Living Thing Biology
Living things make up the world as we know
it. Living things are involved in our
life constantly, seeing that we are
alive. There are five characteristics that
are common to all living things.
Living things are made up of one or more cells.
Each cell is made up of
living matter and is separated by a barrier that
encloses the cell from its
surroundings. However, there are many different kinds
of cells that make up
living things. A single cell can be one organism. These
organisms are known
as unicellular. Most of the organisms that we know best such
as people,
trees, and dogs are all made up of more than one cell. Organisms made
of more
than one cell are said to be multicellular. Another characteristic
that
living things share is that they reproduce. They reproduce, or make
new
organisms of the same sort. In order for a species to survive, it is a
necessity
for them to reproduce because all organisms die eventually. There
are two ways
living things reproduce, sexually and asexually. Sexual
reproduction needs two
cells from two different organisms to merge and form
the first cell of a new
organism. Asexual reproduction is when only one
organism can reproduce without
the assistance of another. The third
characteristic of living things, is that
all living things need to grow and
develop. When an organism is growing, most go
through a cycle called
development. The single cell that starts the cell divides
over and over again
to make all the cells that the organism has when in
adulthood. As the cycle
continues the organism ages. Aging is when the organism
becomes less
efficient in the process of life. The organism will not be able to
reproduce,
and death comes as finally too. The fourth characteristic of a living
thing
is the ability to obtain and use energy. Living things obtain energy
from
their environment or their surroundings. All living things require
energy to
live and build their cells. This process is anabolism. Anabolism is
the process
in a living thing that involves putting together complex
substances from simpler
substances. Plants get their energy from the sunlight
through a process called
photosynthesis. Animals get their energy from food
that is eaten. The food is
then broken down through digestion, resulting in a
release of energy called
catabolism. Living things practice anabolism and
catabolism through the whole
time they are living. The balance of anabolism
and catabolism is called
metabolism. The fifth and final characteristic that
all living things share is
that all living things respond to their
environment. Response to their
environment can be sudden, through behavior,
or gradual, in metabolic process or
growth. Stimulus is anything in the
environment that causes a living thing to
react. Stimuli include light,
temperature, odor, gravity, sound, water, and
pressure. Plants generally act
to stimuli slower than animals. The process in
which living things respond to
stimuli in ways to keep conditions in their body
suitable for life is
homeostasis. These five characteristics of living things
are just the basics
to knowing what makes up living things. Atomic Structure of
Living Things
The basic unit of matter is the atom. Atoms are extremely small,
in fact, if
you placed 100 million atoms in a row one after the other, it would
be one
centimeter long. Even though the atom is small it consists of even
smaller
particles, called subatomic particles. Scientists believe that there is
at
least 200 subatomic particles. The three main subatomic particles are
the
neutron, proton, and electron. In the middle of the atom there is a
nucleus. The
nucleus makes up 99.9 percent of the atoms weight even though it
is a hundred
times smaller than the atom itself. The nucleus contains two
different kind of
subatomic particles, the neutron and the proton. The proton
has a positive
charge and the neutron is a electrically neutral subatomic
particle. Both are
almost equal in mass, 1 amu (atomic mass unit). Another
subatomic particle in
the atom is the electron. It is negatively charged and
it's mass is about 2000
times smaller than that of a neutron or electron.
Usually the number or electron
in an atom is the same as the number of
protons. So, usually the atoms have not
a positive nor negative charge, but
they are neutral. Electron are not in the
nucleus like the protons and
neutrons are. They travel at very high speeds
throughout the atom in energy
levels. The energy levels are like orbits that
surround the nucleus. The
number of protons that are in the nucleus of an atom
is called the atomic
number. The atomic number identifies the atom because no
two atoms have the
same number of protons in there nucleus. For example,
hydrogen has the atomic
number of 1, that means all atoms that have one proton
in its nucleus is
hydrogen. The atomic mass number is the number of neutrons and
protons in the
nucleus. To find the number on neutrons in an atom, you must
round the atomic
mass number to the nearest whole number and then subtract the
atomic number.
Remember the atomic number is the same as the number of protons
in the atom.
To find out the number or electrons an atom contains, you just need
to know
the atomic number because there is the same number of protons as there
is
electrons in atoms. For example, in sodium, the atomic number is 11, and
the
atomic mass number is 22.98977. This means that sodium contains 11
protons, 11
electron, and 12 neutrons. (See Figure 1) Substances known as
elements are made
up of solely on type of atom. Scientists have discovered
109 elements, 90 were
found in nature, and 19 were artificially made in
laboratories by scientists.
