CBSE Notes

By going through these CBSE Class 12 Biology Notes Chapter 14 Ecosystem, students can recall all the concepts quickly.

Ecosystem Notes Class 12 Biology Chapter 14

→ An ecosystem is a structural and functional unit of the biosphere which consists of a community of living beings and the physical environment, both of them interacting and exchanging materials between them. In short, the ecosystem is a self-supporting, stable ecological unit that results from an interaction between the biotic community and its abiotic’ environment.

→ The ecosystem has two main components: an abiotic component that includes all plants, animals, and microorganisms, and an abiotic component that includes soil, water, minerals, CO_2, and oxygen. It receives energy in the form of sunlight.

→ The biotic component of the ecosystem contains all the living members. These are connected to each Other by food and energy. They are divided into producers (autotrophs) and consumers (herbivores and carnivores) and decomposers.

→ Food is manufactured from inorganic raw materials by autotrophs only so they are called producers. They are mainly photosynthetic plants that contain chlorophyll. Consumers are animals that feed on plants (herbivores) directly, are called primary consumers, and animals that feed on other organisms or their parts are called secondary or tertiary consumers (carnivores).

Microorganisms break the dead organic matter into simple substances which are returned to the environment for reuse, they are called decomposers. Based on the source of nutrition every organism occupies a place in an ecosystem. This place is called a trophic level of the organism.

→ Productivity, decomposition, energy flow, and nutrient cycling are the main functions of an ecosystem. The nutrients are used again and again in a cyclic manner but energy trapped from sunlight is lost as heat.

→ A food chain consists of various trophic levels which include a producer, various levels of consumers, and a decomposer.

→ Food chains are of three kinds viz. predator, parasitic and saprophytic chain. The food chains are interlinked to each other. The various food chains in a community form a food web.

→ Primary productivity is the rate of capture of solar energy or biomass production of the producers. It can be, gross primary productivity (GPP) and net primary productivity (NPP). GPP is the rate of capture of solar energy or total production of organic matter. NPP is the remaining biomass or the energy left after the utilization of producers. Secondary productivity is the rate of assimilation of food energy by the consumers. Decomposition is the breakdown of complex organic compounds of detritus into CO₂, water, and inorganic nutrients. It involves three processes: fragmentation of detritus, leaching, and catabolism.

→ Energy flow is unidirectional. The number of materials and energy transferred as food through successive higher trophic levels progressively decreases.

→ The graphic representation of the relationship of food and energy between organisms at different trophic levels is called pyramids. The base of each pyramid represents the producers and the apex represents the tertiary consumer.

The ecological pyramids are of three types:

1. pyramid of number,
2. pyramid of biomass and
3. pyramid of energy.

Mostly the pyramid of number and biomass are upright but sometimes the pyramid of biomass may be of the inverted type, e.g. in a sea. The pyramid of energy is always upright.

The inverted pyramid of biomass. A small standing crop of phytoplankton supports a large standing crop of zooplankton.

→ Biosphere or ecosphere is the part of the earth inhabited by organisms and their living and non-living environment. The earth is a closed system regarding materials. The substances vital for life are limited and must be recycled to sustain life. The earth is an open system regarding energy. It receives energy from the Sun in the form of solar energy, a part of it is trapped by living organisms and the major part is radiated back to outer space. The biosphere consists of the atmosphere, lithosphere, and hydrosphere.

→ The storage and movement of nutrient elements through the various components of the ecosystem is called nutrient cycling or Biogeochemical cycle, bio: living organisms, geo: rocks, air, water.

Nutrient cycles are of two types:

1. Gaseous cycle: It has carbon, hydrogen, oxygen, and nitrogen as a reservoir and exists in the atmosphere and
2. Sedimentary cycle: It has phosphorus, sulfur, calcium, potassium, etc. as a reservoir and is located in the earth’s crust.

The gaseous cycles are more balanced than the sedimentary cycles. The reservoir compensates for the deficit which occurs due to an imbalance in the rate of influx and efflux.

→ Biomes are regional, integrated, natural biotic units, which can be identified by the forum of life of the climax vegetation. Biomes may also include developing and modified communities, within the same climatic region like forest biomes will include young successional forests and open grass-dominated tracts.

The three major biomes are:

1. forest biome,
2. grassland biome, and
3. desert biome.

Each biome has a characteristic array of plants and animal life. Climatic and edaphic factors, latitude, and barriers determine the extent of a biome.

→ Ecotones are the zones present between adjacent biomes, these support some organisms from each adjoining biome and some typical characters of their own.

