The system of flexing and extending muscles makes movement of appendages easy to understand. But how are some actions possible (sticking out your tongue, beating of your heart) when these structures have no bone structure with opposing flexors and extensors in them?
A. Muscle cells running diagonally or crosswise amidst the longitudinal muscles must contract and force the long relaxed muscle cells to elongate.
B. These structures must be empty chambers, and fluids forced into them expand them.
C. One set of muscle cells must therefore be able to both contract and expand.
D. This cannot be explained at present.
Answer: A
You might also like to view...
After mutagenesis, the nitrogen-fixing bacterium Sinorhizobium meliloti could no longer colonize Medicago truncatula plants. This inability to colonize was due to the absence of recognition by the host plant
Which of the following genes is most likely the site of the mutation in these bacteria? A) nitrogenase B) flavonoid-synthesizing enzyme C) Nod factors D) leghemoglobin E) peptidoglycans of the bacterial cell wall
All of the following are located on the exterior
surface of a prokaryote EXCEPT a. flagellum b. pilus c. plasma membrane d. capsule e. none of these
While looking for evidence of early human or humanlike individuals, you discover a cave in which
there are paintings, engravings, and sculptures. Which of the following most likely lived in the cave at some time during their life? a. Australopithecus africanus b. Neandertals c. Homo erectus d. Cro-Magnons e. Homo habilis
DNA barcoding:
A: is a type of reverse genetics. B: is the most commonly used type of DNA fingerprinting used by the FBI. C: attempts to provide a unique sequence identifier for all life forms. D: is based mainly on repetitive DNA. E: is used for prenatal genetic screening.