Relative dating uses ___________ to estimate how old a fossil is.
A. Embryonic structures
B. Radioactive structures
C. A molecular clock
D. Structural features
E. Depth within rock layers
E. Depth within rock layers
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The number of major histocompatability (MHC) protein combinations possible in a given population is enormous. However, an individual in that diverse population has a far more limited array of MHC molecules because _____
A) the MHC proteins are made from several different gene regions that are capable of rearranging in a number of ways B) MHC proteins from one individual can only be of class I or class II C) each of the MHC genes has a large number of alleles, but each individual only inherits two for each gene D) once a B cell has matured in the bone marrow, it is limited to two MHC response categories E) once a T cell has matured in the thymus, it can only respond to two MHC categories
Which of the following represents a germ layer?
a. blastula b. inner cell mass c. ectoderm d. zygote
Chloroplasts are thought to have originated as
endosymbiotic associations when aerobic bacteria engulfed photosynthetic cells. This relationship was favored by the production of ___________ by the endosymbiont. a. glucose b. hydrogen ions c. ATP d. oxygen e. water
Which statement is characteristic of endocrine glands?
a. They release chemical signals into synapses. b. They produce chemical signals that are always stimulatory. c. They are controlled by only negative feedback mechanisms. d. They secrete chemical signals in small amounts over short periods of time. e. Their activity is limited to brain tissue.