Culturing Microorganisms

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Enquiry questions

What is the effect of different antiseptics on the growth of bacteria?

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Concepts

This study delivers 1 primary concept and 4 secondary concepts.

Primary concept: Pathogens and Communicable Disease (BI-KS4-C008)

Type: Knowledge | Teaching weight: 2/6

Pathogens are microorganisms that cause infectious disease. The four types of pathogen are viruses, bacteria, fungi and protists, each with distinct mechanisms of causing harm. Viruses reproduce inside host cells and may destroy them; bacteria may produce toxins; fungi may damage tissues; protists may damage cells directly. Diseases spread through water, air, direct contact, sexual contact, vectors and contaminated food.

Teaching guidance: Use specific examples: influenza and HIV (viral), tuberculosis and salmonella (bacterial), rose black spot (fungal), malaria (protist). For each, require pupils to know the specific mechanism of disease and transmission route. Evaluate evidence for the effectiveness of hygiene measures, vaccinations and treatments. This is an excellent context for socio-scientific reasoning about public health policy. Key vocabulary: pathogen, bacterium, virus, fungus, protist, vector, transmission, infection, malaria, Plasmodium, tuberculosis, influenza, HIV, toxin, host Common misconceptions: Students think antibiotics kill viruses — this is one of the most important misconceptions to address. Antibiotics act on bacterial structures not present in viruses. Students also confuse being 'infected' with being 'ill' — the immune system may destroy a pathogen before symptoms develop.

Differentiation

Model response (Emerging): Influenza (flu) is caused by a virus. Tuberculosis (TB) is caused by a bacterium.

Model response (Developing): Malaria is caused by a protist called Plasmodium, which is transmitted by the bite of infected female Anopheles mosquitoes (the vector). When the mosquito bites, it injects Plasmodium into the blood. It is difficult to control because: the mosquitoes breed in standing water which is abundant in tropical regions; insecticide resistance is developing in mosquito populations; and the Plasmodium parasite has a complex life cycle that makes vaccine development challenging.

Model response (Secure): Viruses are not cells and cannot reproduce independently. They invade host cells and use the cell's machinery to make copies of themselves. The host cell is typically destroyed when new virus particles burst out (lysis), which causes tissue damage and symptoms. Bacteria are living cells that reproduce rapidly by binary fission outside host cells. They cause disease primarily by producing toxins that damage tissues and trigger immune responses. For example, Salmonella bacteria produce toxins that cause inflammation of the gut lining, leading to diarrhoea and vomiting. This mechanistic difference explains why antibiotics work against bacteria (they target bacterial cell structures like cell walls or ribosomes) but not against viruses (which use host cell machinery that antibiotics cannot target without harming the patient).

Model response (Mastery): Antibiotic resistance occurs through natural selection. Within any bacterial population, random mutations may produce individuals with resistance to a particular antibiotic. When the antibiotic is used, susceptible bacteria are killed but resistant individuals survive and reproduce, passing the resistance allele to offspring. Over time, the proportion of resistant bacteria in the population increases. This is accelerated by overuse and misuse of antibiotics (incomplete courses, use in agriculture). The result is that infections become untreatable with existing antibiotics — MRSA, for example, is resistant to methicillin and other common antibiotics. The WHO estimates that by 2050, antibiotic-resistant infections could cause 10 million deaths annually. Solutions require both scientific approaches (developing new antibiotics, using bacteriophages, developing rapid diagnostic tests) and behavioural changes (prescribing antibiotics only when necessary, completing full courses, reducing agricultural antibiotic use).

Secondary concept: Eukaryotic and Prokaryotic Cell Structure (BI-KS4-C001)

Type: Knowledge | Teaching weight: 2/6

Eukaryotic cells (animals, plants, fungi) have a membrane-bound nucleus and extensive internal membrane systems including the endoplasmic reticulum and Golgi apparatus. Prokaryotic cells (bacteria) lack a nucleus, with DNA as a single circular loop in the cytoplasm, and may contain plasmids. Prokaryotes also lack mitochondria and chloroplasts.

