Biology IGCSE
Revision Notes
Section 1: The nature and variety of living
organisms
Characteristics of living organisms include;
M ovement
R espitation
S ensitivity
G rowth
R eproduction
E xcretion
N utrition
In addition, all living organisms contain nucleic acids (DNA) and
have the ability to control their internal conditions. Finally, all
living organisms can die.
Living organisms are classified into 5 groups, each of which has
certain characteristics you need to learn
Plants:
1. Multicellular organisms
2. Cells contain chloroplasts and are able to carry out
photosynthesis
3. Cells have cellulose cell walls
, 4. They store carbohydrates as starch or sucrose.
Examples include flowering plants, such as a cereal (e.g. maize) and
a herbaceous legume (e.g. peas or beans).
Animals:
1. Multicellular organisms
2. Cells do not contain chloroplasts and are not able to carry out
photosynthesis
3. Cells have no cell walls
4. They have a nervous system
5. They often store carbohydrate as glycogen
Examples include mammals (e.g. humans) and insects (e.g. housefly).
Fungi:
1. They are saprophytic and feed by excreting digestive
enzymes onto food and absorbing the digested products
2. Cells do not contain chloroplasts and are not able to carry out
photosynthesis
3. Cells are joined together to form threads, called hyphae.
Hyphae contain many nuclei, because they are made from
many cells.
4. Cell walls are made from chitin (a protein)
5. They store carbohydrates as glycogen.
Examples include Mucor and Yeast (which is single celled).
,Bacteria:
1. Made from single cells
2. Cells do not contain a nucleus, but have a small piece of
circular DNA instead (a bacterial chromosome).
3. Some bacteria can carry out rudimentary photosynthesis, but
most are saprophytes
4. They have the structure below (learn it, it comes up!)
Examples include Lactobacillius bulgaricus (a rod-shaped bacterium
used in the production of yoghurt from milk) and Pneumococcus (a
spherical bacterium that causes Pneumonia)
Protoctisis:
Basically, everything that doesn’t fit into the other kingdoms! Most
are single celled organisms which can either;
1. Have animal-like characteristics (e.g. Amoeba)
2. Have plant-like characteristics (e.g. Chlorella)
However, some protoctisis are multicellular (e.g. seaweeds, yes
they’re NOT plants!)
Viruses:
1. Much smaller than bacteria. They are not made from cells
2. Totally parasitic and reproduce inside host cells.
3. They infect every type of living cell
4. They have the structure below (learn it, it comes up!)
, The Envelope is used to gain entry into host cells.
The Capsid is a protein coat and is used to protect the genetic
information and give the virus structure
The DNA or RNA (a different type of nucleic acid) contain the
code for building new viruses.
Examples include the Tobacco Mosaic Virus and the Influenza virus
(which causes ‘flu).
Section 2: Structures and Functions in
Living Organisms
a) Levels of organization
Organisms are made from organizations of smaller structures. You
need to know the following hierarchy of structures.
Organelles – intracellular structures that carry out specific
functions within a cell
Cells – the basic structural and functional unit from which all
biological organisms are made
Revision Notes
Section 1: The nature and variety of living
organisms
Characteristics of living organisms include;
M ovement
R espitation
S ensitivity
G rowth
R eproduction
E xcretion
N utrition
In addition, all living organisms contain nucleic acids (DNA) and
have the ability to control their internal conditions. Finally, all
living organisms can die.
Living organisms are classified into 5 groups, each of which has
certain characteristics you need to learn
Plants:
1. Multicellular organisms
2. Cells contain chloroplasts and are able to carry out
photosynthesis
3. Cells have cellulose cell walls
, 4. They store carbohydrates as starch or sucrose.
Examples include flowering plants, such as a cereal (e.g. maize) and
a herbaceous legume (e.g. peas or beans).
Animals:
1. Multicellular organisms
2. Cells do not contain chloroplasts and are not able to carry out
photosynthesis
3. Cells have no cell walls
4. They have a nervous system
5. They often store carbohydrate as glycogen
Examples include mammals (e.g. humans) and insects (e.g. housefly).
Fungi:
1. They are saprophytic and feed by excreting digestive
enzymes onto food and absorbing the digested products
2. Cells do not contain chloroplasts and are not able to carry out
photosynthesis
3. Cells are joined together to form threads, called hyphae.
Hyphae contain many nuclei, because they are made from
many cells.
4. Cell walls are made from chitin (a protein)
5. They store carbohydrates as glycogen.
Examples include Mucor and Yeast (which is single celled).
,Bacteria:
1. Made from single cells
2. Cells do not contain a nucleus, but have a small piece of
circular DNA instead (a bacterial chromosome).
3. Some bacteria can carry out rudimentary photosynthesis, but
most are saprophytes
4. They have the structure below (learn it, it comes up!)
Examples include Lactobacillius bulgaricus (a rod-shaped bacterium
used in the production of yoghurt from milk) and Pneumococcus (a
spherical bacterium that causes Pneumonia)
Protoctisis:
Basically, everything that doesn’t fit into the other kingdoms! Most
are single celled organisms which can either;
1. Have animal-like characteristics (e.g. Amoeba)
2. Have plant-like characteristics (e.g. Chlorella)
However, some protoctisis are multicellular (e.g. seaweeds, yes
they’re NOT plants!)
Viruses:
1. Much smaller than bacteria. They are not made from cells
2. Totally parasitic and reproduce inside host cells.
3. They infect every type of living cell
4. They have the structure below (learn it, it comes up!)
, The Envelope is used to gain entry into host cells.
The Capsid is a protein coat and is used to protect the genetic
information and give the virus structure
The DNA or RNA (a different type of nucleic acid) contain the
code for building new viruses.
Examples include the Tobacco Mosaic Virus and the Influenza virus
(which causes ‘flu).
Section 2: Structures and Functions in
Living Organisms
a) Levels of organization
Organisms are made from organizations of smaller structures. You
need to know the following hierarchy of structures.
Organelles – intracellular structures that carry out specific
functions within a cell
Cells – the basic structural and functional unit from which all
biological organisms are made
