CBSE Class 12 Biology Chapter 12: Biotechnology and its Applications NCERT Solutions

Solution: The correct option is (b) toxin is inactive. The bacteria Bacillus thuringiensis produce the Bt toxin in an inactive precursor form called protoxin. This protoxin is not harmful to the bacteria themselves. It is only when the insect ingests the crystalline protoxin that it gets solubilized and converted into the active toxic form within the insect's alkaline digestive system, leading to cell lysis and death of the insect. The bacteria protect themselves by keeping the toxin in its inactive state.

Solution: Transgenic bacteria are microorganisms that have been genetically modified to contain foreign DNA, which is intentionally introduced into their genome. This foreign gene enables the bacteria to express a desired trait or produce a specific product that they would not naturally produce. These bacteria are crucial in biotechnology for the mass production of valuable compounds.

Example: Production of Human Insulin

A significant application of transgenic bacteria is in the production of human insulin. Historically, insulin for treating diabetes was extracted from the pancreases of pigs and cows, which could cause allergic reactions in some patients. Biotechnology revolutionized this process:

1. Gene Isolation: The DNA sequences corresponding to the A and B chains of human insulin are synthesized or isolated.
2. Plasmid Insertion: These synthesized DNA sequences are inserted into a plasmid, which is a small, circular DNA molecule found in bacteria, often using restriction enzymes and ligase.
3. Transformation: The modified plasmid, now carrying the human insulin genes, is introduced into a host bacterium, typically Escherichia coli (E. coli). The bacterium that successfully incorporates this foreign DNA becomes transgenic.
4. Expression and Production: The transgenic E. coli bacteria then express the inserted genes, producing the A and B chains of human insulin.
5. Extraction and Combination: The A and B chains are extracted from the bacterial culture. Subsequently, these chains are chemically combined to form functional human insulin, which is then purified for therapeutic use.

   The diagram illustrates the precursor forms like preproinsulin and proinsulin, which are processed within the bacterium or during subsequent steps to yield the final A and B chains.

Solution: Genetically modified (GM) crops, also known as transgenic crops, are plants whose genetic material has been altered using genetic engineering techniques. They offer significant benefits but also raise concerns.

Advantages of GM Crops:

• Pest Resistance: Many GM crops are engineered to be resistant to specific pests (e.g., Bt crops producing insecticidal toxins), which significantly increases crop productivity and reduces the need for chemical pesticides.
• Enhanced Nutritional Quality: Some GM crops are developed to have improved nutritional profiles. A prime example is 'golden rice', which is enriched with beta-carotene, a precursor to Vitamin A, helping to combat deficiency in populations reliant on rice as a staple.
• Improved Mineral Usage: These plants can be modified to increase the efficiency of mineral uptake from the soil, potentially preventing soil fertility loss.
• Abiotic Stress Tolerance: GM crops can be developed to withstand unfavorable environmental conditions such as drought, salinity, or extreme temperatures.
• Reduced Post-Harvest Losses: Genetic modification can help in developing crops that have a longer shelf life or are less susceptible to spoilage after harvest.

Disadvantages and Concerns Regarding GM Crops:

• Impact on Biodiversity: The widespread use of GM crops can potentially affect native biodiversity. For instance, if genes for toxins like Bt are expressed in pollen, it could harm beneficial insect pollinators such as honeybees, disrupting pollination processes.
• Human Health Concerns: There are ongoing debates about potential health impacts, such as the possibility of GM foods introducing new allergens or antibiotic resistance markers into the human body.
• Genetic Pollution: There is a risk of gene flow from GM crops to their wild relatives through cross-pollination. This 'genetic pollution' could alter the genetic makeup of wild populations, potentially leading to the development of 'superweeds' or impacting natural ecosystems.
• Ethical and Socio-economic Issues: Concerns also exist regarding corporate control over seeds, farmer dependency, and the ethical implications of altering the genetic makeup of organisms.

Solution: Cry proteins are a class of insecticidal proteins produced by certain bacteria, most notably by the soil bacterium Bacillus thuringiensis (Bt). These proteins are encoded by genes called 'cry' genes.

Organism Producing Cry Proteins: The primary organism known for producing Cry proteins is Bacillus thuringiensis (Bt). This bacterium naturally synthesizes these proteins as crystalline inclusions during its sporulation phase.

Human Exploitation of Cry Proteins: Man has effectively exploited the insecticidal properties of Cry proteins for agricultural benefits. The process involves:

1. Identification and Isolation: Specific cry genes that code for toxins effective against particular insect pests are identified and isolated from Bacillus thuringiensis.
2. Genetic Engineering: These cry genes are then introduced into the genome of crop plants, such as cotton (Bt cotton) and maize (Bt corn), using genetic engineering techniques.
3. Crop Protection: The genetically modified plants produce the Cry proteins within their tissues. When insect pests feed on these plants, they ingest the Cry proteins.
4. Mechanism of Action: In the alkaline environment of the insect's gut, the Cry proteins are activated into toxic forms. These toxins create pores in the gut lining, leading to cell disruption, paralysis, and ultimately the death of the insect pest.

This application has significantly reduced the need for synthetic chemical pesticides, leading to more environmentally friendly pest management strategies and increased crop yields.