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    Matter and Energy in Living Systems
            Animals use carbon-containing molecules from food to make a variety of other carbon-containing molecules that be…

Item SB049002: When a sea star regrows lost arms, most of the additional mass comes from atoms that made up the food the sea star ate.

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Sea stars are animals that live on the seashore.  They eat smaller animals like mussels and snails.  They normally have five arms.  A sea star lost two arms while trying to escape from an animal that was trying to eat it. Without the two arms, the sea star weighed 1.1 pounds. A month later, the sea star's body grew two new arms. The sea star now weighs 1.5 pounds.


A sea star growing two new arms. 
Photo (CC) by Dean Franklin on Flickr.


A sea star with all five arms.
Photo(CC) by Brianne on Flickr.

Where did most of the additional mass come from that the sea star's body used to grow the new arms?

  1. Most of the additional mass came from atoms that made up the food the sea star ate.
  2. Most of the additional mass came from atoms that made up the water the sea star drank.
  3. Most of the additional mass came from atoms that made up other parts of the sea star's body.
  4. Most of the additional mass came from atoms that were created as the sea star's cells divided.

For the answer choice you selected, describe the process by which the atoms become part of the sea star’s arms.*

Topic
Matter and Energy in Living Systems
Correct Answer
A
Explanation Scoring Rubric

Reasoning – States the relevant general principles and links them to the claim (4 points)

  • States or uses the general principle that animal body structures are made up of large carbon-containing molecules (polymers).
  • States or uses the general principle that animals break down large carbon-containing molecules (polymers) from food, such as proteins, into small carbon-containing molecules (monomers), such as amino acids, during a chemical reaction with water molecules. (Chemical digestion)
  • States or uses the general principle that animals use small carbon-containing molecules (monomers), such as amino acids, to form large carbon-containing molecules (polymers), such as proteins and water molecules. (Polymer synthesis)
  • Provides a mechanism that links the general principles to the answer choice selected (claim): Atoms that make up food the sea star ate are rearranged into other molecules that become part of the sea star’s arms. (Atom rearrangement and incorporation)


*The prompt shown for the explanation tier reflects revision following its use in the Year 3 study for which student results are shown.

Misconceptions
Answer Choice: D
SCM083: New atoms are created during chemical reactions (AAAS Project 2061, n.d.).
Distribution of Multiple Choice Responses
Chart showing distrubtion of responses for Item ME049002
Multiple Choice Points Earned
Group Correct Total Percent
Overall 113 373 30%
Grades
  6–8 113 373 30%
  9–12 N/A N/A N/A
Gender
  Male6520432%
  Female4816928%
Primary Language
  English10734531%
  Other62821%
Explanation Points Earned
Group Earned Possible Percent
Overall 27 1512 2%
Grades
  6–8 27 1512 2%
  9–12 N/A N/A N/A
Gender
  Male 20 828 2%
  Female 7 684 1%
Primary Language
  English 27 1400 2%
  Other 0 112 0%

View data table

Distribution of Multiple Choice Responses
Chart showing distrubtion of responses for Item ME049002
Multiple Choice Points Earned
Group Correct Total Percent
Overall 304 377 81%
Grades
  6–8 304 377 81%
  9–12 N/A N/A N/A
Gender
  Male17320684%
  Female13117177%
Primary Language
  English28734982%
  Other172861%
Explanation Points Earned
Group Earned Possible Percent
Overall 362 1512 24%
Grades
  6–8 362 1512 24%
  9–12 N/A N/A N/A
Gender
  Male 192 828 23%
  Female 170 684 25%
Primary Language
  English 349 1400 25%
  Other 13 112 12%

View data table