→ Abiotic components: Consists of environmental factors. These are inorganic substances, organic substances, and climatic factors.

→ Biotic components: These comprise various kinds of organisms which are producers. consumers and decomposers.

→ Biome: Biomes are regional, integrated, natural biotic units, which are identified by the life form of the climax vegetation.

→ Biotics: Study of the functions of life.

→ Boreal forest: Another name of the taiga.

→ Biodegradation: Breakdown of organic and inorganic material by bacteria and fungi.

→ Consumers: Organisms that depend upon producers for food. These are herbivores and carnivores.

→ Canopy: Part of a woodland or forest community that ¡s formed by the trees.

→ Community retrogression: The reversal of ecological succession due to a disturbance in some serai stage like the destruction of grass by overgrazing.

→ Decom posers: Heterotrophic organisms like bacteria and fungi. They recycle the nutrients in the ecosýstem.

→ Epilimnion: tipper layer of warm water in a stratified lake.

→ Eutrophic: Water body rich in nutrients.

→ Edge effect: Tendency of ecotone to have a greater number of species and higher population density as compared to adjacent communities.

→ Forb: Any herbaceous plant other than grass.

→ Ecotone: Transitional zone between two vegetation regions.

→ Ecotype: The climate and edaphic factors of a place constitute ecotype.

→ Hygrometer: Instrument to measure the humidity of air or gas.

→ Incomplete ecosystem: Lacks one or more basic components e.g. deep sea, due to absence of light lacks producers.

→ Limnology: Study of freshwater bodies like lakes.

→ Meteorology: Study of atmospheric phenomena like forecasting weather.

→ Nutrient cycle: The movement of nutrient elements through the various components oían ecosystem.

→ Oiigatrohic: Water body poor in nutrients.

→ Productivity: The rate of biomass production.

→ Phenology: Study of periodic phenomena of plant and animal life like breeding, migration in relation to seasonal changes.

→ Rain gauge: Instrument for measuring rainfall.

→ Root detritus: Detritus formed by dead, underground roots of plants.

→ Photosynthetic active radiation (PAR): Visible light which carries about 50% of the energy of total incident solar radiation and iš available to producers for absorption.

→ Standing biomass: The biomass present in an ecosystem at a given time.

→ Standing crop: Amount of living material in a component population of a specific trophic level at a given time.

→ Stratification: Vertical distribution of different species occupying different levels.

→ Species composition: Identification and enumeration of plant and animal species of an ecosystem.

By going through these CBSE Class 12 Biology Notes Chapter 13 Organisms and Populations, students can recall all the concepts quickly.

Organisms and Populations Notes Class 12 Biology Chapter 13

→ Ecology is the study of the relationship of living organisms with the abiotic and biotic components of their environment.

→ Ecology is concerned with four levels of biological organization. These include – organisms, populations, communities, and biomes.

→ Regionals and local variations within each biome lead to the formation of a wide variety of habitats.

→ Temperature, light, water, and soil are the most important physical factors of the environment to which the organisms are adapted in various ways.

→ The physicochemical components alone do not characterize the habitat of an organism completely; the habitat includes biotic components also – pathogens, parasites predators, and competitors of the organism with whom it interacts constantly.

→ In the face of changing external environment, maintenance of a constant internal environment (homeostasis) by the organisms, contributes to optical performance, but only some organisms (regulations) are capable of homeostasis.

→ Some species have evolved adaptations to avoid unfavorable conditions in space (migration) or in time (aestivation, hibernation, and diapause).

→ A population is a group of individuals of a given species sharing or competing for similar resources in a defined geographical area.

→ In a population, the proportion of different age groups of males and females is often presented graphically as an age pyramid. The shape of the pyramid indicates whether a population is stationary, growing, or declining.

→ On a population, the ecological effects of any factors are generally reflected in its size, which may be empressed in different ways depending on the species.

→ The size of a population keeps changing in time, depending on various factors, including food availability, predation pressure, and reduce weather. The changes in population density give us some idea of what is happening to the population – whether it is flourishing or declining.

→ Natality refers to the number of births during a given period in the population that are added to the initial density.

→ Mortality is the number of deaths in the population during a given period.

→ Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.

→ Emigration is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

→ Populations grow through births and immigration and decline through deaths and emigration. Growth in both cases is ultimately limited by the carrying capacity of the environment. The intrinsic rate of natural increase (r) is a measure of the inherent potential of a population to grow.

→ Populations of different species, in nature, in a habitat do not live in isolation but interact in many ways. These interactions between two species are classified as competition, predation parasitism, commensalism, and mutualism.

