Worksheet

Fewer Worms, Cleaner Ears: Changing Traits on a Sheep and Corn Farm

Grade 8 practice: analyze a farm's lamb worm egg counts and a Bt sweet corn test to explain how breeding and genetic engineering change traits.

Grade 8ScienceInteractive · Printable

Aligned toMS-LS4-5

Play online Play as a game

PrintLetter-size worksheet Answer keyPrintable answers

Assign to classAssign to your classes, or get a join code

What’s included

Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
12 questions
Classroom-ready

Details

Format: Interactive · Printable
Grade: Grade 8
Subject: Science
Question types: Fill in the blank, Multiple choice, Sorting, Short answer

About this worksheet

What students practice

Students analyze breeding data to explain how choosing parents changes an inherited trait in livestock over generations.
Students use field test data to explain how an added gene changes a crop and what impacts each technology has on a farm.

How to use

Read the farm passage together and explain what eggs per gram means before students start. Have students finish both parts on their own, then compare the two technologies as a class before the final report.

Curriculum

NGSS standard covered

MS-LS4-5

Explain how technologies such as artificial selection and genetic engineering change the traits of organisms.

Preview

OwlSheets.com

Name Date

Fewer Worms, Cleaner Ears: Changing Traits on a Sheep and Corn Farm

Compare a worm-resistance breeding plan for lambs with an engineered sweet corn test.

Part 1: Breeding lambs that carry fewer worms

Read the passage and Tables 1 and 2, then answer questions 1 to 6.

Worms, Lambs and Sweet Corn

1Seun Bramwell, an eighth grader, lives on his family's farm in a valley of rolling pasture. The family keeps about 120 ewes, female sheep that each raise one or two lambs a year, and grows sweet corn for a roadside farm stand. Two pests cause most of their trouble. The first is a small blood-feeding worm that lives in a sheep's stomach. Lambs swallow young worms with the grass they eat, and a heavy infection can make a lamb weak and pale or even kill it. The second is the corn earworm, a caterpillar that chews into the tip of a sweet corn ear. Customers seldom buy a damaged ear.

2Over the years, the dewormer medicines the farm uses have killed fewer and fewer of its worms. The family's veterinarian, Dr. Marguerite Szabo, suggested breeding the flock to carry fewer worms. She showed Seun how to do an egg count. A little dung from a lamb is mixed with salt water so the worm eggs float, and the eggs are counted under a microscope on a counting slide. The result is given in eggs per gram of dung, and a higher count usually means more worms. Lambs grazing the same pasture can carry very different numbers of worms and still look about equally healthy.

3Since 2016, the farm has counted every lamb at weaning, with no dewormer in the six weeks before. The family keeps the female lambs with the lowest counts as future mothers and sells the rest for meat, and it buys rams whose lambs on other farms had low counts. Each dose of dewormer kills mostly the worms the medicine still works on, so the more doses a farm gives, the faster worms that survive it take over. Across the road, the Ferreira farm grazes similar pasture and counts its lambs the same way, but it chooses parents only for their size. In 2024 the Bramwells also borrowed Ram B from a farm that had never counted its lambs.

4Seun's mother, Mrs. Abimbola Bramwell, tried a new kind of sweet corn this year. To make it, scientists put a gene from a soil bacterium called Bt into corn cells in a lab and grew whole plants from those cells. The gene carries instructions for a protein that harms certain caterpillars that eat the plant. Sweet corn does not make this protein on its own. Many years of tests have not found the protein to harm people, pets or honeybees. Last year, the farm sprayed its regular sweet corn with insecticide 6 times to protect the ears.

5For her test, Mrs. Bramwell planted 4 strips of the Bt corn and 4 strips of the regular version of the same variety, side by side. All 8 strips were planted on the same day and got the same water and fertilizer, and none were sprayed. At harvest, she checked 100 ears from each strip for earworm damage.

Table 1: Average Egg Count of Lambs at Weaning (eggs per gram)
Year	Bramwell farm	Ferreira farm
2016	3,000	2,900
2018	2,600	3,100
2020	2,300	2,800
2022	2,000	3,000
2024	1,800	2,900

Table 2: Bramwell Lambs Born in 2024 That Grazed Together
Father	Lambs counted	Average egg count
Ram A	30	1,200 eggs per gram
Ram B (borrowed)	28	2,700 eggs per gram

Use paragraph 2. Why did the farm need egg counts to breed a flock that carries fewer worms?

