Lecture 6 Domains and Kingdoms


All of the organisms in the world are assembled into three domains and six kingdoms


Domain: Bacteria, Kingdom Bacteria


Domain: Archaea, Kingdom Archaea


Domain: Eukarya:             Kingdom Protista

                                    Kingdom Fungi

                                    Kingdom Plantae

                                    Kingdom Animalia


Members of the Bacteria and Archaea are all prokaryotes (before a  nucleus)


No nucleus.  Single circle of DNA.

They are unicellular, made of one cell.  Prokaryote cells are small and simple.

Unlike eukaryotic cells, there are no in prokaryote cells.


Organelles are structures in cells that carry out specific tasks for the cell.  Example s of organelles  found in Eukaryotic cells are mitochondria, chloroplasts, Golgi apparatus, ribosomes).  Mitochondria are involved in respiration, chloroplasts in photosynthesis, the Golgi apparatus in packaging substances and moving them around the cell, and ribosomes are the sites where DNA is read and translated in proteins.


Cell division in prokaryotes is by binary fission.  The cell splits into two to produce two organisms.




Kingdom Eubacteria (“true” bacteria)


Bacteria are the most abundant organisms on earth.  An estimated 5 X 1030

individuals.   One bacterium can give rise to 10 million in 24 hours.


Both aerobic (with oxygen) and anaerobic (without oxygen) respiration.

Some eubacteria carry out photosynthesis.  Some use carbon dioxide in photosynthesis as plants do, but other  eubacteria use other organic compounds as a source of carbon for photosynthesis.


Other eubacteria fix nitrogen (convert it from Nitrogen gas (N2) to forms plants

can use) as a by product of their respiration.  These eubacteria need an oxygen free (anaerobic) environment to survive.  Plants provide nodules on their roots for these bacteria that are oxygen free.  The plants gain nitrogen and the eubacteria somewhere to live.  This is an example of symbiosis: a close mutually dependent relationship between two organisms.


Kingdom Archaea (“Ancient bacteria”—not a good name as they aren’t any more ancient than the Eubacteria)


Archaea are less widespread than Bacteria.


Differ from Eubacteria in (1) details of cell wall structure.  Different chemicals are used to make the cell walls in the two groups.  Cell wall protects the organism.


In addition, the (2) plasma membranes possess unusual lipids that differ from those found in the plasma membranes of bacteria. 


The plasma membrane acts as a complex barrier that filters out substances letting needed substances in and excluding undesirable substances.


Bacteria and Archaea (3) also differ substantially in DNA structure.


Many Archaebacteria are methanogens. 

This means that to produce energy they use H2 gas to reduce CO2 to CH4 (methane), which releases energy.


Many Archaebacteria are adapted to extreme environments.


Thermophiles: “heat lovers.” Inhabit hot  springs. Tolerate temps from 70 -- >110°C.


Halophiles: “salt lovers.”  Require water that is 15-20% salt (seawater only 3% salt).


Archaebacteria more closely related to the Eukarya than are the Eubacteria.





Domain Eukarya.


Eukaryotes: DNA is arranged in chromosomes in a nucleus.

The eukaryotes include both single-celled (unicellular) and many-celled (multicellular) organisms.

Cells larger and more complex than cells of Prokaryotes. Contain organelles.

Organelles are structures in cells specialized for particular tasks.


E.g. Mitochondria and Chloroplasts. 


Mitochondria and chloroplasts were once free living bacteria.  Over time they came to live inside the eukaryotic cells and established a symbiotic relationship. 


Now  what were once free living organisms have become endosymbionts in Eukaryotic cells.


Symbiosis: very close, mutually dependent relationship between two organisms.


Domain Eukarya 4 kingdoms.

          Kingdom Protista.

          Kingdom Fungi

          Kingdom Plantae

          Kingdom Animalia


Kingdom Protista.


Protista are the oldest of the Eukarya. 


Protistans are a “catch-all” group.  Unlike the other 5 kingdoms cladists would not recognize them as a “true group” because they do not form a group that can be defined by shared derived characteristics.


Most Protistans are unicellular.   However, seaweeds algae are multicellular, but do not

have specialized cells.


Kingdom Protista. Examples:



Chlorophyta: Kelp and other algae. 


Kingdom Plantae: trees, grasses, bushes, flowers.


Plants were the first organisms to colonize the land.  Being on land requires the ability to collect and conserve water.  Plant leaves are covered with a  waxy cuticle, which reduces water loss.  Roots collect water for the plant.  Cells are surrounded by a rigid cell wall that is composed of cellulose.  The cellulose provides support for the plant. 


Key ability of plants is photosynthesis: ability to make sugars from water and carbon dioxide using the energy available in sunlight.


