5 Use of biological resources
- Syllabus
- 2024
- Section
- 5
- Level
- —
Exam analysis
(a) Food production
- Syllabus
- 2024
- Topic
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- Level
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Increase crop yield with a protected growing environment
Glasshouses and polythene tunnels enclose crops so growers can control limiting factors and protect plants, extending the growing season and increasing harvestable yield.
| Protected-environment feature | How it can increase yield |
|---|---|
| transparent covering | admits light for photosynthesis and reduces heat loss, maintaining a warmer environment |
| heaters and ventilation | keep temperature nearer the crop's optimum and prevent excessive heating |
| artificial lighting | lengthens the daily photosynthetic period when natural light is limiting |
| irrigation and mineral supply | prevent water or mineral ions from limiting growth |
| enclosed structure | reduces wind and some water loss, excludes some pests and shields crops from frost or damaging weather |
| timed control | allows earlier planting, later harvesting or year-round production for suitable crops |
A covering does not create energy or guarantee higher yield: light, temperature, carbon dioxide, water and minerals can each become limiting, while heating and lighting require energy inputs.
Raise glasshouse yield by controlling carbon dioxide and temperature
Carbon dioxide concentration and temperature can limit photosynthesis in a glasshouse, so raising either toward an optimum can increase glucose production, growth and crop yield.
| Change | Mechanism | Limit |
|---|---|---|
| increase CO₂ | supplies more reactant for photosynthesis, increasing rate when CO₂ is limiting | once another factor limits, extra CO₂ gives little further gain |
| increase temperature | increases kinetic energy and successful enzyme-controlled reactions up to an optimum | above the optimum, enzymes lose functional shape, respiration costs may rise and photosynthesis falls |
| fuel-burning heater | warms the air and releases CO₂, potentially relieving two limits | fuel cost and pollutant emissions must be considered |
To find a maximum-yield setting, use several CO₂ concentrations or temperatures, identical crop plants and other controlled factors, replicate each treatment, grow for the same time, and compare mean harvest mass or another defined yield measure.
Yield does not rise indefinitely with CO₂ or temperature. Limiting factors shift, and temperature has an optimum rather than a simple always-higher-is-better relationship.
Use fertiliser minerals to build crop biomass
Fertilisers replace mineral ions removed from soil by crops, allowing plants to synthesise essential molecules and grow more harvestable biomass when minerals are limiting.
| Mineral ion | Biological use | Yield link |
|---|---|---|
| nitrate | makes amino acids and therefore proteins | supports enzymes, new cells and growth |
| magnesium | forms part of chlorophyll | supports light absorption and photosynthesis |
| phosphate | used in DNA, cell membranes and ATP-related metabolism | supports cell division and energy transfer |
| potassium | supports enzyme function and control of water movement | supports healthy growth and gas exchange |
Apply a suitable amount: once mineral supply is no longer limiting, another factor controls yield. Excess soluble fertiliser may raise soil solute concentration, leach away or enter water and cause eutrophication.
Fertiliser is not plant food in the energy sense. Plants make organic food by photosynthesis; fertiliser supplies mineral ions needed to build and operate tissues.
Compare pesticide and biological pest control
Pest control protects crop yield by reducing organisms that eat crops, spread disease or compete for light, water and minerals.
| Feature | Chemical pesticide | Biological control |
|---|---|---|
| method | applies a toxic chemical that kills or suppresses the pest | introduces or increases a predator, parasite or pathogen of the pest |
| speed and reliability | often rapid and predictable at first | may establish slowly and depends on environmental conditions |
| specificity | may kill non-target organisms, including pollinators or natural predators | often more specific to the target pest |
| persistence | residues may remain; repeated application may be needed | control agent may reproduce and provide longer-lasting control |
| wider risk | bioaccumulation, food-web disruption and harm to humans can occur | introduced agent may attack non-target species or become invasive |
| evolution and control | pesticide selects for resistant pests | pest is usually reduced rather than eradicated; predator needs some prey |
Judge a method using effectiveness, duration, cost, target specificity and ecosystem evidence. An untreated control helps show whether change is caused by the treatment rather than another factor.
