Inside the Chrysalis: Food Molecules in a Zoo Butterfly Program

Use gas data from pupae and adult butterflies to model how food is broken down and rebuilt.

Ten days in a pupa

Read the passage and study Table 1. Then answer the questions.

Butterflies for the Meadows

1The meadows where a rare checkerspot butterfly lives have shrunk as towns have grown, so the Lakeshore Zoo runs a program to raise these butterflies and release them into restored meadows. Each spring, keepers raise caterpillars in a lab and feed them fresh plantain leaves. Seventh grader Ezra Lindgren volunteers with the zoo's insect keeper, Ms. Thandiwe Mokoena, who asked him to help with a study of what happens to the caterpillars' food.

2Ms. Mokoena shared a model. When a caterpillar eats, digestion breaks large food molecules into smaller ones, such as sugars, amino acids and fatty acids. Its cells use some of these in cellular respiration: food molecules combine with oxygen to form carbon dioxide (CO₂) and water, and energy is released. Cells link others together into new large molecules, such as proteins and fats. A caterpillar stores much of its food as fat. Insects take in oxygen and give off CO₂ and water vapor through tiny holes along their sides called spiracles.

3A fully grown caterpillar stops eating and turns into a pupa, or chrysalis, that hangs from a twig. A pupa does not eat, drink or leave droppings. Over about 10 days, inside the pupal skin, much of the caterpillar's body is taken apart, and an adult butterfly is built, with wings, long legs, antennae, large eyes and flight muscles.

4To study this, Ms. Mokoena placed pupae one at a time in a small chamber at 25 °C with oxygen and CO₂ sensors. Table 1 shows the average for 10 pupae. She explained that when fat is the main fuel, cells give off about 7 mL of CO₂ for every 10 mL of oxygen they use. Ezra also weighed each pupa on day 0 and then weighed what it left on day 10: the new adult, its empty pupal case and a drop of reddish waste fluid that the adult pushes out soon after it comes out (Table 2).

5The adults then spend a few weeks in the zoo's flight house before release. Last year, keepers kept two groups of adults in separate, identical rooms. One group had dishes of plain water, and the other had feeders of sugar water like flower nectar (Table 3).

Table 1. Gas Exchange of a Pupa at 25 °C (average of 10 pupae)
Day	O₂ taken in (µL/h)	CO₂ given off (µL/h)	What Ezra saw
0	60	42	Pupa just formed
2	34	24	No change outside
4	24	17	No change outside
6	30	21	Dark eye spots show
8	52	36	Wing pattern shows through

Use Table 1.

From day 0 to day 4, the pupa's oxygen use fell by µL per hour.

Which pattern does Table 1 show?

A. Oxygen use stayed near 60 µL/h, while CO₂ given off fell to about 17 µL/h.
B. Oxygen use and CO₂ given off both rose until day 4, then both fell through day 8.
C. Oxygen use fell from day 0 to day 8, while CO₂ given off rose from day 0 to day 8.
D. Oxygen use and CO₂ given off both fell until day 4, then both rose through day 8.

From day 4 to day 8, the pupa still did not eat, but its oxygen use more than doubled. Which explanation fits paragraphs 2 and 3 best?

A. The chamber warmed up after day 4, which made the pupa breathe faster as it rested.
B. It was storing up extra oxygen in its body so it would have enough for its first flight.
C. Its cells were building eyes, wings and muscles, using energy released from stored fat.
D. Its cells were turning stored fat straight into oxygen, which the sensor then picked up.

Use the ratio in paragraph 4. Suppose that on day 9 a pupa takes in 70 µL of oxygen per hour and is still using fat as its main fuel.

It would give off about µL of CO₂ per hour.

Complete the model of what happens inside the pupa. Use words from the word bank. One word is left over.

Word bank: amino acids · proteins · fat · oxygen · sunlight

Cells take apart the caterpillar's old muscle proteins into . Then they link these into new for wings and flight muscles. The energy for this work comes from stored , which cells combine with in cellular respiration.

Mass and the adult butterflies

Use paragraphs 2, 4 and 5 and Tables 2 and 3 to answer the questions.

Table 2. Mass Budget of One Pupa (averages)
What was weighed	Mass (mg)
Pupa on day 0	300
New adult butterfly	180
Empty pupal case	15
Drop of waste fluid	70

Use Table 2.

The adult, the case and the waste fluid together had mg less mass than the pupa on day 0.

The pupa did not eat, drink or leave droppings during the 10 days. Where did that missing mass most likely go?

A. It turned into the energy the cells used, so those atoms no longer exist.
B. It left through the spiracles as water vapor and CO₂, with its atoms intact.
C. It stayed inside the adult as tiny molecules too light for the scale to weigh.
D. It was built into the empty pupal case, which hardened as the adult grew.

Table 3. Adults in the Flight House (averages)
Group	Adult life (days)	Eggs laid per female
Plain water only	5	60
Sugar-water feeders	14	180

Use Table 3. Round to the nearest tenth.

Adults with sugar water lived about times as long as adults with plain water only.

Which explanation of the longer lives in the sugar-water group fits the model in paragraph 2 best?

A. Their cells could respire sugar from the feeders for energy instead of using up their stored fat.
B. The sugar passed straight into their wings without being broken down, so the wings lasted longer.
C. Their cells turned the sugar into new oxygen, which let them breathe more slowly in the flight house.
D. The sugar water kept their spiracles closed, so they needed less oxygen to stay alive.

10.

Which path could one carbon atom take from a plantain leaf into the air of the pupa chamber?

A. Leaf sugar → caterpillar's stored fat → pupa's cells → CO₂ in the chamber air
B. Leaf sugar → caterpillar's droppings → pupa's spiracles → CO₂ in the chamber air
C. Leaf sugar → oxygen in the caterpillar's body → pupa's cells → CO₂ in the air
D. Leaf sugar → energy in the caterpillar → new carbon in the pupa → CO₂ in the air

Is anything happening in there?

Write your answer in full sentences.

11.

A zoo visitor says, “Inside the chrysalis, the caterpillar is just sleeping. Nothing happens to its food until the butterfly comes out and starts flying.” Do you agree? Write a claim, use evidence from Tables 1 and 2 and paragraph 3, and use the model in paragraph 2 to explain what happens to the food molecules and the energy.