Explain the life cycle in Gymnosperms.

(N/A) $\rightarrow$ Gymnosperms are heterosporous; they produce haploid microspores and megaspores.
$\rightarrow$ These two kinds of spores are produced within sporangia.
$\rightarrow$ Spores are borne on sporophylls,which are arranged spirally along an axis to form lax or compact strobili or cones.
$\rightarrow$ The strobili bearing microsporophylls and microsporangia are called microsporangiate or male strobili.
$\rightarrow$ The microspores develop into a male gametophytic generation which is highly reduced. This reduced gametophyte is called a pollen grain.
$\rightarrow$ The cones bearing megasporophylls with ovules or megasporangia are called macrosporangiate or female strobili.
$\rightarrow$ In $Pinus$,the male and female cones or strobili may be borne on the same tree. In $Cycas$,male cones and megasporophylls are borne on different trees.
$\rightarrow$ The megaspore mother cell is differentiated from one of the cells of the nucellus. The nucellus is protected by envelopes,and the composite structure is called an ovule.
$\rightarrow$ The ovules are borne on megasporophylls,which may be clustered to form female cones.
$\rightarrow$ One of the megaspores enclosed within the megasporangium (nucellus) develops into a multicellular female gametophyte that bears two or more archegonia (female sex organs).
$\rightarrow$ The multicellular female gametophyte is retained within the megasporangium.
$\rightarrow$ In gymnosperms,the male and female gametophytes do not have an independent free-living existence.
$\rightarrow$ They remain within the sporangia retained on the sporophytes. The pollen grain is released from the microsporangium.
$\rightarrow$ Pollination: The pollen tube carrying the male gametes grows towards the archegonia in the ovules and discharges its contents near the mouth of the archegonia.
$\rightarrow$ Following fertilization,the zygote develops into an embryo and the ovules develop into seeds. These seeds are not covered (naked).