BIOLOGY
Classification
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Notes
Introduction:
Organisms can be classified into groups based on the features they share, a scientific practice
known as taxonomy. Taxonomy is the branch of biology that deals with the identification,
naming, and classification of living organisms. It includes the following:
● Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
○ Species is defined as a group of organisms that consist of similar individuals
capable of interbreeding or exchanging genes among themselves. In other words,
a group of organisms that can reproduce naturally with one another and create
fertile offspring.
● Binomial nomenclature is an internationally agreed biological system of naming the
organisms in which the name is composed of two terms, where, the first term indicates
the genus and the second term indicates the species of the organism.
○ All the scientific names of organisms are usually Latin. Hence, they are written in
italics.
○ There exist two parts of a name. The first word identifies the genus and the
second word identifies the species.
○ When the names are handwritten, they are underlined or italicized if typed. This
is done to specify its Latin origin or to distinguish them from regular text.
○ The name of the genus starts with a capital letter and the name of the species
starts with a small letter.
● A dichotomous key is an important scientific tool, used to identify different organisms,
based on the organism's observable traits. Dichotomous keys consist of a series of
statements with two choices in each step that will lead users to the correct
identification.
, ● Classification systems reflect evolutionary relationships by grouping organisms together
based on their shared ancestry and common evolutionary history. This approach is
known as phylogenetic classification and is rooted in the concept of a phylogenetic tree,
which represents the evolutionary relationships among organisms.
● When classifying organisms based on genetic analysis, scientists must assume that the
more DNA two organisms have in common, the more recently they shared a common
ancestor.
The Five Kingdoms
● Animals
○ 5-10 million different species
○ Multicellular
○ Eukaryotic
○ Non-photosynthetic
○ Lack cell wall
○ Are heterotrophs (get their energy from other organisms)
○ Most reproduce sexually
○ E.g. sponges, hydra, starfish, lion, humans, etc.
● Plantae
○ Around 300.000 species
○ Multicellular
○ Eukaryotic
○ Photosynthetic
○ Have a nucleus
○ Cellulose in cell walls
○ Autotrophs; make their own food (get their energy from Sun)
● Fungi
○ Are eukaryotic
○ Mostly multicellular
○ Heterotrophic
○ Cell wall is present; made up of chitin
○ Most feed using saprophytic nutrition
■ 1. Secrete digestive enzymes onto food outside their body (organic matter
like dead plants, leaves or even living organisms)
■ 2. Break down the food
■ 3. Absorb all the nutrients like sugars, amino acids, minerals.
○ Also feed using parasitic nutrition (involves living off a host organism, utilizing
its resources while potentially causing harm or disease.)
Classification
___
Notes
Introduction:
Organisms can be classified into groups based on the features they share, a scientific practice
known as taxonomy. Taxonomy is the branch of biology that deals with the identification,
naming, and classification of living organisms. It includes the following:
● Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
○ Species is defined as a group of organisms that consist of similar individuals
capable of interbreeding or exchanging genes among themselves. In other words,
a group of organisms that can reproduce naturally with one another and create
fertile offspring.
● Binomial nomenclature is an internationally agreed biological system of naming the
organisms in which the name is composed of two terms, where, the first term indicates
the genus and the second term indicates the species of the organism.
○ All the scientific names of organisms are usually Latin. Hence, they are written in
italics.
○ There exist two parts of a name. The first word identifies the genus and the
second word identifies the species.
○ When the names are handwritten, they are underlined or italicized if typed. This
is done to specify its Latin origin or to distinguish them from regular text.
○ The name of the genus starts with a capital letter and the name of the species
starts with a small letter.
● A dichotomous key is an important scientific tool, used to identify different organisms,
based on the organism's observable traits. Dichotomous keys consist of a series of
statements with two choices in each step that will lead users to the correct
identification.
, ● Classification systems reflect evolutionary relationships by grouping organisms together
based on their shared ancestry and common evolutionary history. This approach is
known as phylogenetic classification and is rooted in the concept of a phylogenetic tree,
which represents the evolutionary relationships among organisms.
● When classifying organisms based on genetic analysis, scientists must assume that the
more DNA two organisms have in common, the more recently they shared a common
ancestor.
The Five Kingdoms
● Animals
○ 5-10 million different species
○ Multicellular
○ Eukaryotic
○ Non-photosynthetic
○ Lack cell wall
○ Are heterotrophs (get their energy from other organisms)
○ Most reproduce sexually
○ E.g. sponges, hydra, starfish, lion, humans, etc.
● Plantae
○ Around 300.000 species
○ Multicellular
○ Eukaryotic
○ Photosynthetic
○ Have a nucleus
○ Cellulose in cell walls
○ Autotrophs; make their own food (get their energy from Sun)
● Fungi
○ Are eukaryotic
○ Mostly multicellular
○ Heterotrophic
○ Cell wall is present; made up of chitin
○ Most feed using saprophytic nutrition
■ 1. Secrete digestive enzymes onto food outside their body (organic matter
like dead plants, leaves or even living organisms)
■ 2. Break down the food
■ 3. Absorb all the nutrients like sugars, amino acids, minerals.
○ Also feed using parasitic nutrition (involves living off a host organism, utilizing
its resources while potentially causing harm or disease.)
