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From Air to Oatmeal to the Finish Line: Photosynthesis and a Runner

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From Air to Oatmeal to the Finish Line: Photosynthesis and a Runner

Use a sealed-box test and food data to trace matter and energy from oat plants to an athlete.

Oat seedlings in a sealed box

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

Where Does Race-Day Fuel Come From?

1Lerato Dlamini, a seventh grader, runs the 800 m for her school's track team. On race mornings she eats a bowl of oatmeal made from 40 g of rolled oats. For the science fair, she and her teacher, Mr. Corwin Fairweather, asked two questions: where do the matter and the energy in her oatmeal come from, and where do they go after she eats it?

2Oats are a kind of grass. Like other green plants, oat plants make food by photosynthesis. In the chloroplasts of their leaf cells, they use light energy to combine carbon dioxide from the air with water into sugar, and they release oxygen. A plant uses some of its sugar for energy and builds the rest into starch and the other substances of its body. The grains that become rolled oats are packed with starch.

3Lerato grew oat seedlings in four trays of moist soil. Tray D had soil only, with no seeds. Two weeks later, she placed one tray at a time inside a clear plastic box with a carbon dioxide sensor and sealed the lid. Each test lasted 60 minutes at 22 °C, and each box started with ordinary classroom air. Trays A, B and C each held the same number of seedlings. Tray A sat under a bright grow light, and Tray B sat under the same light with a shade cloth over the box. For Tray C, the box was covered with a black cloth. Tray D sat under the bright light.

4After a meal, Lerato's digestive system breaks the starch in her oatmeal down into sugar, and her blood carries the sugar to her cells. In cellular respiration, her cells use oxygen to break down the sugar, which releases the energy her muscles use. The carbon atoms from the sugar leave her body in the carbon dioxide she breathes out. Most of the energy her muscles use becomes thermal energy, which warms her body and then the air around her.

Table 1. Carbon Dioxide in the Sealed Box (ppm = parts per million)
Time (min)	A: bright light (ppm)	B: dim light (ppm)	C: dark (ppm)	D: soil only (ppm)
0	800	800	800	800
20	650	760	830	810
40	510	725	860	820
60	380	690	890	830

1.

Use Table 1.

In 60 minutes, the carbon dioxide in the Tray A box fell by ppm, and in the Tray B box it fell by ppm.

2.

Why did Lerato test Tray D, which had soil but no seedlings?

A. To check whether the seeds in the soil needed the black cloth to sproutB. To find out how much light the grow lamp gave off in 60 minutesC. To see how much the soil and box alone changed the carbon dioxideD. To give the seedlings in the other trays extra carbon dioxide to use

3.

Which conclusion do Trays A and B support best?

A. The seedlings took in carbon dioxide faster in bright light than in dim light.B. The seedlings took in about the same amount of carbon dioxide in both boxes.C. The seedlings in dim light gave off carbon dioxide instead of taking it in.D. The shade cloth stopped the carbon dioxide in the air from reaching Tray B.

4.

In the dark box, the carbon dioxide rose from 800 to 890 ppm. Which explanation fits paragraphs 2 and 4 and Table 1 best?

A. The seedlings turned the oxygen in the box into carbon dioxide by photosynthesis.B. The black cloth gave off carbon dioxide as it warmed, which leaked into the box.C. The seedlings kept doing photosynthesis in the dark with light they had stored.D. With no light for photosynthesis, the seedlings' cellular respiration added carbon dioxide.

5.

Assume the soil in Tray C gave off the same amount of carbon dioxide as the soil in Tray D.

In 60 minutes in the dark, the seedlings themselves added about ppm of carbon dioxide to the box.

6.

Sort each statement.

From the oat field to the race

Use the facts below and paragraphs 2 and 4 to answer the questions.

Food facts for Lerato's oatmeal: about 45% of the mass of rolled oats is carbon. Every 44 g of carbon dioxide holds 12 g of carbon. A 40 g serving of rolled oats holds about 600 kJ of chemical energy. During a race, about 25% of the energy her muscles use becomes motion, and about 75% becomes thermal energy.

7.

Lerato's oatmeal uses 40 g of rolled oats. Assume all of the carbon in the oats came from carbon dioxide in the air.

The oats hold g of carbon. The oat plants took in about g of carbon dioxide to get that carbon.

8.

A farmer says most of the mass of an oat grain was pulled up from the soil by the roots. Which reply fits this sheet best?

A. He is wrong: most of the grain's mass is light energy that the leaves trapped.B. He is wrong: most of the grain's mass is carbon and other atoms from air and water.C. He is right: the roots take in starch from the soil and store it in the grains.D. He is right: the soil in Tray D gained mass as it gave off carbon dioxide.

9.

Suppose Lerato's muscles use all 600 kJ of energy from her oatmeal during practice.

About kJ becomes motion, and about kJ becomes thermal energy.

10.

After the race, which part of Lerato's oatmeal could be taken in by an oat plant and used again to make sugar?

A. The carbon atoms she breathes out, because oat leaves take in carbon dioxide from the airB. The light energy stored in her cells, because she gives it off again as she runsC. The thermal energy she gives off, because oat leaves use warm air to make their sugarD. The motion energy of her legs, because it travels through the track to the oat roots

11.

A teammate says, "Oatmeal gives you energy because oat plants soak up energy and food from the soil." Do you agree? Write a claim, use evidence from Table 1 and your answer to question 7, and explain where the matter and the energy in oatmeal come from.