Overview

Lesson Procedure

65-70 minutes of class time across 5 phases.

1. Warm-Up5 minutes
2. Direct Instruction15-20 minutes
3. Guided Practice20 minutes
4. Independent Practice20 minutes
5. Closure5 minutes

1. Warm-Up5 minutes

   Warm-Up Prompt

   A large tree can weigh several tons, yet the ground around it does not sink. Where does the tree's mass come from? Write your best answer and one source (a class, a book, an experiment) you would use to check it.

   Collect three or four answers on the board: the soil, water, the air, sunlight. Many students name sunlight as a source of mass, or the soil; both answers have a long history. Tell students that no single source on today's page settles the question, and that they will build the answer from several sources that sometimes disagree. That is RST.11-12.9: synthesize information from a range of sources into a coherent understanding of a process, resolving conflicting information when possible.

2. Direct Instruction15-20 minutes

   The routine (Diagram 1). (1) Question: write the one question every source will be asked. (2) Claims: record each source's claim with its conditions and method, and its type: a text reporting observations, a history written later, an experiment, a simulation. (3) Sort: group the claims that agree and name each conflict exactly. (4) Resolve: ask whether the conditions differed, whether one method was weaker, and whether a later source settles it. (5) Account: write one explanation that fits every source, and say what is still uncertain. A conflict is resolved only when the explanation accounts for both sides; choosing a favorite source is not resolving.

   Model with Priestley (Source 1). Joseph Priestley's experiments of 1771-1772 are some of the earliest on how plants change the air. He believed in the phlogiston theory, which held that burning releases a substance, phlogiston, that spoils the air. Read Source 1 aloud. Gloss: "vitiated" means spoiled, "burned out" means a candle burned in the air until it went out, and a "vessel immersed in water" is a jar standing upside down in water, which keeps the air in.

   1Though this experiment failed, I have been so happy, as by accident to have hit upon a method of restoring air, which has been injured by the burning of candles, and to have discovered at least one of the restoratives which nature employs for this purpose. It is vegetation. This restoration of vitiated air, I conjecture, is effected by plants imbibing the phlogistic matter with which it is overloaded by the burning of inflammable bodies. But whether there be any foundation for this conjecture or not, the fact is, I think, indisputable. I shall introduce the account of my experiments on this subject, by reciting some of the observations which I made on the growing of plants in confined air, which led to this discovery.

   [...]

   2In repeating this experiment, care must be taken to draw away all the dead leaves from about the plant, lest they should putrefy, and affect the air. I have found that a fresh cabbage leaf, put under a glass vessel filled with common air, for the space of one night only, has so affected the air, that a candle would not burn in it the next morning, and yet the leaf had not acquired any smell of putrefaction.

   3Finding that candles would burn very well in air in which plants had grown a long time, and having had some reason to think, that there was something attending vegetation, which restored air that had been injured by respiration, I thought it was possible that the same process might also restore the air that had been injured by the burning of candles.

   4Accordingly, on the 17th of August 1771, I put a sprig of mint into a quantity of air, in which a wax candle had burned out, and found that, on the 27th of the same month, another candle burned perfectly well in it. This experiment I repeated, without the least variation in the event, not less than eight or ten times in the remainder of the summer.

   5Several times I divided the quantity of air in which the candle had burned out, into two parts, and putting the plant into one of them, left the other in the same exposure, contained, also, in a glass vessel immersed in water, but without any plant; and never failed to find, that a candle would burn in the former, but not in the latter.

   6I generally found that five or six days were sufficient to restore this air, when the plant was in its vigour; whereas I have kept this kind of air in glass vessels, immersed in water many months, without being able to perceive that the least alteration had been made in it. I have also tried a great variety of experiments upon it, as by condensing, rarefying, exposing to the light and heat, &c. and throwing into it the effluvia of many different substances, but without any effect.

   [...]

