PREP RC

[czarczar]

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.




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

OA:E

[Geva@EconomistGMAT]

It is important to do an initial reading of the passage (just a few first senteces of each paragraph) before answering any of the questions of an RC passage. Even specific questions such as this one should be answered in light of your insight into the main idea and topic of the passage as a whole.

The topic of the passage is "the study of tree-ring records to glean information about the past". the first paragraph then goes on to detail how each year a tree adds a new layer of wood between the wood and the bark, with different rings corresponding to different climate: for the beginning of the growing season, the rings are large and thin-walled and later become small and thick walled. The exact process is unimportant - it's important to understand that the passage tells you what you can learn from the predictable growth pattern of tree rings.

The second paragraph begins with "however", signaling a change in direction from the first. This paragraph then goes on to show cases where studying tree rings cannot teach us any information, because the predictable patterns described in the first paragraph are disturbed: for example, trees in an area with a steady supply of groundwater show little variation in ring width (as opposed to the "large and thin -->small and thick" variation we described in the first paragraph). The next sentence , which includes the "uncertainties", continues the same direction: in extremely cdry regions, a tree won't add any rings - so the predictable pattern of ring growth from year to year is disturbed, so the information we glean from the tree ring patterns is less certain. - specifically, a tree may be older than the number of his rings suggest, since he grows for an extra year or two without adding rings.

[czarczar]

It is important to do an initial reading of the passage (just a few first senteces of each paragraph) before answering any of the questions of an RC passage. Even specific questions such as this one should be answered in light of your insight into the main idea and topic of the passage as a whole.

The topic of the passage is "the study of tree-ring records to glean information about the past". the first paragraph then goes on to detail how each year a tree adds a new layer of wood between the wood and the bark, with different rings corresponding to different climate: for the beginning of the growing season, the rings are large and thin-walled and later become small and thick walled. The exact process is unimportant - it's important to understand that the passage tells you what you can learn from the predictable growth pattern of tree rings.

The second paragraph begins with "however", signaling a change in direction from the first. This paragraph then goes on to show cases where studying tree rings cannot teach us any information, because the predictable patterns described in the first paragraph are disturbed: for example, trees in an area with a steady supply of groundwater show little variation in ring width (as opposed to the "large and thin -->small and thick" variation we described in the first paragraph). The next sentence , which includes the "uncertainties", continues the same direction: in extremely cdry regions, a tree won't add any rings - so the predictable pattern of ring growth from year to year is disturbed, so the information we glean from the tree ring patterns is less certain. - specifically, a tree may be older than the number of his rings suggest, since he grows for an extra year or two without adding rings.

Thanks for your reply sir.

I narrowed down btw C and E, but was not able to rule of C.

I thought that uncertainties were occurring because trees were not showing the information that they are expected to show.

[AIM GMAT]

In the highlighted text, "uncertainties" refers to

(C) some tree species' tendency to deviate from the norm [Its already mentioned in passage that without adding any ring => deviating from norm , but what does deviating from norm actually means , it means tht the number of ring is not equal to the age of tree ]


(E) the lack of perfect correlation between the number of a tree's rings and its age [After reading uncertainities in the count the first thought clicked was that the number of rings will not be equal to age of tree , hence age of tree would be wrongly concluded.]

[Geva@EconomistGMAT]

It is important to do an initial reading of the passage (just a few first senteces of each paragraph) before answering any of the questions of an RC passage. Even specific questions such as this one should be answered in light of your insight into the main idea and topic of the passage as a whole.

The topic of the passage is "the study of tree-ring records to glean information about the past". the first paragraph then goes on to detail how each year a tree adds a new layer of wood between the wood and the bark, with different rings corresponding to different climate: for the beginning of the growing season, the rings are large and thin-walled and later become small and thick walled. The exact process is unimportant - it's important to understand that the passage tells you what you can learn from the predictable growth pattern of tree rings.

The second paragraph begins with "however", signaling a change in direction from the first. This paragraph then goes on to show cases where studying tree rings cannot teach us any information, because the predictable patterns described in the first paragraph are disturbed: for example, trees in an area with a steady supply of groundwater show little variation in ring width (as opposed to the "large and thin -->small and thick" variation we described in the first paragraph). The next sentence , which includes the "uncertainties", continues the same direction: in extremely cdry regions, a tree won't add any rings - so the predictable pattern of ring growth from year to year is disturbed, so the information we glean from the tree ring patterns is less certain. - specifically, a tree may be older than the number of his rings suggest, since he grows for an extra year or two without adding rings.

Thanks for your reply sir.

I narrowed down btw C and E, but was not able to rule of C.

I thought that uncertainties were occurring because trees were not showing the information that they are expected to show.

"the norm" is too vague; also, C can be eliminated because it limits the answer to "some tree species" whereas the passage does not refer to trees in a dry year. Presumably, all tree species growing together in the same dry place, so it won't be right to speak of certain species deviating from the norm: more like trees in specific areas, in specific years, and even then all these trees will act "normally" for that region.

[atulmangal]

Two more questions are there in this passage:

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.


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

for Question no 2...how we pick b/w Op B and Op C

[Geva@EconomistGMAT]

Two more questions are there in this passage:

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.


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

for Question no 2...how we pick b/w Op B and Op C

Q2: B is a cunning trap, as the second paragraph does question a method. However, if you read the paragraph carefully, you see that it questions the findings of the method - it shows cases where the method might be fooled by special conditions - but it doesn't question the method used to study the tree ring patterns itself. For B to be true, the second paragraph needs to say something along the lines of "However, the way tree rings are studied - through microscopes (for example) - is problematic, since some tree rings are too small to be detected by microscopes" - this would indeed question "the method used to study tree-ring record."

[Geva@EconomistGMAT]

Two more questions are there in this passage:

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.


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

for Question no 2...how we pick b/w Op B and Op C

Q1: the answer is A. "overlapping" is mentioned in the last sentence of the first paragraph, which tells us that "Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions"

From the beginning of the first paragraph, we learn that studying ring patterns can teach us about climate conditions during those years. This last sentence tells us that several trees with overlapping ages can prvide an extended index - meaning that we can find the climate conditions for a longer time than the life of a single tree. We can infer that the overlapping is important - it allows us to say "these tree grew at the same time", so we can add the "timeline" of climate conditions of both trees together to create our extended index. Since the overlap is the thing that "connects" the two trees, we must assume that the rings created in the overlapping years will be the similiar, allowing the investigator to correlate the two differnt trees to the same time period.

Also, the other answer choices all have major eliminating flaws - which answer choice were you debating? @atulmangal

[gopinath00009]

A question regarding Q1.

Last line of first para says "Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions."

and

Last line of last para says "Certain species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again."

Shouldn't the answer be C. If the two trees are of different species and one of them is from the species mentioned in the last line of last para then the patterns will be different. Hence we need two trees of the same species.