules.
-Terrestrial plants.
-Has 3 orders. (See chart).

Series (iv) Microembryae
-Minute embryo.
-Has 4 orders.(see chart)

Series (v) Daphnales
-Ovary with one carpel.
-Ovary with one ovule.
-It has 5 orders. (See chart)

Series (vi) Achlamydosporeae
-Inferior, unilocular ovary with 1-3 ovules.
-It has 3 orders. (See chart)

Series (vii) Unisexuales
-Unisexual flowers.
-Has 9 orders. (See chart)

Series (viii) Ordines Anomali
-Families of uncertain relationships.
-It has 4 orders. (See chart).

CLASS II- Gymnospermeae (Plants with naked seeds or seed plants without flowers).
This class is in between dicotyledons and monocotyledons. Some characters of it are: -
(i)         These are usually resinous trees or shrubs found predominantly in snowy, cold   regions. E.g. Cycas.Some are very large and live for thousands of years.e.g.Sequoia sempervirens.
(ii)        Leaves are needle like.
(iii)       These have well developed vascular system of xylem (without vessels) and Phloem(without companion cells).
(iv)       Flowers absent. Have two types of sporophylls-Microsporophylls & Megasporo-phylls. The two sporophylls form ‘Cones’- Male cones (Pollen cones) and Female Cones. (Seed cones).
(v)        Seeds are naked i.e. don’t occur inside fruit and lie exposed on surface of mega-sporophyll i.e. ovules are naked and don’t occur inside ovary.
(vi)       Pollination is direct and generally through wind.
(vii)      Male and Female gametophyte present.
(viii)     Male gametophyte forms two gametes, which show Double Fertilization.
(ix)       It has been divided into 3 families- Cycadaceae, Conifereae & Gnetaceae.
(x)        E.g. Cycas, Pinus, Ephedra, Araucaria, Cedrus.
(xi)       It includes 3 orders. (See chart).


CLASS III: Monocotyledons -These are usually herbs with simple large leaves showing parallel venation.
-Trimerous flowers i.e. floral parts exist in sets of three or its multiples.
-Embryo has one cotyledon.
-Primary roots are short-lived. Tap roots absent, Adventitious roots present.
-Vascular bundles scattered and closed type.
-E.g. Smilax, Colocasia, Banana, Palm, Grasses, Orchids, Bamboo, Lilies etc.
-These have been divided into 7 series on basis of nature of perianth and condition of Ovary

Series (i) Microspermae
-Petaloid perianth.
-Ovary inferior, unilocular with epigynous flower.
-Seeds minute, numerous and without endosperm.
-It has 3 orders. (See chart).

Series (ii) Epigynae
-Partly Petaloid perianth.
-Ovary inferior.
-Seeds are endospermic with nutritive tissue.
-It has 4 orders. (See chart).

Series (iii) Coronariae
-Petaloid perianth.
-Ovary superior and free.
-Seeds endospermic.
-It has 8 orders. (See chart).

Series (iv) Calycineae
-Perianth sepaloid.
-Ovary superior and free.
-Seeds endospermic.
-Includes 3 orders. (See chart).

Series (v) Nudiflorae
-Perianth absent or reduced to hair or scales.
-Ovary superior with solitary carpels.
-Endospermic seeds.
-Has 5 orders. (See chart).

Series (vi) Apocarpae
-Perianth with one or two whorls. Sometimes, it may be absent.
-Ovary superior. Carpels free.
-Endosperm absent.
-Has 3 orders. (See chart).

Series (vii) Glumaceae
-Perianth is either absent or is scaly or highly reduced.
-Unilocular ovary with single ovule.
-Has 5 orders. (See chart).

Merits of Bentham and Hooker’s System: -(i)   Every genus and species was studied from actual specimens and preserved herbarium sheets. Their description was based on detailed studies and dissections.
(ii)  The descriptions given were easy to follow and were of practical utility for identification of species upto Family level. Information related to their geographical distribution was also given.
(iii)  In the division Polypetalae, new series Disciflorae is put in between Calyciflorae and Thalamiflorae.
(iv) Unlike de Candolle, who distributed conifers among well defined taxas of dicots, Gymnosperms were considered a third taxon by Bentham and Hooker and placed in Between monocots and dicots.
(v) Genra was further sub-divided into sub-genra, which included important relevant sps. This made study more convenient.
(vi)  Some aspects of system show affinity with modern concept of evolution. E.g. order Ranales is placed in the beginning and recent taxonomic studies have also established Ranales among the most primitive orders.
(vii)  The placing of monocots after dicots is also according to evolutionary trends.

