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The importance of bacteria
The importance of bacteria
Bacteria and
industry
Bacteria are used in many areas of industry. Yogurt and cheese
are made with certain types of bacteria. Some important drugs
like insulin are made with the help of bacteria. Sewage treatment
plants use bacteria to break down waste products. Other bacteria
are used in mining and to clean up oil spills. There is a good
chance that you’ve benefited from bacteria today!
Symbiosis Many kinds of bacteria have developed close relationships with
other organisms. In many relationships the bacteria and the
organism it lives with benefit. This type of symbiosis is called
mutualism. One species of bacteria lives in your intestines. You
provide the bacteria with a warm, safe place to live. In return, the
bacteria help you break down and absorb certain compounds in
foods. Bacteria even make some vitamins that your cells cannot
make on their own.
Life on Earth
depends on
bacteria
Bacteria are an important part of the nutrient cycles that all life
depends upon. For example, plants need nitrogen to make amino
acids, the building blocks of protein. Bacteria in the soil take
nitrogen out of the air and turn it into a form plants can use. When
animals eat plants, they rearrange the amino acids into other
proteins. When an organism dies, bacteria break down the dead
material and turn it back into compounds that living things can
use again (Figure 9.10). Bacteria are “nature’s recyclers.”
Bacteria and
antibiotics
Have you ever had a bacterial infection? If so, you’ve experienced
one of the harmful effects of bacteria. Bacteria cause diseases like
strep throat, respiratory infections, and infected wounds. Bacterial
diseases are treated with drugs called antibiotics. Antibiotics kill
bacteria without harming your own cells. Different antibiotics are
used for fighting different types of bacteria.
Bacteria
Bacteria
“Wash your hands — you don’t want to get sick from bacteria!” How many times have
you heard a command like that? Bacteria are everywhere and some can make you
sick. But did you know that many types of bacteria are helpful? In fact, life on Earth
depends on them. Bacteria take elements like carbon and nitrogen out of the air and
turn them into compounds living things can use. They recycle nutrients from dead
plants and animals so they can be reused. There are even bacteria in your digestive
system (Figure 9.5)! In this section, you’ll learn about the structure and function of
bacterial cells.
What are bacteria?
Bacteria are the
only prokaryotes
Bacteria are organisms that consist of a single, prokaryotic cell.
Bacteria are the only prokaryotes (cells without a nucleus). All
other life forms on Earth are eukaryotes. Bacterial cells have a cell
membrane that is surrounded by a tough cell wall (Figure 9.6).
Where do
bacteria live?
Bacteria live on or in just about every material and environment
on Earth. They live in soil, water, and air. They are found in the
coldest regions of the Arctic and even in boiling waters near
undersea volcanoes. There are many bacteria in each
environment. A square centimeter of your skin has thousands of
bacteria. A teaspoon of soil contains more than a billion bacteria.
1 or 2 kingdoms
of bacteria?
Some scientists group all bacteria into the Kingdom Monera.
Others divide bacteria into two kingdoms, Archaebacteria and
Eubacteria. Archaebacteria are found in extreme environments
like volcanic vents in the ocean. They are thought to be the first
organisms on Earth. Eubacteria are found almost everywhere else
and have a different chemical makeup than archaebacteria. Both
types of bacteria are prokaryotic, single-celled organisms. As
future discoveries are made, these groups may change.
Amazing Cells!
Amazing Cells!
Did you know your body is made of trillions of cells? There
are millions of different types. Where did all of these
different types come from? Part of the answer is a special
type of cell called stem cells.
Many living things need stem cells including animals and
plants. An organism that is not fully developed is called an
embryo. In animal embryos, stem cells can develop into
different types of cells. Your body has over 200,000 different
types of cells. It has blood cells, muscle cells, skin cells, and
stomach cells just to name a few. Each type of cell has its
own structure and function.
The process of differentiation
All stem cells have some certain properties:
• Stem cells divide to make more stem cells.
• Stem cells also have the ability to develop into different types
of cells.
A stem cell divides into two daughter cells. Each daughter
cell is identical to the original parent cell. When mature,
these cells also divide. This is how embryos get a supply of
stem cells. A growing embryo needs a lot of stem cells to
develop tissues and organs. In the laboratory, starting with a
few stem cells, scientists have grown millions in a few
months.
So how do
stem cells
change into
other types of
cells?
Scientists are
studying this
problem.
