Answer the following question given this paragraph: Nuclear Fuels Nuclear fuel consists of a fissionable isotope, such as uranium-235, which must be present in sufficient quantity to provide a self-sustaining chain reaction. In the United States, uranium ores contain from 0.050.3% of the uranium oxide U3O8; the uranium in the ore is about 99.3% nonfissionable U-238 with only 0.7% fissionable U-235. Nuclear reactors require a fuel with a higher concentration of U-235 than is found in nature; it is normally enriched to have about 5% of uranium mass as U-235. At this concentration, it is not possible to achieve the supercritical mass necessary for a nuclear explosion. Uranium can be enriched by gaseous diffusion (the only method currently used in the US), using a gas centrifuge, or by laser separation. In the gaseous diffusion enrichment plant where U-235 fuel is prepared, UF6 (uranium hexafluoride) gas at low pressure moves through barriers that have holes just barely large enough for UF6 to pass through. The slightly lighter 235UF6 molecules diffuse through the barrier slightly faster than the heavier 238UF6 molecules. This process is repeated through hundreds of barriers, gradually increasing the concentration of 235UF6 to the level needed by the nuclear reactor. The basis for this process, Graham's law, is described in the chapter on gases. The enriched UF6 gas is collected, cooled until it solidifies, and then taken to a fabrication facility where it is made into fuel assemblies. Each fuel assembly consists of fuel rods that contain many thimble-sized, ceramic-encased, enriched uranium (usually UO2) fuel pellets. Modern nuclear reactors may contain as many as 10 million fuel pellets. The amount of energy in each of these pellets is equal to that in almost a ton of coal or 150 gallons of oil. Q: Uranium is an important part of the process used to harness which type of power? Choices: - gravitational - solar - wind - nuclear A:
nuclear
Answer the following question given this paragraph: The nervous system is made up of nerves. A nerve is a bundle of nerve cells. A nerve cell that carries messages is called a neuron. The messages carried by neurons are called nerve impulses. Q: A nerve cell that carries messages is called a? Choices: - mitochondria - stem cell - platelet - neuron A:
neuron
Q: Answer the following question given this paragraph: The half-life of titanium-44 is 60.0 y. A sample of titanium contains 0.600 g of titanium-44. How much remains after 100.0 y?. Q: Name the type of system that a jellyfish does not have? Choices: - nervous - reproductive - hereditary - circulatory A:
A: circulatory
Question: Answer the following question given this paragraph: The earliest placental mammals may have evolved about 110 million years ago. The ancestor of placental mammals may be the extinct genus Eomaia . Fossils of Eomaia have been found in what is now China. It was only about 10 centimeters (4 inches) long. It was a tree climber and probably ate insects and worms. Eomaia had several traits of placental mammals. Figure below shows how Eomaia may have looked. Q: What may be the ancestor of placental mammals? Choices: - fungi - spirogyra - amphibians - eomaia A:
Answer: eomaia
*Question*
Answer the following question given this paragraph: In sexually reproducing species, chromosomes are present in cells in pairs. Chromosomes in the same pair are called homologous chromosomes. They have the same genes at the same loci. These may be the same or different alleles. During meiosis, when gametes are produced, homologous chromosomes separate. They go to different gametes. Thus, the alleles for each gene also go to different gametes. Q: What are chromosomes in the same pair called? Choices: - homogeneous chromosomes - regulated chromosomes - reversible chromosomes - homologous chromosomes A:
**Answer**
homologous chromosomes
*Question*
Answer the following question given this paragraph: Q: Are birds and mammals mainly exothermic or endothermic? Choices: - autotrophic - hypothermic - exothermic - endothermic A:
**Answer**
endothermic