TS Inter 2nd Year – Botany Previous Paper 2023

SECTION-B

Note:

(i) Answer ANY SIX questions. (ii) Each question carries FOUR marks. (iii) All are of short answer type questions. (iv) Draw labelled diagrams, wherever necessary.  

 

11. Explain the steps involved in the formation of root nodules.

Answer:

Root nodule formation is a symbiotic interaction between legumes and nitrogen-fixing bacteria (primarily Rhizobium). Here are the key steps involved:

1. Recognition and Attachment: The legume root secretes flavonoids that attract Rhizobium bacteria. The bacteria attach to the root hairs.

2. Root Hair Curling and Infection Thread Formation: The bacteria cause the root hair to curl, forming an infection thread that grows into the cortex of the root.

3. Bacterial Release and Nodule Development: The bacteria are released from the infection thread and differentiate into bacteroids within the plant cells. These infected cells divide and enlarge, forming the root nodule.

4. Nitrogen Fixation: The bacteroids convert atmospheric nitrogen (N2) into ammonia (NH3) in a process called nitrogen fixation. The plant provides the bacteria with carbohydrates and other nutrients, while the bacteria provide the plant with fixed nitrogen.

12. Draw a neat labelled diagram of chloroplast.

Answer:

Unfortunately, I cannot draw diagrams directly. However, I can describe the structure of a chloroplast and the key components you should include in your diagram:

• Outer Membrane: The outermost membrane of the chloroplast.
• Inner Membrane: The inner membrane of the chloroplast, which encloses the stroma.
• Stroma: The fluid-filled space within the chloroplast, where the Calvin cycle takes place.
• Thylakoids: Flattened, disc-like structures within the stroma.
• Grana: Stacks of thylakoids.
• Thylakoid Membrane: The membrane surrounding each thylakoid, containing photosynthetic pigments like chlorophyll.
• Photosystem I and Photosystem II: Protein complexes embedded in the thylakoid membrane, involved in light-dependent reactions.

13. Explain different types of cofactors.

Answer:

Cofactors are non-protein molecules that assist enzymes in catalyzing biochemical reactions. They can be divided into two main types:

• Coenzymes: Organic cofactors derived from vitamins. Examples include NAD+, FAD, and Coenzyme A. They participate directly in the chemical reaction by accepting or donating electrons or chemical groups.

• Metal Ions: Inorganic cofactors such as iron, zinc, copper, and magnesium. They play various roles, such as stabilizing enzyme structure, participating in redox reactions, and facilitating substrate binding.

14. 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)

15. Give a brief account of Bt cotton.

Answer:

Bt cotton is a genetically modified crop that has been engineered to produce its own insecticide. It contains a gene from the bacterium Bacillus thuringiensis (Bt), which produces a protein toxic to certain insect pests like bollworms. This reduces the need for chemical pesticides, making it a more environmentally friendly and sustainable option for cotton farmers.

16. Explain the Co-dominance phenomenon with example.

Answer:

Co-dominance is a type of inheritance where both alleles of a gene are expressed equally in the heterozygous condition.

Example: ABO blood group system. Individuals with the AB blood type inherit both the A and B alleles. Both A and B antigens are expressed on the surface of their red blood cells.

17. Write short notes on seed dormancy.

Answer:

Seed dormancy is a state in which a viable seed fails to germinate even under favorable environmental conditions. It is a mechanism that ensures seed germination occurs at the most appropriate time for seedling establishment.

Types of seed dormancy:

• Physical dormancy: Seed coat prevents water and oxygen uptake.
• Physiological dormancy: Embryo is immature or growth inhibitors are present.
• Morphological dormancy: Embryo is underdeveloped.

18. How many types of RNA polymerases exist in cells? Write their names and functions.

Answer:

In eukaryotic cells, there are three main types of RNA polymerases:

• RNA polymerase I: Transcribes ribosomal RNA (rRNA) genes.
• RNA polymerase II: Transcribes protein-coding genes (mRNA).
• RNA polymerase III: Transcribes transfer RNA (tRNA) genes and other small RNAs.

SECTION-C

Note:

(i) Answer ANY TWO questions. (ii) Each question carries EIGHT marks. (iii) All are long answer type questions. (iv) Draw labelled diagrams, wherever necessary.  

 

19. Explain Calvin cycle.

Answer:

The Calvin cycle, also known as the Calvin-Benson cycle or the dark reactions, is a series of biochemical reactions that take place in the stroma of chloroplasts during photosynthesis. It is a cyclic process that utilizes the energy stored in ATP and NADPH generated during the light-dependent reactions to convert carbon dioxide (CO2) into organic molecules, primarily glucose.  

 

Key Stages of the Calvin Cycle:

1. Carbon Fixation:

   • CO2 is fixed by the enzyme Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) to form an unstable six-carbon intermediate.
   • This intermediate immediately breaks down into two molecules of 3-phosphoglycerate (3-PGA).

2. Reduction:

   • 3-PGA is converted into 1,3-bisphosphoglycerate using ATP.
   • 1,3-bisphosphoglycerate is then reduced to glyceraldehyde-3-phosphate (G3P) using NADPH.

3. Regeneration of RuBP:

   • Some G3P molecules are used to synthesize glucose and other organic molecules.
   • The remaining G3P molecules are used to regenerate RuBP (ribulose-1,5-bisphosphate), the initial carbon acceptor, through a series of complex reactions.

Overall, the Calvin cycle can be summarized as follows:

• Input: CO2, ATP, NADPH
• Output: Glucose, ADP, NADP+

Diagram:

You can find a detailed diagram of the Calvin cycle online or in your textbook. It will show the various steps and intermediates involved in the cycle.

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. Write a brief essay on microbes in sewage treatment.

Answer:

Microorganisms play a crucial role in sewage treatment by breaking down organic matter and converting it into less harmful substances. Sewage treatment typically involves several stages:

• Primary Treatment: This stage involves physical processes like screening and sedimentation to remove large solids and suspended particles.
• Secondary Treatment: This stage involves biological processes where microorganisms break down the remaining organic matter.
  • Aerobic Treatment: In activated sludge processes, microorganisms are aerated to break down organic matter in the presence of oxygen.
  • Anaerobic Treatment: In anaerobic digesters, microorganisms break down organic matter in the absence of oxygen, producing biogas as a byproduct.
• Tertiary Treatment: This stage involves further treatment steps to remove specific pollutants, such as nitrogen and phosphorus, to improve the quality of the treated effluent.

Types of Microbes Involved:

• Bacteria: Various bacterial species are involved in the breakdown of organic matter, including E. coli, Pseudomonas, and Bacillus.
• Archaea: Some archaea are also involved in anaerobic digestion.
• Fungi: Certain fungi can degrade complex organic compounds.

Benefits of Microbes in Sewage Treatment:

• Removal of Organic Matter: Microorganisms break down organic pollutants, reducing their environmental impact.
• Nutrient Removal: Microbes can remove nutrients like nitrogen and phosphorus, which can cause eutrophication in water bodies.
• Production of Biogas: Anaerobic digestion produces biogas (methane), which can be used as a renewable energy source.

In conclusion, microbes are essential for efficient and sustainable sewage treatment. They play a vital role in breaking down organic matter, removing pollutants, and producing valuable byproducts.