A Year in the Maple Grove: Starch, Leaves and Carbon Dioxide

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A Year in the Maple Grove: Starch, Leaves and Carbon Dioxide

Use a year of arboretum data to follow matter and energy through photosynthesis.

Twelve months of data

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

The Maple Grove Through the Year

1Hollowbrook Arboretum is a city park planted with hundreds of kinds of trees. Its largest grove holds about 200 sugar maples, and a tall weather tower stands in the middle of the grove. A busy highway runs along one side of the arboretum, and traffic on it is about the same in every month. Seventh grader Mireille Dubois spent a year volunteering with the arboretum's tree scientist, Dr. Hollis Wainwright, to learn what the maples do in each season.

2Dr. Wainwright began with a model. In the chloroplasts of a leaf, photosynthesis uses light energy to combine carbon dioxide (CO₂) and water into sugar, and oxygen is given off. A tree uses some of its sugar in cellular respiration, which releases energy for its cells and gives off CO₂. It builds the rest into leaves, wood and roots, or links many sugar units together into starch and stores the starch in its twigs, trunk and roots. The living cells of trees, animals and soil organisms carry out respiration day and night, in every season.

3A sensor on the tower measures the CO₂ in the air just above the treetops. For each month, Mireille averaged the readings taken at noon on calm days. Once a month, Dr. Wainwright clipped ten twigs from the same marked maples, always from the sunny side of each tree and always about the same thickness. The arboretum's lab dried and ground the twigs and measured how much of their dry mass was starch (Table 1).

4Mireille also noticed something in early April. The maples' leaves began unfolding from their buds and grew to full size in just a few weeks. Before those leaves opened, the trees had stood bare since the end of October. In fall, the arboretum leaves its fallen leaves on the ground under the grove, where worms, fungi and bacteria break them down over the winter and spring.

Table 1. The Maple Grove at Hollowbrook Arboretum
Month	Maple leaves	Midday CO₂ (ppm)	Twig starch (% dry mass)
January	None	428	20
March	Buds swelling	430	21
April	Unfolding	427	12
June	Full	412	10
August	Full	410	16
October	Turning and falling	420	22
December	None	427	21

1.

Use Table 1.

From March to August, the midday CO₂ above the grove fell by ppm.

2.

Which pattern does Table 1 show?

A. CO₂ and twig starch both stayed within 2 units of their January values.B. CO₂ was lowest in the months with full leaves and higher when trees were bare.C. CO₂ was highest in June and August, when the maples had full leaves.D. Twig starch was highest in June, just after the leaves reached full size.

3.

Traffic on the highway gives off CO₂ in every month. Why was the midday CO₂ above the grove still lowest in summer?

A. In summer, the maples switch from respiration to photosynthesis and stop giving off CO₂.B. Full leaves took in CO₂ for photosynthesis faster than traffic and respiration added it.C. The summer leaves turned the CO₂ straight into oxygen, without making any sugar.D. Warm summer air holds less CO₂, so the sensor reads lower numbers in July and August.

4.

Use paragraphs 2 and 4. Twig starch fell from 21% in March to 12% in April, while the leaves were unfolding. Which explanation fits the model best?

A. Sunlight on the bare twigs broke some of their starch apart and turned it into light.B. Spring rain soaked into the twigs and washed much of their starch down into the soil.C. The trees broke stored starch into sugar for energy and for building their new leaves.D. The unfolding leaves changed the starch into CO₂ gas without using any of its energy.

5.

Mireille claims that the starch in the twigs was made by photosynthesis in the maple leaves. Circle the two results that best support her claim.

6.

Use Table 1. Each sample below is 50 g of dried, ground twigs.

The October sample holds g of starch, and the June sample holds g of starch.

Matter in, matter out

Use the model in paragraph 2, Table 1 and your answers above.

7.

Think about one maple leaf on a sunny June afternoon. Sort each item by whether it enters the leaf or leaves it.

8.

Suppose a hard frost in late April kills the maples' new leaves, and the trees grow a second set of leaves in May. Predict the twig starch in June.

A. About 10%, because the trees grow the same leaves in a cold spring and a warm oneB. About 22%, because the trees take in extra starch from the soil after a frostC. Higher than 10%, because the frozen leaves sent their starch back into the twigsD. Lower than 10%, because the trees used stored starch to build two sets of leaves

9.

In June, a caterpillar eats maple leaves, and a robin eats the caterpillar. Which path best describes the energy that powers the robin's flight muscles?

A. Sunlight → chemical energy in leaf sugar → caterpillar → robin's muscle cells, released by respirationB. Heat from the June air → maple leaf → caterpillar → robin's muscle cells, where it becomes sugarC. Water and minerals from the soil → maple leaf → caterpillar → robin's muscle cellsD. Oxygen in the air → robin's lungs → robin's muscle cells, where the oxygen itself becomes energy

10.

Use paragraph 4 and Table 1. What most likely happens to the carbon atoms in the maple leaves that fall in October?

A. Decomposers break the leaves down, and much of the carbon returns to the air as CO₂.B. They stay in the dead leaves on the ground until the leaves turn back into living leaves.C. They are used up by the decomposers, so that carbon is gone from the grove for good.D. They change into energy as the leaves rot, which warms the soil under the grove.

Where do the new leaves come from?

Write your answer in full sentences.

11.

An arboretum visitor says, “In April the maples grow new leaves before they have any leaves to make food, so they must be feeding on the soil.” Do you agree? Write a claim, use evidence from Table 1, and use the model in paragraph 2 to explain where the matter and energy for the new leaves came from.