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Sweet Peas, Soup Peas and a Leaf Mold

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Sweet Peas, Soup Peas and a Leaf Mold

Follow two pea gene changes from protein to trait.

Part 1: Round seeds and wrinkled seeds

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

A Field Day at Hollow Creek Farm

1Every June, the farm-to-school program at Alder Point Middle School visits Hollow Creek Farm, which grows the peas served in the school cafeteria. This year eighth grader Sora Whitfield asked the farmer, Mr. Tavita Ngata, why he grows two kinds of peas. One kind has smooth, round dry seeds that cooks use for split pea soup. The other has wrinkled dry seeds, and its green peas are sold fresh or frozen because they taste sweet. Mr. Ngata explained that the two kinds differ mainly in one gene.

2A gene is a section of DNA that carries the instructions for building a protein. In a growing pea seed, sugar arrives from the leaves, and the seed links much of it together into starch. A protein called the branching enzyme helps the seed build starch. In wrinkled peas, the gene for the branching enzyme has a mutation, a change in its DNA, and the enzyme the seed builds from it does not work. A lab that tests seeds for the farm also found a pea line with a different change in the same gene. Mr. Ngata calls it line N.

3Sugar dissolved in a seed draws water into it. Near the end of the season, the seeds dry out in the pods, and they shrink as their water leaves. Table 1 shows the lab's results for the three kinds of seeds.

4The farm also tests how well seeds sprout. Each spring, Mr. Ngata plants 100 seeds of each kind in early April, when the soil is cold and wet, and 100 more in late May, when the soil is warm. Seeds take longer to sprout in cold soil, and molds in the soil that rot seeds grow well on sugar leaking out of a seed.

5A second gene matters later in the summer. Powdery mildew is a mold that can coat pea leaves in white powder, and badly coated plants make fewer pods. To get inside a leaf cell, the mildew needs a working MLO protein, which pea leaf cells normally make. Some pea lines have a mutation in the MLO gene, so they make no working MLO protein. Mr. Ngata grew both kinds of plants side by side in a damp year when mildew spread and in a dry year when it did not.

Table 1: Pea Seeds Tested by the Lab (averages)
Seed kindBranching enzymeStarch (% dry mass)Sugar (% dry mass)Water, growing seed (%)Dry seed shape
RoundWorks60555Smooth, round
WrinkledDoes not work331070Wrinkled
Line NWorks60555Smooth, round
1.
Use Table 1. Compare the starch in round seeds and wrinkled seeds.

Wrinkled seeds have percentage points less starch than round seeds.

2.
Use paragraph 2 and Table 1. Why do wrinkled seeds hold about twice as much sugar as round seeds?
Question 2 options
3.
Use paragraph 3 and Table 1. Which explanation of the wrinkled shape fits the evidence best?
Question 3 options
4.
Circle the two results that are evidence that the change in line N's gene has no effect on its seeds.

Part 2: In the field

Use Tables 2 and 3 and paragraphs 4 and 5 to answer questions 5 to 11.

Table 2: Seedlings Up After 3 Weeks (100 seeds of each kind)
Seed kindCold, wet soil (April)Warm soil (May)
Round8694
Wrinkled5892
Line N8595
Table 3: Mildew Trial in a Damp Year and a Dry Year (averages per plant)
MLO proteinDamp: leaf coated (%)Damp: podsDry: leaf coated (%)Dry: pods
Works (typical)4014022
None (mutation)221022
5.
Use Table 2. Compare the round and wrinkled seeds planted in April.

In cold, wet soil, fewer wrinkled seeds than round seeds came up.

6.
Which conclusion do Table 2 and paragraph 4 support best?
Question 6 options
7.
Use Table 3. Compare the pods on the two kinds of plants in the damp year.

Plants with the MLO mutation made more pods per plant than typical plants.

8.
Use paragraph 5 and Table 3. Why were the leaves of plants with the MLO mutation almost free of mildew in the damp year?
Question 8 options
9.
In the dry year, both kinds of plants made 22 pods. What does this result suggest about the MLO mutation?
Question 9 options
10.
Use Tables 2 and 3. Fill in each blank with a word from the word bank. A word may be used more than once.

Compared with round seeds, the wrinkled-seed mutation is for sprouting in cold, wet soil. The change in line N is for sprouting in both soils. In the damp year, the MLO mutation is . In the dry year, the MLO mutation is .

11.
Sora's classmate says, "The wrinkled-seed mutation is helpful to the pea plant, because it makes the peas sweet." Do you agree? Write a claim, give evidence from Tables 1 and 2, and explain your reasoning from the gene to the protein to the trait to the effect on the plant.