Gymnosperms
Gymnosperms
Gymnosperms Definition: Gymnosperms are plants in which seeds are not enclosed in an ovule.
The gymnosperms are seed-forming plants that include conifers, cycads, Ginkgo, and members of the order Gnetales. The term ‘gymnosperm’ comes from the Greek words gymnos (=naked) and sperma (=seed), meaning ‘naked seeds’. The naked condition of their seeds is due to the fact that the carpels do not fuse, enclosing the ovules, to form an ovary.
It is considered that gymnosperms have developed from a type of plant species, called progymnosperms They are intermediate to the pteridophyta and angiosperms. About 900 species of gymnosperms have been discovered so far.
Gymnosperms Distribution: Gymnosperms are present all over the world, but they are found more in the temperate zone, than the equatorial zone.
Read and Learn More: WBCHSE Notes for Class 11 Biology
Gymnosperms General features:
Gymnosperm Plants
1. Most of the gymnosperms are perennial and evergreen in nature, with long, hard and woody stems. Some of them are shrub-like.
2. The main plant body is sporophytic (2n). It is independent, with the body being differentiated into true roots, stems, leaves, flowers and seeds.
3. Plants have a tap root system, that generally persists for a long time. Some adventitious roots also develop along with the primary root. In some cases, blue-green algae and fungi are found in roots in symbiotic association with the roots.
Characteristics and classification of gymnosperms notes PDF
4. The stem is erect and woody. It may be branched (Pinus sp.) or unbranched (Cycas sp., Zamia sp.). Stem branches are of two types—long shoots and dwarf shoots.
5. Long shoots have unlimited growth while dwarf shoots show regulated and limited growth.
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6. Vascular bundles in stems are of two types—open and collateral.
7. In roots, radially arranged xylem is made up of tracheids, parenchyma and xylem fibre. Vessels or trachea are only present in the xylem of Gnetum sp. and Ephedra sp. Phloem consists of sieve cells, phloem parenchyma and phloem fibre. The companion cells are absent.
8. Leaves are of two types—brown scale leaves and green foliage leaves. Long shoots bear scale leaves, while dwarf shoots bear both scale and foliage leaves
9. Venation in leaves may be reticulate (Gnetum sp.) parallel (Pinus wallichiana) or dichotomous (Gingko sp.).
10. The leaves are covered with thick cuticles, sometimes with a wax layer. Stomata are present on the lower surface of the leaves. Mesophyll may (Cycas sp.) or may not be (Pinus sp.) divided into palisade and spongy parenchyma.
Gymnosperms Habitat
11. Secondary growth is present in all members, where the mature metaxylem shows bordered pits (In Stangeria sp. and Zamia sp., the metaxylem shows scalariform thickening).
12. Flowers are monoecious, naked and devoid of accessories whor|s.
13. Male flowers are formed of microsporophylls, and female flowers are formed of megasporophylls, called carpels.
14. Microsporophylls and megasporophylls remain arranged and condensed on an axis to produce male and female cones respectively.
15. Microsporangia are present on the ventral side of the microsporophylls and megasporangia are present on the dorsal side of the megasporophylls.
16. Ovules or megaspores are exposed on the megasporophylls. Each megasporophyll may bear two or more ovules.
Short notes on gymnosperms for quick revision
17. Inside microsporangia, numerous microspores (pollen grains) are produced.
18. Microspores produce male gametophytes. Male gametes are either ciliated or non-ciliated.
19. Megaspores in megasporangia produce female gametophytes. Egg cells are produced in one or more archegonia within female gametophytes.
Structure Of Gymnosperms
20. Pollination occurs mainly by wind. Male gametes come in direct contact with the ovule (siphonogamy).
21. Sometimes more than one embryo may develop from a zygote (polyembryony).
22. Endosperm is haploid (n) and produced within female gametophytes before fertilisation.
23. Ovule (seed) consists of a single jacket or integument (unitegmic). Cotyledon may be one or two (Cycas sp.) or many (Pinus sp.).
24. The alternation of generations observed in gymnosperms is heteromorphic.
Gymnosperms Trees
Some common examples of gymnosperms are— Cycas sp., Pinus sp., Ginkgo sp., Gnetum sp., etc.
Gymnosperms definition, characteristics, and classification
Commercial importance of gymnosperms: Gymnosperms are of great economic importance. The commercial uses of gymnosperms are as follows—
Timber: The coniferous wood may be very light or hard, strong or soft, coarse or grained and durable with distinct annual rings.
Pinus sp., Cedrus sp., Abies sp., etc., yield good quality timber that is used for making furniture, plywood, matchsticks, pencils, etc.
Resin source: Resin exudates from coniferous plants. Resin is a nitrogenous waste produced by plants which is soluble only in organic solvents. The resin is used in varnishes, plasters, enamels, medicine, printing ink, laundry soap, oil, etc.
Gymnosperm Classification
Resins are of different types like—rosin (solid, obtaining Pinus sp. mainly), copals (hard, with essential oils, in Agathis sp.), sandarac (translucent, pale yellow or orange-coloured, in Tetraclinis articulate), Canada balsam (transparent, non-crystalline, in Abies balsamea)
Source of essential oils and gums: Almost all conifers yield volatile essential oils along with resins. Spruce oil is obtained from Picea abies which is used in room sprays, bath salts and deodorant.
The Siberian fir needle oil, obtained from Abies sibirica is also used in deodorant, toilet and shaving soaps, etc. Cedar oil is obtained from Cedrus deodara and Juniperus virginiana and is used in perfumery as well as in microscopic studies.
Source of paper: Conifers yield good quality timbers which are used for making paper pulp, used in the newsprint industry. Writing and printing papers are manufactured from the wood of Picea sp., Abies sp., Larix sp. and Tsuga sp., whereas craft papers are produced from Pinus sp. and Cryptomeria sp.
Production of medicines: Ephedra sp. is an important source of alkaloid, ephedrine. This is used as a bronchodilator in cough mixture used for the treatment of bronchial asthma. The leaves of Ginkgo biloba are an important source of the ginkgolide compound.
This compound is used to antagonize platelet-activating factor (PAF) in vertebrate blood. Another compound bilobalide obtained from Ginkgo leaves used in the treatment of neural disorders like Alzheimer’s disease. Extracts of these leaves are also used in the treatment of muscular disorders, cerebral insufficiency, vertigo, etc.
Class 11 biology gymnosperms notes with examples
Taxus brevifolia is an important source of an anticancer drug, taxol. The leaves of Taxus baccata are useful in the treatment of asthma, bronchitis, hiccups, epilepsy and indigestion. The seeds of Cycas sp., are used as an herbal drug for curing boils, wounds and sores.
Source of tannins: The bark of Tsuga canadensis, Picea alba, Sequoia, etc., yields tannins which are used for different purposes.
As ornamental plants: Several varieties of Cycas sp., Pinussp., Cedrus sp., etc., are widely planted as ornamental plants in gardens, parks temples etc., for their beautiful appearance, symmetrical growth and evergreen nature Their branches and leaves are used as decorations.
Source of food: Spongy pith of Cycas, Zamia, and Macrozamia contain large amounts of starch which is used to prepare sago. It is used as a food. The seeds of Pinus sp., are used in cooking and are eaten raw.
Seeds of Juniperus sp., are used as condiments in cooking. The young unfolded succulent leaves and tender shoots of many species of Cycas sp., are taken as cooked food.
Classification of gymnosperms: The living gymnosperms plants are grouped into four main types—
- Cycadopsida,
- Ginkgopsida,
- Coniferopsida
- Gnetopsida. These groups have been discussed under separate heads.