The appearance of photosynthetic cyanobacteria and aerobic bacteria
A. led to the development of an oxidizing atmosphere on Earth.
B. led to the formation of the ozone shield.
C. The amount of UV light reaching the Earth was reduced and chemical evolution slowed.
D. All of the choices are correct.
Ans: D. All of the choices are correct.
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Two species of tree frogs that live sympatrically in the northeastern United States differ in ploidy: Hyla chrysoscelis is diploid, and Hyla versicolor is tetraploid. The frogs are identical in appearance, but their mating calls, which females use to find
mates, differ. Which difference most likely evolved first? A) polyploidy B) difference in mating calls C) Polyploidy and different mating calls must have evolved at the same time.
Biologists around the world spend a great deal of time studying the cytoskeleton of cells
Some of the tools they use in their research include chemicals that interfere with the structure of the cytoskeletal elements or with the activities of the motor proteins that associate with the cytoskeleton to facilitate movement. For example, a family of compounds called cytochalasins disrupts the normal assembly and disassembly of microfilaments. Another compound called colchicine binds to tubulin and prevents the assembly of microtubules. The function of dynein is prevented by a compound known as EHNA (erythro-9-[3-2- (hydroxynonyl)] adenine), and blebbistatin inhibits the activity of myosin. Use this information to answer the following questions. Based on this information, where would you predict blebbistatin to have the greatest effect? A. sperm cell motility B. leading edge formation of a migrating fibroblast C. the contraction at the trailing edge of a fibroblast D. Blebbistatin would likely have no effect on any of these examples of cell movement.
The most commonly used unit for measuring cell size is a ____
a. decimeter (dm) b. centimeter (cm) c. millimeter (mm) d. micrometer (mm) e. nanometer (nm)
Resistance activities increase muscle mass by ____
a. stretching muscles b. increasing the number of mitochondria in cells c. encouraging the synthesis of more actin and myosin filaments d. encouraging the production of more muscle fibers e. converting red fibers to white fibers