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Students evaluate how ecosystems are impacted by increasing salt concentrations. They first examine the effects on freshwater ecosystems by evaluating the impact of sodium chloride (NaCl) on duckweed (Lemna minor). Then students study how magnesium chloride (MgCl₂) and calcium chloride (CaCl₂) affect the survival of duckweed. In doing this, students calculate the LC50 and create dose response curves for the different solutions. Kit includes materials for 8 groups of students.

Product Details
In these investigations, students evaluate how ecosystems are impacted by increasing salt concentrations. Students first examine the effects on freshwater ecosystems by evaluating the impact of sodium chloride (NaCl) on duckweed (Lemna minor). Then students study how magnesium chloride (MgCl₂) and calcium chloride (CaCl₂) affect the survival of duckweed. In doing this, students calculate the LC50 and create dose response curves for the different solutions. Kit includes materials for 8 groups of students. Note: Kit includes a voucher to request the perishable material later at your convenience. Contact Carolina or return the voucher to request delivery of perishables.

Unit Connection
These laboratory investigations correlate to Unit 8: Aquatic and Terrestrial Pollution, topics 8.2: Human Impacts on Ecosystems, 8.12: Lethal Dose 50%, and 8.13: Dose Response Curve in the AP® Environmental Science Course and Exam Description.

Standards Connection
This kit addresses the following AP® Environmental Science concepts:
Big Idea 3: Interactions Between Different Species and The Environment (EIN). Humans alter natural systems and have had an impact on the environment for millions of years. Technology and population growth have enabled humans to increase both the rate and scale of their impact on the environment.

• EIN-3 Pollutants can have both direct and indirect impacts on the health of organisms, including humans.
• EIN-3.A Define lethal dose 50% (LD50).
• EIN-3.A.1 Lethal dose 50% (LD50) is the dose of a chemical that is lethal to 50% of the population of a particular species.
• EIN-3.B Evaluate dose response curves.
• EIN-3.B.1 A dose response curve describes the effect on an organism or mortality rate in a population based on the dose of a particular toxin or drug.

Big Idea 4: Sustainability (STB). Human survival depends on developing practices that will achieve sustainable systems. A suitable combination of conservation and development is required. The management of resources is essential. Understanding the role of cultural, social, and economic factors is vital to the development of solutions.

• STB-3 Human activities, including the use of resources, have physical, chemical, and biological consequences for ecosystems.
• STB-3.B Describe the impacts of human activities on aquatic ecosystems.
• STB-3.B.1 Organisms have a range of tolerance for various pollutants. Organisms have an optimum range for each factor where they can maintain homeostasis. Outside of this range, organisms may experience physiological stress, limited growth, reduced reproduction, and in extreme cases, death.

Time Requirements
Teacher Preparation (before class):

• Prelab: 15 minutes
• Investigation 1: Prior to Day 1, 35 minutes; Day 1, 15 minutes; Days 2–4, 10 minutes
• Investigation 2: Prior to Day 1, 35 minutes; Day 1, 15 minutes; Days 2–4, 10 minutes

• Prelab: 20 minutes
• Investigation 1: Day 1, 40 minutes; Day 2, 30 minutes; Day 3, 30 minutes; Day 4, 30 minutes
• Investigation 2: Day 1, 35 minutes; Day 2, 25 minutes; Day 3, 25 minutes; Day 4, 25 minutes
• Free-Response Questions: 35 minutes

Digital Resources
Includes 1-year access to digital resources that support instruction. Digital resources may include teacher manual and student guide, prelab activities and setup videos, simulations, and postlab analysis and assessments.

Prior Knowledge and Skills
Students should be familiar with the following skills or concepts:

• An understanding of how changes in salinity impact plant vitality
• An understanding of how pollution can be direct and indirect
• Basic knowledge of conducting an experiment and graphing

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