→ One of the most important processes is predation. Through this process, trophic energy transfer is facilitated and some predators help in controlling the prey populations.

→ In competition, the superior competition eliminates the inferior one. However many closely related species have evolved various mechanisms which facilitate their co-existence.

→ Ecology: A study of the relationship of living organisms with abiotic and biotic components of their environment.

→ Population: A group of individuals of a given species sharing or competing for similar resources in a defined geographical area.

→ Abiotic: Non-living components such as temperature. light. water and soil.

→ Biotic: Living components such as plants, animals, human beings, and micro-organisms.

→ Age pyramids: The age distribution of males and females in a combined diagram.

→ Population density: Refers to population size.

→ Natality: Refers to the number of births during a given period in the population that are added to the initial density.

→ Mortality: Refêrs to the number of deaths in the population during a given period.

→ Immigration: Refers to a number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.

→ Emigration: Refers to a number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

→ Migration: Moving organisms temporarily from the stressful habitat to a more hospitable area and return when the stressful period is over.

→ Hibernation: Refers to winter sleep undertaken by animals to save themselves from extreme cold conditions.

→ Diapause: A stage of suspended development.

→ Mutualism: interspecific interaction in which both the species benefit.

→ Competition: Interspecific interaction in which both the species lose.

→ Parasitism: Interspecific interaction in which one species benefits and the interaction is detrimental to the other species.

→ Commensalism: The interaction where one species is benefitted and the other is neither benefitted nor harmed.

→ Amensalism: The interaction in which one species is harmed whereas the otheî is unaffected.

By going through these CBSE Class 12 Biology Notes Chapter 12 Biotechnology and its Applications, students can recall all the concepts quickly.

Biotechnology and its Applications Notes Class 12 Biology Chapter 12

→ Biotechnology is the interaction between technology and biology. It is as old as human civilization. It may be defined as ‘The controlled use of biological agents, such as micro-organisms or cellular components, for beneficial use’. It deals with the industrial-scale production of biopharmaceuticals using genetically modified organisms.

→ The main objectives of biotechnology are:

1. providing the best catalyst (improved organism) like a pure enzyme or some micro¬organism,
2. Creating optimum conditions for the catalyst to perform,
3. Downstream processing techniques for the purification of the organic compound.

→ Food production can be increased in three ways,

1. Agrochemical based agriculture,
2. Organic agriculture,
3. Genetically engineered crop-based agriculture.

Crop yields are increased by using improved crop varieties and agrochemicals maximise the yield.

→ Genetically Modified Organisms (GMO) are plants, bacteria, fungi and animals whose genes are altered for human or animal consumption using the latest molecular biology techniques. The genetic modifications have made crops more tolerant to abiotic stresses like cold, drought, salt, heat etc.; reduced reliance on chemical pesticides by making pest-resistant crops, helped to reduce post-harvest losses, increased efficiency of mineral usage by plants, enhanced nutritional value of food, for example, vitamin A-rich rice.

The enhancement of desired traits has traditionally been undertaken through breeding, but conventional plant breeding methods can be very time consuming and are often not very accurate. Genetic engineering can create plants with the exact desired traits very rapidly and with great accuracy.

For example, geneticists can isolate a gene responsible for drought-tolerant and insert it into a different plant. The new genetically modified plant will gain drought tolerance. The characteristic of a genetically modified organism depends on the nature of genes transferred and the nature of the host plant as well as some regulatory environmental factors.

→ Recombinant DNA technology or genetic engineering is the latest technique that transfers one or more genes (DNA fragments) from one plant to another. The plant in which a foreign gene is introduced is called a transgenic plant. Two techniques are used to introduce foreign genetic material into the plant cell genome. One is through a vector and the other is direct introduction of DNA.

→ Several transgenic plants have been developed, one example is Bt cotton. Bt is a toxin produced by the bacterium Bacillus Thuringiensis. B toxin gene is cloned from bacterium and expressed in plants to provide resistance from insect without using insecticides. Thus by the application of biotechnology pest-resistant plants are developed. Some other examples are Bt com, Bt rice, Bt tomato, potato and soybean.

→ Bacillus Thuringiensis produces proteins that kill some insects like lepidopterans, e.g. tobacco budworm and armyworm, coleopterans like beetles, dipterans, e.g. flies and mosquitoes. B.Thuringiensis is a soil bacterium that forms some protein crystals which contain a toxic insecticidal protein that is present as inactive protoxin, when an insect ingests it, the inactive toxin is converted to the active toxin by the alkaline pH of the gut. The activated toxin bind to the surface of midgut epithelial cells and creates pores which cause swelling and lysis and ultimately death of the insect.

