Section: A

Marks: 10 x 2 = 20

Note: Answer all questions. Each answer may be limited to 5 lines.

1. Name two amino acids in which sulphur is present.

• Cysteine
• Methionine

2. With reference to transportation of food within a plant. What are source and sink?

• Source: The region in a plant where organic compounds (like sugars) are produced, such as mature leaves.
• Sink: The region in a plant where organic compounds are transported and utilized, such as growing fruits, roots, or storage organs.

3. What is a plasmid? What is its significance?

• Plasmid: A plasmid is a small, extrachromosomal DNA molecule that is capable of replicating independently of the chromosomal DNA within a cell.
• Significance: Plasmids are crucial tools in genetic engineering. They can be used as vectors to carry foreign DNA into host cells for gene cloning and expression.

4. What is point mutation? Give an example.

• Point Mutation: A point mutation is a type of genetic mutation where a single nucleotide base is changed, inserted, or deleted from the DNA sequence.
• Example: Sickle cell anemia is caused by a single point mutation in the gene for hemoglobin.

5. Who proved that DNA is genetic material? What is the organism they worked on?

• Scientists: Alfred Hershey and Martha Chase
• Organism: Bacteriophage T2

6. Define stop codon. Write the codons

• Stop Codon: Stop codons are triplets of nucleotides in mRNA that signal the termination of protein synthesis.
• Codons: UAA, UAG, UGA

7. Name any two artificially restricted plasmids.

• pBR322
• pUC19

8. Can a disease be detected before its symptoms appear? Explain the principle involved.

• Yes, diseases can be detected before their symptoms appear through techniques like molecular diagnostics.
• Principle: These techniques involve detecting the presence of the disease-causing agent (virus, bacteria, etc.) or its genetic material (DNA or RNA) in the body, even at very low levels. This is often done using techniques like PCR (Polymerase Chain Reaction) which amplifies small amounts of DNA.

9. Name any two scientists who were credited for showing the role of penicillin as an antibiotic.

• Alexander Fleming
• Ernst Chain
• Howard Florey

10. Name an immunosuppressive agent. From where is it obtained?

• Cyclosporine: This immunosuppressive agent is obtained from a fungus, Tolypocladium inflatum.

Section: B

Marks: 6 x 4 = 24

Note: Answer any six questions. Each answer may be limited to 20 lines.

11. Write any four physiological effects of cytokinins in plants.

Answer:

Cytokinins are a class of plant hormones that play crucial roles in various physiological processes. Here are four significant effects of cytokinins in plants:

• Cell Division and Growth: Cytokinins promote cell division (cytokinesis) and stimulate cell growth and differentiation. They interact with auxins to regulate cell division and organogenesis.
• Delaying Senescence: Cytokinins delay the aging process in plant tissues, such as leaf senescence (yellowing and leaf drop). They help to maintain chlorophyll content and delay the breakdown of cellular components.
• Breaking Bud Dormancy: Cytokinins can overcome bud dormancy, promoting bud opening and shoot growth.
• Lateral Bud Development: Cytokinins can counteract the apical dominance effect of auxins, promoting the growth of lateral buds and leading to bushier growth.

12. Explain different types of cofactors.

Answer:

Cofactors are non-protein molecules that are essential for the activity of many enzymes. They can be divided into two main types:

• Coenzymes: These are organic cofactors derived from vitamins. They participate directly in the chemical reaction by accepting or donating electrons or chemical groups. Examples include NAD+, FAD, and Coenzyme A.
• Metal Ions: These are inorganic cofactors such as iron, zinc, copper, and magnesium. They play various roles in enzyme function, such as stabilizing enzyme structure, participating in redox reactions, and facilitating substrate binding.

13. Describe in brief photorespiration.

Answer:

Photorespiration is a metabolic process that occurs in plants, particularly in C3 plants. It is a wasteful process that competes with photosynthesis.

Key points:

• Rubisco’s Dual Function: Rubisco, the enzyme responsible for carbon fixation in photosynthesis, can also bind to oxygen under certain conditions.
• Oxygenation Reaction: When Rubisco binds to oxygen instead of carbon dioxide, it catalyzes the oxygenation of RuBP (ribulose-1,5-bisphosphate), resulting in the formation of phosphoglycolate.
• Energy Expenditure: Photorespiration involves a series of reactions that consume ATP and NADPH, reducing the efficiency of photosynthesis.
• Carbon Loss: Photorespiration results in the release of carbon dioxide, further reducing photosynthetic output.

