Question

"Describe the 5 major TRENDS in the evolution of land plants; from Bryophytes to Gymnosperms/Angiosperms, AND explain how these trends contribute to success."I am answering questions for my college biology class (second semester of Biology for science majors). We are doing our Plant Diversity II lab. These evolutionary trends are DIFFERENT from the five uniquely derived traits of land plants according to my lab teacher, which based on what I think I know are:

1. Alternation of generations
2. multicellular, dependent embryos
3. sporopollenin
4. multicellular gametangia
5.apical meristems

please help! Also, I am not confident in the knowledge of my lab teacher, so if she is messing me up and some of those ARE the answers I would like to know that as well. I will happily talk to her about it, because she has told us the wrong information a couple times previously.

Thank you so much in advance!

Answer 1

1. Alternation of generation is more dominant and pronounced in lower plants like bryophytes and pteridophytes but later in angiosperms and gymnosperms, it is not very much highlighted. As gametophyte or haploid generation is the dominant generation in bryophytes and in the remaining groups' sporophyte enjoys the status of being dominant. In gymnosperms and angiosperms, the gametophyte generation remains confined only to the formation of gametes. i.e pollen grains and eggs.

2. In bryophytes and pteridophytes, there is dependence on water for fertilization as sperms need to swim in water and reach towards the egg for fertilization. Whereas in Gymnosperms and Angiosperms water dependence is reduced and many other agents like wind, insects, animals help in pollination.

3. Sporophyte generation grows from the gametophytic generation in bryophytes and is dependent on it. In pteridophytes, sporophytes emerge from archegonium and grow independently from gametophytes and obtain its nourishment without the help of gametophyte. whereas in gymnosperms and angiosperms gametophyte is highly reduced and is dependent on sporophytic generation for nourishment as well as protection.

4. Slowly the overall dependence of water decreased from bryophytes to angiosperms which gave rise to the developed roots in developed groups with the development of well developed vascular tissues such as xylem and phloem from pteridophytes onwards. But in pteridophytes, the nature of these tissues is quite primitive called as stele. In gymnosperms, phloem is devoid of companion cells and xylem is devoid of xylem trachea. Both these tissues are highly developed in Angiosperms. Similarly completely terrestrial life helped in the development of waxy cuticle and stomata later plants.

5. Development of specialized reproductive structures in developed groups occurred. Like the development of flowers and seed occurred only in angiosperms along with the need of pollination before fertilization also occurred. For this reason, pollen grains were protected as these had to travel long distances. In order to maintain their viability spore coat became harder. In angiosperms development of ovary and fruit also occurred and again need to dispersal of fruits and seeds occurred to continue their races. Thus we can see with the complexity in the niches and habitats of various plant groups specialization slowly reached its maximum in the more complex and more specialized group along with the simplicity restricted to initial groups like bryophytes and pteridophytes.