Plants are complex multicellular organisms that possess chloroplasts, carry out photosynthesis and their cells have a cell wall.


There are more than 250,000 plant species in the world.


The pants fall into four major groups:







Mosses:  mosses are small never getting more than a couple of inches tall.  They have to remain small because their cells depend on obtaining water by absorbing it through the outside of the plant.  Water can move efficiently only a short distance through cells and this limits how large the mosses can get.


The other three groups the Ferns, Gymnosperms and Angiosperms all avoid this problem by having a plumbing system.  These plants all have a vascular system a system of tubes that moves water from the roots to al the cells of the plant.


Ferns were the first group to evolve a vascular system and were the first plants to grow large.  Unlike the next two groups the ferns do not produce seeds.


Gymnosperms: These include the pine trees, spruces and other cone producing species.  These were the first to produce seeds.  Gymnosperm seeds are called “naked seeds” because the seeds are small and not covered in a fruit, unlike the seeds of the angiosperms.


Angiosperms: were the first group to evolve flowers.  Flowers signal to pollinator such as bees that there is nectar to be obtained and the plant uses the bee to fertilize itself and to spread its pollen to other flowers.  The angiosperms are the most dominant group of plants on earth and include most of the plants you are familiar with: grasses, roses, tulips, petunias, rhododendrons, etc, etc.  Anything that produces a flower is an Angiosperm.


The flower is a special structure where male and female gametes (sex cells) meet.  The ovary, which contains the female sex cell turns into a fruit that surrounds the seed.  The fruit is a bribe to animals.  The animals eat the fruit and digest it and the seed passes through the digestive tract and develops into a plant at some distance from its parent.


Why are trees tall?


Trees are tall because they have to compete for light with other individuals (of their own and other species).  Trees that grew short in the past did not leave descendents behind because they never reproduced.  Only trees that grew tall succeeded, so natural selection ahs produced the giant trees we see today.




Kingdom Fungi: mushrooms, molds, yeasts, mildew 


Fungi are multicellular and filamentous.

Possess specialized cells.

Have external digestion: they secrete digestive enzymes outside themselves and absorb whatever the enzymes break down..

Fungi do not photosynthesize.


Fungi are specialized to be decomposers.  The main body of a fungus is the mycelium which is made up of a mass of threadlike projections called hyphae  which grow in the soil or in tissues of organisms being broken down.  A mushroom is a reproductive structure.  It produces spores, but the bulk of the fungus is out of view.


The fungal cell wall is made of chitin (same substance insect exoskeletons are made of. Fungi digest food externally by secreting digestive enzymes then absorbing the nutrients.


Fungi spread by spores.


There are parasitic fungi that grow their hyphae through tissues of living organisms.  E.g. athlete’s foot fungus.  Pneumocystis carinii causes a deadly fungal pneumonia.  Dutch Elm disease is a fungus too.


We in the Animalia are more closely related to the Fungi than we are to the Plantae.


Many fungi produce antibiotics which kill bacteria.  The first antibiotic Pennicillin was discovered by Sir Alexander Fleming who isolated it form a mold. 


In the past 50 years many bacteria have evolved resistance to antibiotics (natural selection in action).  This has occurred in large part because of the misuse of antibiotics and their prescription by doctors for diseases that are not caused by bacteria (e.g. colds which are caused by a virus).  This has resulted in selection pressure on bacteria to evolve resistance to antibiotics, which they have done.  As a result, many antibiotics are no longer effective and  antibiotic resistant “super bugs” have become more common.  These super bugs include antibiotic resistant strains of TB and Syphilis.


Kingdom Animalia:


Includes: birds, mammals, reptiles, crabs, worms, fish, jellyfish, starfish, etc.


The Animalia are complex, diverse and have excellent mobility.


Animal cells lack a cell wall.

They do not photosynthesize.



There are several levels of complexity in the Animalia.


Complexity increases from: Specialized cells to tissues to organs to organ systems.


The simplest animals are the sponges.  These have specialized cells that carry out a single task, but have not evolved tissues.


The first group to evolve tissues (Cnidaria Jellyfish).  Sponges have no tissues but many cell types.  A tissue is a group of specialized cells that carry out  a particular task.  Examples include muscle tissue and nervous tissue


Among the first organisms to evolve organs and organ systems were the flatworms.  Organs are made up of a number of tissues, have a defined boundary and carry out a specific task.  An example is the stomach.


The next level of complexity above the organ is the Organ system (e.g. digestive system).  An organ system contains many organs working together to achieve a task.


All animals above the flatworms have organs and organs systems: insects, humans, snakes, spiders, snails, etc.