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placenta : the organ that supports the transport of nutrients and waste between the mothers and fetusâ blood in eutherian mammals | https://openstax.org/books/concepts-biology/pages/18-key-terms |
progesterone : a reproductive hormone in usually present in animals of any sex; in human females it assists in endometrial regrowth and inhibition of FSH and LH release | https://openstax.org/books/concepts-biology/pages/18-key-terms |
prostate gland : a structure that is a mixture of smooth muscle and glandular material and that contributes to semen | https://openstax.org/books/concepts-biology/pages/18-key-terms |
scrotum : a sac containing testes, exterior to body | https://openstax.org/books/concepts-biology/pages/18-key-terms |
semen : a fluid mixture of sperm and supporting materials | https://openstax.org/books/concepts-biology/pages/18-key-terms |
seminal vesicle : a secretory accessory gland in male; contributes to semen | https://openstax.org/books/concepts-biology/pages/18-key-terms |
seminiferous tubule : the structures within which sperm production occurs in the testes | https://openstax.org/books/concepts-biology/pages/18-key-terms |
Sertoli cell : a cell in the walls of the seminiferous tubules that assists developing sperm and secretes inhibin | https://openstax.org/books/concepts-biology/pages/18-key-terms |
sex determination : the mechanism by which the sex of individuals in sexually reproducing organisms is initially established | https://openstax.org/books/concepts-biology/pages/18-key-terms |
sexual reproduction : a form of reproduction in which cells containing genetic material from two individuals combines to produce genetically unique offspring | https://openstax.org/books/concepts-biology/pages/18-key-terms |
spermatogenesis : the process of producing haploid sperm | https://openstax.org/books/concepts-biology/pages/18-key-terms |
testes : a pair of male reproductive organs | https://openstax.org/books/concepts-biology/pages/18-key-terms |
testosterone : a reproductive hormone usually present in animals of any sex, and that assists in sperm production and promoting secondary sexual characteristics | https://openstax.org/books/concepts-biology/pages/18-key-terms |
trophoblast : the outer layer of cells in the blastocyst, which gives rise to the embryoâs contribution to the placenta | https://openstax.org/books/concepts-biology/pages/18-key-terms |
uterus : a female reproductive structure in which an embryo develops | https://openstax.org/books/concepts-biology/pages/18-key-terms |
vagina : a muscular tube for the passage of menstrual flow, copulation, and birth of offspring | https://openstax.org/books/concepts-biology/pages/18-key-terms |
viviparity : a process in which the young develop within the female and are born in a nonembryonic state | https://openstax.org/books/concepts-biology/pages/18-key-terms |
zona pellucida : the protective layer around the mammalian egg | https://openstax.org/books/concepts-biology/pages/18-key-terms |
Populations are individuals of a species that live in a particular habitat. Ecologists measure characteristics of populations: size, density, and distribution pattern. Life tables are useful to calculate life expectancies of individual population members. Survivorship curves show the number of individuals surviving at ... | https://openstax.org/books/concepts-biology/pages/19-chapter-summary |
Populations with unlimited resources grow exponentiallyâwith an accelerating growth rate. When resources become limiting, populations follow a logistic growth curve in which population size will level off at the carrying capacity. | https://openstax.org/books/concepts-biology/pages/19-chapter-summary |
Populations are regulated by a variety of density-dependent and density-independent factors. Life-history characteristics, such as age at first reproduction or numbers of offspring, are characteristics that evolve in populations just as anatomy or behavior can evolve over time. The model ofr- andK-selection suggests th... | https://openstax.org/books/concepts-biology/pages/19-chapter-summary |
Earthâs human population is growing exponentially. Humans have increased their carrying capacity through technology, urbanization, and harnessing the energy of fossil fuels. The age structure of a population allows us to predict population growth. Unchecked human population growth could have dire long-term effects on... | https://openstax.org/books/concepts-biology/pages/19-chapter-summary |
Communities include all the different species living in a given area. The variety of these species is referred to as biodiversity. Many organisms have developed defenses against predation and herbivory, including mechanical defenses, warning coloration, and mimicry. Two species cannot exist indefinitely in the same hab... | https://openstax.org/books/concepts-biology/pages/19-chapter-summary |
