Structure & Reproduction of Microorganisms

This lesson develops the knowledge needed to compare major microorganism groups and explain how their structures relate to reproduction, survival, transmission and control.

StructureReproductionReplication ClassificationApplied microbiologyExam practice

Learning objectives

By the end of the lesson, you should be able to:

describe the key structural features of bacteria, fungi, protozoa, algae and viruses;
compare prokaryotic, eukaryotic and acellular organisation;
explain binary fission, budding, spore formation, cell division and viral replication;
distinguish reproduction from genetic exchange such as bacterial conjugation;
apply structural and reproductive knowledge to unfamiliar microbiology scenarios;
use accurate scientific vocabulary in short-answer and extended-response questions.

1. Starter: What makes a microorganism different?

Before reading the notes, complete the classification prediction. You can change your answers later.

Bacterium

Yeast

Virus

Protozoan

2. Core content notes: comparing microorganism groups

Key idea: structure determines what a microorganism can do. Cell organisation influences nutrient uptake, movement, reproduction, response to the environment and susceptibility to control methods.

Bacteria

Bacteria are prokaryotic cells. They do not have a membrane-bound nucleus. Their DNA is usually a single circular chromosome in the cytoplasm, and many bacteria also contain plasmids. Typical structures include a cell membrane, cytoplasm, ribosomes and a cell wall. Some species also have capsules, pili or flagella.

Cell wall: provides shape and helps prevent osmotic bursting.
Ribosomes: synthesise proteins.
Plasmids: small circular DNA molecules that can carry useful genes, including some antibiotic-resistance genes.
Flagellum: may allow movement.
Capsule/slime layer: may protect against drying or host defences and can assist attachment.

Fungi

Fungi are eukaryotic. Their cells contain a nucleus and membrane-bound organelles. Fungal cell walls contain chitin. Yeasts are unicellular fungi; moulds are usually multicellular and are made from thread-like hyphae that form a mycelium.

Protozoa

Protozoa are mostly unicellular eukaryotes. They have a nucleus and membrane-bound organelles. Some move using cilia, flagella or temporary extensions called pseudopodia. Many reproduce by cell division, although life cycles can be complex.

Algae

Algae are photosynthetic eukaryotes. They contain chlorophyll and other pigments. Some are microscopic and unicellular; others form colonies or multicellular bodies. Their cell walls vary between groups.

Viruses

Viruses are acellular: they are not cells. A virus contains genetic material, either DNA or RNA, enclosed by a protein capsid. Some also have a lipid envelope. Viruses lack ribosomes and independent metabolism, so they require a host cell to produce new virus particles.

Group	Organisation	Key structures	Typical multiplication
Bacteria	Prokaryotic	Cell membrane, cytoplasm, ribosomes, cell wall, circular DNA; sometimes plasmids, capsule, pili, flagella	Binary fission
Fungi	Eukaryotic	Nucleus, organelles, chitin wall; yeast cells or hyphae/mycelium	Budding, spores, fragmentation or other sexual/asexual processes
Protozoa	Eukaryotic	Nucleus, organelles; sometimes cilia, flagella or pseudopodia	Commonly cell division; some complex sexual/asexual cycles
Algae	Eukaryotic	Nucleus, organelles, chloroplasts/pigments; walls vary	Cell division, fragmentation, spores or sexual reproduction depending on group
Viruses	Acellular	DNA or RNA + capsid; some have envelope and surface proteins	Replication only inside a host cell

3. Reproduction and replication

Binary fission in bacteria

The bacterial chromosome is replicated.
The cell grows and the DNA copies move apart.
The plasma membrane and cell wall begin to divide.
Two daughter cells are produced.

Important: conjugation is not the same as reproduction. Conjugation transfers DNA, often plasmid DNA, between bacterial cells. It can increase genetic variation but does not directly produce two new cells.

Budding in yeast

A small outgrowth or bud forms on the parent yeast cell. The nucleus divides, one nucleus enters the bud, and the bud enlarges before separating. The two cells may be unequal in size at first.

Spore formation in fungi

Many fungi produce spores that can disperse through air, water or contact. Under suitable conditions, a spore germinates and forms new hyphae. Spores can be produced through asexual or sexual life cycles depending on the species.

Viral replication

Viruses use host-cell machinery to make viral nucleic acid and proteins. In a simplified lytic cycle, a virus attaches, enters or delivers its genome, uses the host to make viral components, assembles new virions and releases them. Some viruses can also enter a latent or integrated state before later becoming active.

4. Validated video learning

Complete the focus questions while watching. Pause and replay when needed.

Bacteria: structure and reproduction

List four structures found in many bacterial cells.
Explain binary fission in one clear sequence.
Why is conjugation different from binary fission?
What is the significance of plasmids?

Viruses: structure and replication

Identify the two basic components present in all viruses.
Why can a virus not reproduce independently?
Outline the lytic cycle.
What is one important difference between lytic and latent/lysogenic infection?

5. Structure → function challenge

Match each structure to the most appropriate function.

1. Bacterial plasmid

2. Fungal hypha

3. Viral capsid

6. Reproduction sequence activity

Choose the correct process or stage for each description.

1. DNA replicates, the cell elongates and then divides into two daughter cells.

2. A small outgrowth receives a daughter nucleus before separating from the parent yeast cell.

3. Viral components are produced using host machinery, assembled and released.

7. Applied practice questions

1. Which observation most strongly supports identifying an unknown microorganism as a bacterium?

2. Why are viruses described as obligate intracellular parasites?

3. A bacterial population becomes resistant after some cells receive a resistance plasmid from neighbouring bacteria. Which process explains the DNA transfer?

4. Which pairing is most accurate?

8. Extended-response practice

Question A — Compare [6 marks]
Compare the structure and multiplication of a bacterium with a virus.

Credit scientifically accurate comparisons such as: bacterium is a prokaryotic cell whereas a virus is acellular; bacterium has membrane/cytoplasm/ribosomes/cell wall whereas virus has genome and capsid; bacterium contains cellular machinery whereas virus relies on host machinery; bacteria reproduce by binary fission whereas viruses replicate only inside host cells.

Question B — Explain [4 marks]
Explain why a treatment that interferes with bacterial ribosomes could stop bacterial growth but would not directly stop viral protein synthesis in the same way.

Bacteria contain their own ribosomes and require them to synthesise proteins needed for growth and division. Viruses do not contain ribosomes and instead use host-cell ribosomes; therefore a drug specifically targeting bacterial ribosomes acts on a bacterial structure that viruses do not possess.

Question C — Apply [5 marks]
An unknown microorganism is unicellular, contains a nucleus, moves using cilia and divides into two daughter cells. Identify the most likely microorganism group and justify your answer using three pieces of evidence.

Most likely a protozoan. Evidence: it is unicellular; it is eukaryotic because it has a nucleus; cilia are characteristic movement structures in some protozoa; division into daughter cells is consistent with common asexual reproduction in protozoa.

9. Exit ticket

Complete all four before leaving the lesson.

Define: What does acellular mean?
Explain: Why is binary fission reproduction but conjugation is not?
Compare: Give one structural difference between bacteria and fungi.
Apply: A particle contains RNA, a protein coat and no ribosomes. What group does it belong to, and why?

10. Self-assessment

Rate your confidence from 1–4.

I can identify microorganism structures.

I can explain reproduction/replication.

I can compare microorganism groups.

I can answer applied questions.