IGCSE BIOLOGY
SECTION 1 LESSON 3
Content
Section 1
The nature
and variety of
living
organisms
a) Characteristics of living
organisms
b) Variety of living organisms
Content
Lesson 3
b) Variety of
living
organisms
b) Variety of living organisms
Bacteria: These are microscopic single-celled organisms; they have a cell
wall, cell membrane, cytoplasm and plasmids; they lack a nucleus but
contain a circular chromosome of DNA; some bacteria can carry out
photosynthesis but most feed off other living or dead organisms
Examples include Lactobacillus bulgaricus, a rod-shaped bacterium used in
the production of yoghurt from milk, and Pneumococcus, a spherical
bacterium that acts as the pathogen causing pneumonia
Protoctists: These are microscopic single-celled organisms. Some, like
Amoeba, that live in pond water, have features like an animal cell, while
others, like Chlorella, have chloroplasts and are more like plants. A
pathogenic example is Plasmodium, responsible for causing malaria
Viruses: These are small particles, smaller than bacteria; they are parasitic
and can reproduce only inside living cells; they infect every type of living
organism. They have a wide variety of shapes and sizes; they have no cellular
structure but have a protein coat and contain one type of nucleic acid, either
DNA or RNA
Examples include the tobacco mosaic virus that causes
discolouring of the leaves of tobacco plants by preventing the formation of
chloroplasts, the influenza virus that causes ‘flu’ and the HIV virus that
causes AIDS
1.3 recall the term ‘pathogen’ and know that pathogens may be fungi,
bacteria, protoctists or viruses.
Classification
Kingdom
Monera
(Prokaryotes)
Bacteria and Blue-green algae
Protoctista
Amoeba, Paramecium
Fungi
Moulds, Mushrooms, Yeast
Plants
Algae, ferns and mosses,
conifers and flowering plants
Animals
Jellyfish, worms, arthropods, molluscs,
echinoderms, fish, amphibia, reptiles,
birds and mammals.
Classification
Kingdom
Monera
(Prokaryotes)
Bacteria and Blue-green algae
Protoctista
Amoeba, Paramecium
Fungi
Moulds, Mushrooms, Yeast
Plants
Algae, ferns and mosses,
conifers and flowering plants
Animals
Jellyfish, worms, arthropods, molluscs,
echinoderms, fish, amphibia, reptiles,
birds and mammals.
Bacteria: These are microscopic singlecelled organisms; they have a cell wall, cell
membrane, cytoplasm and plasmids; they
lack a nucleus but contain a circular
chromosome of DNA; some bacteria can
carry out photosynthesis but most feed off
other living or dead organisms
Examples include Lactobacillus bulgaricus,
a rod-shaped bacterium used in the
production of yoghurt from milk, and
Pneumococcus, a spherical bacterium that
acts as the pathogen causing pneumonia
Examples of bacteria
Examples of bacteria
Lactobacillus – rod
shaped bacterium used in
the production of
yoghurt from milk.
Examples of bacteria
Lactobacillus – rod
shaped bacterium used in
the production of
yoghurt from milk.
Pneumococcus – spherical
bacterium. A pathogen
causing pneumonia
Examples of bacteria
Pathogen – a microorganism
that causes disease in its host.
The host may be an animal, a
plant or even another
microorganism.
Lactobacillus – rod
shaped bacterium used in
the production of
yoghurt from milk.
Pneumococcus – spherical
bacterium. A pathogen
causing pneumonia
Structure of bacteria
Singular = bacterium
Structure of bacteria
Very small
organisms, rarely
more than 0.01mm in
length, so can only
be seen with more
powerful
microscopes.
Structure of bacteria
Very small
organisms, rarely
more than 0.01mm in
length, so can only
be seen with more
powerful
microscopes.
Cell wall
- Not made of
cellulose but of a
complex mixture of
proteins, sugars and
lipids.
Structure of bacteria
Very small
organisms, rarely
more than 0.01mm in
length, so can only
be seen with more
powerful
microscopes.
Cell wall
- Not made of
cellulose but of a
complex mixture of
proteins, sugars and
lipids.
Some may have
a slime capsule
outside the cell
wall – protects
the bacterium
Structure of bacteria
Very small
organisms, rarely
more than 0.01mm in
length, so can only
be seen with more
powerful
microscopes.
