Tutor profile: Kiera G.
Subject: Basic Chemistry
Why do atoms bond to other atoms?
Atoms are comprised of three main parts; protons, neutrons, and electrons. Protons carry a positive charge, and electrons carry a negative charge; while neutrons lack a charge. The protons and neutrons are within the nucleus, which is the core of the atom, and the number of protons define the element; while the electrons surround the nucleus in layers called shells, which can each hold a certain number of electrons. The charges are canceled when the number of protons equal the number of electrons, so one would assume that to be the stable configuration; however, the shells themselves are most stable when they are full, especially the outermost valence shell. Often, although not always, the valence shell is full at 8 electrons. This is often the state at a different number of electrons than the protons in the nucleus. By sharing (or giving/taking) electrons with another atom, they can fill their valence shells to reach a more stable state.
What are some reasons that detrimental mutations remain in a population?
There are multiple reasons that detrimental mutations may remain in a population. If the mutation is recessive, there may be many carriers for the trait within the population which do not exhibit the detrimental trait; and therefore have the same level of reproductive success as other individuals in the population. When this happens, occasionally the trait is expressed in the offspring when the other parent also carries the trait. Dominant detrimental traits may also remain in the population, when the detrimental trait offers an unexpected benefit to survival in another way, or if the population is reduced to where most of the individuals have the detrimental trait, it can persist indefinitely in the population.
Why can muscles only contract and relax, and cannot forcefully elongate?
Muscle contraction is created from myosin and actin forming cross bridges, and the myosin heads bind to the actin filaments and perform a power stroke. Due to the direction of the myosin heads, they can only bring the Z lines closer together by pulling on the actin connected to the Z lines, causing the muscle to contract. The myosin heads are not able to power stroke in the opposite direction; and even if they could, due to the actin being thin filaments they would be unable to push the Z lines apart.
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