Each element is represented by a chemical
symbol. Each symbol is made up of one
or two letters, usually taken from the
name of the element. The symbol of oxygen
is O, the symbol for phosphorus is
P, and the symbol for Nitrogen is N. Most
chemical elements are solid, like
gold, iron, bronze, and silver to name a few.
They are on the left 3/4 of
the periodic table. Some elements are gases, like
oxygen and carbon. They are
on the right 1/4 of the periodic table. Only a few
elements are liquids,
mercury and bromine are the most common. The noble gases
are located all the
way to the right on the periodic table. The atomic number of
an element is
always the same, this means that an element will always have the
same number
of protons. However, the number of neutrons in the nucleus may
differ from
one atom to the next. For example, the typical hydrogen atom
contains one
proton and no neutrons inside the nucleus. Another form of hydrogen
is called
deuterium. It contains one proton and one neutron in the nucleus. The
third
form of hydrogen is sometimes referred to as tritium. Tritium has on
proton
and two neutrons in the nucleus of the atom. Even though the atomic
mass
number may change the atomic number of hydrogen will be 1, and it will
still
have one proton and one electron. An isotope is an atom with the same
number of
protons and electrons but a different number of neutrons from the
same element.
Isotopes are represented by putting a number in front of
the atomic symbol of
that atom. The number represents the atomic mass.
Regular hydrogen is written
1H, deuterium is 2H, and tritium is 3H.
Compounds and Molecules When elements
combine to form substances of
consisting of two or more atoms, chemical
compounds are produced. A chemical
compound deals with the combination of two or
more atoms in definite
proportions. Most materials in living things happen to be
compounds, so they
are very important to us. Chemical compounds are represented
just as elements
are with chemical symbols. A chemical formula is made up of the
chemical
symbols that make the chemical compound. For example, water contains
two
hydrogen atoms and one oxygen atom. The chemical formula would be H2O.
Table
salt is made from one sodium atom and one chlorine atom, so the
chemical formula
is NaCl. Chemical compounds are formed by the interaction of
atoms. Chemical
bonding is the process in which atoms interact and combine.
An important factor
in chemical bonding is the number of electrons in an
atom's outermost energy
level. Each energy level can only hold a certain
number of electrons. The
innermost energy level, or first energy level can
hold only two electrons. The
second energy level can hold eight electrons.
The third holds eighteen
electrons, the fourth and fifth energy levels hold
up to thirty-two electrons.
The sixth energy level can bear eighteen
electron, the seventh energy level can
hold eight electrons. The eighth and
outermost energy level can accommodate for
a mere two electrons. In order for
there to be electrons in outer energy levels,
the inner energy levels must be
full. There can't be 1 electron on the first
energy level and five on the
second. It would have to be two on the first energy
level and four electrons
on the second. When the electrons of an atom fill the
outermost energy level
they are said to be stable, or unreactive. These atoms
will not bond with
other atoms to form chemical bonds. In order for an atom to
become stable, it
will either have to lose or gain electrons to make it's
outermost energy
level complete. There is one other way an atom can be stable.
It will be
stable if it's outermost energy level contains eight electrons. One
type of
bond to make atoms stable is called an ionic bond. An ionic bond is a
bond
that involves the transfer of electrons. The name comes from the word
ion.
Ion means charged particles. Ions are produced when ionic bonds
occur. For
example, sodium has only one electron on its outermost energy
level and chlorine
has seven on its outermost energy level. These two atoms
want to bond in order
to become stable. That means it wants to get rid of it
to become stable. The
loss of the one electron makes a sodium ion (Na+),
which is positively charged.
It's positively charged because it lost one
of it's negatively charged
electrons. Thus, the electrons and protons don't
balance, because now there is
one more proton than electron, so the ion has a
positive charge. The addition of
one electron makes a negatively charged
chlorine ion (Cl-). The two ions are
oppositely charged and now have an
intense attraction to each other. The
attraction is caused by the transfer of
electrons that holds the ions together
in an ionic bond. (See Figure 2) A
different type of bond is called a covalent
bond. A covalent bond is formed
when atoms share electrons in order to become
stable. The shared electrons
are located in the outermost energy levels of both
atoms. This forms a strong
bond that is in many living things. Covalent bonds
can be in the form of
single bonds, double, or triple. The bond between two
hydrogen atoms and
oxygen atom (H2O), forms a single bond. A single pair of
electron is shared
between the two hydrogen atoms and the oxygen atoms. (See
Figure 2) On
the other hand, the compound that forms carbon dioxide (CO2), forms
a double
bond. The carbon atom shares two pairs of electrons, four total with
the two
oxygen atoms. In covalent bonds the combination of atoms that are caused
from
sharing form molecules. A molecule is the smallest particle of a
covalently
bonded compound. Besides water and carbon dioxide that were
already mentioned,
sugar (C6H12O6) and ammonia (NH3) are compounds. Organic
compounds are compounds
that contain carbon. Carbon is a unique element
because of its ability to form
covalent bonds that are exceptionally strong
and stable. The carbon atom has two
electrons in the first energy level and
four in the second energy level. There
are four open positions in carbon's
outermost energy level, allowing it to form
four single covalent bonds.