Demerits of Bentham and Hooker’s System:
(i)  Placing of gymnosperms between dicots and monocots is anomalous.
(ii)  Among dicots, Monochlamydae is considered highly evolved and Polypetalae as most primitive. Gamopetalae is placed in between the two. This is contrary to evolutionary trends.
(iii)  Monochlamydae is not well-defined group as several families which have affinity with Polypetalae are included in it.
(iv)  The placement of families like Asteraceae in beginning of Gamopetalae and Orchidaceae in Microspermae do not justify recent evolutionary trends.(v)        Some closely related families are kept apart.

PLANT NUTRITION

All living organisms require nutrients for their growth and development. Organisms which can make their own food are autotrophs e.g, Plants. Organisms which cannot make their own food and depend on auto – trophs for food are called Heterotrophs. Plants obtain their nutrients (minerals) from soil. This is known as Mineral Nutrition.  2.1 Essential Mineral Elements:– Elements which are required essentially for plants growth and development are called. ‘Essential Mineral Elements’ The criteria for essentiality of an element is: (i) It should be absolutely necessary for supporting normal growth & development of plant (ii) The element required should be specific (iii) The element cannot be replaced by any other element (iv) The element must be directly involved in metabolism of the plant. Total 105 elements are there, out of which 20 are essential for the plant. Essential elements are divided into two categories:– 1- Macro nutrients 2 -  Micro nutrients Macronutrients are the nutrients present in larger quantity in the plants. Their concentration are 1 – 10 mg per gram of dry matter e.g, C, H, O, N, P, S, K, Ca, Mg, Si. Micronutrients are nutrients present in smaller amounts i.e, less than 0.1 mg per gram of dry matter e.g, Fe, Zn, Mn, Mo, Cu, Cl, B. These are also called ‘Trace Elements’. 2.2 Sources of Essential Elements:– Main sources are air and water. Carbon & oxygen are obtained from air. Hydrogen is obtained from water. C, H, O are the building blocks of macromolecules which form the plant body. Nitrogen is present in the air but plants cannot use it as such. So they get nitrogen from the soil as nitrates. P & S are also obtained from soil as Phosphates & Sulphates.  2.3 Role of Macro – and Micro nutrients:– Essential elements perform many roles like:– * Some synthesize components of the cell. * Some take part in synthesis of materials * Some act as components of enzymes * Some help in oxidation – reduction reactions * Some participate in energy transfer, maintenance of osmotic pressure, buffer action etc. HYDROPONICS:– It helps in determining the role of individual elements. It is a technique in which plants are grown with their roots immersed in nutrient solution without soil. In this, plants are raised in small tanks covered with wire net. It is filled with water solution containing all the required elements. Solution is changed from time to time. Oxygen is bubbled in for proper aeration. For studying deficiency symptom, particular ion? is eliminated from the nutrient medium Role of various elements are:– 1 - NITROGEN:– Source:– Soil. It is absorbed as Nitrate, Nitrite or ammonium salts Function:– It is required in greatest amount by plant. It forms proteins, vitamins, nucleic acids & hormones Deficiency Symptoms:– Stunted growth, Yellowing of leaves, late flowering, purple shoot 2 - PHOSPHOROUS:– Source:– Soil, in the form of phosphate ions Function:– It is a constituent of cell membranes, proteins nucleic acids,  nucleotides Deficiency Symptoms:– Poor growth, delay in seed germination purple/red spots on leaves, premature falling of leaves 3 - POTASSIUM:– Source:– Inorganic compounds like Potassium Sulphate (K2SO4), Potassium nitrate (KNO3). Function:– it helps to maintain anion – cation balance in cell, is involved in protein synthesis, opening – closing of stomata, activation of enzymes, maintaining turgidity of cells. Deficiency Symptoms:– Scorched leaf tips, shorter internodes, premature death, bushy growth. 4 - CALCIUM:–  Source:– Soil, It is absorbed in the form of Ca2+ ions from CaCo3 etc. Function:– formation of mitotic spindle during cell division, for normal functioning of cell membranes, activation of enzymes, regulating metabolic activities. Deficiency Symptoms:– Stunted growth, Necrosis, abnormal cell division. 