In this lesson students identify parts of a microscope, use a microscope to examine banana cells, tomato cells and onion cells and learn the function of a stain when using a microscope.
Introduce the microscope by showing students an example. Ask students how much bigger things look under a microscope.
- Students identify parts of a microscope by completing the worksheet Colour the microscope parts.
- Play ‘Simon says’ with the microscope. Arrange students in pairs with each pair at a microscope (if numbers allow). Ask students to place a finger on various parts of the microscope when the teacher says ‘Simon says touch the ____.’ If the teacher does not say ‘Simon says’ first, then the students should not move their finger. If the student touches the incorrect part of the microscope or if they move their finger without a ‘Simon says’, then they must sit down. The winner is the student left standing at the end.
- Complete the practical activity Using a microscope.
- Watch the video Onion skin epidermal cells: how to prepare a wet mount microscope slide.
- Ask students to prepare a wet mount slide of onion cells and examine these cells under the microscope without any stain. Ask students what the onion cells look like.
- Instruct students to gently add iodine to the onion slide and re-examine the cells. Ask students what difference they see. Ask the students to draw just three cells. Students will be tempted to draw a brick-like arrangement. Limiting the number of cells drawn can prevent this.
Teacher note: If students are unfamiliar with the procedure for staining of cells direct them to watch the short video How to stain a slide.
Discuss with students why scientists might use different types of stains when examining cells.