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 form, known as prototoxin. This prototoxin is a precursor that gets converted into its active insecticidal form only when it is ingested by a susceptible insect larva and encounters the alkaline conditions and specific enzymes present in the insect's gut. The bacteria themselves are not harmed because the toxin remains in its inactive prototoxin state within their cellular environment.

Solution: Transgenic bacteria are microorganisms that have been genetically engineered to contain foreign DNA, meaning they possess genes that were not originally part of their own genome. This intentional introduction of specific genes allows the bacteria to acquire new characteristics or to produce valuable substances that they would not naturally synthesize.

A prominent example is the use of the bacterium Escherichia coli (E. coli) in the production of human insulin. Scientists insert the DNA sequences that code for the A and B chains of human insulin into a plasmid, which is a small, circular piece of DNA found in bacteria. This modified plasmid is then introduced into E. coli cells, transforming them into transgenic bacteria. These engineered bacteria then express the inserted genes and begin producing the human insulin chains. Subsequently, these chains are extracted from the E. coli and chemically joined together to form functional human insulin, which is used to treat diabetes.

The process involves:

1. Isolating the genes for human insulin A and B chains.
2. Inserting these genes into a plasmid vector.
3. Introducing the recombinant plasmid into E. coli.
4. Culturing the transgenic E. coli to produce insulin chains.
5. Extracting and combining the A and B chains to form active insulin.

Solution: The production of genetically modified (GM) crops, also known as transgenic crops, offers significant advantages but also presents potential disadvantages and concerns.

Advantages:

• Pest Resistance: Many GM crops are engineered to be resistant to specific pests, which significantly increases crop yield and reduces the need for chemical pesticides. For example, Bt crops produce an insecticidal protein.
• Enhanced Nutritional Value: GM technology can improve the nutritional content of crops. A prime example is 'golden rice', which is enriched with beta-carotene, a precursor to Vitamin A, helping to combat deficiency.
• Improved Mineral Uptake: Some GM plants are developed to be more efficient in absorbing minerals from the soil, which can help prevent soil nutrient depletion and improve plant growth.
• Abiotic Stress Tolerance: GM crops can be engineered to withstand adverse environmental conditions such as drought, salinity, and extreme temperatures, making agriculture more resilient.
• Reduced Post-Harvest Losses: Genetic modification can extend the shelf life of produce or make it more resistant to spoilage, thereby decreasing losses after harvesting.

Disadvantages and Concerns:

• Impact on Biodiversity: The widespread cultivation of GM crops, especially those with pest resistance, can pose a threat to non-target organisms, including beneficial insects like pollinators (e.g., honeybees), and potentially reduce overall biodiversity.
• Allergenicity and Health Concerns: There are concerns that GM foods might introduce new allergens into the diet or transfer antibiotic resistance markers from the introduced genes to gut bacteria, although regulatory processes aim to mitigate these risks.
• Genetic Pollution: There is a risk of genes from GM crops spreading to wild relatives through cross-pollination, a phenomenon known as genetic pollution, which could alter natural ecosystems.
• Socio-economic Issues: Concerns exist regarding the control of GM seeds by large corporations and the potential impact on small farmers.

In summary, while GM crops offer powerful tools to enhance food production and quality, careful assessment and regulation are necessary to manage potential ecological and health risks.

Solution: Cry proteins are a class of insecticidal proteins produced by the soil bacterium Bacillus thuringiensis (Bt). These proteins are toxic to certain groups of insects, particularly the larvae of moths, butterflies, beetles, and flies, but are generally harmless to humans, other mammals, birds, and fish.

The bacterium Bacillus thuringiensis naturally produces these Cry proteins as part of its survival strategy. When the bacterium sporulates (forms spores), it also produces crystalline inclusions containing these toxic proteins.

Man has exploited the insecticidal properties of Cry proteins for agricultural benefit in several ways:

1. Development of Biopesticides: Preparations containing Bt spores and the Cry proteins are used as biological pesticides. When sprayed on crops, these preparations are ingested by insect larvae, leading to their death. This offers a more environmentally friendly alternative to chemical pesticides.
2. Genetic Engineering of Crops: The genes encoding the Cry proteins (known as cry genes) have been isolated from Bacillus thuringiensis and introduced into the genomes of crop plants, such as cotton (Bt cotton) and maize (Bt corn). This genetic modification allows the plants themselves to produce the insecticidal Cry proteins. As a result, the plants become resistant to the specific insect pests that target them, significantly reducing crop damage and the need for external pesticide application.

This exploitation of Cry proteins has led to increased crop yields and reduced reliance on synthetic chemical insecticides, contributing to more sustainable agricultural practices.