The diploid sporophyte is represented by a dominant, independent,
photosynthetic, vascular plant body. It alternates with multicellular,
saprophytic/autotrophic, independent but short-lived haploid
gametophyte. Such a pattern is known as haplo-diplontic life cycle. All
pteridophytes exhibit this pattern (Figure 3.7 c).
Interestingly, while most algal genera are haplontic, some of them
such as Ectocarpus, Polysiphonia, kelps are haplo-diplontic. Fucus, an
alga is diplontic.


Please explain only the lines given in this paragraph. Please answer fastly its urgent.

The given paragraph explains about a type of life cycle in plants called haplodiplontic Life Cycle. The plant life cycle has two different plant bodies - One is represented by gamete producing haploid gametophyte and other one is spore producing diploid Sporophyte. This type of life cycle is an intermediate condition where both gametophyte and sporophyte are free-living and multicellular, but have different dominant phases. .This type of life cycle is shown by pteridophytes and some types of algae like Ectocarpus, Polysiphonia, kelps. 
In pteridophytes, diploid sporophyte is dominant, independent and photosynthetic. The diploid sporophyte produces spores which when fall on substrate germinate and grow into gametophyte. The gametophyte is short lived and produces male and female gametes which fuse to form zygote. The zygote undergoes division to produce sporophyte again. Hence, sporophyte alternates with short-lived haploid gametophyte, which is independent of sporophyte.


This can be illustrated as: