Plant Kingdom – Gymnosperms YouTube Lecture Handouts Part – 1
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Plant Kingdom & Classification: Gymnosperms - NEET/AIIMS/MCAT
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
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
- 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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✍ Manishika