The Variety of Life (2007)
Idea of classification
What is classification?
- Grouping different impressions and observations into categories
- is a learning procedure -- to learn concepts from groups of similar things
Reasons for classification
- to deal with large volume of information of organisms, to arrange them in good order so that future study and reference can be
made.
- When an organism is given a single universally accepted name, scientists may communicate about it without risk of ambiguity.
- Classification indicates similarities and evolutionary relationship between members of one group.
Classifying living organisms
There is no ‘correct’ scheme of classification, since organisms form a continuum, but division solely for human
convenience. Two general systems :
1. Artificial system
- using easily observed phenotypic (morphological) characters
-not necessarily indicating phylogenetic relationships.
--> for convenience.
2. Natural system
- a hierarchical of modern classification based on hypothetical phylogenetic relationships such that the
members of each category in the classification share a single common ancestor.
The classification system is subject to change as new evidences appears.
Carolus Linnaeus (1707 - 1778)
- Founder of modern taxonomy (‘Taxonomy’ = the science of classifying and naming organisms )
- developed the binomial system of nomenclature (Binomial nomenclature)
-a system based on a unique two-part name for each organism (printed in italic characters or written
underlined separately, always in Latin):
e. g. Man: Homo sapiens / Homo sapiens
(Capitalized genus name+ not capitalized specific epithet)
Linnaeus's hierarchical system of classification of living organisms:
Kingdom
Phylum (animal) or Division (Plant)
Class
Order
Family
Genus
Species
Kingdoms
- Initially, organisms were classified into plant and animal kingdoms only.
- With the discovery of more morphological, biochemical and physiological features of a greater, variety of
living organisms, a new classification scheme must be adopted.
- Five-kingdom scheme
(suggested by ecologist Robert Whittaker)
-- is now generally adopted by most biologist :
Kingdom Monera ( Prokaryotae)
Kingdom Protista ( now: K. Protoctista)
Kingdom Fungi
Kingdom Plantae
Kingdom Animalia
Species
- is the basic unit of classification
- is a group of organisms with similarities in
| structure
|.
| function, and |
| development |
- that breed with one another to produce fertile offspring, and do not interbreed with members of other
species under natural conditions.
- members of a species share a common evolutionary ancestry.
e. g. donkey + horse  infertile mule
hence donkey and horse are different species.
Genus (plural, genera)
- the next higher unit of classification of species with closely related species grouped together.
Family
- a number of related genera constitutes a family.
.
.
. and so on built up the hierarchy.
Subspecies
- the species is the fundamental unit of classification, but not the smallest in use. Geographically distinct
populations within a species often display certain consistent characteristics that serve to distinguish them
from other populations of the same species. If they interbreed, however, they are not truly separate species
but are termed instead subspecies, or varieties. For small organisms such as bacteria, the term strain is
used.
Domains
- the taxonomic categoriser larger than kingdoms proposed by some biologists.
(see table)
1. Prokaryota - lack a nucleus
- DNA not incorporated in chromosomes but comprising a single, circular strand
- no spindle forms at cell division
- flagella lack microtubules
- 70S ribosomes (smaller)
- membrane-bounded organelles are absent (e.g. Golgi,
endoplasmic reticulum,
mitochondria,
chloroplasts, and
lysosomes...etc.)
- no large vacuoles
- cell wall of protein and polysaccharide (composition varies with genera).
- monera kingdom
2. Eukaryota - with a true nucleus
(with double nuclear membranes and one or more nucleoli inside)
- linear DNA in form of chromatin inside nucleus
- 80S ribosomes (larger), may attach to ER
- and may have membranous organelles.
- other kingdoms
Others
- e.g. virus
Living organisms
Virus (?)
Viruses are not included in the
system since the body
organization is completely
different from other organisms
and their origin and evolution
had not yet been clarified.
Prokaryotes
- Monera
Eukaryotes
- Fungi
- Protista
- Plantae
- Animalia
The Five Kingdom System of grouping organisms
The most widely accepted system in recent years is the Five Kingdom System.
The five-kingdom classification in current use recognises the kingdoms Prokaryotae, Protoctista, Fungi, Plantae, and Animalia.
Prokaryotes appeared about 3,500 million years ago and comprise a variety of organisms collectively known as bacteria.
Eukaryotes include protoctists, fungi, plants and animals. They appeared about 2,000 million years ago, and probably evolved
from prokaryotes.
