A birth defect known as spina bifida results from the incomplete closure of the embryonic neural tube. Which germ layer is affected?
A) endoderm B) mesoderm C) ectoderm D) myotome
Answer: C
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Given the following list of organic molecules, which includes hormones?
1. nucleic acid derivatives 2. polypeptides 3. steroids 4. proteins A) 1, 3, 4 B) 1, 2, 3 C) 2, 3, 4 D) 1, 2, 3, 4 E) 1, 2, 4
Individual cells of a ________ produce secretions.
Fill in the blank(s) with the appropriate word(s).
The processes of intramembranous and endochondral ossification are similar in several respects. Which of the following statements applies to both intramembranous ossification and endochondral ossification?
A. Both processes form woven bone. B. In both processes, bone replaces cartilage. C. Chondrocytes participate in both processes. D. Both processes require a precursor of connective tissue membranes. E. Both only form flat bones.
A scientist measuring the rate of uptake of radiolabeled alanine by cultured cells finds that rates are faster when the experiments are carried out in a buffered, balanced salts solution than when the experiments are carried out in a complete (containing all nutrients required for survival and growth) medium. The most likely explanation for this observation is
a. the concentration gradient for alanine is steeper in the former case than the latter. b. the crenation (shrinkage of cells) in the salts solution increases the surface area-to-volume ratio for the cells increasing the rate of diffusion. c. the absence of amino acids in the balanced salts solution decreases the abundance of molecules competing for transport, and therefore increases the apparent transport rate. d. the temperature of the balanced salt solution is higher, so rates of transport are greater. e. no response provides a valid answer.