Differentiation

Secondary concept: Mitosis and the Cell Cycle (BI-KS4-C003)

Type: Knowledge | Teaching weight: 3/6

The cell cycle is the series of events leading to cell division. DNA is replicated during interphase, after which mitosis produces two genetically identical daughter cells, each with the same number of chromosomes as the parent cell. Mitosis is used for growth, repair of tissues and asexual reproduction.

Differentiation

Secondary concept: Immune System and Vaccination (BI-KS4-C009)

Type: Process | Teaching weight: 3/6

The immune system responds to pathogens through phagocytosis (non-specific) and antibody production (specific). Lymphocytes produce antibodies complementary to antigens on the pathogen surface. Memory cells persist after infection, enabling a rapid secondary response. Vaccination introduces antigens to stimulate an immune response without causing disease, producing immunity.

Differentiation

Secondary concept: Evolution by Natural Selection (BI-KS4-C016)

Type: Knowledge | Teaching weight: 3/6

Evolution by natural selection occurs when: there is variation within a population; some of that variation is heritable; individuals compete for limited resources; individuals with advantageous traits are more likely to survive and reproduce; advantageous alleles become more common in the population over generations. Speciation occurs when populations become reproductively isolated and evolve independently.

Differentiation

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Thinking lens: Patterns (primary)

Key question: What patterns can I notice here, and what do they allow me to predict? Why this lens fits: Data from repeated investigations reveals patterns that allow pupils to generalise their findings beyond the specific test conditions. Question stems for KS4:

How would you formalise this pattern mathematically?

What are the limits of this pattern — where does it break down?

Could this pattern be an artefact of how the data was collected?

Does identifying the pattern tell us why it occurs?

Secondary lens: Cause and Effect — Fair testing and investigations are designed to isolate variables and establish causal relationships — the cognitive demand is reasoning from controlled evidence to causal claims.

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Session structure: Fair Test

Fair Test

The classic scientific enquiry: formulating a testable question, making a prediction based on scientific understanding, designing a method that controls variables, collecting and recording data systematically, analysing results, and drawing a conclusion linked back to the original hypothesis.

question → hypothesis → method → data_collection → analysis → conclusion Assessment: Structured scientific report including question, hypothesis with reasoning, method with variables identified, results table/graph, and conclusion evaluating whether results support the hypothesis. Teacher note: Use the FAIR TEST template: expect pupils to derive a testable hypothesis from scientific theory and design a rigorous method with appropriate controls, precision, and sample size. Guide analysis using statistical techniques or mathematical modelling where appropriate. Demand critical evaluation of validity, reliability, accuracy, and the extent to which results support or refute the hypothesis. KS4 question stems:

How does your hypothesis follow from the underlying scientific theory?

How have you ensured sufficient precision, accuracy, and reliability in your method?

What statistical analysis supports your conclusion?

To what extent do your results support the hypothesis, and what are the limitations?

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Variables

Independent: type or concentration of antiseptic Dependent: area of zone of inhibition (mm²) Controlled: volume of antiseptic on each disc, size of filter paper disc, type and concentration of bacterial culture, incubation temperature and time, same agar plate preparation

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Equipment and safety

Equipment:

nutrient agar plates (pre-poured)

bacterial culture (non-pathogenic, e.g. E. coli K-12)

filter paper discs

antiseptic solutions (different concentrations or types)

sterile forceps

Bunsen burner

marker pen

ruler (mm)

incubator (25°C maximum in schools)

autoclave tape

Safety notes: Strict aseptic technique throughout: flame the inoculating loop, sterilise the neck of bottles, work near a Bunsen burner. Incubate at a maximum of 25°C in schools (not 37°C) to prevent growth of human pathogens. Do NOT open Petri dishes after incubation. Seal plates with two strips of tape (not fully sealed, to allow aerobic conditions). Autoclave or disinfect all plates before disposal. Wash hands with antibacterial soap before and after the practical. (Hazard level: standard)

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Expected outcome

Antiseptics produce clear zones of inhibition around the filter paper discs where bacteria cannot grow. More effective antiseptics produce larger zones. Pupils calculate the area of the zone of inhibition using πr². A control disc (soaked in sterile water) shows no zone, confirming it is the antiseptic, not the disc, that prevents growth.