Carbon can easily bond with hydrogen, oxygen,
nitrogen, phosphorus, and
sulfur atoms. Carbon also has the extraordinary
ability to form long chains
with other carbon atoms. The bonds between carbon
can be single, double, or
triple covalent bonds. No other element has this rare
ability. (See Figure 2)
Cell Structures Cells from a living thing come in many
different sizes and
shapes. Even though cells differ in size and shape, certain
parts of the
cells are the same. The cells of animals, plants, and other
organisms have
three major but basic structures in common: the cell membrane,
the nucleus,
and the cytoplasm. The cell membrane acts as the cell's outer wall
and
protects it from it's surroundings. It also moderates what goes in, and
what
comes out of the cell. The cell membrane is made up of several different
types
of molecules. The most important of these is lipids. Most of the cell
membrane
is made up of a double layer of lipids. The cell membrane is also
made up of
proteins and carbohydrates. In plants the cell membrane is
surrounded by the
cell wall of the plant. The cell wall helps protect and
support the plant. The
cell wall lets water, oxygen, and carbon dioxide pass
through easily. The cell
wall is made up of three layers which are extremely
porous. In the majority of
cells there is a dark structure we know as the
nucleus. Not all cells have
nuclei though. Bacteria and other small
unicellular organisms don't have a
nucleus. These are said to be prokaryotes,
or cells without nuclei. Cells that
do have a nucleus are called eukaryotes.
The nucleus is very important to the
cell, it is the information center and
contains DNA. DNA stores genetic
information that is passed to one generation
to the next. The DNA in a cell is
attached to special proteins. These
proteins are called chromosomes. Chromosomes
contain genetic information that
is passed through generations. The nucleus of a
cell tend to be about two to
five micrometers in diameter. Surrounding the
nucleus there are two membranes
called the nuclear envelope. The nuclear
envelope contains dozens of small
pores, through which molecules move in and out
of the nucleus. In most
nuclei, there is a small region called the nucleolus. It
is made up of RNA
and proteins. In the nucleolus, ribosomes are made. Ribosomes
are important
because they help out with the productions or proteins in a cell.
The
space inside of a cell can be divided into two parts, the nucleus and
the
cytoplasm. The cytoplasm is the area between the nucleus and the cell
membrane.
The cytoplasm contains other important structures in the cell.
Structures inside
the cell are called organelles. An organelle is a tiny
structure in the cell
that preforms a special function within the cell. The
mitochondria is greatly
important to the cell. In animals, the mitochondria
changes the stored chemical
energy from food into more useful energy for the
cell. In plants, an organelle
called the chloroplast changes energy from
sunlight to energy that can be used
by the cell. The mitochondria is found in
both the cells of plants and animals,
where as the chloroplast is only found
in plants. Ribosomes are the structures
in which proteins are produced. They
are made out of protein and RNA. Some
ribosomes in a cell are attached to
membranes, while some are free in the
cytoplasm. Ribosomes are one of the
smallest organelles in a cell. Many cells
are filled with a network of
channels we call the endoplasmic reticulum. The
endoplasmic reticulum
transports through the inside of the cell. There happens
to be two different
types of endoplasmic reticulums. The smooth endoplasmic
reticulum has
channels that are smooth. In some cells special enzymes and
chemicals are
stored within the smooth endoplasmic reticulum. The other type of
endoplasmic
reticulum is called the rough endoplasmic reticulum. It is called
rough
because it has ribosomes that are attached to the surface making it
look
rough. Many proteins that are released are transported from the cell in
the
rough endoplasmic reticulum. The newly formed proteins are often first
moved
into special compartments known as the Golgi apparatus. In the Golgi
apparatus
the proteins are modified and then releases it. The Golgi
apparatus' function is
to modify, collect, package, and finally distribute
molecules made in one
location to another location. When foreign materials
that are too big to move in
the cell get into the cell, the cell membrane
forms a pocket around it. Then the
lysosomes come in and digest, then break
down the particle. Lysosomes are small
structures that contain chemicals and
enzymes that help break down and digest
foreign particles in the cell.
