B5.2: The five kingdoms of life

Lesson focus: models organise diversity using shared cellular and nutritional features, while modern evidence shows that some traditional groups need revision.

Learning objective

Compare plants, animals, fungi, protoctists and , and explain why viruses do not belong to these cellular groups.

Build on earlier learning

Characteristics of living organisms

The previous lesson established evidence for life. This lesson applies it to cellular groups and viruses.

You will be successful when you can…

Compare the five traditional kingdoms.
Distinguish eukaryotic and prokaryotic cells.
Classify an organism from evidence.
Explain limitations of the five-kingdom model.

KEY VOCABULARY

Words that carry the science

classification: Organising organisms into groups using shared characteristics and evidence of relationships.
eukaryote: An organism whose cells contain a nucleus and membrane-bound organelles.
prokaryote: A cellular organism without a nucleus; its main DNA is free in the cytoplasm.
hypha: A thread-like fungal structure; a network of hyphae forms a mycelium.
saprotrophic nutrition: External digestion followed by absorption of soluble products.
pathogen: A microorganism or infectious agent (including viruses) that causes disease.

BUILD YOUR UNDERSTANDING

Cell evidence separates major groups

01Cell evidence separates major groups

Plants, animals, fungi and protoctists are . Plant cells have cellulose walls and chloroplasts in photosynthetic tissues; animal cells lack cell walls and chloroplasts; fungi have chitin walls and absorb externally digested nutrients.

such as bacteria are usually unicellular and much smaller. They have a cell membrane, cytoplasm, ribosomes, a cell wall, circular chromosomal DNA and may contain plasmids, but they do not have a nucleus.

02Nutrition and organisation refine identification

Plants are multicellular photosynthetic organisms that commonly store carbohydrate as starch or sucrose. Animals are multicellular consumers that often show nervous coordination and store glycogen. Most fungi form hyphae, although yeast is unicellular, and may store glycogen.

are a diverse collection of mostly microscopic . Amoeba has animal-like features, Chlorella photosynthesises, and Plasmodium is a pathogenic parasite.

03Classification is a scientific model

The traditional is useful for comparing broad cellular patterns, but genetic evidence has changed modern . “Protoctists” do not form one simple natural lineage, and many systems place prokaryotes across two domains.

Viruses have genetic material inside a protein coat but no cellular structure or independent metabolism. They replicate only inside host cells and are not placed in the five kingdoms.

Figure · The traditional model is a useful comparison tool, not a final map of evolutionary relationships. Genetic evidence supports more detailed modern classifications.

Interactive model

Classifying living things

Biologists sort living things into five kingdoms: plants, animals, fungi, protoctists and prokaryotes. Pick an organism and follow the key one question at a time. Each answer is evidence about its cells, not just how it looks.

Controls

GroupKeep answering…

EvidenceChitin cell walls and thread-like hyphae; it digests food outside its body.

The five-kingdom model is a useful simplification: DNA evidence has changed how scientists group protoctists and prokaryotes.

Cell features of each organism
Organism	Cells	Nucleus	Chitin wall	Many cells	Chloroplasts
Oak tree	Yes	Yes	No	Yes	Yes
Earthworm	Yes	Yes	No	Yes	No
Mushroom	Yes	Yes	Yes	Yes	No
Yeast	Yes	Yes	Yes	No	No
Amoeba	Yes	Yes	No	No	No
Chlorella	Yes	Yes	No	No	Yes
Lactobacillus	Yes	No	No	No	No
Flu virus	No	No	No	No	No

WORKED EXAMPLE

Classify from evidence

An organism is multicellular, lacks chloroplasts, has chitin cell walls and secretes digestive enzymes onto dead material.

A nucleus would place it among eukaryotes.
No chloroplasts rules against a typical photosynthetic plant.
Chitin cell walls are characteristic of fungi.
External digestion and absorption identify .

How to make the reasoning visible: The converging evidence supports classification as a fungus; no single feature should be used in isolation.

LEARN BY DOING

Build an evidence matrix

Use the features to identify broad groups without relying on appearance alone.

Sample	Cell evidence	Nutrition or organisation	Best classification
A	cellulose walls, chloroplasts	multicellular; stores starch	plant
B	no wall or chloroplasts	multicellular; nervous coordination	animal
C	chitin walls	hyphae; external digestion	fungus
D	nucleus; single cell	engulfs smaller cells	protoctist
E	no nucleus; circular DNA	single cell; plasmids present	prokaryote

Why is chlorophyll alone weak evidence for a plant?
Your answer
Which observation most directly distinguishes sample E from the eukaryotes?
Your answer

RETRIEVE · APPLY · CHECK

Check your understanding

Answer from memory, then check against the suggested answer.

Which four listed groups are eukaryotic?

What are fungal cell walls made from?

Why are viruses excluded from the kingdoms?

Apply the idea

A photosynthetic single-celled organism has a nucleus. Why is “plant” not an automatic classification?

Stretch and challenge

Why can DNA evidence overturn a classification based on appearance?

Exam Question Practice

B5.2Compare6 marks

Exam Question Practice

Mark points shown after marking

Fungi (such as yeast and moulds) are eukaryotes. Bacteria are prokaryotes.

(a)

Compare the cell structure of fungi and bacteria.

(4)

(b)

Describe how fungi and bacteria obtain nutrients.

(2)

Total for this question: 6 marks

Command word: For , make paired statements using both groups rather than writing two disconnected lists.