NCERT Solutions

The Meristem (apical and axillary) is best suited for making virus-free plants.

Even if the plant is infected with a virus, the meristem is free of virus. This is because the meristematic cells divide actively and faster than the rate of viral multiplication. Hence, culturing the meristem in vitro produces virus-free plants.

The major advantages of micropropagation (tissue culture) are:

1. Rapid Multiplication: A large number of plants (thousands) can be produced in a very short duration.
2. Somaclones: The plants produced are genetically identical to the original plant (parent), ensuring desired traits are preserved.
3. Disease-free Plants: It allows recovery of healthy plants from diseased plants using meristem culture.

The nutrient medium (e.g., MS Medium) typically contains:

• Carbon Source: Usually Sucrose.
• Inorganic Salts: Macro and micronutrients.
• Vitamins & Amino Acids: For growth support.
• Growth Regulators: Auxins (like 2,4-D) and Cytokinins (like BAP) to regulate cell division and differentiation.
• Solidifying Agent: Agar (if solid medium is required).

(c) toxin is inactive.

Explanation: The Bt toxin protein exists as an inactive protoxin in the bacteria. It gets converted into an active form only when it enters the gut of the insect, where the alkaline pH of the gut solubilizes the crystals and activates the toxin.

Transgenic Bacteria: Bacteria whose DNA has been manipulated to carry and express a foreign gene (from another organism) are called transgenic bacteria.

• The gene for human insulin is inserted into the plasmid of Escherichia coli (E. coli).
• This transgenic E. coli is then cultured in large bioreactors.
• The bacteria produce the human insulin chains (Chain A and Chain B), which are extracted, purified, and joined by disulfide bonds to form active Humulin.

• Cry Proteins: These are toxic insecticidal proteins encoded by the cry genes. They form crystalline inclusions.
• Organism: The soil bacterium Bacillus thuringiensis.
• Exploitation: Scientists have isolated the cry genes (like cryIAc, cryIIAb) and introduced them into crop plants (Cotton, Corn). The plants express the Cry protein and become resistant to specific insect pests (like Cotton Bollworm, Corn borer), reducing the need for chemical insecticides.

Gene Therapy: It is a collection of methods that allows correction of a gene defect that has been diagnosed in a child or embryo. It involves delivery of a normal gene into the individual to take over the function of and compensate for the non-functional gene.

• Cause: Deletion of the gene for Adenosine Deaminase enzyme (crucial for the immune system).
• Treatment Steps:
  1. Lymphocytes are extracted from the patient’s blood.
  2. A functional ADA cDNA is introduced into these lymphocytes using a retroviral vector.
  3. The genetically engineered lymphocytes are returned to the patient.
• Limitation: Cells are not immortal, so periodic infusions are needed. A permanent cure is possible if the gene is introduced into marrow cells at the embryonic stage.

1. Isolation: Isolate the DNA containing the gene for human growth hormone.
2. Vector Preparation: Cut the plasmid vector (e.g., pBR322) using specific restriction enzymes.
3. Ligation: Join the gene of interest with the plasmid using DNA Ligase to form Recombinant DNA (rDNA).
4. Transformation: Introduce the rDNA into the host bacterium E. coli.
5. Culturing: Grow the transformed bacteria in a bioreactor to express the protein.
6. Extraction: Isolate and purify the human growth hormone (Downstream processing).

To remove oil (lipids) or prevent its synthesis in seeds, we can use RNA Interference (RNAi) or Antisense RNA technology.

• Oils are synthesized by specific enzymes (fatty acid synthases, glycerol acyltransferases).
• By identifying the genes coding for these key enzymes and introducing a complementary dsRNA (RNAi) or antisense gene, we can silence the mRNA of these enzymes.
• This prevents the translation of the enzyme, thereby stopping oil synthesis in the seeds.

Golden Rice is a genetically modified variety of rice (Oryza sativa).

• Modification: It has been engineered to produce beta-carotene, a precursor of Vitamin A, in the edible part (endosperm) of the rice.
• Genes Used: Genes from the daffodil plant (Narcissus pseudonarcissus) and a bacterium (Erwinia uredovora).
• Purpose: To combat Vitamin A deficiency (VAD), which causes night blindness and childhood blindness in developing countries where rice is the staple diet.

• Proteases: No (Active forms). Blood plasma contains protease precursors (zymogens) involved in clotting (e.g., Prothrombin) and complement systems, but active proteases are tightly regulated to prevent damage to blood vessels and cells. However, for the context of digestion, they are absent.
• Nucleases: Yes. Blood serum contains nucleases (DNases and RNases) to degrade extracellular DNA/RNA released from dead or damaged cells, preventing potential autoimmune reactions or transformation.

Major Problem: Proteins are digested by proteolytic enzymes (pepsin, trypsin) in the stomach and intestine. The acidic pH of the stomach also denatures them. They have low absorption across the intestinal epithelium due to large size.

• Enteric Coating: Coating the tablet/capsule to resist stomach acid and dissolve only in the intestine.
• Enzyme Inhibitors: Co-administering protease inhibitors to prevent degradation.
• Liposomes/Nanoparticles: Encapsulating the protein in lipid vesicles to facilitate absorption.
• Permeation Enhancers: Substances that temporarily increase intestinal permeability.