age structure : the distribution of the proportion of population members in each age class | https://openstax.org/books/concepts-biology/pages/19-key-terms |
birth rate : the number of births within a population at a specific point in time | https://openstax.org/books/concepts-biology/pages/19-key-terms |
carrying capacity : the maximum number of individuals of a population that can be supported by the limited resources of a habitat | https://openstax.org/books/concepts-biology/pages/19-key-terms |
climax community : the final stage of succession, where a stable community is formed by a characteristic assortment of plant and animal species | https://openstax.org/books/concepts-biology/pages/19-key-terms |
competitive exclusion principle : no two species within a habitat can coexist indefinitely when they compete for the same resources at the same time and place | https://openstax.org/books/concepts-biology/pages/19-key-terms |
death rate : the number of deaths within a population at a specific point in time | https://openstax.org/books/concepts-biology/pages/19-key-terms |
demography : the statistical study of changes in populations over time | https://openstax.org/books/concepts-biology/pages/19-key-terms |
density-dependent regulation : the regulation of population in which birth and death rates are dependent on population size | https://openstax.org/books/concepts-biology/pages/19-key-terms |
density-independent regulation : the regulation of population in which the death rate is independent of the population size | https://openstax.org/books/concepts-biology/pages/19-key-terms |
environmental disturbance : a change in the environment caused by natural disasters or human activities | https://openstax.org/books/concepts-biology/pages/19-key-terms |
exponential growth : an accelerating growth pattern seen in populations where resources are not limiting | https://openstax.org/books/concepts-biology/pages/19-key-terms |
foundation species : a species which often forms the major structural portion of the habitat | https://openstax.org/books/concepts-biology/pages/19-key-terms |
host : an organism a parasite lives on | https://openstax.org/books/concepts-biology/pages/19-key-terms |
intraspecific competition : the competition among members of the same species | https://openstax.org/books/concepts-biology/pages/19-key-terms |
island biogeography : the study of life on island chains and how their geography interacts with the diversity of species found there | https://openstax.org/books/concepts-biology/pages/19-key-terms |
J-shaped growth curve : the shape of an exponential growth curve | https://openstax.org/books/concepts-biology/pages/19-key-terms |
K-selected species : a species suited to stable environments that produce a few, relatively large offspring and provide parental care | https://openstax.org/books/concepts-biology/pages/19-key-terms |
keystone species : a species whose presence is key to maintaining biodiversity in an ecosystem and to upholding an ecological communityâs structure | https://openstax.org/books/concepts-biology/pages/19-key-terms |
life table : a table showing the life expectancy of a population member based on its age | https://openstax.org/books/concepts-biology/pages/19-key-terms |
logistic growth : the leveling off of exponential growth due to limiting resources | https://openstax.org/books/concepts-biology/pages/19-key-terms |
mark and recapture : a method used to determine population size in mobile organisms | https://openstax.org/books/concepts-biology/pages/19-key-terms |
mimicry : an adaptation in which an organism looks like another organism that is dangerous, toxic, or distasteful to its predators | https://openstax.org/books/concepts-biology/pages/19-key-terms |
mortality rate : the proportion of population surviving to the beginning of an age interval that dies during that age interval | https://openstax.org/books/concepts-biology/pages/19-key-terms |
mutualism : a symbiotic relationship between two species where both species benefit | https://openstax.org/books/concepts-biology/pages/19-key-terms |
one-child policy : a policy in China to limit population growth by limiting urban couples to have only one child or face a penalty of a fine | https://openstax.org/books/concepts-biology/pages/19-key-terms |
parasite : an organism that uses resources from another species: the host | https://openstax.org/books/concepts-biology/pages/19-key-terms |
pioneer species : the first species to appear in primary and secondary succession | https://openstax.org/books/concepts-biology/pages/19-key-terms |
population density : the number of population members divided by the area being measured | https://openstax.org/books/concepts-biology/pages/19-key-terms |
population size : the number of individuals in a population | https://openstax.org/books/concepts-biology/pages/19-key-terms |
