AP Bio Chapter 4

Microscopy Three important aspects: Light microscope (LM) – Magnification – how large the object appears compared to actual size Resolution – how clear the image appear; how well two points can be distinguished Contrast – visible differences in parts of the sample Light microscope (LM) – Visible light passes through the specimen and then through glass lenses Lenses refract light and magnify the image Highest magnification ~ 1000 x Living cells can be observed Subcellular organelles are generally too small for accurate resolution Stains are used to enhance the contrast These microscopes are used in most high school and college biology courses

Microscopy… Electron microscope (EM) – use a beam of electrons; two types: Scanning electron microscope (SEM) Focuses the electrons on the surface of the specimen; image appears ‘3-D’ Transmission electron microscope (TEM) The beam of electrons goes through the specimen, allowing the internal study of cells A specimen must be treated with a thin layer of metal (usually gold) and then placed in a vacuum chamber before being observed Information is sent to a computer which then projects the image on its screen Living organisms cannot be observed For these reasons as well as cost and practicality these microscopes are not used in high school biology courses

Cell parts ALL cells have these basic features: Plasma membrane Semifluid substance called cytosol Chromosomes (carry genes) Ribosomes (make proteins) Prokaryotic cells – no internal membrane system Bacteria and Archaea Eukaryotic cells – internal membrane system Protists, fungi, plants, animals Separates different areas of the cell for different jobs

Eukaryotic cells Metabolic requirements set upper limits on the size of cells The ratio of surface area to volume of a cell is critical Small cells have a greater surface area relative to volume

Cellular organelles Describe the structure and function of the following: Lysosomes Vacuoles Nucleus Mitochondria Nuclear envelope Chloroplasts Nucleolus Cytoskeleton Ribosomes Cilia and flagella Rough endoplasmic reticulum Cell walls Smooth endoplasmic reticulum Cell junctions Golgi apparatus