Photosynthesis: how plants make food from light, water and air

Grade 7 Science Worksheet - Challenge Me

Circle the best answer.

2. 1.

   Ari’s friend says plants get their food from the soil, so soil is plant food. Which response is best?

   • Disagree: leaves make their sugar from carbon dioxide and water
   • Agree: the roots pull the plant’s food out of the soil for it
   • Agree: fertilizer is the food that plants live on
   • Disagree: plants live on water and nothing else
3. 2.

   Esme’s friend says sunlight is a plant’s food. Which response is best?

   Use the picture in question 1.

   • Disagree: soil is the plant’s real food
   • Agree: leaves soak up light and store it inside as plant matter
   • Agree: plants grow by turning light into wood
   • Disagree: light gives energy; the food is sugar the leaf makes

4. Read this first

   Read-about history card

   In the 1600s Jan Baptist van Helmont grew a willow in a pot for five years, adding only water. The tree gained about 164 pounds; the dry soil lost only about 2 ounces.

5. 3.

   Jun reads about van Helmont’s willow. He decided the tree’s new mass came from water. What did he miss?

   • Nothing: water is where plant mass comes from
   • The mass really came from the soil
   • The mass came from the sunlight, which he left unweighed
   • Much of the mass came from carbon dioxide in the air

6. Investigation card

   Plant 1 sat in a sunny window and was watered every day. Plant 2 sat in a dark closet and was watered once a week. After two weeks Plant 1 was taller.

7. 4.

   Kira tested whether light helps a plant grow. What is the flaw in this test?

   • Plant height is not a thing a class can measure
   • Two things changed, light and water, so the cause is unclear
   • Both plants should have been kept in the dark the whole time
   • There is no flaw, because light caused the growth

8. Investigation card (model data)

   Two matching water plants in sealed jars of water, the same size and temperature. Bubbles counted in 10 minutes: under an LED lamp, 40; in the dark, 0.

9. 5.

   Luz’s class compared two water plants in sealed jars, one under a lamp and one in the dark. Which conclusion is strongest?

   • Light turned into the gas in the bubbles
   • Light is needed for the plant to give off oxygen
   • The lamp plant took in oxygen from the jar
   • The dark plant kept its bubbles for later

10. Use this

    Leaf arrow diagram, not to scale. Boxes: Sun, leaf (green cells with chloroplasts), air, roots and stem, rest of the plant. Arrows: Sun to leaf; roots and stem to leaf; air to leaf; leaf to air; leaf to rest of the plant. Every arrow is labeled. Table (model data), carbon dioxide level in a sealed clear box holding a potted plant, in units: start, 400; after 6 hours in bright light, 300; after 6 more hours in the dark, 350.

11. 6.

    Milo reads two figures. Why did the carbon dioxide level fall during the 6 hours of light?

    • The plant took in carbon dioxide to make sugar
    • The plant gave off carbon dioxide while making sugar
    • The roots pushed the carbon dioxide into the soil
    • The light turned the carbon dioxide into energy
12. 7.

    Noah reads two figures. Why did the carbon dioxide level rise again during the 6 hours of dark?

    • The plant turned stored light into carbon dioxide
    • Carbon dioxide leaked out of the potting soil
    • The plant made even more sugar in the dark than it did in the light
    • No sugar was made, but the cells still released carbon dioxide
13. 8.

    Pia’s teacher coats the underside of some leaves with petroleum jelly. Use both figures to predict the result for those leaves.

    • Less sugar, because light cannot pass the jelly underneath
    • Less sugar, because carbon dioxide cannot enter the leaf
    • More sugar, because the oxygen cannot leave the leaf
    • No change, because the roots supply the carbon

14. Use this

    Drawing of a leaf with green patches and white patches, not to scale. Test result (read about; an adult did a starch test): starch, the stored form of sugar, found in the green parts, none in the white parts.

15. 9.

    Tala reads about a leaf with green and white patches kept in light. A starch test found stored sugar in the green parts but not the white parts. Why?

    • The white parts take sugar from the soil instead
    • The white parts lack the green chloroplasts that make sugar
    • The white parts got less light than the green parts
    • The white parts give off carbon dioxide instead of oxygen
16. 10.

    Bubbles in 10 minutes under the same lamp: tap water, 40; boiled and cooled water, 8. Zee reads that a water plant gave off fewer bubbles in water an adult had boiled and cooled first. Which explains it?

    • Boiling took the plant food out of the water
    • The cooled water blocked the lamp’s light
    • Boiling took out the oxygen that the plant needs to take in
    • Boiling removed carbon dioxide, an input the plant needs