Human embryos contain a dorsal, hollow nerve cord, a notochord, pharyngeal slits, and a post-anal tail. What other phylum contains these shared characteristics?
a. Mollusca
b. Osteichthyes
c. Amphibians
d. Chordata
Answer: d. Chordata
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DNA varies from species to species in _____
a. how many adenine bases bind with thymine rather than with cytosine b. whether DNA is a double or a single helix c. the variation in the backbone structure d. how many different bases it contains e. the sequence of its base pairs
Embryonic stem cells derived from blastocysts are called pluripotent because they ________
A. are viable under a wide range of laboratory conditions B. can form most cells, tissues, and organs of the human body C. can form all cells, tissues, and organs of the human body D. are viable under a wide range of laboratory conditions and can form most cells, tissues, and organs of the human body E. are viable under a wide range of laboratory conditions and can form all cells, tissues, and organs of the human body
Phosphorus, which is often a limiting nutrient in ecosystems, is important because it
A) is found only in sedimentary rocks. B) is part of the hydrologic cycle. C) evaporates quickly. D) is necessary for the production of cellulose so that autotrophs can grow and provide food for heterotrophs. E) is needed for molecules such as adenosine triphosphate (ATP), cell membranes, and nucleic acids.
Botulinum toxin- A toxin produced by the bacterium Clostridium botulinum.Known for sometimes lethal poisoning from infected meat products. In modern controlled medical or cosmetic use, the very same toxin is known as Botox.Tetanus toxin- Another very potent neurotoxin produced by Clostridium tetani.Strichnine- A highly poisonous alkaloid produced by the Strychnos nux-vomica tree,historically used to kill rats and other pests.Botulinum toxin, or "botox," has become popular for cosmetic surgery. The toxin prevents neurosecretory vesicles from docking at the plasma membrane and releasing neurotransmitter. How would this toxin affect the neuromuscular junction?
A. Since ACh is not released, the muscles are not activated to contract and remain relaxed. B. Buildup of ACh causes promiscuous activation of all nearby sensory neurons. C. Buildup of ACh leaks back into the brain, creating a calming effect. D. Since ACh is not released, the muscles stay in a state of repeated contraction.