PCR (polymerase chain reaction) is a technique used to make multiple copies (amplify) of a specific segment of DNA in a test tube (in vitro). It uses primers and a heat-stable DNA polymerase (Taq polymerase from Thermus aquaticus). Its three steps, repeated in cycles, are: (1) denaturation - the DNA is heated to separate the two strands; (2) annealing - the primers bind to the complementary sequences on the single strands at a lower temperature; and (3) extension - Taq polymerase extends the primers to synthesise new strands. Repeating the cycles increases the DNA exponentially.

A bioreactor is a large vessel (often thousands of litres) in which the raw materials are biologically converted into specific products by microbes, plant or animal cells or enzymes, under optimum controlled conditions of temperature, pH, oxygen and so on. The most commonly used type is the stirred-tank bioreactor. Downstream processing refers to all the processes carried out after the product has been formed in the bioreactor, such as separation and purification of the product, and its formulation with preservatives and quality control, before it is marketed as a finished product.

Genetically modified organisms (GMOs) are plants, animals or microbes whose genes have been altered (modified) by genetic engineering to introduce a desired character. Advantages of GM (genetically modified) crops: (1) they can be made more tolerant to abiotic stresses such as cold, drought, salt and heat; (2) they can be made resistant to pests, reducing the need for chemical pesticides (for example Bt cotton); (3) they can have improved nutritional value (biofortification, e.g. golden rice rich in vitamin A) and a longer shelf life; and (4) they can increase crop yield.

Bt cotton is a genetically modified variety of cotton that carries a gene (a cry gene) taken from the soil bacterium Bacillus thuringiensis (Bt). This gene codes for a protein (the Bt toxin) that is toxic to certain insect pests such as the cotton bollworm. The toxin is produced as an inactive protoxin (crystal), which, when eaten by the insect, is activated in the alkaline gut of the insect, binds to the gut cells and kills the insect. Thus Bt cotton is protected from the pest without using chemical insecticides.

Human insulin is produced by recombinant DNA technology (the product is called Humulin). Insulin consists of two short polypeptide chains, A and B, joined by disulphide bonds. In the method developed by the company Eli Lilly, the DNA sequences coding for the A and B chains were prepared and introduced separately into the bacterium E. coli; the bacteria produced the two chains separately. These chains were then extracted and joined together by disulphide bonds to form functional human insulin. This insulin is identical to human insulin and does not cause the allergies that animal insulin sometimes did.

Gene therapy is a collection of methods that allow the correction of a gene defect that has been diagnosed in a person; a normal (healthy) functional gene is introduced into the individual (or embryo) to replace or compensate for the non-functional defective gene, so that the normal function is restored. The first clinical gene therapy was given in 1990 to a girl suffering from adenosine deaminase (ADA) deficiency, a disorder of the immune system, in which functional ADA genes (in her lymphocytes) were introduced into her body.

Transgenic animals are animals whose DNA has been altered (manipulated) to carry and express an extra (foreign) gene from another organism. Uses: (1) they are used to study how a gene contributes to the development of a disease and to study normal physiology (for example, transgenic mice used to study diseases); (2) they are used to produce useful biological products, such as human proteins in their milk (for example, a transgenic cow producing human alpha-lactalbumin); and (3) they are used for testing the safety of vaccines and the toxicity of chemicals.

Biopiracy is the unauthorised use and exploitation of the bio-resources (plants, animals and microbes) and the traditional knowledge of a country or community by other organisations or nations, usually without proper permission or fair payment (for example, patenting the medicinal use of a plant known traditionally in India). The GEAC (Genetic Engineering Appraisal Committee) is an Indian government body that makes decisions regarding the validity and safety of genetically modified (GM) research and the safety of introducing GM organisms for public use.

Population density is the number of individuals of a population present per unit area or volume at a given time. Natality (birth rate) is the number of births (new individuals added to the population) per unit time. Mortality (death rate) is the number of deaths (individuals lost from the population) per unit time. A population grows when natality and immigration exceed mortality and emigration.

Exponential (geometric) growth occurs when resources (food, space) are unlimited; the population grows without any check and its growth curve is J-shaped. Logistic growth occurs when resources are limited; the population grows slowly at first, then rapidly, and finally slows down and levels off at the carrying capacity (the maximum number the environment can support), giving an S-shaped (sigmoid) curve. In nature, resources are usually limited, so logistic growth is more realistic.