Cell wall
- Not made of
cellulose but of a
complex mixture of
proteins, sugars and
lipids.
No nuclear membrane
(prokaryotes), but
instead have a single
chromosome, a strand
of DNA
Some may have
a slime capsule
outside the cell
wall – protects
the bacterium
Structure of bacteria
Very small
organisms, rarely
more than 0.01mm in
length, so can only
be seen with more
powerful
microscopes.
Cell wall
- Not made of
cellulose but of a
complex mixture of
proteins, sugars and
lipids.
No nuclear membrane
(prokaryotes), but
instead have a single
chromosome, a strand
of DNA
Cytoplasm
Glycogen granules
Some may have
a slime capsule
outside the cell
wall – protects
the bacterium
Structure of bacteria
Very small
organisms, rarely
more than 0.01mm in
length, so can only
be seen with more
powerful
microscopes.
Cell wall
- Not made of
cellulose but of a
complex mixture of
proteins, sugars and
lipids.
Bacteria may also
have flagella
No nuclear membrane
(prokaryotes), but
instead have a single
chromosome, a strand
of DNA
Cytoplasm
Glycogen granules
Some may have
a slime capsule
outside the cell
wall – protects
the bacterium
Structure of bacteria
Very small
organisms, rarely
more than 0.01mm in
length, so can only
be seen with more
powerful
microscopes.
Cell wall
- Not made of
cellulose but of a
complex mixture of
proteins, sugars and
lipids.
Bacteria may also
have flagella
No nuclear membrane
(prokaryotes), but
instead have a single
chromosome, a strand
of DNA
Cytoplasm
Glycogen granules
Some may have
a slime capsule
outside the cell
wall – protects
the bacterium
Plasmid – a small
circular piece of DNA.
Often carry genes
which give the
bacterium resistance to
antibiotics
Physiology of bacteria
Streptococcus
Physiology of bacteria
Nutrition – a few species
of bacteria are able to
photosynthesise and make
their own food.
The majority live on their
food – they release
enzymes which digest the
food and then they absorb
the liquid products back
into the cell.
Streptococcus
Physiology of bacteria
Streptococcus
Reproduction – bacteria
reproduce asexually by a
process called binary
fission. One cell divides
into two, then two into four,
and so on. This can happen
every twenty minutes. If
this were to occur, then
after 12 hours there would
be 34,359,738,368
bacteria formed from a
single cell!
Useful and harmful bacteria
Useful and harmful bacteria
Making cheese
Making yoghurt
Antibiotics
Sewage treatment
Oil spill clean up
Mining metals
Fuels
Decay
Genetic engineering
Fixing nitrogen
Useful and harmful bacteria
Sore throat
Boils
Pneumonia
Anthrax
Typhoid fever
Scarlet fever
Syphilis
Cholera
Food poisoning
Whooping cough
Classification
Kingdom
Monera
(Prokaryotes)
Bacteria and Blue-green algae
Protoctista
Amoeba, Paramecium
Fungi
Moulds, Mushrooms, Yeast
Plants
Algae, ferns and mosses,
conifers and flowering plants
Animals
Jellyfish, worms, arthropods, molluscs,
echinoderms, fish, amphibia, reptiles,
birds and mammals.
Protoctists: These are microscopic singlecelled organisms. Some, like Amoeba, that
live in pond water, have features like an
animal cell, while others, like Chlorella,
have chloroplasts and are more like plants.
A pathogenic example is Plasmodium,
responsible for causing malaria
Examples of Protoctists
Examples of Protoctists
Amoeba
Examples of Protoctists
Amoeba
Chlorella
Examples of Protoctists
Amoeba
Chlorella
Plasmodium
Examples of Protoctists
Amoeba fact file:
Microscopic, one-celled
organism.
Live in fresh water (puddles,
ponds)
Amoeba
Examples of Protoctists
Amoeba fact file:
Microscopic, one-celled
organism.
Live in fresh water (puddles,
ponds)
Typical animal cell, porous
cell membrane, cytoplasm,
nucleus.
Amoeba
Examples of Protoctists
Amoeba fact file:
Amoeba
Microscopic, one-celled
organism.
Live in fresh water (puddles,
ponds)
Typical animal cell, porous
cell membrane, cytoplasm,
nucleus.
