Why must the lenses and specimen be in a vacuum when using an electron microscope?
A. Electrons are highly radioactive, and the chamber must be completely sealed and under vacuum to prevent them from escaping and contaminating the lab area.
B. The vacuum bends rays of visible light through the lenses and specimen so that details of the specimen can be clearly visualized from all angles.
C. Electrons are particles but there are other particles in air as well. Without a vacuum, the electrons would strike and be scattered by the particles within the air.
D. The vacuum fixing the specimen to the slide grid. Without fixing the specimen by vacuum, it would slide off and we wouldn't be able to visualize it.
E. None of the answer choices is true.
Answer: C. Electrons are particles but there are other particles in air as well. Without a vacuum, the electrons would strike and be scattered by the particles within the air.
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Which of the following statements is true regarding cell-cell adhesion?
A) Adhesion is coordinated with many cellular processes except cell survival. B) Adhesion molecules include plakoglobulin, which cements two cells together. C) Adherens junctions are exclusive to plant cells. D) Adhesive junctions are characterized by the attachment of long molecules of hyaluronate. E) Adhesive junctions are dynamic in response to cellular signals.
Which of the following traits is unique to arthropods?
a. Appendages b. Segmentation c. A ventral nerve cord d. A dorsal anterior brain e. An exoskeleton
Most taxonomic groups with simple multicellular organisms never gave rise to complex multicellular descendants
A. true B. false