Click4Biology

5.5.1 Binomial system

Each species has two names. These are used together to give a precise reference to this species.

Genus is given first and is always written with an upper case letter. e.g. Homo
Species epithet follows the genus and is written in lower case e.g. sapiens

Therefore the species name for humans is Homo sapiens

Conventions:

If written by hand the name should also be underlined
If typed the name should really be in italics but this convention is often ignored
Often the name will be followed by another name in brackets e.g. (Dickson) which refers to the first person to scientifically identify the species.

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5.5.2 Hierarchical system of classification.

When classifying organisms those that share characteristics are placed into similar groups.

The more similar their characteristics then the closer the grouping.

The purpose of classification is to

clearly identify an organism with a name that is unique to the species and avoids confusion with local naming.

studying the similarities of one group with another establishes the evolutionary relationship between groups

knowing a species classification allows us to predict anatomical, physiological and genetic characteristics it may share with other organisms.

In section 5.5.1 the binomial system introduces two levels of taxon, that of species and genus. The Hierarchical system presented here has seven levels. Each taxon (level of Hierarchical classification) can contain one or more of the sub-group below it. That is a Kingdom many contain one or more phyla and each phylum may contain one or more classes. Two examples are provided.

When Carlolus Linnaeus invented the system in the mid 1700's he did so with no notion of the evolutionary theories that would follow in the mid 1800's.

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5.5.3 Plant phyla.

Kingdom: Plantae

Characteristics:

Photosynthetic
Chlorophyll
Cellulose cell wall
Vacuoles permanent
Store starch

Classification of the major plant phyla is based on external observable structures:

Phylum: Bryophyta (mosses, liverworts and hornworts)

stems radial symmetry (mosses)
stems bilateral symmetry (liverworts), no lignin
no true leaves or roots
no cuticle.
reproductive structure are called sporangium which are on long stalks with capsules on end. In this image the spore is released from the sporangium to develop into another plant.

Phylum: Filicinophyta (ferns)

leaves
roots non woody stems
divided leaves
height up to 20m
reproduction: sporangia (sori) contain reproductive spores

Phylum: Coniferophytes (conifers and pines)

trees (100m), shrubs,
woody (lignin) stems,
waxy narrow needle like leaves.
vascular system (tracheids)
reproduction:monoecious, microsporophylls (male) non motile gametes often with air bladders for water/ air dispersal. macrosporophylls (female) ovule on cone scale

Phylum: Angiospermophyta (flowering plants and grasses)

roots
stems
leaves.
vascular bundles (xylem/ phloem )
waxy cuticle,
annual or perennial up to 100m

reproduction:

ovules in an enclosed carple structure.
pollen grains produced from anthers
variety of pollen transfers vectors

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5.5.4 Animal phyla.

The syllabus specifies six of the 30 or more phyla from the animal kingdom. The ones selected are what might be called invertebrates. This term describes the common feature of the group which is the lack of a notochord (spinal cord ). However this is term has limited use in the classification of these groups. The Kingdom of animals is classified according to these characteristics:

Heterotrophic
no cell walls
no vacuoles
no chlorophyll
store glycogen

The six phyla are classified according to features such as the number of layers in the body plant, the opening for mouth and anus and the method of support. Phylogenic studies (evolutionary relationship) relies on more genetic studies to support the modern classification of these groups.

Phylum: Porifera (sponges)

No body layers rather there is an aggregate of different cell types.
Support is from either silica or calcium based spicules which link together to provide some support.
Body plan is built around water canals that circulate nutrient through the sponge for ingestion by specialised cells.
There is no mouth or anus

Phylum: Cnidaria (Jelly fish, Sea anemones, Corals)

These have 2 layers in the body plan.
There is a radial symmetry.
Jelly fish are mobile organisms. Sea anemones are sessile organisms.
Single entrance that serves the the cavity that functions of the circulation of respiratory gases and nutrient. These organisms are secondary consumers and posses stinging cells with toxins called nematocysts to disable prey.
Corals secrete a CaCO₃ skeleton

Phylum: Platyhelminthes (flatworms)

3 layers in the body plan.

One entrance to 'gut' which can have many folds to increase surface area.

largely parasitic includes flukes

Phylum: Annelida (segment worms)

3 layers to the body plan / bilateral symmetry

body divided into ringed segments with some specialisation of segments

Mouth connected via gut to a separate anus.

Skin surface used for gas exchange.

Many marine forms but also terrestrial species usually soil burrowing

Phylum: Mollusca (Snails, slugs and octopus)

Bilateral symmetry with significant modification.

An extraordinarily varied group which has developed some radically divergence from other groups.
Phylogenic studies place them closer to annelids than other groups.
Body plan has three major features:
Foot, a muscular structure used for movement and burrowing.
Central visceral mass containing all the organ structures (separate mouth and anus)
Mantle a folded membrane structure that can surround other tissues and create a cavity containing a gill.
The mantle frequently secretes a calcareous shell.

Phylum: Arthropoda ( Insects, Crustaceans, Spiders, Scorpions, Millipedes)

3 layer body plant with bilateral symmetry.
Hard exoskeleton composed of chitin.
Jointed body segments.
Jointed appendages.
Some flying organisms in the class Insecta. ( 10⁶⁺ species)
Separate mouth and anus.

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5.5.5 Dichotomous keys

Design Principles:

Each question divides the group of organisms into two smaller groups based on a pair of alternative characteristics
Subsequent groups may focus on more minor detail
In most cases the characteristic will be readily observed or measurable
It is better to choose characteristics that are uninfluenced by environmental variation
Shape and number are often good characteristics on which to base alternative pairings
A complete key will have each type of organism being classified separated with a final identifying name.

Below is a gallery of species with their common names