Factors Favoring Photorespiration:

• High temperatures
• High oxygen concentrations
• Low carbon dioxide concentrations

Significance:

While photorespiration is generally considered wasteful, it may have some protective functions under certain conditions. For example, it may help to protect plants from photooxidative damage under stress conditions.

14. Transpiration and photosynthesis – a compromise. Explain.

Answer:

The statement “Transpiration and photosynthesis – a compromise” highlights the intricate relationship and trade-off between these two vital plant processes.

• Transpiration: The loss of water vapor from plant surfaces, primarily through stomata. It is essential for the upward movement of water and minerals from roots to leaves, cooling the plant, and maintaining turgor pressure.

• Photosynthesis: The process by which plants convert light energy into chemical energy, using carbon dioxide and water to produce glucose. It requires the stomata to be open for the uptake of carbon dioxide.  

   

The Compromise:

• Open stomata are necessary for photosynthesis to occur, but they also lead to water loss through transpiration.
• Plants have evolved mechanisms to regulate stomatal opening and closing, balancing the need for carbon dioxide uptake with the risk of water loss.
• Factors like environmental conditions (light intensity, temperature, humidity) influence stomatal behavior and the balance between transpiration and photosynthesis.

Therefore, the relationship between transpiration and photosynthesis is a compromise, where plants strive to optimize carbon dioxide uptake for photosynthesis while minimizing water loss through transpiration.

15. What is ICTV? How are viruses named?

Answer:

• ICTV: The International Committee on Taxonomy of Viruses is the body responsible for classifying and naming viruses.

• Virus Naming: Virus names typically reflect:

  • The type of disease they cause (e.g., Influenza virus)
  • Their host organism (e.g., Tobacco mosaic virus)
  • Their morphological characteristics (e.g., Bacteriophage)
  • The scientist who discovered them (e.g., Epstein-Barr virus)

16. Mention the advantages of selecting pea plant for experiment by Mendel.

Answer:

Mendel chose pea plants (Pisum sativum) for his experiments due to several advantages:

• Easy to Grow and Cultivate: Peas are relatively easy to grow and maintain in experimental gardens.
• Short Life Cycle: Peas have a short life cycle, allowing Mendel to conduct multiple generations of experiments within a short period.
• Self-Pollinating: Pea plants are naturally self-pollinating, which allowed Mendel to control the mating of plants and obtain pure-breeding lines.
• Distinct Traits: Peas exhibit several easily observable and contrasting traits, such as flower color, seed shape, and pod shape.
• Large Number of Offspring: Pea plants produce a large number of offspring, providing sufficient data for statistical analysis.

These characteristics made pea plants an ideal model system for Mendel’s experiments on inheritance.

17. What are the contributions of George Gamow, H.G. Khorana, Marshall Nirenberg in deciphering the genetic code?

Answer:

The deciphering of the genetic code, which specifies the relationship between the sequence of nucleotides in DNA and the sequence of amino acids in proteins, was a monumental achievement in molecular biology. Several scientists contributed to this breakthrough, including:

• George Gamow: He proposed that the genetic code might be a triplet code, meaning that three nucleotides (a codon) specify one amino acid.
• H.G. Khorana: He synthesized artificial RNA molecules with known sequences and used them to decipher the genetic code. He established the triplet nature of the code and identified the codons for several amino acids.
• Marshall Nirenberg: He conducted groundbreaking experiments using synthetic mRNA molecules to decipher the genetic code. He identified the codons for many amino acids and established the nature of the genetic code.

Their combined efforts provided a fundamental understanding of how genetic information is translated into proteins, paving the way for advancements in molecular biology and biotechnology.

18. Give a brief account of pest resistant plants.

Answer:

Pest-resistant plants are genetically modified or bred to resist attacks from insects, pests, and diseases. These plants play a crucial role in sustainable agriculture by reducing the reliance on chemical pesticides.

Methods of Developing Pest-Resistant Plants:

• Genetic Engineering: Introducing genes from other organisms into plants to confer resistance. For example, Bt cotton contains a gene from Bacillus thuringiensis that produces a protein toxic to certain insects.
• Conventional Breeding: Selecting and breeding plants with natural resistance to pests. This involves crossing different varieties and selecting offspring with desired traits.
• Gene Editing: Precisely modifying the plant’s own genes using techniques like CRISPR-Cas9 to enhance resistance.

