Integrated writingAnimal 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 appeare

Essay topics:

Integrated writing
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 speaker refuted the conclusion that the recent findings in the T. rex's leg bone are remains of blood vessels, red blood cells, and collagen matrix, mainly by three counter explanations of the three points claimed in the passage.

First, despite the possibility that the soft, flexible organic substance inside the channels may be blood vessels, there is still another explanation. It may be the remains of bacteria which invaded the bones after the T. rex died, and, keeping in mind that bacteria usually leaving some traces, the clues could just be the left-behind of those creatures.

Seco...

*** The full content of this essay is available to VIP readers

Votes
Average: 9.3 (3 votes)
This essay topic by users
Post date Users Rates Link to Content
2013-04-17 yjc1989 93 view
Essay Categories
Essays by user yjc1989 :

Comments

It is on top list:
http://www.testbig.com/essay-categories/toefl

Attribute Value Ideal
Score: 27 in 30
Category: Excellent Excellent
No. of Grammatical Errors: 0 2
No. of Spelling Errors: 0 2
No. of Sentences: 8 10
No. of Words: 255 250
No. of Characters: 1187 1200
No. of Different Words: 138 150
Fourth Root of Number of Words: 3.996 4.7
Average Word Length: 4.655 4.6
Word Length SD: 2.443 2.4
No. of Words greater than 5 chars: 79 80
No. of Words greater than 6 chars: 58 60
No. of Words greater than 7 chars: 33 40
No. of Words greater than 8 chars: 18 20
Use of Passive Voice (%): 0 0
Avg. Sentence Length: 31.875 21.0
Sentence Length SD: 8.447 7.5
Use of Discourse Markers (%): 0.875 0.12
Sentence-Text Coherence: 0.446 0.35
Sentence-Para Coherence: 0.722 0.50
Sentence-Sentence Coherence: 0.081 0.07
Number of Paragraphs: 4 4