Microworlds
Lesson 11
Looking Inside an Onion
Students will have their first experience with cells in this lesson. They will be looking at an onion from the outside in.
3. Lesson Set-up and Management
4-5 INQI Scientists report the results of their investigations honestly, even when those results show their predictions were wrong, or when they cannot explain them.
- Students will examine and describe the internal structure of an onion.
- Students will observe and describe the cells in an onion.
- Teacher will evaluate student process by looking at Activity Sheet 6.
3. Lesson Set-Up and Management
Materials:
- Photocopy Activity Sheet 6.
- The teacher will need to purchase onions for the classroom. Leave a few whole for the students to look. Also, it helps for time if the teacher chops up one onion ahead of time. The pieces should be about an inch square.
- You will need to have a knife and cutting board to cut the onion in front of the students.
- You will need to have a slide cleaning station set up with warm water to clean the slides.
Student Management:
- It seems to be easier for more students to separate the onion with their fingernail. They have to be very gentle with the forceps or the skin will break.
- Make sure the students lay the skin flat – smoothing it with a toothpick.
- Remind students to keep their hands away from their eyes. They should wash their hands as part of the clean up process.
- The teacher background section does a great job of explaining the parts of an onion cell. Make sure you allow the students to have the concrete experiences in this lesson before you start discussing the scientific names and functions.
- Sometimes iodine is recommended for view onion cells. You can make an iodine solution by mixing one part Tincture of Iodine with ten parts water. Iodine can stain clothing, so you have to be very careful. It is said that lemon juice can remove iodine stains.
- Go over Activity Sheet 6. Make sure student do detailed drawings. Also, make sure students do not go back and change their predictions.
- Cut an onion once all students have their predictions. Give each group a half an onion to observe closely and use for their drawing.
- For Procedure 3, the teacher can pass out precut inch square sections of the onion to each student.
- For Procedure 5, after students have made their observations, the teacher should introduce and discuss the new vocabulary words related to the cell and its structure. Students should be able to look at their own cell to try and identify the parts.
- Make sure you discuss Final Activity 1 with students about Robert Hooke’s discovery and naming of cells.
- Wait until Lesson 12 to do the reading selection on Volvox. Remember current science research says that students should have the activity before the content.
Reading Support:
- Find trade books or internet information on Robert Hooke and his discovery of cells.
Last updated 02/20/2010