1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Title: Defence Mechanisms
Starter (from the end of last lesson)
• 1.What are the similarities between a
virus and bacteria?
• 2. What are the main differences
between a virus and bacteria?
• 3. Draw a flow diagram to explain how
viruses replicate.
• 4. Name three viral diseases.
• 5. Why are viral diseases much harder
to treat than bacterial diseases?
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Ways of Spreading Diseases
There are four main ways that pathogens
are spread from one person to another.
•Droplet Infection
•Direct Contact
•Contaminated Food and Drink
•Through a break in the skin
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Droplet Infection
• When you cough, sneeze or talk, tiny droplets
full of pathogens are expelled into the air.
Other people breathe these in.
• E.g. Tuberculosis, Influenze, Common Cold
1. How are
diseases
spread?
2.How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Direct Contact
• Some diseases spread by direct contact
of the skin.
• e.g. Impetigo, Genital Herpes
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Contaminated Food and Drink
• Eating raw or undercooked food, or
drinking water containing sewage can
spread disease.
• E.g. Salmonella, Cholera
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Through a Break in the Skin
Pathogens can enter the body through
cuts, scratches and needle punctures
E.g. HIV, Hepatitis
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Task 1
• Describe the four main ways in which
infectious diseases are spread.
1. How are
diseases
spread?
2.How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Preventing Microbes Getting In
• There are three main barriers to
infection.
•The Skin
•Scabbing
•Mucus and Stomach Acid
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Preventing Microbes Getting In
• The skin prevents bacteria and viruses
from getting to your tissues
underneath.
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Preventing Microbes Getting In
• If you cut your skin, you bleed. Your
blood quickly clots and forms a scab.
This prevents any pathogens from
entering.
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Preventing Microbes Getting In
• When you breathe, you draw in air full
of pathogens. Your breathing system
produces mucus which traps them.
1. How are
diseases
spread?
2.How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Preventing Microbes Getting In
• The mucus can then be removed from
the body (blowing your nose) or
swallowed into the gut, where stomach
acid destroys the pathogens.
1. How are
diseases
spread?
2.How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Task 2
• Copy and complete the following table
Barrier
Skin
Scabbing
Mucus and
Stomach Acid
How it protects against infection
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
How White Blood Cells Protect Against
Disease
• Some pathogens
still get through the
barriers to infection.
The body however
has a second line of
defence - the white
blood cells of the
immune system.
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
How White Blood Cells Protect Against
Disease
• White blood cells protect fight pathogens in
three main ways.
•Ingesting Microorganisms
•Producing Antibodies
•Producing Antitoxins
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Ingesting Microorganisms
• Some white blood cells ingest (take in)
pathogens, destroying them so they can’t
make you ill.
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Producing Antibodies
• Some white blood cells produce
antibodies that bind to antigens on
bacteria and viruses and destroy them.
1. How are
diseases
spread?
2. How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Producing Antibodies
• Once your white blood cells have made an
antibody for a specific pathogen, if you get reinfected, these antibodies can be made very
quickly. This is immunity.
1. How are
diseases
spread?
2.How does
your body
stop
pathogens
getting in?
3. How do
white blood
cells protect
us from
disease?
Defence Mechanisms
Task 3
• Explain how white blood cells work
using combination of sentences and
labelled diagrams.
– Key words: Antibodies, antigens,
antitoxins,