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Plant Kingdom Practice Sample Paper | Theory | Notes | Previous Year | Answer Key

Plant Kingdom Neet AIPMT Biology

Plant Kingdom Neet AIPMT

Download Plant Kingdom Practice Sample Question Paper, Notes & Previous Years 

Subtopics of Plant Kingdom : Algae, Bryophytes, Pteridophytes, Gymnosperms, Angiosperms, Plant Life Cycles and Alternation of Generations

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PLANT CLASSIFICATION

SYSTEM

¨   Artificial

  • Classification based on one or few morphological characters.
  • Gave equal weightage to vegetative and sexual characteristics, this is not acceptable as vegetative characters are more easily affected by environment.
  • This system is not followed because it results in separation of closely related families.
  • Most famous system is given by Linnaeus, which is based upon  number of stamen, due to this it is also known as sexual system of classification.
  • Theophrastus (370-285 B.C.), a Greek botanist, classified plants into four groups herbs, undershrubs, shrubs and trees on the basis of their habit.
  • Pliny the Elder (23-79 A.D.) distinguished animals into flight and nonflight ones. Flight animals included bats, birds and insects. He divided plants into herbs, shrubs, undershrubs, trees, vines, succulents, aquatic and terrestrial.
  • Carolus Linnaeus (1707-1778), classified plants into 24 classes on the basis of sexual characters. He took only the number, length and union of stamens and carpels into consideration for 23 classes. For example, he proposed classes Monandria (1. stamen), Diandria (2. stamens), Tri ­and Polyandria (3 and more stamens). 24th class was Cryptogamia, for flowerless plants. Hence, Linnaeus’s system is also known sexual system of classification or numerical system of classification.
  • Artificial system is simpler and easier to practice in the field, however it has several drawbacks; such as
  • It lacks the natural relationship amongst the organism.
  • Organisms do not show a clear-cut evolutionary line.
  • It leads to heterogeneous assemblage of unrelated organisms.

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The traits used for artificial system are liable to change.

¨   Natural System

  • Based on natural affinities among the organisms.
  • Along with morphology it also includes ultra structure, anatomy, embryology and phyto-chemistry.
  • Most famous natural system is Bentham and Hooker system. This system is followed in India.
  • Bentham and Hooker published their classification in 3-volumes of Genera Plantarum, they studied 97,205 species of plants.

¨   Phylogenetic System

  • The term phylogeny is coined by Lamarck and the concept of phylogeny was given by Haeckel.
  • First phylogenetic system was given by Eichler.
  • In this system all the evidences along with Fossil evidence is taken into account.
  • This system assumes that organisms belonging to same taxa have a common ancestor.

Phylogenetic system

The evolutionary history of a group of organisms is called phylogeny. The system of classification reflecting the evolutionary sequence as well as the genetic interrelationships of organisms is called phylogenetic system. Adolf Engler (1884-1930) and his associate Karl Prantl (1849-1893) published a phylogenetic system in the monograph Die Naturlichen Pflanzenfamilien. They placed families and orders of the flowering plants in ascending series based on the complexity of floral morphology. The characters like one whorl of perianth or no perianth, unisexual flowers and pollination by wind were considered primitive as compared to perianth with two whorls, bisexual flowers and pollination by insects. The plant Kingdom according to their classification is further divided into divisions, sub-divisions, classes, orders and families. Asteraceae (Compositae) among dicots and Orchidaceae (Orchid family) among monocots are considered highly advanced. According to them monocots are more primitive than dicots.

TYPES OF TAXONOMY

Numerical Taxonomy / Adansonian taxonomy – In this all the characters were given equal importance. Number and codes are assigned to all the characters at the same time hundreds of characters are analysed using computers.

Karyotaxonomy / Cytotaxonomy – It is based on cytological information like chromosome number, structure, behavior.

Chemotaxonomy – Chemical constituent of plant is used to resolve taxonomical problem.

CLASSIFICATION OF ALGAE

Algae are usually differentiated on the basis of their pigments and storage products. Algae included under kingdom Plantae by Whittaker (1969) are of three types: red algae, brown algae and green algae.