5 - MAGNESIUM:– Source:– Soil, absorbed as Mg2+ ion Function:– Activation of enzyme in respiration & photosynthesis, synthesis of DNA & RNA, maintains ribosome structure Deficiency Symptoms:– Chlorosis, Necrosis, Premature leaf abcission 6 - SULPHUR:–  Source:– Soil as sulphates (So42–) Function:– Forms aminoacids cysteine & methionine, constituent of coenzymes, vitamins Deficiency Symptoms:– Chlorosis, stunted growth, anthocyanin accumulation, change in pigmientation 7 - IRON:–  Source:– Soil, It is obtained as Ferric ion (Fe3+) Function:– It is important constituent of proteins like Ferredoxin. Takes part in electron transport, photosynthesis development of chloroplast Deficiency Symptoms:– Chlorosis of leaves, reduced growth 8 - MANGANESE:–  Source:– from soil as Mn2+ Function:– Activation of enzymes involved in photosynthesis respiration and nitrogen metabolism Deficiency Symptoms:– Chlorosis, grey spots on leaves, sterile flowers 9 - ZINC:–  Source:– obtained as Zn2+ ions from minerals containing zinc Function:– Activation of enzymes, synthesis of Auxins Deficiency Symptoms:– Distortion of leaves, reduction in fruits and leaves, smaller leaves 10 - COPPER:–  Source:– From soil as Cupric ion (Cu2+) Function:– Overall metabolism of plant, chlorophyll synthesis Deficiency symptoms:– Necrosis of leaf, dieback of shoot, rough bark 11 - BORON:–  Source:– From soil as BO33– or B4O72– Function:– Helps in uptake & utilization of Ca2+, membrane function pollen germination, cell elongation, cell differentiation. Deficiency Symptoms:– Death of root/shoot tips, loss of apical dominance, small fruit size, stunted growth. 12 - MOLYBDENUM:–  Source:– Absorbed as molybdate ion (MoO22+) Function:– Component of enzymes participating in Nitrogen metabolism Deficiency Symptoms:– ‘Whiptail’ disease in cabbage where young leaves get distorted causes nitrogen deficiency 13 - CHLORINE:–  Source:– As chlorine gas or chlorides in soil Function:– Cell division, in photosynthesis Deficiency Symptoms:– Wilted leaves, stunted growth, reduced fruiting 2.4 Mechanism of Absorption of Elements:– Plants absorb mineral ions from the soil through roots and then translocate these to other parts of the plant. In this process, two main phases are seen:– 1 - In first phase, ions are taken into ‘free space’ / ‘outer space’ of the cells. It includes intercellular space & cell wall. Here ions can be exchanged freely. Energy is not required in this process, so this is passive 2 - In second phase, ions are taken into ‘inner space’ which means cytoplasm & vacuoles. Here ions are not exchangeable. This process requires metabolic energy and so it is an active process. Flux:– The movement of ions is called ‘Flux’ Influx:– Movement of ions into the cell is ‘Influx’ Efflux:– Outward movement of ions is ‘Efflux’. Mineral absorption occurs by 2 methods – Passive and Active (A) Passive Absorption:– Energy is not required in this type of absorption. It occurs along concentration gradient for unchanged minerals (i.e, from higher concentration to lower concentration) and along electrochemical gradient for ions (as ions have charge also). Passageway is provided by membrane channels Various theories of passive absorption are:–  (i) Ion Exchange:– Exchange of ions takes place between roots and soil. Cations are exchanged with H+ ions Anions are exchanged with OH– or HCO3– ions. It can occur either bycarbonic acid exchange or by contact exchange. In carbonic acid exchange, CO2 dissolves in H2O to form H2CO3 which breakes up into H+ & HCO3– . These can then be exchanged. In contact exchange, ions present on the surface of roots come in contact with ions in the soil & get exchanged. (ii) Donnan Equilibrium:– All cells have some fixed ions present on inner side which cannot diffuse out So, for reaching the equilibrium, additional ions (opposite in change to the ones fixed inside) are required. This continues till Donnan Equilibrium is reached when product of anions & cations in internal solution becomes equal to the product of anion & cations in external solution.          [ Ci+] [Ai–] = [Co+] [Ao–] where            Ci+ = cations inside      Co+ = cations outside A i – = Anions inside    Ao– = Anions outside (iii) Mass Flow Hypothesis:– According to this theory, ions are absorbed by the root along with mass flow of water under the influence of transpiration (B) Active Absorption:– It is the absorption of mineral ions which involves the use of energy. The movement of ions is against concentration gradient. It occurs with the help of certain carriers present in the plasma membrane. Activated ions combine with these carrier proteins to form ion – carrier complex. This complex moves across the membrane & reaches inside where it breaks to release the ions into the cytoplasm. Ion Traffic Into the Root:– Mineral ions are absorbed by roots and then carried to xylem. It occurs by two pathways:– * Apoplastic:– Water & ions move through the cell walls without crossing any membrane and reach xylem. * Symplastic:– Water & ions move across the cytoplasms of cell through plasmodesmata & reach xylem. So in this, they cross membranes & reach cytoplasm 2.5 Translocation of Solutes:–  Solutes move up in the plant along with the upward moving water. Water is moving up due to transpirational pull. So, the rate at which solutes are translocated corresponds to the rate of translocation of water. 