Austin Lee
austinklee7@gmail.com
Monday, March 28, 2011
From Blobs to Bodies
Ch. 6 and 7 explain how bodies emerge from clumps of cells and the factors that shape them. Also, it is explained when bodies began to form, instead of blobs without complex systems. As humans, we have multiple systems that control the way we live. Why did bodies start forming and how did they change life on Earth? How do our separate systems (Circulatory, digestive, nervous, etc.) give us a selective advantage in our daily processes? Compare and contrast the human body plan with those of other organisms referencing Shubin, Campbell, and any other sources.
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As discussed in Chapter 47 of Campbell, many different types of development occur. For example, different processes of cleavage occur in sea urchins, frogs, chickens, and humans. Bodies began forming because of these different types of cleavages. Also, because of cleavages, bodies started forming. Certain types of cleavages helped create certain systems within the body. The endoderm within a vertebrate embryo would become the digestive tract as well as the reproductive system whereas the mesoderm within a vertebrate embryo would become the skeletal, muscular, circulatory, and excretory system. Thus, cleavages allowed for more detailed beings to be born, thus changing life on earth. Having these separate systems allows for specialized cells to do specialized work. With these specialized cells, more detail is able to be looked upon, and in many cases, broken down. With the digestive system, more types of food and nutrients are able to be absorbed as compared to a species without a digestive system. Separate systems allows for a selective advantage because it allows our bodies to process with detail.
ReplyDeleteHumans, with a closed circulatory system, replenish blood with oxygen by allowing for oxygen to enter the lungs as a part of the respiratory system. This oxygen is then diffused across a membrane into capillaries which lead to the pulmonary vein which takes oxygenated blood back to the left atrium of the heart. The blood is always in a closed loop contained within arteries, veins, and capillaries. However, within Arthropods, an open circulatory system is present. Within this system, hemolymph is pumped throughout the body through muscular contractions, almost like the contractions seen in the esophagus of humans (peristalsis). Hemolymph not only contains blood, but also water, carbohydrates, lipids, proteins, and inorganic salts. Hemolymph also contains hemocyanin which is a copper based protein which carries oxygen to different parts of the body. Hemocyanin is similar to hemoglobin in human blood. Containing an open circulatory system as compared to a closed circulatory system can be beneficial. Closed circulatory systems are advantageous in humans as they can circulate CO2 and O2 as well as replenish cells throughout the body. With smaller bodies, an open circulatory system is advantageous. Spiders are able to exchange CO2 and O2 through their tracheal system. Thus, the circulatory system is not responsible for exchange of the 2 gases. The circulatory system only focuses on the replenishing of cells with oxygen, thus putting less demand on the circulatory system. It may seem as though a closed circulatory system is advantageous. But because of the different sizes and needs of different organisms, different systems are necessary to suit their situations.
Sources:
http://en.wikipedia.org/wiki/Circulatory_system#Open_circulatory_system
http://en.wikipedia.org/wiki/Hemolymph
Shreeraj Patel (shreeraj.patel1@gmail.com)
Body plans started forming over 600 million years ago, when multicellular life emerged. Bodies increased competition on Earth, allowing bigger organisms to acquire more resources. Being bigger also allows organisms to avoid being eaten by other organisms. This selective advantage would promote organisms with bodies to multiply, while other species would die off. However, this power comes at a cost, and bodied organisms could not rise until the Earth had developed the proper resources to provide a stable environment for them. Animals with bodies need much more energy than single celled organisms, as well as oxygen, which was once very limited.
ReplyDeleteBodies function by the work of multiple separate systems. These systems are all just different parts that work together to help the body as a whole function properly and effectively. As evolution has progressed, different variations on these systems have formed to give organisms a greater selective advantage over others, in order to survive and eventually reproduce. An example of this is the formation of lungs in terrestrial animals and gills in aquatic organisms. These organs create a massive surface area for gas exchange to take place, from the body to the outside environment. These gasses are exchanged into and out of blood vessels, which carry gasses to and from the rest of the body’s cells. These blood vessels are a part of the circulatory system. The circulatory system of humans and other vertebrates is also called the cardiovascular system. Humans have a closed circulatory system, in which the blood is confined into the vessels and is never mixed with the interstitial fluid. The advantages to this type of circulation include high blood pressure, which allows quick and effective delivery of oxygen and nutrients to the cells of larger organisms. In comparison, an open circulatory system exists in many smaller organisms, in which hemolymph is the circulatory fluid and the interstitial fluid. These systems have lower hydrostatic pressures, requiring less energy. Also, the human digestive system’s organs produce many enzymes to break down the food we eat, so we can take in as much energy as possible. In comparison, organisms without bodies must take in nutrients through direct diffusion. Many other vertebrates develop similar enzymes to break down their own sources of energy, but some that have a less complex digestive system cannot consume as much.
Sources:
Campbell
Your Inner Fish
http://en.wikipedia.org/wiki/Body_plan
http://www.hsc.on.ca/moffatt/bio3a/digestive/vartheme.htm
There is a long history behind what made a body. Though the cleavage and development of living animals is one way to study body plans, one could say the original body started with the cell clumping that happened during the conditions of early life on earth. Cells could be a lot more efficient in energy use if they worked together, showing an early start to combining cells for a purpose. From there, after a long period of time, at one point a prokaryotic bacterium entered a pre-eukaryotic cell, becoming one part functional cell and one part energy powerhouse, the eukaryotic cell(http://facstaff.gpc.edu/~pgore/students/w96/joshbond/symb.htm). This idea of an endo-symbiotic theory shows the beginnings of cells specializing to be used for certain things. This is advantageous because it saves energy, and allows for each part of the body to be in charge of one thing. From here, the building blocks were set, allowing groups of cells to organize and distribute the workload.
ReplyDeleteAt this point, cells needed a way to “stick together” in a way, and groups of cells that developed these functional units proved to be at an advantage. Some functional units included “the rivets that hold cells together; the various devices that help cells signal to one another; and many of the molecules that lie between cells” (132). As time went on, some organisms needed more and more of these molecular ties. As Shubin later says, starfish have a fraction of the amount of rivets than chordates.
In this way, the idea of cells being held together by other cells was the original body. With each part being in charge of a process and a system for holding up the organism, one could say that the origins of the body started in simple cells working together in order to live through the harsh conditions of the planet.
(Alex Sapozhnikov marijio@gmail.com)