How to use these notes
Read the explanation first, then look at the example and laboratory connection. After that, try the Quick Check without opening the answer. If you can explain the result in your own words, you have understood more than if you have only memorised the definition.
Some sections also contain common mistakes. These are included because closely related terms are often confused in first-year examinations and practical classes.
History and Development of Microbiology
What is microbiology?
Microbiology is the study of microorganisms and other microscopic biological agents. It includes their structure, growth, physiology, genetics, classification, interactions with hosts and applications in medicine, food, agriculture, industry and environmental science.
Microorganisms are not simply disease-causing organisms. Many are essential to nutrient cycling, food production and biotechnology. A useful first-year distinction is therefore: microbial life can be harmful, useful or simply part of the normal environment.
Important developments
| Scientist | Important contribution | Why it matters |
|---|---|---|
| Antonie van Leeuwenhoek | Observed microorganisms using microscopes he constructed. | Provided early direct observations of the microbial world. |
| Louis Pasteur | Supported the role of microorganisms in fermentation and helped disprove spontaneous generation. | Connected microorganisms with biological processes and disease. |
| Robert Koch | Developed important methods for linking particular microorganisms with particular diseases. | Helped establish medical bacteriology. |
| Joseph Lister | Applied germ theory to surgical practice and antisepsis. | Reduced infection associated with surgery. |
| Edward Jenner | Introduced an early successful vaccination approach against smallpox. | Important milestone in preventive medicine. |
Pasteur's work is easier to remember when connected to food. If a sugary liquid changes because microorganisms metabolise its contents, the change is biological rather than simply a chemical event occurring for no reason. Fermentation studies helped show that specific microorganisms could be associated with specific processes.
Suppose a sealed nutrient liquid remains clear while an contaminated sample becomes turbid. What does this tell you? Turbidity by itself does not identify the organism, but it provides evidence that microbial growth has occurred in the sample.
Do not write that Pasteur and Koch made the microscope. Their contributions came later and were related mainly to germ theory, fermentation, disease causation and microbiological methods.
Quick Check
Who is associated with early microscopic observation of microorganisms?
Antonie van Leeuwenhoek.
Why was Pasteur's work important to microbiology?
His work provided strong evidence for the role of microorganisms in fermentation and helped disprove spontaneous generation.
Classification and Nomenclature of Microorganisms
Why classify microorganisms?
The microbial world contains organisms with very different structures, nutritional requirements and genetic characteristics. Classification provides a system for arranging organisms according to shared characteristics and evolutionary relationships.
Major cellular groups
| Group | Cell type | Example |
|---|---|---|
| Bacteria | Prokaryotic | Escherichia coli |
| Archaea | Prokaryotic | Methanogenic archaea |
| Fungi | Eukaryotic | Saccharomyces cerevisiae |
| Protozoa | Eukaryotic | Entamoeba histolytica |
| Algae | Mostly eukaryotic | Chlorella |
| Viruses | Acellular | Influenza virus |
Binomial nomenclature
Scientific names normally contain two parts: the genus name followed by the species name.
For example: Escherichia coli. The genus begins with a capital letter, while the species name begins with a lowercase letter. When typed, the complete scientific name is normally italicised.
"E. coli" and "Gram-negative rod" do not mean the same thing. E. coli identifies a particular organism, while Gram-negative rod describes characteristics that can be shared by many different bacteria.
A bacterial isolate may first be described using observations such as colony appearance, Gram reaction and cell shape. These observations narrow the possibilities but may not by themselves establish the species identity.
Classification is not simply memorising names. If you are asked to compare two organisms, include the characteristic used for the comparison instead of listing only their names.
Quick Check
What is the correct order in a binomial scientific name?
Genus followed by species.
Does "Gram-negative rod" identify one bacterial species?
No. It describes staining reaction and shape and can apply to many different bacterial species.