2.6 Metabolism of Nitrogen:– Nitrogen is absorbed in the form of nitrate (NO3–) and ammonium (NH4+) from the soil. It is essential for living organisms. Nitrogen Cycle:– Atmospheric nitrogen is present in fixed forms as aminoacids, proteins, nucleic acids etc. in living organisms. When they die and decay, inorganic nitrogen is released. Dead remains decompose to produce ammonia. Ammonia converts into nitrites & then nitrates by process of Nitrification. Bacteria Nitrosomonas converts ammonia to nitrate. Bacteria Nitrobacter converts nitrite to nitrate. Nitrate is then available to plant or gets converted into Nitrogen gas by process of Denitrification. Bacteria like Pseudomonas helps in this process. Nitrogen gas may then be fixed again in the form of NH4 by biological fixation Biological Nitrogen Fixation:– Nitrogen fixation done by microorganisms is called biological Nitrogen fixation. It is done by two ways:– * By free living bacteria:– Free living N2 – fixers include cyanobacteria, Azotobacter, Clostridium * By Symbiotic bacteria:– Most common symbiotic bacteria is Rhizobium which lives in root nodules of leguminous plants. In symbiotic association, both the partners are mutually benefited. Nodules are the outgrowths of roots and act as site for N2 – fixation. These contains enzyme – Nitrogenase (a Mo – Fe protein), pink colour pigment – Leghaemoglobin (which protects nitrogenase from oxygen) Formation of Root Nodules:– Root hair of a plant curls when it comes in contact with Rhizobium due to chemicals secreted by it. At the place of curling, bacteria invades root tissues and sometimes forms large structures called – Bacteroids. Cell walls of root hairs degrade and membrane forms infection thread by growing inwards Cell division in infected tissues continues and nodules are formed. Auxins (produced by plant cells) and cytokinins (produced by invading bacteria), together, promote cell division and formation of nodule. N2 – fixation is controlled by genes:– plant ‘nod’ genes, bacterial ‘nod’ genes, ‘nif’ & ‘fix’ gene clusters Mechanism of N2 fixation:– In N2 fixation, atmospheric nitrogen gets reduced by addition of H – atoms. The three bonds (N º N) between two nitrogen atoms are broken. NH3is formed which is used for the synthesis of amino acid. N2 fixation requires 3 components:– (i) A strong reducing agent (ii) ATP (iii) Enzyme systems Synthesis of Aminoacids:– Aminoacids are initial products of nitrogen assimilation Each amino acid has an –NH2 (amino) group and –COOH (carboxyl) group. Aminoacid synthesis occurs in following step: (i) Reductive amination:– Amino acid reacts with  – ketoglutaric acid (comes from kreb’s cycle) and forms Glutamic acid. (ii) Transamination:– In this, amino group from one amino acid is transferred to the keto group of keto acid 17 amino acids can be made from Glutamic acid by transamination. Enzyme acting is Transaminase Amides:– eg, Asparagine, Glutamine. These are formed from aspartic acid and Glutamic acid when – OH part of acid is replaced by –NH2. Enzymes Glutamine synthetase or Asparagine synthetase help in the reaction Amides form proteins. Protein Synthesis:– Many amino acids join to form a protein (or polypeptide). Peptide bonds join the amino acids or amides to form proteins. 2.7 Heterotrophic Nutrition:–  Organisms not capable of making their own food are called Heterotrophs. e.g, Phanerogams, fungi, bacteria etc. Heterotrophs can be:– (a) Parasitic:– These obtain food from tissues of other plants. They have haustoria which penetrate into host plants vascular bundle and draws nutrition (b) Saprophytic:– These grow on decaying animal or vegetable matter and absorb organic food from it eg Monotropa. (c) Symbionts:– In this, two organisms live together and benefit each other mutually e.g, Lichen, mycorrhiza (d) Insectivorous:– These plants obtain their food by catching insects and digesting them. Trapped insects are killed & their protein is digested byu proteolytic enzymes. Amino acids formed are absorbed by plant e.g, Drosera, Utricularia, Nepenthes.

