Science Assessment ~ Topics ~ Matter and Energy in Living Systems ~ Item ME049002 ~ Student Performance

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?

Most of the additional mass came from atoms that made up the food the sea star ate.
Most of the additional mass came from atoms that made up the water the sea star drank.
Most of the additional mass came from atoms that made up other parts of the sea star's body.
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.*

Pre-Test

Distribution of responses
Answer Choice		Overall	Grades		Gender		Primary Language
		n = 373	6–8 n = 373	9–12 n = 0	Male n = 204	Female n = 169	English n = 345	Other n = 28
A.	Most of the additional mass came from atoms that made up the food the sea star ate.	30%	30%	NAN%	32%	28%	31%	21%
B.	Most of the additional mass came from atoms that made up the water the sea star drank.	3%	3%	NAN%	3%	2%	3%	4%
C.	Most of the additional mass came from atoms that made up other parts of the sea star's body.	14%	14%	NAN%	15%	14%	14%	14%
D.	Most of the additional mass came from atoms that were created as the sea star's cells divided.	53%	53%	NAN%	50%	56%	52%	61%

Post-Test

Distribution of responses
Answer Choice		Overall	Grades		Gender		Primary Language
		n = 377	6–8 n = 377	9–12 n = 0	Male n = 206	Female n = 171	English n = 349	Other n = 28
A.	Most of the additional mass came from atoms that made up the food the sea star ate.	81%	81%	NAN%	84%	77%	82%	61%
B.	Most of the additional mass came from atoms that made up the water the sea star drank.	2%	2%	NAN%	1%	2%	2%	0%
C.	Most of the additional mass came from atoms that made up other parts of the sea star's body.	7%	7%	NAN%	5%	10%	6%	21%
D.	Most of the additional mass came from atoms that were created as the sea star's cells divided.	11%	11%	NAN%	10%	11%	10%	18%

Science Assessment

Item ME049002: When a sea star regrows lost arms, most of the additional mass comes from atoms that made up the food the sea star ate.

Pre-Test

Post-Test