Cells Lesson 4

How can we prove that cells exist if we can’t see them? In your table groups you have got 2 minutes to discuss your ideas and then we will talk about them as a class Use your scientific thinking Make sure you listen to everyone in your group

Learning intentions At the end of this lesson: All will have: used a microscope safely and effectively and produced a labelled diagram of an animal cell and a model aniaml cell. Most will have: peer-assessed a labelled diagram of an animal cell and be able to recall the functions of parts of an animal cell, completed the crossword Some will have: demonstrated their understanding by completing ‘Microscopes, size and scale’.

Responsible use of microscopes Microscopes are fragile and delicate: They should always be carried with two hands: one underneath and one holding the curved part of the body. You should not touch the lenses. Persistent mistakes include: holding the microscope with one hand focussing down onto the slide and breaking it turning the objective lens around and crashing into the slide forgetting to mop up excess liquid.

How to use a microscope Now follow the instructions below carefully. Make sure you have selected the low power objective lens (it’s the smallest). Look down the eyepiece and adjust the mirror until it is as light as you can get it. Move the focussing knob until the objective lens is as far down as it will go. Put your slide on the stage and secure it with the stage clips. Using the focussing knob, move the objective lens slowly up. Until you can see something. (You will need to keep looking down the eyepiece as you do this). When you think you can see something, check with the teacher before drawing what you see. When you have finished, remember to remove the slide from the microscope before packing it away.

1. Collect your equipment 2. Carefully wipe the side of your cheek with a cotton bud 3. Gently wipe the sample onto the slide 4. Stain the sample with methylene blue 5. Cover the sample with a cover slip 6. Have a look at your cells. How are we going to look at an animal cell?

Remember the rules?

Recording what you can see: Cheek Cells Things outlined in black are probably air bubbles! Get me to help you if you can’t see!

Write a clear heading. Use a sharp HB pencil. Draw firm, continuous lines and avoid using too much shading. Include the magnification. Draw label lines with a ruler. These must not touch the structure they are labelling and should not cross each other. Write labels horizontally on the page (pupils often write along the same angle as the label lines) and arrange them neatly around (not over) the drawing.

Recording what you can see: Animal Cell Cell membrane Cytoplasm Nucleus

What do all the parts do? What do the organelles do? Nucleus Cell membrane Cytoplasm Chloroplast Cell wall Vacuole Controls what happens in the cell (contains DNA) Jelly-like substance where reactions happen Keeps substances in the cell and controls what goes in and out Contain chlorophyll – where photosynthesis happens Contains cell sap – keeps the cell firm Made of cellulose and supports the cell

Complete the activity: Microscopes, size and scale. This activity will help develop your thinking skills.

Cell membrane Cytoplasm NucleusEye piece Objective lens Coarse focus Fine focus Slide Stage Light