Grade Level/Subject

Grade Level/Subject High School / Biology

Unit Cell Structure and Function - Osmosis

Enduring Understanding  Osmosis refers to the movement of water molecules through a semi-permeable membrane from an area of greater water concentration or pressure (lower solute concentration) to an area of lesser water concentration or pressure (higher solute concentration).

SOL Objectives BIO.3 The student will investigate and understand relationships between cell structure and function. Key concepts include a) evidence supporting the cell theory; b) characteristics of prokaryotic and eukaryotic cells; c) similarities between the activities of the organelles in a single cell and a whole organism; d) the cell membrane model; and the impact of surface area to volume ratio on cell division, material transport, and other life processes.

BIO.1 The student will demonstrate an understanding of scientific reasoning, logic, and the nature of science by planning and conducting investigations. Title Shipwrecked Sailor – Osmosis Lab

Lesson Objective To observe osmosis in cells.

Inquiry Level Level 3 – Question and materials are given. Students must come up with their own procedures to answer the question.

Materials Required Electronic scale, one potato, sharp instrument to slice potato, water, salt, beakers, graduated cylinder, metric ruler, stirrer, other? Shipwrecked Sailor - Osmosis Lab

Name:______Period:______

Background:

Water passes through cell membranes from areas of high water concentration to areas of lower water concentration. This movement of water is called osmosis. If a cell is placed in an environment in which the concentration of water is less than inside the cell, water will flow from the cytoplasm through the membrane into the environment. The cytoplasm of the cell shrinks. In an animal cell the entire cell shrivels. In a plant cell, the cytoplasm shrinks away from the cell wall.

A scientist can observe the effects of water loss by observing the shrinking of a cell’s cytoplasm with a microscope. This observation is a qualitative measurement. In measuring the amount of water loss in grams, a scientist makes a quantitative measurement.

Scenario:

A shipwrecked sailor is stranded on a small desert island with no fresh water to drink. She knows she could last without food for up to a month, but if she didn't have water to drink she would be dead within a week. Hoping to postpone the inevitable, her thirst drove her to drink the salty seawater. She was dead in two days. Why do you think drinking seawater killed the sailor faster than not drinking any water at all? Today we explore the cause of the sailor's death. We'll prepare solutions of salt water to represent the sea, and we'll cut up slices of potato to represent the sailor. Potatoes are made of cells, as is the sailor!

Purpose:

To determine the cause of the sailor's death, we will determine the effects of salt water on slices of potato. Our assumption is that potato cells will behave like the sailor's cells in her body. We will compare salt water to fresh water so we can see if there is an effect caused by the salt in the water. The fresh water acts as a control in this experiment.

 Materials: electronic scale, one potato, sharp instrument to slice potato, water, salt, beakers, graduated cylinder, metric ruler, stirrer, other?

 IMPORTANT:

o You will need two Quantitative Measurements: one needs to mass and the other must be length of potato

o You will need one Qualitative Measurement

o You will need to make three to four solutions with one being the control (distilled water). The others will need to be differing salt concentration. You will have two days to conduct your experiment.

o Make sure everything is controlled in your experiment Question: What type of water will provide the best opportunity for the sailor to survive?

 Day 1

o Meet with your group and come up with an experiment that can help answer the question posed above.

o Develop the hypothesis (under the hypothesis list your variables), materials list, and procedures. Plan on more than one trial.

o Show your teacher your plan.

 Day 2

o Make solutions. Prepare your potatoes.

o Set up your experiment. Make initial measurements.

o Make your data table.

 Day 3

o Make final measurements.

o Graph results

o Write conclusion.

o Present findings to class. Shipwrecked Sailor - Osmosis Lab

Name:______Period:______Question: What type of water will provide the best opportunity for the sailor to survive?

1. Procedures:

2. Materials:

3. Independent Variable ______

4. Dependent Variable (s) ______

5. Constants

6. Hypothesis: 6. Attach Data Tables and Graphs

7. Conclusion Paragraph: (Summarize the results of your experiment. How do these results relate back to the original questions about the sailor? How does this relate to the concept of osmosis? How could the experiment be improved or expanded?)