Growing Leaves and Swelling Beads in the School Greenhouse

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Growing Leaves and Swelling Beads in the School Greenhouse

Use cell evidence to tell living things from things that only get bigger.

Part 1: Two things that got bigger

Read the passage and Table 1, then answer questions 1–4.

What Is Growing in the Greenhouse?

1Every spring, the garden club at Cypress Bend Middle School grows tomato seedlings in the school greenhouse to sell at the town plant sale. This year, club leader Mr. Esteban Villalobos mixed water beads into the potting soil. A water bead is a tiny ball of a man-made gel that soaks up water. The club also adds perlite, small white bits that keep the soil loose. Perlite is volcanic glass that is heated in a factory until it puffs up like popcorn.

2Sixth grader Wanjiru Kamau noticed that the tomato leaves and the water beads both got bigger over a few days. She wondered whether that meant they were both alive. On Day 0, she marked one young tomato leaf and dropped one dry water bead into a cup of water. Every few days she measured the leaf's length and the bead's width. She also peeled a thin layer from the leaf and counted the cells along a 1 mm line under the microscope. Table 1 shows her results.

3On Day 8, Wanjiru took the bead out of the water and left it on a dry dish. By Day 10, it had shrunk back to about 2 mm. She put it back into water, and by the next day it was 12 mm wide again.

4The club also looked at other samples from the greenhouse at 400× magnification. A green film had grown on a wet bench. A patch of white fuzz had spread along the stem of one drooping seedling, from about 2 mm to about 9 mm in three days. Tiny worm-like larvae of fungus gnats were wiggling in the damp soil of one tray. The club's findings are in Table 2.

Table 1: Wanjiru's Growth Records
Day	Leaf length (mm)	Leaf cells along 1 mm	Bead width (mm)
0	4	20	2
2	6	20	12
4	9	21	12
8	16	20	12

1.

Use Table 1. Cells along the whole leaf = leaf length in mm × cells along 1 mm.

On Day 0, there were about cells along the leaf's length. On Day 8, there were about cells.

2.

Which statement best describes how the tomato leaf grew from Day 0 to Day 8?

A. It gained new cells while each cell stayed about the same size, so the leaf got longer.B. It lost cells as it grew, so the cells that were left got larger to fill the space.C. Its cells each stretched to about four times their length, so the leaf got four times longer.D. It soaked up water the way the bead did, so it got longer without any change in its cells.

3.

Use Table 1.

From Day 0 to Day 2, the bead's width grew to times as large, and then it stayed at mm until Day 8.

4.

Use paragraph 3 and Table 1. Why is the bead's growth not good evidence that the bead is alive?

A. It grew faster than the leaf at first, and living things usually grow more slowly than that.B. It swelled by soaking up water and shrank back when it dried, with no new cells made.C. It stopped growing after Day 2, which shows that it died once it was full of water.D. It is clear instead of green, so it does not use sunlight the way the tomato leaf does.

Part 2: The greenhouse microscope log

Use Table 2 and paragraphs 1 and 4 to answer questions 5–9.

Table 2: Greenhouse Samples at 400×
Sample	What the club saw	Cells splitting?	Nucleus seen?
Tomato leaf peel	Puzzle-shaped cells and pore cells	None seen	Yes
Tomato root tip	Small boxy cells in neat rows	6 of the 50 in view	Yes
Green film from the bench	Separate round green cells that swim	Some	Yes
White fuzz on a stem	Threads split into cells by cross walls	None seen	Yes
Fungus gnat larva (prepared slide)	Skin, muscle and gut cells	None seen	Yes
Water bead	Clear, even jelly; no walls or membranes	No cells	No
Perlite bit	Glassy walls around air pockets	No cells	No

5.

Which pair of samples is the best evidence that one tomato plant is made of more than one kind of cell?

A. The tomato leaf peel and the tomato root tipB. The white fuzz and the fungus gnat larvaC. The tomato root tip and the green filmD. The tomato leaf peel and the perlite bit

6.

Use Table 2. Look at the tomato root tip.

Of the cells in view, % were splitting in two.

7.

Wanjiru's friend says, "The green film is one big flat plant, and each round green cell is just one piece of it." Which evidence from Table 2 best shows the friend is mistaken?

A. The green cells are round, while the tomato leaf cells are puzzle-shaped.B. The green film grew on a wet bench instead of in the pots of potting soil.C. Each green cell lives apart, swims on its own and splits on its own.D. The green cells each have a nucleus, the same as the cells in the tomato leaf.

8.

Circle each sample that comes from a multicellular organism.

9.

A club member says, "The air pockets in perlite look like the empty boxes in cork, so perlite must be made of cells." Which is the best reply?

A. You're right: the pockets are old plant cells left inside the volcanic rock.B. Not quite: perlite's pockets are cells, but they are too big to belong to a plant.C. You're right: perlite helps the tomato roots grow, so it is part of the living plant.D. Not quite: perlite is puffed-up glass, and its pockets have no membranes or nuclei.

Make your case

Use everything on the page to answer question 10.

10.

Wanjiru's younger brother says, "The water beads are alive, just like the tomato plants. They grow bigger, and they need water." Do you agree? Write a claim, give at least three pieces of evidence from the tables and the passage, and explain your reasoning about cells.