Zoology MCQs for NEET — Practice Questions with Answers

The Earth, like other planets, formed from a cloud of gas and dust known as the solar nebula. This process is part of the nebular hypothesis, which describes the formation of the solar system. The gravitational collapse of part of the nebula led to the formation of the Sun and the remaining material coalesced to form the planets.

The first formed organism, often referred to as a riboorganism, used RNA for catalyzing reactions. This is because RNA has the unique ability to both store genetic information and catalyze chemical reactions, a property not shared by DNA or proteins. This dual functionality of RNA supports the RNA world hypothesis, which suggests that self-replicating RNA molecules were precursors to current life forms.

The evolution of autotrophs, organisms that can produce their own food through processes like photosynthesis, required the evolution of chlorophyll. Chlorophyll is the pigment that allows these organisms to capture and convert light energy into chemical energy, setting the stage for autotrophic life forms.

The era called the ‘age of prokaryotic microbes’ is known as the Archaezoic era. This era is characterized by the dominance of prokaryotic life forms, such as bacteria and archaea, before the emergence of more complex eukaryotic life forms.

Stanley Miller's experiment, conducted in 1953, aimed to simulate the conditions of the early Earth's atmosphere. The apparatus he used contained a mixture of hydrogen, ammonia, methane, and water vapour. This combination was chosen based on the hypothesis that the early Earth had a reducing atmosphere, which is conducive to the formation of organic molecules. The experiment demonstrated that amino acids and other organic compounds could form spontaneously under these conditions, supporting the theory of abiogenesis.

The famous experiment to prove the origin of life was conducted by Stanley Miller and Harold Urey in 1953. Known as the Miller-Urey experiment, it simulated the conditions thought to be present on the early Earth and demonstrated that organic molecules necessary for life could be synthesized from inorganic precursors under these conditions. This experiment provided significant evidence supporting the theory of abiogenesis, the idea that life arose naturally from non-living matter.

The statement A is true because the first molecules thought to be formed for replicating cells were RNA, which is supported by the RNA world hypothesis. This hypothesis suggests that RNA, which can both store genetic information and catalyze chemical reactions, was the first self-replicating molecule. The statement R is also true because Thomas Cech's discovery of ribozymes in 1987 provided evidence that RNA could have catalytic functions. Therefore, R is the correct explanation for A.

The correct matches are: I (Core of the earth) – B (Fe-Ni), II (Life originated) – A (Archaeozoic era), III (Stromatolites) – D (Photosynthesizing algae), IV (TMC is an example) – C (Inter-micromolecular assembly). The core of the Earth is composed of iron and nickel (Fe-Ni). Life is believed to have originated during the Archaeozoic era. Stromatolites are layered structures formed by photosynthesizing algae. TMC (Thermochemical conversion) is an example of an inter-micromolecular assembly.

Coacervates are colloidal droplets and they contain nucleoproteins. Coacervates are formed when organic molecules, such as proteins and nucleic acids, aggregate into microspheres. These droplets can encapsulate enzymes and other molecules, creating a primitive form of compartmentalization that is essential for the beginning of life processes. Therefore, both options 1 and 2 are correct.

The earliest organisms were heterotrophic and anaerobic because the early Earth lacked oxygen in its atmosphere. These organisms obtained their energy by consuming organic molecules present in their environment and did not require oxygen for their metabolic processes.