Learning target: I can graph and calculate from data to show that living seeds use oxygen faster when warmer, and use real energy-per-gram values to explain why fat is the body's long-term energy store.
This sheet has two parts. Part A uses a teaching dataset about sprouting pea seeds in a gas-measuring tube; the numbers were invented to be realistic, not measured in a real lab. Part B uses real, rounded values for the energy in food. Graph with a ruler, label units on every number, and show every calculation so a partner could check it.
You will need: This worksheet, Pencil, Ruler, Calculator
A class placed 25 sprouting pea seeds in a sealed glass tube with a thin side tube marked in milliliters. A small packet inside the tube soaked up any carbon dioxide the seeds released, so the only gas change left to measure was the oxygen the seeds used. As the seeds used oxygen, a drop of colored water in the side tube moved inward, and the class read how many milliliters of oxygen had been used every five minutes. They ran the test in the dark in water baths at three temperatures, and they ran one more tube with boiled (killed) seeds as a comparison.
| Time (min) | Sprouting seeds, 10 °C (mL) | Sprouting seeds, 20 °C (mL) | Sprouting seeds, 30 °C (mL) | Boiled seeds, 20 °C (mL) |
|---|---|---|---|---|
| 0 | 0.0 | 0.0 | 0.0 | 0.0 |
| 5 | 0.2 | 0.5 | 0.9 | 0.0 |
| 10 | 0.4 | 1.1 | 1.9 | 0.1 |
| 15 | 0.7 | 1.5 | 2.8 | 0.1 |
| 20 | 0.8 | 2.0 | 3.8 | 0.1 |
| Oxygen used in 20 min (mL) | Rate (mL per min) |
|---|---|
| Sprouting, 10 °C | |
| Sprouting, 20 °C | |
| Sprouting, 30 °C | |
| Boiled, 20 °C |
Scientists measure the energy a food can release by burning a weighed sample and measuring the heat, much as Lavoisier did. The table gives real, rounded values. A kilocalorie (kcal) is the unit printed as 'Calories' on food labels in the United States; 1 kcal is about 4.2 kilojoules (kJ).
| Food molecule | Energy per gram (kcal) | Energy per gram (kJ) | Main role in the body |
|---|---|---|---|
| Carbohydrate (sugar, starch) | 4 | 17 | quick fuel; short-term storage as glycogen |
| Fat | 9 | 37 | long-term energy storage; part of cell membranes |
| Protein | 4 | 17 | building material for muscle and other structures; can be used as fuel |
A trail-mix serving contains 18 g of carbohydrate, 8 g of fat and 5 g of protein (these amounts are typical for a small handful; treat them as the serving for the questions below).
A rate is an amount divided by a time. For q1 and q2, write the amount used in 20 minutes on top, the 20 minutes on the bottom, and divide: for example, 1.0 mL ÷ 20 min = 0.05 mL per minute. The unit of your answer is always 'mL per min.' For the percentage in q8, divide the part (energy from fat) by the whole (total energy) and multiply by 100.
In the overall reaction, six oxygen molecules are used for every sugar molecule, and in gas form 1 mL of oxygen at room conditions holds about 2.5 × 10¹⁹ molecules. Use the 20 °C data to estimate how many oxygen molecules the seeds used in 20 minutes, then how many sugar molecules that corresponds to. One sugar molecule has a mass of about 3.0 × 10⁻²² g; estimate the mass of sugar used in 20 minutes and explain why a balance that reads to 0.01 g could not have detected this change.