According to geological evidence, oxygen levels in the atmosphere began to increase about 2 billion years ago. This favored the evolution of multicellular, terrestrial organisms because:
A. More oxygen was available for cell respiration
B. More oxygen was available for photosynthesis
C. Some of the oxygen was used to help establish the ozone layer, and protect against harmful UV radiation
D. All multicellular organisms require oxygen to survive
E. More than one above is correct
Answer: E. More than one above is correct
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Gardeners sometimes plant clover between productive growing seasons. Why would this practice be beneficial?
A. Several types of nitrogen-fixing bacteria form a symbiotic relationship with the roots of clover. This would increase the amount of nitrogen in the soil available for subsequent seasons of other plants' growth. B. Clover is consumed by a number of animals. This would encourage the animals to feed/graze on the areas, leaving behind nitrogen-rich manure that would act as a natural fertilizer for subsequent seasons of other plants' growth. C. Clover is a unique plant that is capable of atmospheric nitrogen-fixation (pulling nitrogen directly out of the air and turning it into ammonia or amino acids). This directly provides nitrogen compounds for the soil for subsequent seasons of other plants' growth. D. The beneficial effect is more for water retention and elimination of soil erosion in between growing seasons. It has nothing to do with nitrogen compounds in the soil.
Transducing virulent phages do not lyse the cells they invade because
A. transformation is taking place in the phage and this is transferred to the bacterium. B. bacterial DNA has replaced critical viral DNA in the phage. C. their virulence is dependent on the bacteria and virus replicating together. D. the lytic genes are unable to enter during penetration and are shed outside the host.
Four of the five regions listed below are located
within the spinal cord. Select the exception. a. dorsal root ganglion b. interneurons between sensory input and motor outputs c. major ascending and descending nerve tracts d. interneurons connecting with other neurons e. direct reflex connections between sensory and motor neurons
_______ are responsible for antibody-mediated immunity
a. Natural killer cells b. Macrophages c. T cells d. B cells e. Dendritic cells