   7This restoration of air, I found, depended upon the vegetating state of the plant; for though I kept a great number of the fresh leaves of mint in a small quantity of air in which candles had burned out, and changed them frequently, for a long space of time, I could perceive no melioration in the state of the air.

   • Stating a claim with its conditions (Source 1, paragraphs 4-6)

     What exactly did Priestley find about mint and burned air, under what conditions, and what conditions does he leave out?

     Result: Claim with conditions: on August 17, 1771, he put a sprig of mint into air "in which a wax candle had burned out," and on August 27, ten days later, "another candle burned perfectly well in it"; he repeated this "not less than eight or ten times," and a matching jar of the same air without a plant never recovered. Usually "five or six days were sufficient" when "the plant was in its vigour." Left out: where the jars stood, how much light they got, how big the jars and plants were. A synthesis records these gaps, because a later source may show that one of them matters.

   • Naming a conflict (Source 1, paragraph 2)

     Paragraph 2 reports a result that seems to clash with the mint trials. State the conflict precisely.

     Result: A fresh cabbage leaf under a glass of ordinary air, "for the space of one night only," so spoiled the air "that a candle would not burn in it the next morning," although the leaf "had not acquired any smell of putrefaction." A living leaf spoiled air in one trial, while living mint restored air in others. Priestley's own warning, that dead leaves may "putrefy, and affect the air," does not fit, because this leaf was fresh and did not smell. The conflict cannot be resolved from Source 1 alone; write it down and look for a source that tells what was different.

   A second, older claim (Source 2). Read Sachs's account of Van Helmont's willow, an experiment from the first half of the 1600s. Do not resolve it yet. Ask students only to state Van Helmont's data and his conclusion separately, and to predict which later sources will bear on it.

   1Johann Baptist van Helmont[117], physician and chemist, and a contemporary of Jung, took up a position still more decidedly opposed to Aristotelian doctrines. He rejected the four elements of that philosophy, and regarding water as a chief constituent of all things he considered that the whole substance of plants, the mineral parts (the ash) as well as the combustible, was formed from water. Thus while Aristotle made the component parts of plants be introduced into them by water in a state ready for use, Van Helmont, on the contrary, ascribed to the plant the power of producing all kinds of material from water. It would scarcely have been necessary to mention this resistance to old dogmas, originating as it did in the notions of the alchemists, if Van Helmont had not made an attempt to establish his views by experiment; this was the first experiment in vegetation undertaken for a scientific purpose of which we have any information, and it was repeatedly quoted by many later physiologists, and employed in support of their theories. He placed in a pot a certain quantity of earth, which when highly dried weighed two hundred pounds; a willow-branch weighing five pounds was set in this pot, which was protected by a cover from dust, and daily watered with rain-water. In five years’ time the willow had grown to be large and strong, and had increased in weight by a hundred and sixty-four pounds, though the earth in the pot, when once more dried, only showed a loss of two ounces. Van Helmont concluded from this experiment that the considerable increase of weight in the plant had been gained entirely at the cost of the water, and consequently that all the materials in the plant, though distinct from water, nevertheless come from it.

3. Guided Practice20 minutes

   Pairs read Source 3, Sachs's account of what happened in 1779, and then Source 6, a simulation written for this page. A simulation is a source of a different kind: it shows what follows from a set of rules, so it can test whether an explanation works, but it cannot show that its rules are true of a real plant. Post Diagram 2, which graphs the model's output.

   1A work of Priestley’s appeared in 1779, which was translated into German in the following year under the title, ‘Versuche und Beobachtungen über verschiedene Theile der Naturlehre,’ and contained among other things the writer’s experiments on plants. His way of managing them was eminently unsuitable, nor did he arrive at any definite and important result, though he expressed the idea which had led him to make them clearly enough, where he says, ‘If the air exhaled by the plant is of better character (richer in oxygen) than atmospheric air, it follows that the phlogiston of the air is retained in the plant and used there for its nourishment, while the part which escapes, being deprived of its phlogiston, necessarily attains a higher degree of purity.’ After he had ceased his experiments with plants in 1778, he observed that there was a deposit of matter in the water in some vessels which he had used for them, and that it gave off a very ‘pure air’; a number of further observations taught him that this air was given off only under the influence of sun-light; Priestley himself did not suspect that the deposit in question, afterwards known as Priestley’s matter and found to consist of Algae, was a vegetable substance.

