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Prokaryotes and eukaryotes
Two types of •There are two types of cells. Organisms areclassified according to the
cells type of cells they possess. Bacteria have prokaryotic cells and are called
prokaryotes. Other types of organisms have eukaryotic cells and are called
eukaryotes. What are the differences between these types of cells?
Prokaryotic Prokaryotic cells do not have a nucleus.
cells The nucleus is a structure that holds DNA
and controls the functions of a cell. The
Greek word prokaryotic jneans "before
nucleus." Scientists believe that all life on
Earth came from these cells. The oldest
fossils of prokaryotes are estimated to be
3.5 billion years old. The DNA in a
prokaryotic cell is bunched up in the center
of the cell. All prokaryotic cells are much
smaller than eukaryotic cells (Figure 15.2).
Eukaryotic Eukaryotic cells have a nucleus (with
cells the exception of the red blood cells of
mammals). The Greek word
eukaryotic means "true nucleus."
The oldest fossils of eukaryotic cells
are about 2 billion years old. There
is more DNA in these types of cells
than what is found in prokaryotic
cells. This DNA of a eukaryotic cell
is found in the nucleus. Eukaryotic
cells tend to be about ten times larger
than prokaryotic cells (Figure 15.2).
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Unit 5 Organismsand Ecosystems
prokaryotic cell - a cell that does
not have a nucleus
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nucleus - a structure inside a cell
that holds DNA and controls the
functions of the cell
eukaryotic
a nucleus
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Autotrc
cell - a cell that has
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Other type
autotrc
Heterotrc
Membrane-bound
nucleus containing DNA
Prokaryotic
cell
Eukaryotic cell
Eukaryotic cells are
usually about 10 times bigger than
prokaryotic cells.
Figure 15.2:
Energy
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utotrophs and heterotrophs .
Organisms
need energy
Autotrophs
All organisms, including cells, need a constant supply of energy in order to
stay alive. They get this energy from food. Organisms canbe classified into
two groups according to how they obtain energy. Those groups are called
autotrophs and heterotrophs.
are organisms that can make their own food. Some autotrophs,
such as plants and algae, make their own food through a process called
photosynthesis. Photosynthesis is a process in which energy from
sunlight is used to combine water and carbon dioxide to produce energyrich food sugar (glucose) molecules. Plant cells have tiny structures called
chloroplasts where photosynthesis occurs (Figure 15.3). Once the glucose
molecules are made in the chloroplasts, they can be used later by plant cells
to release the stored energy. Some of the glucose molecules are used to
make larger molecules that become part of the plant's tissues.
Autotrophs
autotroph - an organism that
makes its own food
a
photosynthesis - process in
which sunlight is used to produce
energy-rich glucose molecules
heterotroph - an organism that
cannot make its own food
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Other types of Not all autotrophs make their food through photosynthesis. For example;
autotrophs
bacteria that live around undersea volcanic vents can make their own food
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without sunlight. They use heat energy and chemicals instead of energy
from the Sun to produce their food. This process is called chemosynthesis.
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Heterotrophs
Energy and
food
are organisms that cannot make their own food ..A
heterotroph must obtain its energy from the molecules originally made by
autotrophs. This occurs either when heterotrophs eat autotrophs, or when
heterotrophs eat other heterotrophs which have eaten autotrophs. The cells
of heterotrophs break down the food molecules to release energy required to
keep the cells alive. The cells of heterotrophs do not contain chloroplasts.
Heterotrophs
All of the energy available to most organisms originally comes from
sunlight. If a heterotroph is a plant-eater, it obtains the energy directly from
the plant that originally transformed sunlight into food energy. Meat-eaters
still obtain their energy from sunlight, but that energy has already been
changed from the sunlight originally captured by a plant, into food energy
inside the organism that ate the plant. How do you get your energy, from
autotrophs, heterotrophs, or both?
Glucose + Oxygen
Figure 15.3: Plant cells have
structures called chloroplasts where
photosynthesis occurs.
Reading 15.1 Cells
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15.2 Clas
Types of reproduction
Two types of There are thousands of species (unique types) of organisms. Each species
reproduction produces more of its own. A species of bacteria splits to make two identical
bacteria. A eucalyptus tree produces 'more eucalyptus trees. Humans
produce more humans. The formation of new organisms of the same species
is called reproduction. Reproduction is an important life function. There
are two types of reproduction: asexual and sexual.
reproduction - the formation of
new organisms of the same species
,
asexual reproduction - a type
of reproduction that involves only
one parent
sexual reproduction
a type
of reproduction that involves
two parents
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Asexual
reproduction
Asexual reproduction
is reproduction that requires only one parent. Most
unicellular organisms reproduce this way. In asexual reproduction, the DNA
and internal structures are copied. Then the parent cell divides, forming two
cells that are exact copies of the original.
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Sexual Sexual reproduction involves two parents. Most multicellular organisms
reproduction reproduce this way. In sexual reproduction, special cells from each parent
unite to form a single celL That cell quickly divides multiple times and
develops into a new organism.
Reading 15.1 Check Your Understanding
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importance c
classificatio-
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1. What is the basic unit of structure and function in a living
thing called?
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Fill in this Graphic Organizer and add it to your notebook.
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2. What are three similarities that all cells share?
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Use the cbart
3. What are the major differences between prokaryotic and
eukaryotic cells?
4. How do autotrophs get energy?
5. How do heterotrophs get energy?
6.
Name an example of an autotroph and an example of a heterotroph.
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7. What is reproduction? Name two ways organisms reproduce.
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Unit 5 Organisms and Ecosystems
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