Angela's Tools · Chapter 4 · Capturing the Sun's Energy
Worksheet 8 of 10
Follow the Evidence: A Photosynthesis Jigsaw
Learning target: I can work with a team to sort twelve pieces of evidence by the question each one answers, build a claim for each question that cites the cards, and defend our claims to another group.
Collaborative investigationAbout 50 minJigsaw
MS-LS1-6 · practiceMS-LS2-3 · supports
collaborationdiscussionreading
NameDatePeriod
Directions
Work in home groups of four. Step 1 (expert round, 10 minutes): each member takes one expert set of three cards (Set A: cards 1, 5, 9; Set B: cards 2, 6, 10; Set C: cards 3, 7, 11; Set D: cards 4, 8, 12), reads them, and meets with the other students holding the same set to agree on what each card shows and what it does not show. Step 2 (home round, 20 minutes): return to your home group, teach your cards in one minute each, and complete the group task. Step 3 (defense, 10 minutes): present one of your claims to a neighboring group, who will try to find a card that weakens it. Step 4 (individual, 10 minutes): answer Part C alone.
You will need: Twelve cards per group, cut from the card sheet, Group record table, Pencils, Timer
Twelve evidence cards
1 Card 1: The willow and the soil (1648)A physician planted a 5-pound willow in 200 pounds of dried soil, added only rainwater, and kept dust out. Five years later the tree had gained about 164 pounds. The soil, dried again, had lost about 2 ounces.
2 Card 2: The sealed jars (1804)A chemist grew plants in sealed containers with measured amounts of carbon dioxide. Plants given carbon dioxide grew; plants in air with the carbon dioxide removed barely grew. The plants gained more mass than the carbon dioxide they took in.
3 Card 3: What a dried plant is made of (modern)Dry a plant completely and analyze the powder: about 45 percent is carbon, about 45 percent oxygen, about 6 percent hydrogen, and only around 4 percent is minerals. The only carbon a plant can reach is the carbon dioxide in air or water.
4 Card 4: Bubbling leaves (1779)Green leaves held under water in bright sunlight gave off streams of tiny bubbles; the collected gas made a glowing splint burst into flame. In shade or darkness the bubbles stopped. Roots, flowers and non-green parts never bubbled.
5 Card 5: The foil-covered leafA strip of foil was clipped over part of a leaf on a living plant for two days in sunlight. The leaf was then boiled, soaked in alcohol to remove its color, and tested with iodine. The uncovered part turned blue-black, which means starch was present. The covered part stayed yellow-brown: no starch.
6 Card 6: The pond sensorAn oxygen sensor left in a pond full of water plants records the same pattern every day: dissolved oxygen rises through the morning and afternoon, peaks in the late afternoon, and falls steadily through the night to a low point just before dawn.
7 Card 7: The mint and the mouse (1772)A candle sealed in a glass jar soon went out, and a mouse sealed in a jar could not survive. After a sprig of mint had grown in the jar for several days, the candle burned again and a mouse could breathe. The plant had restored something to the air.
8 Card 8: The two-colored leafSome plants have leaves with green patches and white patches. A leaf like this was left in sunlight, then color-stripped and tested with iodine. Only the patches that had been green turned blue-black. The white patches, which have no chlorophyll, showed no starch.
9 Card 9: Under the microscopeA thin slice of a leaf shows cells crowded with small green structures, the chloroplasts; a single cell can hold dozens. A slice of a root from the same plant shows cells with none. In a living elodea leaf you can watch the chloroplasts drifting inside each cell.
10 Card 10: The sprouting potatoA potato left in a dark cupboard for six weeks grew long, pale shoots and became soft and lighter. Iodine testing showed much less starch inside than in a fresh potato. The potato received no light, no soil and no water, yet the shoots grew.
11 Card 11: Cotton and woodCotton fiber is nearly pure cellulose, and cellulose is the largest single ingredient of wood. Chemists can break cellulose apart with acid and heat, and what they get is sugar. Cellulose is a long chain made of thousands of linked sugar units.
12 Card 12: The dark jarA leafy plant was sealed in a jar inside a dark box with gas sensors. Over several hours the carbon dioxide level rose steadily and the oxygen level fell. The plant was alive and green when the jar was opened, but it had lost a little mass.
Part A: Expert round (one set per person)
1.Your expert set: ______. For each of your three cards, write one sentence saying what the card shows and one phrase saying what it does not show (for example, 'does not say what the gas is').
Part B: Home group task
- Lay all twelve cards on the desk. Sort them under the four questions in the group record table. Every card goes under exactly one question, the one it answers best. Expect disagreement; settle it by asking what the card actually measured.
- For each question, write a one-sentence claim that the cards under it support. Cite the card numbers in parentheses.
- Find the one card in each column that gives the weakest support for your claim, and write why. (Old evidence is not automatically weak; ask what the card could not rule out.)
- Choose one claim to defend. Prepare a one-minute defense that names the cards and explains how they fit together. Every member must be able to give it.
- Listen to the neighboring group's challenge, and record the strongest one together with your reply.
Group record (fill in the card numbers)
| Question | Card numbers | Our claim (one sentence, cite cards) |
|---|
| Q1. Where does a producer's new matter come from? | | |
| Q2. Is light required, and what is it needed for? | | |
| Q3. What does photosynthesis produce, and where in the plant does it happen? | | |
| Q4. What happens to the sugar after it is made? | | |
2.Group answer: Which card did your group argue about longest, and under which question did you finally put it? What settled the argument?
3.Group answer: Write the strongest challenge the neighboring group made to your claim, and your reply. Name the cards used on both sides.
Part C: Individual accountability (complete alone)
4.Cards 1 and 2 are more than 200 years old. Explain why Card 3, from modern instruments, does not make them useless. What does each old card show that Card 3 alone cannot?
5.Cards 5 and 8 use the same iodine test but answer different questions. Explain what each one holds constant and what each one changes, and why that matters.
6.Cards 10 and 12 both describe plants in the dark. Using both cards, write a short explanation of what a producer does with its sugar when there is no light, and what that tells you about where the lost mass went.
7.Suppose a thirteenth card arrived: 'A plant grown under a green-only lamp for two weeks grew, but only about half as much as an identical plant under a white lamp.' Under which question would you file it, and what would it add that Card 8 does not?
Ask what was measured
If a card is hard to place, do not ask what it is about; ask what was measured. A balance measures matter, so a card about mass goes under Q1. A card that compares light with dark or green with not-green goes under Q2 or Q3, depending on whether it is about a requirement (light, chlorophyll) or about a product and its location (oxygen, starch, chloroplasts). A card about what happens to starch, cellulose or stored sugar goes under Q4.
The missing card
Your deck has no card that directly shows water being used in photosynthesis; Card 2 only hints at it. Design the experiment that would produce that card. Describe what you would hold constant, what you would change, what you would measure, and what result would support the claim that water contributes matter to the plant. Explain why this is harder to test than carbon dioxide.