Feed on algae, bacteria,
plant cells, protozoa.
Cytoplasm surrounds food
particles to form a food
vacuole where digestion
takes place.
Examples of Protoctists
Amoeba fact file:
Amoeba
Microscopic, one-celled
organism.
Pseudopodia
= “false feet”. Amoebas
in fresh
move byLive
changing
thewater
shape(puddles,
of their
ponds)
body,
forming pseudopods.
Typical animal cell, porous
cell membrane, cytoplasm,
nucleus.
Feed on algae, bacteria,
plant cells, protozoa.
Cytoplasm surrounds food
particles to form a food
vacuole where digestion
takes place.
Examples of Protoctists
Chlorella fact file:
Single-celled green algae.
Spherical in shape.
Chlorella
Examples of Protoctists
Chlorella fact file:
Single-celled green algae.
Spherical in shape.
Contains chlorophyll which
enables it to
photosynthesise.
Chlorella
Examples of Protoctists
Plasmodium fact file:
A single-celled Protozoan
that causes the disease
known as malaria.
Spread from person to
person by the female
mosquito as they suck blood.
Plasmodium
Examples of Protoctists
Plasmodium fact file:
A single-celled Protozoan
that causes the disease
known as malaria.
Spread from person to
person by the female
mosquito as they suck blood.
Plasmodium invades the red
blood cells of the host and
feeds on the cytoplasm.
Plasmodium
Examples of Protoctists
Plasmodium fact file:
A single-celled Protozoan
that causes the disease
known as malaria.
Spread from person to
person by the female
mosquito as they suck blood.
Plasmodium invades the red
blood cells of the host and
feeds on the cytoplasm.
Nearly 3 million people each
year die from malaria.
Plasmodium
Viruses: These are small particles, smaller than
bacteria; they are parasitic and can reproduce
only inside living cells; they infect every type of
living organism. They have a wide variety of
shapes and sizes; they have no cellular
structure but have a protein coat and contain
one type of nucleic acid, either DNA or RNA.
Examples include the tobacco mosaic virus that
causes discolouring of the leaves of tobacco
plants by preventing the formation of
chloroplasts, the influenza virus that causes
‘flu’ and the HIV virus that causes AIDS
Examples of viruses
Tobacco Mosaic Virus
(virology.wisc.edu)
Examples of viruses
Tobacco Mosaic Virus
(virology.wisc.edu)
InfluenzaVirus
(medimoon.com)
Examples of viruses
Tobacco Mosaic Virus
(virology.wisc.edu)
HIV Virus
(123rf.com)
InfluenzaVirus
(medimoon.com)
Examples of viruses
Tobacco Mosaic Virus
(virology.wisc.edu)
TMV was the first virus to be
discovered in 1930.
Causes mottling and discoloration
of tobacco leaves. HIV Virus
(123rf.com)
Rod-like appearance, surrounded
by a resistant protein coat
InfluenzaVirus
(medimoon.com)
Examples of viruses
Highly contagious,
Tobacco
Mosaic Virus
(virology.wisc.edu)
infects
the respiratory
tract.
It affects all ages, but
children tend to get it
more than adults
Spread by droplets that
are coughed or sneezed.
HIV Virus
(123rf.com)
InfluenzaVirus
(medimoon.com)
Examples of viruses
Tobacco Mosaic Virus
(virology.wisc.edu)
InfluenzaVirus
(medimoon.com)
A slowly-replicating
HIV Virus
(123rf.com)
retrovirus
that causes
acquired
immunodeficiency
syndrome (AIDS), which
causes the immune
system to fail. Infection
through body fluids.
Examples of viruses
Retrovirus - a
virus that
replicates in a
host cell
Tobacco Mosaic Virus
(virology.wisc.edu)
InfluenzaVirus
(medimoon.com)
A slowly-replicating
HIV Virus
(123rf.com)
retrovirus
that causes
acquired
immunodeficiency
syndrome (AIDS), which
causes the immune
system to fail. Infection
through body fluids.
Structure of viruses
Structure of viruses
Injection
Tube
Protein
Coat
Genetic
Material
Tail Plate
Structure of viruses
Much smaller
than a
bacterium, can
only be seen
with electron
microscopes
Structure of viruses
All viruses have a central
core of RNA or DNA
surrounded by a protein
coat.
