bio

biology

evolution

change over time; the process by which modern organisms have descended from ancient organisms

artificial selection

selective breeding of plants and animals to promote the occurrence of desirable traits in offspring

adaptation

heritiable traits that enhance an organism's ability to survive and reproduce in its environment.

fitness

how well an organism can survive and reproduce in its environment

natural selection/ survival of the fittest

the process by which organisms better adapted to their environment tend to survive and produce more offspring.

gene pool

all genes, including the different alleles for each gene, that are present in a population at any one time

allele frequency

the number of times that an allele occurs in a gene pool compared with the number of alleles in that pool for the same gene

directional selection

a mode of natural selection in which an extreme phenotype is favored over other phenotypes, leading to a shift in the population's phenotype distribution.

stabilizing selection

form of natural selection in which individuals near the center of a distribution curve have higher fitness than individuals at either end of the curve

disruptive selection

natural selection in which individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle of the curve

lateral gene transfer

the process by which an organism incorporates genetic material from another organism without being the offspring of that organism. This can occur in bacteria and can contribute to genetic diversity.

gene flow

the transfer of genetic material between populations through migration of individuals or gametes.

genetic drift

random change in allele frequency caused by a series of chance occurrences that cause an allele to become more or less common in a population

bottleneck effect

a change in alleles frequency following a dramatic reduction in population size

founder effect

change in allele frequencies as a result of the migration of a small subgroup of a population

genetic equilibrium

situation in which allele frequencies in a population remain the same

Hardy-Weinberg principle

States that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences.

reproductive isolation

separation of a species or population so that they no longer interbreed. They will evolve into two different species.

speciation

formation of a new species

behavioral isolation

Two populations that were once able to interbreed may evolve differences in a mating ritual or other behavior. This can prevent interbreeding and ultimately lead to speciation.

Geographic Isolation

occurs when physical barriers prevent populations from interbreeding, leading to divergence and speciation.

Temporal Isolation

a form of reproductive isolation where two species breed at different times of the day, season, or year, preventing them from interbreeding.

Index fossils

distinctive fossils used to establish and compare the relative age of rock layers and the fossils they contain. A useful index fossil must be easy to recognize and occur only in a few rock layers.

Relative dating

method of determining the age of a fossil by comparing its placement with that of fossils in other rock layers

radiometric dating

Radiometric dating finds the age of rocks by measuring how much of a radioactive element has changed into a stable one.

half life

length of time required for half of the radioactive atoms in a sample to decay

Geological time scale

timeline used to represent Earth’s history

biogeography

the study of past and present distribution of organisms

homologous structures

similar physical features in organisms that share a common ancestor, but the features serve completely different functions.

analogous structure

common traits found in different groups of species which are anatomically different, serve the same function, but evolved independently in the different groups of species.

vestigial structure

structure that is inherited from ancestors but has lost much or all of its original function

hox gene

a group of homeotic genes clustered together that determine the head to tail identity of body parts in animals. All hox genes contain the homeobox DNA sequence.

phylogeny

study of evolutionary relationships among organisms

clade

evolutionary branch of a cladogram that includes a single ancestor and all its descendants

cladogram

diagram depicting patterns of shared traits among species

endosymbiotic theory

theory that proposes that eukaryotic cells formed from a symbiotic relationship among several different prokaryotic cells

macroevolutionary patterns

changes in anatomy, phylogeny, ecology, and behavior that take place in clades larger than a single species

coevolution

process by which two species evolve in response to changes in each other over time

adaptive radiation

process by which a single species or a small group of species evolves into several different forms that live in different ways

convergent evolution

process by which unrelated organisms independently evolve similarities when adapting to similar environments

background extinction

extinction caused by slow and steady process of natural selection

mass extinction

event during which many species become extinct during a relatively short period of time

gradualism

the evolution of a species by gradual accumulation of small genetic changes over long periods of time

punctuated equilibrium

pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change

tissue

group of similar cells that perform a particular function

organ

group of tissues that work together to perform closely related functions

organ system

group of organs that work together to perform a specific function

homeostasis

relatively constant internal physical and chemical conditions that organisms maintain

feedback inhibition

process in which a stimulus produces a response that opposes the original stimulus; also called negative feedback

ectotherm

animal whose body temperature is determined by the temperature of its environment

endotherm

animal whose body temperature is regulated, at least in part, using heat generated within its body

symbiosis

relationship in which two species live close together

open circulatory system

An open circulatory system is a type of blood circulation found in many invertebrates, like insects and crustaceans. In this system, the heart pumps blood into open spaces called sinuses, where it directly bathes the organs and tissues. Unlike closed systems (like in humans), the blood isn’t always inside vessels and returns to the heart more slowly. This system uses less energy but is less efficient at transporting oxygen quickly.