→ The toxin produced by B.thuringiensis is called Cry protein. The gene encoding Cry protein is called the Cry gene. There are several kinds of Cry proteins that are toxic to different groups of insects for example genes Cry-I AC and Cry-II Ab control the cotton bollworms, Cry-I Ab controls corn borer, Cry III Ab controls Colorado potato beetle and Cry-III Bb controls com rootworm.

→ Biotechnologists isolated the toxin-producing genes arid introduced into other crop plants with the help of Agrobacterium Ti-plasmid. These transgenic plants are resistant to insects and pests. Their prime advantage is the production of labour free insect protection of plants and also restrict the use of pesticides which helps in making soil and groundwater pollution-free.

Cotton boll (a) destroyed by bollworms and (b) a fully mature cotton boll (to be redrawn)

→ Another strategy is used to control nematode infestation of tobacco plant roots. Two normal nematode genes were introduced into the tobacco plant by the Agrobacterium vector. The tobacco plant makes a double-stranded RNA (dsRNA) with these genes. The dsRNA binds to mRNA and interfere with nematode RNA. This neutralises the nematode and it dies. The transgenic tobacco plant is protected from the parasite.

→ Modem biotechnology is contributing a lot to the field of medicine, for disease diagnosis and disease therapy. For example, insulin used to cure diabetes was earlier extracted from slaughtered cows and pigs, which may develop allergies. It was quite tiresome and difficult and the yield was very low.

Now by using recombinant DNA technology insulin can be produced by the fermentation of appropriate recombinant E.Coli clones. This method can produce large quantities of pure insulin in a short time and a small space. On 5th July 1983, an American firm Eli Lilly launched the first genetically engineered human insulin, which was named Humulin.

→ Insulin consists of 51 amino acids arranged in two short polypeptide chains viz. Chain A (21 amino acids) and Chain B (30 amino acids). Chain-A and Chain-B are linked together by (S-S) disulphide bridges.
proinsulin

Maturation of pro-insulin into insulin after removal of C-peptide (to be simplified)

In mammals, insulin is produced as a prohormone which contains an extra stretch of C-peptide. This C-peptide is removed during the processing and maturation of prohormone and produces functional and fully mature insulin.
In recombinant techniques, the genes corresponding to both chains A and B are introduced in plasmids of E.Coli, which produces insulin chains. Chain-A and Chain-B are produced separately, extracted and joined together by disulphide bonds. This produces human insulin.

→ Gene therapy is a collection of methods that allows the correction of a gene defect present in an embryo or a child. It involves the delivery of a normal gene into the individual to take over the function of the defective gene. A genetic disorder caused by a single defective gene can be corrected by replacing this with a normal gene. Some genetic diseases like severe combined immunodeficiency (SCID) can be cured using gene therapy.

The SCID patients have adenosine deaminase (ADA) deficiency, this enzyme is crucial for the immune system to function. The patient lacks functional T-lymphocytes and fails to fight the infecting pathogens. Children with ADA deficiency are cured by bone marrow transplantation or by enzyme replacement therapy, where ADA is given by injection. By using gene therapy techniques, lymphocytes are taken from the patient’s bone marrow and the normal gene for ADA is introduced into the lymphocytes using retrovirus. These cells are reintroduced in the patient’s immune system.

→ Polymerase Chain Reaction (PCR) helps a lot in the early diagnosis of a disease, prenatal disorders and even the presence of the HIV virus. It is a powerful technique to find many genetic disorders, suspected cancer patients, and disease before the arrival of the symptoms. Genetic cloning helps in developing sensitive diagnostic techniques like ELISA and to identify a normal mutant gene.

→ Transgenic animals have their DNA manipulated to contain and express an extra or foreign gene. These are produced for various reasons like to study the process of gene regulation, how gene help in the development of diseases like cancer, Alzheimer etc., to produce useful biological products for humans, for testing medicines and vaccines before using them for humans, for testing the toxicity of any new drug in less time.

→ Intellectual Property Right (IPRs) are the rights to make, use and sell a new product or technology for 20 years. A patent is an official document to give all rights to make, use or sell an invention and prevent others from copying it.

→ Biopatents are government protection for biological agents and their products. It can be granted for genetically modified microbes, newly established cell times, genetically modified plants and animals, gene sequences, protein sequences, biotechnological procedures, production processes, new products and production applications.

→ Biopiracy is the use of bio-resources and genetic resources indigenous to a country by some organisations without proper authorisation or compensatory payment. Bio-piracy is widespread in Asia, Africa and Latin America which have the most diverse ecosystems in the world and produce abundant bio-resources.