Recording format: data table of zone diameters for each antiseptic, zone of inhibition area calculation (πr²), bar chart comparing effectiveness of antiseptics

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Enquiry type

Observation Over Time

A systematic enquiry where changes are observed and recorded at intervals over a period of time — hours, days, weeks, or longer. Used when the process being studied is too slow for a single lesson or when the pattern only emerges through repeated observation. Develops patience, systematic recording, and the ability to identify trends.

Question stems:

How does [thing being observed] change over time?

What happens to [variable] over [time period]?

What pattern can you see in how [process] changes?

Teacher scaffold:

What do you think will happen over time? Why?

How often should we observe and record?

What exactly will we look for or measure each time?

What pattern can you see in the observations?

Can you explain why this pattern happens?

Fair Test

A controlled investigation where one variable is deliberately changed while all others are kept the same, to determine whether the changed variable has an effect on a measured outcome. The gold-standard enquiry type for causal questions in science.

Question stems:

How does [independent variable] affect [dependent variable]?

Does changing [variable] make a difference to [outcome]?

What is the relationship between [variable A] and [variable B]?

Teacher scaffold:

What will you change? (independent variable)

What will you measure or observe? (dependent variable)

What will you keep the same? (controlled variables)

What do you predict will happen? Why?

Was your prediction correct? What does the evidence show?

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Known misconceptions

Animal cells have no structure

What pupils may say: Animal cells do not have any structure — they are just blobs of jelly. Correct explanation: Animal cells have a well-defined internal structure including: a cell membrane (controls what enters and leaves), cytoplasm (where chemical reactions occur), a nucleus (contains DNA and controls the cell), mitochondria (where respiration releases energy), and ribosomes (where proteins are made). What animal cells lack compared to plant cells is a cell wall, chloroplasts, and a large permanent vacuole. Diagnostic questions:

What structures would you find inside an animal cell?

What does the nucleus do?

What is the difference between a cell membrane and a cell wall?

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Why this study matters

This required practical is one of the few opportunities for pupils to work with living microorganisms. The aseptic technique develops essential laboratory discipline, while measuring zones of inhibition and calculating areas using πr² integrates mathematical skills with biological concepts. Comparing antiseptic effectiveness introduces the idea of evidence-based medicine and connects to real-world applications of microbiology.

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Pitfalls to avoid

Pupils measure the diameter of the zone including the disc — the zone of inhibition is the clear area around the disc, not including the disc itself

Poor aseptic technique leads to contaminated plates — demonstrate each step explicitly before pupils begin

Pupils may think all bacteria are harmful — emphasise that most bacteria are harmless or beneficial and only pathogens cause disease

Sensitive content

Some pupils may be anxious about handling bacteria — reassure them that school strains are non-pathogenic and aseptic technique provides protection

Antibiotic resistance is a sensitive current affairs topic — present the science objectively without causing undue alarm

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Vocabulary word mat

Prior knowledge (retrieval plan)

Pupils should already know the following from earlier units:

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Scaffolding and inclusion (Y10)

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Knowledge organiser

Key terms:

pathogen

bacteria

aseptic technique

zone of inhibition

antiseptic

antibiotic

contamination

incubation

colony

Core facts (expected standard):

Pathogens and Communicable Disease: Explains how each type of pathogen causes disease mechanistically, compares transmission routes, and evaluates prevention strategies including hygiene measures and public health interventions.

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Graph context

Node type: ScienceEnquiry | Study ID: SE-KS4-003 Concept IDs:

BI-KS4-C008: Pathogens and Communicable Disease (primary)

BI-KS4-C001: Eukaryotic and Prokaryotic Cell Structure

BI-KS4-C003: Mitosis and the Cell Cycle

BI-KS4-C009: Immune System and Vaccination

BI-KS4-C016: Evolution by Natural Selection

Cypher query:

``cypher

MATCH (ts:ScienceEnquiry {enquiry_id: 'SE-KS4-003'})

-[:DELIVERS_VIA]->(c:Concept)

-[:HAS_DIFFICULTY_LEVEL]->(dl)

RETURN c.name, dl.label, dl.description

``

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Generated from the UK Curriculum Knowledge Graph — zero LLM generation.