(a) Food production
- Syllabus
- 2024
- Topic
- —
- Level
- —
Learning objectives
5.1Glasshouses and polythene tunnelsDescribe how glasshouses and polythene tunnels can be used to increase the yield of certain crops.5.2Effects on crop yield of increased carbon dioxideUnderstand the effects on crop yield of increased carbon dioxide and increased temperature in glasshouses.5.3Fertilisers and crop yieldUnderstand how the use of fertiliser can increase crop yield.5.4Pest controlUnderstand the reasons for pest control and the advantages and disadvantages of using pesticides and biological control with crop plants.5.5Yeast in the production of foodUnderstand the role of yeast in the production of food including bread.5.6Yeast anaerobic respirationPractical: investigate the role of anaerobic respiration by yeast in different conditions.5.7Lactobacillus in yoghurt productionUnderstand the role of bacteria (Lactobacillus) in the production of yoghurt.5.8Industrial fermenter conditionsUnderstand the use of an industrial fermenter and explain the need to provide suitable conditions in the fermenter, including aseptic precautions, nutrients, optimum temperature and pH, oxygenation and agitation, for the growth of micro-organisms.59B Fish farmingUnderstand the methods used to farm large numbers of fish to provide a source of protein, including maintaining water quality, controlling intraspecific and interspecific predation, controlling disease, removing waste products, controlling the quality and frequency of feeding, and selective breeding.
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.