Something called a signal tells stem cells to become different
types of cells. Genes are pieces of DNA that carry
information from the parent cell to the offspring cells. The
genes inside stem cells provide internal signals. The
environment outside of the cell provides external signals.
The cell's environment includes chemicals from other cells.
Different types of
specialized animal cells
There are two main types of
animal stem cells. More than
twenty years ago, scientists
extracted stem cells from the
embryos of mice. These stem
cells are described as
embryonic. The other main
type of stem cells is described
as adult. Embryonic stem
cells and adult stem cells are
very different.
Embryonic stem cells can divide to make more stem cells.
They wait for a signal. Then they start producing specialized
cells. These specialized cells form the tissues, which in turn
form the organs. Parent cell Two daughter cells
Bacteria and the beginning of life on Earth
Bacteria and the beginning of life on Earth
Bacteria were the
first organisms
Scientists believe that bacteria were the first organisms on Earth.
Evidence comes from fossils of single-celled prokaryotes found in
rocks that are more than 3 billion years old. At that time, there was
little oxygen in the atmosphere. The earliest life was therefore
anaerobic (Latin for “without oxygen”). Anaerobic bacteria do not
require oxygen for cellular respiration. Today, anaerobic bacteria
thrive in places that have little or no oxygen, like swamps.
Bacteria
increased oxygen
in Earth’s
atmosphere
Over time, some bacteria developed the ability to use
photosynthesis. Cyanobacteria, still in existence today, were
one of the first photosynthetic bacteria. One of the products of
photosynthesis is oxygen. Over hundreds of millions of years, the
amount of oxygen in Earth’s atmosphere increased. This allowed
aerobic bacteria to develop. Aerobic bacteria use oxygen for
cellular respiration. There are many different species of aerobic
bacteria living today.
Eukaryotic cells
developed from
prokaryotic cells
Eventually, eukaryotic cells developed from bacteria. A scientific
theory states that long ago, smaller prokaryotic cells were engulfed
by larger prokaryotic cells. The smaller cells began to survive by
living inside of the larger cells. Over time they took on specific
functions inside the larger cells like producing energy. Eventually,
the smaller cells became the organelles (like mitochondria) inside
of eukaryotic cells (Figure 9.9).
Cells and Energy
Cells and Energy
To stay alive, you need a constant supply of energy. You need energy to move, think,
grow, and even sleep. Where does that energy come from? It all starts with the sun.
Plant cells store energy from the sun in the form of molecules. In this section you’ll
learn about how cells store and release energy.
What is photosynthesis?
Solar cells and
chloroplasts
A solar calculator has solar cells that convert light into electrical
energy. The electrical energy powers the calculator. Some of
it is stored in a battery. A plant cell has chloroplasts that also
convert energy. Chloroplasts are where photosynthesis occurs.
Photosynthesis is a process where plants use the energy of
sunlight to produce energy-rich molecules (carbohydrates).
Photosynthesis takes place in the
chloroplasts.
How does a tiny
seed grow into a
massive tree?
Before our knowledge of photosynthesis, gardeners wondered how
a tiny seed could grow into a massive tree. Where did all of that
mass come from? In the 1600s, a Flemish scientist named Jan Van
Helmont (1580–1644) conducted an important experiment. He
grew a willow tree in a carefully weighed amount of soil. He
noticed that the mass of the soil barely changed while the mass of
the tree greatly increased. He concluded that the extra mass did
not come from the soil.
Photosynthesis
is a chemical
reaction
Later experiments carried out by other scientists showed that
plants use carbon dioxide (from the air) and water to make a
simple carbohydrate (glucose). They also release oxygen. This
chemical reaction (photosynthesis) takes place only in the
presence of light (Figure 8.6).
Light and color
Visible light The Sun provides Earth with a steady source of light. Your eyes
perceive sunlight as white light. However, it is really made up of
different colors of light. The colors that make up sunlight are called
visible light. There are other forms of light we cannot see such as
ultraviolet and infrared light.
Light is a wave Light is a wave, like a ripple on a pond. Waves can be described by
their wavelength (the length from peak to peak), and energy. Light
is part of a continuum of waves known as the electromagnetic
spectrum. Light waves have very short wavelengths. They range
from 800 nm (red light) to 400 nm (violet light). One nanometer
(nm) is equal to one-billionth of a meter!
Color A prism splits white light into all of its colors. Color is how we
perceive the energy of light. All of the colors of visible light have
different energies. Red light has the lowest energy and violet light
has the highest energy. As we move through the rainbow from red
to violet, the energy of the light increases (Figure 8.7).