→ Genetically modified crops and organisms have found higher acceptance in industry and agriculture but these deprive farmers to use their year’s harvest as seed for next year or share it with someone else. The plant variety protection and Farmer’s Right Act grants plant breeders, right on a new variety of seeds. The Farmer’s Rights Act has granted farmers to save, use, sow, and exchange, share or sell their farm product.

→ Antibiotics: An antibiotic is an organic compound produced by a microorganism that inhibits the growth of the other-micro organism.

→ Antisense nucleic acid: This is single-stranded molecules of DNA or RAN which base pairs with mRNA of virus and block their translation.

→ Bt cotton: It is a variety of cotton which contains the Bt toxin from Bacillus thuringienSis that kills certain insects.

→ Biopiracy: Biopiracy is the theft of biological and genetic resources without proper authorisation or compensation from the concerned countries.

→ Biopatent: Biopatents are patents given to biological agents and their products, exclusive right for their manufacturing, using and selling fr a specific period.

→ DNA vaccines: DNA vaccines use one or more isolated genes of a pathogen. incorporate into plasmids and inject them into the muscle or delivered into the human body.

→ Enzymes: Enzymes are bio-catalysis which catalyse biological reactions without undergoing any change. They are proteinaceOuS in nature.

→ Humulin: Humulin is a commercial name given to human insulin.

→ Monoclonal antibodies: Monoclonal antibodies are derived from a single parent and are specific for antigens.

→ Probe: A probe is a piece of single-stranded DNA that is tagged with a radioactive molecule.

→ Recombinant proteins: These are proteins produced by transgenes. These are used to treat diseases and as vaccines.

→ Stem cells: The cells of a young embryo are called stern cells. These are pluripotent i.e.: they can transform into any of 220 cell types of the human body.

→ Steroids: Steroids are complex crystallisable lipids of high molecular weight which possess a tetracyclic hydrocarbon core and along side chain, e.g. cholesterol.

→ Transgenic organisms: These are organisms that have had their DNA manipulated to contain and express an extra (foreign) gene.

→ Terminator seeds: The seeds produced by genetic engineering develop into fertile parents but produce non-germinable seeds.

→ Vaccines: Vaccine ¡sa liquid containing dead or attenuated pathogen or its antigen which provides temporary or permanent immunity to a disease.

→ Vitamins: Vitamins are accessory food factors that are required in small quantities for various metabolic processes of the body.

By going through these CBSE Class 12 Biology Notes Chapter 11 Biotechnology: Principles and Processes, students can recall all the concepts quickly.

Biotechnology: Principles and Processes Notes Class 12 Biology Chapter 11

→ The European Federation of Biotechnology (FEB) has defined biotechnology as ‘The integration of natural science and organisms, cells, parts thereof, and molecular analogues for products and services. Biotechnology is a science which deals with techniques of using live organisms or enzymes from organisms to produce products and processes useful for man.

All microbes mediated processes, genetically modified organisms, test-tube babies, in vitro fertilization, synthesising a gene, developing a DNA vaccine all processes are a part of biotechnology.

→ Genetic engineering is the science that deals with the synthesis of artificial genes, repair of genes, combining genes from two organisms (recombinant DNA) and manipulation of artificial genes for the improvement of living organisms.

To grow the desired microbe in large quantities for the production of antibiotics, vaccines or enzymes etc., it is very important to maintain microbial-contamination free sterile conditions.

→ For genetically modifying an organism three things are necessary which are:

1. modification of DNA,
2. the introduction of modified DNA into the host,
3. maintenance of introduced DNA in the host and transfer of this DNA in the next progeny.

→ In 1972, Stanley Cohen and Herbert Boyer constructed the first recombinant DNA molecule. They isolated an antibiotic resistance gene and linked it with a native plasmid of Salmonella typhimurium.

→ Plasmids are autonomously replicating circular extrachromosomal DNA. Plasmids are the most widely used cloning vectors. These are double-stranded, circular DNA molecules that can self replicate. A suitable plasmid vector has three properties like low molecular weight, ability to confer readily with selected phenotype traits on host cells and single sites for a large number of restriction endonucleases.

The plasmids carry genes for sexuality, antibiotic resistance etc., but not any vital genes. The cell can survive without them. They can replicate independently of the main genome and being small, can easily come out or get into a cell.

→ Recombinant DNA techniques include DNA at specific sites by using enzymes restriction endonucleases and joining the fragments by enzyme ligases.

