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General Education
Lesson 4: Kingdoms and Domains
Kingdoms and domains are the broadest levels of biological classification. The domain is the very largest group (separating prokaryotes from eukaryotes), and kingdoms are the second level (grouping organisms by major characteristics). Together, they help us organize all life on Earth into manageable categories.
- Domains separate prokaryotes (no nucleus) from eukaryotes (with nucleus). Kingdoms separate organisms by how they get energy and what type of cells they have.
The Three Domains
All life on Earth is divided into three domains: Archaea, Bacteria, and Eukarya. The first two domains contain prokaryotic organisms (no nucleus), while Eukarya contains eukaryotic organisms (with nucleus).
Domain Archaea
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| Image from ThoughtCo |
Archaea (pronounced "ar-KAY-uh") is one of the three domains of life. Archaea organisms are prokaryotic, meaning they do not have a nucleus.
Kingdom in this domain:
Kingdom Archaebacteria
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| Image from Examples |
Archaebacteria are ancient microorganisms that live in some of the most extreme and severe environments on Earth.
Where they live:
- In hot springs and geysers
- In salt lakes and salt marshes
- In acidic environments
- In oxygen-free environments
- Other extreme environments that most organisms cannot survive in
Types of archaebacteria:
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| Image from EurekAlert |
1. Methanogens - are archaebacteria that produce methane gas. They live in oxygen-free environments like swamps, mud, and the stomachs of cows. They break down organic material and release methane.
2. Halophiles - are salt-loving archaebacteria. They live in extremely salty environments like salt lakes and salt marshes. They can survive in salt concentrations that would kill other organisms.
3. Thermophiles - are heat-loving archaebacteria. They live in extremely hot environments like hot springs and geysers where temperatures can exceed 100°C (212°F). They thrive where other organisms would die.
Archaebacteria are tough microorganisms that can survive in extreme conditions that would kill almost everything else.
- Example: In Yellowstone National Park, thermophiles live in hot springs at temperatures that would boil water. In the Dead Sea, halophiles live in salt water so salty that nothing else can survive there.
Domain Bacteria
Bacteria is the second domain of life. Bacteria are prokaryotic organisms (no nucleus).
Kingdom in this domain:
Kingdom Eubacteria
(also called Monera in older classification systems)
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| Image from Study |
Kingdom Eubacteria - also called "true bacteria," are the bacteria that we commonly know and encounter every day. They are simple, single-celled prokaryotic organisms.
Characteristics:
- Single-celled prokaryotes (no nucleus)
- Found almost everywhere on Earth
- Can be helpful (like bacteria in yogurt) or harmful (like bacteria that cause disease)
- Much smaller than eukaryotic cells
- Reproduce through binary fission (splitting in two)
Eubacteria are the common bacteria found everywhere. They are the "true bacteria."
- Example: E. coli bacteria in your intestines, Streptococcus bacteria that causes strep throat, bacteria in soil, bacteria in the ocean.
Domain Eukarya
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| Image from PeachBio |
Eukarya is the third domain containing all organisms with eukaryotic cells (cells with a nucleus). This is the largest and most diverse domain, including protists, fungi, animals, and plants.
Kingdoms in this domain:
- Kingdom Protista
- Kingdom Fungi
- Kingdom Animalia
- Kingdom Plantae
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| Image from testbook |
Kingdom Protista - are mostly single-celled eukaryotic organisms. They are very diverse and do not fit neatly into other kingdoms, so protista is sometimes called a "catch-all" kingdom.
Characteristics:
- Eukaryotic (have a nucleus)
- Mostly single-celled (though some are multicellular)
- Live in water or moist environments
- Very diverse group
Examples of protists:
1. Diatoms - are single-celled algae with beautiful glass-like shells. They are common in oceans and freshwater. They produce much of the oxygen in the atmosphere.
2. Algae - are photosynthetic protists that come in different colors:
- Green algae - contain chlorophyll
- Golden algae - contain golden pigments
- Brown algae - contain brown pigments (includes kelp and seaweed)
- Red algae - contain red pigments
3. Entamoeba histolytica - is a parasitic protist that causes a disease called amoebiasis. It infects the intestines and causes diarrhea and other symptoms.
4. Plasmodium - is a parasitic protist that causes malaria. It is spread by mosquitoes and infects red blood cells, causing fever, chills, and serious illness.
Protists are mostly single-celled organisms that live in water. Some are helpful (like algae that make oxygen), and some are harmful (like parasites that cause disease).
