GYMNOSPERMS (NAKED SEED)

• The term 'naked' seeds refers to the fact that the seed is no enclosed in a fruit, but is naked
• Four Types of Gymnosperms

  1. Conifers
  2. Cycads
  3. Gnetales
  4. Ginkgo
• The sporophyte generation is the dominant generation- represented by the vegetative plant (adult pine tree)
• Not a thallus, has true roots, stems and leave
• The roots consist of a well-developed taproot system with lateral roots
• The stem is woody and covered with bark
• Two types of leaves in pine:

  1. needle-shaped green leaves
  2. Brown scales
• Vascular tissue (xylem and phloem) is present in Gymnosperms
• Pines trees bear different male and female cones
• Male cones are small are borne in clusters, bear the pollen sacs containing pollen grains (male spores)
• Female cones are larger and occur singly on the ends on branches. They bear the ovules containing female spores on the upper surface of each seed scale
• Pines have separate male and female spores
• Pollen grains (male spores) released during spring and are dispersed by wind
• Pollen lands on female cones, seed scales are open if ready for pollination, so pollen grain can be deposited on the ovule
• Pollen grain (male spores) germinates in favourable conditions and develops a pollen tube containing two male gametes
• Germinating pollen grain represents the male gametophyte- contains male gametes
• One of four female spores within ovule develops into female gametophyte (embryo sac)
• The female gametophyte (inside ovule) contains two or three female sex organs, each contain an ovum
• the male gametophyte (germinating pollen grain) produces male gametes (sperm).

  the female gametophyte (tissue in the ovule/embryo sac) produces female gametes (ova).
• The pollen tube of germinating pollen grain grows into ovule and enters one of the female sex organs
• The two male gametes are released and one gamete fuses with the ovum to from a zygote
• water in not required for fertilisation
• Ovule (on seed scale in female cone)

  
• The zygote is the beginning of the sporophyte generation. It develops into an embryo
• The fertilised ovule (containing embryo) develops into a seed
• Seed is not enclosed in a fruit- naked seed
• The seed scales open in dry conditions, seed is released and dispersed by the wind
• When conditions are favourable, the seed germinates to give rise to a new pine tree (sporophyte generation)