Microscope terminology Micrometers – (μm): unit of measurement used for light microscopy (millimeters are too large of a unit). 1 mm = 1000 μm Resolving power: a measure of the smallest distance between two points in the image of an optical system when the two points can be distinguished as separate Parfocal: microscope objectives stay in focus when magnification is changed; i.e., if the microscope is switched from a higher power objective (e.g., 40×) to a lower power objective (e.g., 10×), the object stays in focus

Theories in Biology Theory: proposed explanation for a wide variety of observations and experimental results. 3 important theories in biology: Alvarez Theory Theory of Natural Selection (Evolution) Cell Theory (covered in Biology 30 in detail)

Alvarez Theory Developed by Luis and Walter Alvarez Explain the extinction of the dinosaurs 65 million years ago (Cretaceous-Tertiary extinction event). Small asteroid or a large meteorite impacted planet Earth Caused a great deal of smoke and dust that blocked out sunlight for possibly years, caused a “nuclear winter” effect Evidence based on high levels of rare earth element iridium found at the precise fossil layer of dinosaur extinction

Chicxulub Crater Crater found – off the coast of Yucatan Peninsula in Mexico called the Chicxulub Crater – 180 km across, supports Alvarez Theory

Alvarez Theory - continued Theory has gotten stronger support because of seismic and other data Extinction of the dinosaurs allowed mammals to flourish (we are now in the “Age of Mammals”) – Cenozoic Era

What killed the dinosaurs?

Natural Selection (Evolution) Commonly referred to as “evolution” Developed by Charles Darwin – British Naturalist Term used: “survival of the fittest” Darwin sailed the world oceans on the ship HMS “Beagle”, stopped in the Galapagos Islands (in the Pacific off the coast of Peru) Studied many organisms but most famously studies numerous species of finches Darwin observed many different beak shapes based on the food source the finch relied on.

Evolution - continued Darwin concluded that species that were the most suited for a certain environment survived and reproduce Mutations in a species DNA take place over millions of years and most mutations are harmful. However, some mutations give a new species an adaptive advantage (ex: polar bears – white fur allows them to hide from prey species

Charles Darwin