[1] About 542
million years ago, a large diversity of animal phyla appeared. This spurt of
evolution is called The Cambrian Explosion and is backed up by further fossil
evidence. Over the course of the first 10 million years, marine animals
developed the basic body forms now seen in modern groups. The record includes
fossils of crustaceans, molluscs, sponges, algae, and starfish. However, animal
fossils from the Precambrian era have been found, indicating that many animal
phyla actually developed prior to the Cambrian explosion. In fact, plant
fossils have been found dating back to 1400 million years ago in Montana, USA,
and China. These fossils represent organisms that do not resemble any modern
organism yet prove that animal life did exist.
[2] The
Cambrian Explosion lasted for about 20 to 25 million years, resulting in the
divergence of most modern metazoan phyla. Prior to the Cambrian Explosion, many
animals were unicellular organisms. Over the course of the explosion, the rate
of diversification accelerated, resulting in many of the phyla we have today.
[3] The
appearance of Cambrian fauna provokes several questions. These questions
include "why was there was such a huge diversification of complex
organisms over a specific period of time?" and "What is the source of
this change and what does it suggest about the origin of animal life?".
Trilobites were the first fossils of the Cambrian Explosion to be discovered.
In his book, On the Origin of Species, Charles Darwin names this appearance of
trilobites as troubling to his theory of natural
selection, because this group has no apparent antecedents.
[4]
Paleontologist Charles Walcott suggests that an interval of time – he calls it
the ‘Lipalian’ Era – actually existed but is not proven by a fossil record, and
the predecessors of Cambrian animals lived during this time. Harry B.
Whittington did a new analysis on Burgess Shale fossils in the 1970s with
the conclusion that many were complex but different to modern animals. For
example, the spiny slug-like Wiwaxia was different from any modern animal.
Whittington and other researchers suggested that modern animal phyla developed
at the same time during a specific period of time. This idea led to the theory
of punctuated equilibrium. This theory develops
Darwin’s theory of evolution as a series of long intervals, punctuated by short
periods of fast change. Another theory suggests these unique animals – such as
the Wiwaxia – evolved prior to the Cambrian era.
[5] When
examining fossils, it’s important to remember that two-thirds of fossils of
living fossils have never been found; therefore, the fossil record of animal
phyla is incomplete. It is rare to find fossils of soft-tissued
animals. However, the Cambrian fossil record includes many lagerstatten
fossils, which preserved soft tissues. These
permit paleontologists to study the internal anatomy of animals.
Trace fossils are made up of tracks and burrows and marks left by feeding.
These types of fossils represent another source that is not limited to animals
with hard parts. We can also study the behavior of organisms from these
fossils. These trace fossils might supply the earliest physical proof of the
appearance of complex animals.
[6] Around the
start of the Cambrian Explosions, many chemical markers point to a huge change
in the environment. These markers are consistent with a mass extinction or
warming resulting from the release of methane ice. Indeed, this sudden change
could have been a cause of the Cambrian Explosion. Undeterred by the
uncertainties, the chemical evidence encourages scientists to concentrate
on theories consistent with an environmental change.
[7] Cladistics
is a technique in biological classification in which animals are
grouped together based on whether or not they have one or more shared, a unique
set of traits that are inherited from the group's last common ancestor.
This technique results in a set or group of clades. This technique helps to
ascertain the date that these lineages first appeared. We can also guess how
long two living clades had diverged from the last ancestor. This results in an
approximate dating of the lineages.
1 Which of
the following can be inferred from paragraph 1 about animal phyla?
- Fossil records indicate animal
phyla began to exist during the Cambrian Explosion.
- Fossil records indicate animal
phyla existed prior to the Cambrian Explosion.
- Fossil records indicate animal
phyla existed as far back as 1400 years ago.
- Fossil records indicate animal
phyla began to exist before the Precambrian Era.
ANSWER
EXPLANATION
Question is
worth: 1 point.
Correct Answer:
b
Your Selection: Not Answered
(B) is the
correct answer because there is evidence to support this statement in paragraph
1.
The key to answering this question correctly is to find the general meaning of
the text that refers to animal phyla. Find the referral in the text and
underline key statements around it:
However, animal fossils from the Precambrian era have also been found,
indicating that many animal phyla actually developed prior to the Cambrian
explosion. In fact, plant fossils have been found dating back to 1400 million
years ago in Montana, USA, and China.
We can safely conclude that animal phyla began to exist (developed) before (prior)
the Cambrian Explosion – during the pre-Cambrian era. Hence, answer (B) is
correct.
(A) is not the correct answer because we learn from the text that animal phyla
began to exist before (not during) the Cambrian Explosion.