PLANT - WATER REALTIONS

Cells are functional and structural units of all organisms. In plants, these cells have cell wall and protoplast. Each cell has its own internal environment. Plasmodesmata connect the protoplasm of adjacent cells. Water is major raw material absorbed by plants and it is essential for all physiological activities of plants. Important roles of water in plant are: - * It acts as solvent. * Helps in uptake and distribution of solutes & minerals for plant growth. * Has a key role in photosynthesis. * Acts as source of oxygen * WATER POTENTIALS: - Plants need free energy to grow and reproduce. Free energy is the potential to do work. The potential energy of water is known as'Water Potential'. Water moves from greater water potential area to lesser water potential. Water potential is measured in relative quantity. It is expressed as the difference between the potential of a solution in a given state and the potential of same solution in standard state. Symbol: -It is represented by greek letter, Psi (ψ). Unit: -Its measurement unit is'Pascal', Pa. 1 Mpa (1 Megapascal) = 10 bars. Factors affecting water potential: -3 factors are there, which affect water potential Amount of solute, pressure and gravity. So, water potential (w) of any solution is the sum total of these three potentials and can be represented as: - w =S +P +g WhereS ='Solute potential' or'Osmotic potential'; presence of solute particle decreases the water potential of pure water. P ='Pressure potential' or'Hydrostatic pressure'. IfP is positive, w gets raised. IfP is negative. w gets reduced. PositiveP is called'Turgor pressure'. g ='Gravity potential'.It depends on height of water, density of water and acceleration due to gravity. In plant cell,g is negligible. So, it is ignored. The equation, thus gets simplified as: - equation, thus w =S +P. According to this equation, If water enters into cell, thep increases. Sow also increases. Thus difference between inside and outside. i.e. w is reduced. If solute concentration increase thenS decreases. Sow also decreases. A water potential gradient develops and water enters into cell from outside. Remember that water always moves from highw to low w. 1.2. Absorption & Movement of Water: - Roots absorb water from the soil in plants. Root hairs present on the root increase the surface area for absorption. Water moves from root hairs to cortex and then to xylem. It moves by two pathways: - * Apoplast pathway: - In this, water moves exclusively through cell wall. Cortex cells are loosely packed here, so water flows without any resistance till endodermis, where casparian strips block the flow. Major part of water flows via apoplast. * Symplast pathway: -In this, water flows from cell to cell through plasmodesmata. So symplast has a network of cytoplasm of all cells interconnected by plasmodesmata. Beyond endodermis, water flows through cell membranes. This is called'Transmembrane Pathway' Water may also cross tonoplast. DIFFUSION: -It is defined as the movement of molecules from the region of higher concentration to the region of lower concentration. A state of equilibrium is reached when there is no further movement of molecules. In plants, uptake of water, gases and solutes occurs by diffusion. PERMEABILITY: -The extent to which a membrane permits or restricts the movement of a substance is called Permeability. It depends upon (i) Composition of membrane and (ii) Chemical nature of solute. It can be measured by calculating the rate at which solute passes through membrane under specific conditions. OSMOSIS: -The movement of water or solvent from a region of higher diffusion pressure to lower diffusion pressure through a semi-permeable membrane is called as'Osmosis'. Demonstration of Osmosis by Thistle Funnel Experiment: - Tie the mouth of thistle funnel with a semi permeable membrane (egg membrane). Put sugar solution inside it. Dip it in a beaker containing water with the help of stand. After some time, water rises in the thistle funnel. This is due to diffusion of water into thistle funnel through semipermeable membrane. i.e. by Osmosis. Osmotic Pressure (O.P): -It is the external pressure which must be applied to stop entry of water/solvent due to osmosis. O.P. is measured by instrument called'Osmometer'. Its unit is Pascal, Pa (1 Pa = 1 Newton/m2) Osmotic Potential / Solvent Potential: -(S)- It is defined as the amount by which water potential is reduced as a result of presence of solute. As chemical potential of water is taken as zero, so the value of solute potential always comes out to be negative. S = - where - means negative of osmotic pressure. Reverse Osmosis: -If more than required osmotic pressure is applied, then water flows out from the solution (in thistle funnel) back into the beaker (containing water). This is Reverse Osmosis. It is used for removing salts from saline water. Factors affecting Osmosis: - (i) Concentration of dissolved solutes in a solution (ii) Pressure difference Plasmolysis: -Shrinkage of the protoplast of a cell