How to Break Down a Science Reading Comprehension Passage

by Beat The GMAT, Aug 25, 2010


On Friday August 20, famed Beat The GMAT member Dana Jinaru (DanaJ) held a live workshop on tackling one of the toughest problems on the GMAT, Reading Comprehension Science passages. Like many of you in this community, Dana is not a native-English speaker. But when she took the GMAT, Dana was able to score a 770 on the GMAT and had a near-100% hit rate when it came to her reading comprehension practice.

During this workshop, Dana shared some of her best RC tips by breaking down an example of a very tough science RC passage. Her full video session can be seen above, with the science passage/questions that she examined below.

This science passage was provided by Beat The GMAT Practice Questions.

Highlights from this Video

3:05 - Today's agenda

4:27 - A detailed analysis of the first paragraph of the text

5:32 - Explanation of the concept of "lead actor" or "hero"

6:48 - Explanations of the concept of "connectors"

8:48 - We move on to the second paragraph of the text

10:07 - Last but not least, the third paragraph of the text

12:58 - Some interesting note taking advice

14:59 - General breakdown of RC questions types: detail and general

16:20 - The session's first question

22:58 - Our second question

29:00 - The final, general question

34:47 - Key takeaways

37:40 - Q&A session

The Science Passage in This Workshop

In their relationship to the general ecology of the reefs, the Mollusca as a group of animals play a highly significant role. Because of the nature of their shells, mollusc remains may be found among the limestone debris of a reef dating back to its very earliest stages of evolution in the geological past, and may, therefore, be considered as having aided in its construction. Yet, as boring organisms, in both living and dead coral, certain species of molluscs rank among the most destructive agents to be found on the reefs. Mollusc eggs are laid in tens of millions, and the floating larval stages form a very important part of the zooplankton that sustains life in the waters over the reefs. In their vast numbers, as herbivores and carnivores, the molluscs are both prey and predator on the reefs.

Most molluscs obtain their oxygen directly from the seawater by means of gills in the mantle cavity. Molluscs with two valves, or shells, hinged together are referred to as bivalves. In bivalves the gills have become so developed that in many species they also act as the food-catching apparatus. Because most bivalves are filterfeeding animals, sieving minute organisms from the surrounding seawater, they have no differentiated head region and no radula (tonguelike organ).

It is in the method of feeding that the clams of the family Tridacnidae display their remarkable adaption to their environment. In the course of their evolution, the various members have become structurally modified to best enable them to develop in their particular habitat. These clams normally live with the animal lying on the hinge side of the shell, and the edges of the shell valves pointing upwards. The result of this mode of living is that the internal organs in their relationship to the mantle and shell differ from those of all other bivalve molluscs. The mantle tissue, by reason of the animals way of life, is capable of considerable expansion, and is exposed to the direct rays of the sun to the greatest possible extent. This is undoubtedly associated with the most unusual feature of all displayed by these remarkable molluscs: Within this mantle tissue are millions of tiny zooxanthellae, closely resembling the symbiotic algae found in the corals and the alcyonarians. It has been definitely established that these zooxanthellae form a considerable part of the diet of the Tridacnas, and the modifications found in these molluscs indicate that they are not only specialized for harboring these minute algae, but that they also deliberately farm them. This must surely be one of the most fascinating examples of symbiosis to be found in nature. The whole ecology of the clams, bound exclusively to warm, shallow waters of tropical seas, appears linked to an increase in the efficiency of that symbiosis, which gives food and protection to the algae and very considerable additional nutrient from its symbionts to the clams.

The Questions

1. According to this passage, the ability of the clams of the family Tridacnidae to harbor microscopic zooxanthellae in their mantles is an illustration of:

(A) symbiosis

(B) an inability to adapt to ones environment

(C) bivalve function

(D) oxygen replenishment

(E) evolution

2. Bivalve molluscs possess neither differentiated heads nor radula for which of the following reasons?

(A) Better locomotion on the ocean floor is accomplished without the need for a differentiated head or radula.

(B) Visual apparatus is located in antennae, which obviates the need for a differentiated head or radula.

(C) They strain plankton through their gills, which eliminates the need for a differentiated head and radula.

(D) They trap their prey by closing their hinged shell, which performs all the functions of a differentiated head and radula.

(E)These apiary would interfere with their symbiotic relationships with other organisms.

3. An appropriate title for this passage would be:

(A) Filter Feeding in Bivalve Molluscs

(B) Plankton in Coral Reef Ecology

(C) Prey and Predator in the Tropical Seas

(D) Role of Molluscs in the Reef Ecosystem

(E) Molluscs and Coelenterates of the Coral Reef

See other tough GMAT practice problems like this, with full video explanations in Beat The GMAT Practice Questions.