(C) is wrong because Fossil records indicate animal phyla existed as far back
as 1400 million years ago, not 1400 years ago. This is a trick question that
tries to confuse the reader.
(D) is incorrect because the Precambrian era already means prior to, so stating
before the Precambrian era is like saying "before prior to" and is
grammatically incorrect.
2 In
paragraph 2, what happened after the beginning of the Cambrian Explosion?
- There was a slow rate of
diversification over millions of years.
- There was a development of unicellular
organisms.
- There was a rapid rate of
diversification.
- There was a sudden burst of
diversification of unicellular organisms.
ANSWER
EXPLANATION
Question is
worth: 1 point.
Correct Answer:
c
Your Selection: Not Answered
(C) is the
correct answer because there is evidence to support this statement in paragraph
2.
The key to answering the question successfully is to highlight the sentence in
the text that refers to during the Cambrian Explosion, as stated in the
question. Then, read the information describing developments during this time
(with matching synonyms and words) to find the right answer.
The Cambrian Explosion lasted for about 20 to 25 million years, resulting in
the divergence of most modern metazoan phyla. Prior to the Cambrian Explosion,
many animals were unicellular organisms. Over the course of the explosion, the
rate of diversification accelerated, resulting in many of the phyla we have
today.
Over the course is a synonym of during
The rate of diversification accelerated matches the statement There was a rapid
rate of diversification – Answer (C) is correct.
(A) is not the correct answer because it contradicts the true statement from
the text.
(B) is incorrect because there is no mention in the text of the development of
unicellular organisms. This question aims to confuse the reader as the author
does mention unicellular organisms in this paragraph.
(D) is not the correct answer as it inverts the point that the diversification
accelerated – it did not have a single sudden burst.
3 According
to paragraph 3, why did Charles Darwin find the appearance of trilobites
troubling?
- Because they appeared to have no
predecessors and therefore, posed a flaw in this theory of evolution.
- Because trilobites had no
descendants and therefore no fossil records to track their evolution.
- Because trilobites did not evolve
in the way Darwin suggested animals developed in his book On the Origin of
the Species.
- Because trilobites were the first
fossils discovered and therefore, difficult to examine.
ANSWER
EXPLANATION
Question is
worth: 1 point.
Correct Answer:
a
Your Selection: Not Answered
(A) is the
correct answer because there is evidence to support this statement in paragraph
3
The key to answering the question is to discover the general meaning of the
sentences referring to trilobites and then, to connect the reason for Darwin’s
concern. We find the reason signposted by the word because:
In his book, On Origin of the Species, Charles Darwin names this appearance of
trilobites as troubling to his theory of natural selection, because this group
has no apparent antecedents.
Now that we have found the key sentence, let’s identify the synonyms and
matching words in the correct answer:
Predecessors = antecedents:
...because they appeared to have no predecessors and therefore, posed a flaw in
this theory of evolution.
Answer (A) is correct.
(B) is not the correct answer because it contradicts the true statement. The
word descendents is the antonym of antecedents.
(C) is incorrect as there is no reference in the text that trilobites did not
evolve in the way Darwin suggested other animals developed.
(D) is wrong as there is no mention in the paragraph that trilobites were the
first fossils. They are mentioned as the first fossils of the Cambrian
Explosion only. Moreover, there is no reference that they were difficult to
examine.
4 According
to paragraph 4, all of the following statements are true about animal phyla
evolution, EXCEPT:
- It’s possible that the ancestors of
Cambrian animal phyla existed during the ‘Lipalian’ Era.
- Charles Walcott proved the idea of
the ‘Lipalian’ Era with a fossil record.
- Harry Whittington noted that
Burgess Shale fossils were those of animals not existing in modern times.
- Modern animals may have developed
during a specific period of time.
ANSWER
EXPLANATION
Question is
worth: 1 point.
Correct Answer:
b
Your Selection: Not Answered
(B) is the
correct answer.
It is correct because this sentence contradicts the first two sentences of
paragraph 4, Paleontologist Charles Walcott suggests that an interval of time –
he calls it the ‘Lipalian’ Era – actually existed but is not proven by a fossil
record,...
Charles Walcott did not prove the idea of the ‘Lipalian’ Era as he had no
fossil record.
Answer (B) is the only false statement.
(A), (C) and (D) are all found in the text:
(A) the predecessors of Cambrian animals lived during this time.
(C) Harry B. Whittington did a new analysis or Burgess Shale fossils in the
1970s with the conclusion that many organisms were complex but different to modern
animals.
(D) Whittington and other researchers suggested that modern animal phyla
developed in the same era, during a specific period of time.
5 Paragraph
4 supports which of the following statements about a ‘punctuated equilibrium’:
- The theory of a punctuated
equilibrium suggests that evolution occurred over short periods of time,
interspersed with longer moments of slow change.
