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Mites, Fungi and Mulch: Interactions in a School Greenhouse

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Mites, Fungi and Mulch: Interactions in a School Greenhouse

Use three garden club studies to explain predation, mutualism and competition.

Study 1: Mites on the bean benches

Read the passage and study Table 1. Then answer the questions.

The Garden Club Investigates

1The garden club at Ridgeview Middle School looks after a small greenhouse, a vegetable garden and a row of young apple trees. Last year, seventh grader Hamza Qureshi and the club's adviser, Ms. Lorraine Achterberg, ran three studies to find out how the living things in and around the greenhouse affect one another.

2Spider mites are tiny relatives of spiders, about half a millimeter long. They pierce the cells of a leaf and suck out what is inside, leaving pale specks, and a female can lay a few eggs every day. Predatory mites are slightly larger mites that hunt. They catch spider mites and their eggs and suck them dry. The club grew 40 bean plants on each of two greenhouse benches with the same light, water and temperature. In week 0, both benches had about 4 spider mites per leaf. That week, the club released predatory mites bought from a garden supplier onto Bench A only. Every week, Hamza used a hand lens to count the mites on 20 leaves per bench and recorded the averages (Table 1).

3Many plants have partners in the soil. Some fungi grow fine threads into the roots of a plant and far out into the soil around it. The threads take up phosphorus, a nutrient plants need to grow, and pass some of it to the roots. The plant passes some of the sugar it makes in its leaves to the fungus. To test how much the tomato seedlings gain, the club grew them for 8 weeks in four groups of 5 pots of sterilized potting mix. Two groups had a mix low in phosphorus, and two had phosphorus fertilizer added. In each pair, one group got spores of the fungus and the other did not. All pots got the same water and light (Table 2).

4Outside, the club planted 15 young apple trees of the same size and kind. Five trees had lawn grass growing right up to the trunk. Five had a 1 m circle of bare soil that was hoed every week to keep grass out. Five had a 1 m circle of bare soil covered with wood chips. In July, after three weeks with no rain, the club measured the water in the soil 20 cm down. In the fall, they measured each tree's new shoot growth (Table 3).

Table 1. Mites on the Bean Benches (average per leaf)
WeekSpider mites, Bench APredatory mites, Bench ASpider mites, Bench B
0414
1729
210418
36634
43555
52370
62272
Bench B got no predatory mites. In week 6, 10% of the leaves on Bench A and 85% of the leaves on Bench B were pale and speckled.
1.

In week 5, Bench B had how many times as many spider mites per leaf as Bench A? times as many

2.
From week 2 to week 5, the spider mites on Bench A dropped from 10 to 2 per leaf. Which explanation fits the passage and Table 1 best?
Question 2 options
3.
Circle the two pieces of data that, together, are the best evidence that the predatory mites kept the spider mites low on Bench A.

4.
By week 6, there were only 2 predatory mites per leaf on Bench A, down from 6. Suppose the club now moves 20 bean plants with many spider mites from Bench B onto Bench A. Which prediction fits the pattern in Table 1 best?
Question 4 options

Study 2: Tomatoes and root fungus

Use paragraph 3 and Table 2 to answer the questions.

Table 2. Tomato Seedlings After 8 Weeks (averages of 5 pots)
Potting mixFungus spores added?Dry mass of plant (g)Roots with fungus (%)
Low phosphorusNo1.20
Low phosphorusYes365
Phosphorus addedNo3.40
Phosphorus addedYes3.415
5.

In the low-phosphorus mix, the plants with the fungus had how many times the dry mass of the plants without it? Do not round. times

6.
Which kind of interaction do the tomato plants and the root fungus have, based on paragraph 3 and Table 2?
Question 6 options
7.
In the mix with phosphorus added, the fungus made no difference to the plants’ dry mass. Which explanation fits Table 2 best?
Question 7 options
8.
A rainforest grows on very old soil that holds little phosphorus. Based on Table 2, which prediction about its trees is best supported?
Question 8 options

Study 3: Grass and young apple trees, and patterns elsewhere

Use paragraph 4 and Table 3. Then use the whole sheet.

Table 3. Young Apple Trees (averages of 5 trees)
Ground around the trunkSoil water in July (%)New shoot growth (cm)
Grass up to the trunk815
Bare soil, hoed1738
Bare soil with wood chips2044
9.

How many more centimeters of new shoots did the trees in hoed bare soil grow than the trees with grass up to the trunk? cm

10.
Why did the club include the trees in hoed bare soil, with no wood chips?
Question 10 options
11.
Which statement about the grass and the young apple trees do paragraph 4 and Table 3 support best?
Question 11 options
12.
The same kinds of interactions show up in very different ecosystems. Sort each example.
13.
A club member says, “The root fungus is a pest. It steals sugar from the tomatoes, so we should keep it out of our pots.” Do you agree? Write a claim, use evidence from paragraph 3 and Table 2, and explain your reasoning about the kind of interaction.