A. Unity and Diversity

Hydrogen bond in water

Weak bond between the slightly positive H of one water molecule and the slightly negative O of another, due to water's polarity

Cohesion

Attraction between water molecules due to hydrogen bonding; responsible for surface tension and transpiration pull in plants

Adhesion

Attraction between water molecules and other polar surfaces (e.g. xylem walls); works with cohesion in water transport

Specific heat capacity of water

High — water resists temperature change, helping organisms/habitats maintain thermal stability

Water as a solvent

Polar water molecules surround and dissolve charged/polar solutes (hydrophilic substances), important for transport in blood/cytoplasm

Thermal properties relevant to life

High latent heat of vaporization (cooling effect via sweating/transpiration); high boiling point relative to molecular size due to hydrogen bonding

Hydrophilic vs hydrophobic

Hydrophilic = polar/charged, dissolves in water; hydrophobic = non-polar, repels water (e.g. lipids)

Nucleotide structure

Pentose sugar + nitrogenous base (attached at C1') + phosphate group (attached at C5')

DNA vs RNA sugar

DNA = deoxyribose (no OH at C2'); RNA = ribose (has OH at C2')

Purines

Adenine and Guanine (double ring)

Pyrimidines

Cytosine and Thymine (RNA: Uracil instead of Thymine) (single ring)

Phosphodiester bond

Covalent bond linking nucleotides, between the C5' phosphate of one sugar and the C3' OH of the next; formed by condensation

Base pairing rule

A-T (2 H-bonds), G-C (3 H-bonds); purine always pairs with pyrimidine to keep helix width constant

DNA double helix structure

Two antiparallel strands (5'→3' and 3'→5'), sugar-phosphate backbone outside, bases project inward and pair via H-bonds

Cell theory (3 tenets)

All living organisms are composed of cells; cells are the smallest units of life; cells arise only from pre-existing cells

Exception to cell theory

Striated muscle cells — formed by fusion of multiple cells, resulting in large multinucleate cells

Spontaneous generation

The (disproven) idea that living organisms can arise from non-living matter

How spontaneous generation was disproven

Pasteur's swan-neck flask experiment — broth stayed sterile while curved neck trapped microorganisms; grew microbes once neck broken/tilted

Endosymbiotic theory

Mitochondria and chloroplasts originated from free-living prokaryotes engulfed by a host cell, forming a mutualistic relationship

Endosymbiotic theory evidence

Double membrane; own circular DNA; 70S ribosomes (matching prokaryotes); independent binary fission; similar size/shape to prokaryotes

RNA world hypothesis

RNA was likely the first genetic material because it can both store information and catalyze reactions (as ribozymes), solving the DNA-needs-protein/protein-needs-DNA problem

Prokaryotic vs eukaryotic cells

Prokaryotes lack a nucleus/membrane-bound organelles, have circular DNA, smaller (70S) ribosomes; eukaryotes have a nucleus, membrane-bound organelles, larger (80S) ribosomes

Organelles unique to plant cells

Cell wall (cellulose), chloroplasts, large permanent vacuole

Organelles unique to animal cells

Centrioles, lysosomes (common), small/no permanent vacuole

Rough vs smooth ER

Rough ER (ribosomes attached) — protein synthesis/processing; Smooth ER — lipid synthesis, detoxification

Golgi apparatus function

Modifies, packages, and sorts proteins/lipids for secretion or delivery to organelles

Cell surface area to volume ratio

Decreases as cell size increases, limiting maximum cell size — surface area must be sufficient for exchange of materials

Function of mitochondria

Site of aerobic respiration/ATP production; has own DNA and 70S ribosomes

Structure of a virus

Nucleic acid core (DNA or RNA) surrounded by a protein coat (capsid); some have a lipid envelope

Why viruses are not considered living

No cell structure, cannot reproduce independently (need a host cell's machinery), no independent metabolism

Lytic cycle (brief)

Virus attaches to host, injects genetic material, host machinery replicates virus components, new viruses assemble and burst out, destroying the host cell

Retrovirus

A virus that uses RNA as its genetic material and reverse transcriptase to convert RNA into DNA inside the host cell (e.g. HIV)

Specificity of viruses

Viruses infect specific host cells based on surface receptor compatibility (e.g. HIV targets cells with CD4 receptors)

Binomial nomenclature

Two-part naming system: genus (capitalized) + species (lowercase), both italicized, e.g. Homo sapiens

Taxonomic hierarchy (order)

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

Three domains of life

Archaea, Bacteria, Eukarya

Species concept

A group of organisms capable of interbreeding and producing fertile offspring

Natural classification

Grouping organisms based on evolutionary relationships/shared ancestry, not just superficial similarities

Cladogram

A diagram showing hypothesized evolutionary relationships between organisms, based on shared derived characteristics

Clade

A group consisting of an ancestor and all its descendants

Shared derived characteristic

A trait that evolved in a common ancestor and is shared by all its descendants, used to group organisms in cladistics

Molecular evidence in cladistics

DNA/protein sequence similarities used to determine evolutionary relatedness — more similarity generally indicates closer relatedness

Why cladistics can reclassify organisms

New molecular evidence can reveal relationships not obvious from physical appearance alone, leading to reclassification (e.g. some organisms once grouped by similarity are now known to be unrelated via convergent evolution)

Evolution

The cumulative change in heritable characteristics of a population over generations

Natural selection requirements

Variation in a population, heritability of traits, differential survival/reproduction (fitness) based on those traits, overproduction of offspring

Speciation

The formation of new species from existing ones, typically via reproductive isolation

Allopatric speciation

Speciation due to geographic separation of populations, preventing gene flow

Sympatric speciation

Speciation without geographic separation, e.g. due to behavioral or reproductive isolation within the same area

Evidence for evolution

Fossil record, comparative anatomy (homologous structures), molecular/DNA evidence, biogeography

Biodiversity

The variety of life, measured at genetic, species, and ecosystem levels

Reasons for declining biodiversity

Habitat destruction, climate change, pollution, invasive species, overexploitation

In-situ conservation

Conservation of species within their natural habitat (e.g. national parks, protected areas)

Ex-situ conservation

Conservation outside the natural habitat (e.g. zoos, seed banks, captive breeding programs)

Value of biodiversity

Ecological (ecosystem services), economic (resources, medicine), and ethical/intrinsic value