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Levels of Biological Organization
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Biology us the study of living things, but biologists do not limit their study
to just individual organisms. To understand how a car functions, you must
study its parts, such as the carburetor, the engine, and the transmission. You
may even have to study the parts of the parts. Similarly, to understand
organisms, biologists study the workings of organisms, of their parts, and of
the parts of their parts. Biologists also study the interrelationships between
various organisms and their environment. Figure 1 illustrates the levels of
organization of life on Earth from simplest to most complex.
Atoms & Molecular Level
Like all matter, the simplest parts of a living system are the atoms and
molecules of which an organism is made. Of the nearly 100 naturally
occurring elements on Earth, only six are especially important to life:
carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.
(CHNOPS)
Atom of Matter
Water Molecule
Atoms join together and form larger structures called molecules. The most
important types of molecules found in living organisms are carbohydrates,
lipids, proteins, and nucleic acids.
Cellular Level
Many different molecules interact within one cell. The cell is the smallest
unit of life capable of carrying out all the functions of living things. All
living organisms are made of cells. Cells are the basic unit of structure and
function for all life. There are two different types of cells we will discuss:
animal cells and plant cells.
Animal Cell
Plant Cell
Living things that are made up of only one cell are called unicellular
organisms. Examples of unicellular organisms include amoeba and
paramecium. Organisms that are made up of more than one cell are called
multicellular organisms. Some multicellular organisms, such as humans,
are made up of billions of cells. Each separate, functioning cell in a
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multicellular organism is alive and has all the characteristics of living
things.
Tissue Levels
In most multicellular organisms, cells are organized into tissues. A tissue is
a group of cells that has the same origin and structure, and performs a
specific function in an organism. Muscle is a familiar type of animal tissue.
The cells in a muscle work together to make parts of the organism move.
Nervous tissue consists of cells specialized for carrying messages from
nerve to nerve and to and from the spinal cord and brain. Additional
examples of animal tissue include bones, skin, nerves, fat, and blood. Plant
tissues include protective areas such as bark and outer surfaces of leaves,
conductive tissue which transports water and food, and special regions of
growth. The four types of tissue we will discuss are: Connective tissue,
Epithelial tissue, Muscle tissue and Nervous tissue.
Organ Level
Several different types of tissue that function together for a specific purpose
to make up an organ. Most multicellular organisms contain organs. The
heart is and organ made of muscle, nerve, connective and other kinds of
tissues. Together the tissues of the heart pump blood to every part of the
body. The eye is also an organ. Muscle tissue controls the movement of the
eye. Nervous tissue responds to light and sends messages to the brain.
Other types of tissue protect and nourish the eyeball. All these tissues are
necessary if the eye is to perform its special function of seeing. Other
examples of human organs include the lungs, kidneys, stomach, liver and
heart. Leaves and roots are examples of organ in plants.
Stomach
Heart
Lungs
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Organ System Level
In complex multicellular organisms, many asks are to great for a single
organ. They require a system or a group of organs that cooperate in a series
of related functions. An organ system, therefore, is made of several organs
working together to perform a function. For example, the digestive system
is an organ system. It consists of several organs including you esophagus,
stomach, small intestine, large intestine, and liver. The circulatory, skeletal,
and reproductive systems are some of the other organ systems in the human
body.
Digestive System
Organism Level
An organism is any individual living thing. Some multicellular organisms
consist of several organ systems working
together. Organ systems are organized into an
organism or individual. Organisms breed with
organisms of the same species. A species is a
group of organisms which normally interbreed
in nature to produce fertile offspring (offspring
which can also interbreed).
Monarch Butterfly
Population Level
The field of biology does not end with an
understanding of individual organisms. Many
biologists study the interactions of organisms
with each other, and with their environments. A
group of organisms of the same species that lives
together in a particular location at the same time
is a Population. The sugar maples in a forest or
the pigeons in a city are examples of populations.
