Plant Kingdom – Gymnosperms YouTube Lecture Handouts Part – 1

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Plant Kingdom & Classification: Gymnosperms - NEET/AIIMS/MCAT

Illustration: Plant Kingdom – Gymnosperms YouTube Lecture Handouts Part – 1

Seed Plants (Spermatophyta)

Illustration: Seed Plants (Spermatophyta)

Ovule includes integument & nucellus (both are diploid & belong to sporophytic generation)

Adaptation to Land plants

  • No external water supply 👏
  • Development of pollination
  • Transform megasporangium to ovule (has 1 megaspore mother cell) , fertilize egg in ovule & production of embryo
  • Transformation of ovule into seed for dispersal
  • Extensive root system
  • Vascular system/tissues
  • Cambium for secondary growth
  • Bark for protection

Gymnosperms

Seeds exposed (naked) on megasporophyll as latter are not folded as pistils

900 species

Perennial & woody (tallest is Sequoia sempervirens & smallest is Zamia pygmia)

Pollen cones & seed cones

Pollination is direct/wind (anemophily)

👌 Male gametophyte – 2 male gametes & one is functional

Seed contains endosperm (for future growth of seedling)

👌 Xylem – no vessels (except some gnetophyte)

👌 Phloem – without companion cells & sieve tubes

👌 Sieve cells – no arranged end to end in rows

Illustration: Gymnosperms

4 species (arrangement of sporophylls & primitive vessels in xylem)

  • Cycadopsida - cycads
  • Ginkgopsida – Maiden tree hair (Ginkgo biloba)
  • Coniferopsida - conifers
  • Gnetopsida – Gnetum, Ephedra & Welwitschia

Cycas

  • Living fossil – number of characters of extinct pteridosperms & cycads
  • Palm like habit and fern like foliage (petiolate & unipinnate)
  • Dioecious – microsporophyll & megasporophyll on separate plants
  • Xerophytic & warm weather
  • Population is decreasing due to agriculture 👏
  • Now ornamental
  • Unbranched columnar stem with spiral rhomboidal leaf base
Illustration: Cycas
  • 2 types of leaves – ramental hair
  • Leaflet apex is spiny & margins can be straight or ovulate
  • Young leaves – circinate ptyxis
  • Roots – Normal & coralloid (irregular, negative geotropic, dichotomously branched coral like roots- which do not have root hair or root cap – symbiotic association with BGA like Nostoc & Anabaena)
  • 👌 Microsporophyll (arranged in boat shape) – flat fertile proximal region (bears pollen sac in sori) & distal bent sterile region (apophysis)
  • Female cone – rosette of brown megasporophyll – ovules of cycas is largest & eggs are largest in plant kingdom
  • 👌 Sperms of Cycas are largest in biological world
  • Pollination by wind – before pollination, pollens develop in 3 cells as prothallial, generative & tube cell

Conifers

  • 500 living species
  • Evergreen, dense and massive vascular tissue and non-motiel gametes
  • Monoecious
  • Cones are compact & woody
  • Leaves – thick cuticle, sunken stomata, needle like, small flat and leathery
  • 👌 Mainly in temperate north except Araucaria (S. America, New Zealand & E. Australia) in warm weather, foothills and plains
  • Angiosperms shed leaves but they are evergreen
  • Have xerophytic characteristics and conserve water
  • Enzymes are functional even at in conifers

Pinus – Christmas Tree

  • Stem – monopodial branching – long & dwarf
  • Roots – horizontally spreading tap root – normal (with root hair and caps) & mycorrhizal (devoid of root hair and cap)
  • Male cones – subterminally in lower branches – 2 oblong & parallel microsporangia
  • Pollens spread by air currents – form yellow clouds in pine forest – pollen grains have 2 air sacs for making it light
  • Female cone- lower part is bract and upper is ovuliferous – with 2 ovules at basal region (megasporophyll) – 26 months for maturity – winged seeds dispersed by air & new plant forms on suitable soil

Ginkgoales

  • Primitive gymnosperm
  • Deciduous leaves
  • Furcate venation
  • Unisexual plant
  • Catkin like inflorescence

Ginkgo Biloba

  • 👌 Living fossil – 1st in Triassic period
  • Upto 30 m height
  • Leaves are fan shaped – bilobed on long shoots
  • Furcate venation
  • Dioecious
  • Endosperm of roasted seed is edible
  • Ovule – 3 layered integument, microphyle & pollen chamber
  • 👏 Male plant is preferred by horticulturist as female plant gives unpleasant smell

Importance of Gymnosperms

  • Edible seeds - endopserm
  • Softwood – timber
  • Paper – Pinus, Picea, Abies, Larix
  • Fiber Boards
  • Linoleum (requires saw dust)
  • Resin – semifluid by special tubes containing terpenes, resin acids and esters
  • Resin retains water
  • Resin is antiseptic and toxic to pests – prevents microbial attacks - also in pains, bronchitis and expel worms
  • 👌 Resin commercially exploited for turpentine (solvent in paint, polish and wax) & rosin (water proofing, sealing joints and preparing writing papers)
  • Ephedrine from gymnosperm (Ephedra) – to cure respiratory ailment & asthma

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