UNIT 1: CHARACTERISTICS AND CLASSIFICATION
OF LIVING ORGANISMS
CHARACTERISTICS OF LIVING ORGANISMS
There are 7 characteristics of living organisms:
o Movement: An action by which an organism or part of an organism causing a
change in position or place.
o Respiration: The chemical reactions in cells that break down nutrient molecules
and release energy for metabolism.
o Sensitivity: The ability to detect and respond to changes in internal or external
environment.
o Growth: The permanent increase in size or dry mass.
o Reproduction: The process that makes more of the same kind of organism.
o Excretion: Removal of waste products of metabolism and substances in excess
requirements.
o Nutrition: The taking in of materials for energy, growth and development.
These 7 characteristics can be remembered as MRS GREN.
CONCEPT AND USES OF CLASSIFICATION SYSTEMS
Species: A group of organisms that can reproduce to produce a fertile offspring.
Species can be classified into their groups by the features they share.
THE BINOMIAL SYSTEM
A system of naming species in which the scientific name of an organism is made up of
two parts: The genus and species.
A genus is a group of related species.
This system allows sub-division of living organisms into smaller groups.
The species in these groups have more and more features in common, the more sub-
divided they get.
In this system, the name of the organism is made up of two parts: The genus, then
the species.
The genus starts with a capital letter, the species starts with a small letter.
When typed, binomial names are always written in italics, this indicates that they are
Latin, or in the exams, they can be.
DICHOTOMOUS KEYS
They are used to identify organisms based on a series of questions about their
features.
CLASSIFICATION
Classification basically means putting things into groups.
The main reason to classify living beings is to make sure it is easier to study them.
There are 8 levels of classifying living organisms:
o Domain
o Kingdom
o Phylum
o Class
o Order
o Family
o Genus
o Species
Reflecting revolutionary relationships
Classification systems aim to reflect revolutionary relationships between species
Traditionally, organisms were classified based on the features that they shared such
as:
o Colour
o Shape
o Size
Due to this, it was said that: The more features’ organisms shared, the closer they
were.
DNA sequencing of different species helped to classify organisms using a more
scientific approach.
The more similar the base sequences in the DNA of two species, the more closely
related those two species are and the more recent their common ancestor is.
FEATURES OF CLASSIFYING ORGANISMS
The first step to classify living organisms is to put them into five kingdoms:
o Animals
o Plants
o Fungi
o Protoctists
o Prokaryotes
ANIMALS
Characteristics common to all animals include:
o They are multicellular.
o Their cells have a nucleus but no cell walls or chloroplasts.
o They get nutrition by eating other living things.
Nucleus
Mitochondria
Ribosomes
Cytoplasm
Cell membrane
PLANTS
Characteristics common to all plants are:
o They are multicellular.
o Their cells have a nucleus, chloroplast and cell wall made up of cellulose.
o They get their own nutrition by making their own food through a process
called photosynthesis.
Ribosomes
Mitochondria
Cytoplasm
Cell membrane
Cell wall
Chloroplast
Vacuole
Nucleus
FUNGI
Characteristics common to all fungi are:
o They are usually multicellular
o Their cells have a nucleus and have a cell wall made out of chitin
o They feed by a method known as saprophytic nutrition, this means that they
feed on dead or decaying material. This is also done by another method
called parasitic nutrition, in which they feed on living material.
PROTOCTISTS
Characteristics common to all protoctists are:
o Most are unicellular, but some are multicellular.
o They have a nucleus, some may have cell walls and chloroplasts
o Some get their nutrition by making their own food through photosynthesis
while some feed on living organisms (Dead, decaying or alive).
PROKARYOTES
Characteristics common to all prokaryotes are:
o Often unicellular.
o They have cell walls made up of peptidoglycan and cytoplasm but no nucleus
or mitochondria, instead they have nucleoids (genetic material present
randomly in the cytoplasm).
Prokaryotes are also known as bacteria
Strand of DNA (Nucleoid)
Plasmid
Cytoplasm
Cell membrane
Cell wall
Ribosomes
Flagellum
CLASSIFICATION WITHIN THE ANIMAL KINGDOM:
Some of the major groups into which the animal kingdom is classified can be broken
down to: Vertebrates and invertebrates
VERTEBRATES
Vertebrates are animals that have a backbone.
There are 5 classes of vertebrates:
o Mammals
o Birds
o Reptiles
o Amphibians
o Fish
MAMMALS
Humans belong to this group
Some characteristics of mammals are:
o They have fur or hair
o Young feed on milk from mammary glands
o Their heart has 4 chambers
o They have different types of teeth (incisors, canines, premolars and molars)
o They are hot blooded
BIRDS
Some characteristics of birds are:
o They have feathers
o They lay eggs with hard shells
o They have a beak
o They have wings instead of forelimbs
o They are hot blooded
Reptiles
Some characteristics of reptiles are:
o They have scaly skin
o They lay eggs with rubbery shells
o They are cold blooded
o Most reptiles have 3 chambers in their heart, except for crocodiles in which
they have 4 chambers.
Amphibians
Amphibians live on land and water
Some characteristics of amphibians are:
o They have moist skin without scales
o They lay eggs in water
o Larvae have gills and live in water, but as they grow up, they start to build
lungs and often live on land
o They are cold blooded
Fish
All fish live in water, except for two types
Some characteristics of fish are:
o They have scales on their skin
o They have a streamlined body
o They have gills
o They have fins
o They lay eggs in water which usually have soft shells
o They are cold blooded
INVERTEBRATES
Invertebrates are animals that do not have a backbone
Arthropods are invertebrates that have jointed legs
There are four main classes of arthropods:
o Myriapods
o Insects
o Arachnids
o Crustaceans
CLASSIFICATION WITHIN THE PLANT KINGDOM
Plants can be divided into two main parts:
o Ferns
o Flowering plants
Flowering plants can further be classified into:
o Monocotyledons
o Dicotyledons
FERNS
Some characteristics of ferns are:
o They have leaves called fronds
o They reproduce by spores, not flowers
FLOWERING PLANTS
Characteristics of flowering plants are:
o They reproduce by flowers and seeds
o Seeds are produced inside the ovary, inside the flower
Flowering plants can further be divided into monocotyledons and dicotyledons
Monocotyledons Dicotyledons
Root system Branching root system Top root system
Leaves Veins run parallel to each Broader leaves and have a
other network of branching veins
Flowers Contains petals in multiples Contains petals in multiple
of 3 of 4 or 5
Cotyledons Have only 1 cotyledon Have only 2 cotyledons
VIRUSES
Viruses are not considered to be living things since they cannot carry out the seven
life processes on their own (They need a host to carry it out)
Therefore, they are not part of any classification system
They can only take over another living cell in order to make multiple copies of
themselves
A virus is made of a cell- its simply genetic material surrounded by a protein coat