Scope and Applications of Microbiology
Microbiology in different fields
Microbiology connects laboratory science with many practical areas. The same basic microbial principles can be used in medicine, agriculture, food production, environmental studies and industry.
| Area | Application | Example |
|---|---|---|
| Medical microbiology | Study of infectious agents and laboratory diagnosis. | Identification of bacterial pathogens. |
| Food microbiology | Study of useful and harmful microorganisms in food. | Fermentation and food spoilage. |
| Agricultural microbiology | Study of microorganisms associated with soil and plants. | Nitrogen-fixing bacteria. |
| Environmental microbiology | Study of microorganisms in natural environments. | Microbial decomposition. |
| Industrial microbiology | Use of microorganisms to produce useful products. | Production of antibiotics or enzymes. |
Yeasts are a good example of why microorganisms should not simply be divided into "good" and "bad." Saccharomyces cerevisiae can be used in bread and beverage fermentation, while another microbial species may be associated with disease or spoilage.
If a microorganism is found degrading organic material in soil, environmental microbiology is relevant. If a related process is deliberately used to produce a commercial enzyme, industrial microbiology becomes relevant.
Quick Check
Which branch studies microorganisms associated with food?
Food microbiology.
Why is microbiology important in agriculture?
Microorganisms influence soil fertility, nutrient cycling, decomposition, plant health and processes such as nitrogen fixation.
Morphology and Structure of Bacteria
Common bacterial shapes
Bacterial morphology refers to the observable form and arrangement of bacterial cells. Shape is useful during preliminary laboratory observation, although shape alone is rarely enough to identify a bacterial species.
| Shape | Description | Example |
|---|---|---|
| Coccus | Spherical or nearly spherical cells. | Staphylococcus aureus |
| Bacillus | Rod-shaped cells. | Escherichia coli |
| Vibrio | Curved or comma-shaped rod. | Vibrio cholerae |
| Spirillum | Rigid spiral-shaped cells. | Spirillum species |
| Spirochete | Thin flexible spiral-shaped cells. | Treponema species |
Important bacterial structures
- Cell wall: provides structural strength and helps maintain cell shape.
- Cell membrane: controls movement of substances and contains important transport and energy-related functions.
- Cytoplasm: contains enzymes, ribosomes and other cellular components.
- Nucleoid: region containing the main bacterial chromosome.
- Ribosomes: involved in protein synthesis.
- Capsule or slime layer: may help some bacteria attach to surfaces and avoid host defence mechanisms.
- Flagella: associated with bacterial motility.
- Fimbriae or pili: can contribute to attachment and, in some bacteria, genetic exchange.
- Endospores: highly resistant structures formed by some bacteria such as Bacillus and Clostridium.
Staphylococcus aureus is a useful example when studying cocci in clusters. The name and the observed arrangement should not be confused with the Gram reaction. In a Gram stain, S. aureus is characteristically observed as Gram-positive cocci arranged in clusters.
A purple Gram-positive result is not simply a colour label. It reflects the ability of the bacterial cell envelope to retain the primary stain-iodine complex during the decolorisation step. Gram-negative bacteria do not retain the complex in the same way and therefore take up the counterstain.
Do not write "all cocci are Gram-positive" or "all rods are Gram-negative." Shape and Gram reaction describe different characteristics.
Quick Check
What is the difference between shape and Gram reaction?
Shape describes the physical form of the cell, such as coccus or rod. Gram reaction describes how the cell responds to the Gram staining procedure.
Which bacterial structures are associated with motility?
Flagella are the main structures associated with bacterial motility.
Growth and Physiology of Bacteria
What does bacterial growth mean?
In microbiology, growth generally refers to an increase in the number of cells rather than simply an increase in the size of one cell. Under suitable conditions, bacterial cells divide and produce a population.
Bacterial growth curve
| Phase | What happens |
|---|---|
| Lag phase | Cells adapt to the new environment and prepare for active growth. |
| Log phase | Cells divide rapidly and the population increases at a high rate. |
| Stationary phase | Growth slows because nutrients become limited and waste products accumulate. |
| Death phase | Viable cells decline when unfavourable conditions persist. |
Generation time
Generation time is the time required for a population to double under a particular set of conditions.
If a bacterial culture is transferred to a fresh suitable medium, there may be an initial period with little visible change. This does not necessarily mean that the cells are inactive. They may be adapting to the new conditions before entering rapid multiplication.
Oxygen requirement
| Type | Relationship with oxygen |
|---|---|
| Obligate aerobe | Requires oxygen for growth. |
| Obligate anaerobe | Oxygen is harmful or not tolerated. |
| Facultative anaerobe | Can grow with or without oxygen, often growing better when oxygen is available. |
| Microaerophile | Requires oxygen at lower concentrations than atmospheric levels. |
| Aerotolerant anaerobe | Does not use oxygen for energy generation but tolerates its presence. |
If growth appears mainly near the top, the organism may require oxygen. If growth occurs throughout but is heavier near the top, a facultative anaerobe is a possible interpretation. If growth occurs throughout with little difference between the top and bottom, aerotolerance may be considered.