Kingdom Fungi
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| Image from Pablo |
Fungi are eukaryotic organisms that get energy by decomposing dead organic material. They are not plants (they cannot make their own food) and not animals (they do not eat). Fungi are their own unique kingdom.
Characteristics:
- Eukaryotic cells
- Cannot make their own food (not photosynthetic)
- Get energy by breaking down dead organic material
- Have cell walls made of chitin (same material as insect exoskeletons)
- Mostly multicellular, though some are single-celled
Examples of fungi:
1. Molds - are multicellular fungi that grow on bread, cheese, and other foods. They break down the food and help decompose it. Some molds produce penicillin, an important antibiotic.
2. Mushrooms - are the fruiting bodies of fungi. They release spores that spread the fungus. Some mushrooms are edible; some are poisonous.
3. Yeasts - are single-celled fungi. They are used in baking to make bread rise and in brewing to make beer and wine.
4. Microsporidia - are microscopic fungi that can parasitize animals and cause disease.
Fungi break down dead things and return nutrients to the soil. They include molds, mushrooms, and yeasts.
Kingdom Animalia
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| Image from Biology Online |
Animals are eukaryotic organisms that eat food to get energy. They are multicellular, can move, and have specialized body systems.
Two major groups:
Invertebrates (No Backbone)
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| Image from Science Notes and Projects |
Invertebrates make up about 97% of all animal species. They do not have a backbone or internal skeleton.
a. Cnidaria - have stinging cells called nematocysts that they use to capture food and protect themselves.
Characteristics:
- Radial symmetry (symmetrical in all directions from a center point)
- Have tentacles around their mouth
- Live in water
Examples:
- Jellyfish
- Coral
- Sea anemones
Cnidarians have stinging cells that hurt anything that touches them. Jellyfish and coral are cnidarians.
b. Arthropoda - the largest and most diverse animal phylum. Arthropods have jointed legs and segmented bodies.
Characteristics:
- Jointed legs (arthro = joint, pod = leg)
- Segmented bodies divided into sections
- Hard external skeleton called an exoskeleton
- Go through molting (ecdysis) to grow
What is Molting (Ecdysis)?
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| Image from ScoutLabs |
Molting is when insects shed off their old outer skin (cuticle) so they can grow bigger. The old skin is too small and tight, so they grow a new, larger skin underneath. They shed the old skin and continue growing until the new skin hardens.
Examples of arthropods:
Insects:
- Mosquitoes
- Butterflies
- Beetles
- Dragonflies
- Ants
Crustaceans:
- Crabs
- Shrimp
- Lobsters
Arachnids:
- Spiders
- Scorpions
- Ticks
Centipedes and Millipedes:
- Centipedes have one pair of legs per body segment
- Millipedes have two pairs of legs per body segment
Arthropods have jointed legs and segmented bodies. Insects, spiders, and crabs are arthropods. They shed their skin to grow.
c. Nematoda (Roundworms) - are parasitic worms that have unsegmented, cylindrical bodies.
Characteristics:
- Unsegmented, smooth, round-shaped bodies
- Many are parasites that live inside other animals
- Cause diseases in humans and animals
Examples:
- Pinworm - infects the intestines of children
- Ascaris - large roundworm that infects the intestines
- Hookworm - attaches to the intestinal wall and causes anemia
- Filarial worm - causes a disease called filariasis
Roundworms are parasitic worms that infect animals and humans, usually living in the intestines.
d. Platyhelminthes (Flatworms) - are parasitic worms with flat, soft bodies. They are unsegmented.
Characteristics:
- Flat, ribbon-like or leaf-like bodies
- Soft tissues
- Unsegmented
- Many are parasites
Examples:
- Flukes - parasitic flatworms that infect the liver, blood, or intestines
- Tapeworms - long, segmented parasitic flatworms that live in the intestines
- Planaria - small freshwater flatworms used in biology experiments
Flatworms are flat, soft parasitic worms. Tapeworms and flukes are flatworms.
e. Annelida (Segmented Worms) - have bodies divided into many ring-like segments.
Characteristics:
- Bodies divided into visible segments or rings
- Each segment can move somewhat independently
- Have a primitive circulatory system
Examples:
- Leech - parasitic worm that sucks blood
- Earthworm - lives in soil, helps decompose organic material
Earthworms are hermaphroditic, meaning both male and female reproductive organs are found in the same worm. Even though they are hermaphrodites, two earthworms must still mate together to reproduce.