   2In the same year (1779) appeared the first book by INGEN-HOUSS[132], in which the subject was treated at length; it was called, ‘Experiments on Vegetables, discovering their great power of purifying the common air in the sunshine and of injuring it in the shade and at night,’ and was at once translated into German, Dutch and French. The title itself shows that the author had observed more and more correctly than Priestley. [...] He had discovered, he says, in the summer of 1779, that all vegetables incessantly give out carbonic acid gas, but that the green leaves and shoots only exhale oxygen in sun-light or clear daylight. It appears therefore that Ingen-Houss not only discovered the assimilation of carbon and the true respiration of plants, but also kept the conditions and the meaning of the two phenomena distinct from one another. Accordingly he had a clear idea of the great distinction between the nutrition of germinating plants and of older green ones, the independence of the one, the dependence of the other, on light; and that he considered the carbon dioxide of the atmosphere to be the main if not the only source of the carbon in the plant, is shown by his remark on a foolish assertion of Hassenfratz that the carbon is taken from the earth by the roots; he replied that it was scarcely conceivable that a large tree should in that case find its food for hundreds of years in the same spot. [...]

   1What the model does. This computer model follows the oxygen in a 1-liter jar of air, standing over water, in which a candle has burned until it went out. The jar starts at 16 percent oxygen, about where a candle flame goes out, and the model counts the air as restored when it is back to 19 percent, enough for a candle to burn again: a gain of 30 mL of oxygen. The jar holds a sprig of mint with about 20 cm² of leaves, its stem in water. The settings are invented for teaching but typical of a real sprig.

   2The rules. Every hour the sprig makes oxygen by photosynthesis at a rate that depends on the light level L: 2.0 × L ÷ (L + 200) mL per hour. L is measured in micromoles of light per square meter per second: full summer sun is about 2,000, a sunny windowsill about 500, bright shade about 100 and a lit room about 10. Every hour, day and night, the sprig also uses 0.2 mL of oxygen in respiration. The model assumes the jar always holds enough carbon dioxide and stays at 22 °C.

   3Output: net change in the jar's oxygen per hour (photosynthesis minus respiration)
   L = 0: -0.20 mL per hour
   L = 10: -0.10 mL per hour
   L = 50: +0.20 mL per hour
   L = 100: +0.47 mL per hour
   L = 200: +0.80 mL per hour
   L = 500: +1.23 mL per hour
   L = 1,000: +1.47 mL per hour
   L = 2,000: +1.62 mL per hour

   4Running a scenario. Choose a light level for the 12 daytime hours and use L = 0 for the 12 night hours. Add the day's changes to get the net change per 24 hours, then divide 30 mL by it to find how many days the sprig needs to restore the jar.

   • Resolving a conflict with a later source (Source 3)

     How does Source 3 resolve the conflict between the cabbage leaf and the mint trials?

     Result: The title of Ingen-Houss's book states the rule: vegetables have "great power of purifying the common air in the sunshine and of injuring it in the shade and at night." He also found that "all vegetables incessantly give out carbonic acid gas, but that the green leaves and shoots only exhale oxygen in sun-light or clear daylight." The cabbage leaf sat under its glass through a night, when a leaf only takes up oxygen and gives off carbon dioxide; the mint trials ran for days that included daylight. The conflict is resolved by a difference in conditions, light, that Priestley did not record.

   • Testing the resolution with the simulation (Source 6)

     Run the model for a sprig on a sunny windowsill (L = 500 for 12 hours, then 12 dark hours). How long does it need to restore the jar, and how does that compare with Priestley's five or six days?

