How are plants and animals cloned, and how are microorganisms and immobilised enzymes used in biotechnology?
6.1.4 Cloning and biotechnology: natural and artificial cloning of plants (including micropropagation and tissue culture) and animals; the use of microorganisms in biotechnology and the conditions in an industrial fermenter; the principles and advantages of using immobilised enzymes; and the asepsis and growth curve of a microbial culture.
A focused answer to the OCR H420 6.1.4 dot point on cloning and biotechnology. Covers natural and artificial cloning of plants and animals, micropropagation and tissue culture, the use of microorganisms and the conditions in an industrial fermenter, immobilised enzymes, and the microbial growth curve.
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What this dot point is asking
OCR wants you to describe natural and artificial cloning of plants and animals (including micropropagation), explain the use of microorganisms in biotechnology and the conditions in an industrial fermenter, explain the principles and advantages of immobilised enzymes, and describe aseptic technique and the microbial growth curve.
The answer
Cloning plants
A clone is a genetically identical copy. Plants clone naturally by vegetative propagation (for example runners, bulbs and tubers). Artificial cloning includes:
- Cuttings: a section of stem is planted and grows into a new plant.
- Micropropagation (tissue culture): used to mass-produce identical plants. A small explant (often a meristem, usually virus-free) is grown under aseptic conditions on a sterile nutrient medium with plant hormones (auxins and cytokinins). The totipotent cells form a callus, which is then induced to differentiate into plantlets that are grown on. All are clones of the parent.
Advantages: rapid production of many identical, disease-free plants from one parent, and propagation of plants that are hard to grow from seed. Disadvantage: no genetic variation, so the whole crop is vulnerable to the same disease.
Cloning animals
- Artificial twinning (embryo splitting): an early embryo is split, and each part develops into a genetically identical animal.
- Somatic cell nuclear transfer (SCNT): the nucleus of a body cell is transferred into an enucleated egg cell, which is stimulated to develop into a clone of the nucleus donor (the method used for Dolly the sheep).
Microorganisms and industrial fermenters
Microorganisms are used in biotechnology to make foods (yoghurt, bread), drugs (antibiotics, insulin), enzymes and biofuels, because they reproduce fast, can be genetically modified, and grow on cheap substrates. An industrial fermenter keeps conditions optimal:
- temperature controlled by a water jacket (the culture generates heat);
- pH monitored and kept optimal;
- oxygen supplied by aeration (for aerobic processes), and the culture stirred to mix nutrients, oxygen and microorganisms evenly;
- nutrients added and the culture kept sterile (asepsis) to prevent contamination.
The microbial growth curve
In a closed (batch) culture, the population shows: a lag phase (cells adjust and synthesise enzymes, little division), an exponential (log) phase (rapid division while resources are plentiful), a stationary phase (births equal deaths as nutrients run low and waste accumulates), and a death (decline) phase (deaths exceed births).
Immobilised enzymes
Immobilised enzymes are attached to or trapped in an inert support (beads, gels or membranes). Advantages:
- the enzyme is not mixed into the product, so the product is not contaminated and needs less purification;
- the enzyme can be recovered and reused, lowering cost;
- the enzyme is more stable to temperature and pH (the support protects its tertiary structure), so harsher conditions and longer continuous runs are possible.
For example, immobilised lactase makes lactose-free milk.
Examples in context
Example 1. Dolly the sheep. Dolly was produced by somatic cell nuclear transfer: an adult udder cell nucleus was placed into an enucleated egg, showing that a differentiated nucleus can be reprogrammed to make a whole clone.
Example 2. Lactose-free milk. Milk is passed over immobilised lactase, which hydrolyses lactose to glucose and galactose; because the enzyme is immobilised, it is not in the milk and can be reused continuously, a clear industrial application.
Try this
Q1. State one advantage and one disadvantage of producing crop plants by micropropagation. [2 marks]
- Cue. Advantage: rapid production of many identical, disease-free plants from one parent. Disadvantage: no genetic variation, so the whole crop is vulnerable to the same disease.
Q2. Explain why an industrial fermenter is stirred. [2 marks]
- Cue. Stirring mixes the microorganisms, nutrients and oxygen evenly and distributes heat, so all the cells have access to resources and conditions stay uniform, maximising growth.
Q3. Name the phase of the microbial growth curve in which the number of cells produced equals the number dying. [1 mark]
- Cue. The stationary phase.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR H420/02 20195 marksDescribe how micropropagation (tissue culture) is used to produce many genetically identical plants from a single parent plant.Show worked answer →
Take the steps from explant to plantlet, noting asepsis and the hormones.
A small piece of tissue (an explant) is taken from the parent plant, often from a meristem (which is usually free of viruses). Working under aseptic conditions, the explant is placed on a sterile nutrient growth medium containing plant hormones (auxins and cytokinins).
The cells, being totipotent, divide to form a mass of undifferentiated cells (a callus). Adjusting the hormones makes the callus differentiate into tiny plantlets with roots and shoots, which are grown on and transferred to soil.
All the plants are genetically identical clones of the parent. Markers reward an explant from a meristem, aseptic technique, a nutrient medium with hormones, callus formation and differentiation into identical plantlets.
OCR H420/02 20214 marksExplain the advantages of using immobilised enzymes rather than free enzymes in an industrial process.Show worked answer →
Give the practical and economic advantages, with reasons.
Immobilised enzymes are attached to or trapped in an inert support (for example beads or a membrane), so they are not mixed into the product. This means the product is not contaminated with enzyme (less downstream purification) and the enzymes can be recovered and reused, lowering cost.
They are also more stable to changes in temperature and pH (the support protects the tertiary structure), so they can be used at conditions that would denature free enzymes, and a continuous flow process can run for longer.
Markers reward easy recovery and reuse, no contamination of the product, and greater stability to temperature and pH.
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Sources & how we know this
- OCR A Level Biology A (H420) Specification — OCR (2023)