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

Image of Plants

Seed Plants (Spermatophyta)

Image of 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 Seed

Image of Unfertilized Ovule, Fertilized Ovule and Gymnosperm Seed

Image of Unfertilized Ovule, Fertilized Ovule And Gymnosperm Seed

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

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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