A. Lambs with high counts grow thicker wool, so the counts show the best wool.
B. Counting the eggs adds worm-fighting genes to each lamb that is tested.
C. Lambs that look equally healthy can carry very different numbers of worms.
D. Counting the eggs clears the worms out of each lamb, so the parents stay healthy.

Use Table 1. Compare the Bramwell farm's averages for 2016 and 2024.

The Bramwell lambs' average count fell by eggs per gram. That drop is % of the 2016 average.

Use Table 1 and paragraph 3. Why are the Ferreira farm's counts useful for judging the Bramwell results?

A. Their counts rose from 2016 to 2024, which shows that worms crossed the road onto their pasture.
B. Their counts stayed near 2,800 to 3,100, so weather and pasture do not explain the Bramwell drop.
C. Their lambs were chosen for size, which shows that bigger lambs carry more worms than small ones.
D. Their counts fell about as fast as the Bramwell counts, which shows the weather caused both drops.

Use Table 2.

On average, Ram B's lambs carried more eggs per gram than Ram A's lambs.

Use Table 2 and paragraph 3. The family can keep one of the two rams to father next year's lambs. Which choice fits their breeding plan best?

A. Ram A, since his lambs grazed with Ram B's lambs yet carried fewer worms.
B. Ram A, since his lambs got dewormer more often than Ram B's lambs did.
C. Ram B, since he fathered fewer lambs, so each lamb got more of his genes.
D. Ram B, since his lambs met more worms and will pass on stronger resistance.

Use paragraphs 2 and 3. What is one likely benefit for the farm of a flock whose lambs carry fewer worms?

A. Fewer lambs would need dewormer, which would slow the rise of worms the medicine fails to kill.
B. The lambs would need less grass, since lambs with low counts eat much less than other lambs.
C. The worms in the pasture would take in the lambs' resistance genes and stop laying eggs.
D. The lambs would grow back their wool faster after each spring shearing on the farm.

Part 2: The sweet corn test

Use Table 3 and paragraphs 4 and 5 to answer questions 7 to 10. Then use the whole page for questions 11 and 12.

Table 3: Sweet Corn Ears Checked at Harvest (4 strips of each kind)
Kind of corn	Ears checked	Ears with earworm damage
Regular	400	152
Bt	400	12

Use Table 3.

Of the regular ears, % had earworm damage. Of the Bt ears, % had earworm damage.

The farm harvests about 30,000 sweet corn ears in a season. Suppose the damage rates match your answers to question 7 and no insecticide is used.

Planting all Bt corn would give about more undamaged ears than planting all regular corn.

Use paragraph 4. Which statement best explains why the Bt strips had so little earworm damage?

A. They were sprayed with insecticide during the test, while the regular strips were not.
B. Their cells carry a bacterium's gene for a protein that harms earworms that eat it.
C. They were bred from the sweet corn plants that had the fewest earworms in past years.
D. Their seeds were planted earlier, so the ears ripened before the earworms hatched.

10.

Use paragraph 4 and Table 3. If the farm switched all of its sweet corn to the Bt kind, which change would most likely follow?

A. The farm would need more sprays, since Bt plants draw more earworm moths to the fields.
B. Earworms would carry the Bt gene, since caterpillars take in the genes of the plants they eat.
C. The lambs would carry fewer worms, since the Bt protein also harms worms in their stomachs.
D. The farm could spray far less often and still sell more undamaged ears at its stand.

11.

Sort each step by the technology it belongs to.

Keeping the female lambs with the lowest egg counts as future mothersPutting a soil bacterium's gene into corn cells in a labBuying rams whose lambs on other farms had low egg countsGrowing whole corn plants from cells that carry the new geneSelling the lambs with high egg counts for meat instead of breeding them

Artificial selection	Genetic engineering

12.

Mrs. Bramwell asks Seun for a short report: "How did each technology change a trait on our farm, and what is one impact of each?" Write a claim, use at least one number from Table 1 or Table 2 and one number from Table 3 as evidence, and explain your reasoning about how each technology changes inherited traits.