| Item Description:
In the passage (page 4 of the booklet) the student is introduced
to the idea of using a "flow chart" or "key" to classify animals
into categories. The student is given the first two steps
of one possible dichotomous classification scheme and is asked,
in Question 1, to continue classifying the animals
in a similar manner until each animal is in a group by itself.
Based on student's responses, the students were given pictures
of the following animals: alligator, fish, frog, goose, gorilla,
monkey, owl, salmon, shark, snake, and whale.
In a dichotomous classification scheme, animals are
split into two different groups at each branch point,
depending on whether the animal has a particular characteristic
or not. For example, as shown in the first branch point on
page 4, the animals can be classified into two distinct
(non-overlapping) groups depending on whether they have
"legs" or "no legs." Then, the group of animals with legs
can be further split into two groups by separating them based
on whether the animals have "less than four legs" or "4 or
more legs." Note that in this second case, it would be unacceptable
to classify animals according to the "number of legs" because
this characteristic could split the animals into more than
two groups, such as "two legs," "four legs," and "six
legs."
When building a dichotomous classification scheme, it is best
to select characteristics that separate animals in a meaningful
way. But, what is meaningful? Biologists tend to think of
meaningful classifications schemes as those that reflect evolutionary
descent: more closely related species are clustered closer
together than more distantly related species. Ideally, the
first characteristic used to classify a snake, turtle and
rabbit would first separate the rabbit (a mammal) from the
two reptiles. This, the trait of "fur" versus "no fur" would
be more meaningful than the trait of "legs" versus "no legs."
All mammals have fur and all reptiles do not, while the majority
of both mammals and reptiles have legs and only a few, such
as the snake, do not. Thus the former trait is better suited
to a classifying scheme.
However, from the point of view of an eighth-grader, "meaningful"
characteristics might reflect nothing about the evolutionary
descent among a variety of species. Nevertheless, a similar
strategy can be applied to keep the most closely related
animals together -- that is, the best characteristics
for building a classification scheme are those that can separate
all individuals of one species (Species A) from all individuals
of another species (Species B) despite the fact that there
is variation among individuals of both Species A and Species
B.
Question 3 sets the stage for this level of understanding
by providing an example of a characteristic that is not well-suited
to classifying (fur color) and explaining its limitations
(white and brown rabbits would end up in different groups).
This suggests to the student that the best characteristics
are those that keep members of the same species together while
separating them from other species. The student is left to
decide which types of characteristics are well-suited
to this task. The best answers will include not just a
list of characteristics, but either a general statement
or concrete example accompanied by an explanation showing
that the best traits are those that keep all members of one
species together while separating them from all other species.
Students at this grade level are more likely to present a
specific example rather than an abstract generalization. Thus,
we expect students to demonstrate this understanding by presenting
specific traits and merely explaining why one particular trait
(fur versus no fur) is better than another (legs versus no
legs).
In response to Question 2, the best students will realize
that there is more than one possible way to classify a group
of animals. There are numerous ways -- some better than others,
others equally good. Either different characteristics can
be used, or the characteristics can be used in a different
order. Students may cite other classification schemes (such
as those of classmates) or other traits (that they didn't
use but could've used) to support this view.
ME129 Rubric
Criterion #1. In response to Question 1, student
builds a flow chart that satisfies EITHER A OR B below:
-
- NOTE: Students were told that they can use "scratch paper"
at the back of the book. Some did this but never rewrote
their flow chart. Be sure to check the back page if Question
1 is left blank. Credit will be given if the flow chart
is written elsewhere in the booklet.
EITHER
A. Animals are classified according to a dichotomous
classification scheme. The student selects characteristics
that split the animals into two distinct groups at each branch
point. The student need only complete TWO steps (branch
points) of the flow chart to demonstrate his/her understanding
of the process. The characteristics need not be mutually exclusive,
even though it is preferable that they are. The characteristics
need not be scientifically accurate.
Acceptable characteristics can be either physical or
behavioral, realistic or not. The key requirement is that the
characteristics can be used to split these particular animals
into two distinct groups at each branch point. Examples of acceptable
traits include: (1) hair versus no hair, (2) swims versus doesn't
swim, (3) can breathe in water versus can breathe in air, (4)
eats meat versus doesn't eat meat, (5) has a 4-chambered heart
versus doesn't, (6) is a mammal versus is a reptile (note that
this last example will work in certain cases but isn't mutually
exclusive).
Students will not be penalized for misclassifying animals. For
example a student will receive credit even if he or she mistakenly
classifies a whale as a fish, or says it lays eggs, or cannot
breathe air. An effective classification scheme can be developed
even if the student knows little about the animals themselves.