     Result: Day: 12 × 1.23 = 14.76 mL gained. Night: 12 × 0.20 = 2.40 mL used. Net: 14.76 - 2.40 = 12.36 mL per 24 hours, so 30 ÷ 12.36 ≈ 2.4 days. The model's sprig restores the jar faster than Priestley's usually did. That does not make either source wrong: the model's sprig, jar and light are invented, and Priestley did not record his. What the model adds is the mechanism: the same sprig gains oxygen over a sunny day and loses some every night, so the answer depends on how the light and dark hours balance.

   Debrief: Which source did the most to resolve the conflict, and which did the most to explain it? Source 3 resolves it with observations of light and dark; Source 6 explains it, by showing how a steady use of oxygen and a light-dependent production add up. Students should notice that the resolution needed a source written after Priestley, and that Sachs himself judges Priestley's later method "eminently unsuitable."

4. Independent Practice20 minutes

   Students read Sources 4, 5 and 7 on their own and answer quiz questions 1-20. Questions 1-5 and 17 use Source 4 with Sources 2 and 7; questions 6-9, 15 and 16 use the lab report (Source 5); questions 10 and 18 use the simulation (Source 6); question 11 uses Diagram 2; questions 12-14 use Sources 3 and 2; and questions 19 and 20 draw on several sources. Gloss: "assimilation of carbon" means taking carbon into the plant's own substance, and "dry substance" is what is left of a plant when its water is removed.

   1[...] That the greater part at least of the carbon of plants comes from the atmosphere could scarcely be a matter of doubt with those who knew the writings of Ingen-Houss; but Senebier devotes special attention to this question; he endeavours to take all the co-operating factors into the calculation, and especially to prove once more that the oxygen given off from the plant in light comes from the carbon dioxide which has been absorbed, that the green parts only and no others are able to effect this decomposition, and that there is a sufficiency of carbon dioxide in nature to supply the food of plants. But although he convinced himself that green leaves decompose the carbon dioxide which surrounds them in a gaseous form, he supposed that it is chiefly through the roots that this substance finds its way with the ascending sap into the leaves, and this view often gave occasion to further error in later writers.

   [...]

   2The processes of vegetation examined by de Saussure were, for the most part, the same as those which Ingen-Houss and Senebier had studied at length and correctly described in their general outlines. But de Saussure went beyond this, and by means of quantitative determinations struck a balance between the amount of matter taken up and given off by the plant, thereby showing what it retains. In this way he made two great discoveries: that the elements of water are fixed in the plant at the same time as the carbon, and that there is no normal nutrition of the plant without the introduction of nitrates and mineral matter. But we cannot form a due idea of de Saussure’s services to physiology without going further into the detail of his work.

   3We will first consider his investigations respecting the assimilation of carbon in plants. Here we have the important result, that larger quantities of carbon dioxide in the atmosphere surrounding the plants are only favourable to vegetation if the latter are in a condition to decompose them, that is, if they are in sufficiently strong light; that every increase in the amount of carbon dioxide in the air in shade or in darkness is unfavourable to vegetation, and that if that increase is greater than eight times in the hundred it is absolutely injurious. On the other hand he found, that the decomposition of carbon dioxide by the green parts in light is an occupation that is necessary to them, that plants die when they are deprived of it. The first clear insight into the chemical processes which accompany the decomposition of carbon dioxide in the interior of the plant was obtained by perceiving, that plants by appropriating a definite quantity of carbon make a much more than proportionate addition to their dry substance, and that this is due to the simultaneous fixation of the component parts of water. The full significance of this fact could only be apprehended at a later time, when the theory of the combinations of carbon, organic chemistry, had been further developed. As regards the importance of the decomposition of carbon dioxide by the green organs under the influence of light to the whole nourishment of the plant, de Saussure arrived by more definite proofs than Ingen-Houss had given at the result, that only a small portion of the substance of plants is derived from the constituents of the soil in solution in water, but that the great mass of the vegetable body is built up from the carbon dioxide of the atmosphere and the constituents of water; [...]

