Both gymnosperms and angiosperms bear seeds, then why are they classified separately?

A group of students visited a tropical forest and enlisted the plants which belongs to various groups like thallophyta, bryophyta, pteridophyta, gymnosperms and angiosperm as follows. From the histogram they made it was found that the most dominating group is angiosperms. Can you find the reasons?

In reptiles, birds, mammals, gymnosperms and angiosperms the fertilisation is

Organisms belonging to pteridophytes, gymnosperms, angiosperms and most of the animals including human beings.

Transfer of pollen grains from the anther to the stigma of a flower is called pollination. Grass plants generally have small , inconspicuous flowers while plants belonging to many angiosperm bear conspicuous coloured flowers. What are the salient features present in these two groups for effective pollination?

Why are living organisms are classified?