GMAT Prep RC: Dendrochronology, the study of tree-ring

[smilepinks]

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.




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

The answers are A and C
My answers are: B and B
Please explain why my answers are wrong and how A and C are the correct answers

[tim]

Okay, for the first question, the passage does nothing at all to suggest that climate conditions are unreliable if only one tree gives us data. In addition, for the second question, the passage is definitely not trying to throw out the whole science of dendrochronology. It seems both of your incorrect answers have the same root cause - you appear to be reading controversy and hostility into the passage where there is none. If you let that go, i would guess that it will become obvious why the correct answers are correct..

[jp.jprasanna]

Hi Tim thanks for your response. Could you please also clarify the below questions.

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

Could you please let me know what makes answer choice C wrong.

And why is E correct?

How can uncertainties here mean to "lack of perfect correlation between the number of a tree's rings and "ITS AGE"

The excerpt from the passage i referred to was
"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."

I took all this to mean that it would be difficult to determine the climate because of certain "irregularities" in the tree-rings.

What am i missing here?

Cheers

[jlucero]

Your mistake is reading too much of the passage. This word concerns itself with only a single sentence:

And trees in extremely dry regions may go a year or two without adding any rings, thereby introducing uncertainties into the count.

Trees in dry regions may go a year (or two) without extra rings, introducing uncertainties into the count (of years that the tree had been alive)

[peter_griffin]

For the 1st question posted by the reader,

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.

I eliminated all choices but A&C.

I liked A because it kind of was more wishy washy with "often"
And then C kind of took in the info from the last para abt some trees acting differently , but dropped the "often" making it more definite..Hence A is better .

Although i picked C while Answering , Is my reasoning WRT choosing A correct ?

Thanks in advance

[RonPurewal]

the relevant part of the passage says ...

Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions.

(A) The rings corresponding to the overlapping years would often exhibit similar patterns.

if they can "be correlated", then some degree of similarity is necessary.
also, as you noticed, "often" here matches "often" in the passage. that's important; if this choice suggested that this were always the case, then it'd be wrong.

(C) The rings corresponding to the overlapping years would exhibit similar patterns only if the trees were of the same species.

there's no mention of inter-species differences at all; the idea of species is irrelevant here.

[Jazmet]

Hi Ron,

Could you please explain why is E wrong in the following question?

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

[RonPurewal]

Hi Ron,

Could you please explain why is E wrong in the following question?

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

(e) is wrong because it's ... well, totally wrong.
not only is that not the "primary purpose", but, in fact, it's not in the passage at all, in any way whatsoever.

i.e., "tracing the development of a scientific method..." implies that the passage is giving a history or a description of the origins of the method itself. that's definitely not happening here.

[Jazmet]

Thank you

The phrase 'Tracing the development' was exactly what I wanted to understand.

Thank you once again.

[tim]

Cool. Let us know if there are any other questions here.

[TooLong150]

I dismissed E and chose C, because E had the phrase "perfect correlation", which is not discussed in the passage and C talked about the "deviation" that certain species have on the count. Can someone explain where I made a mistake?

[RonPurewal]

I dismissed E and chose C, because E had the phrase "perfect correlation", which is not discussed in the passage

If those weird years (the ones that introduce "uncertainties" didn't happen, then there would be exactly one ring for each year. In other words, there would be a perfect correlation.

If they point you to an exact location in the passage, then, clearly, you're going to have to make logical deductions and/or rephrase things. (If they pointed you to an exact location AND you just had to regurgitate the words that appear there, then no one would ever get the problem wrong!)

[NL]

the relevant part of the passage says ...

Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions.

- How did you know you need to find a part that deals with "one tree" only?

The question asked about "the ring patterns of two trees that grew in the same area and that were of different, but overlapping, ages?"

[RonPurewal]

the relevant part of the passage says ...

Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions.

- How did you know you need to find a part that deals with "one tree" only?

The question asked about "the ring patterns of two trees that grew in the same area and that were of different, but overlapping, ages?"

I'm confused.

The quoted excerpt is about correlating ring patterns from dead trees of different ages. If the trees have different ages, then, clearly, there are at least two trees. (One tree can't have different ages, nor can you "correlate" one tree to itself.)

Where is there an excerpt about an individual tree?

[NL]

If the trees have different ages, then, clearly, there are at least two trees.

Well, don't you see a 30 year old man with his hair turning from black to white? That "tree" has different ages!

(haha, I'm confused with my brain too. How could it has such brilliant moment?)