<span>It may be difficult for ecologists to determine the size of a bird population if that population migrates to different locations throughout the year. During migration, some birds may split off from the group and not return, others may die, and still others may join. Therefore, the bird population will be in constant flux. It is hard to know, when the birds return to their prior location, if the population consists of the same group of birds (in addition to deaths and births) or whether it has grown or shrank through other means. However, to estimate the size, an ecologist can track a migratory flock through several years, counting each year to get a general sense of the population size. Additionally, given one measurement, an ecologist could consider the average lifespan and birth rates of the population to extrapolate the size of the population in subsequent years.</span>
Answer:
This is an example of Harrison's central nervous system working closely with his autonomic nervous system to give him energy and awareness to escape.
Explanation:
Harrison interprets the presence of the group of teenagers as an imminent danger and so he is on the run, which corresponds to a set of reactions that are triggered in the human body when a danger is around. At this point, the central nervous system and the subtonic nervous system are working together to get the adrenaline in Harrison's body to rise to a level that allows him to escape the group of teenagers. The central nervous system was then responsible for receiving and processing information that indicates to Harrison that he may be in danger. On the other hand, the autonomic nervous system is responsible for regulating the body's involuntary responses, being responsible for controlling various vital functions and at this time for the release of adrenaline in response to the dangerous situation.
Answer: Polychlorinated biphenyls (PCBs) are a group of manmade chemicals. They are oily liquids or solids, clear to yellow in color, with no smell or taste. PCBs are very stable mixtures that are resistant to extreme temperature and pressure. PCBs were used widely in electrical equipment like capacitors and transformers. They also were used in hydraulic fluids, heat transfer fluids, lubricants, and plasticizers. The primary company that made PCBs in the United States was Monsanto Inc., mainly using the name Aroclor. Commercial production of PCBs ended in 1977 because of health effects associated with exposure. In 1979, the U.S. Environmental Protection Agency (USEPA) banned the use of PCBs; however, PCBs are still present in many pre-1979 products.
Answer:
B
Explanation:
Natural selection and selective breeding can cause changes in animals and plants. The difference between the two is that natural selection happens naturally, but selective breeding only occurs when humans intervene. For this reason, selective breeding is sometimes called artificial selection.
Gel electrophoresis separates DNA fragments according to size<span>. Samples containing a mixture of DNA molecules of different sizes are loaded on to the gel. When an electric current is applied DNA moves towards the positive electrode since DNA is negatively charged.</span>