Resources: Microscopes, glass slides, cover slips, knife or scalpel, tweezers, cotton buds, methylene blue, disinfectant in a beaker and the handout.
Core Handout: An investigation sheet for the students to fill in.
Revise KS2 learning to ensure that students understand that living things are made up of cells, and that there are differences between animal and plant cells. The students may be familiar with the structure of an animal cell and its key components, such as the cell membrane, cytoplasm, nucleus and mitochondria.
Ask the students: what are living things made of?
Go through the presentation slides to explain the additional organelles found inside an animal cell and the function of these additional roles. To assess learning objectives 1 and 3, monitor the students as they label and animal cell and describe the function of the organelles on the handout. To assess learning objective 2, monitor the students as they observe the animal cell during the practical activity and draw their observations.
Expert Film: Tegan Brown works as a Registered Veterinary Nurse for Rackheath Vets. Tegan explains the structure of animal cells.
Observing Cells
The students will be preparing slides to observe cells under the microscope. They should sketch what they observe and label any notable organelles.
Cheek Cells
The students will prepare a slide of cheek cells. The key is to generously smear the inside of the cheek and smear the slide over a small area. This is then stained with methyl blue. The students should then complete the "The Cheek of it!" page on the handout. The slides should be dropped in a beaker of disinfectant when finished with.
Support: To provide further support, the students could use pre-prepared animal cell slides.
Challenge: Ask the students to label the parts of the cell from their observations.
Have a class discussion where students share their understanding of the different components of an animal cell, their functions, and how they work together to maintain cell function and survival. This can help to reinforce the lesson's key points and allow students to build on each other's knowledge.
Microscopes are used to observe cells. Before the can be viewed under a microscope, they need to be prepared and placed on a slide. For example, this can be seen when taking a sample of a human cheek cell. Initially, a small drop of water is placed on a microscope slide and a swab is taken from the inside of the cheek. This can be done with a cotton bud. This is then rubbed onto the drop of water. A coverslip is then placed over the sample and a stain or dye is used to make the structures more visible. For the cheek cells, methylene blue can be used. This ensures that the nucleus is blue and thus visible to the naked eye. For plant cells, iodine is used. After all of this preparation is done, it is ready for viewing under a light microscope.
Microscopes produce magnified images of existing images or samples. There are two different main types. Light microscopes are of low magnification and resolution and are used to observe living cells. Electron microscopes provide a higher resolution and magnification but cannot be used to observe living cells.
Microscopes contain an eyepiece lens and objective lenses. These lenses allow the user to zoom in and out of the specimen so that observation is clearer. The objective lenses have an enhanced ability to zoom in. The individual using the microscope will look through the eyepiece lens initially. It is at the top of the microscope. Normally, microscopes contain about 3 or 4 objective lenses. You can rotate between them by using a turret. A coarse focus knob is used for moving the objective lenses closer and further away from the specimen. Fine focus knobs are used for fine-tuning. Illuminators are used so that the specimen can be seen more easily on the slide.
Let’s have a look at how we investigate an onion cell under the microscope. Initially, a water drop is added to the centre of the microscope slide. The thin membrane of the onion layer is put at the centre of the slide. A drop of iodine solution is added to the layer or sometimes, even methylene blue. The microscopic cover slip is then placed on top of the membrane and air bubbles can be removed by gentle prodding with an instrument. Excess iodine solution and water is removed using blotting paper. The slide is then ready for observation under the microscope. You should be able to see a dark and stained nucleus, a large vacuole at the centre, a cell wall, large and interlocking cells and even small granules (of starch) too.