Biological does not mean automatically harmless, and chemical does not mean automatically ineffective. The relevant comparison is the actual target, control agent, dose, persistence and non-target effects.
Make bread rise with yeast respiration
Yeast is a single-celled fungus that uses sugars in dough and releases carbon dioxide; trapped gas expands the dough and gives bread its porous texture.
| Stage | Role of yeast and dough |
|---|---|
| 1 | sugars become available from added sugar or breakdown of flour carbohydrates |
| 2 | yeast respires; as oxygen becomes limited, anaerobic respiration produces ethanol and carbon dioxide |
| 3 | carbon dioxide bubbles are trapped by the elastic dough network |
| 4 | bubbles expand during proving and early heating, so dough rises |
| 5 | oven heat kills yeast, sets the bread structure and evaporates much of the ethanol |
It is carbon dioxide—not oxygen—that inflates the dough. Yeast does not raise bread by increasing its own mass alone; the essential product is trapped gas.
Investigate anaerobic respiration in yeast
Yeast anaerobically converts glucose into ethanol and carbon dioxide; carbon-dioxide production provides a measurable rate of fermentation.
glucose → ethanol + carbon dioxide
| Investigation decision | Strong method |
|---|---|
| independent variable | change one factor such as temperature, glucose concentration or pH across at least three levels |
| anaerobic condition | place liquid paraffin above the yeast-glucose mixture to limit oxygen entry |
| dependent variable | collect CO₂ in a gas syringe and calculate volume ÷ time; avoid counting unequal bubbles |
| controls | keep yeast strain and mass, solution volume, glucose concentration, pH and time constant except for the chosen variable |
| temperature control | use thermostatically controlled water baths and verify with a thermometer |
| reliability | repeat each condition and compare mean rates; use smaller intervals around the apparent optimum |
Rate rises toward an optimum because enzyme-controlled collisions become more frequent. Above the optimum, enzyme active sites lose shape, so fermentation slows; later decline can also result from substrate depletion or ethanol accumulation.
A faster initial rate is not the same as a greater final yield. State whether the measurement is CO₂ per unit time, total CO₂, or ethanol produced.
Turn milk into yoghurt with Lactobacillus
Lactobacillus ferments the milk sugar lactose to lactic acid; falling pH changes milk proteins and creates yoghurt's texture and acidic conditions.
| Stage | Purpose |
|---|---|
| 1 heat milk | pasteurises it, killing unwanted microorganisms that could cause disease or compete |
| 2 cool to about 40–45 °C | prevents the starter bacteria being killed and provides a suitable enzyme temperature |
| 3 add Lactobacillus culture | supplies the desired microorganism |
| 4 incubate with limited oxygen | bacteria ferment lactose and produce lactic acid |
| 5 monitor pH and texture | acid lowers pH and causes milk proteins to coagulate, thickening the yoghurt |
| 6 cool the product | slows bacterial enzymes and further acid production |
Heating and incubation have different temperature goals: high initial temperature reduces contamination, but the culture is added only after cooling to a temperature it can survive.
Control an industrial fermenter
An industrial fermenter grows microorganisms at scale by maintaining conditions that maximise the desired growth or product while preventing contamination.
| Condition or feature | Why it is controlled |
|---|---|
| aseptic precautions: steam sterilisation, sterile vessel and filtered inlets | kill or exclude unwanted microbes that compete, spoil product or release toxins |
| nutrients | provide carbon, nitrogen, minerals and other substrates for growth and product formation |
| optimum temperature | keeps microbial enzymes near maximum rate; respiration releases heat, so sensors and a cooling jacket remove excess heat |
| optimum pH | maintains enzyme and membrane function; probes and acid or alkali addition correct change |
| oxygenation | sterile air supplies oxygen when aerobic respiration is required |
| agitation | paddles mix microbes with nutrients and oxygen, distribute heat and pH evenly, and prevent settling |
A fermenter is controlled rather than simply kept warm. The target microorganism and product determine whether oxygen is supplied; anaerobic processes must instead exclude oxygen.