The stationary phase does not mean that every cell has suddenly stopped functioning. Cells can remain metabolically active even when the total population shows little net increase.
Quick Check
Which phase shows the most rapid population increase?
The log or exponential phase.
What does heavy growth near the top of an oxygen-gradient medium suggest?
It suggests an organism that benefits from oxygen availability, such as an obligate aerobe, depending on the complete growth pattern.
Isolation, Enumeration and Culture of Bacteria
Why isolate microorganisms?
A natural specimen may contain many microorganisms at the same time. If the purpose is to study one organism, it must be separated from the mixed population and obtained as an isolated culture.
Pure culture and mixed culture
| Culture | Meaning |
|---|---|
| Pure culture | Contains one microbial type under the conditions used for observation. |
| Mixed culture | Contains more than one microbial type. |
Streak plate principle
The streak plate method is based on progressively separating cells across the surface of a solid medium. As the number of cells placed in each successive area decreases, individual cells can become separated enough to form individual colonies.
A colony is visible because many cells have multiplied from an initially small number of cells or a cell-containing unit. Colony morphology can provide useful preliminary information, such as size, shape, margin, elevation and pigmentation.
When examining a culture plate, do not immediately identify an organism from colony colour alone. A careful observation combines colony characteristics with microscopy, staining and appropriate identification tests.
Enumeration
Enumeration means estimating the number of microorganisms present in a sample. Viable counts are often expressed as colony-forming units rather than simply as individual cells because one colony may arise from more than one cell.
Suppose a plate contains 85 colonies, the dilution represented by the plate is 10-4, and 0.1 mL was plated.
The volume correction is important. Forgetting the 0.1 mL factor would produce a result that is ten times too low.
- Using the dilution instead of the dilution factor.
- Forgetting to account for plated volume.
- Writing CFU without including the volume unit.
- Using a crowded or nearly empty plate without considering whether the count is suitable.
Quick Check
Why is the term CFU used instead of simply "cells per mL"?
Because one visible colony may originate from a cell or a group of cells capable of producing a colony.
What is the main purpose of streaking?
To progressively separate microbial cells so that isolated colonies can develop.
Microbial Metabolism
Meaning of metabolism
Metabolism includes the chemical reactions occurring inside a cell. These reactions provide energy, produce cellular building materials and allow microorganisms to respond to their environment.
| Term | Main idea |
|---|---|
| Catabolism | Breakdown of molecules, often releasing energy. |
| Anabolism | Synthesis of cellular components, requiring energy. |
Respiration and fermentation
Respiration and fermentation are different ways microorganisms obtain energy. In respiration, an electron transport system is involved, whereas fermentation does not use an external electron acceptor in the same way.
In a carbohydrate fermentation test, a colour change may indicate acid production. A Durham tube or similar gas-detection arrangement can provide evidence of gas production. Acid and gas are separate observations and should not be treated as the same result.
If the medium becomes acidic but no gas is visible, the correct interpretation is acid production without detectable gas under the test conditions. If acid and gas are both observed, both results should be reported.
Do not assume that fermentation always produces gas. Different organisms metabolise the same substrate differently.
Quick Check
What is the main difference between catabolism and anabolism?
Catabolism breaks molecules down and often releases energy, while anabolism builds cellular components and requires energy.
Are acid production and gas production the same observation?
No. They are separate outcomes of carbohydrate metabolism and should be interpreted separately.
Microbial Genetics
Basic genetic terms
- DNA: the major hereditary material in cellular organisms.
- Gene: a segment of genetic material associated with a functional product or characteristic.
- Genome: the complete genetic material of an organism.
- Mutation: a change in genetic material.
- Plasmid: a usually circular extrachromosomal DNA molecule found in many bacteria.
