Chapter 6: A Tour of the Cell
Concept 6.1 Biologists use microscopes and the tools of biochemistry to study cells 1. The study of cells has been limited by their small size, and so they were not seen and described until 1665, when Robert Hooke first looked at dead cells from an oak tree. His contemporary, Anton van Leeuwenhoek, crafted lenses and with the improvements in optical aids, a new world was opened. Magnification and resolving power limit what can be seen. Explain the difference. Magnification is the ratio of an object’s image size to its real size. Resolution is a measure of the clarity of the image; it is the minimum distance two points can be separated and still be distinguished as two points. 2. The development of electron microscopes has further opened our window on the cell and its organelles. What is considered a major disadvantage of electron microscopes? The methods used to prepare the specimen kill the cells. 3. Study the electron micrographs in your text. Describe the different types of images obtained from: scanning electron microscopy (SEM): Answers may vary, but should describe the 3-D component of the specimen image. transmission electron microscopy (TEM) Answers may vary, but should mention that this type of microscopy profiles a thin section of a specimen, resulting in various views of the cells prepared. 4. In cell fractionation, whole cells are broken up in a blender, and this slurry is centrifuged several times. Each time, smaller and smaller cell parts are isolated. This will isolate different organelles and allow study of their biochemical activities. Which organelles are the smallest ones isolated in this procedure? Ribosomes Concept 6.2 Eukaryotic cells have internal membranes that compartmentalize their functions 5. Which two domains consist of prokaryotic cells? Bacteria and Archaea 6. A major difference between prokaryotic and eukaryotic cells is the location of their DNA. Describe this difference.
In a eukaryotic cell, most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane. In a prokaryotic cell, the DNA is concentrated in a region that is not membrane enclosed, called a nucleoid. Copyright © 2011 Pearson Education, Inc. -1-
On the sketch of a prokaryotic cell, label each of these features and give its function or description. See page 98 in your text for the labeled figure. cell wall: rigid structure outside the plasma membrane plasma membrane: membrane enclosing the cytoplasm bacterial chromosome: carries genes in the form of DNA nucleoid: region where the cell’s DNA is located (not enclosed by a membrane) cytoplasm: interior of cell flagella: locomotion organelles of some bacteria
Why are cells so small? Explain the relationship of surface area to volume. Cells are small because a high surface-to-volume ratio facilitates the exchange of materials between a cell and its environment. As a cell (or any other object) increases in size, its volume grows proportionally more than its surface area. (Area is proportional to a linear dimension cubed.) Thus, a smaller object has a greater ratio of surface area to volume.
What are microvilli? How do these structures relate to the function of intestinal cells? Microvilli are long, thin projections from the cell surface, which increase surface area without an appreciable increase in volume. A sufficiently high ratio of surface area to volume is especially important in cells that exchange a lot of materials with their surroundings, such as intestinal cells.
Concept 6.3 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes 10. In the following figure, label the nuclear envelope, nuclear pores, and pore complex. See page 103 of your text for the labeled figure. 11. Describe the nuclear envelope. How many layers is it? What connects the layers? The nuclear envelope encloses the nucleus,...
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