   1Question. Do pieces of a green leaf give off gas in light, and do they need carbon dioxide to do it? We ran this test in class. The class and its data are invented for teaching; the method is a standard one.

   2Method. We punched 40 disks from fresh spinach leaves with a paper hole punch. With a plastic syringe we pulled the air out of the disks while they sat in liquid, so that the liquid filled the air spaces inside the leaf and the disks sank. For Cups A, B and C the liquid was baking-soda solution (2 g of sodium bicarbonate per liter of water, with one drop of dish soap); baking soda supplies dissolved carbon dioxide. For Cup D it was plain water with one drop of soap. We put 10 sunken disks into each cup of the same liquid, 3 cm deep, at 22 °C, and counted the floating disks every 3 minutes for 30 minutes. A disk floats again when gas made inside it fills its air spaces.

   3Cup A: baking-soda solution, LED desk lamp 10 cm away.
   Cup B: baking-soda solution, the same lamp 30 cm away.
   Cup C: baking-soda solution, lamp 10 cm away, cup wrapped in foil.
   Cup D: plain water, lamp 10 cm away.

   4Results. Disks floating at 3, 6, 9, 12, 15, 18, 21, 24, 27 and 30 minutes:
   Cup A: 0, 1, 4, 7, 9, 10, 10, 10, 10, 10
   Cup B: 0, 0, 0, 1, 2, 3, 5, 6, 8, 9
   Cup C: 0 at every count
   Cup D: 0, 0, 0, 0, 0, 0, 0, 1, 1, 1

   5Notes. At the end we wrapped Cup A in foil; 25 minutes later, 6 of its 10 disks had sunk again. The water in Cup A warmed from 22 °C to 23 °C under the lamp. We did not test the gas inside the disks; we assume it is mostly oxygen.

   1Where does the oxygen come from? In 1941 Samuel Ruben, Merle Randall, Martin Kamen and James Hyde, chemists at the University of California, Berkeley, grew the green alga Chlorella in water that contained extra oxygen-18, a heavy but harmless isotope of oxygen, and in other runs gave the extra oxygen-18 to the carbon dioxide (supplied as bicarbonate) instead. The oxygen gas the algae released matched the oxygen-18 share of the water, not that of the carbon dioxide. Later work with better methods confirmed the result: the oxygen a plant releases comes from water.

   2The modern summary. Photosynthesis, in light, in the green parts of a plant: 6 CO₂ + 12 H₂O → C₆H₁₂O₆ (a sugar) + 6 O₂ + 6 H₂O, often shortened to 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂. The carbon and the oxygen atoms of the sugar come from carbon dioxide, its hydrogen from water, and all of the released oxygen from water; the water on the right is new water, made with the rest of the oxygen from carbon dioxide. Respiration, in every living cell, day and night: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O. A plant improves the air only when its photosynthesis outruns its respiration.

5. Closure5 minutes

   Exit ticket: "Name one conflict between two of today's sources. Say whether you resolved it, and write the one sentence of your explanation that accounts for both sides." Sort the tickets into "resolved with both sides explained," "resolved by picking a side" and "conflict not named" to plan the next lesson.

   Teacher note on the historical texts. Priestley, Sachs and the scientists Sachs describes use the chemistry of their time: "phlogiston" and "phlogistic matter" (a substance once thought to be given off in burning) and "carbonic acid gas" (carbon dioxide). Sachs calls one chemist's assertion "foolish" and, in a paragraph not excerpted here, faults the "tedious prolixity" of Senebier's book; these are his judgments, and students can weigh them like any other claim. The texts contain no slurs. Priestley's other experiments, not excerpted here, used mice; if students read further, discuss them as part of the history. The simulation and the lab report are written for this page and their data are invented; the oxygen-18 experiments on the modern finding card are real (Ruben, Randall, Kamen and Hyde, Journal of the American Chemical Society, 1941).

