Biotechnology
Core 0610 focus: microorganisms in food production (bread, beer, yoghurt); industrial fermenter features; mycoprotein (Quorn) production; genetic modification of bacteria to produce insulin; GM crops. Extension background only (beyond 0610 direct recall): PCR, gel electrophoresis, cloning, and stem cells are included for enrichment — these details are not required for Cambridge IGCSE Biology 0610 examinations.
Biotechnology
CORE EXTENDEDMicroorganisms in Food Production
Microorganisms have been used in food and drink production for thousands of years. The key processes are driven by fermentation — anaerobic respiration by microorganisms.
| Product | Microorganism | Process | Useful products |
|---|---|---|---|
| Bread | Saccharomyces cerevisiae (yeast) | Yeast ferments sugars in dough → CO₂ makes dough rise; alcohol is driven off during baking | CO₂ (leavening); ethanol (evaporated) |
| Beer / Wine | Saccharomyces cerevisiae (yeast) | Yeast ferments glucose (from malted barley or grape juice) → ethanol + CO₂; kept anaerobic to prevent oxidation | Ethanol (alcohol); CO₂ |
| Yoghurt | Lactic acid bacteria (e.g. Lactobacillus) | Bacteria ferment lactose in milk → lactic acid; acid denatures milk proteins (casein) → milk thickens and sets; also lowers pH → preserves the product | Lactic acid (preservation; texture) |
| Cheese | Various bacteria + rennet (enzyme) | Bacteria ferment lactose; rennet coagulates milk proteins (curds); whey removed; curds pressed and matured | Lactic acid; solid curd product |
Industrial Fermenters
A fermenter (bioreactor) is a large vessel used to grow microorganisms or cells under controlled conditions to produce a useful product at industrial scale.
| Feature | Why it is needed |
|---|---|
| Temperature control (water jacket / cooling coils) | Maintain optimum temperature for enzyme activity; microbial metabolism generates heat that must be removed |
| pH monitoring and control | Maintain optimum pH for enzyme activity; metabolic products (acids) can lower pH and reduce yield |
| Sterile conditions (steam sterilisation before use) | Prevent contamination by other microorganisms that would compete with the production organism or produce unwanted products |
| Nutrient supply | Carbon source, nitrogen source, vitamins, and mineral ions must be supplied continuously at correct concentration |
| Stirrer / paddle | Mixes contents → even distribution of nutrients and temperature; maximises contact between microorganisms and substrate |
| Air supply / sparger | Supplies oxygen for aerobic processes; removed or replaced with N₂ for anaerobic fermentations |
| Sampling port | Allows regular removal of small samples to monitor growth rate, pH, and product concentration without contaminating the vessel |
Organism: Fusarium venenatum — a fungus grown in a large continuous-flow fermenter.
Substrate: Glucose syrup (from starch hydrolysis); ammonia as nitrogen source.
Conditions: Aerobic (air supplied); controlled temperature and pH; sterile.
Product: Fungal mycoprotein — a protein-rich food with high fibre content, low fat, suitable as meat substitute. Harvested continuously; processed (texture adjusted) before sale.
Advantage over livestock farming: Much more efficient energy conversion (less energy lost as heat per kg of protein); can use waste agricultural starch; lower land and water use.
Genetic Engineering — Review and Extension
Genetic engineering (covered in Topic 18) is extended here with the specific tools and techniques at a more detailed level for Extended candidates.
| Tool/technique | Function |
|---|---|
| Restriction endonucleases | Cut DNA at specific recognition sequences, producing “sticky ends” — short, single-stranded overhangs that allow complementary sequences to anneal |
| DNA ligase | Joins (seals) the sticky ends of two DNA fragments together — catalyses formation of phosphodiester bonds between adjacent nucleotides |
| Plasmids | Circular, extrachromosomal DNA found in bacteria; used as vectors to carry recombinant DNA into host cells; can replicate independently |
| Vectors | Vehicles for introducing foreign DNA into a host cell; includes plasmids, bacteriophages (viruses that infect bacteria), and liposomes |
| Transformation | Process by which a host cell takes up the recombinant vector; bacteria can be made “competent” (able to take up DNA) by heat shock or electroporation |
Polymerase Chain Reaction (PCR) — Extended BEYOND 0610
This section goes beyond the direct requirements of the Cambridge IGCSE Biology 0610 syllabus. It is included for enrichment and wider understanding; the specific PCR steps, temperatures, and Taq polymerase details are not required recall for 0610 examinations.