All the bullfrogs in Guajome Park pond make up
a population. The same pond may also have a
water lily population and a perch population.
Population of
Monarch Butterflies
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Community Level
A biological Community includes all the populations of different kinds of
organisms living in the same place and interacting with each other. All of
the living organisms make up the Biotic Factors that create both the
individual populations and collectively the community. All the populations
of organisms living in Guajome park pond
(plants, fish, insects, Shellfish, birds,
amphibians, etc) make up the biotic factors
within the pond community. A lawn is also an
example of a community. The lawn
community contains populations of grasses,
insects, worms, bacteria, and other organisms.
Populations in a community interact in many ways. The most obvious form
of interaction is eating (predator) or being eaten (prey). Every animal
population depends on different species of plants or animals as their source
of food. Populations of one type of organism often depend on individuals of
other species for such things as shelter, food, or protection. For example,
some animals live in hollow trees; some birds use twigs and grass to build
their nests; some birds feed off of the insects/organisms that live on or in
other animals.
A Spur-winged Plover finds nourishment
cleaning a Nile Crocodile's teeth of leeches, first
recorded by Herodotus in 440 BC, by J. M. Cook
in 1876 and illustrated in "Popular Natrual
History" by Henry Scherren in 1909.
Increasing the number of organisms and the number of different species of
organisms within a community leads to a high level of Biodiversity. Recall,
“Bio” means life, and “diversity” means a great amount of variation. The
greater the biodiversity the more likely a large number of organisms will
survive if there are drastic changes within the ecosystem in which these
organism inhabit (live).
Ecosystem Level
An Ecosystem includes not only the biotic factors creating the community
of organisms in an area, but also all of the non-living (Abiotic),
physical/chemical factors of the environment. In an ecosystem, living things
(for example fish, birds, bacteria, mammals, and plants) interact with
members of their own species as well as with members of other species.
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Additionally, these biotic organisms interact with the abiotic factors of their
physical environment, such as the water, air, temperature, and soil. While
the organisms in a forest makes up the forest community, the forest
ecosystem also includes the water, minerals, and climate of the area.
Temperature,
Wind, Carbon
Dioxide, Oxygen
trees
rocks
water
Fish, Algae,
Crayfish, Moss,
Bacteria Living in
Water
pH of water = 7.2
Water Temp. = 590 F
River in a Forest
Biome Level
A biome is a large geographic area with a characteristic climate. Geographic
and climatic factors such as temperature, amount of rainfall, amount of
sunlight, soil type and condition, slope of the lad, etc., affect the type of
plants that can grow in an area. The types of plants, in turn, affect the other
life forms.
The United States has six major biomes: tundra, taiga (coniferous forest),
temperate deciduous forest, grasslands, chaparral, and desert. The
whole earth has only 10 or 15 major biomes. A biome consists of several
communities. The coniferous forest that stretches from the Pacific
Northwest, across Canada and into
Alaska is a biome. Like all biomes, it
has a characteristic set of plants ad
animals. These plants and animals occur
in the communities which make up the
biome. Among the communities which
make up the coniferous forest biome are
lake communities, pond communities,
bog communities, etc.
Biosphere Level
The biosphere is the region on earth in which life
exists. Organisms live in the lower part of the
atmosphere. They also live in almost all bodies of
water in earth. They live on the soil and in the first
meter or two of the soil. This thin layer from the
lower atmosphere (about 100m above the earth’s
surface) to the bottom of oceans (about 100m
down) makes up the biosphere. This 200m “skin” on the surface of the
planet is home for about 500 million kinds of organisms.
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Biological Levels
1. Atoms &
Molecules
2. Cells
2b. Multicellular
2a. Unicellular
3. Tissues
4. Organ
5. Organ System
6. Organism
7. Population
7a. Species
8. Community
9a. Abiotic
9. Ecosystem
9b. Biotic
10. Biome
11. Biosphere
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