Q2641. Which nematode infects the roots of tobacco plants causing a great reduction in yield, which is countered by RNAi technology?
RAS Prelims MCQ Practice
9,654 RAS Prelims practice MCQs with the correct answer and a clear explanation for each. Filter by subject and chapter.
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Q2642. Genetic variations observed in plants regenerated from tissue culture are called:
Explanation
Genetic variations seen in plants regenerated from tissue culture are called somaclonal variations.
Q2643. To produce virus-free plants from a virus-infected plant via tissue culture, which specific part of the plant is used as an explant?
Explanation
To get virus-free plants, the meristem (apical or axillary) is used as the explant, because the cells of the meristem are free of virus.
Q2644. The fusion of isolated protoplasts from two different plant species to create a hybrid (like the Pomato) is an example of:
Explanation
Somatic hybridization is a technique where the cell walls of two different plant species are removed to create protoplasts, which are then fused together to form a hybrid cell. This allows for the combination of traits from species that cannot be crossed through sexual reproduction. A famous example is the Pomato, a hybrid produced by fusing protoplasts from potato and tomato.
Q2645. What is the role of polyethylene glycol (PEG) in agricultural biotechnology?
Explanation
Polyethylene glycol is a chemical agent used in agricultural biotechnology to facilitate the fusion of plant protoplasts during somatic hybridization. Because protoplasts are negatively charged, they naturally repel each other. Adding PEG acts as a molecular bridge that reduces this repulsion and alters the cell membrane properties, allowing the protoplasts from two different species to come into close contact and merge.
Q2646. Which of the following best describes the principle of RNA interference (RNAi)?
Explanation
RNA interference is a natural biological process where double-stranded RNA molecules inhibit gene expression or translation. When dsRNA enters a cell, it is processed into short fragments that guide a protein complex to a specific messenger RNA molecule. The complex then binds to and cleaves the mRNA, preventing it from being translated into a protein. This results in specific gene silencing.
Q2647. Match List-I with List-II regarding nanomaterials:
| Nanomaterial | Characteristic |
|---|---|
| A. Graphene | i. Hollow spherical cages of 60 carbon atoms |
| B. Carbon Nanotubes (CNTs) | ii. Semiconductor nanocrystals with unique optical properties |
| C. Quantum dots | iii. Cylindrical carbon structures with exceptional tensile strength |
| D. Fullerenes (Buckyballs) | iv. A single layer of carbon atoms arranged in a 2D hexagonal lattice |
Explanation
Nanomaterials come in various structural forms. Graphene is a single, two-dimensional layer of carbon atoms in a hexagonal lattice. Carbon Nanotubes are cylindrical structures with immense strength. Quantum dots are tiny semiconductor crystals with unique optical properties, such as size-dependent light emission. Fullerenes are hollow spherical molecules composed of sixty carbon atoms arranged in a pattern resembling a soccer ball.
Q2648. Consider the following statements about nanotechnology:
I. Nanomaterials exhibit significantly different physical and chemical properties compared to their bulk counterparts.
II. An increase in the surface area-to-volume ratio at the nanoscale often increases chemical reactivity.
III. Richard Feynman is widely considered a founding father of nanotechnology concepts.
Which of the above statement(s) is/are correct?
I. Nanomaterials exhibit significantly different physical and chemical properties compared to their bulk counterparts.
II. An increase in the surface area-to-volume ratio at the nanoscale often increases chemical reactivity.
III. Richard Feynman is widely considered a founding father of nanotechnology concepts.
Which of the above statement(s) is/are correct?
Explanation
Nanomaterials possess distinct properties compared to bulk materials due to quantum effects and a drastically increased surface area-to-volume ratio, which often significantly enhances their chemical reactivity. The theoretical foundation for the field was famously laid by physicist Richard Feynman in his 1959 lecture. These three points form the fundamental basis for understanding why nanotechnology is so versatile across diverse disciplines.
Q2649. A nanometer is equal to:
Explanation
A nanometer is a unit of length in the metric system equal to one-billionth of a meter. In scientific notation, this is expressed as 10 to the power of negative nine meters. To provide perspective, a single human hair is approximately 80,000 to 100,000 nanometers wide. This extreme miniaturization is what allows nanotechnology to interact with biological molecules on their own scale.
Q2650. Which phenomenon explains why quantum dots emit light of varying colors depending on their size?
Explanation
The unique ability of quantum dots to emit light of specific colors based on their size is a result of a phenomenon called quantum confinement. When a semiconductor crystal becomes smaller than a certain threshold, its electronic properties change. Smaller dots have a larger energy gap and emit shorter wavelengths, while larger dots have a smaller gap and emit longer wavelengths of light.Answer key for these questions
| Q | Correct answer |
|---|---|
| 2641 | (c) Meloidogyne incognita |
| 2642 | (b) Somaclonal variations |
| 2643 | (d) Meristem (apical or axillary) |
| 2644 | (a) Somatic hybridization |
| 2645 | (c) It induces the fusion of plant protoplasts. |
| 2646 | (a) Gene silencing via complementary double- stranded RNA |
| 2647 | (a) A-iv, B-iii, C-ii, D-i |
| 2648 | (d) I, II and III |
| 2649 | (b) 10-9 meters |
| 2650 | (c) Quantum confinement |
Frequently asked questions
How many RAS Prelims practice MCQs are there on RAS Prelims?
This page has 9654 practice MCQs on the RAS Prelims syllabus. Each has the correct answer, and most have an explanation.
How should I practise MCQs for RAS Prelims?
Attempt each question first, then open the answer and read the explanation. Practise one chapter at a time, note the facts you got wrong and revise them. Repeat the chapter after a few days.
Are these actual RAS Prelims past-paper questions?
No. These are practice questions written for the RAS Prelims syllabus. They follow the pattern the exam uses: factual questions, statement-based questions, match-the-list and assertion-reason.