PCR is a technique that amplifies (copies) a specific segment of DNA in vitro, producing millions of identical copies from a tiny starting sample.
Why needed: DNA samples from crime scenes, archaeological specimens, or clinical samples are often too small to analyse directly. PCR allows any usable quantity to be amplified to a detectable level.
1. Denaturation (~95°C): The double-stranded DNA is heated to break hydrogen bonds between complementary bases → two single strands separate.
2. Annealing (~55°C): Temperature is lowered → short DNA primers (complementary to the ends of the target sequence) bind to the single-stranded templates.
3. Extension (~72°C): DNA polymerase (heat-stable Taq polymerase) extends the primers, synthesising new complementary DNA strands from the template → two double-stranded copies made from one.
Each cycle doubles the number of copies. After 30 cycles: 2³⁰ ≈ 10⁹ copies (over one billion).
| Application of PCR | How it helps |
|---|---|
| Forensic science | Amplify tiny DNA samples from crime scenes → DNA fingerprinting to identify suspects |
| Medical diagnosis | Detect viral or bacterial DNA in patient samples (e.g. COVID-19 PCR test, HIV viral load) |
| Evolutionary biology | Amplify ancient DNA from fossils or museum specimens to study evolutionary relationships |
| Genetic research | Amplify gene of interest before cloning, sequencing, or genetic engineering |
Gel Electrophoresis — Extended BEYOND 0610
Principle: DNA fragments are negatively charged (due to phosphate groups). When placed in an electric field in a gel (agarose), fragments migrate toward the positive electrode. Smaller fragments move faster and travel further; larger fragments are slowed by the gel matrix and travel less far.
Steps:
1. DNA samples digested with restriction enzymes to produce fragments of different sizes.
2. Fragments loaded into wells at one end of an agarose gel submerged in buffer solution.
3. Electric current applied → DNA migrates toward positive electrode.
4. Gel stained with a fluorescent dye (e.g. ethidium bromide) and viewed under UV light → bands visible.
5. A size ladder (DNA marker with fragments of known size) run alongside the samples to determine fragment sizes.
DNA fingerprinting (DNA profiling) identifies individuals by their unique pattern of short tandem repeats (STRs) at multiple loci in their genome.
Process: DNA collected → PCR amplifies STR regions → gel electrophoresis produces a banding pattern unique to that individual (except identical twins) → pattern compared to suspect or database.
Used in: criminal investigations; paternity testing; identifying disaster victims; wildlife conservation (identifying poached animals).
Cloning — Extended BEYOND 0610
| Type of cloning | Method | Application |
|---|---|---|
| Micropropagation (plant tissue culture) |
Small pieces of plant tissue (explants) taken from the desired plant and grown on sterile nutrient agar containing growth hormones → each explant grows into a genetically identical plantlet | Rapid propagation of rare or valuable plants; disease-free stock; orchid production; banana farming |
| Somatic cell nuclear transfer (animal cloning) |
Nucleus removed from an egg cell; nucleus from a body cell of the donor animal inserted; egg stimulated to divide → embryo implanted into surrogate mother → offspring genetically identical to the donor | Conservation of endangered species; producing animals that make pharmaceutical proteins in milk; research into genetic diseases |
Cloning: reduced genetic diversity; animal welfare concerns in somatic cell nuclear transfer (high failure rate, premature ageing); ethical concerns about applying techniques to humans.
Genetic engineering: unknown long-term effects on ecosystems (GM organisms released into environment); transfer of genes to wild relatives; ethical concerns about “designer babies” and germline editing; corporate control of food supply through patented GM seeds.
