Tuesday, March 10, 2009
Traits from Common Ancestors
Sean Carroll says that there exists a "descent of all living species from common ancestors," implying that different groups of living things share certain traits which came from a common ancestor between the groups. Using your knowledge from previous units we have studied, choose EITHER two phyla of animals OR two kingdoms and note at least three similarities derived from a common ancestor between the two groups, and three differences between the two groups.
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Gymnosperms and angiosperms are two groups of seed-bearing plants derived from the common ancestor progymnosperms.
ReplyDeleteGymnosperms and angiosperms share a number of characteristics, all of which originated from progymnosperms. Both angiosperms and gymnosperms produce seeds, have vascular tissue, and produce wood composed of lignin.
However, through the course of time, gymnosperms and angiosperms have produced different characteristics, and have evolved to fit their unique environments. Gymnosperms lack enclosed chambers where seeds and ovules develop, while angiosperms have these enclosed chambers, which are called ovaries. Gymnosperm ovules and seeds develop on the surface of specialized leaves called sporophylls.
Angiosperms produce reproductive structures called flowers and fruit, that gymnosperms lack.
The wood of angiosperms also varies with the wood of gymnosperms. The structure of angiosperm wood is more inhomogenous and variable than that of gymnosperms.
Both phylum Cnidaria and Phylum Ctenophore were once combined in phylum Coelenterata but as time passed, scientists realized that although both groups had many similarities, there were also distinct differences.
ReplyDeleteOne similarity between the two phyla is that they both have a simple nervous system which lacks a brain and instead have a nerve net. A nerve net is made up of interconnected neurons which allow the organism to respond to physical contact. Another similarity is that both phyla rely on water flow through the body cavity to complete the processes of digestion and respiration. Lastly, both phyla have bodies that are made up of 2 layers, an outer dermis and an inner gastrodermis, which aid in protection as well as internal transport.
A difference between these phyla is that cnidarians have nematocysts while ctenophores do not. These nematocysts are used to capture food and for defense. Another difference is that cnidarians have radial symmetry while ctenophora have biradial symmetry (radial + bilateral). Lastly, ctenophores, which are the largest animals that use cilia to swim, have eight rows of swimming "combs" made up of fused cilia while cnidarians do not.
As the previous comments have addressed phyla, I will compare and contrast two kingdoms: animals and fungi. Both animals and fungi are eukaryotes, signifying that both stemmed from a later common ancestor (one that came after the LUCA described on pg. 87 of the Campbell). Additionally, both exist as multicellular organisms, meaning individual cells are incapable of living independently. Though some fungi do exist as single celled organisms, examples are far and few and do not represent the general propensities of the kingdom as a whole. Perhaps most significant among their similarities, these animals and fungi are strict heterotrophs, meaning that they drive their nutrition from other organisms rather than producing compounds like glucoes on their own. Because of this trait (among others and DNA evidence), it is believed that fungi are the closest evolutionary relatives of animals. Although these kingdoms are indeed closely related in a comparative sense, make no mistake; animals and fungi are vastly different. Though both are heterotrophs, each obtains food via different methods. Animals ingest any nutritious substances they require. Thus, all animals have some sort of oral opening through which to consume food and a gastrovascular cavity of some kind to hold ingested food. Alternatively, fungi use absorption to get their food. Fungi are thus lacking in the aforementioned structures found in animals. Instead, fungi have extensive networks of tendril-like hyphae through which absorption occurs. One could argue that the animal nutritional method of ingestion is more complicated, as it requires coordination of multiple groups of body cells, whereas absorption in fungi does not. Facilitating this complex action in animals is the presence of muscular and nervous tissue (with the exception, of course, of Phyla Porifera). Fungi do not have the muscular and nervous tissues unique to Kingdom Animalia. Tied in with these differences is the freedom of movement allowed of each kingdom. Though there are sessile animals such as sponges and anemones, and fungi can grow so rapidly that they may seem to move, fungi are mostly stuck in place, and animals are able to relocate themselves. The most significant implication of this trait is that fungal offspring must land on a source of nutrition. In contrast, animals can live and grow in a wider variety of locations and environments. Even sessile animals are not limited by their reduced mobility; animals like clams and sponges are underwater filter feeders, where, regardless of their resting place, food is brought to them through water currents. Obviously land animals and non-sessile marine and aquatic animals have even greater freedom, as these animals may move about to and from nutritional sources at will. As a result, animals are much less limited in their range of habitats when compared to fungi.
ReplyDeletePhylum Rotifera and Phylum Platyhelminthes most probably shared a common ancestor. Organisms of both phyla have bilateral symmetry. Organisms of both phyla are also protostomes because both types of organisms form their mouth first instead of their anus. Organisms of both phyla also lack a true coelom. However while organisms of phylum Rotifera have complete digestive tracts (digestive tube with 2 openings) organisms of Platyhelminthes have an incomplete digestive tract with one opening serving as the mouth and anus. Also while organisms of Platyhelminthes are acoelomates with no body cavity, Rotiferans are psuedocoelomates that have a body cavity not completely lined by mesodermal tissue. Lastly, Rotiferan reproduction is more unusual than reproduction seen in organisms of Platyhelminthes because some Rotiferans reproduce through parthenogenesis (unfertilized eggs develop into normal organisms).
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