   Homework. The homework uses all seven sources; no new passage is needed.

Differentiation Strategies

Assessment Guidance

1. Question 1 of 20 · Multiple Choice

   In Source 4, paragraph 1, Senebier tries "to prove once more that the oxygen given off from the plant in light comes from the carbon dioxide which has been absorbed." How does the 1941 finding on the card (Source 7) bear on this claim?

   AIt supports Senebier: the released oxygen matched the carbon dioxide BIt contradicts Senebier: the released oxygen matched the water, not the carbon dioxide CIt cannot bear on it, because algae are not plants with leaves DIt supports both sides equally, because both water and carbon dioxide contain oxygen

2. Question 2 of 20 · Multiple Choice

   Source 4, paragraph 2, names de Saussure's "two great discoveries." How does the first of them bear on Van Helmont's conclusion in Source 2?

   AIt shows that Van Helmont was wholly right: all of a plant's substance comes from water BIt shows that Van Helmont was wholly wrong: water plays no part in a plant's substance CIt shows that water does become part of the plant, together with carbon from the air DIt shows that the missing mass came from the soil, which Van Helmont failed to weigh

3. Question 3 of 20 · Multiple Choice

   Source 4, paragraph 3, says plants "by appropriating a definite quantity of carbon make a much more than proportionate addition to their dry substance." What does this mean?

   AThe dry mass a plant gains is greater than the mass of the carbon it takes in BA plant takes in more carbon than it keeps, and gives the rest back to the air CThe carbon a plant takes in weighs more than the dry mass it adds to the plant DA plant's dry mass grows in proportion to the water it takes up through its roots

4. Question 4 of 20 · Multiple Choice

   De Saussure found that more carbon dioxide helps a plant only "if they are in sufficiently strong light" (Source 4, paragraph 3). Which result in the lab report (Source 5) agrees with this finding?

   ACup A, where most disks floated within 15 minutes BCup D, where only one disk floated in 30 minutes CCup B, where the disks floated more slowly than in Cup A DCup C, where no disk floated in the baking-soda solution

5. Question 5 of 20 · Multiple Choice

   Van Helmont's soil "only showed a loss of two ounces" (Source 2), and de Saussure concluded that "only a small portion of the substance of plants is derived from the constituents of the soil" (Source 4). How are these two findings related?

   AThey conflict, because Van Helmont found that the soil supplied the plant's mass BThey agree that the soil supplies little of a plant's substance CThey conflict, because de Saussure found that minerals are not needed at all DThey agree that water supplies all of a plant's substance

6. Question 6 of 20 · Multiple Choice

   In Source 5, the lab counts the time at which at least 5 of the 10 disks in a cup are floating. At what count did Cup B first reach 5 floating disks?

   AAt 12 minutes BAt 27 minutes CAt 21 minutes DAt 30 minutes

7. Question 7 of 20 · Multiple Choice

   Why does the lab report (Source 5) include Cup D, with plain water and the lamp 10 cm away?

   ATo test the need for carbon dioxide, since Cup D differs from Cup A only in having no baking soda BTo test whether the disks need light, since Cup D was kept in the dark CTo test whether the lamp's heat makes the disks float, since Cup D sat farther from the lamp DTo give the class a larger sample of disks, since Cup D used the same liquid as Cup A

8. Question 8 of 20 · Multiple Choice

   After the test, Cup A was wrapped in foil, and "25 minutes later, 6 of its 10 disks had sunk again" (Source 5). Which source best explains this observation?

   ASource 2, because Van Helmont found that plants are made from water BSource 4, because de Saussure found that too much carbon dioxide in the air harms plants CSource 1, because Priestley found that burned air stays spoiled without a plant DSource 3, because Ingen-Houss found that plants give off carbon dioxide all the time

9. Question 9 of 20 · Multiple Choice

   Cup B's lamp was 30 cm away and Cup A's 10 cm away (Source 5). If the light from the lamp spreads out like light from a small bulb, following the inverse-square law, about what fraction of Cup A's light did Cup B receive?