from its cell wall when it is placed in a hypertonic solution is called Plasmolysis. Hypertonic solution has more solutes than solvent (water). So water moves out from cell. This causes shrinkage. Imbibition: -It is the phenomenon of absorption of water or any other liquid without forming a solution. Material which absorbs water & swells up is called an Adsorbant. e.g Wood, Seeds, Agar-Agar. These are also known as'Imbibants'. Due to imbibition (water absorption), things swell up & lot of pressure is built. This is called Imbibition pressure / Matric Potential. ( water potential of matrix) Conditions important for imbibition: - * Water potential gradient between adsorbant and liquid. * Affinity between adsorbant and imbibed liquid. * Materials which have negative water potential allow rapid imbibition of water. 1.3 THEORIES OF WATER TRANSLOCATION: - The movement of water from the roots to the tip of plant is called water Translocation. There are 3 main theories for water translocation: - * Root Pressure Theory: -given by Priestley (1916). Root pressure is the pressure developing in elements of xylem due to metabolic activities of root. Water is absorbed by root hairs from the soil. If a plant stem is cut just above soil, water oozes out of it. This is due to root pressure. Mineral ions from soil accumulate in xylem of roots and lower the osmotic potential which lowers the water potential. So water flows into the root. * Capillarity Theory: -When water rises up in small tubes with small diameter which are kept in vessel filled with water, this is called'Capillarity'. Rise in water is due to forces of adhesion and cohesion. In this theory, first water is taken in because of adhesive forces (between water & xylem vessel walls). Then cohesive forces act between water molecules and so water moves up. * Cohesion Theory: -Given by Henry Dixon in 1914. It is the most accepted theory. It states there is a continuous water column in plants because of cohesive forces between water molecules. When water evaporates from leaf, then the water potential decreases. Water from adjacent cells replaces the loss. Then water from xylem compensates this loss. So there is a continuous water column. The pull exerted on the water filled in xylem is known as'Transpiration Pull'. It results in upward movement of water. 1.4. Transpiration: - Definition: -Loss of water, in the form of vapours, from the aerial parts of the plant is known as Transpiration. Most of the transpiration occurs through pores called'Stomata' present on the leaf. Significance: -(i) It results in movement of water. Because when transpiration occurs water is absorbed from soil. (ii) If extra water is absorbed, then transpiration removes it. * It causes cooling effect on leaves (as transpiration involves evaporation which results in cooling). * Increases the absorption of mineral nutrients. Factors affecting Transpiration: - * Humidity: -Rate of Transpiration is inversely proportional to relative humidity. * Temperature: -Transpiration increases with increases in temperature. Higher temperature open the stomata. Lower temperatures close the stomata. * Wind: -Transpiration increases with the wind speed (upto 20-30 km/hr) but if wind speed is too high, then stomata close and become dry. This decreases transpiration. * Atmospheric Pressure: -Low atmospheric pressure increases rate of transpiration * Light: -Stomata open in presence of light & close in darknes. So transpiration is more in light & lesser in darkness. 1.5. Opening & Closing of Stomata: - Definition: -Stomata are tiny pores located on the surface of epidermal layers of leaves. Size of stomatal pore: -3 - 12 mm wide, 10-14 mm long. Number of pores: -1000-60,000 per cm2 of leaf surface. Location: -These occur on upper as well as lower surface of leaf. In monocots, their number is same on both the surfaces but in Dicots, these are more on lower surface. Mechanism of opening and closing of stomata: -Each stomata has two guard cells surrounding the pore. These control opening and closing of stomata. When the guard cells are turgid (i.e. full of water), the stomatal pore opens. When guard cells are flaccid (i.e. have very less water), the pores close. Guard cells take solutes from neighbouring epidermal & mesophyll cells. This lowers osmotic potential and water potential. It creates a gradient and water moves into guard cells which makes them turgid.Major solute taken in is k+ (potassium). Rise in k+ level causes stomatal opening. Decrease in k+ level closes the stomata. Factors affecting stomatal movement: - * Light: -Stomata generally open in light & close in dark. * Temperature: - High temperature (above 35° C) can open stomata even in darkness. Lower temperature (less than 8° C) closes the stomata. * Water: -If less water is available & transpiration is high, there is'water stress' or'water deficit' in plants. It closes stomata. * pH: -High pH opens stomata. Low pH closes it * CO2: -Stomata close when concentration of CO2 is high. These open when concentration of CO2 is low.