Unit 1 Learning Outcomes
Section E- Cellular response in defence in animals and plants.
Content
Notes
A. The nature of viruses and their invasion of Viruses are very small structures. They
cells. Alteration of cell instructions to produce are smaller than bacteria. They can only
more viruses.
reproduce within the living cells of
another organism (the host). They are
described as obligate parasites.
LO 1. Describe the main components of viruses
and draw a diagram of a virus particle.
Viruses are often specific with respect
to their chosen type of host cell.
LO 2. Explain the process by which virus
particles invade host cells, take over the host A virus is not a cell. It consists of
cells metabolism and replicate.
either DNA or RNA surrounded by a
protective coat, called a capsid. This is
normally made of protein.
Viruses invade cells and take over their
metabolism so that the cell replicates
the virus DNA. The cell is then made to
synthesise viral protein coats and new
virus particles are assembled. These are
then released when the host cell bursts
(called lysis) and are then free to invade
other cells.
Extra
Some viruses can invade a cell and
remain dormant for many years. That
means that there is no infection
produced at the time.
LO 3. Explain the difference between a If a virus contains RNA it is called a
retrovirus and a DNA virus.
retrovirus. There is no DNA to
transcribe into mRNA it has to use a
different strategy. These viruses inject
their RNA and an enzyme called reverse
transcriptase into the host cells.
Some viruses you should know: Polio,
Rabies, HIV (AIDS), Pneumonia, Herpes,
Bacteriophage.
B. Cellular defence mechanisms in animals.
The main mechanisms of cellular
LO 4. Give examples of the first line defence. defence in animals are Phagocytosis and
antibody production (brought about by
LO 5. Give the 2 main second lines of defence white blood cells).
carried out by white blood cells.
Phagocytosis (cell eating) is the process
LO 6. State the name of white blood cells by which foreign bodies such as bacteria
which carry out phagocytosis and explain this are engulfed and destroyed.
process.
Cells that perform Phagocytosis are
called phagocytes.
Invading particles are engulfed in the
phagocyte and enclosed in a vacuole.
LO 7. Explain the function of a lysosome.
Lysosomes are bags filled with enzymes.
Lysosomes fuse with the vacuole and the
enzymes digest the foreign particle.
LO 8, State the names of the white blood cells Antibodies are specific Y shaped protein
which produce antibodies and explain the molecules
which
attack
invading
reason for their production.
organisms. Antibodies are made by
another type of white blood cell called
LO 9. State that antibodies are proteins and lymphocytes. These recognise foreign
use this to explain their reaction with invaders as foreign by their surface
antigens.
antigens.
Lymphocytes produce the particular
antibody required to combat that
particular antigen.
LO 10. Explain how antibodies are specific.
LO 11. Explain what is meant by memory cells.
Each antibody is specific to one antigen.
Antibodies attach themselves to the
invader and attract phagocytes to
destroy them.
After each attack a few of the
lymphocytes remain as memory cells so
that the response to that particular
antigen will be both faster and stronger
in a future invasion.
LO 12. Explain why transplanted organs are Transplanted organs also have antigens
sometimes rejected by the recipient.
that are recognised as foreign by
lymphocytes. Antibodies attempt to
destroy the invader- this is known as
LO 13. Explain how doctors reduce the chance tissue rejection. Doctors reduce this
of tissue rejection.
chance of rejection by matching the
antigens of the donor and recipient as
closely as possible and by using drugs to
suppress the immune system.
LO 14. Explain active immunity and describe Naturally acquired activity immunity
how this can be acquired naturally and results in a previous exposure to an
artificially.
antigen that has caused a response. This
can be through a previous infection.
Artificially acquired immunity results
from exposure to antigens. This is
usually through vaccination.
LO 15. Explain passive immunity.
Passive immunity results from ready
made antibodies being passed into the
body, this occurs naturally when the
antibodies cross the placenta or through
breast milk. It can also occur artificially
by extracting antibodies that have been
made by one mammal and injected into
another. This is short lived protection.
LO 16. Describe the difference between a You must know the primary
primary and secondary response.
secondary response graphs.
and
You must know the types of specific
immunity and passive immunity.
C. Cellular defence mechanisms in plants.
Two main means of cellular defence in
plants are: the production of poisonous
LO 17. Describe and explain two methods of chemicals and the isolation of injured
cellular defence.
areas to prevent the spread of
infection.
LO 18. Name several examples of chemical Plant cells can produce various toxic
substances produced by plants as a means of chemicals when attacked these include
defence.
tannins,
cyanide,
nicotine
and
phytoalexins.
LO 19. Describe two methods of physical Infections can be prevented from
defence used by plants to prevent infection.
spreading by isolating the injured area
by means of substances such as insect
galls and resin.