Cloning and biotechnology — OCR A-Level Biology

Natural cloning in plants is asexual reproduction producing genetically identical offspring from one parent. Structures include runners (strawberry), tubers (potato), bulbs (onion), rhizomes (couch grass) and offsets. Each new plantlet arises by mitosis from the parent, so it carries the same alleles. Horticulturists exploit this by taking cuttings, dividing clumps, or separating runners and tubers to propagate desirable varieties cheaply and quickly while preserving the genotype. Advantages include speed, low cost and identical, uniform crops; disadvantages include no genetic variation, so a single pest or disease can devastate a whole clone, and the accumulation of pathogens over generations. Understanding natural cloning underpins vegetative propagation techniques used in commercial horticulture.

Taking cuttings is a simple cloning technique because the new plant is genetically identical to its parent. A shoot or stem cutting is removed from a healthy parent plant with a clean, sharp blade, cutting just below a node. Lower leaves are stripped so the stem can be inserted into a rooting medium such as compost or water. The cut end may be dipped in rooting powder containing auxin to encourage root formation. The cutting is kept warm and humid, often under a plastic bag or propagator, to reduce water loss by transpiration while roots develop. Once roots form, the cutting is potted on. Because no meiosis or fertilisation occurs, the offspring retains the parent's genotype, which is why cuttings are used to propagate desirable varieties quickly and reliably.

Micropropagation uses tissue culture to produce many genetically identical plantlets from a small piece of tissue. A small explant, such as a shoot tip or meristem, is taken from a healthy parent plant and sterilised to remove microorganisms. It is placed on a sterile nutrient agar containing sugars, minerals, vitamins and plant hormones. Auxin and cytokinin are adjusted to promote shoot formation, then roots. The cultures are kept sterile and under controlled light and temperature. Because the explant is grown by mitosis, all plantlets are clones of the parent. Meristem tissue is often used because it is usually virus-free, giving disease-free offspring. Micropropagation allows rapid, large-scale production of uniform plants, including rare or endangered species.

Artificial cloning in plants means producing genetically identical offspring from one parent plant by vegetative propagation or tissue culture, rather than by sexual reproduction. A strong answer weighs both sides. For: identical genotypes give predictable, uniform crops; desirable traits such as yield, disease resistance or flavour are preserved exactly; large numbers of plants can be produced quickly from small amounts of tissue; rare or endangered plants and difficult-to-propagate species can be multiplied; stock is free of pathogens if cultured aseptically.

A clone is a genetically identical organism or group of cells derived from a single parent or original cell. Natural cloning occurs in animals in several ways. Identical (monozygotic) twins form when a single fertilised egg divides and the two embryos develop separately; they are clones of each other because they arose from one zygote, though they are not identical to either parent. Some animals reproduce asexually, for example by budding or fragmentation, producing offspring genetically identical to the parent. Learners should distinguish these: identical twins are clones of each other from one fertilised egg, whereas asexual reproduction produces clones of the parent. A question may ask how a named example arises or whether offspring are genetically identical to the parent.

Artificial cloning makes genetically identical animals without fertilisation of a new egg by a sperm. In artificial embryo twinning, an early embryo is split before cells specialise: the embryo is divided into separate cells or groups, each is cultured briefly, and each group is implanted into a surrogate so several identical offspring develop. In SCNT, a somatic (body) cell is taken from the animal to be cloned and its nucleus is kept. An egg cell from a donor is enucleated, meaning its own nucleus is removed. The somatic nucleus is transferred into the enucleated egg, and the reconstructed cell is stimulated to divide and develop as an embryo, which is then implanted. Both routes give clones because the nuclear genetic material is identical; SCNT can clone an existing adult, whereas twinning clones an embryo that already exists.

Artificial cloning in animals raises scientific, ethical, welfare and economic arguments. For: cloning can preserve desirable traits such as high yield or disease resistance, produce many identical animals quickly, help conserve endangered species, and support research and medicine by giving genetically uniform animals. Against: cloned embryos and offspring can suffer health and welfare problems, success rates are low, and clones may have shortened lifespans or abnormalities. Cloning reduces genetic variation, making populations vulnerable to disease. There are ethical concerns about animal suffering and about creating animals for human use, plus cost and the question of whether cloning animals for food is acceptable. A strong answer balances benefits against harms and reaches a supported judgement rather than listing points.