   AAbout 1/3 BAbout 1/9 CAbout 1/27 DAbout 3 times as much

10. Question 10 of 20 · Multiple Choice

    Use the output table in Source 6. A sprig in bright shade gets L = 100 for 12 hours a day and darkness for 12 hours. About how many days does it need to restore the jar?

    AAbout 5 days BAbout 3 days CIt never restores the jar DAbout 9 days

11. Question 11 of 20 · Multiple Choice

    In Diagram 2, about where does the curve cross zero, the light level at which the model sprig makes exactly as much oxygen as it uses?

    AAt about L = 20 BAt about L = 200 CAt about L = 500 DAt L = 0

12. Question 12 of 20 · Multiple Choice

    Sachs says Priestley's way of managing his plant experiments in 1779 "was eminently unsuitable, nor did he arrive at any definite and important result" (Source 3). Which detail in Source 3 best explains why Priestley's later results were hard to interpret?

    AHis book was translated into German in the year after it appeared BThe gas from a deposit in his vessels came off only in sunlight, a condition he did not control CHe expected plants to take phlogiston from the air and to use it there for their own nourishment DHe stopped experimenting with plants in 1778, before Ingen-Houss's book appeared

13. Question 13 of 20 · Multiple Choice

    Sachs writes that Ingen-Houss "kept the conditions and the meaning of the two phenomena distinct from one another" (Source 3). Which two phenomena does he mean?

    AThe absorption of water by the roots and the loss of that same water from the leaves BPriestley's discovery of oxygen and Lavoisier's new chemistry COxygen from green parts in light, and carbon dioxide from all parts at all times DThe growth of plants in sunshine and their growth in shade

14. Question 14 of 20 · Multiple Choice

    Which part of Van Helmont's conclusion in Source 2 goes furthest beyond his data?

    AThat the soil in the pot lost only two ounces in five years BThat the willow gained a hundred and sixty-four pounds CThat the pot was covered to keep out dust DThat all the materials in the plant come from water

15. Question 15 of 20 · Short Answer

    Priestley found that picked mint leaves never improved the air, even when he "changed them frequently" (Source 1, paragraph 7). The leaf disks in Source 5 are also picked pieces of leaf, yet they gave off gas in light. Resolve this conflict, or explain why it can be only partly resolved.

    Show model answer

16. Question 16 of 20 · Short Answer

    Source 5 ends: "We did not test the gas inside the disks; we assume it is mostly oxygen." Which other sources on this page support that assumption, and what would a stronger experiment add?

    Show model answer

17. Question 17 of 20 · Short Answer

    Use the equation on the modern finding card (Source 7). About what percent of the mass of the sugar C₆H₁₂O₆ comes from carbon dioxide? (Atomic masses: C 12.0, H 1.0, O 16.0.) How does your answer bear on Van Helmont's conclusion (Source 2)?

    Show model answer

18. Question 18 of 20 · Short Answer

    Run Source 6 for a lit room: L = 10 for 12 hours and darkness for 12 hours. What is the net change in the jar's oxygen per 24 hours? What does this suggest about the conflict between Priestley's "never failed" (Source 1) and Ingen-Houss's "injuring it in the shade and at night" (Source 3)?

    Show model answer

19. Question 19 of 20 · Short Answer

    Name one difference among the sources on this page that you cannot resolve with the information given, and say what evidence would resolve it.

    Show model answer

20. Question 20 of 20 · Short Answer

    In four or five sentences, explain why the same kind of plant can improve the air in one jar and spoil it in another. Use at least four sources, including one experiment and one simulation, and name the source of each point.

    Show model answer

These standards connect to RST.11-12.9: prerequisites to review first, parallel standards at the same level, and next steps that build on it.

Standard text: Common Core State Standards for English Language Arts & Literacy. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.