WorksheetPremium

Normal Hearts in Dirty Water: Killifish of the Harbor Marsh

Grade 8 natural selection practice: use killifish embryo tests from a polluted harbor marsh and a clean marsh to explain who survives and reproduces.

Grade 8ScienceInteractive · Printable

Aligned toMS-LS4-4

Buy this worksheet: $1.50

Or unlock every Premium worksheet with Premium

PrintUnlock to print

Answer keyUnlock to see answers

Assign to classUnlock to assign with a class code

What’s included

Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
11 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 use embryo survival data to explain how an inherited trait raises the chance of surviving in one environment.
Students tell inherited variation apart from changes caused by an individual's surroundings.

How to use

Read the field trip story together and make sure students can name the two things the lab changed. Let them work the table and the model, then discuss the quote on the board before the written explanation.

Curriculum

NGSS standard covered

MS-LS4-4

Explain how genetic variation in traits makes some individuals more likely to survive and reproduce.

Preview

OwlSheets.com

Name Date

Normal Hearts in Dirty Water: Killifish of the Harbor Marsh

Use embryo test data to explain why some killifish are more likely to survive and reproduce in a polluted marsh.

Part 1: The embryo test

Read the field trip story and Table 1, then answer questions 1–5.

Two Marshes, One Kind of Fish

1Ms. Gwendolyn Achebe's eighth grade marine biology class took a field trip to two salt marshes on the same stretch of coast. One lies beside an old industrial harbor. The other, Sedge Point, is about 40 km away and was never built on. At low tide the marsh creeks shrink into shallow pools, and the students netted small, silvery-brown fish called Atlantic killifish, then let them go. Killifish are common in salt marshes along the Atlantic coast, and most adults spend their lives within a few hundred meters of where they hatched, so each marsh has its own population.

2Dr. Pilar Henriksen, a biologist at the state university, met the class at the harbor. Decades ago, factories along the harbor released oily wastes and chemicals called PCBs into the water. The factories closed long ago, but much of the pollution is still in the mud. In killifish from clean marshes, these chemicals can keep an embryo's heart from forming properly, and an embryo with a badly formed heart usually dies before or soon after hatching. Yet killifish are plentiful in the harbor marsh.

3To find out why, Dr. Henriksen's lab ran a test. The scientists collected eggs from adults in each marsh and raised them in the lab, all at the same temperature and in the same clean salt water. Half of each marsh's embryos were raised in water mixed with a small amount of harbor mud, and the other half in water without it. After two weeks, the scientists counted how many embryos in each group had hatched with a normal heart.

4The lab also raised harbor-marsh killifish in clean water for two generations. None of these fish, and none of their parents, had ever touched harbor mud. When their embryos were tested in harbor-mud water, 79 of 100 hatched with a normal heart.

5Dr. Henriksen explained that how well an embryo develops in polluted water depends partly on which versions of certain genes it inherited from its parents. Killifish usually begin to breed at about one year old and spawn every spring and summer, so the harbor population has gone through dozens of generations since the pollution began.