Phylogenetic Relationships of the Five Kingdoms
Six Kingdoms of classification ----- The classification system is subject to change as new
evidences appears:
Most biologists accepted the five-kingdom classification system proposed by Whittaker until the later 1980s, when
molecular work verified the presence of two very different groups of bacteria. As a result, it was proposed to separate
Prokaryota into two kingdoms: Archaebacteria (they are able to survive in extreme conditions) and Eubacteria
(comprises all the other bacteria).
Such a system is subject to changes in the future, as viruses are not yet assigned to any of the kingdom.
Dichotomous key - based on morphological (external / observable) features
Example: To construct simple dichotomous key to identify the following kinds of organisms:
Cells with cell wall ………………………………………2
Cells with no cell wall ……………………………………3
Presence of vascular tissues………………………………Fern
Absence of vascular tissues…………….…………………Algae
Unicellular organism………………………………………Amoeba
Multicellular organism…………………………………….Fish
1a
1b
2a
2b
3a
3b
Way of using the dichotomous key:
1a
2b
Algae
Exercises:
1. To construct a dichotomous key to identify the following types of organisms.
Suggested Simple Dichotomous Key to the Above Classification
COLUMN A
COLUMN B
1a
1b
Flowering
Non-flowering
6
2
2a
2b
Seed-bearing
Seedless
Gymnosperm
3
3a
3b
Plant body differentiated into stem, leaves or roots
Plant body not differentiated into stem, leaves or roots
4
5
4a
4b
Have distinct ‘stem’ and ‘leaves’ but no true roots
Stem, leaves and true roots
Moss
Ferns
5a
Cellulose cell wall, chloroplast or other photosynthetic
pigments present
No cellulose cell wall and photosynthetic pigment
Algae
5b
6a
6b
Fungi
One cotyledon; floral parts in 3s; fibrous root system; parallel Monocotyledons
leaf venation; stem usually herbaceous and slender
Two cotyledons; floral parts in 4s or 5s; tap root system; net Dicotyledons
leaf venation; stem hard, woody with secondary thickening
Life forms
Non-cellular structures:
With cellular structures:
Viruses (be known as virions outside clles)
Organisms
(e.g.: Influenza viruses、human immunodeficiency virus、Severe
acute respiratory syndrome (SARS) coronavirus)
- protein coat
- genetic materials (DNA or RNA)
- can only multiply inside living cells
- microscopic, only be seen under electron microscope
- many can be crystallized
- surrounded by plasma
membrane
- with cytoplasm and other
organelles
- 7 characteristics
- 5 Kingdoms
Without nucleus (Prokaryotes):
Chromatins inside nucleus (Eukaryotes):
1. K. Monera / K. Prokaryota
- genetic materials in cytoplasm
- single-celled (unicellular)
- microscopic, only be visible under
high power light microscope
- non-cellulose cell wall
- no membrane bound organelles, e.g.
mitochondrion, chloroplast, nucleus…
- mesosome (inwardly folded cell
membrane) for respiration
- exist everywhere
- include:
i. all bacteria
(e.g.: Bacillus anthracis、cholera)
ii. cyanobacteria
(∵ with bateriochlorophyll,
∴ also be called blue-green algae)
(Distinguish of Eubacteria and Archaebacteria
is not required)
Cells with little or no
differentiation:
2. K. Protoctista
- multi- or uni-cellular
- include:
i. Protozoa
(animal-like cells)
e.g. Amoeba,
Paramecium
ii. Algae (plant-like cells)
- with cellulose cell
wall and
chlorophyll
e.g. Spirogyra, Fucus,
Diatoms
iii. Slime moulds (fungi-like)
have structural constituents and
composition different from those of
fungi.