Microorganisms are used in biotechnology because they grow rapidly, have simple growth requirements and can be genetically modified. In this section you learn how bacteria and fungi are exploited in processes such as fermentation, the production of enzymes, antibiotics, insulin and other proteins, and in food production such as cheese and yoghurt making. You should be able to link each process to the microorganism involved, the conditions it needs (for example a controlled temperature, a suitable substrate and aseptic technique) and the product formed. You should also recognise why microorganisms are chosen: fast reproduction, large surface area to volume ratio, ability to use waste materials as substrates and ease of genetic engineering. A multiple-choice question may ask you to identify a product, a suitable microorganism or a reason for using microbes rather than plants or animals.

Microorganisms such as bacteria, yeasts and fungi are used to make foods including cheese, yoghurt, bread, beer, mycoprotein and fermented products. Their advantages include rapid growth, high protein yield per unit area, ability to use cheap or waste substrates, independence from climate and season, and ease of genetic modification to improve products. Disadvantages include the risk of contamination or food poisoning if pathogenic microbes are present, the need for strict aseptic conditions and controlled temperature and pH, possible allergic reactions, consumer acceptability and the cost of sterilising equipment. You should be able to weigh these points and reach a supported judgement about whether using microorganisms to make food is beneficial, referring to specific examples such as mycoprotein production or cheese making.

Culturing microorganisms means providing a suitable nutrient medium, the right temperature and oxygen availability so that a population grows predictably, while excluding unwanted contaminants. Aseptic technique is the set of precautions that keeps the culture pure: sterilising apparatus and media before use, working close to a lit Bunsen flame so rising air carries contaminants away, flaming the neck of the vessel, using sterile loops and keeping lids on when not inoculating. Effectiveness also depends on choosing the medium, controlling temperature in an incubator and not opening plates unnecessarily. In an MCQ, expect to distinguish genuine aseptic steps from actions that merely look careful, such as wiping a bench with a dry cloth or leaving a plate open to cool.

Fermentation uses microorganisms to make a product, and yield depends on controlling conditions such as temperature, pH, oxygen supply and nutrient concentration. In batch fermentation the culture is closed: nutrients are added at the start, the microorganism grows through lag, exponential and stationary phases, and the product is harvested at the end before the culture is emptied and restarted. In continuous fermentation nutrients are added and product removed continuously, keeping the culture in exponential growth so product forms steadily over a long period. Manipulating conditions matters because too high a temperature or wrong pH reduces enzyme activity and product formation, while oxygen and nutrient levels control growth rate. An MCQ may ask which change would raise yield in a given system.

A closed culture (batch culture) contains a fixed volume of nutrient medium with no additions or removals, so nutrients fall and waste accumulates. The standard growth curve plots population size, often as log₁₀ of cell number, against time and has four phases. In the lag phase cells are metabolically active but not yet dividing, synthesising enzymes and ribosomes. In the exponential (log) phase, provided nutrients are plentiful and conditions suitable, the population doubles at a constant rate, giving a straight line on a logarithmic plot. Growth then slows in the stationary phase as nutrients become limiting and toxic waste builds up, so reproduction balances death. In the decline (death) phase, death exceeds reproduction and the population falls. Interpreting which phase a point lies in, and why the curve changes shape, is the core skill.

Practical investigations measure how factors such as temperature, nutrient concentration, pH or oxygen availability affect microbial growth. Learners plan a controlled investigation, choosing an independent variable and measuring a dependent variable such as turbidity, colony count or mass. Aseptic technique is essential: sterilising equipment, working near a flame and sealing plates to prevent contamination. Control variables such as volume, medium and incubation time must be kept constant. Results are recorded, often as a mean of replicates, and analysed to identify trends. Safety matters because microorganisms may be pathogens, so plates are incubated at safe temperatures and not opened after growth. Evaluation considers reliability through repeats and validity through controlling variables.

Immobilised enzymes are catalysts fixed to a solid support or trapped in a matrix so they stay in place while substrate flows past. This lets a product be made continuously, allows the enzyme to be recovered and reused, and reduces contamination of the product. Uses in biotechnology include producing lactose-free milk by immobilised lactase, making glucose syrup from starch using immobilised amylase, and producing high-fructose syrup with immobilised glucose isomerase. Methods of immobilisation include adsorption onto an inert support such as clay, covalent bonding to a support, entrapment in a gel such as alginate, and encapsulation in a semi-permeable membrane or microcapsule. Each method trades enzyme leakage against reduced activity or diffusion limits.