It includes the following steps:

1. DNA fragments coding for proteins of interest is synthesized chemically or isolated from an organism.
2. These DNA fragments are inserted in a restriction endonuclease cleavage site of the vector that does not inactive any gene required for vector’s maintenance.
3. The recombinant DNA molecules are now introduced into a host to replicate.
4. Recipient host cells that have acquired the recombinant DNA, are selected. Selection pressure is applied to enrich bacteria with a selectable marker.
5. Desired clones are then characterised to ensure that they maintain true copies of the DNA segment that was originally cloned.

Sequential steps in the formation of recombinant DNA

→ The tools for genetic engineering or recombinant DNA technology are restriction enzymes, polymerase enzymes, biases, vectors and the host organism. After cutting a suitable gene with a restriction enzyme, it is associated with an origin of replication, only then it can multiply itself after insertion into the host genome.

→ Restriction enzymes are also called molecular scissors. In 1968, H.O. Smith, K.W. Wilcoxand T.J. Kelley isolated and characterised the first restriction endonuclease. Hind II from Haemophilus Influenzae bacteria. They found that Hind II always cut DNA at a specific sequence known as recognition sequence. With the help of restriction enzymes, it is possible to cut a DNA sequence. Restriction enzymes belong to class nucleases. These may be of two types-endonucleases and exonucleases.

The action of DNA cleaving enzymes

→ Restriction exonucleases, cut the DNA from the ends and restriction endonucleases cut at a specific position within the DNA, e.g. Restriction endonuclease ECORI will cut DNA only if sequence:
5′ — GAATTC — 3′
3′ — CTTAAG — 5′
is present. It cuts the DNA between bases G and A only when sequence GAATTC is present in the DNA (shown in the figure above)

→ The restriction enzyme will act on both the strands and produce a break. If the vector and the source DNA are cleaved using the same restriction enzyme they will have the same kind of sticky ends which can be joined by DNA ligases to produce a recombinant vector.

→ When restriction enzymes make a cut in the DNA strand, it will leave single-stranded portions at the ends. These are overhanging, called sticky ends. Sticky ends can form hydrogen bonds with their complementary cut counterparts by DNA ligases.

→ Palindromes are DNA sequences with base pairs that read the same on the two strands when the orientation of reading is kept the same. For example:
5′ — GAATTC — 3′
3′ — CTTAAG — 5′
In both the strands if read from 5? direction it will be the same. These are the sites for restriction enzymes.

→ After cutting the DNA with restriction enzymes, the fragments of DNA are separated by gel electrophoresis. DNA molecules being negatively charged move towards an anode under an electric field. The matrix used is a natural polymer, agarose. It acts as a sieve and DNA fragments separate according to their size.

DNA fragments can be seen after staining with ethidium bromide, an orange coloured bands when exposed to UV light. The separate strands can be cut from agarose gel and eluted by using various techniques. The selected DNA fragments, purified by gel electrophoresis are used for recombinant DNA construction.

→ Cloning vectors: The vector is an agent which is used to transfer DNA into the host cell. For example plasmid, bacteriophages. The vector is cut with the same restriction endonuclease which was used for chromosomal DNA fragments. The linearized vector and chromosomal DNA fragments are joined together by DNA ligases. Those plasmids which contain an inserted DNA fragment are called recombinant plasmids.

→ Similar to plasmids, bacteriophages can replicate within the bacterial cell independently of the control of chromosomal DNA.

Sometimes there are several copies of plasmids or a high number of bacteriophages per cell if an airy foreign DNA segment is inserted into these vectors a large number of a selected gene can be produced.

To attach a desirable gene to these vectors, the vectors are to be modified: The inserted gene must be attached with an origin of replication to start replication in the host cell, the vector needs a selectable marker so as to identify the recombinant vector. For example, a normal E.Coli cell does not carry resistance to antibiotics like tetracycline, ampicillin etc. so if the cells show resistance towards these antibiotics they are suitable recombinant vectors with suitable markers.

→ To link the desirable DNA with the vector, one or very few recognition sites for restriction enzymes is required. One recognition site will linearise the vector, several recognition sites will complicate the process. The recombinant vectors from non-recombinant vectors can be selected by a replica plating process or by using enzyme β-galactosidase activity on its colour producing substrate. The non-recombinants will produce colour due to active β-galactosidase and recombinants do not produce any colour.

→ For the purpose of clearing genes in plants and animals some vectors like disarmed (cancerous) retroviruses and modified (tumour inducing) plasmid of Agrobacterium tumefacient are used to deliver desirable genes into animals and plants cells respectively.

