Biology IB HL - Classification

Has no vascularisation (i.e. lacks xylem and phloem)

Has no ‘true’ leaves, roots or stems (are anchored by a root-like structure called a rhizoid)

Reproduce by releasing spores from sporangia (reproductive stalks)

Small and restricted to moist, terrestrial environment

Examples include mosses and liverworts

Has vascularisation (i.e xylem and phloem)

-Have leaves, roots and stems, as well as stomata (leaves are pinnate – consisting of large fronds divided into leaflets)

-Reproduce by releasing spores from clusters called sori on the underside of the leaves

Examples include ferns

Has vascularisation

Have leaves, roots and stems (stems are woody and leaves are waxy and needle-like)

Reproduce by non-motile gametes (seeds) which are found in cones

Examples include pine trees and conifers

Has vascularisation

Have leaves, roots and stems (individual species may be highly variable in structure)

Reproduce by seeds produced in ovules within flowers (seeds may develop in fruits)

Examples include all flowering plants and grasses

flower parts in multiples of 3

leaf veins are parallel

pollen with single furrow or pore

flower parts in multiples of 4/5

leaf veins are reticulated

pollen with 3 furrows or pores

are aquatic

reproduce asexually by budding

lack organs

lack body symmetry

no mouth or anus (have pores to facilitate the circulation of material)

no nervous system

may have silica or calcium carbonate-based spicules for structural support

Examples include sea sponges

Have radial symmetry

Have a mouth but no anus (single entrance body cavity)

May have tentacles with stinging cells for capturing and disabling prey

all aquatic

diploblastic (polyp and medusa - may alternate between these life cycles)

Examples include jellyfish, sea anemones and coral

Have bilateral symmetry

Have a mouth but no anus (single entrance body cavity)

Have a flattened body shape to increase SA:Vol ratio and may be parasitic

unsegmented

Examples include tapeworms and planaria

Have bilateral symmetry

Have a separate mouth and anus

Body composed of ringed segments with a specialisation of segments

body has chaetae (bristles)

move using hydrostatic skeleton or parapodia

Examples include earthworms and leeches

Have bilateral symmetry

Have a separate mouth and anus

Have jointed body sections/appendages and have a hard exoskeleton (chitin)

jointed body sections/appendages

hard exoskeleton of chitin

open circulation

compound eyes

Examples include insects, crustaceans, spiders, scorpions and centipedes

Have bilateral symmetry

Have a separate mouth and anus

Body is composed of a visceral mass (organs), a muscular foot and a mantle (may produce shell)

soft bodied

most have radula (rasping tongue)

aquatic (with gills) and terrestrial

Examples include snails, slugs, octopi, squid and bivalves (e.g. clams)

tube feet for movement

water vascular system

rigid body wall

internal skeleton made of calcareous plates

many possess spines

ventral mouth and dorsal anus

external fertilisation

unsegmented

dorsal and tubular nerve cord

post-anal tail at some part of development

circulation closed in most

pharyngeal slits

heart on ventral side

internal skeleton of cartillage/bone

vertebral column replaces notochord

two pairs of appendages attached to girdles

have developed nervous system

skeleton of cartillage

no swim bladder

all aquatic

swim bladder present

all aquatic

bony endoskeleton

Moist skin, permeable to gases and water

Reproduce via external fertilisation (usually spend larval state in water, adult state on land)

Can breathe through skin but also possess simple lungs

Do not maintain a constant internal body temperature (ectothermic)

Covered in scales made out of keratin

Reproduce via internal fertilisation and females lay eggs with soft shells

Breathe through lungs that have extensive folding (increases SA:Vol ratio)

Do not maintain a constant internal body temperature (ectothermic)

Covered in feathers (made out of keratin)

Reproduce via internal fertilisation and females lay eggs with hard shells

Breathe through lungs with parabronchial tubes

Maintain a constant internal body temperature (endothermic)

Skin has follicles which produce hair made out of keratin

Reproduce via internal fertilisation and females feed young with milk from mammary glands

Breathe through lungs with alveoli

Maintain a constant internal body temperature (endothermic)

The binomial system of nomenclature is the formal system by which all living species are classified (taxonomy)

It was initially developed by a Swedish botanist named Carolus Linnaeus in 1735

It is periodically assessed and updated at a series of international congresses which occur every 4 years

