Cells Under the Microscope Measuring Cell Structures

Transcription

1 Copy into Note Packet and Return to Teacher Chapter 3 Cell Structure Section 1: Looking at Cells Objectives Describe how scientists measure the length of objects. Relate magnification and resolution in the use of microscopes. Analyze how light microscopes function. Compare light microscopes with electron microscopes. Describe the scanning tunneling microscope. Cells Under the Microscope Measuring Cell Structures Measurements taken by scientists are expressed in metric units. The official name of the metric system is the International System of Measurements, abbreviated SI. The table below summarizes the SI units used to measure length. Unit Prefix Metric equivalent Real-life equivalent Kilometer (km) Kilo- 1,000 m About two-thirds of a mile Meter (m) 1 m (SI base unit) A little more than a yard Centimeter (cm) Centi m About half the diameter of a penny Millimeter (mm) Milli m About the width of a pencil tip Micrometer (µm) Micro m About the length of an average bacterial cell Nanometer (nm) Nano m About the length of a water molecule Magnification is the quality of making an image appear larger than its actual size. Resolution is a measure of the clarity of an image. Both high magnification and good resolution are needed to view the details of extremely small objects clearly. Electron microscopes have much higher magnifying and resolving powers than light microscopes.

2 Parts of a Light Microscope Refer to page 1028 in your textbook and label. Eyepiece Body tube Revolving nosepiece High power objective lens Low power objective lens Stage clips Diaphragm lever Diaphragm Light source Arm Stage Aperture or stage opening Fine adjustment knob Coarse adjustment knob Base Types of Microscopes Light microscopes form an image when light passes through one or more lenses to produce an enlarged image of a specimen. Electron Microscopes Electron microscopes form an image of a specimen using a beam of electrons rather than light. The electron beam and specimen must be in a vacuum so that the electron beam will not bounce off of gas molecules. Live organisms cannot be viewed with an electron microscope. Transmission Electron Microscope An electron beam is directed at a very thin slice of a specimen stained with metal ions. Some structures become more heavily stained than others. The heavily stained parts absorb electrons, those that are lightly stained allow electrons to pass through. The electrons that pass through strike a fluorescent screen, forming an image.

3 Scanning Electron Microscope An electron beam is focused on a specimen coated with a very thin layer of metal. The electrons that bounce off the specimen form an image on a fluorescent screen. The image shows three-dimensional details of the surface of a specimen. Scanning Tunneling Microscope A needle-like probe measures differences in voltage caused by electrons that leak, or tunnel, from the surface of the object being viewed. A computer tracks the movement of the probe across the surface of the object. The image shows three-dimensional details of the surface of a specimen. Live specimens and objects as small as atoms can be viewed. Section 2: Cell Features Objectives List the three parts of the cell theory. Determine why cells must be relatively small. Compare the structure of prokaryotic cells with that of eukaryotic cells. Describe the structure of cell membranes. The Cell Theory The Cell Theory has three parts: 1. All living things are made of one or more cells. 2. Cells are the basic units of structure and function in organisms. 3. All cells arise from existing cells. Cell Size Small cells function more efficiently than large cells. If a cell s surface area to-volume ratio is too low, substances cannot enter and leave the cell well enough to meet the cell s needs.

4 Common Cell Features Cells share common structural features, including: an outer boundary called the cell membrane, interior substance called cytoplasm, structural support called the cytoskeleton, genetic material in the form of DNA cellular structures that make proteins, called ribosomes

5 Prokaryotes Prokaryotes are organisms that and other internal compartments. They have a, may have cilia or flagella, and have a circular molecule of DNA. Structure of Cilia and Flagella Cilia Microtubules Cell membrane Extracellular matrix Eukaryotic Cells Flagellum Eukaryotic cells have: A which contains the cell s DNA Other internal compartments called.

6 Comparing Prokaryotes and Eukaryotes Prokaryote Eukaryote 1. No nucleus 1. True nucleus 2. Circular DNA 2. Linear DNA 3. No membrane covered organelles 3. Many membrane covered organelles 4. Relatively small 4. Relatively large 5. Reproduce quickly (20 minutes) 5. Reproduce slowly (24+ hours) Ex: Bacteria Ex : Plants, animals, fungi & protists Parts of an Animal Cell (Label) Flagellum

7 Eukaryotic Cells The cytoskeleton provides the interior framework of a cell. There are three basic kinds of cytoskeletal fibers. 1. Microfilaments: long slender filaments made of the protein actin 2. Microtubules: hollow tubes made of the protein tubulin. 3. Intermediate fibers: thick ropes made of protein. The cytoskeleton s network of protein fibers anchors the cell s organelles and other components of the cytoplasm. The Cell Membrane The cell membrane is a selectively permeable barrier that determines which substances enter and leave the cell. The selective permeability of the cell is mainly caused by the way phospholipids interact with water. A phospholipid is a lipid made of a phosphate group and two fatty acids. Cell membranes are made of a double layer of phospholipids, called a bilayer.

8 Check with another student to label these pictures. Refer to page 61 (Label)