Horizontal gene transfer
Bacteria can acquire genetic information from sources other than direct inheritance from a parent cell. Three important mechanisms are transformation, transduction and conjugation.
| Mechanism | Basic idea |
|---|---|
| Transformation | Uptake of free DNA from the surrounding environment. |
| Transduction | Transfer of bacterial genetic material through a bacteriophage. |
| Conjugation | Transfer of genetic material through direct cell-to-cell contact, commonly involving plasmid DNA. |
Some antibiotic-resistance genes can be carried on mobile genetic elements. This means resistance is not always a simple story of one bacterium developing a change and then passing only that change to its descendants. Genetic exchange can also contribute to the spread of resistance characteristics.
If two bacterial populations suddenly show a similar resistance characteristic, do not automatically conclude that both populations independently developed the same mutation. Horizontal gene transfer is another possible biological explanation.
Transformation, transduction and conjugation are not three names for mutation. They describe different mechanisms by which genetic information can move between cells or enter a cell.
Quick Check
Which process involves a bacteriophage?
Transduction.
Which process involves uptake of free DNA?
Transformation.
Microscopy and Techniques for Handling Microorganisms
Why microscopy is important
Most bacterial cells are too small to be seen clearly with the naked eye. Microscopy allows students to examine cell shape, arrangement, staining reactions and other microscopic features.
Common microscopy methods
| Method | Useful for |
|---|---|
| Bright-field microscopy | General observation of stained or naturally visible specimens. |
| Dark-field microscopy | Viewing organisms that are difficult to observe by ordinary bright-field methods. |
| Phase-contrast microscopy | Viewing living, relatively transparent cells without ordinary staining. |
| Fluorescence microscopy | Detection of fluorescently labelled structures or organisms. |
| Electron microscopy | Very high-resolution study of ultrastructural details. |
Magnification and resolution
Magnification makes an object appear larger. Resolution refers to the ability to distinguish two closely spaced objects as separate. A very large image is not automatically a highly detailed image.
If a microscope has a 10× eyepiece and a 40× objective:
A microscope observation should be recorded as an observation, not as an unsupported identification. For example, "Gram-positive cocci in clusters observed" is a microscopic observation. It is stronger scientifically than immediately writing a species name without additional evidence.
Do not confuse magnification with resolution. Increasing magnification without sufficient resolution can simply produce a larger blurred image.
Quick Check
What is the total magnification with a 10× eyepiece and 100× objective?
1000×.
What does resolution mean?
The ability to distinguish two closely spaced objects as separate details.
Control of Microorganisms
Why control microorganisms?
Microbial control is important when microorganisms need to be removed, reduced or prevented from multiplying. The required level of control depends on the situation.
| Term | Meaning |
|---|---|
| Sterilization | Destruction or removal of all forms of viable microbial life, including resistant forms where applicable. |
| Disinfection | Reduction or destruction of harmful microorganisms on inanimate objects. |
| Antisepsis | Use of antimicrobial chemicals on living tissue. |
| Sanitization | Reduction of microbial numbers to a level considered acceptable by relevant standards. |
Physical methods
- Moist heat
- Dry heat
- Filtration
- Radiation
- Low temperature methods
Chemical methods
Chemical agents include alcohols, halogens, phenolic compounds, aldehydes and other disinfecting or antiseptic agents. Their effectiveness depends on concentration, contact time, microbial characteristics and environmental conditions.
A method suitable for a heat-stable metal instrument may not be suitable for a heat-sensitive material. Microbial control is therefore not simply a matter of choosing the strongest chemical or highest temperature. The material and purpose must also be considered.
Sterilization and disinfection are not synonyms. Sterilization aims at complete elimination of viable microorganisms, while disinfection has a different scope and is generally applied to inanimate surfaces.
Quick Check
Which term applies to antimicrobial treatment of living tissue?
Antisepsis.
Is disinfection the same as sterilization?
No. Sterilization aims to eliminate all viable microbial life, whereas disinfection is intended to reduce or destroy harmful microorganisms on inanimate objects.
Host-Parasite Interaction
Host and parasite
A host is an organism that provides an environment in which another organism can live. In medical microbiology, the term parasite is commonly used for an organism that obtains resources from a host and may cause harm.
Normal microbiota
Microorganisms normally associated with healthy body sites are often referred to as normal microbiota. Their presence does not automatically mean disease.
Finding bacteria on a body surface is not automatically evidence of infection. The site, organism, quantity, host condition and clinical context all influence interpretation.
