Blog

Virtual Lab – Microscopy – Plant Cells (Onion Epidermal Cells) The following image is of another plant, called Elodea, which has visible chloroplasts (the tiny, small green circles in each rectangular cell). One of the cellular activities that can be observed with a live specimen is cytoplasmic streaming. Cytoplasmic streaming is the movement of the cytoplasm within particular kinds of cells, like these Elodea cells. As the cytoskeleton directs the cytoplasm to flow, nutrients created from the chloroplasts, macromolecules and organelles are circulated and distributed throughout the cell. For more practice, calculate the estimated width (in

One of the most common instruments used in biology is the microscope. The invention of the microscope revolutionized biology. It helped establish that living things are made of cells and that microorganisms exist that are invisible to the naked eye. Microscopes are valuable tools in biology because they can increase both the magnification and resolution of the observed specimen. Magnification refers to the apparent size of the specimen, whereas resolution refers to the clarity of seeing two objects as distinctly separate.The magnification power of a compound light microscope is determined by its ocular and the objective, which is why we refer to the microscope as a compound light microscope. A typical ocular has a magnification power of ten (10X). The objectives are magnifying lenses fastened on the rotating nosepiece. The objectives on student microscopes are 4X, 10X, 40X, and sometimes 100X (for oil immersion). To calculate the total magnification of the specimen, one would multiply the ocular power by the objective power as below: Total magnification = magnification of ocular X magnification of objective used We will be introducing a compound light microscope by first acquainting you with the parts and functions of the parts of the microscope and then by viewing a variety of cell specimens. Eukaryotic cells are those that contain a nucleus and membrane-bound organelles. Prokaryotic cells, or bacterial cells, are much smaller in size and do not contain a nucleus or membrane-bound organelles. MICROSCOPE FIELD OF VIEWWhen you look into a microscope that has the power turned on, you should see a bright circle. This bright circle of light shows you the area of the slide that is being magnified and is called the field of view. As you increase objective magnification power, the field of view gets smaller. This does not mean the bright circle that you see through the microscope becomes smaller. It simply means a smaller area of the slide is being magnified. One can use the diameter of the field of view to estimate the size of the object that is being observed under the microscope.To estimate the size of the object observed, use the following steps: Select a suitable magnification for size estimation. It is important that you choose a magnification that allows you to observe the entire object. If the object is very small, use the highest magnification available for your estimation. Place the object in the center of the field of view. Estimate the number of objects that can fit across the diameter of the field of view. Estimated object size = Diameter of the chosen field of view ÷ Estimated number of object across the diameter of the field of view.  

Virtual Lab – Microscopy – Plant Cells (Onion Epidermal Cells) In plant cells such as Elodea cells, chloroplasts are typically present. However, onion cells often lack chloroplasts. This is because onions are storage organs that do not perform photosynthesis; instead, they store nutrients. Elodea, being a green aquatic plant, needs chloroplasts to perform photosynthesis, so it contains them.

Virtual Lab – Operation of Bright Field Microscope How does changing light intensity affect the contrast of an image in a microscope?

Virtual Lab – Osmosis – Tonicity in Elodea Cells (Plant Cells) When solute concentration is lower in an environment compared to the other side of the membrane, it is known as a _____________ environment.

Virtual Lab – Diffusion Across a Selective Permeable Membrane How do we test for the presence of starch using iodine (IKI)?

Virtual Lab – Microscopy – Plant Cells (Onion Epidermal Cells) Follow the steps provided in the reading section of this study guide for assistance to calculate the estimated width (in

Virtual Lab – Operation of Bright Field Microscope What is the difference between resolution and contrast?

Virtual Lab – Operation of Bright Field Microscope What is the relationship between objective, magnification power and the field of view?

Dialysis tubing is a selectively permeable membrane made with the macromolecule, cellulose. Starch, glucose, water and the IKI reagent arecontained within the dialysis membrane in solution B shown below. Solution A in the beaker, at the start of the experiment in panel (a) contains just water. Diffusion of these molecules occurs, over time, from panels (a)-(c). The only selective criterion for diffusion across a dialysis membrane is the size of the molecule. Which of these molecules will diffuse the fastest?