Silicon is an element that, like carbon, has four vacancies in its outer electron shell and therefore has the same bonding chemistry as carbon. Silicon is not found to any significant degree in the molecules found in living systems, however
Does this difference arise because elemental carbon is more abundant than silicon? What other explanations are there for the preferential selection of carbon over silicon as the basis for the molecules of life?
On the basis of Figure 2–4 in your textbook, silicon is actually more abundant in the Earth's crust than carbon, so this is not likely to be the reason that carbon was used preferentially. Carbon might have been the element of choice in living systems because it is lighter than silicon and forms shorter covalent bonds with other elements. Shorter bonds are typically stronger and more stable.
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In a _______ translocation, two non homologous chromosomes exchange parts and no genetic information is gained or lost from the cell in exchange.
Fill in the blank(s) with the appropriate word(s).
Mutations that result in the production of much less of a protein or a protein that functions less efficiently than wild type are
A) null mutations. B) hypomorphic mutations. C) hypermorphic mutations. D) conditional mutations. E) neomorphic mutations.
PET (positron-emission tomography) scans use radioisotopes attached to what substances to detect
abnormalities? a. other radioisotopes b. subatomic particles c. carbon atoms d. glucose or other biological molecules e. plutonium
Countercurrent exchange in the gills of fish is an adaptation that accomplishes which of the following?
a. It limits the amount of blood going to the gills. b. It decreases the thermal gradient between water and blood. c. It improves the ability of blood to dissolve oxygen. d. It maximizes oxygen transfer from water to the blood. e. It maximizes heat retention in the fish.