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Goal 3 Concepts Of Biology

Expectation 3.4 The student will explain the mechanism of evolutionary change.

Indicator 3.4.1 The student will explain how new traits may result from new combinations of existing genes or from mutations of genes in reproductive cells within a population.

Assessment Limits:

  • natural selection (definition; effects of environmental pressure)
  • adaptations (effects on survival)
  • variation (effects on survival and reproductive success)

Brief Constructed Response (BCR) Item - Released in 2007

Marine and land iguanas are two different species that inhabit the Galapagos Islands. Some scientists believe that both species diverged from a common ancestor. Marine iguanas eat algae. Land iguanas feed on cacti. Algae are more abundant in the ocean than cacti are on the islands. Both species lay their eggs in the sand.

Rats, cats, and goats have recently been introduced to the islands. Rats often feed on iguana eggs, cats eat baby iguanas, and goats eat cacti.

Explain how the two species of iguanas could have developed from a common ancestor. In your response, be sure to

  • name the process that explains how marine and land iguanas developed from a common ancestor
  • describe the steps involved in this process
  • explain how the introduction of rats, cats, and goats might affect both iguana species

Write your answer in your Answer Book.

The following 7 Anchor Papers represent a range of score points and are used in conjunction with the rubric to assess student responses.

Anchor Paper #1

image of student response

Score for Anchor Paper #1: Rubric Score 1

Annotation: This response demonstrates some understanding of the question. The process is correctly identified (natural selection). Though not a definition of natural selection, the description does refer to reproduction (gametes randomly combine). No information beyond that given in the prompt is provided for the effects on the iguana population. The supporting details are only minimally effective.


Anchor Paper #2

image of student response

Score for Anchor Paper #2: Rubric Score 1

Annotation: This response demonstrates some understanding of the question. The process is identified (evolution). A few steps in the process are listed (migrates; adapts to new environments). The effects of cats, rats, and goats are briefly listed (result in a decrease of population; land iguanas will have competition for food). The supporting details are only minimally effective.


Anchor Paper #3

image of student response

Score for Anchor Paper #3: Rubric Score 2

Annotation: This response demonstrates a basic understanding of the question. The process is identified (Natural selection). Some possible steps are discussed (a group of iguanas were seperate from the other iguana because of a natural disaster; iguanas would begin to change & adapt to the new environment). The effects of rats, cats, and goats are explained (rats would eat both species eggs, decreasing potential population; the goat would eat much of the main food source for the land iguanas; Decreasing their population). Overall, the supporting details are adequate.


Anchor Paper #4

image of student response

Score for Anchor Paper #4: Rubric Score 2

Annotation: This response demonstrates a basic understanding of the question. The process is identified (natural selection). Some steps of the process are outlined sequentially in a chart (population growth; scarcity; competition; adaptation; accumulation). The effects of rats, cats, and goats on both species are addressed (they could feed on them; scarcity of mates and the population would not grow). Overall, the supporting details are adequate.


Anchor Paper #5

image of student response

Score for Anchor Paper #5: Rubric Score 3

Annotation: This response demonstrates a good understanding of the question. The process is identified (natural selection). Several details are provided about the steps of the process (food was scarce; adapations on the limbs to help the marine iguanas move more effectively; teeth would gradually change; iguanas that are not very well adapted to the ocean gradually die out; gene pool that produces these slight adapations more and more frequent). The discussion of the effects of rats, cats, and goats demonstrates synthesis and includes a common effect on both species (the rats and cats feed on the eggs and young iguanas of both species) and an effect unique to each (the goats would diminish their food supply [cacti] but not the algae). Overall, the supporting details are generally complete.


Anchor Paper #6

image of student response

Score for Anchor Paper #6: Rubric Score 3

Annotation: This response demonstrates a good understanding of the question. The process is identified (evolution). The description of the process includes steps at the cellular level (random mutation in DNA), adaptation (became better adapted to live in a different environment), and reproduction (passing on the mutated gene to its offspring). Synthesis is demonstrated in the description of the effects of rats and cats on both iguana species (they eat the offspring … This will hurt the populations of both species). The more severe impact on land iguanas is described (their food source, cacti, is being eaten by goat; it is likely this species will die out). Terminology strengthens the response (random mutation).


Anchor Paper #7

image of student response

Score for Anchor Paper #7: Rubric Score 4

Annotation: This response demonstrates a full and complete understanding of the question. The process is identified (Through the process of natural selection the species split; iguanas evolved into what they are today). The student uses pertinent and complete supporting details that demonstrate an integration of ideas as the steps in the process are tied in to how the two species could have developed from a common ancestor (natural adaptation that allowed it to digest alge better; the iguana reproduced and created a new species; Survival of the fittest allowed the iguanas to reproduce more offspring so the trait that allowed the iguana to digest algae got passed down from generation to generation). Synthesis of information is demonstrated by relating evolution of iguanas to the effect of cats and rats (through the process of natural selection and survival of the fittest, the fastest and most elusive baby iguanas will survive and evolve). Synthesis continues with the effects due to goats (less food for the iguanas to eat; iguanas that can survive with the least amount of food have a better chance of reproducing). Terminology enhances the response (natural adaptation; trait; survival of the fittest).


Brief Constructed Response (BCR) Rubric

Print: Scoring Rubric (pdf)
Score 4

There is evidence in this response that the student has a full and complete understanding of the question or problem.

  • Pertinent and complete supporting details demonstrate an integration of ideas.
  • The use of accurate scientific terminology enhances the response.
  • An effective application of the concept to a practical problem or real-world situation reveals an insight into scientific principles.*
  • The response reflects a complete synthesis of information.
Score 3

There is evidence in this response that the student has a good understanding of the question or problem.

  • The supporting details are generally complete.
  • The use of accurate scientific terminology strengthens the response.
  • The concept has been applied to a practical problem or real-world situation.*
  • The response reflects some synthesis of information.
Score 2

There is evidence in this response that the student has a basic understanding of the question or problem.

  • The supporting details are adequate.
  • The use of accurate scientific terminology may be present in the response.
  • The application of the concept to a practical problem or real-world situation is inadequate.*
  • The response provides little or no synthesis of information.
Score 1

There is evidence in this response that the student has some understanding of the question or problem.

  • The supporting details are only minimally effective.
  • The use of accurate scientific terminology is not present in the response.
  • The application, if attempted, is irrelevant.*
  • The response addresses the question.
Score 0

There is evidence that the student has no understanding of the question or problem.

  • The response is completely incorrect or irrelevant or there is no response.

* On the High School Assessment, the application of a concept to a practical problem or real-world situation will be scored when it is required in the response and requested in the item stem.

Updated 2002

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