Grade 11A
Name:______________________________ Class: _________________
Active reading 11A – Microbiology and Biotechnology
Topic 1: Bacteria
Prokaryotes are single-celled organisms that do not have nuclei or other
membrane-bound organelles. Scientists divide prokaryotes into two major
groups: the domain Archaea and the domain Bacteria. Although members of the
domain Archaea are prokaryotes, some of their molecules are similar to those of
eukaryotes. Many Archaea live in harsh environments, such as hot springs. Most
prokaryotes belong to the domain bacteria. Organisms in both prokaryote
domains are generally referred to as bacteria.
Bacteria have a single chromosome made up of DNA. This chromosome is a large
loop gathered into a mass called nucleoid. In addition, bacteria often have small
extra loops of DNA called plasmids. The bacteria cell membrane is made up of
two lipid layers. A cell wall surrounds the cell membrane. The cell wall is made of
a protein-carbohydrate compound called peptidoglycan. In some bacteria such as
E. coli shown below, an outer membrane covers the cell wall.
Grade 11A
Name:______________________________ Class: _________________
Scientists classify bacteria based on their structure using a technique called Gram
staining. Gram staining involves colored dyes. As shown below Gram-positive
bacteria have a thick layer of peptidoglycan in their cell wall and no outer
membrane. They stain darkly with Gram staining dyes because their
peptidoglycan layer is very thick. Gram-negative bacteria have a thin layer of
peptidoglycan in their cell walls covered by an outer membrane. The thin
peptidoglycan layer does not trap the dark dye, but does absorb the pink dye.
Their outer membrane makes them more resistant to medicines and the body’s
defenses than Gram-positive bacteria.
Bacteria can be divided into three groups based on their energy sources. These
groups are photoautotrophs, chemoautotrophs, and heterotrophs. Bacteria that
use energy from sunlight to make their own food are photoautotrophs. Recall
that this process of making food is called photosynthesis. Bacteria that use energy
from inorganic molecules, such as sulfur and ammonia, to make their own food
are chemoautotrophs. These bacteria are the only organisms that can obtain
energy from inorganic sources. Bacteria that use other organisms for food are
called heterotrophs. These bacteria cannot make their own food. Most
heterotrophic bacteria absorb nutrients from dead organisms. However, some
heterotrophic bacteria obtain nutrients from living organisms.
Grade 11A
Name:______________________________ Class: _________________
Bacteria reproduce by binary fission. They can form new genetic combinations by
conjugation, transformation, and transduction. They can also survive harsh
conditions by forming endospores.
Bacteria reproduce asexually by binary fission. In this process, a single cell divides
to produce two genetically identical cells. Mutations often occur during binary
fission that can produce new genetic forms of bacteria.
Bacteria can transfer genetic material in a process called conjugation. Conjugation
occurs when a thin tube, called a pilus, attaches between two bacterial cells. The
cells join and exchange genetic information.
In conjugation, a pilus
extends from one bacterium
and attaches to the seconds
bacterium. Genetic material
is then transferred through
the pilus from the first
bacterium to the second
bacterium.
Bacteria can also form new genetic combinations by transformation and
transduction. In transformation, bacteria take up small pieces of DNA around
them. In transduction, viruses transfer DNA between bacteria.
Some bacteria survive harsh conditions by forming thick-walled structures called
endospores. Endospores form inside bacteria. They contain a copy of the
bacteria’s DNA and a small bit of cytoplasm. Endospores can survive conditions
that kill most bacteria, such as heat, radiation, and acids. When conditions
improve, endospores form new bacteria.
Grade 11A
Name:______________________________ Class: _________________
Key words
Prokaryotes
Plasmid
chemoautotrophs
Transduction
Archaea
Peptidoglycan
Heterotrophs
Endospore
Bacteria
Gram staining
conjugation
Nucleoid
photoautotrophs
Transformation
Vocabulary
Conjugation in prokaryotes, algae, and
fungi, a type of sexual reproduction in
which two cells join temporarily to
recombine nuclear material
Peptidoglycan a protein-carbohydrate
compound that makes the cell walls of
bacteria rigid
Endospore a thick-walled protective
spore that forms inside a bacterial cell
and resists harsh conditions
Plasmid a genetic structure that can
replicate independently of the main
chromosome(s) of a cell; usually, a
circular DNA molecule in bacteria
(prokaryotes)
Gram-negative describes a type of
Transduction the transfer of a bacterial
prokaryote that has a small amount of
gene from one bacterium to another
peptidoglycan in its cell wall, has an
through a bacteriophage ( a virus)
outer membrane, and is stained pink by
a counterstain during gram staining
Gram-positive describes a type of
prokaryote that has a large amount of
peptidoglycan in its cell wall and is
stained violet during gram staining
Transformation the transfer of genetic
material in the form of DNA fragments
from one cell to another or from one
organism to another
Grade 11A
Name:______________________________ Class: _________________
A. Write one or more sentences to answer the following questions
1. What are the two major domains of prokaryotes? And which domain do
most prokaryotes belong to?
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2. How many chromosomes does a bacterium have?
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3. Are the ribosomes of E. coli surrounded by a membrane? Explain your
answer.
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4. Why can an infection by Gram-negative bacteria be more dangerous
than an infection by Gram-positive bacteria?
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5. Identify what type of bacteria cannot make their own food
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6. What is a pilus? And what is its function?
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7. If eight bacterial cells undergo binary fission, how many bacterial cells
will result?
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Grade 11A
Name:______________________________ Class: _________________
B. Describe ways in which the structure of Gram-positive bacteria is
different from that of Gram-negative bacteria.
Gram-negative bacteria
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Gram-positive bacteria
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C. Compare between bacteria according to their energy source:
D. Explain how do endospores help bacteria survive harsh conditions?
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Grade 11A
Name:______________________________ Class: _________________
E. Circle the letter of the phrase that best answers the question.
1. Pili are tubular shafts in bacteria that serve as a means of ...
A) genetic exchange
B) attachment
C) genetic exchange
D) protection
2. Bacterial endospores function in
A) reproduction
B) survival
C) protein synthesis
D) storage
3. Some bacteria form a thick-walled __________ in response to poor nutrient
conditions.
A) endospore
B) capsule
C) sheath
D) pilus
4. Bacteria normally contain their genome in
A) a nucleoid region
B) an endospore
C) a plasmid
D) a pilus