Important terms
| Term | Meaning |
|---|---|
| Pathogen | A microorganism capable of causing disease. |
| Opportunistic pathogen | Can cause disease particularly when host defences or normal barriers are compromised. |
| Infection | Entry and multiplication of an infectious agent in a host. |
| Disease | A condition in which infection or another cause produces abnormal signs or symptoms. |
| Virulence | The degree of pathogenicity or disease-producing capacity of an organism or strain. |
Infection and disease are related but are not identical terms. A microorganism may enter and multiply in a host without producing obvious disease in every situation.
Do not write that every microorganism found on or in the human body is a pathogen. Normal microbiota are an important part of the microbial environment of the body.
Quick Check
Does the presence of a microorganism always mean disease?
No. The organism may be part of the normal microbiota, may cause colonisation without disease, or may be an opportunistic organism whose significance depends on the host and site.
What is an opportunistic pathogen?
An organism that can cause disease especially when normal host defences are weakened or barriers are disrupted.
Introduction to Virology
What are viruses?
Viruses are acellular infectious agents consisting of genetic material enclosed by a protein coat. Some viruses also possess a lipid envelope. They depend on host cells for replication.
Basic viral components
- Genome: DNA or RNA containing viral genetic information.
- Capsid: protein coat surrounding the viral genome.
- Envelope: lipid-containing outer layer present in some viruses.
- Surface proteins: may help a virus attach to host cells.
| Feature | Virus | Bacterium |
|---|---|---|
| Cellular? | No | Yes |
| Independent cellular metabolism? | No | Yes |
| Genetic material | DNA or RNA | DNA |
| Replication | Requires host cell machinery | Cell division |
Influenza virus contains RNA as its genetic material and has an envelope. Viral surface proteins participate in attachment and entry into host cells. These structural features are useful when understanding why viral structure matters to infection.
Antibiotics are designed to target bacterial structures or processes. Viruses do not have bacterial cell walls, bacterial ribosomes or independent bacterial metabolism. Therefore, antibacterial antibiotics do not directly target viruses in the same way they target bacteria.
Do not describe a virus as a small bacterium. Viruses are fundamentally different because they are acellular and depend on host cells for replication.
Quick Check
Do all viruses contain both DNA and RNA?
No. A virus has either DNA or RNA as its genome.
Why must viruses use host cells?
They lack the complete cellular machinery required for independent replication.
Introduction to Parasitology
What is parasitology?
Parasitology is the study of parasites, their hosts and the relationships between them. Medical parasitology commonly deals with protozoa and helminths of importance to humans.
| Group | General feature | Example |
|---|---|---|
| Protozoa | Microscopic unicellular eukaryotic organisms. | Entamoeba histolytica |
| Nematodes | Roundworms. | Ascaris lumbricoides |
| Cestodes | Tapeworms. | Taenia species |
| Trematodes | Flukes. | Fasciola species |
Host terminology
- Definitive host: host in which the adult parasite or sexual stage develops, depending on the parasite.
- Intermediate host: host supporting a developmental or larval stage.
- Reservoir host: host that can maintain an infectious agent and serve as a source of infection.
- Vector: an organism that transmits an infectious agent between hosts.
A parasite may require more than one host to complete its life cycle. This is why identifying the host associated with a particular developmental stage is often more useful than trying to memorise the entire life cycle as one long paragraph.
When learning a parasite, organise your notes under the same headings each time: habitat, infective stage, mode of transmission, diagnostic stage, major disease and important prevention measures. This makes comparison between parasites easier.
A vector and an intermediate host are not automatically the same thing. A vector is defined by its role in transmission, while an intermediate host is defined by the developmental stage of the parasite that occurs within it.
Quick Check
What is a vector?
An organism that transmits an infectious agent between hosts.
What is an intermediate host?
A host in which a developmental or larval stage of a parasite occurs.
Introduction to Mycology
What is mycology?
Mycology is the study of fungi. Fungi are eukaryotic organisms that obtain nutrients by absorption. They include yeasts, moulds and larger multicellular forms.
| Type | General appearance | Example |
|---|---|---|
| Yeast | Usually unicellular; many reproduce by budding. | Saccharomyces cerevisiae |
| Mould | Filamentous growth composed of hyphae. | Rhizopus species |
| Dimorphic fungus | Can occur in different forms depending on conditions. | Histoplasma species |
Hyphae and mycelium
A hypha is a filamentous fungal structure. A mass or network of hyphae is called a mycelium. These terms are frequently used when describing moulds.
