Q: Answer the following question given this paragraph: levels. If a solid has a filled valence band with a relatively low-lying empty band above it (a conduction band), then electrons can be excited by thermal energy from the filled band into the vacant band where they can then migrate through the crystal, resulting in electrical conductivity. Electrical insulators are poor conductors because their valence bands are full. Semiconductors have electrical conductivities intermediate between those of insulators and metals. The electrical conductivity of semiconductors increases rapidly with increasing temperature, whereas the electrical conductivity of metals decreases slowly with increasing temperature. The properties of semiconductors can be modified by doping, or introducing impurities. Adding an element with more valence electrons than the atoms of the host populates the conduction band, resulting in an n-type semiconductor with increased electrical conductivity. Adding an element with fewer valence electrons than the atoms of the host generates holes in the valence band, resulting in a p-type semiconductor that also exhibits increased electrical conductivity. Q: What happens to the electrical conductivity of metals when placed in a pot of boiling water? Choices: - stays the same - increases slowly - increases quickly - decreases slowly A:
A: decreases slowly

Q: Answer the following question given this paragraph: The strong affinity of concentrated sulfuric acid for water makes it a good dehydrating agent. It is possible to dry gases and immiscible liquids that do not react with the acid by passing them through the acid. Sulfuric acid is a strong diprotic acid that ionizes in two stages. In aqueous solution, the first stage is essentially complete. The secondary ionization is not nearly so complete, and HSO 4 is a moderately strong acid (about 25% ionized in solution of a HSO 4 salt: Ka = 1.2 102). Being a diprotic acid, sulfuric acid forms both sulfates, such as Na2SO4, and hydrogen sulfates, such as NaHSO4. Most sulfates are soluble in water; however, the sulfates of barium, strontium, calcium, and lead are only slightly soluble in water. Among the important sulfates are Na2SO410H2O and Epsom salts, MgSO47H2O. Because the HSO 4 ion is an acid, hydrogen sulfates, such as NaHSO4, exhibit acidic behavior, and this compound is the primary ingredient in some household cleansers. Hot, concentrated sulfuric acid is an oxidizing agent. Depending on its concentration, the temperature, and the strength of the reducing agent, sulfuric acid oxidizes many compounds and, in the process, undergoes reduction to SO2, HSO 3 , SO 3 2, S, H2S, or S2. Sulfur dioxide dissolves in water to form a solution of sulfurous acid, as expected for the oxide of a nonmetal. Sulfurous acid is unstable, and it is not possible to isolate anhydrous H2SO3. Heating a solution of sulfurous acid expels the sulfur dioxide. Like other diprotic acids, sulfurous acid ionizes in two steps: The hydrogen sulfite ion, HSO 3 , and the sulfite ion, SO 3 2, form. Sulfurous acid is a moderately strong acid. Ionization is about 25% in the first stage, but it is much less in the second (Ka1 = 1.2 102 and Ka2 = 6.2 108). In order to prepare solid sulfite and hydrogen sulfite salts, it is necessary to add a stoichiometric amount of a base to a sulfurous acid solution and then evaporate the water. These salts also form from the reaction of SO2 with... Q: The strong affinity of concentrated sulfuric acid for water makes it a good agent of what? Choices: - diluting - hydrating - concentrating - dehydrating A:
A: dehydrating

Q: Answer the following question given this paragraph: Matched pairs of chromosomes in a diploid organism are called homologous ("same knowledge") chromosomes. Homologous chromosomes are the same length and have specific nucleotide segments called genes in exactly the same location, or locus. Genes, the functional units of chromosomes, determine specific characteristics by coding for specific proteins. Traits are the variations of those characteristics. For example, hair color is a characteristic with traits that are blonde, brown, or black. Each copy of a homologous pair of chromosomes originates from a different parent; therefore, the genes themselves are not identical. The variation of individuals within a species is due to the specific combination of the genes inherited from both parents. Even a slightly altered sequence of nucleotides within a gene can result in an alternative trait. For example, there are three possible gene sequences on the human chromosome that code for blood type: sequence A, sequence B, and sequence O. Because all diploid human cells have two copies of the chromosome that determines blood type, the blood type (the trait) is determined by which two versions of the marker gene are inherited. It is possible to have two copies of the same gene sequence on both homologous chromosomes, with one on each (for example, AA, BB, or OO), or two different sequences, such as AB. Minor variations of traits, such as blood type, eye color, and handedness, contribute to the natural variation found within a species. However, if the entire DNA sequence from any pair of human homologous chromosomes is compared, the difference is less than one percent. The sex chromosomes, X and Y, are the single exception to the rule of homologous chromosome uniformity: Other than a small amount of homology that is necessary to accurately produce gametes, the genes found on the X and Y chromosomes are different. Q: What functional units of chromosomes determine specific characteristics by coding for specific proteins? Choices: - chromosomes - DNA - cells - genes A:
A: genes

Q: Answer the following question given this paragraph: Echinoderms lack respiratory and excretory systems. Instead, the thin walls of their tube feet allow oxygen to diffuse in and wastes to diffuse out. Echinoderms also lack a centralized nervous system. They have an open circulatory system and lack a heart. On the other hand, echinoderms have a well-developed coelom and a complete digestive system. Echinoderms use pheromones to communicate with each other. They detect the chemicals with sensory cells on their body surface. Some echinoderms also have simple eyes ( ocelli ) that can sense light. Like annelids, echinoderms have the ability to regenerate a missing body part. Q: Echinoderms lack what type of system that in humans consists of the brain and spinal cord? Choices: - autonomic system - endocrine system - peripheral nervous system - centralized nervous system A:
A: centralized nervous system