Practical: The Microscope. Identifying the problem. The aim of this practical is to investigate how the microscope is able to magnify minute objects. Using a transparent ruler, we are going to focus on the mm lines first using the ________ power (i.e. x4 objective lens), then the medium power (i.e. the x_______ objective lens), and finally the _________ power (i.e. the x40 objective _________). Observing these magnified images of the same object, we will then discuss what other uses can the microscope have to study Biology. Experimental Design. Apparatus to be used: microscope, transparent ruler, 1. Put the lowest power objective in the working position. 2. Adjust the __________ as to see light when looking through the eyepiece lens. 3. Turn the coarse focus so that the objective lens is as close to the stage as it will go. 4. Place the transparent ruler across the stage and focus on the edge that has the mm markings. 5. Adjust the distance of the objective lens from the stage using the focusing knobs until through the eyepiece you will see a clear magnified image. 6. Take note of the image. 7. Change to the next higher objective (__________ power) and observe the field of view. 8. Change to the higher objective and observe the last field of view. Factors that will be changed – objective lenses Factors that will be kept constant – eyepiece lens, mm of ruler, mirror in position to see light. Measurements to be taken – diameter of field of view Evaluation of the investigation. Low power eyepiece lens = x________ Objective lens = x _______ Magnification = eyepiece x objective = _________ x ________ = ______ Field of view of low power Medium power eyepiece lens = x________ Objective lens = x _______ Magnification = eyepiece x objective = _________ x ________ = ______ Field of view of medium power High power eyepiece lens = x________ Objective lens = x _______ Magnification = eyepiece x objective = _________ x ________ = ______ Field of view of high power Presentation of data. Objective lens Overall magnification Diameter Radius Area of view ¶r2 Low power 10 x 4 = 40 4mm 2mm 12.6mm2 Conclusion: The higher the magnification, the ______________ the field of view. Discussion: what other uses can the microscope have to study Biology Second Practical: Studying Onion Cells under the Microscope. Aim: _____________________________________________________ Apparatus: 2 microscope slides, 2 cover slips, filter paper, onion, iodine solution, distilled water. Method: 1. The onion was cut vertically and one of the inner scales was removed. 2. The onion was bent until it snapped and a very thin transparent scale was stripped off. 3. 2 pieces of the epidermis were cut and each one was put on the slides. 4. 2-3 drops of distilled water were dropped on one of the epidermal strips and 2-3 drops of iodine solution were dropped on the other 5. A cover slip was taken between the finger and thumb and it was lowered very carefully on each piece of onion epidermis. 6. Any excess water or iodine solution was soaked up with filter paper. Each slide was labelled. 7. Each preparation was examined carefully under the low power of the microscope and the shape was observed. 8. A diagram showing clearly the shape and arrangement of cells was drawn. 9. Under high power, in turn both preparations were examined. A single epidermal cell stained with iodine was drawn and labelled. Results and Conclusions. 1. Under the high power, the cells can be seen in more / less detail? 2. Why did we mount the epidermal cells both in distilled water and in iodine solution? What was the difference? Draw diagrams of onion cells in distilled water and onion cells in iodine solution.
