Question

sea stars

1. scientists have puzzled over the strange shape of sea stars, commonly known

as starfish, for hundreds of years. the common name is a bit misleading, as the
animals are technically not fish. this is because they do not have gills, fins, or
scales. in fact, sea stars do not even have blood. they are most closely related
to sea urchins and sand dollars, and resemble animated or moving coral.

1. until very recently, scientists believed that sea stars had no heads because sea

stars do not have a visible trunk or torso. the five extensions, long described as
arms, appear to act independently of one another and any one of them can take
the lead when the sea star moves along the ocean floor. their structure lacks
the symmetry most often associated with animals, which has made it difficult to
determine the \sides\ of the animal, or which side is the \front\ and which side
is the \back.\

1. since scientists most often identify the front of an animal as the head and the

back as the tail, the prevailing opinion has been that sea stars must not have
heads. however, labs at stanford university and uc berkeley have made a
discovery that changes everything. rather than study the visible structure of sea
stars, they analyzed dna sequences. this helped them to understand the
genetic code of the animals. they also used micro - ct scans to get a better
sense of the internal structure of sea stars.

1. the labs focused on dna markers that usually indicate a head or tail. they also

searched for markers that would describe an axis. this might help identify the
sides, front, and back of the star. what they found was surprising. and exciting.
the genes looked similar to the forebrain and midbrain in humans. the forebrain
genes stretched down the center of each arm. toward the edges of each arm,
genes resembled the midbrain.

1. what does all of this mean? rather than being an animal with no head, sea stars

may be almost all head. they need to do more research, of course, but one
thing is certain: we are on the bring of a much stronger understanding of sea
stars.
their structure lacks the symmetry most often associated with animals, which has
made it difficult to determine the \sides\ of the animal, or which side is the \front\
and which side is the \back.\
use your knowledge of greek and latin roots to determine the mostly likely meaning
of symmetry in context.
a measurably dichotomous
b measurably identical
c measurably separate
d measurably aligned

Explanation:

The word "symmetry" comes from the Greek roots "sym-" (meaning together or with) and "metron" (meaning measure). In the context of the text, it is used to describe a balanced and proportionate arrangement. When something is symmetrical, its parts are arranged in a way that is measurably identical on either side of a central axis. For example, a human face has symmetry as the left and right sides are (roughly) identical in shape and feature placement. In the case of sea stars, the lack of symmetry (as per the text) makes it hard to determine front, back, etc., which implies that symmetry usually means having identical - like parts for easy orientation.

Answer:

B. Measurably identical