When membrane-bound receptors like HER2 bind to molecules outside of a human cell, they must move laterally within the bilayer and also bind to a second HER2 receptor, forming a dimer (2-part molecule), in order for the signal to be further transferred inside the cell through the membrane. This is possible because the cell membrane is
A. a selectively permeable barrier.
B. both selectively permeable and a fluid mosaic.
C. hydrophobic.
D. rigid like a cell wall.
E. a fluid mosaic.
E. a fluid mosaic.
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An immediate source of energy for exercising muscle cells is _____
a. creatine phosphate b. aerobic respiration c. anaerobic respiration d. fermentation e. glycolysis
At the arteriole end of the capillary, more fluid leaves
the capillary than enters as a result of a. osmotic pressure. b. hydrostatic pressure c. gap junctions. d. vasodilation. e. all of these.
Why do harmful agents cause the most severe birth defects during the embryonic period?
A) This is a period of rapid differentiation when cells and tissues acquire specific functions and organs form. B) This is the period when substances pass most easily through the placenta. C) The mother's hormones are at the highest levels at this time. D) The embryo has not yet implanted into the uterus.
The best explanation for the phenotypic differences between humans and chimps despite the great similarities in their gene-coding sequences is
A. the vast differences in exons between their genomes. B. the "junk" DNA of humans contains important sequences not present in chimps. C. the vast differences in the introns between their genomes. D. differences in gene expression between species.