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Updated on: 14 Aug 2019, 22:07
Originally posted by maybeam on 22 Jul 2012, 02:41.
Last edited by Sajjad1994 on 14 Aug 2019, 22:07, edited 1 time in total.
Last edited by Sajjad1994 on 14 Aug 2019, 22:07, edited 1 time in total.
Updated - Complete topic (148).
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Question 1
E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
35%
(medium)
Question Stats:
64% (02:37) correct
36%
(02:50) wrong
based on 3644
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Time
Result
Not Attempted Yet
Question 2
A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
45%
(medium)
Question Stats:
61% (01:47) correct 39%
(02:02) wrong
based on 3538
sessions
History
Date
Time
Result
Not Attempted Yet
Question 3
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
35%
(medium)
Question Stats:
61% (00:51) correct 39%
(00:59) wrong
based on 3499
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History
Date
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Not Attempted Yet
Dendrochronology, the study of tree-ring records to glean information about the past, is possible because each year a tree adds a new layer of wood between the existing wood and the bark. In temperate and subpolar climates, cells added at the growing season's start are large and thin-walled, but later the new cells that develop are smaller and thick-walled; the growing season is followed by a period of dormancy. When a tree trunk is viewed in cross section, a boundary line is normally visible between the small-celled wood added at the end of the growing season in the previous year and the large-celled spring wood of the following year's growing season. The annual growth pattern appears as a series of larger and larger rings. In wet years rings are broad; during drought years they are narrow, since the trees grow less. Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions.
However, trees that grew in areas with a steady supply of groundwater show little variation in ring width from year to year; these "complacent" rings tell nothing about changes in climate. And trees in extremely dry regions may go a year or two without adding any rings, thereby introducing uncertainties into the count. Certain species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again.
However, trees that grew in areas with a steady supply of groundwater show little variation in ring width from year to year; these "complacent" rings tell nothing about changes in climate. And trees in extremely dry regions may go a year or two without adding any rings, thereby introducing uncertainties into the count. Certain species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again.
1. In the highlighted text, "uncertainties" refers to
(A) dendrochronologists' failure to consider the prevalence of erratic weather patterns
(B) inconsistencies introduced because of changes in methodology
(C) some tree species' tendency to deviate from the norm
(D) the lack of detectable variation in trees with complacent rings
(E) the lack of perfect correlation between the number of a tree's rings and its age
(A) dendrochronologists' failure to consider the prevalence of erratic weather patterns
(B) inconsistencies introduced because of changes in methodology
(C) some tree species' tendency to deviate from the norm
(D) the lack of detectable variation in trees with complacent rings
(E) the lack of perfect correlation between the number of a tree's rings and its age
2. The passage suggests which of the following about the ring patterns of two trees that grew in the same area and that were of different, but overlapping, ages?
(A) The rings corresponding to the overlapping years would often exhibit similar patterns.
(B) The rings corresponding to the years in which only one of the trees was alive would not reliably indicate the climate conditions of those years.
(C) The rings corresponding to the overlapping years would exhibit similar patterns only if the trees were of the same species.
(D) The rings corresponding to the overlapping years could not be complacent rings.
(E) The rings corresponding to the overlapping years would provide a more reliable index of dry climate conditions than of wet conditions.
(A) The rings corresponding to the overlapping years would often exhibit similar patterns.
(B) The rings corresponding to the years in which only one of the trees was alive would not reliably indicate the climate conditions of those years.
(C) The rings corresponding to the overlapping years would exhibit similar patterns only if the trees were of the same species.
(D) The rings corresponding to the overlapping years could not be complacent rings.
(E) The rings corresponding to the overlapping years would provide a more reliable index of dry climate conditions than of wet conditions.
3. The passage is primarily concerned with
(A) evaluating the effect of climate on the growth of trees of different species
(B) questioning the validity of a method used to study tree-ring records
(C) explaining how climatic conditions can be deduced from tree-ring patterns
(D) outlining the relation between tree size and cell structure within the tree
(E) tracing the development of a scientific method of analyzing tree-ring patterns
(A) evaluating the effect of climate on the growth of trees of different species
(B) questioning the validity of a method used to study tree-ring records
(C) explaining how climatic conditions can be deduced from tree-ring patterns
(D) outlining the relation between tree size and cell structure within the tree
(E) tracing the development of a scientific method of analyzing tree-ring patterns
09 Nov 2017, 16:38
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Alisher_Pardaev
Hm. I see your point!
Wait... no. No, I don't. Moving on...
Question 3
DIII
The author describes the method in the first paragraph and then, in the second paragraph, explains a couple limitations of that method. The author does not imply that the method is invalid or that it should not be used. Rather, the author explains how climatic conditions can be deduced from tree-ring patterns and then describes conditions under which that method would not be reliable. In other word, the author believes that the method is valid but that it doesn't work under certain circumstances.
So the main purpose is to describe how (and under what conditions) the method can be used, not to question the validity of the method.
So choice (C) is more accurate than choice (B).
I hope this helps!
Updated on: 22 May 2020, 09:35
Originally posted by GMATNinja on 24 Jan 2018, 20:22.
Last edited by GMATNinjaTwo on 22 May 2020, 09:35, edited 1 time in total.
Last edited by GMATNinjaTwo on 22 May 2020, 09:35, edited 1 time in total.
corrected years
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Shivikaa
Quote:
For the first question, refer to the following portion: "In wet years rings are broad; during drought years they are narrow, since the trees grow less. Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions."
So if we look at the ring patterns of dead trees, we should be able to tell which years were dry and which years were wet based on the width of the rings. If we only have one tree, then we would obviously only be able to gather data for the years in which that tree was alive. But now imagine we have two trees. One of the trees died in 1960 at the age of 50, and the other was born in 1950 and lived for 60 years (a 10 year overlap). In that case, we would have ring data from 1910 - 2010 and could use that data to help figure out which years were wet and which were dry.
Now consider the 10-year overlap. Because we are talking about different trees, the actual widths of the rings from those years might not be exactly the same. However, during wet years, we would expect RELATIVELY broad rings. During dry years, we would expect relatively narrow rings. So even though the precise widths might not be exactly the same for both trees, the PATTERNS (i.e. narrow-narrow-broad-narrow-broad-broad-broad-etc) will likely be the same. Now the second paragraph does explain why this is not ALWAYS the case, but the passage suggests that the patterns will OFTEN exhibit similar patterns.
Hopefully that helps you arrive at the correct answer!
Quote:
The highlighted portion specifically refers to trees that may go a year or two without adding rings. According to the first paragraph, it is often possible to determine a tree's age by counting the rings. Why? Because there is typically an annual boundary line at the end of the growing season. With a regular annual growth pattern, you can count the rings to determine the age.
But what if a tree goes a year or two without adding any rings? In that case, if you count the rings to determine the age, your number will be LESS than the tree's actual age. For example, if you count 40 rings, the tree could actually be 41, 42, 45, 50, or 60+ years old! We would have no way to determine the number of years in which rings were not added. This corresponds to choice (E).
As for choice (D), the highlighted portion refers to the uncertainty in ring count, not to the lack of variation in ring width in complacent trees. We are indeed told that trees with "complacent" rings show little variation in ring width from year to year. However, you should still be able to count rings to determine the AGE of complacent trees. You would not be able to tell which years were wet/dry, but you should still be able to determine the age.
Choice (E) is the best answer.
