Characteristics of Life:
1. All living things are composed of cells:
a. The cell is the simplest unit that is classified as living, anything smaller is not
considered alive (i.e. atoms, molecules)
i. Unicellular: microscopic organisms composed of only one cell (includes
bacteria, archaea, and some eukaryotes); simple and self-sufficient
ii. Multicellular: organisms made of more than one cell (eukaryotes);
different types of cells perform specialized functions within an
organism—each cell is NOT self-sufficient
2. All Living things reproduce:
a. Organisms reproduce to continue their species
b. Organisms do not need to reproduce for their own individual survival, but
are driven to in order to promote the survival of their species
c. Organisms can reproduce in two ways:
i. Asexual Reproduction: An organism essentially clones itself; offspring
are produced from a single parent who contributes 100% of the DNA
ii. Sexual Reproduction: Two organisms combine genetic material to
produce offspring; 50% of the offspring’s DNA comes from each parent
3. All living things display heredity:
a. Organisms pass traits to offspring via a hereditary molecule—
Deoxyribonucleic Acid (DNA)
i. Organisms receive their DNA and traits from their parent/parents (body
structure, behaviors, appearance, etc.)
4. All living things grow and develop
a. Living things can increase the number of cells, size of cells, arrangement of
cells, and function of cells to grow (size) and develop (functionality)
i. Cell enlargement (hypertrophy): Cells grow larger; cells are limited by
the laws of physics on how large they can grow
ii. Cell division (mitosis): Cells divide and increase in number; 1 become 2,
2 becomes 4, 4 becomes 8, etc.
5. All living things respond to stimuli
a. Organisms will respond to stimuli from their environment in order to
continue life functions
b. A stimulus (singular form of stimuli) is a sensory cue from the environment
that causes a response from an organism—typically to aid survival or
reproduction.
6. All living things undergo the processes of adaptation and evolution
a. Adaptation is modification an organism undergoes in order to maximize
survival in a given environment
b. Over time and many generations, an organism can evolve through continual
adaptation to improve its survivability and reproductive success
c. Genetic variation and diversity are important factors for adaptation and
evolution
7. All living things require energy
a. In order to maintain life functions (growth, development, reproduction,
metabolism, etc.) organisms need to obtain and process energy
b. The ultimate source of energy that enables life on earth is the SUN.
8. All living things maintain homeostasis
a. Living things maintain a stable and relatively constant internal conditions
b. An organism has a range (temperature, pH, hydration, etc.) that is must stay
in or risk harm/death.
c. Some organisms have evolved mechanisms of dormancy or hibernation to
endure in particularly harsh environmental conditions.
Ecology
The study of interactions between organisms and their environments. Ecology includes the
study of individuals, populations, communities, and ecosystems, biomes, and the biosphere.
Biotic
Anything that is, or has ever been, alive. Examples of biotic factors in an environment include
organisms, organic molecules, and cells. Biotic is the opposite of abiotic.
Abiotic
Anything that is not, nor has ever been, alive. Some examples of abiotic factors in an
environment include precipitation, sunlight, and minerals. Abiotic is the opposite of biotic.
Niche
An organism's role in an environment, including how it uses its resources, relates to other
organisms, and times its reproduction. Each individual organism has a niche in its population,
community, and ecosystem, but niches are flexible and change depending on circumstances.
Habitat
The physical environment where a population of a single species lives, or inhabits. A habitat
consists of all the abiotic, or nonliving, resources influencing the population. A habitat is only
understood in terms of the population it describes. For instance, we say "the black bear habitat"
or "the whale habitat." It doesn’t describe the entire ecosystem, or a community of organisms, or
even the home of a single individual. Habitats of different species can and almost
always do overlap.
Autotroph
Any living organism that makes its own food by converting simple inorganic molecules into
complex organic compounds like carbohydrates, fats, and proteins. Autotrophs are often the
"producers" in a food chain or web. Photoautotrophs use energy from light to make food,
while chemoautotrophs obtain their energy from chemical reactions.
Heterotroph
An organism that cannot convert sunlight or chemicals into "food" (and by food, we mean
carbohydrates). Heterotrophs must obtain their nutrients by consuming other organisms. All
animals, all fungi, and some kinds of bacteria are heterotrophs. This means that all carnivores,
herbivores, and omnivores are also heterotrophs.
Trophic Level
A description of the position occupied by an organism in a food chain or food web. Simply put,
an organism’s trophic level is defined by what it eats and what eats it. Examples of trophic levels
include producers, consumers, and decomposers.
Primary Producer
An autotrophic (food-making) organism at the base of a food chain or food web that obtains all
of its energy from the nonliving environment. Examples of primary producers include plants,
algae, and some types of bacteria. Primary producers obtain their energy either from the Sun,
through photosynthesis, or from the surrounding abiotic environment, through chemosynthesis.
Primary producers are always the first biotic sources of energy for an ecosystem. That’s why we
call them "primary." They are eaten by primary consumers.
Primary Consumer
A heterotrophic organism near the base of a food chain or food web (see definitions) that
obtains all or some of its energy by consuming primary producers (see definition). Examples of
primary consumers include all the strict herbivores, like bovines, deer, and most insects, and all
the omnivores, like most humans, many birds, and some monkeys. Strict herbivores are always
primary consumers and are only eaten by secondary consumers. Omnivores can be primary,
secondary, and even tertiary consumers, depending on what they are eating. They, themselves,
can be eaten by secondary or, tertiary consumers.