3. K. Fungi
- with chitinous cell wall
- no chlorophyll
- usually saprophytic or
parasitic
- body (mycelium)
consists of thread-like
hyphae
i. moulds
e.g. rhizopus,
penicillium
ii. compacted into
massive body
e.g. mushrooms
4. K. Plantae
5. K. Animalia
- with cellulose cell wall - no cell wall
- with chlorophyll inside - no chlorophyll and
chloroplast
chloroplast
- include:
i. non-flowering
plants
- mosses
- ferns
- Gymnosperms
- include:
i. Invertebrates
ii. Vertebrates
- Fish
(Class Pisces)
- Amphibian
ii. Angiosperms
- Monocotyledons
- Dicotyledons
(Class Amphibia)
- Reptile
(Class Reptilia)
- Bird
(Class Aves)
- unicellular
iii. yeast
- Mammal
(Class Mammalia )
Kingdom Plantae:
Kingdom:
Plantae
Divisions: Bryophyta
Filicinophyta
Classes:
Coniferophyta
Angiospermophyta
Moncotyledoneae
Dicotyledoneae
Comparison between different Divisions of Plants:
Bryophyta
Division
eukaryotes / prokaryotes
main
photosynthetic
pigment
main component of cell
wall
Differentiation of cells differentiated into
simple ‘stem’, ‘leaves’
and tissues
Filicinophyta
Coniferophyta
All are eukaryotes
Chlorophyll
Angiospermophyta
Cellulose
has true roots, stems has true vascular roots,
and leaves with
stems and leaves, with
and ‘rhizoid’ with
vascular tissues;
cones and naked seeds
reproductive structure1 gametophyte reduced
for reproduction.
into small heart-shape
prothallus.
has true vascular roots,
stems and leaves, with
flowers and seeds
inside fruit for
reproduction. Presence
of vessels in xylem and
companion cells in
pholem.
Damp, shady cool
Places (e.g. open areas Various
terrestrial Various terrestrial and
Habitat
places
near hillside) where habitat, especially in aquatic habitat.
moisture is available the temperate regions.
during the period of
reproduction
Not important because fertilization is
Importance of water to Important for mobile male gamete to reach the
female gamete for reproduction.
independent of water medium.
fertilization
Funaria
Dryopteris filix
Pinus sylvestris
(any correct example)
Example
Comparison of Class Monocotyledoneae and Class Dicotyledoneae
Monocotyledoneae
Dicotyledoneae
Embryo has one cotyledon
Embryo has two cotyledons
Narrow leaf with parallel venation
Broad leaf with net-like venation
adventitious roots
tap root and lateral roots
Scattered vascular bundles in stem
Ring of vascular bundles in stem
Flower parts usually in threes
Flower parts usually in fours or fives
e.g.
Lilium --- lily
e.g Bellis --- daisy
Kingdom Animalia:
Symmetry
Support
Cnidaria
Radial symmetry
some have chitinous
exoskeleton (Perisarc)
in Obelia
unique /
- gut (enteron) with
specific
one opening as both
characteristics the mouth and anus
generally
found in the
- unique Nematocysts
phylum
(sting cells /
cnidocytes) in
tentacles for defence
and capturing food
- polymorphism
shown: sessile
hydroid form and
mobile medusoid
form
Example(s)
Habitat of the
example(s)
Obelia
(Class Hydrozoa)
Marine / shallow
coastal waters
Platyhelminthes
Bilateral symmetry
nil
-----------
Annelida
Bilateral symmetry
Arthropoda
Bilateral symmetry
Coelomic fluid act as
hydroskeleton
External dorsal shell
Chitinous
exoskeleton with
jointed appendages
on body segments
-expanded
-reduced coelom, blood
haemocoel as main (with haemocyanin) flow in
body cavity
haemocoel
- flat dorsoventrally - cylindrical
segmented body
- unsegmented
covered by nonworm
chitinous cuticle
- beginning of
cephalization
- separated opening of
mouth and anus
- one opening serve -cephalization but may
as mouth and anus
be not distinct in
some members
- may have chaetae in
segments
Planaria
(Class
Turbellaria)
Quiet fresh water
stream, ponds and
under stones
Earthworm /
Lumbricus
(Class Oligochaeta)
Moist terrestrial soil
habitats / damp earth
-body basically
divided into head,
thorax and
abdomen
(may be fused)
-may have
compound eyes
Mollusca
Bilateral symmetry
-soft body covered by a
dorsal shell (calcareous)
-body divided into head,
visceral mass / visceral
hump (covered by mantle
inside mantle cavity) and
muscular foot
-separated mouth and -most (e.g. snails) have
anus
radula (but absent in
bivalves)
- Growth in stages
after moulting.