Stem Cells — Extended BEYOND 0610
Stem cells, somatic cell nuclear transfer, and induced pluripotent stem cells (iPSCs) go beyond the Cambridge IGCSE Biology 0610 syllabus. These sections are included as background enrichment only.
Stem cells are undifferentiated cells that can divide and differentiate into specialised cell types.
Embryonic stem cells: derived from early embryos; pluripotent (can become almost any cell type in the body) — highest therapeutic potential but significant ethical concerns (embryo is destroyed).
Adult stem cells: found in bone marrow, skin, gut lining, etc.; more limited (multipotent — can produce only certain cell types); fewer ethical concerns.
Induced pluripotent stem cells (iPSCs): adult cells reprogrammed to act like embryonic stem cells — avoids embryo destruction; increasingly used in research.
| Potential therapeutic use | How stem cells could help |
|---|---|
| Leukaemia treatment | Bone marrow transplant replaces damaged blood stem cells with healthy donor cells → restores blood cell production (already in clinical use) |
| Diabetes (Type 1) | Stem cells differentiated into insulin-producing β cells and transplanted into pancreas to restore insulin production |
| Spinal cord injury | Stem cells differentiated into neurones or supporting cells to repair damaged spinal cord tissue |
| Heart disease | Stem cells differentiated into cardiac muscle cells to replace scar tissue after heart attack |
In a fermenter used to produce yoghurt cultures, the temperature must be carefully controlled. Why is temperature control important?
- A. To prevent the bacteria from producing lactic acid
- B. To ensure the bacteria only carry out aerobic respiration
- C. To maintain the optimum temperature for bacterial enzymes and prevent denaturation at high temperatures
- D. To keep the pH of the culture neutral throughout fermentation
PCR is used to amplify DNA from a blood sample found at a crime scene. Describe the three steps of one PCR cycle and explain how the amount of DNA changes after 3 complete cycles. [5 marks]
- Denaturation (~95°C): DNA is heated; hydrogen bonds between complementary bases break; double-stranded DNA separates into two single strands [1 mark]
- Annealing (~55°C): Temperature lowered; short DNA primers bind to complementary sequences at the ends of the target region on each single strand [1 mark]
- Extension (~72°C): DNA polymerase (Taq polymerase) extends the primers, synthesising new complementary strands → two complete double-stranded DNA molecules produced from one [1 mark]
- After each cycle, copies double; after 3 cycles: 2³ = 8 copies [1 mark]
- After 30 cycles: 2³⁰ ≈ 1 billion copies — sufficient for forensic analysis / detection [1 mark]
Comprehensive Practice Questions
Mixed questions across Topic 21.
Yoghurt production involves the fermentation of lactose by bacteria. Which correctly describes this process?
- A. Bacteria carry out aerobic respiration, producing CO₂ that acidifies the milk
- B. Bacteria ferment lactose anaerobically, producing lactic acid that denatures milk proteins and lowers pH
- C. Yeast ferments lactose to produce ethanol, which preserves the yoghurt
- D. Bacteria produce CO₂ that causes the milk to expand and set
A fermenter is used to produce a protein by genetically engineered bacteria. Explain the importance of the following features:
(a) Steam sterilisation before use [2 marks]
(b) Temperature monitoring and control [2 marks]
(c) A stirrer [2 marks]
- (a) Steam sterilisation kills all microorganisms before the production strain is added [1 mark]; prevents contamination by other species that would compete with the production bacteria or produce unwanted/harmful products, reducing yield and purity [1 mark]
- (b) Temperature must be kept at the optimum for bacterial enzymes [1 mark]; microbial metabolism generates heat — if temperature rises too high, enzymes denature and fermentation stops; too low reduces enzyme activity and slows production [1 mark]
- (c) Stirrer mixes the contents [1 mark]; ensures even distribution of nutrients and temperature throughout the vessel; maximises contact between bacteria and substrate → maintains maximum rate of growth and product formation [1 mark]
(a) Explain how gel electrophoresis can be used to separate DNA fragments of different sizes. [4 marks]