Energy Pyramid
A triangularly shaped drawing showing how energy from the Sun moves through the biological
components of an ecosystem. Producers, like plants and algae, are at the bottom of the pyramid,
and tertiary consumers, like carnivores that eat carnivores, and detritivores, or decomposers, are
at the top.
Food Chain
A simple, direct, and trophic, or eating, relationship among a group of organisms, where one
organism, like a plant, is the food source for the next organism, like a cow, which in turn is the
food source for the next organism, like a human, and so on and so forth.
Food Web
A complex trophic relationship among a group of organisms, consisting of interactions among
multiple food chains (see definition above). A food web describes how
multiple producers and consumers directly or indirectly interact in an ecosystem.
Biomagnification
The process by which some substances increase in concentration in a food chain or food web.
Biomagnification occurs because certain substances, including some pesticides and heavy
metals, are not easily degraded and can accumulate in organisms’ tissues or internal organs.
Pregnant women are advised not to eat certain kinds of fish because of the potential for
biomagnification of mercury, a heavy metal, in aquatic systems.
Herbivore
An organism that only eats tissue from autotrophic organisms, like plants and algae. Some
examples of herbivores include members of the bovine family, like cows, bison, antelope, and
sheep; members of the deer family, like moose, reindeer, and elk; and many insects, like leaf
beetles, lady bugs, and aphids.
Carnivore
An organism that only eats animal tissue. Most predators and scavengers are exclusively
carnivorous. Some examples of carnivores include members of the feline family, like lions,
tigers, and house cats, and birds of prey, like eagles, hawks, and owls.
Omnivore
An organism that eats tissue from both plants and animals. Some examples of omnivores include
members of the hominid family, like humans, chimpanzees, and orangutans, and many bird
species, like hummingbirds, ducks, and woodpeckers.
Decomposer
An organism that feeds on and breaks down dead or decaying matter in the process of ecological
decomposition. Examples of decomposers include fungi, like mushrooms and molds; worms,
like earthworms and some nematodes; and some bacteria. Decomposers are also
called saprotrophs, meaning "putrid eaters."
Detritivore
An organism that consumes detritus, aka decomposing organic matter, to obtain nutrients. All
decomposers are detritivores, including fungi, worms, and some bacteria.
Competition
An interaction where individuals of different species—interspecific competition—or the same
species—intraspecific competition—vie for limited resources. Examples of interspecific
competition include trees of different species vying for limited sunlight in a rainforest, birds of
different species vying for limited prey in a prairie, and even bacteria of different species vying
for limited oxygen in your large intestine. Examples of intraspecific competition include lions
vying for limited antelope in the Savannah; piglets vying for limited milk from their sow, or
mom-pig; and even humans vying for limited space to build a home.
Predation
A type of species interaction where one organism, aka the predator, consumes, in part or in
whole, another organism, aka the prey. Examples of predators include snakes and members of
the big cat family, such as lynx. The difference between parasitism and predation is not always
clear, but in general, predators kill their prey almost immediately while parasites live in or on
their hosts for an extended period of time.
Symbiosis
An interaction between individuals of different species. Symbiotic relationships
include mutualism, parasitism, and commensalism. They do not include predator-prey
interactions.
Mutualism: Two organisms interact in a way that is BENEFICIAL to both
Ex. Bees and Flowers
Commensalism: Two organisms interact in a way that is BENEFICIAL to one organism and
has no impact (either beneficial or harmful) on the other.
Ex. Clownfish and Sea Anemone
Parasitism: Two organisms interact in a way that is BENEFICIAL to one organism and
HARMFUL to the other
Organism
A single living member of a species. Ex. Humans, wolf, cucumber plant, etc.
Population
A group of organisms of the same species living in the same geographic area, like a swamp, a
lake, a mountaintop, or an island. Ecologists sometimes debate the concept of a population, but
in general, they accept that a population consists of individuals that all have a greater chance of
breeding with each other than with individuals inhabiting areas beyond the population’s
geographic "borders." Keep in mind, though, that population "borders" are often fuzzy and may
overlap with other populations. Hey, we told you that there was a debate.
Community
A group of two or more populations of organisms from different species inhabiting the same
location at the same time. While humans often refer to their "community" as being a part of a
group of other humans who live in the same small geographic location, a human population’s
true ecological community includes all of the other organisms from other species in the area as
well. Communities are composed only of biotic factors, aka living organisms. Abiotic factors
like sunlight, temperature, and terrain are not considered part of a community; these factors are
part of the ecosystem, which can contain one or more communities of organisms.
Ecosystem
A term describing all the living and nonliving things in a certain location. Ecosystem studies in
ecology explore the interactions between organisms, like individuals, populations, or
communities, and the abiotic components in the environment, like chemicals, landscapes, and the
like.
Biome
A large grouping of area that contains a number of different ecosystems. The defining
characteristics of a biome are the dominant plant life and the climate. Examples include Deserts,
Rainforests, Deciduous Forests, Savannahs, etc.
Biosphere
The entire area of the earth that supports life. The biosphere is made up of all of the individuals,
populations, communities, ecosystems, and biomes found on Earth.