21.2 Biotechnology
- Syllabus
- 0610–2026–2027
- Topic
- 21.2
- Level
- —
Learning objectives
21.2.1Role of anaerobic respiration in yeast• Describe the role of anaerobic respiration in yeast during the production of ethanol for biofuels21.2.2Role of anaerobic respiration in yeast• Describe the role of anaerobic respiration in yeast during bread-making21.2.3Use of pectinase in fruit juice• Describe the use of pectinase in fruit juice production21.2.4Use of biological washing powders that• Investigate and describe the use of biological washing powders that contain enzymes21.2.5Use of lactase to produce lactose-• Explain the use of lactase to produce lactose- free milk21.2.6Fermenters can be used• Describe how fermenters can be used for the large-scale production of useful products by bacteria and fungi, including insulin, penicillin and mycoprotein21.2.7Conditions that need to be controlled• Describe and explain the conditions that need to be controlled in a fermenter, including: temperature, pH, oxygen, nutrient supply and waste products
Use yeast respiration to produce ethanol fuel
Yeast respires anaerobically when oxygen is absent, converting glucose into ethanol and carbon dioxide while releasing some energy.
In biofuel production, yeast is supplied with sugars from plant material in oxygen-limited conditions. The ethanol produced is separated and used as a fuel.
Ethanol is the useful biofuel product; carbon dioxide is the other product. Oxygen must be limited so yeast carries out anaerobic rather than aerobic respiration.
Use yeast carbon dioxide to raise bread
In bread-making, yeast respires sugars anaerobically and releases carbon dioxide and ethanol.
Carbon dioxide forms bubbles that become trapped in the dough, causing it to expand and rise. During baking, heat kills the yeast and the ethanol evaporates, while the gas spaces remain in the bread.
Warm conditions speed yeast enzymes and respiration up to a suitable temperature; excessive heat denatures enzymes and kills the yeast.
Carbon dioxide—not ethanol—makes dough rise. Baking provides heat after the gas-producing stage; it does not supply the energy for yeast respiration.
Use pectinase to extract fruit juice
Pectinase breaks down pectin in fruit tissues during fruit-juice production.
Breaking pectin helps cells separate and releases more liquid, increasing the volume of juice that can be filtered. It also reduces suspended pectin, producing clearer juice.
Crushed fruit is mixed with pectinase under a suitable temperature and pH, then the juice is filtered from the remaining solids.
Pectinase acts on pectin; it is not lactase, protease or lipase. A water-only sample is a useful control when testing its effect.
Investigate enzyme washing powders fairly
Biological washing powders contain enzymes that digest stain molecules into smaller, more soluble products.
| Stain molecule | Enzyme | Products |
|---|---|---|
| starch | amylase | simple sugars |
| protein | protease | amino acids |
| fat | lipase | fatty acids and glycerol |
Compare equal stained fabric samples using equal volumes of water, equal powder amounts and the same washing time. Change only powder type or temperature, then measure stain removal using colour or percentage light reflected. Repeat and calculate a mean.
Biological powder can work well at moderate temperatures; above the enzymes' optimum, active sites change shape and activity falls through denaturation.
Match the enzyme to the stain substrate. A fair investigation changes one independent variable and controls the fabric, stain, time, water and powder amount.
Use lactase to make lactose-free milk
Lactase hydrolyses lactose in milk into glucose and galactose, producing milk suitable for people with lactose intolerance.
Milk can flow over lactase immobilised in alginate beads. Lactose molecules contact the enzyme and are broken down while the enzyme remains in the column.
Immobilised lactase can be reused, is easy to separate from the milk and does not contaminate the final product with enzyme.
Lactase breaks down lactose; it does not remove lactose by filtration and it is not lipase.
Use fermenters for large-scale products
Fermenters grow bacteria or fungi in large, controlled cultures so useful products can be made consistently at scale.
| Product | Production organism or role |
|---|---|
| insulin | genetically modified bacteria manufacture human insulin |
| penicillin | Penicillium fungus produces the antibiotic |
| mycoprotein | fungal biomass is grown as a protein-rich food product |
A sterile fermenter is inoculated with the chosen microorganism, supplied with nutrients and maintained under controlled conditions. The culture or product is harvested, separated and purified when required.
The useful output differs: insulin and penicillin are molecules recovered from the process, while mycoprotein is the fungal biomass itself.
Control five conditions inside a fermenter
Fermenter conditions are monitored and controlled to maximise microorganism growth or product yield without contamination or enzyme damage.
| Condition | Why and how it is controlled |
|---|---|
| temperature | respiration releases heat; a water jacket keeps the culture near the enzyme optimum and prevents denaturation |
| pH | metabolism can change acidity; probes and acid, alkali or buffers maintain an enzyme-suitable pH |
| oxygen | aerobic organisms need oxygen for respiration; sterile air is bubbled through and mixing distributes it |
| nutrient supply | carbon, nitrogen and mineral sources support respiration, growth and product formation; sterile feed is supplied at a suitable rate |
| waste products | wastes may become toxic or alter pH; gases leave through an outlet and culture products or liquid can be removed |
Stirrers keep temperature, pH, oxygen, nutrients and organisms evenly distributed and prevent cells from settling.
Sterility prevents competing microorganisms from using nutrients or contaminating the product. It is a process requirement, not a substitute for controlling the five named conditions.