(b) Explain why embryonic stem cells are considered more useful for treating disease than adult stem cells, and state one ethical concern about using embryonic stem cells. [3 marks]
- DNA fragments are loaded into wells in an agarose gel; an electric current is applied [1 mark]
- DNA is negatively charged and migrates toward the positive electrode [1 mark]
- Smaller fragments move faster (less resistance from gel matrix) and travel further from the wells; larger fragments travel less far [1 mark]
- Fragments appear as bands when stained; comparing band positions with a size ladder determines fragment sizes [1 mark]
- Embryonic stem cells are pluripotent — they can differentiate into almost any cell type in the body [1 mark]
- Adult stem cells are more limited (multipotent) — they can only produce a restricted range of cell types related to their tissue of origin [1 mark]
- Ethical concern: using embryonic stem cells requires destruction of a human embryo, which some consider to be the ending of a human life [1 mark]
High-Frequency Mistakes — Topic 21 Overall
- 🪪Saying yeast is used to make yoghurtYoghurt is made by lactic acid bacteria (e.g. Lactobacillus) — not yeast. Yeast (Saccharomyces cerevisiae) is used for bread, beer, and wine. In yoghurt, bacteria ferment lactose to lactic acid. In bread, yeast ferments sugars to CO₂. Always match the microorganism to the correct product.
- ⚗Saying the stirrer in a fermenter adds oxygenThe stirrer mixes the contents for even nutrient distribution and temperature — it does not supply oxygen. Oxygen is supplied by a separate sparger (air inlet). For anaerobic fermentations, no oxygen is supplied. Confusing stirrer function with air supply loses the mark.
- 📊Ext: Saying smaller DNA fragments travel less far in electrophoresisSmaller fragments travel FURTHER (toward the positive electrode) because they experience less resistance from the gel matrix. Larger fragments are slowed down and remain closer to the wells. Remember: small = fast = far; large = slow = near wells. Many students reverse this.
- 💉Ext: Saying DNA is positively charged in electrophoresisDNA has a net NEGATIVE charge due to the phosphate groups in its sugar-phosphate backbone. It therefore migrates toward the POSITIVE electrode (anode) when current is applied. Never say DNA is neutral or positive.
- 💧Ext: Saying restriction enzymes join DNA fragmentsRestriction endonucleases CUT DNA at specific sequences. DNA LIGASE joins (seals) the fragments together. These are opposite functions — confusing them in a genetic engineering question directly loses marks. Memory: Restriction = cuts Restrictions into the DNA; Ligase = LIGAtes (joins) DNA.
- 🧲Ext: Saying all stem cells are pluripotentEmbryonic stem cells are pluripotent (can become almost any cell type). Adult stem cells are multipotent (more limited — can only produce certain cell types from their tissue of origin). Only embryonic stem cells and induced pluripotent stem cells (iPSCs) are pluripotent. This distinction is specifically tested.
- 📋Ext: Saying PCR uses normal DNA polymerasePCR uses Taq DNA polymerase — a heat-stable polymerase isolated from Thermus aquaticus, a bacterium that lives in hot springs. Normal DNA polymerase would denature at the 95°C denaturation step. Taq polymerase withstands repeated heating and cooling cycles.
Highest-yield Core items: the four food products with correct microorganisms and processes (bread/beer/wine = yeast + anaerobic fermentation; yoghurt = lactic acid bacteria + lactic acid production); fermenter features and why each is needed (temperature control/sterility/stirrer/pH monitoring are the most tested four). For Extended: PCR three steps in order (denaturation → annealing → extension) with temperatures and roles; gel electrophoresis principle (negative charge, small fragments travel further, bands visible after staining); genetic engineering tools (restriction endonuclease cuts, DNA ligase joins, plasmid = vector); stem cell types (embryonic = pluripotent; adult = multipotent) and therapeutic applications. Note: PCR, gel electrophoresis, somatic cell cloning, and stem cells go beyond the 0610 syllabus and appear in A Level / IGCSE Extended science courses. They are included here as enrichment for Extended candidates but will not be directly examined in 0610 Paper 4.