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Effect of Salt Concentration on Plants (4 Favorites)

LAB in Mixtures, Interdisciplinary, Concentration, Measurements, Scientific Method. Last updated February 4, 2019.


Summary

In this lab, students will observe how salt concentration can affect the structure of a potato tuber.

Grade Level

Middle and High School

Objectives

By the end of this lab, students should be able to

  • generate and test a hypothesis
  • explain how osmosis in plant cells is affected by salt concentration
  • graph and interpret self-measured data (quantitative and qualitative)

Chemistry Topics

This lab supports students’ understanding of

  • Solutions
  • Concentration
  • Properties of water
  • Osmosis
  • Scientific method
  • Plant growth

Time

Teacher Preparation: 30 minutes

Lesson: Two-three 50-minute class periods

Materials

  • Potato (1 potato for every two groups)
  • Cork borer
  • Potato peeler
  • 150 mL beakers (4 per group) *plastic cups can be substituted
  • Distilled water
  • Balances (triple beam or digital)
  • Rulers
  • 1% salt solution
  • 5% salt solution
  • 10% salt solution
  • Paper towels

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • Do not consume lab solutions, even if they’re otherwise edible products.
  • Food in the lab should be considered a chemical not for consumption.

Teacher Notes

  • Prior to teaching this lesson, students should be taught about osmosis and its importance to cells.
  • Prepare stock salt solutions in advance (1%, 5%, 10%)
  • Peel and core potatoes (cores should be approximately 3 cm long)
    • Prior to lab, measure 100mL in a measuring cup if you do not have beakers available. Mark “100mL”on one cup per group so that each group has a measuring cup to use
  • Classroom management tips
    • Have students work in groups of 3-4 (pre-determined based on abilities)
    • Assign students roles (you can assign or allow students to self-assign roles)
  • Differentiation
    • Groups: You can use your grouping to pair students who are weak in data collection with students who may be able to give pointers
    • Data presentation: Students who are weak in graphing could be allowed to complete one graph instead of three. Higher-level students can be challenged to create an additional graph to show the volume of the cores.
  • 1%= 1 g salt dissolved in 1L water
  • 5%= 5g salt dissolved in 1 L water
  • 10% = 10g salt dissolved in 1 L water
  • Length measurer: in charge of measuring lengths and widths of potato cores
  • Mass measurer: in charge or measuring masses
  • Solution preparer: in charge of obtaining solutions for the lab and labeling cups
  • Data recorder: in charge of recording all measurements and ensuring other members are recording their own data.

For the Student

Background

In all cells, the cell membrane acts as barrier that allows materials to pass into and out of the cell. This membrane is involved in both active and passive transport.

Osmosis is a type of passive transport that involves the movement of water across a selectively permeable membrane. In passive transport, molecules tend to move from an area of high concentration towards an area of lower concentration. Osmosis is important in both plants and animals.

We can see osmosis in play during droughts. Plants with too little water will wilt when water moves out of the cells due to osmosis. If the plants happen to get a lot of rain, water will move back into the cells via osmosis and the plants will perk up!
Lab saltconcentrationonplants background

Image Credit: source: http://iws.collin.edu/biopage/faculty/mcculloch/1406/notes/membranes/images/Plant%20Cell%20Tonicity.jpg

Sometimes the rain that plants receive is not just water. During hurricane season, the rain that plants receive contains seawater, which contains a lot of salt. Because osmosis is a passive process, plants have little control over when it occurs. The purpose this lab is to investigate how salt-water affect plants via osmosis.

Pre-lab Questions

Complete these before class:

  • What is osmosis?
  • What cell organelle controls what may enter and leave the cell?
  • What is distilled water?
  • How is a cell wall different from a cell membrane?

Problem Statements

How does salt water affect crop growth?

How does salt water affect the mass and size of a potato?

Hypothesis (If/then):

Independent Variable:

Dependent Variable:

Hypothesis:

Materials

For this lab, your group will need the following items:

  • 12 potato cores
  • Four 150 mL beakers (4 per group)
  • 100 mL distilled water
  • 100mL 1% salt solution
  • 100mL 5% salt solution
  • 100mL 10% salt solution
  • 1 balance (triple beam or digital)
  • 1 ruler
  • Paper towels

Safety

  • Safety goggles & aprons should be worn at all times during this lab.
  • Wash your hands thoroughly before and after the lab.
  • Food in the lab should be considered a chemical not for consumption.
  • Do not drink the salt-solutions
  • Clean-Up
    • Potato cores go in trash
    • Salt solutions and distilled water should be poured into your sinks
    • Beakers must be washed with soap, rinsed, and dried.
    • Goggles and aprons should be returned to their storage containers

Procedure

Day 1

  1. Within your group determine each person’s role and record it below:
    • Length measurer:
    • Mass measurer:
    • Solution preparer:
    • Data recorder:
  2. Label your four beakers with your solution preparer’s initials and the following names: 0% salt, 1% salt, 5% salt, 10% salt.
  3. The solution preparer should collect 100mL of each of the various salt solutions in their appropriate containers.
  4. Measure the mass, length, and height of three cores. Record these measurements in your data table for the 0% salt solution and place cores the correct labeled beaker.
  5. Repeat step 4 for 1% salt solution, 5% salt solution, and 10% salt solution.

    Day 2
  6. Allow cores to sit in the solutions for 24 hours
  7. After 24 hours, remove cores from their containers.
  8. Using a paper towel, dry off cores to remove excessive water
  9. Re-measure and record the mass, length, and height of each core from each solution.
  10. Rate the flexibility of the cores on a scale of 1-5 and record in the data table for flexibility (1= rigid, not flexible, hard to bend; 5= very flexible)
  11. Dispose of the solutions and potato cores
  12. Calculate the average mass, length, and height measurement for each core from each solution.
  13. Complete the calculations and graphing section of the lab.


Download the Student Activity to view the rest of this lesson.