Manage intensive fish farming for high protein yield
Intensive fish farming raises many fish in a managed volume, so yield depends on controlling water, feeding, predation, disease, waste and breeding without allowing density to damage the stock.
| Management need | Method and yield link |
|---|---|
| water quality | monitor temperature, pH and dissolved oxygen; aerate or renew water so respiration and enzyme function continue |
| intraspecific predation | separate fish by age or size and provide enough food to reduce cannibalism |
| interspecific predation | use secure nets or cages and exclude predatory species |
| disease | avoid excessive stocking, inspect stock, isolate sick fish, remove dead fish and use vaccination or treatment carefully |
| waste products | filter or replace water and remove faeces and uneaten feed before decomposition lowers oxygen or nutrients cause eutrophication |
| feeding | provide nutritionally balanced, protein-containing feed in controlled amounts and at suitable frequency to maximise growth without waste |
| selective breeding | breed fish with useful inherited traits such as rapid growth or disease resistance |
Multi-trophic systems can route waste food and faeces to other farmed consumers and dissolved minerals to seaweed, reducing pollution while producing additional biomass.
High stocking density can raise total output per area but also intensifies oxygen demand, disease transmission, competition and waste. Maximum production therefore requires control, not simply adding more fish or feed.
(b) Selective breeding
- Syllabus
- 2024
- Topic
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- Level
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Develop a plant variety by selective breeding
Selective breeding uses existing inherited variation: humans choose plant parents with desired phenotypes and repeatedly breed the best offspring so the associated alleles become more common.
| Stage | Plant-breeding decision |
|---|---|
| 1 define the goal | choose measurable characteristics such as high grain yield, disease resistance, short strong stems or a desired flower colour and scent |
| 2 choose parents | identify plants that show the desired characteristic or complementary characteristics |
| 3 control pollination | transfer pollen between selected parents and prevent unwanted pollen reaching the stigma |
| 4 grow many seeds | raise offspring under comparable conditions so inherited differences can be judged |
| 5 select offspring | measure the target phenotype and keep the strongest combination |
| 6 repeat | cross or self-pollinate selected plants over many generations until the characteristic is reliably inherited |
To combine red flowers with scent, cross a red unscented variety with a white scented variety, select offspring that are both red and scented, then breed those selected offspring repeatedly.
Selective breeding does not create a chosen allele on demand; it changes the frequency and combinations of alleles already present through differential reproduction. Environment must be controlled when comparing phenotypes.
Develop animal traits by selective breeding
Animal selective breeding chooses parents with useful inherited traits, measures those traits in their offspring and repeats the selection across generations.
| Stage | Animal-breeding decision |
|---|---|
| 1 define the goal | choose a measurable trait such as rapid growth, high milk yield, disease resistance or efficient feed conversion |
| 2 identify parents | use phenotype, health, pedigree and offspring records to choose animals likely to carry useful alleles |
| 3 mate selected animals | use controlled mating or artificial insemination while avoiding animals with harmful traits |
| 4 raise comparable offspring | keep nutrition and other environmental factors similar |
| 5 measure and select | breed from offspring with the strongest inherited performance |
| 6 repeat | continue over many generations so useful alleles increase in the population |
A bull does not produce milk, so compare milk yield across many daughters produced with comparable cows. Select the bull whose daughters have the highest mean yield, not the bull with the largest body.
An individual phenotype reflects genes and environment, so records from many offspring are stronger than one observation. Repeated use of closely related animals can reduce genetic diversity and increase the chance that harmful recessive alleles meet.
(c) Genetic modification (genetic engineering)
- Syllabus
- 2024
- Topic
- —
- Level
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Cut and join DNA with two enzyme tools
Genetic engineering uses restriction enzymes as sequence-specific DNA cutters and DNA ligase as the enzyme that joins DNA fragments.
| Enzyme | Action | Use in recombinant DNA |
|---|---|---|
| restriction enzyme | recognises a specific base sequence and cuts the DNA backbone at that site | cuts out the desired gene and opens vector DNA such as a plasmid |
| same restriction enzyme on donor and vector | produces matching ends on both DNA pieces | complementary ends can align by base pairing |
| DNA ligase | seals the sugar-phosphate backbones of adjacent DNA pieces | permanently joins the desired gene into the vector, forming recombinant DNA |
Cut donor DNA and vector with the same restriction enzyme, allow matching ends to pair, then use ligase to seal the join. Enzyme names must match their actions.
