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Q: A very small artery that leads to a capillary is known as what? Read this paragraph and choose the correct option from the provided answers: Arterioles An arteriole is a very small artery that leads to a capillary. Arterioles have the same three tunics as the larger vessels, but the thickness of each is greatly diminished. The critical endothelial lining of the tunica intima is intact. The tunica media is restricted to one or two smooth muscle cell layers in thickness. The tunica externa remains but is very thin (see Figure 20.4). With a lumen averaging 30 micrometers or less in diameter, arterioles are critical in slowing downor resistingblood flow and, thus, causing a substantial drop in blood pressure. Because of this, you may see them referred to as resistance vessels. The muscle fibers in arterioles are normally slightly contracted, causing arterioles to maintain a consistent muscle tonein this case referred to as vascular tonein a similar manner to the muscular tone of skeletal muscle. In reality, all blood vessels exhibit vascular tone due to the partial contraction of smooth muscle. The importance of the arterioles is that they will be the primary site of both resistance and regulation of blood pressure. The precise diameter of the lumen of an arteriole at any given moment is determined by neural and chemical controls, and vasoconstriction and vasodilation in the arterioles are the primary mechanisms for distribution of blood flow. Choices: - capillary junction - vein - arterium - arteriole A:
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arteriole

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Q: What were the first forms of life on earth? Read this paragraph and choose the correct option from the provided answers: Prokaryotes, the First Inhabitants of Earth When and where did life begin? What were the conditions on Earth when life began? Prokaryotes were the first forms of life on Earth, and they existed for billions of years before plants and animals appeared. The Earth and its moon are thought to be about 4.54 billion years old. This estimate is based on evidence from radiometric dating of meteorite material together with other substrate material from Earth and the moon. Early Earth had a very different atmosphere (contained less molecular oxygen) than it does today and was subjected to strong radiation; thus, the first organisms would have flourished where they were more protected, such as in ocean depths or beneath the surface of the Earth. At this time too, strong volcanic activity was common on Earth, so it is likely that these first organismsthe first prokaryoteswere adapted to very high temperatures. Early Earth was prone to geological upheaval and volcanic eruption, and was subject to bombardment by mutagenic radiation from the sun. The first organisms were prokaryotes that could withstand these harsh conditions. Microbial Mats Microbial mats or large biofilms may represent the earliest forms of life on Earth; there is fossil evidence of their presence starting about 3.5 billion years ago. A microbial mat is a multi-layered sheet of prokaryotes (Figure 22.2) that includes mostly bacteria, but also archaea. Microbial mats are a few centimeters thick, and they typically grow where different types of materials interface, mostly on moist surfaces. The various types of prokaryotes that comprise them carry out different metabolic pathways, and that is the reason for their various colors. Prokaryotes in a microbial mat are held together by a glue-like sticky substance that they secrete called extracellular matrix. The first microbial mats likely obtained their energy from chemicals found near hydrothermal vents. A hydrothermal vent is a breakage or fissure in the Earth's surface that releases geothermally heated... Choices: - aniryotes - eukaryotes - protists - prokaryotes A:
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prokaryotes

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Q: Cell communication that occurs over short distances is known as what? Read this paragraph and choose the correct option from the provided answers: Cells that are communicating may be right next to each other or far apart. In juxtacrine signaling , also known as contact-dependent signaling, two adjacent cells must make physical contact in order to communicate. Cell communication may also occur over short distances, which is known as paracrine signaling , or over large distances, which is known as endocrine signaling . Choices: - hypersignaling - contraposition signaling - cell echo - paracrine signaling A:
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paracrine signaling