Lysosomes are made in the Golgi apparatus, and
plants don't have lysosomes.
Vacuoles are sac-like structures in a cell that
store water, salts, proteins,
and carbohydrates. Plants also have a structure
besides the vacuole called
the plastid. The plastid also stores food as well as
pigments for the plant.
The cytoskeleton in a cell is the frame work that holds
the cell together and
gives it their shape. The cytoskeleton is made from
filaments and fibers. One
of the main parts in a cytoskeleton is a component
called microtubules. They
are made out of hollow tubules made from proteins.
They help move
organelles throughout the cell. (See Figure 3) The Cell As a
Living Thing
Living things are made up of cells and they grow in size. In most
instances,
a living thing grows because it produces more and more cells. Cells
in an
adult human are no bigger that cells in a human baby, there is just more
of
them. In a cell, water, oxygen, and food enter the cell through the
cell
membrane, and waste products exit the cell. The time it takes to
exchange these
materials depends on the surface area of the cell. How quickly
food and oxygen
is used, and how quickly waste products are produced depends
on the volume of
the cell. As a cell gets bigger, the volume increases faster
than the rate of
its surface area. This can be a problem for the cell. If the
diameter of a cell
increases 5 times, the surface area would increase 25
times, and the volume
would increase 125 times. The bigger the cell is the
harder time it has getting
the nutrients and oxygen it needs in order to
support it's massive volume. Cell
growth is controlled in multicellular
organisms. Cells in parts of the body like
the heart and liver rarely divide.
These cells are unlike skin cells that divide
rapidly through a person's
lifetime. Controls on cell growth can be turned on
and off like a light
switch. If a bone or skin is broken, cells divide in order
it repair the
damage that needs to be fixed. Uncontrolled cell growth can be
very harmful
to multicellular organisms. Cancer is a disorder when cells have
lost the
ability to control their growth. Cancer cells keep growing and growing
until
the supply of nutrients shuts off. Cancer is a very serious disease
that
shows the importance of controls on cell growth. Eukaryote cells divide
in order
to slow down cell growth. Cell division is the process in which a
cell divides
to form two daughter cells. The first stage of cell division is
called mitosis.
Mitosis is the process when the nucleus of a cell is
divided into two nuclei,
and both have the same number and type of
chromosomes as the parent cell.
Mitosis can be split into four parts.
Interpahse occurs before mitosis can
begin. It is the period in between cell
division and is the longest part of the
cell cycle. The cell cycle is the
process when a cell grows, prepares for
division, divides, and begins a new
cell cycle. Interphase itself is divided
into three phases: G1, S, and G2.
G1, called growth 1, or gap 1, is the stage in
which a cell grows. The S
stage is called the DNA synthesis stage. During this
stage of interphase the
DNA is replicated in DNA replication. Proteins are also
synthesized in the S
phase. G2, or growth 2, takes place when the S stage is
finished. During G2
the synthesis or organelles and other materials happens
furthermore preparing
the cell for division. While interphase is taking place
the nucleus is busy
in synthesizing messenger RNA to direct all the steps. The
first phase in
mitosis is called prophase. Prophase takes the longest time in
mitosis,
consuming 50-60% of the time it takes mitosis to occur. In prophase
the
chromosomes in a cell condense and coil up, making them more visible.
The
centrioles separate and go to opposite sides of the cell. Centrioles are
small
structures in the cytoplasm that contain tubulin, a microtubule
protein. Plant
cells don't contain centrioles. The condensed chromosomes
become attached to
fibers in the spindle. The spindle is a mesh-like
structure that helps move the
chromosomes apart. At the end of prophase the
chromosomes condense tighter, the
nucleolus disappears, and the nuclear
envelope begins to break down. Metaphase
is the second phase of mitosis, and
is the shortest as well. During this phase
the chromosomes line up across the
center of the cell. Anaphase is the next
phase in mitosis. It begins when the
sister chromatids split. Chromatids are the
identical parts that form the
chromosome. The chromatids become individual
chromosomes and continue to
split until they reach the opposite poles. Anaphase
ends when the new
chromosomes stop moving. Telophase is the fourth and final
stage of mitosis.
The chromosomes begin o uncoil into a tangle of chromatin.
Chromatin is
the material that makes up chromosomes and itself is made from
protein and
DNA. All of this takes place where the two new daughter cells are
taking
shape. Two nuclear envelopes begin to reappear around the chromatin.
