How does Catling define the “biosphere,” and what additional elements do other definitions sometimes include?
The sum of all living and dead organisms. Other definitions are broader, including the various environments in which life is found.
Compare the distribution of carbon mass between the land and the oceans in Earth’s modern biosphere.
On land, there are 2×10^15 kg of carbon, with 30–50% of that being living matter. In the oceans, there is 1×10^15 kg of carbon, though only 0.1–0.2% of it is living.
What is the estimated significance of Earth’s subsurface biosphere in terms of total living biomass?
The exact size of the subsurface biosphere is uncertain, but it is considered potentially significant. Estimates suggest it may account for 1% to 30% of Earth’s total living biomass.
Which group of organisms constitutes the largest fraction of Earth’s total biomass?
Plants. Most of Earth’s biomass is terrestrial rather than marine or deep subsurface.
What are arthropods, and what is their status regarding Earth’s animal biomass?
Arthropods are invertebrates characterized by exoskeletons and segmented bodies. They are highly successful, making up half of the total animal biomass on Earth.
Define a “cell” and describe the fundamental physical difference between a prokaryotic and eukaryotic cell.
Cells are living, microscopic structures where the interior contents are separated from the external environment. Eukaryotic cells contain a nucleus separated by a membrane, whereas prokaryotic cells lack a nucleus.
How do prokaryotic and eukaryotic cells typically differ in size?
Prokaryotic cells are generally smaller, typically ranging from 0.1 to 5 microns across. In contrast, eukaryotic cells are much larger, usually measuring between 10 and 100 microns.
Explain the concept of endosymbiosis and its importance in the evolutionary history of eukaryotic cells.
Endosymbiosis is a form of symbiosis where two organisms benefit from each other while one lives inside the other. This process is crucial to eukaryotes because it is how they acquired complex internal organelles.
According to current scientific belief, what were the specific prokaryotic ancestors of mitochondria and chloroplasts?
Mitochondria are believed to have descended from endosymbiotic bacteria. Chloroplasts are believed to have descended from endosymbiotic cyanobacteria.
Describe the three domains of life currently used to categorize all living organisms.
The three domains are Archaea (prokaryotic, often extremophiles), Bacteria (prokaryotic), and Eukarya (complex organisms with nuclei). Archaea and Bacteria are single-celled, while Eukarya can be single-celled or multicellular.
Are Archaea or Bacteria more likely to exist in extreme conditions?
Archaea
Eukarya cells are roughly how much longer than prokaryotic cells?
10x
How does the genetic material of Eukarya differ from that of Archaea and Bacteria?
Eukarya have multiple open-ended strands of DNA stored within a nucleus. Archaea and Bacteria typically have a single circular strand of DNA and no nucleus.
What specific chemical characteristics make archaean cell membranes “hardier” than those of bacteria or eukaryotes?
Archaean membranes are stronger and more durable because they use ether bonds instead of ester bonds. They are also “stickier” and harder to separate due to branched side chains rather than linear ones.
On the tree of life, Archaea are more closely related to _____ than they are to Bacteria.
Eukarya
Define taxonomy and identify the specific level of classification referred to as a “taxon.”
Taxonomy is the formal classification of life. A “taxon” (plural: taxa) is any level of this classification system, such as a kingdom or a genus.
List the taxonomic categories of life in order from most general to most specific.
The categories from general to specific are: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species. A human, for example, is in the Domain Eukarya and Species Sapiens.
What are valence electrons, and what is their role in chemical reactions?
A valence electron is an electron located in the outermost shell of an atom, farthest from the nucleus. These are the specific electrons that participate in chemical reactions and bonding with other atoms.
Distinguish between covalent bonds and ionic bonds.
Covalent bonds occur when two atoms or ions share an electron to achieve stability. Ionic bonds occur when one atom (the donor) transfers an electron entirely to another atom (the acceptor).
Explain the chemical process of “reduction” and define what a “reducing agent” does.
Reduction is the process of gaining electrons, which decreases the oxidation state of an atom. A reducing agent is the atom that provides the electrons, causing another atom to be reduced.
Explain the chemical process of “oxidation” and define what an “oxidizing agent” does.
Oxidation is the process of losing electrons, which increases the oxidation state of an atom. An oxidizing agent is the atom that accepts the electrons, causing another atom to be oxidized.
How does the periodic table organize elements into “periods,” and what is the formula to determine the electron capacity of a shell in period n?
Each row of the periodic table is called a period. For elements in any period n, the outermost shell has space for 2n^2 electrons.
In the formation of table salt (NaCl), describe the exchange of electrons and identify which ions become the cation and anion.
In table salt, sodium (Na) gives an electron to chlorine (Cl). The sodium becomes a positively charged cation, while the chlorine becomes a negatively charged anion called chloride.
What is each vertical column of the periodic table called?
A group.
Elements within the same group of the periodic table share similar bonding properties.
