Description:

Students design and carry out an exercise to determine if a given fruit or vegetable is composed of cells.

Students choose a representative sample and decide what materials, procedures, and kinds of evidence are required in order to determine if their fruit or vegetable is composed of cells.

The task assesses students' abilities to design an investigation, make simple observations, make generalized inferences from their observations, and apply their understanding to an everyday situation.

This task is designed to take students 1-2 class periods (40-45 minutes each, with introduction given before the class period) to complete.

Overall Task Content Area:

Life Science

Specific Knowledge Areas:

The cell

Performance Expectations:

• conducting investigations
• using equipment
• formulating conclusions from investigational data
• applying scientific principles to develop explanations and solve new problems

National Science Education Standards:

12 A SI 1: Abilities necessary to do scientific inquiry: Grades 9-12
1.4 Formulate and revise scientific explanations and models using logic and evidence. Student inquiries should culminate in formulating an explanation or model. Models should be physical, conceptual, and mathematical. In the process of answering the questions, the students should engage in discussions and arguments that result in the revision of their explanations. These discussions should be based on scientific knowledge, the use of logic, and evidence from their investigation.

12 C LS 1: The cell: Grades 9-12
1.1 Cells have particular structures that underlie their functions. Every cell is surrounded by a membrane that separates it from the outside world. Inside the cell is a concentrated mixture of thousands of different molecules which form a variety of specialized structures that carry out such cell functions as energy production, transport of molecules, waste disposal, synthesis of new molecules, and the storage of genetic material.

(Use the "hot" link on the PALS home page to check the full text of related National Science Education Standards, if desired.)

General Instructions to the Teacher:

This task is designed to take students approximately 1-2 class periods to complete.

This assessment would be given to students after they had done the classical onion and cheek cell lab, and preparing wet mounts.

Having the students design an exercise that the teacher approves before the students begin their work has purposefully been left out. The idea behind this assessment is what can the students do on their own: here is a problem, solve it. Part of this assessment is to see what the students really do in going about the solving of the problem. The teacher must be available for help throughout the task, whether solicited or not.

Students should be ready to work as soon as the period begins. The materials should be set out at each lab station, if possible. A central supply area, if needed, should be easily accessible. All supplies should be clearly labeled.

Materials for "Are Fruits and Vegetables Really Made of Cells?":

• compound microscope
• slides and cover slips
• stains (iodine, methylene blue)
• plant dissection equipment
• cotton swabs
• beakers
• paper towels
• toothpicks
• a variety of fruits and vegetables (as described below)

Advance Preparation:

• A wide sampling of fruits and vegetables should be available to the students: apple, pear, potato, celery, banana, squash, tomato, turnip, radish, and cucumber are all good choices. These may be supplied by the teacher or students may be asked to bring them from home. The samples should be checked for easily seen cells. Samples such as oranges and grapefruits are generally not good for use unless some tissue is taken from the rind. Samples such as kidney beans, peas, peaches, strawberries, and blueberries should be avoided. Students should not be asked to bring in just any fruit or vegetable from home without checking with the teacher first.

Safety:

• Be careful.
• Teachers and students should always exercise appropriate safety precautions and utilize appropriate laboratory safety procedures and equipment when working on science performance tasks.

Extensions/modifications:

• N/A