Benefits of Pest-Resistant Plants:

• Reduced reliance on chemical pesticides, which can harm the environment and human health.
• Increased crop yields and reduced crop losses due to pest damage.
• Improved sustainability of agricultural practices.

Examples:

• Bt cotton
• Virus-resistant papaya
• Insect-resistant corn

Section: C

Marks: 2 x 8 = 16

19. Explain the reactions of Krebs Cycle.

Answer:

The Krebs Cycle, also known as the Citric Acid Cycle or Tricarboxylic Acid (TCA) cycle, is a series of biochemical reactions that oxidize acetyl-CoA, derived from carbohydrates, fats, and proteins, to produce energy in the form of ATP. It takes place within the mitochondrial matrix of eukaryotic cells.  

 

Key Stages of the Krebs Cycle:

1. Acetyl-CoA Condensation: Acetyl-CoA, a two-carbon molecule, combines with oxaloacetate (a four-carbon molecule) to form citrate (a six-carbon molecule).  

2. Isomerization: Citrate is converted into its isomer, isocitrate.

3. Oxidative Decarboxylation: Isocitrate is oxidized and decarboxylated (loses a carbon dioxide molecule), forming alpha-ketoglutarate. This step also produces NADH.

4. Second Oxidative Decarboxylation: Alpha-ketoglutarate is oxidized and decarboxylated, forming succinyl-CoA. This step also produces NADH.

5. Substrate-Level Phosphorylation: Succinyl-CoA is converted to succinate, releasing energy that is used to synthesize GTP (guanosine triphosphate), which can be readily converted to ATP.

6. Oxidation of Succinate: Succinate is oxidized to fumarate, producing FADH2.

7. Hydration: Fumarate is hydrated to form malate.

8. Oxidation of Malate: Malate is oxidized to oxaloacetate, regenerating the starting molecule of the cycle and producing NADH.

End Products:

• For each acetyl-CoA molecule oxidized:
  • 3 molecules of NADH
  • 1 molecule of FADH2
  • 1 molecule of GTP (equivalent to ATP)
  • 2 molecules of CO2

20. Give a brief account of the tools of recombinant DNA technology.

Answer:

Recombinant DNA technology involves manipulating DNA sequences to create new combinations of genetic material. Several key tools are essential for this technology:

• Restriction Enzymes: These enzymes cut DNA molecules at specific recognition sites, generating fragments with defined ends.
• DNA Ligase: This enzyme joins DNA fragments together, creating recombinant DNA molecules.
• Vectors: These are DNA molecules that can carry foreign DNA into a host cell. Examples include plasmids, bacteriophages, and cosmids.
• Host Cells: These are living cells that can replicate recombinant DNA molecules. Commonly used host cells include bacteria (e.g., E. coli), yeast, and mammalian cells.
• Polymerase Chain Reaction (PCR): This technique allows for the amplification of specific DNA sequences, making it possible to obtain large quantities of DNA from small samples.

21. Describe the tissue culture technique. What are the advantages of tissue culture over conventional method of plant breeding in crop improvement programmes?

Answer:

Tissue culture, also known as micropropagation, is a technique for growing plant cells, tissues, or organs in a sterile environment on a nutrient medium. It involves the following steps:  

 

Explant Selection: A small piece of plant tissue (explant) is taken from the parent plant.

1. Sterilization: The explant is sterilized to prevent contamination by microorganisms.
2. Culture Establishment: The explant is placed on a nutrient medium containing hormones and other growth factors.
3. Cell Division and Growth: The plant cells divide and grow to form a callus, a mass of undifferentiated cells.
4. Organogenesis or Somatic Embryogenesis: The callus can be induced to differentiate into shoots and roots, or directly into somatic embryos.
5. Plantlet Regeneration: The plantlets are transferred to soil and grown into mature plants.

Advantages of Tissue Culture Over Conventional Plant Breeding:

• Rapid Propagation: Tissue culture allows for the rapid multiplication of plants in a short period.
• Clonal Propagation: It produces genetically identical plants (clones), preserving desirable traits.
• Disease-Free Plants: Tissue culture can be used to produce disease-free plants by eliminating pathogens.
• Production of Novel Plants: It enables the production of genetically modified plants and the generation of novel varieties through genetic engineering.
• Conservation of Endangered Species: Tissue culture can be used to conserve rare and endangered plant species.