A yeast colony may appear smooth and creamy, while a mould colony may develop a filamentous or cottony appearance. Colony appearance is useful as a preliminary observation but should be supported by microscopic and other appropriate characteristics.
When observing a suspected fungal culture, students should record visible features such as texture, pigmentation and surface appearance, followed by appropriate microscopic observations. A description is different from a final identification.
Do not use "fungus" and "bacterium" as interchangeable terms. Fungi are eukaryotic, whereas bacteria are prokaryotic.
Quick Check
What is a hypha?
A filamentous fungal structure.
What is a mycelium?
A mass or network of fungal hyphae.
How to build a good examination answer
A longer answer should contain more than a longer definition. The marks should be supported by organised information.
Give the direct definition or statement first. Add one important characteristic or example if appropriate.
Start with a short definition or introduction, then use clear headings or numbered points. Include an example, comparison or simple diagram where it actually helps.
Begin with the definition or introduction, then develop the answer under logical headings. Include classification, mechanism, important characteristics, examples and a suitable table or labelled diagram where relevant. End with a short concluding statement.
A strong long answer should not simply list lag, log, stationary and death phases. Explain what happens in each phase and connect the changes with nutrient availability, cell division and accumulation of waste products.
Practical interpretation: observe before you identify
One useful habit in microbiology is to separate an observation from an interpretation and from a final identification.
| Level | Example |
|---|---|
| Observation | Purple spherical cells are seen in clusters. |
| Interpretation | Gram-positive cocci in clusters. |
| Further identification | Additional tests would be used before identifying a particular species. |
This distinction is useful in practical classes and also makes written answers more scientifically accurate.
Commonly confused terms
| Do not confuse | Difference |
|---|---|
| Magnification vs resolution | Magnification enlarges an image; resolution determines the ability to distinguish close details. |
| Infection vs disease | Infection involves entry and multiplication; disease refers to the resulting abnormal condition. |
| Sterilization vs disinfection | Sterilization aims at complete elimination of viable microbial life; disinfection has a narrower purpose. |
| Shape vs Gram reaction | Shape describes morphology; Gram reaction describes staining behaviour. |
| Mutation vs horizontal gene transfer | Mutation changes genetic material; horizontal gene transfer moves genetic information between cells. |
| Yeast vs mould | Yeasts are generally unicellular; moulds are filamentous. |
| Vector vs intermediate host | Vector is defined by transmission; intermediate host is defined by parasite development. |
| Virus vs bacterium | Viruses are acellular and require host cells for replication; bacteria are cellular organisms. |
Final Revision Checklist
Before an examination, make sure you can explain these points without looking at the notes.
Explain the major contributions of Leeuwenhoek, Pasteur, Koch, Lister and Jenner.
Distinguish bacteria, archaea, fungi, protozoa and viruses.
Explain cell wall, membrane, capsule, flagella, pili, ribosomes and endospores.
Draw and explain the four phases of the bacterial growth curve.
Compare obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles and aerotolerant anaerobes.
Explain the principle of obtaining isolated colonies from a mixed population.
Use the CFU/mL formula and correctly handle dilution factor and plated volume.
Distinguish catabolism, anabolism, respiration and fermentation.
Compare transformation, transduction and conjugation.
Distinguish magnification from resolution and calculate total magnification.
Distinguish sterilization, disinfection, antisepsis and sanitization.
Distinguish pathogen, opportunistic pathogen, infection, disease and virulence.
Explain viral genome, capsid, envelope and dependence on host cells.
Distinguish definitive host, intermediate host and vector.
Distinguish yeast, mould, hypha and mycelium.
Separate what you observe from what you interpret and what you finally identify.
A final study note
Microbiology becomes easier when you stop treating every topic as a separate list of facts. Try to connect structure with function, function with growth, growth with laboratory observation and laboratory observation with interpretation.
For example, the structure of a bacterial cell helps explain Gram staining; growth requirements help explain culture results; metabolism helps explain biochemical reactions; and genetics helps explain how microbial characteristics can change or spread.
When revising, practise explaining these connections in your own words. That is especially useful for 5-mark and 10-mark answers.