CHAPTER 7:: ADVENTURES IN BODY BUILDING

Q Elaborate on the polymorphic characteristic characteristics portrayed by cells.

- Organisms are classified as single celled organisms and multi-celled organisms based on their size. Fossils prove that single celled organisms have evolved before multicellular organisms, as they are less complex and utilize a lesser amount of energy. Multicellular organisms require large amounts of energy, in order to supply energy to a numerous cells. A cell that uses oxygen produces 20 times more useful energy than a cell that does not. 

- Martin Borass performed an experiment in which he grew algal cells for a thousand generations, after which a predator was introduced.  Masses of algal cells were held together by proteins and other cellular produced compounds between the 10^th and 20^th generations.  Within another few tens of generations, the size of the proto-bodies became stable at 8 cells per body.  This size was large enough to prevent the predators from eating  the cell mass and small enough to ensure that all the 8 cells would get sufficient nutrients.  The cells had formed the first proto-body, for the first time.

- Volvox is a colony of green algal cells, which have begun specialize, thereby showing traits of polymorphism (when two things doing the same thing, one can change/evolve and the other can continue the original task). When a volvox cell is split in half, two smaller cells are produced. However when a human cell has been split in half the cell can no longer survive without the presence of other organelles.

CHAPTER 6:: THE BEST- LAID (BODY) PLANS

-All tetrapods have the same body plan, one head and four limb arrangements. This chapter also introduces a new term atavism, which is the reappearance of traits that had disappeared generations ago.

-The sixth day after conception, the zygote which has been duplication eventually forms a blastocyst which is embedded into the lining of the uterus wall. After implantation the cells begin individualizing. Within each organism a hollow tube, consisting of three layers is formed. One end of the tube becomes the mouth , the middle section becomes the digestive track and the other end becomes the anus. The three layers of the tube then constitute the various organs of the organism.

- The specific differentiation of the tube into these three major regions is due to the presence/ absence of a certain set of chemicals which are produced by the cells themselves. The region with a high concentration of these chemicals turns into the head; subsequently the region with a low concentration becomes the anus.

- The same genes in every organism result in the formation of these chemicals and thus in the formation of such tubes.  Sea anemones have sides, a front and a back.  Even though they are radially symmetrical (humans and most other animals are bilaterally symmetrical), they still have a head region and a tail region.  Those same genes that form the head and tail ends are in other animals, including humans.

CHAPTER 5:: GETTING AHEAD

Q: How can the branchial arches provide evidence to common ancestry?

 

- The head is one of the most substantial parts of the human body, as it houses the brain. It might be astonishing to realize that the human's head and a shark's gill originate from the same pieces of an embryo. Every vertebrate animal starts with these four arches known branchial arches, having the same shape. They are labeled as 1, 2, 3 and 4.

- In humans, the first arch develops into the upper and lower jaw, the malleus and incus bones in the inner ear, and the blood vessels and muscle that attach to them.  The second arch turns into the third ear bone (stapes), a bone in the throat, and the muscles that control facial expressions.  The third arch forms the muscles, bones, and nerves of the throat (swallowing).  The fourth arch forms the larynx and other parts deep in the throat.

- Whereas in sharks the branchial arches develop into the different features. The first arch becomes the jaw, same as us.  The second arch in sharks becomes a bar of cartilage and muscle.  In humans that bar breaks up to become the stapes and some small structures of the throat.  In the shark, the bar becomes the structure that allows sharks to extend their jaw slightly out of their mouth while feeding.  The bone that allows this in sharks, if you carefully trace its evolutionary history becomes our stapes.

- Humans sometimes get ruptured disks in our spines.  Those disks are a holdover from Amphioxus, a worm.  A non-vertebrate that does have a notocord and gill slits, the precursors of our own spine and allowing to speak

CHAPTER 4:: TEETH EVERYWHERE

Q. Where did teeth originate from?

- The importance of teeth has been outlined in this chapter. Being one of the hardest structues of an organism (due to hydroxyapatite enamel), teeth prove to be a perfect fossil material. Characteristics of an animal can be found by studying the structure of its tooth. For example, its diet, its prey and even its predators as well its chewing patterns. By observing the teeth of a tritheledont, we can see a link between reptiles and mammals. A mammal’s teeth fit together when bitten down, while that of a reptile's do not. The tritheledont’s teeth were in between; the inner surface of the upper teeth slid against the outside of the bottom teeth like scissors.

- Humans have specialized teeth. Incisors for cutting, canines for holding and molars for grinding. The entire order of carnivores is defined by four teeth called carnassials. Ifan organism posses those kind of teeth, they are a member of the carnivore family.

- Teeth help constitue scales, feathers, and breasts possible by the revolutionary way they are formed inside developing skin. They develop while the skin is still developing, through an interaction betwee two layers of tissue. Teeth were the first things that were made like this, which then was modified to make scales, feathers, breasts etc.

Chapter 2:: GETTING A GRIP

Q. What did further examination of Tiktaalik’s fins reveal about the creature and its lifestyle?



- In the second chapter Shubin mentions the similarity between the basic skeletal structure of all organisms, with emphasis on the hand. Shubin believes that studying the variations in limbs that have evolved over the years will help constitute our map of evolution. Now when comparing the human torso with that of a pig, we notice that their resemblance is comparable. However when evaluating the limbs in the hands of these two orgainisms, we realize that not only are their structures different, but the human hand shows skeletons representing the thumb, which is a signature human structure.

- Sir Richard O Wen, in 1822 began investigating the evolution of the thumb. Bats, horses, gorillas, humans even dinosaurs all had exactly the same limb structure; one bone, two bones, bunch of little bones. Sir Owen recognized the coinciding features in all of these organisms while examing their skulls as well as the backbones.Thus he concluded that there is a fundamental design in all vertebrates.

- This theory also helped discover how and where Tiktaalic was habitauted. The wrist bone in its fin, was due to the fact that it either lived on the ocean floor, or in shallow streams. Thus it  should have been able to lift its body off the floor in order  to maneuver its way around. This was an important discovery in this chapter of the book, as it provides us with further evidence that humans are related to fish like Tiktaalik.