It allows for the identification and comparison of organisms based on recognised characteristics

It allows all organisms to be named according to a globally recognised scheme

It can show how closely related organisms are, allowing for the prediction of evolutionary links

It makes it easier to collect, sort and group information about organisms

According to the binomial system of nomenclature, every organism is designated a scientific name with two parts:

Genus is written first and is capitalised (e.g. Homo)

Species follows and is written in lower case (e.g. Homo sapiens)

Some species may occasionally have a sub-species designation (e.g. Homo sapiens sapiens – modern man)

Writing conventions:

When typing the scientific name, it should be presented in italics

When hand writing the scientific name, it is customary to underline

eukarya

archaea

eubacteria

eukaryotic organisms that contain a membrane-bound nucleus (includes protist, plants, fungi and animals)

prokaryotic cells lacking a nucleus and consist of the extremophiles (e.g. methanogens, thermophiles, etc.)

prokaryotic cells lacking a nucleus and consist of the common pathogenic forms (e.g. E. coli, S. aureus, etc.)

Originally, the two prokaryotic domains were considered only as a single kingdom (Monera), however biochemical differences were discovered between the two groups which warranted their reclassification into separate domains

Taxonomy is the science involved with classifying groups of organisms on the basis of shared characteristics

Organisms are grouped according to a series of hierarchical taxa – the more taxa organisms share, the more similar they are

The taxa used are kingdom, phylum, class, order, family, genus and species (genus + species = scientific name)

All plant and animal species belong to the same domain (Eukarya) as they are composed of eukaryotic cells

Historically, there have been two main classification schemes used to identify living organisms – artificial and natural classification

Both use prominent features as the basis for classification, however differ in the way these characteristics are established

Artificial classification involves arbitrarily selecting unifying characteristics first and then grouping organisms accordingly

The advantage of artificial classification is that such schemes are easy to develop and relatively stable (unlikely to change)

The disadvantage is that they do not generally show evolutionary relationships and for this reason are not commonly used

For example, if organisms were classified according to the presence of fins then whales would be grouped with fish

If organisms were classified based on the presence of shells then snails would be grouped with turtles and not with squid

Natural classification involves grouping organisms based on similarities first and then identifying shared characteristics

According to a natural classification system, all members of a particular group would have shared a common ancestor

his means that natural classification schemes can be used to predict characteristics shared by species within a group

A disadvantage of such schemes is that they are highly mutable and tend to change as new information is discovered

A third type of classification – phylogenetic classification – is now being used to differentiate organisms based on genetics

Organisms who share a greater level of homology in their DNA or amino acid sequences are expected to be more closely related

An advantage of natural classification is that it identifies traits based on groupings, rather than assigning groups based on traits

This means that it can be used to show evolutionary relationships and predict characteristics shared by species within a group

According to natural classification, each taxonomic level includes all species that would have evolved from a common ancestor

Species of the same genus would have a common genus ancestor and be more closely related than species of the same order

Hence, organisms that share a lower taxa must share all higher taxa (e.g. if the same order then must also be the same class)

A disadvantage of natural classifications is that because they predict evolutionary relationships, they change with new information

Taxonomists will reclassify groups of species when new evidence arises to compromise the traditional classification scheme

Groups of species may be separated into different genera if new evidence suggests they evolved from different ancestral species

Species originally classified as figworts have been reclassified into different genera based on DNA sequence comparisons

Alternatively, different species may be grouped into a shared taxon if new evidence suggests more recent common ancestry

The Homininae sub-family was created to include gorillas and chimpanzees when it was deduced that they share more common ancestry with humans than with other great apes (e.g. orang-utan)

A dichotomous key is a method of identification whereby groups of organisms are divided into two categories repeatedly

With each sequential division, more information is revealed about the specific features of a particular organism

When the organism no longer shares its totality of selected characteristics with any organism, it has been identified

When using a dichotomous key to identify specimens it is preferable to use immutable features (i.e. features that do not change)

Size, colouration and behavioural patterns may all vary amongst individuals and across lifetimes

Physical structures (e.g number of limbs) and biological processes (e.g. reproduction methods) make for better characteristics

Dichotomous keys are usually represented in one of two ways:

As a branching flowchart (diagrammatic representation)

As a series of paired statements laid out in a numbered sequence (descriptive representation)