Question

Week 3 Critical Thinking ?? Exercise The different Phyla (or Divisions as they are called in Botany) represent a different stage in the transition of plants from being aquatic to completely terrestrial. This took millions of years, and yet we still see very "primitive" plants alive today. 1. Apply the characteristics of each phylum to this trend of increasing adaptation of plants to terrestrial life. What specific trait evolved to allow each step "away" from water? 2. Compare and contrast the existence of "primitive" plants to the continued presence of ancient, anaerobic bacteria that can still be found. How is this possible?

Answer 1

1. Apply the charactersitics of each phylum to this trend of increasing adaptation of plants to terrestrial life. What specific trait evolved to allow each step "away" from water?

Boddy support: the effects of gravity where different in land, so the plants developed structural support to endure this pressure. These could be achieved with rigid cell walls, and supportive tissues like wood in trees.

Transport of materials: another challenge was the transport of water and nutrients from cell to cell. The plants in water get nutrients from their surrounding, but the plants in land have to get it from the soil. The plants in land resolved this issue with the development of conducting vessels, functioning as tubes to conduct water and nutrients around the organism.

Differentiation of parts: so they could take better the new pressures of the environment in land, the differentiation of parts in the plant helped to deal more efficiently with issues. The leafs specialized in producing food. The stem and branches specialized in supporting the plant mainly, and the root specialized in providing water and nutrients for the plant.

Alternation of generations: in water the sperm of the plants could swim to the eggs directly, but in land it was not always possible. So, the alternation of generations occured. The sporophyte generation (adult) produces gametophytes (the other generation that is miscroscopic) inside special structures that provide water and nutrients. The male gametophyte is the sperm that grows inside pollen grains. The female gametophyte is the egg that grow in scales (conifers) or ovaries (plants with flowers). The polen moves with the wind, so the plants no longer need the water for the sperm to find the eggs.

Development and dispersal of the embryo: The embryo in land is in danger of dehydrating, which never happened in water. Also, in water it had constant supply of water and nutrients from the surrounding environment. To overcome the dehydration and the need for nutrients, the plans in land developed the seeds. The seeds provided a moist environment, no danger of dehydrating, and also the nutrients needed.

2. Compare and contrast the existence of "primitive" plants to the continued presence of ancient, anaerobic bacteria that can still be found. How is this possible?

It is possible because the Earth still provides them with the conditions necessary for these organisms to continue surviving and reproducing. Also, they continue to have adaptations to the changes in their environment that let them use the resources to continue surviving and reproducing. The evolution of new organisms means that they are adapting to new conditions, but that doesn´t always mean that the "old" conditions doesn´t exist anymore, that is why these organisms continue living in these "old" habitats . Probably, the "primitive" plants in contrast with the bacteria, specialized and organized more so they could take new niches and could use more efficiently the resources. But, the ancient bacteria and the "primitive" plants continue in habitats that have existed for thousands of years, that are older than the land, and it is possible that the changes is those environments doesn´t ocurred too fast, so they could adapt.