Essay topics: Question
Summarize the points made in the lecture, being sure to explain how they challenge the specific theories presented in the reading passage.
Animal fossils usually provide very little opportunity to study the actual animal tissues, because in fossils the animals' living tissues have been largely replaced by minerals. Thus, scientists were very excited recently when it appeared that a 70-million-year-old fossil of Tyrannosaurus rex (T. rex), a dinosaur, might still contain remains of the actual tissues of the animal. The discovery was made when researchers deliberately broke open the T. rex’s leg bone, thereby exposing its insides to reveal materials that seem to be remains of blood vessels, red blood cells, and collagen matrix.
First, the breaking of the fossilized leg bone revealed many small branching channels inside, which probably correspond to hollows in the bones where blood vessels were once located. The exciting finding was the presence of a soft, flexible organic substance inside the channels. This soft substance may very well represent the remains of the actual blood vessels of T. rex.
Second, microscopic examination of the various parts of the inner bone revealed the presence of spheres that could be the remains of red blood cells. Tests showed that the spheres contained iron-a material vital to the role of red blood cells in transporting oxygen to tissues. Moreover, the spheres had dark red centers (substances with iron tend to be reddish in color) and were also about the size of red blood cells.
Third, scientists performed a test on the dinosaur leg bone that showed that it contained collagen. Collagen is a fibrous protein that is a main component of living bone tissue, in which it forms a so-called collagen matrix. Collagen (or its chemical derivatives) is exactly the kind of biochemical material that one would expect to find in association with bone tissue.
The reading passage asserts three points that could indicate that the T. rex's fossils contains materials which seem to be remains of blood vessels, red blood cells, and collagen matrix. However, the professor mentions the following reasons and examples to cast doubt on the reading passage's assumptions.
First, the reading passages contends that the presence of a soft, flexible organic substance inside the channel would be the actual blood vessels of T. rex. However, the professor says that the substance may not necessarily represent the remains of the blood vessels of T. rex. The substance may come from the bacteria.
Second, the reading passages argues that the presence of spheres of the inner bone could be the remains of red blood cells. Nevertheless, the professor casts doubt on the assumption. The professor says that other animals which has iron in their bodies does not have red blood cells. Furthermore, the professor mentions that the spheres which had dark red centers may just be the red minerals.
Third, the reading passage argues that the collagen which are found on the dinosaur leg bone indicates the evidence of bone tissue. However, the professor mentions that collagen is only found on the animals in recent years. It is not reasonable for T. rex, which lived a long times ago, has collagen.
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