The Five Kingdoms

Lesson Description

This lesson introduces the concept of biological classification and the five kingdom system. Students learn how living things are grouped based on their structural and nutritional features. The lesson examines the characteristics of:
• Plants: multicellular, have chloroplasts, photosynthesise, cellulose cell walls, store carbohydrates as starch or sucrose.
• Animals: multicellular, no chloroplasts, no cell walls, show nervous coordination, move, store carbohydrates as glycogen.
• Fungi: usually organised into mycelium made of hyphae, cell walls of chitin, feed by saprotrophic nutrition (extracellular digestion), store glycogen.
• Protoctists: mostly single-celled, some like animal cells (e.g. Amoeba), some like plant cells (e.g. Chlorella).
• Bacteria: prokaryotic, single-celled, no nucleus, have cell wall and plasmids, some photosynthesise, most feed off other organisms.
Students also review the structures and functions of cell parts (nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes, vacuole) and compare plant and animal cells.

Specification Reference

1.2: Describe the common features shown by eukaryotic organisms: plants, animals, fungi and protoctists.
1.3: Describe the common features shown by prokaryotic organisms such as bacteria.
2.2: Describe the structure and functions of the nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes and vacuole.
2.3: Know the similarities and differences in the structure of plant and animal cells.

Learning Objectives

Identify the five major kingdoms: plants, animals, fungi, protoctists, bacteria.
Describe the structural and nutritional features of each group.
Compare eukaryotic and prokaryotic organisms.
Explain why organisms are classified into these groups.
Describe cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, mitochondria, chloroplasts, ribosomes and vacuole.
Describe the functions of these cell structures.
Know the similarities and differences in the structure of plant and animal cells.

Key Words

Kingdom, Classification, Eukaryote, Prokaryote, Multicellular, Unicellular, Chloroplast, Cell wall, Saprotrophic

Lesson Notes: The 5 Kingdoms

Eukaryotes and Prokaryotes

All living things can be classified into two broad groups based on the type of cells they have: eukaryotes and prokaryotes.

• Eukaryotic organisms have cells that contain a nucleus and other organelles like mitochondria and chloroplasts. This group includes plants, animals, fungi, and protoctists.
• Prokaryotic organisms have much simpler and smaller cells without a nucleus. Their genetic material lies freely in the cytoplasm. They do not have mitochondria or chloroplasts. Bacteria are the main example of prokaryotes.

Plants

Plants are multicellular organisms made up of many cells. Their cells have distinctive features:

• Cell wall: made of cellulose, provides shape and support.
• Cell membrane: controls what enters and leaves the cell.
• Vacuole: a large central space filled with cell sap that helps keep the cell firm and stores dissolved substances.
• Chloroplasts: contain chlorophyll to capture sunlight for photosynthesis, producing carbohydrates.

Plants store carbohydrates mainly as starch or sucrose. They come in many forms, from tall trees to tiny flowers, and are essential for food, giving us cereals like rice and maize, and legumes like peas and beans.

Animals

Animals are also multicellular organisms but differ from plants in several key ways:

• No cell walls and no chloroplasts, so they cannot photosynthesise. They must eat other organisms for energy.
• Animal cells have a cell membrane and cytoplasm.
• Many animals have nerves to coordinate movement and can move from place to place.
• They store carbohydrates as glycogen and may also store lipids as fat under the skin or around organs.

Animals range enormously in size, from huge whales to tiny insects like ants.

Fungi

Fungi include single-celled organisms like yeast and multicellular forms like moulds and mushrooms. Most fungi consist of fine threads called hyphae, which may have many nuclei. These hyphae form a tangled mass called a mycelium.

• Their cell walls are made of chitin, not cellulose.
• They do not contain chlorophyll and cannot photosynthesise.
• Fungi feed by releasing digestive enzymes outside their cells onto dead or decaying material and absorbing the nutrients — this is called saprotrophic nutrition (or extracellular digestion).
• They often store carbohydrate as glycogen.

Some fungi are pathogens that cause disease, like the fungus that causes ringworm in humans or rust diseases in plants. While mushrooms and toadstools are often the only visible part of a fungus, these are just reproductive structures — the main body (mycelium) is hidden in the ground or rotting material.

Protoctists

Protoctists are mostly single-celled microscopic organisms that are usually larger than bacteria. They are eukaryotic, meaning they have a nucleus. Some protoctists are more like animal cells, such as Amoeba which lives in ponds and feeds on smaller organisms. Others, like Chlorella, are more like plant cells because they have chloroplasts and can photosynthesise.

Some protoctists can also be pathogens. For example, Plasmodium is a protoctist that causes malaria in humans, spread by the bite of infected Anopheles mosquitoes.

Bacteria

Bacteria are prokaryotic, single-celled organisms that are smaller than plant or animal cells and come in many shapes. Their key features include:

• No nucleus; instead, they have a single circular chromosome of DNA in the cytoplasm.
• Often contain extra small circles of DNA called plasmids.
• Have a cell wall, although its chemical structure varies between different types of bacteria.
• Some bacteria can photosynthesise, but most feed off other living or dead organisms.

Some bacteria are helpful, like Lactobacillus bulgaricus used to make yoghurt. Others are harmful pathogens, such as Pneumococcus which causes pneumonia. Plasmids can be transferred between bacteria, helping spread genes like those for antibiotic resistance — this makes them useful in genetic engineering.