Characteristics of Living Organisms:
How Organisms are Classified
•There are millions of species of organisms on Earth
•A species is defined as a group of organisms that can reproduce to produce fertile
offspring
•These species can be classified into groups by the features that they share e.g. all
mammals have bodies covered in hair, feed young from mammary glands and have
external ears (pinnas)
The Binomial System
•Organisms were first classified by a Swedish naturalist called Linnaeus in a way that allows the
subdivision of living organisms into smaller and more specialized groups
•The species in these groups have more and more features in common the more subdivided they
get
•He named organisms in Latin using the binomial system where the scientific name of an
organism is made up of two parts starting with the genus (always given a capital letter) and
followed by the species (starting with a lower case letter)
•When typed binomial names are always in italics (which indicates they are Latin) e.g. Homo
sapiens
•The sequence of classification is: Kingdom, Phylum, Class, Order, Family, Genus, Species
Put every organism into a group (the science of TAXONOMY)
Give every organism a name (the science of NOMENCLATURE).
All life forms are categorized into a scheme that had 7 categorical terms.
The biggest group are Kingdom, the smallest one is Species.
Each kingdom is divided into smaller group, which include genus and species. Organisms can
exist in only one group at each level of classification. For example, an organism can only
belong to one kingdom or one genus.
Common Cell Structures
The Five Kingdoms
•The first division of living things in the classification
system is to put them into one of five kingdoms. They
are:
• Animals
• Plants
• Fungi
• Protoctists
• Prokaryotes
•Main features of all animals:
• they are multicellular
• their cells contain a nucleus but no cell walls or
chloroplasts
• they feed on organic substances made by other
living things
•Main features of all plants:
• they are multicellular
• their cells contain a nucleus, chloroplasts and
cellulose cell walls
• they all feed by photosynthesis
•Main features of all fungi (e.g. moulds, mushrooms,
yeast)
• usually multicellular
• cells have nuclei and cell walls not made from
cellulose
• do not photosynthesize but feed by
saprophytic (on dead or decaying material) or
parasitic (on live material) nutrition
•Main features of all Protoctists (e.g. Amoeba,
Paramecium, Plasmodium)
• most are unicellular but some are multicellular
• all have a nucleus, some may have cell walls and
chloroplasts
• meaning some protoctists
photosynthesise and some feed on organic
substances made by other living things
•Main features of all Prokaryotes (bacteria, blue-green
algae)
• often unicellular
• cells have cell walls (not made of cellulose)
and cytoplasm but no nucleus or mitochondria
Animal Kingdom – Classification
The animal kingdom contains many phyla.
Some of them are: Vertebrates, Arthropods, Annelids, Molluscs, Nematodes.
It is not always easy to recognize an animal.
For a very long time, people thought that’s sea anemones were plants, because
they tend to stay in one place and their tentacles look rather kike petals.
Now we know that they are animals.
Phylum Vertebrates
Vertebrates are animals with backbones.
They are divided into 5 groups called classes:
Fish, Amphibians, Reptiles, Birds and Mammals.
Phylum Arthropods
Insects, Crustaceans, Arachnids and Myriapods.
1. Insects
Insects are a very successful group, due to their exoskeleton
and tracheae, which are very good at stopping water from
evaporating from insects’s body, so they can live in very dry
places.
Other groups of invertebrates
Plant Kingdom
Viruses
When viruses encounter a cell, they take over cell’s machinery.
A series of chemical reactions occur that lead to the production
of new viruses.
Theses new viruses burst out of the cell and invade others,
where the process is repeated.
The host cell is usually killed when this happens.
These steps are completely passive, that is, they are predefined
by the nature of the molecules that comprise the virus particle.
Viruses don’t actually ‘do’ anything. Without cells, viruses
would not be able to multiply
Bacteria Kingdom
Fungi Kingdom
For a very long time, fungi were classified as plants.
However, they are very different from plants and belong to
their own kingdom.
Fungi do not have chlorophyll and do not photosynthesise.
They feed saprophytically, or parasitically, on organic material
like faeces, human foods and dead plants or animals
Constructing & Using a Key