Plant Kingdom – Gymnosperms YouTube Lecture Handouts

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Watch Video Lecture on YouTube: Plant Kingdom & Classification: Gymnosperms - NEET/ AIIMS / MCAT

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

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Image of Plants

Image of Plants

Seed Plants (Spermatophyta)

Image of Seed Plants (Spermatophyta)

Image of 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

Image of Unfertilized Ovule, Fertilized Ovule And Gymnosperm …

Image of Unfertilized Ovule, Fertilized Ovule and Gymnosperm …

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

Image of Cycas. A single foliage leaf

Image of Cycas. A Single Foliage Leaf

  • 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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