An adaptation is any attribute (morphological, physiological or behavioural) of an organism that enables it to survive and reproduce in its habitat. For example, the desert kangaroo rat is adapted to conserve water: it can meet almost all its water requirement from the internal oxidation of the food it eats (fat) and it produces very concentrated urine, so it loses very little water. Similarly, desert plants have thick cuticles and sunken stomata to reduce water loss (transpiration).

The carrying capacity (denoted by K) of an environment is the maximum population size of a species that the resources of that particular environment can support and sustain indefinitely, without being degraded. When a population grows logistically, it increases until it reaches the carrying capacity, and then it levels off, because the limited resources cannot support any further increase. If the population exceeds K, it declines back due to shortage of resources.

An age pyramid is a diagram that shows the distribution of the individuals of a population in different age groups (pre-reproductive, reproductive and post-reproductive) at a given time. Its shape indicates the growth status of the population: a broad-based (triangular) pyramid indicates a rapidly growing (expanding) population with many young individuals; a bell-shaped pyramid indicates a stable population; and an urn-shaped (narrow-based) pyramid indicates a declining population.

Mutualism is a close, positive interaction between two different species in which both the species are benefited. Examples: (1) lichens, which are a mutualistic association between a fungus and an alga (the fungus provides shelter and absorbs water and minerals, while the alga provides food by photosynthesis); and (2) mycorrhiza, an association between a fungus and the roots of higher plants; and (3) the pollination of flowers by insects, where the plant is pollinated and the insect gets nectar as food.

An ecosystem is a functional unit of nature in which the living organisms (the biotic community) interact among themselves and with their physical (non-living) environment, exchanging energy and matter. Its two basic components are: (1) the abiotic (non-living) components, which include physical factors such as light, temperature, water, air, soil and inorganic nutrients; and (2) the biotic (living) components, which include producers (green plants), consumers (herbivores and carnivores) and decomposers (microbes).

A food chain is a linear sequence of organisms through which food energy passes from one trophic (feeding) level to the next, starting from the producers, for example: grass -> grasshopper -> frog -> snake -> hawk. A food web is a network formed by the interconnection of many food chains in an ecosystem, because most organisms feed on more than one type of food and are eaten by more than one type of predator. A food web gives greater stability to an ecosystem than a single food chain.

An ecological pyramid is a graphical representation of the relationship between the organisms at the various trophic levels of a food chain, with the producers at the base and the top carnivores at the apex. There are three types: (1) the pyramid of numbers (based on the number of individuals at each level); (2) the pyramid of biomass (based on the total dry weight of organisms at each level); and (3) the pyramid of energy (based on the amount of energy at each level). The pyramid of energy is always upright, whereas the pyramids of number and biomass may sometimes be inverted.

Gross primary productivity (GPP) is the total amount of organic matter (or energy) produced by the producers (green plants) during photosynthesis per unit area per unit time. Net primary productivity (NPP) is the amount of organic matter that is left and available to consumers after the producers have used up some of the gross production in their own respiration. Thus NPP = GPP - respiration (R). NPP represents the biomass available for the herbivores and decomposers.

NPP = GPP - respiration

Decomposition is the process by which decomposers (bacteria and fungi) break down the complex organic matter of dead plants and animals (detritus) into simple inorganic substances such as carbon dioxide, water and nutrients, which are released back into the environment. The main steps in decomposition are: fragmentation (breaking of detritus into smaller pieces by detritivores), leaching (water-soluble nutrients go down into the soil), catabolism (enzymatic breakdown into simpler compounds), humification (formation of dark humus) and mineralisation (release of inorganic nutrients).

Nutrient cycling (biogeochemical cycling) is the movement of nutrient elements through the various components (living and non-living) of an ecosystem in a cyclic manner, so that they are used again and again. In the carbon cycle, carbon (as carbon dioxide) is taken from the atmosphere by green plants during photosynthesis and fixed into organic compounds; it passes along the food chain to animals; and it is returned to the atmosphere as carbon dioxide through respiration by plants and animals, decomposition of dead matter by microbes, and the burning of fuels and wood.