→ DNA is a hydrophilic molecule that cannot pass through cell membranes. The bacterial cells are made competent or forced to take up DNA. It can be done by the specific concentration of divalent ions like calcium (Ca²⁺) which increases the efficiency of DNA uptake through cell wall pores. Then the cells are incubated on ice followed by heat shock (at 42°C) and then back to ice. Other ways are microinjection i.e.; direct injection of recombinant DNA by animal cell by using a small needle. Gene gun or biolistics is used for plant cells, cells are bombarded with high-velocity micro gold or tungsten particles coated with DNA.

→ Polymerase chain reaction (PCR) is used to produce many copies of the same gene without using cells. The DNA is incubated in a test tube with DNA polymerases and a mixture of deoxy-ribonucleotides and primers. PCR can make billions of copies of DNA in few hours whereas using bacteria for the same thing will take days. It is the best way to detect an elusive infection, rapid prenatal diagnosis of genetic disorders, and even identification of criminals from tiny samples of blood, tissue or semen by amplification and identification.

→ Bioreactors provide the optimum conditions for getting the desired product by providing optimum growth conditions like temperature, pH, substrate, salts, vitamins and oxygen etc. Bioreactors can be aerobic, submerged, surface and anaerobic type. The most commonly used is the stirring type. A stirrer type bioreactor has an agitator system, an oxygen delivery system, a foam control system, a temperature control system, a pH control system, sampling pouts to withdraw small volumes of culture.

→ Genetic engineering: It is a process by which manipulation of the genetic material of an organism is done.

→ Biotechnology: It is the use of living organisms or of substances obtained from them in the industrial process.

→ Bioreactor: The fermentation tank where fermentation is carried out in the presence of micro-organisms.

→ Broad-spectrum antibiotics: These are the antibiotics that have the ability to act on several pathogenic species.

→ Hybridomas: The hybrid cells of the same clone themselves are known as hybridomas.

→ Monoclonal antibody: The same type of antibody produced by the same clone of all the hybrids.

→ Restriction enzyme: An endonuclease that recogniseS Specific nucleotide sequences in DNA and then makes a double-strand cleavage of DNA molecule.

By going through these CBSE Class 12 Biology Notes Chapter 10 Microbes in Human Welfare, students can recall all the concepts quickly.

Microbes in Human Welfare Notes Class 12 Biology Chapter 10

→ Microorganisms are present everywhere in soil, air, and water and inside plant and animal bodies. They can withstand severe climatic conditions like very high (100°C) or very low (~50°C) temperatures, high acidic (pH2) conditions, etc. These may be bacteria, viruses, fungi, cyanobacteria, bacteriophages, viroids, and prions.

→ In the middle of the nineteenth century, Louis Pasteur observed that alcoholic fermentation of sugar required the multiplication of yeast cells.

→ Fermentation is the oldest microbial process.
It is of two types:

1. Batch process and
2. Continuous process.

→ An antibiotic is an organic compound produced by a microorganism that inhibits or kills another microorganism.

→ Although there are around 7000 antibiotics, known to exist, only about 150 are marketed, 10 are produced on large scale and about 300 new antibiotics are discovered every year.

→ The most common antibiotics and their sources are – Penicillin (Penicillium Notatum), Poly mixin-B (Bacillus Polymixa), Neomycin (Streptomyces Fradiae), Erythromycin (Streptomyces Erythraens), Chloramphenicol (Streptomyces Venezuela).

→ Vitamins are essential dietary factors that are required by us in small amounts. Out of all vitamins produced during the normal metabolism of microorganisms only two viz. Vitamin Bp and Vitamin B, are manufactured biotechnologically.

→ The important organic acids produced on a commercial scale by using microorganisms are acetic acid, citric acid, lactic acid, fumaric acid, gluconic acid, itaconic acid, kojic acid, butyric acid, and gibberellic acids.

→ Many microorganisms are known to transform naturally occurring steroids. These modified steroids have much medicinal importance.

→ By using recombinant DNA technology insulin is being produced using micro-organisms, which is similar to human insulin and is called humulin.

→ Streptokinase from streptococcus bacterium acts like a clot buster. It is helpful for patients who have undergone myocardial infarction.

→ Cyclosporin: A from the fungus Trichoderma polypore is used as an immunosuppressive agent and useful in organ transplantation.

→ Statins from yeast Monascus purpose is a blood cholesterol-lowering agent.

→ The municipal wastewater is called sewage. It contains large amounts of organic matter and many pathogenic microbes. In sewage treatment plants the treatment of wastewater is done by the heterotrophic microbes present in sewage.

