5.5 – Classification
5.5.1 – Outline the binomial system of nomenclature
In this system, each species has two names – a noun and an adjective. The first is the genus, which starts with an upper case letter, followed by the species written in lower case.
i.e. Homo sapiens
When such names are handwritten, they must be underlined, whilst typed names must be in italics. If it is followed by a name in brackets, this is the name of the person who first scientifically identified the species
5.5.2 – List seven levels in the hierarchy of taxa – kingdom, phylum, class, order, family, genus and species – using an example from two different kingdoms for each level
Organisms that share characteristics are placed in similar groups. The groups become closer as the organisms become more similar. Using this system, organisms can be clearly identified without the confusion of local naming. Also, it shows the evolutionary relationships between groups. Simply based on the name, we can predict anatomical, physiological and genetic characteristics it may share with other organisms.
5.5.3 – Distinguish between the following phyla of plants, using simple external recognition features: bryophyta, filicinophyta, coniferophyta, and angiospermophyta
Any organism belonging to the plant kingdom has the following characteristics:
- They are photosynthetic
- Contain chlorophyll
- Their cells have a cell wall of cellulose
- They contain permanent vacuoles
- They store starch
Bryophyta – moss, liverworts and hornworts
These have no true leaves or roots, having only hair-like rhizoids, nor a cuticle. They reproduce through sporangium, which are long stalks with capsules on the end. They inhabit damp environments.
Filicinophyta – ferns
These have elaborate leaves and roots that conduct water and nutrients. They have divided leaves with a waxy cuticle and non-woody stems. They reproduce through sporangia, which are found clustered on the under-surface of the leaves and contain the reproductive spores. Ferns favour moist conditions.
Coniferophytes – conifers and pines
These are trees and shrubs that have woody steps due to the presence of lignin. They have waxy, narrow, needle-like leaves and vascular systems. They are typically evergreen plants that are resistant to low temperatures. They reproduce using cones.
Angiospermophyta – flowering plants and grasses
These have roots, stems and leaves with vascular bundles. The leaves have a waxy cuticle and pores on the surface called stomata. They reproduce using flowers, with the ovules in the carpal structure and the polled grains produced in the anthers. This phylum is then split into the monocotyledons and the dicotyledons. Monocots have parallel veins in the leaves and a single embryonic leaf. Dicots, on the other hand, have net-like veins and two embryonic leaves.
5.5.4 – Distinguish between the following phyla of animals, using simple external recognition features: porifera, cnidaria, platyhelminthes, annelida, mollusca, and arthropoda
All animals have the following characteristics:
- They are heterotrophic
- Their cells have no cell walls or vacuoles
- There is no chlorophyll in their cells
- They store glycogen
Porifera – sponges
These have no body layers, but are merely an aggregate of different cell types. They have no nervous system, mouth or anus. They use silica or calcium based spicules for support, and water canals for the circulation of nutrients. They form marine colonies of cells.
Cnidaria – jellyfish, sea anemones, corals
These have a two-layered body plan with radial symmetry. They only have one opening, and contain stinging cells with toxins nematocysts to disable prey. Coral secrete a CaCO3 skeleton.
Platyhelminthes – flatworms
These have a three-layered body plan. They have a flat, unsegmented body with a single opening. Their gut has folds to increase surface area, and they have both female and male sex organs, although self-fertilisation rarely occurs. Flatworms are usually parasites.
Annelida – segmented worms
These have a three layered body plan with bilateral symmetry, divided into ringed segment with some specialisation of segments. They have two openings – a mouth and anus, with gas exchange taking place on the skin surface.
Mollusca – Snails, slugs and octopi
These have bilateral symmetry with significant modification, including a muscular foot for burrowing and movement. They have two openings: the mouth and anus, with all their organs in a central mass. They will often secrete a calcareous shell.
Arthropoda – Insects, Crustaceans, Spiders, Scorpions, Millipedes
These have a three-layer body plan with bilateral symmetry, a hard, chitin exoskeleton. They have two openings: the mouth and anus. They have joined body segments and appendages.
5.5.5 – Apply and design a key for a group of up to eight organisms
To make a dichotomous key:
- Divide the group into two smaller groups based on a pair of alternative characteristics
- Subsequent groups will focus on more minor details
- Characteristics should be readily measurable or observable, but uninfluenced by environmental variation
- Shape and number are good characteristics
- The result should have each organism classified with a final identifying name
A dichotomous key may look like this: 1.
1. Animal has no openings…………………………. Porifera
Animal has openings……………………………… go to 2
2. One opening…………………………………………. go to 3
Two openings……………………………………….. go to 4
3. Three layered body plan………………………… Platyhelminthes
Two layered body plan…………………………… Cnidaria
4. Segmented body…………………………………… go to 5
Unsegmented body……………………………….. Mollusca
5. Appendages………………………………………….. Arthropoda
No appendages……………………………………… Annelida