The
spindle begin to break apart and the nucleolus forms around the nucleus
of the
daughter cells. Mitosis is over but there is still one more step.
Cytokenesis
follows quickly after mitosis is finished. In cytokenesis the
cytoplasm of the
parent cell splits into two to form the daughter cells. In
animals, the cell
membrane moves together and pinches the cells, giving
making the daughter cells
have their own nucleus and organelles. In plants
the cell plate appears and
forms a barrier between the two daughter cells.
The cell plate then forms into a
cell membrane, then the cell wall develops.
(See Figure 4) Tissues and Organs In
multicellular organisms, cells are
organized in specialized groups, known as
tissues. A tissue is a group of
similar cells that preform similar functions.
Different tissues form many
different tasks. For example, a kind of tissue is
made up of cells that
produce digestive enzymes in the pancreas, and the cells
in an eye respond to
light. Most multicellular organisms have four main types of
tissues: muscle,
epithelial, nerve, and connective. Some tasks in the body are
too complicated
to be preformed by only one type of tissue. So, organs preform
these duties.
An organ is a group of tissues that work together to preform a
specific
function. Many types of tissues may be used to form one organ. For
example, a
muscle in an organism is classified as an organ because not only
muscle
tissue makes up the muscle. There is nerve tissue, connective tissue, as
well
as a special tissue that connects the muscle with certain parts of the
body.
All the tissues in an organ work together to preform one common
function.
Sometimes not just one organ can complete one task, so an organ
system is
needed. An organ system is a group of organs that work together to
preform one
function. There are many organ systems in our body. We have a
muscular system,
skeletal system, nervous system, and circulatory system.
Multicellular Organisms
A multicellular organism is a living thing that
is made up of more than one
cell. These organisms can contain hundreds,
thousands, even billions of cells or
more. We see multicellular organisms
everyday: people, plants, and house pets.
To describe a multicellular
organism, we have to put them into levels of
organization. The levels of
organization in multicellular organisms include
cells, tissues, organs, and
organ systems. The first level is cells, the second
is tissues, next is the
organs, and finally the fourth level is the organ
system. Multicellular
organisms start off with one basic unit, the atom, and
build up to make
bigger things. Atoms combine to form compounds which then form
organelles.
Organelles then come together to make a cell. Cells then form
tissues, which
could then make organs. After organs are formed, then organs can
be in an
organ system. Eagle The eagle is sometimes referred to as the
"king of
flight" because of the power it shows while in flight. The
eagle has been a
symbol or strength and courage since ancient times. In 1782,
Congress
chose the American bald eagle to be the symbol of our nation. The
national
seal was the bird with its wings spread outward. It holds an olive
branch in
one claw and arrows in the other. The eagle appears in many places
today in
the United States. Only two species of eagles are found in North
America
today: the American bald eagle, and the golden eagle. The bald eagle is
more
common than the golden eagle. This extraordinary bird has white tail
feathers
and white plumes on its head and neck. The bald eagle lives in open
areas, or
forests, near water. The bald eagle is usually 35-40 inches in length,
and
have a wingspan of 7.5 feet. The female bald eagle is more ferocious than
the
male, and is a couple inches larger. A bald eagle migrates only if the
water
it feeds in freezes in the winter months. It returns every year to the
same nest
and the same mate. The nests are built in trees or on cliffs, and
sometimes on
the ground. The eagle adds to it every year, making it bigger
and bigger as time
goes on. The nests can weigh up to one thousand pounds.
The nests are made from
sticks, weeds, and dirt. Bald eagles eat carrion,
waterfowl, and especially
fish. The golden eagle was more common than the
bald eagle when settlers first
came here, but this is not the case today.
It's found in the western portion of
North America, from Alaska, south to
Mexico. The golden eagle is about the same
size as a bald eagle. It's
feathers are much darker than that of its famous
counterpart. There are
feathers on the head and the neck of the bird that shine
like gold when
they're in the sun. The toes and claws of the golden eagle are
feathered,
where as the bald eagle has no feathers on its legs. With their
claws, golden
eagles eat squirrels, prairie dogs, and rabbits. The golden eagle
is very
brave and can attack large animals such as deer, but can't carry them
away.
They build nests in trees and rocky cliffs with sticks. The golden eagle
has
been known to defend its nest up to 75 square miles. As you can see, the
two
types of eagles in North America are similar and different in many ways.
Both of
the eagles are very powerful birds. One thing is for sure, the eagle
is a very
beautiful bird that is extremely interesting.