Characteristics And Classification Of Gymnosperms - Practice Questions & MCQ

• Gymnosperms are embryo forming, vascular tissue containing plants. 
• These are usually evergreen trees, rarely shrubs and very rarely perennial herbs. Sequoia is one of the tallest trees.
• Ginkgo is a living fossil.
• The dominant stage in the life cycle is the sporophyte and divided into root, stem and leaf.
•  The root system is usually a taproot system.
•  Roots of some plants are associated with fungal mycelia and form Mycorrhizal roots (Pinus), while in others they are associated with Cyanobacteria like Nostoc and Anabaena as in Cycas. 
• The stem of gymnosperms can be branched (Pinus, Cedrus) or unbranched (Cycas).
• Leaves can be simple as in Ginkgo and Gnetum or Pinnately compound as in Cycas. 
•  Leaves persist for a few years and they are well adapted to withstand extremes temperature, humidity and wind.
• In conifers like Pinus, the needle-like leaves with sunken stomata and thick cuticle reduce the surface area to minimize water loss (xerophytic adaptation). 
• Anatomically the stem has Eustele with conjoint, collateral and open vascular bundles. 
• Xylem usually lacks vessels and companion cells are absent in phloem. 
• Stem and root show secondary growth.
   

• Gymnosperms are heterosporous and produce both mega and microspores on the same plant (Monoecious - Pinus) or on different plants (Dioecious – Cycas). 
• Microspores and megaspores are formed on microsporangia and megasporangia respectively, which in return are formed on microsporophylls and megasporophylls respectively.
• The microsporophyll and megasporophyll aggregate and form cone-like structures Strobili. 
• Megasporophylls possess integumented megasporangium known as ovules which bear female gametophyte.
• Female gametophyte possess archegonia i.e. female sex organ.
• Microspores include male gametophyte which produces only two male gametes or sperm. 
• The pollen grains or microspores are liberated at more than 2-celled stage from microsporangium. 
• Water is not required for transport of male gamete. A pollen tube is formed that delivers male gametes to archegonia. 
• Fertilization produces a zygote which later turns into an embryo.
• Endosperm in gymnosperms is formed before fertilization. It represents the haploid female gametophyte generation.
• The seeds are naked i.e. they are not formed inside fruit as in angiosperms. 
   

Gymnosperms are divided into four groups:

1-Cycadopsida- Wood is manoxylic, Siphonogamous fertilization, male gametes are winged, they are commonly called cycads. E.g Cycas 
 
2-Coniferopsida- commonly called conifers, e.g. Pinus. Wood is pycnoxylic, small ephemeral cones formed in groups, large and perennial female cones, siphonogamous fertilization, male gametes non-motile. 
 
3-Ginkgopsida- represented by Ginkgo, also known as maidenhair tree. It is known as a living fossil. It is the only one living organism in this group, it has leathery and fan-shaped leaves, The veins are dichotomously branched, male gametes are motile and multiflagellate.
 
4-Gnetopsida- includes Gnetum, Ephedra, Welwitschia. Vessels are present in secondary xylem, orthotropous ovules with long tubular micropyle are present,  resin canals absent.