closed circulatory system

A closed circulatory system is one where blood always stays inside blood vessels as it travels through the body. The heart pumps blood through arteries, veins, and capillaries, allowing for faster and more efficient transport of oxygen and nutrients. This system is found in humans, other mammals, birds, reptiles, amphibians, and some invertebrates like earthworms. It supports higher activity levels and more complex organs.

atrium

upper chamber of the heart that receives blood from the rest of the body

ventricle

lower chamber of the heart that pumps blood out of the heart to the rest of the body

hormone

chemical produced in one part of an organism that affects another part of the organism

metamorphosis

a developmental process that involves dramatic changes in shape and form

neuron

nerve cell; specialized for carrying messages throughout the nervous system

stimulus

signal to which an organism responds

sensory neuron

type of nerve cell that receives information from sensory receptors and conveys signals to the central nervous system

interneuron

type of neuron that processes information and may relay information to motor neurons

response

specific reaction to a stimulus

motor neuron

type of nerve cell that carries directions from interneurons to either muscle cells or glands

cephalization

concentration of sense organs and nerve cells at the anterior end of an animal

reflex

an action that is a rapid response to a stimulus without conscious thought

infectious disease

disease caused by microorganisms that disrupt normal body functions

pathogen

disease causing agent

vaccine

preparation of weakened or killed pathogens used to produce immunity to a disease

antibiotic

a group of drugs used to block the growth and reproduction of bacterial pathogens

virus

particle made of proteins, nucleic acids, and sometimes lipids that can replicate only by infecting living cells

capsid

protein coat surrounding a virus

retrovirus

RNA virus that contains RNA as its genetic information

inflammatory response

nonspecific defense reaction to tissue damage cause by injury or infection

antigen

any substance that triggers an immune response

humoral immunity

immunity against antigens in body fluid, such as blood and lymph

cell mediated immunity

immune response that defends the body against viruses, fungi, and abnormal cancer cells inside living cells

emerging disease

a previously unknown disease that appears in a population for the first time or a well-known disease that suddenly becomes harder to control

zoonosis

a disease that can spread from animals to humans

epidemic

a infectious disease that becomes widespread in a particular population

pandemic

an epidemic occurring in multiple countries throughout the world

xylem

vascular tissue that carries water upward from the roots to every part of a plant

phloem

vascular tissue that transports solutions of nutrients and carbohydrates produced by photosynthesis through the plant

meristem

regions of unspecialized cells responsible for continuing growth throughout a plant’s lifetime

alternation of generations

life cycle that has two alternating phases - a haploid (N) phase and a diploid (2N) phase

sporophyte

spore-producing plant; the multicellular diploid phase of a plant life cycle

gametophyte

gamete-producing plant; multicellular haploid phase of a plant life cycle

bryophyte

group of plants that have specialized reproductive organs but lack vascular tissue; includes mosses and their relatives

vascular tissue

specialized tissue in plants that carry water and nutrients

seed

plant embryo and a food supply encased in a protective covering

gymnosperm

group of seed plants that bear their seeds directly on the scales of cones

angiosperm

group of seed plants that bear their seeds within a layer of tissue that protects the seed; also called a flowering plant

pollination

transfer of pollen from the male reproductive structure to the female reproductive structure

fruit

structure in angiosperms that contains one or more matured ovaries

double fertilization

process of fertilization in angiosperms in which the first event produces the zygote and the second, the second the endosperm within the seed

vegetative reproduction

method of asexual reproduction in plants, which enables a single plant to produce offspring that are genetically identical to itself

dormancy

period of time during which a plant embryo is alive but not growing

germination

resumption of the growth of the plant embryo following dormancy

tracheid

hollow plant cell in xylem with thick cell walls strengthened by lignin

epidermis

in plants, single layer of cells that makes up dermal tissue