Why is sexual reproduction more beneficial to a species living in an unpredictable environment than to one living in a constant environment?
What will be an ideal response?
The real benefit in sexual reproduction seems to be that parents produce children that are genetically unlike either parent and that are not genetically identical to each other. Sexual reproduction provides more variation in the population than asexual reproduction could provide, and is an advantage if the environment is variable, because any one combination of the parents' characteristics, however well adapted to the prevailing conditions, may or may not be the best in a new situation.
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Substances that induce an immune response are known as
A) immunogens. B) antigens. C) immunoglobins. D) antigen-presenting cells.
Bacteria can act as probiotic agents, such as species of ________ added to yogurt, to help impart health effects to the intestinal tract.
What will be an ideal response?
Why was it necessary to culture E. coli for multiple generations in the 14N-rich medium to rule out the dispersive model?
a. Nitrogen is frequently lost by cells during meiosis, so multiple generations were required to ensure that residual-free 15N in the cytoplasm was replaced by 14N from the new medium. b. Multiple generations were required to ensure that the samples did not contain significant quantities of DNA from other organisms, which would confound the analysis of E. coli DNA. c. After only a single generation, it was expected that the DNA extracted from E. coli would contain equal proportions of 15N and 14N in both the semi-conservative and dispersive models. d. Multiple generations of replication in the 14N-rich medium were required to rule out the possibility that the changes to the DNA mass were not the result of inevitable statistical noise.
The findings of Pasteur and others have established that
A) living organisms regularly self-assemble (arise spontaneously) from nonliving matter. B) living organisms do not arise from nonliving matter today, nor did they arise from nonlife in the past. C) advanced organisms cannot arise from nonliving matter, but simple microbial life often does arise from nonlife today. D) life does not arise from nonliving matter today, but in the conditions of early Earth, such an event could have occurred.