- The theory of a punctuated
equilibrium suggests that evolution occurred over periods of time of
approximately equal length.
- The theory of a punctuated
equilibrium suggests that evolution occurred during the ‘Lipalian Era’
when most animal phyla developed.
- The theory of a punctuated
equilibrium suggests that evolution occurred over long periods of time,
interspersed with short moments of rapid change.
ANSWER
EXPLANATION
Question is
worth: 1 point.
Correct Answer:
d
Your Selection: Not Answered
(D) is the
correct answer.
It is the correct answer because there is evidence to support this statement in
paragraph 4:
The trick in answering the question is to identify the part of the paragraph
that mentions punctuated equilibrium. Then, clarify the meaning of the
statement that refers to and find its matching sentence in the answers.
Whittington and other researchers suggested that modern animal phyla developed
in the same era, during a specific period of time. This idea led to the theory
of punctuated equilibrium. This theory develops Darwin’s proposal of evolution
as a series of long intervals, punctuated by short periods of fast change.
We understand from the extract in the paragraph that evolution happened over a
series of long intervals (long periods of time), punctuated (interspersed) by
short periods of fast change (short moments of rapid change). Note the matching
expressions from answer (D)
(A) is wrong as it changes short periods of fast change to longer moments of
slow change.
(B) is incorrect because it doesn’t define the meaning of a punctuated
equilibrium as described in the text.
(C) is not the correct answer because again, it does not define the meaning of
a punctuated equilibrium as described in the text.
6 The word
'common' in paragraph 7 is closest in meaning to:
- Regular
- Unique
- Mutual
- Routine
ANSWER
EXPLANATION
Question is
worth: 1 point.
Correct Answer:
c
Your Selection: Not Answered
(C) is the
correct answer.
It is the correct answer because it’s closest in meaning to the word common.
To answer this question successfully, highlight the word in the sentence and
clarify its meaning in the greater context of the passage. Common is a
descriptive adjective, modifying the word ancestor. From the paragraph, we
understand this ancestor is shared – or mutual – among the same group of
animals which leads to the classification of animal groups.
We read that Cladistics is a technique in biological classification in which
animals are grouped together based on whether or not they have one or more
shared, unique set of traits that is inherited from the group's last common
ancestor.
Therefore, mutual (C) is correct.
(A) is not the correct answer because regular can mean common or normal.
However, the signification is different to that of common in this context.
(B) is wrong because unique means one-of-a-kind. It is not a synonym of common.
(D) is incorrect as routine means regular. This word would be illogical in the
statement.
7 Which of
the sentences below best expresses the essential information in the following
sentence?
When examining
fossils, it’s important to remember that two-thirds of living fossils have never
been found; therefore, the fossil record of animal phyla is incomplete.
- As we study fossils, we should
remember that more than half of living fossils have been discovered; so,
the fossil record is sufficient to fully understand the range of animal
phyla.
- As we study fossils, it’s possible
that one third of living fossils have never been discovered; so, the
fossil record is insufficient to fully understand the range of animal
phyla.
- As we study fossils, we should
remember that more than half of living fossils have never been discovered;
so, the fossil record is sufficient to fully understand the range of
animal phyla.
- As we study fossils, we should
remember that more than half of living fossils have never been discovered;
so, the fossil record is insufficient to fully understand the range of
animal phyla.
ANSWER
EXPLANATION
Question is
worth: 1 point.
Correct Answer:
d
Your Selection: Not Answered
(D) is the
correct answer.
The strategy in answering this question accurately is to highlight the key
words in the sentence, clarify the general meaning and then match both to the
correct answer.
Let’s look at the synonyms between the statement from the text and the first
answer:
When examining fossils = As we study fossils
...it’s important to remember = we should remember
...that two-thirds of living fossils have never been found = more than half of
living fossils have never been discovered
...the fossil record of animal phyla is incomplete = the fossil record is
insufficient to fully understand the range of animal phyla.
Therefore, (D) is the right answer as the phrases and synonyms match
appropriately.
(A) is not the correct answer as it states that the fossil record is
sufficient. The original sentence clearly states that fossil record is
insufficient.
(B) is incorrect as it changes the meaning of the statement that one third of
living fossils have never been discovered. In the original text, it states that
two-thirds of living fossils have never been found.
(C) is also wrong as the sentence states that the fossil record is sufficient
and the original text states is was insufficient.
8 Which of
the following is true, according to the passage?
- There is a unified consensus among
scientists regarding the cause of the Cambrian Explosion.
- There are theories regarding the
cause of the Cambrian Explosion and some suggestions for flaws in these
theories.
- The cause of the Cambrian Explosion
was a mass extinction or warming resulting from the release of methane
ice.