Restriction enzymes cut; ligase joins. Ligase does not remove the gene, and a restriction enzyme does not by itself insert or seal it into another DNA molecule.
Deliver recombinant DNA with plasmid or viral vectors
A vector carries recombinant DNA into a recipient cell; plasmids and modified viruses can both perform this delivery role.
| Vector | How recombinant DNA is carried and delivered |
|---|---|
| plasmid | a small circular DNA molecule is cut, joined to the desired gene and taken up by a recipient cell such as a bacterium |
| virus | viral genetic material is modified to include the desired DNA; infection delivers that DNA into a host cell |
| after delivery | cells containing the recombinant DNA can express the inserted gene if the required control sequences and cellular machinery are available |
Recombinant DNA contains DNA joined from different sources. The vector is the carrier; the inserted DNA is the genetic cargo; the recipient is the cell that takes it up.
A plasmid and a virus are not enzymes. Restriction enzyme and ligase construct recombinant DNA; the vector transports that DNA into another cell.
Manufacture human insulin with GM bacteria
Large amounts of human insulin can be made by inserting the human insulin gene into bacterial plasmids, growing the modified bacteria and recovering their protein product.
| Stage | Process |
|---|---|
| 1 obtain the gene | isolate or prepare DNA carrying the human insulin coding sequence |
| 2 construct vector | cut the insulin DNA and a bacterial plasmid with a restriction enzyme, then join them with ligase |
| 3 modify bacteria | introduce recombinant plasmids into bacterial cells and select cells that contain them |
| 4 scale growth | culture the selected GM bacteria in a fermenter with sterile nutrients, suitable temperature and pH, mixing and oxygen when required |
| 5 recover product | bacteria express the human gene; insulin is harvested and purified for medical use |
Bacteria reproduce rapidly and plasmids are copied as cells divide, so a controlled fermenter produces a large population expressing the same inserted gene.
The insulin gene is human, but the production cells are bacteria. The process requires both genetic modification and controlled culture; inserting a gene alone does not purify a usable medicine.
Improve food production with GM plants
A GM plant carries deliberately altered DNA so it expresses a characteristic that can increase usable yield, reduce losses or improve the food produced.
| Engineered characteristic | Food-production benefit | Important limit or risk |
|---|---|---|
| insect resistance | less crop eaten and potentially less insecticide needed | resistant pest populations may evolve; non-target effects must be assessed |
| herbicide resistance | weeds can be killed while the crop survives, reducing competition | herbicide use may affect other plants and gene flow to wild relatives is possible |
| resistance to viral disease | fewer plants become diseased, stabilising yield | effectiveness depends on the disease and trait |
| improved nutritional content | food can provide more of a needed nutrient, such as vitamin-A precursor in golden rice | access, diet, safety and acceptance still matter |
| stress tolerance or delayed spoilage | more crop survives difficult conditions or reaches consumers | ecological and food-safety evidence must be evaluated case by case |
Benefits are trait-specific, not properties of every GM crop. Compare yield, pesticide use, non-target organisms, gene flow, health evidence and farmer access for the actual plant and inserted gene.
GM changes DNA directly; selective breeding chooses parents and recombines existing alleles over generations. Neither method guarantees a higher yield in every environment.
Use the term transgenic precisely
A transgenic organism contains genetic material transferred from a different species.
| Description | Transgenic? |
|---|---|
| a bacterial cell receives a human insulin gene | yes: DNA crossed a species boundary |
| a crop receives a bacterial gene for an insect-resistant protein | yes: the donor and recipient are different species |
| DNA is altered without adding genetic material from another species | genetically modified, but not necessarily transgenic |
| two varieties of the same plant are selectively crossed | no: this is selective breeding, not direct interspecies gene transfer |
All transgenic organisms are genetically modified, but not every genetic modification is transgenic. The defining condition is transfer of genetic material between different species, not simply a changed phenotype.