Unacceptable characteristics are those that do not
split the animals into two distinct groups at a particular
branch point. For example, the student fails to meet this criterion
if the student assigns non-dichotomous traits such as (1) number
of legs and then splits the animals into three groups: "zero,"
"two," and "four" or (2) type of animal and splits them into
four groups: "mammals" and "reptiles" "birds" and "fish."
OR
B. Each of the animals ends up in a group by itself.
Criterion #2. In response to Question 2,
the student satisfies BOTH A and B below.
BOTH
A. The student says "NO."
AND
B. Provides EITHER (1) an explicit example
of an alternative classification scheme
Acceptable responses include a concrete example.
(a) The student may specifically refer to a particular classmate
and say that the classmate classified his/her animals differently.
For example: "Susan's flow chart is different than mine." (b)
Or the student may draw or describe another scheme using
either the same traits but in a different order. For example:
"I could have started with fur or no fur rather than legs or
no legs."
Unacceptable responses may indicate that other ways are
possible but do not provide a specific, concrete example
of another way. For example: "There are many ways to do it."
Or "People do it all kinds of different ways." Or "I could have
done it differently." Or "I didn't have to start with legs or
no legs."
OR (2) a specific example of a trait that he/she
didn't use in Question 1 but could have.
Acceptable responses include a concrete example.
For example: "I could have used tail or no tail but I didn't."
Or "I could have used fur but I didn't."
Unacceptable responses may indicate that other traits
can be used but do not provide a specific example. For
example: "Many characteristics could be used." Or "I could have
started with a different one." Or "There are many ways to do
it."
Criterion #3. In response to Question 3,
the student cites (or lists) at least THREE distinct dichotomous
characteristics (or types of characteristics) that can be
used to classify animals. No explanation/defense is required.
The traits must be distinct from one another and dichotomous.
Acceptable characteristics include the following examples.
- "Legs" or "no legs" counts as ONE dichotomous trait.
Another way to express this same idea is to say "whether
or not the animal has legs."
- "More than four legs" or "four or less" counts as ONE
dichotomous trait, and is distinct from the previous trait.
- "Warm blooded" and "cold blooded" can be considered a
dichotomous trait since (from an eighth-grader's point of
view) the groups are mutually exclusive and all animals
can be assigned to one category or the other.
- "Meat eater" and "plant eater" can be considered a dichotomous
trait since (from an eighth-grader's point of view) the
groups are mutually exclusive and animals are commonly assigned
to one group or the other. "Meat eater" and "non-meat eater"
would be a better way to say the same idea.
Unacceptable characteristics include the following examples.
- "Number of legs" is NOT a dichotomous trait since it
can split animals into more than groups: "zero legs," "two
legs," "four legs" etc.
- "Type of teeth" is NOT dichotomous because there are
numerous types of teeth.
- "Type of food they eat" is NOT dichotomous unless the
student explicitly states two distinct groups of food such
as "meat eaters and plant eaters." Otherwise, types of food
could refer to anything such as: seed eaters, leaf eaters,
insect eaters, decomposers, etc.
- In general "types of _____" is not a dichotomous trait
unless the student explicitly specifies two distinct types.
Criterion #4. In response to Question 3,
the student explains why a certain trait (or set of traits or
type of trait) is better suited than another. The student satisfies
Either A or B below.
EITHER
A. Student provides a general statement explaining
that the best traits are those that keep all members of one
species together while separating them from all other species.
This general statement need not be accompanied by a specific
example.
Acceptable responses include the following: (1) The best
traits separate one type of animal from another but not from
its own type of animal. Or (2) Better traits are traits that
are the same for a certain type of animal but different for
others. Note: There are a variety of ways to get this point
across, but the statement must be explicit.
Unacceptable responses are not explicit. For example:
(1) Better traits separate animals into the right groups. Or
(2) The best traits keep certain animals together. Or (3) Biologists
know which traits are best.
OR
B. Student provides a concrete example accompanied
by an explanation showing that the best traits are those
that keep all members of one species together while separating
them from all other species.
Acceptable responses include a concrete example and
explanation. For example: (1) Fur and not fur is better
than legs or no legs because all mammals have fur and all reptiles
do not. Or (2) Eye color would not work well because some rabbits
have pink eyes and some rabbits have brown eyes. Or (3) Legs
and no legs is not very good because it splits up the alligator
and snake. Or (4) Legs and no legs is bad because it puts the
snake with the whale and the alligator with the goose.
Unacceptable responses are vague or do not convey the
general idea stated above. For example (1) Fur and no fur is
better than legs and no legs because most animals have legs
and only some animals have fur. Or (2) Fur and no fur is better
because it worked for me |
