SEED GERMINATION

• Seed germination is the first step in the life cycle of Gymnosperms
• When conditions are favorable, gymnosperm seeds germinate, initiating the growth of a new plant.
• The seed germinates and the diploid embryo divides and grows leading to the formation of the main plant body called Sporophyte which is the diploid plant body.
• The Sporophyte develops into a tall tree and is well differentiated into Root, Stem and Leaves.

SPORE AND GAMETE FORMATION

• Some leaves are modified into specialised spore forming structures called Sporophylls.
• Sporophylls are grouped to form compact structures called Strobilus or Cones.
• Male cones are formed by compact arrangement of Microsporophylls and are the site of Microsporogenesis or Microspore formation.
• The male cones contain Microspore Mother Cells which divides by meiosis to form Microspores or male spores.
• The microspores develops into Pollen grains and contains 3-4 haploid cells.
• Female cones are formed by compact arrangement of Megasporophylls and are the site of Megasporogenesis or Megaspore formation.
• The female cones contain Megaspore Mother Cells which divides by meiosis to from 4 haploid Megaspores or female spores.
• Out of 4 megaspores only one remains functional.
• The functional megaspore divides and develops into the female gametophyte called Endosperm.
• Inside the endosperm, the 2 to 8 female sex organs called Archegonium develops. Each archegonium contains a haploid female gamete called Egg/ Ovum.

POLLINATION 

• Pollination in gymnosperms involves the transfer of pollen from male cones to female cones, usually facilitated by wind.
• Pollen grains land on the ovules of female cones and adhere to a sticky substance known as the pollination drop.
• The pollen grain germinates and forms a pollen tube, through which sperm cells travel to reach the egg cells within the ovule.

FERTILIZATION

• Once the pollen tube reaches the egg cell, fertilization occurs, resulting in the formation of a zygote.
• This fertilization process is unique in gymnosperms because it takes place within the ovule, which remains on the parent plant rather than being dispersed immediately.

SEED DEVELOPMENT

• After fertilization, the zygote develops into an embryo within the ovule, which eventually matures into a seed.
• Gymnosperm seeds are typically surrounded by a protective seed coat, derived from the integument of the ovule.
• Unlike angiosperms, gymnosperms lack fruit structures, so their seeds are often dispersed by wind, water, or animals.

#class 11 biology #class 11 botany #Plant kingdom