Which of the following is a reason for the occurrence of a lag phase in a bacterial growth curve?
A. The organisms may have been injured and require time to recover.
B. The medium may be different from the previous growth medium so that the cells must synthesize new enzymes to use different nutrients.
C. The cells may be old and depleted of ATP, essential cofactors, and ribosomes that must be synthesized before growth can begin.
D. All of these are potential reasons.
Answer: D
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What is the function of xylem?
a. It conducts water downward in the plant. b. It transports food upward in the plant. c. It transports minerals and water throughout the plant. d. It transports photosynthetic materials from stem to leaf. e. It slows the evaporation of water from the plant.
The white cliffs of Dover are composed mostly of foraminiferans shells. These organisms move by pseudopodia and feed by phagocytosis. Foraminiferans are an example of which of the following?
a. A protozoa b. An apicomplexan c. An algae d. A slime mold e. A diatom
A testcross consists of
a. a cross of two pure-breeding forms to find out which form of a gene is dominant. b. a cross between two unknown forms to determine their genotypes. c. a cross between an offspring and its parent. d. a cross of an F1 hybrid to an individual that is homozygous recessive. e. a cross of two F2 individuals to produce an F3 generation.
In the annual rings of woody trees, how does the cell size within the xylem of the spring and summer wood compare to the fall and winter wood?
A. It is more dense. B. It is younger. C. The cells are larger. D. It has smaller vessels. E. The cell walls are thicker.