primary succession : the succession on land that previously has had no life | https://openstax.org/books/concepts-biology/pages/19-key-terms |
quadrat : a square within which a count of individuals is made that is combined with other such counts to determine population size and density in slow moving or stationary organisms | https://openstax.org/books/concepts-biology/pages/19-key-terms |
r-selected species : a species suited to changing environments that produce many offspring and provide little or no parental care | https://openstax.org/books/concepts-biology/pages/19-key-terms |
relative species abundance : the absolute population size of a particular species relative to the population size of other species within the community | https://openstax.org/books/concepts-biology/pages/19-key-terms |
S-shaped growth curve : the shape of a logistic growth curve | https://openstax.org/books/concepts-biology/pages/19-key-terms |
secondary succession : the succession in response to environmental disturbances that move a community away from its equilibrium | https://openstax.org/books/concepts-biology/pages/19-key-terms |
species distribution pattern : the distribution of individuals within a habitat at a given point in time | https://openstax.org/books/concepts-biology/pages/19-key-terms |
species richness : the number of different species in a community | https://openstax.org/books/concepts-biology/pages/19-key-terms |
survivorship curve : a graph of the number of surviving population members versus the relative age of the member | https://openstax.org/books/concepts-biology/pages/19-key-terms |
zero population growth : the steady population size where birth rates and death rates are equal | https://openstax.org/books/concepts-biology/pages/19-key-terms |
Ecosystems exist underground, on land, at sea, and in the air. Organisms in an ecosystem acquire energy in a variety of ways, which is transferred between trophic levels as the energy flows from the base to the top of the food web, with energy being lost at each transfer. There is energy lost at each trophic level, so ... | https://openstax.org/books/concepts-biology/pages/20-chapter-summary |
Mineral nutrients are cycled through ecosystems and their environment. Of particular importance are water, carbon, nitrogen, phosphorus, and sulfur. All of these cycles have major impacts on ecosystem structure and function. As human activities have caused major disturbances to these cycles, their study and modeling is... | https://openstax.org/books/concepts-biology/pages/20-chapter-summary |
Earth has terrestrial and aquatic biomes. Aquatic biomes include both freshwater and marine environments. There are eight major terrestrial biomes: tropical rainforests, savannas, subtropical deserts, chaparral, temperate grasslands, temperate forests, boreal forests, and Arctic tundra. The same biome can occur in diff... | https://openstax.org/books/concepts-biology/pages/20-chapter-summary |
Aquatic biomes include both saltwater and freshwater biomes. The abiotic factors important for the structuring of aquatic biomes can be different than those seen in terrestrial biomes. Sunlight is an important factor in bodies of water, especially those that are very deep, because of the role of photosynthesis in susta... | https://openstax.org/books/concepts-biology/pages/20-chapter-summary |
abyssal zone : the deepest part of the ocean at depths of 4000 m or greater | https://openstax.org/books/concepts-biology/pages/20-key-terms |
acid rain : a corrosive rain caused by rainwater mixing with sulfur dioxide gas as it fall through the atmosphere, turning it into weak sulfuric acid, causing damage to aquatic ecosystems | https://openstax.org/books/concepts-biology/pages/20-key-terms |
algal bloom : a rapid increase of algae in an aquatic system | https://openstax.org/books/concepts-biology/pages/20-key-terms |
apex consumer : an organism at the top of the food chain | https://openstax.org/books/concepts-biology/pages/20-key-terms |
aphotic zone : the part of the ocean where photosynthesis cannot occur | https://openstax.org/books/concepts-biology/pages/20-key-terms |
arctic tundra : a biome characterized by low average temperatures, brief growing seasons, the presence of permafrost, and limited precipitation largely in the form of snow in which the dominant vegetation are low shrubs, lichens, mosses, and small herbaceous plants | https://openstax.org/books/concepts-biology/pages/20-key-terms |
autotroph : an organism capable of synthesizing its own food molecules from smaller inorganic molecules | https://openstax.org/books/concepts-biology/pages/20-key-terms |
benthic realm : (also, benthic zone) the part of the ocean that extends along the ocean bottom from the shoreline to the deepest parts of the ocean floor | https://openstax.org/books/concepts-biology/pages/20-key-terms |
biogeochemical cycle : the cycling of minerals and nutrients through the biotic and abiotic world | https://openstax.org/books/concepts-biology/pages/20-key-terms |
