4.3.4 Classification of the Five Kingdoms

Question 1

What are the 5 kingdoms?

Answer 1

Before the three domains of life (Bacteria, Archaea and Eukarya) were introduced and then widely accepted as the highest rank in the classification of life on Earth, most people thought there to be five kingdoms at the top of the classification hierarchy
These five kingdoms include:
Prokaryota
Protoctista
Fungi
Plantae
Animalia

Question 2

What are Prokaryotes?

Answer 2

This kingdom includes bacteria and blue-green bacteria
The main features of all organisms within Prokaryota include:
Most are unicellular (some can be found as filaments of cells or groupings of similar cells known as colonies)
Their cells have cell walls (not made of cellulose) and cytoplasm but no nucleus or mitochondria
They vary in size over a wide range: the smallest are bigger than the largest known viruses and the largest are smaller than the smallest known single-celled eukaryotes
Their cells divide by binary fission
Blue-green bacteria and some bacteria are autotrophic (they are photosynthetic)
Many bacteria are heterotrophic (feeding by decomposing living or dead organic materials)

Question 3

What can all the other kingdoms be classifies into?

Answer 3

The other kingdoms can all be classified within the domain Eukarya, which can be divided into the following four kingdoms:
Protoctista
Fungi
Plantae
Animalia
Organisms from each of these four kingdoms have distinct characteristics and features, but share similarities in that they have cells with membrane-bound nuclei separating genetic material from the cytoplasm, and compartmentalisation within their cells as a result of the presence of other organelles

Question 4

What are protoctists?

Answer 4

All Protoctista are eukaryotic, and this broad group of cellular life encompasses all eukaryotic cells that do not belong to the other three eukaryotic kingdoms
Members of this kingdom show great diversity in all aspects of life including structure, life cycle, feeding and trophic levels and well as modes of locomotion
Protoctists can exist as single-celled organisms or as a group of similar cells
A group of Protoctista known as protozoa possess cells similar to animal cells
Their cells have no cell wall
Another group of Protoctista known as algae possess cells similar to plant cells
Their cells have cellulose cell walls and chloroplasts

Question 5

What are Fungi?

Answer 5

All fungi are eukaryotic cells
The cells of fungi:
Possess non-cellulose cell walls (often made of the polysaccharide chitin)
Don’t have cilia
Fungi are heterotrophs:
They use organic compounds made by other organisms as their source of energy and molecules for metabolism
They obtain this energy and carbon by digesting dead/decaying matter extracellularly or from being parasites on living organisms
Fungi reproduce using spores that disperse onto the ground nearby
Fungi have a simple body form:
They can be unicellular (like the common baker’s yeast Saccharomyces cerevisiae
Some consist of long threads called hyphae that grow from the main fungus body and form a network of filaments called the mycelium
Larger fungi possess fruiting bodies that release large numbers of spores (this is how many fungi reproduce)
The mould found on bread is actually a fungus: Rhizopus nigricans

Question 6

What are plants?

Answer 6

Plants are multicellular eukaryotic organisms
Plant cells:
All have cell walls composed of cellulose
Possess large (and usually permanent) vacuoles that provide structural support
Are able to differentiate into specialized cells to form tissues and organs
Possess chloroplasts that enable photosynthesis (not all plant cells have chloroplasts)
Can sometimes have flagella
They are autotrophs
This means they can synthesize their organic compounds and molecules for energy use and building biomass from inorganic compounds
Plants have complex body forms
They have branching systems above and below the ground

Question 7

What are animals?

Answer 7

Animals are also multicellular eukaryotic organisms
Animal cells:
Are able to differentiate into many different specialised cell types that can form tissues and organs
Have small temporary vacuoles (for example, lysosomes)
Have no cell walls
Sometimes have cilia
They are heterotrophs and have a wide range of feeding mechanisms
Communication within their complex body forms takes place through a nervous system and chemical signalling