Download Chapter 4 Viruses and Bacteria

6th Grade Study Guide
VIRUSES
A virus is a small, non-living particle that invades then reproduces inside a living cell.
Viruses are not considered living because they are:
• Not made of cells
• Do not respond to their environment, and
• Do not use energy to grow.
Viruses are similar to most organisms, however, because they can reproduce (they just
need a host cell in order to do so). Viruses inject their genetic material into a host cell, and the
genetic material includes instructions for stopping normal cell functions and using energy to build
viruses instead. Some viruses remain hidden for a period of time before they become active.
Viruses are generally considered parasites because they live in or on a host and cause
harm to their host.
The name bacteriophage means “bacteria eater” because it is a virus that infects
bacteria.
6th Grade Study Guide
BACTERIA
Bacteria (singular bacterium) are small, unicellular (or one-celled) organisms.
They are different from animal cells because they do not have a nucleus. Instead, their
genetic material can be found in the cytoplasm. They are also surrounded by a thick cell walls,
which surround the cell membrane. The cell wall give a bacterium a variety of different shapes:
spherical (ball-shaped), rodlike shapes (long and skinny), and spiral-shaped. Some bacteria
are mobile and can be propelled by a flagellum (plural flagella), which is a long whip-like
structure that works like a propeller.
There are two kingdoms of bacteria: archaebacteria which are thought to have existed
billions of years before dinosaurs and eubacteria which are more numerous. Archaebateria live
in extreme environments: hot, salty, acidic, or basic locales while eubacteria are more familiar.
Bacteria can reproduce by either sexual or asexual reproduction. Asexual reproduction
(also called binary fission) occurs when a bacterium simply divides into two exact copies.
Sexual reproduction occurs when a bacterium combines its DNA with another bacterium through
a process called conjugation and produces offspring that are slightly different from the parents.
Bacteria can be autotrophs (producing their own food) or heterotrophs (relying on other
organisms for food). When food is hard to find (or in other harsh conditions like freezing, heating,
or drying), bacteria can form endospores which are a sort of suspended animation where
bacterial cells can safely hibernate for long periods of time.
While bacteria are often associated with germs, they are also helpful. They help produce
medicines, food, and fuel, and can aid in recycling and environmental cleanup.