the five kingdoms Flashcards
what are the five kingdoms
Living organisms can be classified into five kingdoms:
-prokaryotae (bacteria)
-protoctista (the unicellular eukaryotes)
-fungi (eg yeasts,moulds and mushrooms)
-plantae (the plants)
-animalia (the animals)
Organisms were originally classified into these kingdoms based on similarities in their observable features.
prokaryotae
general features:
-unicellular
-no nucleus or other membrane-bound organelles-a ring of ‘naked’ DNA-small ribosomes
-no visible feeding mechanism-nutrients are absorbed through the cell wall or produced internally by photosynthesis.
protoctista
general features:
-(mainly) unicellular
-a nucleus and other membrane-bound organelles
-some have chloroplasts
-some are sessile, but others move by cilia,flagella, or by amoeboid mechanisms
-nutrients are acquired by photosynthesis (autotrophic feeders), ingestion of other organisms(heterotrophic feeders), or both-some are parasitic.
fungi
general features:
-unicellular or multicellular
-a nucleus and other membrane-bound organelles and a cell wall mainly composed of chitin.
-no chloroplasts or chlorophyll
-no mechanisms for locomotion
-most have a body or mycelium made of threads or hyphae
-nutrients are acquired by absorption-mainly from decaying material-they are saprophytic feeders-some are parasitic
-most store their food as glycogen.
plantae
with over 250,000 species, the plant kingdom is the second largest of the kingdoms.
General features:
-multicellular
-a nucleus and other membrane-bound organelles including chloroplasts, and a cell wall mainly composed of cellulose.
-all contain chlorophyll
-most do not move, although gametes of some plants move using cilia or flagella.
-nutrients are acquired by photosynthesis-they are
autotrophic feeders😁-organisms that make their own food.
-store food as starch
animalia
The animal kingdom is the largest kingdom with over 1 million known species.
General features:
-multicellular
-a nucleus and other membrane-bound organelles (no cell walls)
-no chloroplasts
-move with the aid of cilia,flagella, or contractile proteins, sometimes in the form of muscular organs.
-nutrients are acquired by ingestion-they are heterotrophic feeders
-food stored as glycogen.
recent changes to classification systems
As scientists learn more about organisms, classification systems change.
Originally classification systems were based on observable features.
Through the study of genetics and other biological molecules, scientists are now able to study the evolutionary relationships between organisms.
These links can then be used to classify organisms.
When organisms evolve, their internal and external features change, as does their DNA. This is because their DNA determines the proteins that are made, which in turn determines the organism’s characteristics.
In order for their characteristics to have changed, their DNA must also have changed. By comparing the similarities in the DNA and proteins of different species, scientists can discover the evolutionary relationships between them. You will learn more about DNA sequencing and its use in studying evolutionary relationships in Topic 10.4, Evidence for evolution.
An example of a protein that has changed in structure is haemoglobin.
Haemoglobin has four polypeptide chains, each made up of a fixed number of amino acids. The haemoglobin of humans differs from chimpanzees in only one amino acid, from gorillas in three amino acids and from gibbons in eight amino acids. As the structure of haemoglobin is remarkably similar, it indicates a common ancestry between the various primate groups.
are there now six kingdoms
The current classification system used by scientists is known as the Three Domain System’, and was proposed by Carl Woese, an American microbiologist in 1977, reusing the word ‘Kingdom’. In 1990 it was renamed ‘Domain’. Domains are a further level of classification at the top of the hierarchy.
Woese’s system groups organisms using differences in the sequences of nucleotides in the cells’ ribosomal RNA (RNA), as well as the cells’ membrane lipid structure and their sensitivity to antibiotics.
Observation of these differences was made possible through advances in scientific techniques.
Under the Three Domain System, organisms are classified into three domains and six kingdoms. The three domains are Archaea, Bacteria, and Eukarya. The organisms in the different domains contain a unique form of RNA and different ribosomes:
• Eukarya - have 80s ribosomes
-RNA polymerase (responsible for most mRNA transcription) contains 12 proteins.
• Archaea - have 70s ribosomes
-RNA polymerase of different organisms contains between eight and 10 proteins and is very similar to eukaryotic ribosome.
• Bacteria - have 70s ribosomes
-RNA polymerase contains five proteins.
In Woese’s system the Prokaryotae kingdom becomes divided into two kingdoms - Archaebacteria and Eubacteria. The six kingdoms are therefore:
Archaebacteria, Eubacteria, Protoctista, Fungi, Plantae and Animalia.
Although both Archaebacteria and Eubacteria are single-celled prokaryotes, Eubacteria are classified in their own kingdom because their chemical makeup is different from Archaebacteria. For example, they contain peptidoglycan (a polymer of sugars and amino acids) in their cell wall whereas Archaebacteria do not.
archaebacteria
Archaebacteria, also known as ancient bacteria, can live in extreme environments. These include hot thermal vents, anaerobic conditions, and highly acidic environments. For example, methanogens live in anaerobic environments such as sewage treatment plants and make methane.
eubacteria
Eubacteria, also known as true bacteria, are found in all environments and are the ones you will be most familiar with. Most bacteria are of the Eubacteria kingdom.
Some scientists still use the traditional five kingdom system, but since Archaebacteria have been found to be different chemically from Eubacteria, most scientists now use the three domain, six kingdom system.