- The cause of the Cambrian Explosion
was global warming.
ANSWER
EXPLANATION
Question is
worth: 1 point.
Correct Answer:
b
Your Selection: Not Answered
(B) is the
correct answer because it is inferred in the passage through references to the
Cambrian Explosion, theories and possible flaws.
The strategy in answering this question correctly is to read through the
answers and highlight key words that match the reference theories regarding the
cause of the Cambrian Explosion and some suggestions for flaws in these
theories. Paragraph 3 refers to the theories around the cause of the Cambrian
Explosion and the reference to trilobites that caused Darwin to cast doubt on
his own theory of evolution. We can now perfectly assume that (B) is the
correct answer.
(A) is wrong as there is no reference in the text to an agreement among
scientists regarding the cause of the Cambrian Explosion.
(C) is not the correct answer because warming resulting from the release of
methane ice may have caused the Cambrian Explosion. However, there is no proof
of this point, so it is not a fact. This answer tries to trick the reader.
(D) is wrong because there are only theories but no definite causes of the
Cambrian Explosion. This answer claims the cause of the Cambrian Explosion
which must be incorrect.
9 Examine
the four █ in the selection below and indicate at which block the following
sentence could be inserted into the passage:
It’s also possible they were the result of increased levels of biological
activity, possibly causing the explosion.
█
[A] Around the start of the Cambrian Explosion, many chemical markers
point to a huge change in the environment. These markers are consistent with a
mass extinction or warming resulting from the release of methane ice █
[B] Indeed, this sudden change could have been a cause of the Cambrian
Explosion. █ [C] Undeterred by the uncertainties, the chemical
evidence encourages scientists to concentrate on theories consistent with an
environmental change. █ [D] .
- [A]
- [B]
- [C]
- [D]
ANSWER
EXPLANATION
Question is
worth: 1 point.
Correct Answer:
c
Your Selection: Not Answered
(C) is correct
because the sample sentence should follow the first two sentences that
introduce chemical markers and sudden change. This is because of the word also
in the sample sentence that indicates a second reference to the markers. It
should also precede the sentence beginning with This evidence which refers to
the markers from the sample sentence.
(A), (B) and (D) are all incorrect as the sentence would be illogical if placed
at these points.
10Directions: An
introductory sentence for a brief summary of the passage is provided below.
Complete the summary by selecting the THREE answer choices that express the
most important ideas in the passage. Some sentences do not belong in the
summary because they express ideas that are not presented in the passage or are
minor ideas in the passage. This question is worth 2 points.
Drag your
answer choices to the spaces where they belong. To remove an answer choice,
drag it back. To review the passage, click VIEW TEXT.
Cladistics is a
technique in biological classification in which animals are grouped
together based on whether or not they have one or more shared, unique set of
traits that are inherited from the group's last common ancestor.
- a. Clades are animal groups classed
because they share characteristics of a common ancestor.
- b. Cladistics assists us in
estimating the period when these groups of animals began to appear.
- c. With Cladistics, it’s possible
to estimate the duration of time two classed, animal groups had existed
and diverged from their common ancestor.
- a. Clades are animal groups classed
because they share characteristics of a common ancestor.
- b. Cladistics assists us in
estimating the period when these groups of animals began to appear.
- c. With Cladistics, it’s possible to
estimate the duration of time two classed, animal groups had existed and
diverged from their common ancestor.
- d. Cladistics is a technique in
which animals are categorized together as they share a common ancestor.
- e. Cladistics is used to estimate
the date the Cambrian Explosion began.
ANSWER
EXPLANATION
Question is
worth: 2 points.
Correct Answer:
a,b,c
Your Selection: Not Answered
(A), (B) and
(C) are the correct answers because there is evidence in the passage supporting
each point.
To answer the question successfully, read the sentences carefully, highlight
key words and scan the entire passage to find matching sentences with synonyms
and the same meaning. Make sure to avoid confusing or deceptive answers.
Here are the statements from the passage to support the correct answers:
(A) Cladistics is a technique in biological classification in which animals are
grouped together based on whether or not they have one or more shared, unique
set of traits that is inherited from the group's last common ancestor. This
method results in a set or group of clades.
(B) This method results in a set or group of clades. This technique helps to
ascertain the date that these lineages first appeared.
(C) We can also guess how long two living clades had diverged from the last
ancestor. This results in an approximate dating of the lineages.
(D) is not the correct answer as Cladistics is not a technique to group animals
based on a shared common ancestor, but on sets of traits inherited from the
common ancestor. Be careful to read this answer carefully to avoid selecting is
as a correct answer.
(E) is not the correct answer because there is no reference to Cladistics being
a technique to estimate when the Cambrian Explosion began.
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