biomagnification : an increasing concentration of persistent, toxic substances in organisms at each trophic level, from the producers to the apex consumers | https://openstax.org/books/concepts-biology/pages/20-key-terms |
biome : a large-scale community of organisms, primarily defined on land by the dominant plant types that exist in geographic regions of the planet with similar climatic conditions | https://openstax.org/books/concepts-biology/pages/20-key-terms |
boreal forest : a biome found in temperate and subarctic regions characterized by short growing seasons and dominated structurally by coniferous trees | https://openstax.org/books/concepts-biology/pages/20-key-terms |
canopy : the branches and foliage of trees that form a layer of overhead coverage in a forest | https://openstax.org/books/concepts-biology/pages/20-key-terms |
channel : the bed and banks of a river or stream | https://openstax.org/books/concepts-biology/pages/20-key-terms |
chaparral : a biome found in temperate coastal regions characterized by low trees and dry-adapted shrubs and forbs | https://openstax.org/books/concepts-biology/pages/20-key-terms |
chemoautotroph : an organism capable of synthesizing its own food using energy from inorganic molecules | https://openstax.org/books/concepts-biology/pages/20-key-terms |
coral reef : an ocean ridge formed by marine invertebrates living in warm shallow waters within the photic zone | https://openstax.org/books/concepts-biology/pages/20-key-terms |
cryptofauna : the invertebrates found within the calcium carbonate substrate of coral reefs | https://openstax.org/books/concepts-biology/pages/20-key-terms |
dead zone : an area in a lake and ocean near the mouths of rivers where large areas are depleted of their normal flora and fauna; these zones can be caused by eutrophication, oil spills, dumping of toxic chemicals, and other human activities | https://openstax.org/books/concepts-biology/pages/20-key-terms |
detrital food web : a type of food web that is supported by dead or decaying organisms rather than by living autotrophs; these are often associated with grazing food webs within the same ecosystem | https://openstax.org/books/concepts-biology/pages/20-key-terms |
ecosystem : a community of living organisms and their interactions with their abiotic environment | https://openstax.org/books/concepts-biology/pages/20-key-terms |
ecosystem services : the human benefits provided by natural ecosystems | https://openstax.org/books/concepts-biology/pages/20-key-terms |
emergent vegetation : the plants living in bodies of water that are rooted in the soil but have portions of leaves, stems, and flowers extending above the waterâs surface | https://openstax.org/books/concepts-biology/pages/20-key-terms |
equilibrium : the steady state of a system in which the relationships between elements of the system do not change | https://openstax.org/books/concepts-biology/pages/20-key-terms |
estuary : a region where fresh water and salt water mix where a river discharges into an ocean or sea | https://openstax.org/books/concepts-biology/pages/20-key-terms |
eutrophication : the process whereby nutrient runoff causes the excess growth of microorganisms and plants in aquatic systems | https://openstax.org/books/concepts-biology/pages/20-key-terms |
fallout : the direct deposition of solid minerals on land or in the ocean from the atmosphere | https://openstax.org/books/concepts-biology/pages/20-key-terms |
food chain : a linear sequence of trophic (feeding) relationships of producers, primary consumers, and higher level consumers | https://openstax.org/books/concepts-biology/pages/20-key-terms |
food web : a web of trophic (feeding) relationships among producers, primary consumers, and higher level consumers in an ecosystem | https://openstax.org/books/concepts-biology/pages/20-key-terms |
grazing food web : a type of food web in which the producers are either plants on land or phytoplankton in the water; often associated with a detrital food web within the same ecosystem | https://openstax.org/books/concepts-biology/pages/20-key-terms |
gross primary productivity : the rate at which photosynthetic producers incorporate energy from the Sun | https://openstax.org/books/concepts-biology/pages/20-key-terms |
hydrosphere : the region of the planet in which water exists, including the atmosphere that contains water vapor and the region beneath the ground that contains groundwater | https://openstax.org/books/concepts-biology/pages/20-key-terms |
intertidal zone : the part of the ocean that is closest to land; parts extend above the water at low tide | https://openstax.org/books/concepts-biology/pages/20-key-terms |
neritic zone : the part of the ocean that extends from low tide to the edge of the continental shelf | https://openstax.org/books/concepts-biology/pages/20-key-terms |
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