IB Biology SL flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Biological species concept

A species is a group of organisms that can interbreed to produce fertile offspring. Members of different species normally cannot, though some hybrids such as mules are sterile.

Binomial nomenclature rules

Each species has a two-part Latin name: genus capitalized, species lowercase, both italicized in print or underlined in handwriting, for example Homo sapiens.

Three domains of life

Bacteria, Archaea, and Eukarya. The classification is based largely on ribosomal RNA sequence comparisons, with Archaea more closely related to Eukarya than to Bacteria.

Homologous versus analogous structures

Homologous structures share a common ancestry despite different functions, such as the pentadactyl limb. Analogous structures have the same function but different origins, such as insect and bird wings.

Cladistics and derived characters

Cladistics groups organisms using shared derived characters inherited from a common ancestor. Only homologous traits are used, and the result is represented by a cladogram.

Dichotomous key design

A key consists of paired, mutually exclusive statements based on observable, measurable features. Each choice leads to another pair until a single species is identified.

Taxonomic hierarchy order

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. Moving down the hierarchy, the groups contain fewer organisms that share more characteristics.

Evidence for evolution

Fossils including transitional forms, homologous structures, selective breeding, and comparison of DNA or protein sequences all provide evidence that organisms have evolved over time.

Surface area to volume ratio

As a cell grows larger, its volume increases faster than its surface area, so the ratio falls. Small or flattened cells keep the ratio high enough for diffusion.

Prokaryote versus eukaryote

Prokaryotes lack membrane-bound organelles and have 70S ribosomes and circular DNA. Eukaryotes have membrane-bound compartments, 80S ribosomes, and linear chromosomes in a nucleus.

Fluid mosaic membrane model

The membrane is a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins. It is fluid because lipids and proteins can move laterally within the layer.

Simple versus facilitated diffusion

Simple diffusion moves small non-polar molecules directly through the bilayer. Facilitated diffusion uses channel or carrier proteins for ions and polar molecules, down the concentration gradient and without ATP.

Active transport and pumps

Active transport moves substances against a concentration gradient using ATP, for example the sodium-potassium pump. It requires specific carrier proteins and is saturable.

Enzyme denaturation

High temperature or extreme pH breaks bonds maintaining the active site's shape. The substrate no longer fits, so activity falls and the change is usually irreversible.

Competitive versus non-competitive inhibition

A competitive inhibitor binds the active site and is overcome by more substrate. A non-competitive inhibitor binds elsewhere and changes the active site, so extra substrate does not help.

Photosynthesis in chloroplasts

Light-dependent reactions in thylakoid membranes produce ATP and NADPH. The Calvin cycle in the stroma uses these to fix carbon dioxide into carbohydrate with the enzyme rubisco.

Alveoli adaptations

Alveoli provide a large total surface area, walls one cell thick, a moist lining, and dense capillaries. These features maintain steep diffusion gradients for oxygen and carbon dioxide.

Vesicle transport

Exocytosis fuses vesicles with the plasma membrane to release contents. Endocytosis invaginates the membrane to engulf material, forming a vesicle inside the cell.

Autotroph versus heterotroph

Autotrophs synthesize organic molecules from inorganic sources using photosynthesis or chemosynthesis. Heterotrophs obtain organic carbon by consuming other organisms or their remains.

Trophic levels and energy loss

Producers occupy the first trophic level, primary consumers the second, and so on. Only about ten percent of energy passes between levels, the rest lost mainly as heat.

Symbiosis types

Mutualism benefits both species, commensalism benefits one while the other is unaffected, and parasitism benefits one at the host's expense.

Carrying capacity and logistic growth

Exponential growth occurs with unlimited resources. Logistic growth slows as population size approaches the carrying capacity K, the maximum the environment can sustain.

Greenhouse effect mechanism

Greenhouse gases absorb outgoing infrared radiation and re-emit it, warming the atmosphere. Increasing their concentration raises the mean global temperature.

Carbon cycle processes

Carbon moves through photosynthesis, respiration, combustion, decomposition, and fossilization. Oceans and forests act as carbon sinks, while burning fossil fuels releases stored carbon dioxide.

Capture-mark-recapture estimate

Population size is estimated as (number marked × total caught second time) ÷ number of marked individuals in the second catch. Assumes random mixing and no deaths or migration.

Saprotrophs and decomposers

Saprotrophs secrete enzymes onto dead organic matter and absorb the digested products. They recycle nutrients such as carbon and nitrogen back into the ecosystem.

Semi-conservative replication

Helicase unwinds DNA; DNA polymerase adds nucleotides 5′ to 3′ matching the template; ligase joins fragments. Each new molecule keeps one original strand.

Transcription and translation

RNA polymerase builds mRNA from the template strand. Ribosomes read codons 5′ to 3′ while tRNA anticodons deliver the matching amino acids in sequence.

Meiosis and variation

Meiosis produces four haploid cells. Crossing over in prophase I and independent assortment in metaphase I create genetic variation among gametes.

Monohybrid cross ratios

Crossing two heterozygotes gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio. A test cross with a recessive parent reveals whether a dominant phenotype is heterozygous.

Codominance and multiple alleles

ABO blood groups show three alleles and codominance: IA and IB are both expressed in type AB, while i is recessive. Genotype determines phenotype directly.

Gene mutation as variation source

Mutations are random changes in base sequence that may alter a protein. They create the genetic variation on which natural selection acts over generations.