Science - Exemplar Problems

Options 1 and 2 are correct: Microbes like bacteria and many fungi can be grown on nutritive media to form colonies that can be seen with the naked eyes. Such cultures are useful in studies on micro-organisms.

Option 3 is not correct: Unlike bacteria, many of which can be grown on an artificial nutrient medium, viruses require a living host cell for replication. Infected host cells (eukaryotic or prokaryotic) can be cultured and grown, and then the growth medium can be harvested as a source of virus.

Source: NCERT: Chapter Microbes in Human Welfare

RNA interference (RNAi) is a gene silencing technology that inhibits protein synthesis in target cells using double-stranded RNA.

RNAi has huge significance within the Indian context, considering the deep-seated resistance over the years to Bt cotton and other genetically modified seeds. RNA-reliant solutions could be a viable alternative.

RNAi is used in functional genomics (systematic analysis of loss-of-function phenotypes induced by RNAi triggers) and developing therapies for the treatment of viral infection, dominant disorders, neurological disorders, and many types of cancers (in vivo inactivation of gene products linked to human disease progression and pathology).

Source Attribution: NCERT

Crystallization of sodium chloride and melting of ice are physical changes as they involve a change of state. Souring of milk is a chemical change because it results in the formation of new substances.

Source: 7th NCERT: Science Chapter

Option 1: Each individual droplet of water acts as a tiny prism that both disperses the light and reflects it back to our eye.

Option 2: Since water is more dense than air, light is refracted as it enters the drop.

Option 3: Some of the light will reflect off the back of the drop if the angle is larger than the critical angle (48° for water).

Source: NCERT: Class X Science

The carbon cycle is a crucial process that involves the movement of carbon among the atmosphere, oceans, soil, and living organisms. Several natural processes contribute to the addition of carbon dioxide (CO₂) into this cycle:

• Volcanic action: Volcanic eruptions release significant amounts of carbon dioxide into the atmosphere.
• Respiration: All aerobic organisms, including humans, release carbon dioxide as a byproduct of respiration.
• Photosynthesis: This process, performed by plants, algae, and some bacteria, actually removes carbon dioxide from the atmosphere, rather than adding it.
• Decay of organic matter: The decomposition of dead organisms by microbes releases carbon dioxide back into the atmosphere.

In summary, the processes that add carbon dioxide to the carbon cycle are volcanic action, respiration, and decay of organic matter.

Source: 11th NCERT: Geography Chapter