Much smaller
than a
bacterium, can
only be seen
with electron
microscopes
Structure of viruses
All viruses have a central
core of RNA or DNA
surrounded by a protein
coat.
Much smaller
than a
bacterium, can
only be seen
with electron
microscopes
No nucleus,
cytoplasm, cell
organelles or cell
membrane
Structure of viruses
All viruses have a central
core of RNA or DNA
surrounded by a protein
coat.
Much smaller
than a
bacterium, can
only be seen
with electron
microscopes
No nucleus,
cytoplasm, cell
organelles or cell
membrane
So, are
they
really
cells at
all?
Structure of viruses
All viruses have a central
core of RNA or DNA
surrounded by a protein
coat.
Much smaller
than a
bacterium, can
only be seen
with electron
microscopes
MRS GREN
No nucleus,
cytoplasm, cell
organelles or cell
membrane
So, are
they
really
cells at
all?
Structure of viruses
All viruses have a central
core of RNA or DNA
surrounded by a protein
coat.
Much smaller
than a
bacterium, can
only be seen
with electron
microscopes
MRS GREN
No nucleus,
cytoplasm, cell
organelles or cell
membrane
So, are
they
really
cells at
all?
Viruses do
reproduce, but only
inside the cells of
living organisms,
using materials
obtained from the
host cell.
Structure of viruses
All viruses have a central
core of RNA or DNA
surrounded by a protein
coat.
Much smaller
than a
bacterium, can
only be seen
with electron
microscopes
MRS GREN
No nucleus,
cytoplasm, cell
organelles or cell
membrane
So, are
they
really
cells at
all?
Viruses do
reproduce, but only
inside the cells of
living organisms,
using materials
obtained from the
host cell.
The protein coat
is called a capsid,
and is made up of
regularly packed
protein units
called
capsomeres.
Multiplication of viruses
Multiplication of viruses
Viruses are able to
survive outside the
host cell, but they must
penetrate into a host in
order to reproduce.
Multiplication of viruses
1. The virus sticks
to the cell
membrane of a
suitable host cell.
Multiplication of viruses
1. The virus sticks
to the cell
membrane of a
suitable host cell.
2. An ‘injection’
tube ‘injects’ the
DNA or RNA into
the host cell.
Multiplication of viruses
1. The virus sticks
to the cell
membrane of a
suitable host cell.
2. An ‘injection’
tube ‘injects’ the
DNA or RNA into
the host cell.
Multiplication of viruses
3. The viral DNA
uses the cell’s
contents to make
new strands and
capsomeres
Multiplication of viruses
3. The viral DNA
uses the cell’s
contents to make
new strands and
capsomeres
4. The DNA and
capsomeres make
new virus particles
which escape from
the cell
Diseases caused by viruses
Common cold
Poliomyelitis
Measles
Mumps
Chickenpox
Herpes
Rubella
Influenza
AIDS
Pathogen – a
microorganism that
causes disease in its
host. The host may
be an animal, a plant
or even another
microorganism.
Pathogen – a
microorganism that
causes disease in its
host. The host may
be an animal, a plant
or even another
microorganism.
Bacterium
Pneumococcus –
causes pneumonia
Pathogen – a
microorganism that
causes disease in its
host. The host may
be an animal, a plant
or even another
microorganism.
Bacterium
Virus
Pneumococcus –
causes pneumonia
InfluenzaVirus
(medimoon.com)
Pathogen – a
microorganism that
causes disease in its
host. The host may
be an animal, a plant
or even another
microorganism.
Bacterium
Virus
Protoctist
Pneumococcus –
causes pneumonia
InfluenzaVirus
(medimoon.com)
Plasmodium –
causes malaria
Pathogen – a
microorganism that
causes disease in its
host. The host may
be an animal, a plant
or even another
microorganism.
Fungus
Fusarium – fungal
pathogen that
infects wheat
crops
(bbsrc.ac.uk)
Bacterium
Virus
Protoctist
Pneumococcus –
causes pneumonia
InfluenzaVirus
(medimoon.com)
Plasmodium –
causes malaria
End of Section 1 Lesson 3
In this lesson we have covered:
• Outline of the monera kingdom
• Outline of the protoctist kingdom
• Outline of viruses
• Examples of pathogens