CHLOROPHYCEAE: GREEN ALGAE

About 90% of the total species grow in fresh water habitats and 10% are marine. They are cosmopolitan in distribution. They may be

  • Terrestrial– growing on moist soil, walls and rocks, e.g., Fritschiella
  • Epiphytes– growing on other plants, e.g., Trenteopohlia, Protococcus,
  • Endophytes– growing inside the other plants, e.g., Coleoeheate nitellum inside the thaIlus of
  • Epizoic– growing on the surface of animals, e.g., Cladophora and Charaeilum on mollusc shells and crustaceans, respectively.
  • Endozoic– living inside body of animals, e.g., Zoochlorella inside sponges, Chlorella in the body of
  • Cryophytes– growing in the polar region on ice and snow, e.g., Chlamydomonas nivalis, (causing red snow ball).
  • Thermophilic– growing in hot springs, e.g., Chlorella
  • Parasitic– growing as pathogens and causing diseases, e.g., Cephaleuros (causing red rust disease of tea and coffee).
  • Symbionts – as components of certain lichens.

CHLAMYDOMONAS: LIFE CYCLE

HABITAT

Chlamydomonas is widely distributed fresh water unicellular alga, commonly occurring in standing or stagnant rainwater, ponds, pools, ditches and on moist soils. It grows, in abundance in water rich in ammonium compounds.

SEXUAL REPRODUCTION

Some species of Chlamydomonas are homothallic, while others are heterothallic. Gametic union may be isogamous, anisogamous, or oogamous.

HOLOGAMY

¨   In most of the isogamous species any vegetative cell may function as gamete and their walls fuse prior to the gametic union e.g., C. debaryana.

PHYSIOLOGICAL ANISOGAMY

¨   In species where the two uniting gametes, though they are morphologically similar, behave differently such as the cell contents of one gamete may pass into another gamete, the process is called as physiological anisogamy.

ANISOGAMY

In anisogamous species like C. braunii, 2-4 large female gametes are formed in one cell and 8-16 small male gametes are formed in another cell. Both the gametes are provided with a wall. The male and female gametes join by their anterior ends. At the point of contact, their membranes dissolve and contents of the male gamete pass into the female gamete with the result of formation of zygote. The gametes do not shed their walls at the time of gametic union.

OOGAMY

In oogamous species, like C. coccifera the male cell divides to form 8, 16 or 32 small biflagellate antherozoids. The large female cell loses its flagella and becomes an egg cell or oogonium. Fusion takes place between a male gamete and an egg. Both the gametes are covered with a cell wall and form a zygote.

ZYGOTE AND ITS GERMINATION

Disappearance of flagella from quadriflagellate zygote of isogamous or anisogamous species is followed by the formation of a wall around it. The two nuclei fuse and it becomes a spherical structure, which undergoes a period of rest. It secretes a thick wall, which may be smooth and spiny. The resting zygote enlarges to 2-5 times of its original size, owing to the accumulation of reserve food material during photosynthesis. However, there are few species, in which there is no increase in size of the resting zygote that develops a red pigment, called hematochrome. In C. eugametos, however, zygotes remain green.

ULOTHRIX: LIFE CYCLE

OCCURRENCE

Ulothrix with its about 30 species, largely grown in fresh water ponds, pools, tanks and running streams. Some species like U. zonata, are distinctly cold water forms.

THE PLANT BODY

STRUCTURE OF THE THALLUS

The plant body is a thallus consisting of an extremely fine unbranched filament. The filament comprises of single row of cells placed end to end, and firmly united. The filaments appear slender, thread like and may be upto 0.04 mm in diameter. Except for basal one, all the cells of the filament are similar in structure and behaviour. The basal cell (holdfast) is slightly elongated, hyaline or achlorophyllous and through it, the filament remains attached to the substratum. The remaining cells of a filament are barrel shaped and are often wider than long. However, the apical cell is down-shaped. The growth is apical.

SEXUAL REPRODUCTION

Isogamous type of sexual reproduction is found in Ulothrix and in majority, the plants are heterothallic, The gametes are formed in large number i.e., 32 to 64 in number in each gametangium. Each gamete looks quite similar to biflagellate microzoospore. However, gametes are smaller in size. These are formed and liberated in a way similar to zoospores. Each gamete is biflagellate, pyriform and has prominent stigma and a chloroplast. They look like Chlamydomonas. but are naked. Since, male and female gametes are indistinguishable, they are denoted as (+) or (–) strain gametes.

SPIROGYRA: LIFE CYCLE

OCCURRENCE

¨   Spirogyra is a large genus consisting of about 300 species widely distributed throughout the world. It grows as free floating extensive masses and hence commonly called pond scum. It grows frequently in fresh water, stagnant reservoirs and in slow running streams and rivers. In natural conditions, Spirogyra looks like a mass of shining silky long filaments and hence it is popularly known as pond silk.