-most aquatic and have gills
Superclass
Crustacea:
Palaemon
(a common prawn)
Class Insecta:
Chorthippus
(a grasshopper)
Fresh water / marine
Terrestrial (e.g.
grassland)
-separated mouth and anus
Mussel
(Class Bivalvia)
Marine
Echinodermata
Pentamerous (5rayed) symmetry
Mesodermal
calcareous plates
bearing spines as
endoskeleton
-with mouth and
anus separated
Chordata
Bilateral symmetry
-unqiue water
vascular system
-notochord replaced by
vertebral column in
adults of vertebrates
Endoskeleton with
notochord or backbone
-presence of notochord
in embryo
--water-filled
coelomic tubes
-a single, dorsal and
hollow nerve cord in
--with extension of notochord or vertebral
column ??
tube feet
--asexual
regeneration
-separated mouth and anus
-gill slits in embryo
Starfish
(Class
Stelleroidea)
Marine
fish, amphibian, reptile,
bird and mammal
Classification of arthropods
Phylum Arthropoda
Class Crustacea
(crustaceans)
Class Insecta
(insects)
Cephalothorax covered by a
carapace,
strong & massive exoskeleton
hardened by CaCO3 etc.
2 pairs of antennae,
3 pairs of mouth parts,
Class Arachnida
(arachnids)
Body divided into 2 regions:
1. cephalothorax (prosoma):
bears 1 pair of chelicerae
and 1 pair of pedipalps
(sensory & prehensile) and 4
pairs of walking legs.
a pair of stalked compound eyes
(crab) or compound eyes may
fuse to form single eye (daphnia),
One pair of appendages on each
segment on both thorax and
abdomen bears 1 pair of
biramous appendages (divided
into 2 branches at the base)
modified for various purposes e.g.
food capture, swimming, walking
Examples:
etc.
shore crab, prawn, daphnia (water
flea), barnacles
Class
Myriapoda
Simple eyes only and no
antennae.
2. Abdomen (opisthosoma): no
appendages
Examples: garden spider
Body divided into head, thorax and
abdomen,
head bears 1pair of antennae,
1 pair of compound eyes;
thorax bears 3 segments, each bear 1 pair
of jointed legs totally 3 pairs,
Eyes simple, compound or
absent;
1 pair of antennae;
numerous body segments;
each segment bearing 1 pair
(e.g. in centipede) or 2 pairs
of appendages (e.g. in
millipede).
2 / 1 / no pairs of wings.
Examples:
cockroach, grasshopper, mosquito
Examples:
centipede, millipede
Construct a dichotomous key using distinguishing external feature of organisms to identify the
following organisms:
4.2.10
CRUSTACEANS
Name the phylum in which crab is being classified with reasons:
Name the class in which crab is being classified with reasons:
Name the phylum in which shrimp is being classified with reasons:
Name the class in which shrimp is being classified with reasons:
Name the phylum in which daphnia (water flea) is being classified with
reasons:
Name the class in which daphnia (water flea) is being classified with
reasons:
Name the phylum in which barnacles are being classified with reasons:
Name the class in which barnacles are being classified with reasons:
4.2.11
INSECTS
Name the phylum in which cockroach is being classified with reasons:
Name the class in which cockroach is being classified with reasons:
Name the phylum in which grasshopper is being classified with reasons:
Name the class in which grasshopper is being classified with reasons:
Name the phylum in which mosquito is being classified with reasons:
Name the class in which mosquito is being classified with reasons:
4.2.12
ARACHNIDS
Name the phylum in which spider is being classified with reasons:
Name the class in which spider is being classified with reasons:
4.2.13
MYRIAPODS
Name the phylum in which centipede is being classified with reasons:
Name the class in which centipede is being classified with reasons:
Sub-phylum Vertebrata (Craniata)
CLASSIFICATION OF VERTEBRATES
[ 生物學探究 (上冊) P. 134 ]
Phylum Chordata (Vertebrates)
Class Pisces
(fishes)
- Well developed head with brain
encased in cranium.
- With vertebral column.
Class Amphibia Class Reptilia
(amphibians)
(reptiles)
-fins
-gills
Cartilaginous fish
-cartilaginous endoskeleton
-no operculum
-heterocercal tail fin
-no swin bladder
Bony fishes
-operculum over gills
-wet bony scales
-homocercal tail fin
-swim bladder
Class Aves
(birds)
Class
Mammalia
(mammals)
- dry skin with
horny scales
- teeth – all same
type (homodont)
- eggs with yolk
and leathery
shell
- no gills
- no larval stages
- endothermic
- hair
- sweat and
sebaceous glands
- mammary glands
- pinna
- heterodont
- diaphragm
Examples:
Examples:
Examples:
- no scale
- tympanum (eardrum)
visible
- lungs in adult
- aquatic larvae
- metamorphosis
- endothermic
- feathers
- beak (no teeth)
- fore limbs
modified to wings
- air sacs in light
bones
Examples:
Examples:
Can you construct a dichotomous key to identify vertebrates you come across?