(d) Cloning
- Syllabus
- 2024
- Topic
- —
- Level
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Grow plant clones by micropropagation
Micropropagation is tissue culture in which small plant explants are grown in vitro under sterile, controlled conditions and develop into whole plants.
| Stage | Procedure and purpose |
|---|---|
| 1 choose tissue | take a small explant, often from a shoot tip, from a healthy plant with the desired genotype |
| 2 work aseptically | sterilise instruments, vessel and explant surface without killing plant cells; this prevents bacteria and fungi overgrowing the culture |
| 3 place on medium | transfer the explant to sterile agar containing water, sugar, mineral ions and suitable plant growth regulators |
| 4 multiply shoots | cells divide by mitosis and form a mass of tissue or many shoots; pieces can be subcultured to increase number |
| 5 form roots | move shoots to a medium with conditions that promote root development |
| 6 acclimatise | transfer plantlets to compost and humid protected conditions, then gradually to a glasshouse or outside |
In vitro means outside the organism in laboratory culture, such as a sterile vessel. Every new cell forms by mitosis, preserving the explant's genotype unless mutation occurs.
Sterilisation must remove contaminating microbes without boiling or otherwise killing the living explant. Nutrient medium supports growth but does not replace light once plantlets photosynthesise.
Scale a desirable plant genotype commercially
Commercial micropropagation repeatedly subdivides tissue from one selected plant, producing large numbers of genetically identical plants that preserve its desirable characteristics.
| Commercial advantage | Why micropropagation provides it |
|---|---|
| genetic uniformity | all clones retain the selected genotype, so a GM gene, flower form, fruit quality or other inherited trait is copied |
| rapid multiplication | many explants and repeated subculture produce far more plants than one parent could by conventional cuttings |
| year-round production | in vitro culture is controlled and not restricted to the outdoor growing season |
| propagation of difficult plants | plants with few seeds, poor germination or slow conventional reproduction can be multiplied |
| clean starting stock | carefully selected and tested tissue can provide uniform pathogen-free material |
Uniformity is valuable only when the selected genotype suits the environment. A genetically uniform crop has little variation, so one disease or environmental change may affect most plants similarly.
Micropropagation copies a desirable genotype; it does not create the characteristic. The useful parent must first be selected or genetically modified, and sterile culture still requires acclimatisation before field planting.
Clone a mammal by nuclear transfer
A cloned mammal can be produced by transferring a diploid nucleus from a mature body cell into an egg cell whose own nucleus has been removed.
| Stage | Nuclear-transfer process |
|---|---|
| 1 donor nucleus | take a mature diploid body cell from the animal to be cloned and isolate its nucleus |
| 2 enucleated egg | obtain an unfertilised egg cell from a donor female and remove its haploid nucleus |
| 3 nuclear transfer | insert the diploid body-cell nucleus into the enucleated egg, or fuse the body cell with it |
| 4 activation | apply an electric shock to stimulate the reconstructed cell to divide |
| 5 embryo | mitosis produces an early embryo with nuclear DNA from the adult donor |
| 6 implantation | place the embryo into the uterus of a surrogate mother for development and birth |
Dolly's nuclear DNA matched the mature-cell nucleus donor, not the egg donor or surrogate. Many reconstructed eggs are needed because activation, division, implantation and development often fail.
The transferred nucleus must be diploid and comes from a mature body cell; meiosis and fertilisation are not part of this cloning route. A clone can still differ in phenotype because environment and non-nuclear factors differ.
Clone transgenic animals to manufacture human proteins
A transgenic animal can carry and express a human gene; cloning that animal creates many individuals with the same inserted gene, allowing repeated production of the human protein.
| Stage | Production logic |
|---|---|
| 1 create a transgenic founder | insert a human gene with suitable control DNA into an animal cell or embryo |
| 2 confirm expression | identify an animal that produces the required human protein, often in an accessible secretion such as milk |
| 3 clone the selected genotype | use nuclear transfer from the successful transgenic animal to create genetically identical embryos |
| 4 produce a herd | implant embryos into surrogates and raise cloned transgenic offspring |
| 5 recover protein | collect the protein-containing material and extract and purify the human protein for its intended use |
Cloning preserves the exact gene insertion and productive genotype instead of relying on sexual reproduction, which would reshuffle alleles and may not pass the transgene to every offspring.
The animal produces a human protein because it expresses transferred human genetic material; the whole animal does not become human. Cloning scales a verified transgenic genotype but does not replace purification or safety testing.