ILEARN Biology ECA flashcards

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

Cell Theory

All living organisms are composed of one or more cells, the cell is the basic unit of life, and all cells arise from existing cells by cell division.

Prokaryotic Cell

A cell lacking a membrane-bound nucleus and membrane-bound organelles; its circular DNA lies in the cytoplasm, and bacteria and archaea are examples.

Mitochondrion

Organelle with a double membrane and folded inner cristae where aerobic respiration and most ATP production occur; it contains its own circular DNA and ribosomes.

Active Transport

Movement of molecules across a membrane from low to high concentration using carrier proteins and ATP energy; the sodium-potassium pump is one example.

Photosynthesis Equation

6CO2 + 6H2O + light energy yields C6H12O6 + 6O2; light reactions occur in thylakoid membranes and the Calvin cycle occurs in the stroma.

Glycolysis

First stage of cellular respiration, occurring in the cytoplasm, that splits one glucose into two pyruvate molecules with a net gain of two ATP and two NADH.

Enzyme Denaturation

Loss of an enzyme's three-dimensional shape and active site caused by high temperature or extreme pH, which reduces or eliminates its catalytic activity.

Negative Feedback

A control mechanism in which a change in a body variable triggers a response that reverses that change, keeping conditions such as temperature and blood glucose near a set point.

Law of Segregation

Mendel's principle that the two alleles of a gene separate during meiosis so that each gamete carries only one allele for that gene.

Monohybrid Cross Ratio

Crossing two heterozygotes (Aa x Aa) for a single gene gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio in the offspring.

Incomplete Dominance

Inheritance in which the heterozygote shows a blended intermediate phenotype, as when red and white snapdragons produce pink offspring; neither allele is fully expressed.

Codominance

Inheritance in which both alleles are fully expressed at the same time in the heterozygote, as in human AB blood type.

Base Pairing Rule

In DNA, adenine pairs with thymine using two hydrogen bonds and guanine pairs with cytosine using three, making the two antiparallel strands complementary.

Frameshift Mutation

An insertion or deletion of nucleotides not in multiples of three, which shifts the reading frame and usually changes every amino acid encoded after the mutation.

Crossing Over

Exchange of corresponding DNA segments between homologous chromosomes during prophase I of meiosis, producing new combinations of alleles on the resulting chromosomes.

Testcross

Crossing an individual of unknown genotype with a homozygous recessive individual; any recessive offspring show that the unknown parent carries the recessive allele.

Natural Selection

Process in which individuals with heritable traits that improve survival and reproduction leave more offspring, so those traits increase in frequency over generations.

Homologous Structures

Body parts in different species that share underlying anatomical structure and embryonic origin, indicating common ancestry, such as the forelimbs of humans, bats, and whales.

Analogous Structures

Body parts with similar function but different underlying structure and origin, such as bird wings and insect wings, resulting from convergent evolution rather than shared ancestry.

Hardy-Weinberg Equilibrium

Conditions of no mutation, no gene flow, no selection, random mating, and a large population keep allele frequencies constant, with p + q = 1 and p^2 + 2pq + q^2 = 1.

Genetic Drift

Random change in allele frequencies due to chance, most noticeable in small populations; bottleneck and founder effects are examples that reduce genetic variation.

Allopatric Speciation

Formation of new species when a geographic barrier separates populations, preventing gene flow so each group independently accumulates genetic differences over time.

Evolutionary Fitness

An organism's relative contribution of offspring to the next generation; it depends on survival and successful reproduction rather than on strength or body size.

Adaptive Radiation

Rapid diversification of a single ancestral lineage into many species that fill different ecological niches, often after colonizing new habitats such as island chains.

Ten Percent Rule

On average only about ten percent of the energy at one trophic level is transferred to the next; the remainder is lost mainly as heat through respiration.

Carrying Capacity

The maximum population size of a species that an ecosystem can sustain indefinitely given available food, water, space, and other limiting resources; symbolized K.

Mutualism

A symbiotic relationship in which both interacting species benefit, such as bees obtaining nectar while transferring pollen between flowers.

Parasitism

A symbiotic relationship in which one organism benefits by feeding on a host that is harmed; parasites usually do not kill their hosts quickly.

Primary Succession

Ecological succession that begins on bare rock or newly formed land with no soil, starting with pioneer species such as lichens and mosses.

Keystone Species

A species whose effect on its ecosystem is disproportionately large relative to its abundance; its removal causes major change, as when sea otters control urchin populations.

Biomagnification

Increase in concentration of a persistent toxin such as mercury at each higher trophic level, because organisms accumulate the toxin faster than they excrete it.

Nitrogen Fixation

Conversion of atmospheric nitrogen gas into ammonia by bacteria such as Rhizobium living in root nodules, making nitrogen usable for building proteins and nucleic acids.