- Segmented worms have bodies divided into rings. Earthworms are segmented worms, and they are hermaphrodites.
f. Mollusca - mollusks have soft bodies, usually protected by a hard shell.
Characteristics:
- Soft-bodied animals
- Most have a shell for protection
- Some have tentacles or arms
- Very diverse group
Examples:
- Squids - intelligent mollusk with tentacles, no shell
- Clams - mollusk with two shells
- Snails - mollusk with one spiral shell
- Octopi - intelligent mollusk with eight arms, no shell
Mollusks have soft bodies usually protected by shells. Snails, clams, and squids are mollusks.
g. Echinodermata - have spiny or bumpy bodies. The name means "spiny skin."
Characteristics:
- Spiny or bumpy skin
- Radial symmetry (star-shaped arrangements)
- Have tube feet for movement
- Live in the ocean
Examples:
- Sea star (starfish) - five-armed star shape
- Sea urchin - round, covered with long spines
- Sand dollar - flat, disk-shaped
- Sea cucumber - soft, elongated body
- Brittle star - similar to sea star but with more delicate arms
Echinoderms have spiny bodies and live in the ocean. Sea stars and sea urchins are echinoderms.
h. Chordata - have a backbone or notochord (a rod-like structure supporting the body).
Vertebrates (Have Backbone)
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| Image from Kidddiz Adventure |
Vertebrates have a backbone or spine that protects their spinal cord.
Chordata (Pisces) - Fish
Characteristics:
- Have scales covering their bodies
- Breathe through gills
- Have fins for movement
- Live in water
Examples:
- Sharks and rays
- Lampreys (eel-like fish)
- Common fish like salmon and tuna
Fish have scales, gills, and fins. They live in water.
Amphibia (Amphibians)
Characteristics:
- Can live both on land and in water
- Lay eggs in water
- Have moist skin
- Breathe through lungs and skin
Examples:
- Frogs
- Toads
- Salamanders
- Newts
Amphibians live part of their life in water and part on land. Frogs are amphibians.
Reptilia (Reptiles)
Characteristics:
- Have dry, scaly bodies
- Lay eggs with tough shells
- Breathe through lungs
- Cold-blooded (body temperature depends on environment)
Examples:
- Crocodiles and alligators
- Snakes
- Turtles
- Lizards
Reptiles have scaly bodies and lay eggs. Snakes and turtles are reptiles.
Aves (Birds)
Characteristics:
- Have two legs and two wings
- Covered with feathers
- Lay eggs with hard shells
- Warm-blooded (maintain constant body temperature)
- Have hollow bones to reduce weight for flying
Examples:
- Eagles and hawks
- Penguins (flightless birds with two legs and flippers instead of wings)
- Ostriches (flightless birds with very long legs)
- Sparrows and pigeons
Birds have wings, feathers, and lay eggs. Penguins and ostriches are birds even though they cannot fly.
Mammalia (Mammals)
Characteristics:
- Have mammary glands to produce milk for young
- Have hair or fur covering their bodies
- Warm-blooded
- Most give birth to live young (but some lay eggs)
- Have specialized teeth
Examples:
- Humans
- Platypus (one of the few mammals that lays eggs)
- Marsupials (like kangaroos and koalas that carry young in a pouch)
- Walrus - a marine mammal with long ivory tusks that lives in Arctic ice environments
Mammals have fur or hair, produce milk for babies, and are usually warm-blooded. Humans and walruses are mammals.
Kingdom Plantae
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| Image from 7active Studio |
Plants are eukaryotic organisms that make their own food through photosynthesis using sunlight.
Characteristics:
- Eukaryotic cells
- Can make their own food (photosynthetic)
- Have cell walls made of cellulose
- Cannot move from place to place
- Multicellular
Two major groups:
Nonvascular Plants
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| Image from ThoughtCo |
Nonvascular plants do not have tissues to transport water and food. They are small because they must absorb water directly from their environment.
Examples:
- Mosses
- Liverworts
- Hornworts
Vascular Plants
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| Image from Sciencing |
Vascular plants have special tissues that transport water and food throughout the plant. This allows them to grow larger and thrive in drier environments.
Vascular tissues:
- Xylem - Conducts most of the water and minerals from the roots up through the plant.
- Phloem - Distributes sugars and other organic products (food) made by photosynthesis throughout the plant.
Vascular plants have tubes inside them that transport water and food. This is why they can grow bigger and taller than nonvascular plants.
Kingdoms and Domains Quiz: click here
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