→ Sewage treatment takes place in two main steps:

1. primary treatment and
2. secondary treatment.

In some advanced sewage treatment plants, it also undergoes tertiary treatment.

→ Primary treatment is done to remove large objects from the sewage. Sewage is passed through 2-8 cm apart steel bars, then through the wire mesh of reducing pores. It is passed through the grit chamber and then through the settling tank where most suspended material settles down as sludge.

→ The effluent flows for secondary treatment. First, the effluent is passed into aeration tanks where it continuously agitated and allows microbial growth. The microbes consume the organic matter and decrease the biological oxygen demand (BOD) of the effluent. It then passes to the settling tank where the sediment is called activated sludge.

It is passed to anaerobic sludge digesters where the anaerobic bacteria digest it further and produce gases like methane, H₂S, and CO₂. This is called biogas and can be used as fuel. The effluent may undergo tertiary treatment or released into natural water bodies.

→ Methanogens are bacteria that grow anaerobically on cellulose-rich materials and produce a large amount of methane gas with CO₂ and H₂. It is called biogas and is used as fuel. Methanogens are found in anaerobic sludge and also in cattle rumen where they come out in dung, so dung (rich in cellulose) can be used to generate biogas.

Biogas plant

→ Biofertilizers are the microorganisms that enrich the soil with nutrients and maximize the ecological benefits and minimize environmental hazards. These include nitrogen-fixing bacteria, cyanobacteria, and fungi.

→ Manures are partially decomposed organic materials added to the soil to increase fertility of the soil.
These are of three types:

1. farm-yard manure,
2. compost, and
3. green manure.

→ The disadvantages of chemical fertilizers and pesticides can be overcome by the use of alternative harmless manures, biofertilizers, biological control methods, and biopesticides.

→ The various types of biofertilizers are:

1. Microphones bio fertilisers,
2. Free-living nitrogen-fixing bacteria like Azotobacter,
3. Symbiotic nitrogen-fixing bacteria forming an association with legumes like Rhizobium,
4. A loose association of nitrogen-fixing bacteria like Azospirillum,
5. Cyanobacterial biofertilizers and
6. Azolla-Anabaena symbiosis.

→ Mycorrhizae are the symbiotic association of fungi with the roots of higher plants. These may be ectomycorrhizae and endomycorrhizal.

→ The ectomycorrhiza is characterized by the formation of a sheath or mantle on the surface of roots. They help in the absorption of water, absorption of inorganic nutrients, and protection of plants from pathogen attack.

→ The endomycorrhiza does not form an external sheath or mantle. The fungi mycelium penetrates into the roots and lives in the intercellular spaces as well as intracellularly in the cortical cells. Some endomycorrhizal are called vesicular-arbuscular mycorrhizae (VAM). They develop vesicles and arbuscules within the cells of the root. These fungi stimulate the absorption of phosphorus, zinc, copper, sulfur, potassium, and various other elements by the roots.

→ Biopesticides are pesticides of biological origin or biological control agents which are used to control weeds and pests.
They are two main types

1. Bioherbicides and
2. Bioinsecticides.

→ Bioherbicides or biological control of weeds involve the utilization of biological agents (such as insects, fungi, bacteria, nematodes, parasitic plants, etc.) which suppress or kill the weedy plants without causing significant injuries to other plants.

→ Bioinsecticides or the control of harmful insects by biological methods include

1. The use of pathogens, parasites, and predators;
2. Sterilization strategy;
3. Use of insect hormones; and
4. Use of natural insecticides.

→ Antibiotic: An antibiotic is a substance produced by a microorganism that inhibits the growth of other microorganisms.

→ Bioreactor: The fermentation tank where fermentation is carried out in the presence of micro-organisms.

→ Broad-spectrum antibiotics: The antibiotics which have the ability to act on several pathogenic species differing from each other in structure and composition of the cell wall.

→ Biological control: introduction of living organism which destroys other harmful organisms.

→ Chemical control: Use of chemical substances such as smoke, gas, dust, and sprays to poison pests.

→ Fermentation: The anaerobic oxidation of food in the presence of micro ‘organisms which result in the production of alcohol and waste ga CO₂.

→ Fertilizer: Substance added to soil to increase the yield of crop plants.

→ Fungicide: Substances used for killing fungi.

→ Farmyard manure: The manure consisting of a mixture of cattle dung a4id crop residue.

→ Legume: The plants of the pea family i.e. Luguminosae e.g. pea plant beans etc.

→ Manure: The substances which are added to soil to increase crop yield.