 

THE PLANT BODY (THE GAMETOPHYTE)

STRUCTURE OF THE THALLUS

The plant body consists of slender, un-branched filament. The young filament of Spirogyra is found attached to some substratum by a modified basal cell, while adult plant is always free floating. The basal cell that helps in the attachment is called as hapteron. Each filament consists of a single row of cylindrical cells.

STRUCTURE OF A CELL

Each cell consists of a firm cell wall enclosing a mass of protoplast. Cell wall is commonly two layered, the inner composed of cellulose while outer of pectic substances. The pectic substances gelatinize in the presence of water and render the plants slimy touch.

REPRODUCTION

Spirogyra reproduces by vegetative and sexual methods. However, aplanospores formation has been reported in S. aplanosporum and akinetes in S. farlowii.

VEGETATIVE REPRODUCTION

Fragmentation is the common method of vegetative reproduction in Spirogyra. Accidental breaking or injury breaks the filaments into 2-3 celled pieces, each germinates to produce a new plant. However, in certain cases, cross walls also play a role in separating the two cells apart by the process of invagination.

SEXUAL REPRODUCTION

The sexual reproduction in Spirogyra is called conjugation, which involves fusion of two morphologically identical but physiologically dissimilar gametes. It is called as physiological anisogamy. The gametes are aflagellate (aplanogametes). For development of gametes some of the cells start to act like male and female gametangia. The cell contents taking part in development of gametangia become separated from the cell wall and shrink and are ultimately converted into gametes. The process of conjugation involves following methods:

PARTHENOGENESIS

Sometimes conjugation does not take place. The gametangia then are converted into thick walled bodies identical to zygospores. These bodies, formed parthenogenetically, are called azygospores or parthenospores. They germinate like zygospores to form new filaments but without the meiotic division.

Fertilization

Water is indispensable for fertilization (zooidiogamy).

Many antherozoids swim to the neck to archegonium.

All the neck canal cells and venter canal cell disorganize to form mucilage, carbohydrate, proteins, K+, etc. These chemicals not only provide the medium for swimming of antherozoids but also chemotract them. Many antherozoids enter into the venter but only one, the most active one, fuses with egg to form diploid zygote (oospore).

With the formation of diploid zygote, the gametophytic generation ends and the sporophytic generation starts.

Liverworts

Present in moist and shady habitats, such as banks of streams, marshy ground, damp soil, bark of trees and deep in woods. E.g., Marchantaia, Riccia.

Liverworts are thalloid and thallus is dorsiventral which is closely appressed to the substratum.

Some members like Pelia and Porella is leafy having tiny leaf like appendages in rows on the stem like structure.

SEX ORGANS

¨   The male and female reproductive structures are antheridia and archegonia, respectively. The prothalli are strictly monoecious or homothallic and protandrous (antheridia maturing earlier than archegonia). Both the sex organs are produced on the ventral surface of the thallus.

ANTHERIDIA

The antheridia develop in the basal region of the prothallus, among the rhizoidal cushion. Mature antheridium is a dome shaped structure that projects beyond the surface of the prothallus. The wall of the antheridium is composed of only three cells. Two cells form a ring around antheridium and are known as first ring cell and second ring cell. The third cell, which forms a cap of the antheridium, is known as cap cell. In each antheridium, there are usually 32 spirally coiled multiflagellate antherozoids. The antherozoids of ferns thus resemble with those of Cycas in their multiflagellate nature.

ARCHEGONIA

The archegonia are produced in the thickened portion of the prothallus,just behind the apical notch. Mature archegonium is a flask shaped structure. It has a basal enlarged venter that is deeply sunken in the tissue of the prothallus and a neck that project beyond the surface of the prothallus. The wall of the neck consists of four rows of neck cells. The venter has a large egg and a small venter canal cell. The neck canal of the young archegonium is occupied by an axial formation between the two neck canal cells and, therefore, almost invariably there is a single binucleate neck canal cell.

Plant Life Cycles and Alternation of Generation

¨   In plants, both haploid and diploid cell can divide by mitosis.

¨   The haploid plant body produces gametes by mitosis, this plant represents gametophyte.

¨   After fertilization diploid zygote also divides by mitosis to produce sporophyte.

¨   As a result of meiosis in sporophyte haploid spores are produced.

¨   Syngamy and meiosis are two important factor which are responsible for alternation of generation.

Updated: July 15, 2018 — 1:15 pm
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