IGCSE Topic 32: Classification

Envelope

Layer of membrane surrounding some viruses; derived from the infected cell.

Reproduction

Characteristic of living organisms. The ability to produce new members of the same species.

Fungi

Group of organisms distinct from bacteria and plants. Grow as single cells or as long threads known as hyphae. Obtain nutrition by secreting digestive enzymes into the environment. Include yeasts and moulds.

Hybrid

The product of a cross between two species - usually infertile

Mule

A hybrid obtained by crossing a horse and a donkey

Key

A set of questions designed to allow you to identify a species easily

Genus

The seventh major taxonomic rank in the hierarchical classification of life below family and above species. For example Canis are dogs which in turn belong to the Family Canidae.

Species

The eighth and final major level of taxonomic grouping. It defines a group of organisms with similar characteristics that can breed and produce fertile offspring.

Cellulose

Polymer of glucose that is a key component of plant cell walls

Vector

An organism that is responsible for carrying a parasite from one host to another.

Pathogen

A microorganism that can infect and harm a plant or animal.

Binomial system

The naming system for species that involves a genus and species name

Chitin

Carbohydrate polymer that forms the cell walls in fungi and the external skeleton of insects.

Invertebrate

An animal without a backbone

Joint

The interface between two bones

Parasite

An organism that lives on or in another organism known as a host, which it uses as a source of food and usually harms in the process.

Protozoa

A group of single celled organisms that include simple animals like amoeba and pathogens like Plasmodium that cause malaria. Like alga, belong to the protoctist kingdom.

Slime layer

Another name for the bacterial capsule.

Vertebra (vertebrae)

The bones that make up the spinal column. Form a protective tube for the spinal cord.

Vertebrate

An animal with a backbone

Kingdom

The second major taxonomic rank in the hierarchical classification of life below domain and above phylum. Divided into animals, plants, protoctists, fungi, and bacteria.

Phylum

The third major taxonomic rank in the hierarchical classification of life below kingdom and above class. In the animal kingdom examples include chordates, arthropods and molluscs.

Class

The fourth major taxonomic rank in the hierarchical classification of life below phylum and above order. For example Chordates include mammals, birds and reptiles.

Order

The fifth major taxonomic rank in the hierarchical classification of life below class and above family. For example, we are Primates.

Family

The sixth major taxonomic rank in the hierarchical classification of life below order and above genus. For example, dog-like animals are Canidae of the order Carnivora.

Carl Linnaeus

Swedish naturalist born in 1707 who was the founder of modern taxonomy. Had the idea of a hierarchical structure of classification based upon observable characteristics and invented the binomial classification system.

Classification

The grouping and categorizing of organisms into groups such as family, genus or species.

Taxonomy

The scientific classification of biological organisms on the basis of shared characteristics and giving names to those groups.

Reptiles

A class of vertebrates that have dry scaly skin and laying leathery eggs that do not have to be kept in water.

Amphibians

A class of vertebrates that have moist permeable skin and laying soft eggs that have to be kept in water.

Fish

A class of vertebrates that live in water, have scales and use gills for gas exchange throughout their life.

Birds

A class of vertebrates that have feathers, a beak and lay eggs with a hard shell.

Mammals

A class of vertebrates that have fur, give birth to live young and feed their young with milk.

Cnidarians

The class of invertebrates to which jellyfish belong.

Flatworms

A class of invertebrates consisting of simple unsegmented worms without a gut that are often parasitic.

Roundworms

A class of invertebrates, also known as nematodes, made up of unsegmented worms with a simple gut. Often parasitic.

Annelids

These are a class of invertebrates that is made up of the segmented worms, including earthworms, ragworms and leeches.

Molluscs

A type of invertebrate that includes snails, slugs and many marine organisms such as squid and octopus.

Echinoderm

A type of invertebrate that has five-fold symmetry such as starfish and sea-urchins.

Arthropod

An abundant type of invertebrate that made up of organisms with an exoskeleton and jointed legs.

Crustacean

A large group of arthropods with limbs made of two parts. They need water for breeding and include shrimp, lobsters and woodlice.

Myriapod

A group of arthropods with many segments that include the centipedes and millipedes.

Insect

The largest group of arthropods that have a three-part body (head, thorax and abdomen) and three pairs of legs.

Arachnid

A group of arthropods that have four pairs of jointed legs. Includes the spiders, mites and scorpions.

Plant

A kingdom of multicellular organisms that can make their own food through photosynthesis and possess cellulose cell walls.

Moss

A type of simple plant that lacks roots, stems and a vascular system. Reproduces with spores.

Fern

A simple type of plant with stems, leaves and a vascular system. Reproduces with spores.

Conifer

A type of woody plant that reproduces with seeds in cones.

Flowering plant

A plant that reproduces by seed that is not in a cone.

Euglena

A unicellular protist with both plant and animal characteristics. Although it can move using its flagellum, is sensitive to light, and can ingest prey, it also photosynthesises due to the presence of chloroplasts.

Amoeba

A unicellular protist that engulfs its prey by phagocytosis.

Plasmodium

A unicellular protist that is the parasite that causes malaria

Anopheles

The genus of species that most commonly acts as the vector for the malaria parasite plasmodium.

Homo sapiens

The scientific (binomial) name for our species.