Cell

11. For protein synthesis, the amino acids are recognized and carried by :

For protein synthesis, the amino acids are recognized and carried by :

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mRNA
snRNA
miRNA
tRNA
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UPSC CAPF – 2023
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Transfer RNA (tRNA) molecules are essential components of protein synthesis (translation). Each tRNA molecule has an anticodon loop that recognizes and binds to a specific codon on the messenger RNA (mRNA). At the other end, the tRNA is attached to a specific amino acid corresponding to that codon. Thus, tRNAs act as adapters, bringing the correct amino acid to the ribosome for incorporation into the growing polypeptide chain based on the mRNA sequence.
– Protein synthesis involves mRNA, ribosomes, and tRNA.
– mRNA carries the genetic code (codons).
– tRNA carries the specific amino acid corresponding to an mRNA codon and recognizes the codon via its anticodon.
Ribosomal RNA (rRNA) is a structural and catalytic component of ribosomes, where protein synthesis takes place. snRNA (small nuclear RNA) is involved in splicing, while miRNA (microRNA) and siRNA (small interfering RNA) are involved in post-transcriptional gene regulation. None of these directly recognize codons and carry amino acids for translation.

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12. Which organelle other than nucleus in eukaryotic cells has its own DNA

Which organelle other than nucleus in eukaryotic cells has its own DNA, ribosomes and proteins ?

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Golgi
Mitochondria
Lysosomes
Nucleosomes
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UPSC CAPF – 2023
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In eukaryotic cells, besides the nucleus, mitochondria (and chloroplasts in plant cells) contain their own DNA (typically circular), ribosomes (different from cytoplasmic ribosomes), and the machinery for synthesizing some of their own proteins. This makes them semi-autonomous organelles.
Mitochondria are organelles responsible for cellular respiration and ATP production. The presence of their own genetic material and protein synthesis machinery is strong evidence supporting the endosymbiotic theory, which posits that mitochondria evolved from free-living prokaryotic organisms that were engulfed by early eukaryotic cells.
The Golgi apparatus, lysosomes, and nucleosomes (which are part of the chromatin structure within the nucleus and mitochondria/chloroplasts) do not possess their own independent DNA or ribosomes and are not capable of synthesizing proteins independently of the cytoplasmic protein synthesis machinery directed by nuclear DNA.

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13. Which of the following best represents the cells of a meristem of

Which of the following best represents the cells of a meristem of plant?

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Dense cytoplasm, thin cell wall, large nuclei and absence of vacuoles
Dense cytoplasm, thin cell wall, large nuclei and large vacuoles
Dense cytoplasm, thin cell wall, small nuclei and absence of vacuoles
Dense cytoplasm, thick cell wall, small nuclei and large vacuoles
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UPSC CAPF – 2022
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The correct answer is A) Dense cytoplasm, thin cell wall, large nuclei and absence of vacuoles.
Meristematic cells are undifferentiated plant cells that are actively undergoing cell division. Characteristics of these cells include dense cytoplasm, thin primary cell walls (as they are rapidly growing and dividing), relatively large and prominent nuclei (controlling the cell cycle), and usually small or absent vacuoles, which would otherwise occupy significant volume and potentially hinder rapid division.
Mature plant cells typically have thick cell walls and a large central vacuole that can occupy up to 90% of the cell volume. Meristematic cells are found in regions of active growth, such as root tips, shoot tips, and vascular cambium.

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14. Lysosomes are sacs of the cell filled with digestive enzymes. These di

Lysosomes are sacs of the cell filled with digestive enzymes. These digestive enzymes are synthesized by

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Golgi bodies
smooth endoplasmic reticulum
rough endoplasmic reticulum
lysosome itself
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UPSC CAPF – 2022
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The correct answer is C) rough endoplasmic reticulum.
Lysosomal enzymes are hydrolytic enzymes that are proteins. Proteins destined for secretion or for inclusion in membrane-bound organelles like lysosomes are synthesized on ribosomes attached to the rough endoplasmic reticulum (RER). These proteins are then processed within the RER and subsequently transported to the Golgi apparatus for further modification and packaging into vesicles, which bud off to form lysosomes.
Golgi bodies are involved in modifying, sorting, and packaging proteins and lipids. Smooth endoplasmic reticulum (SER) is involved in lipid synthesis, detoxification, and calcium storage. Lysosomes themselves are membrane-bound organelles containing the digestive enzymes; they do not synthesize the enzymes.

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15. Which of the following combinations correctly represents the genetic m

Which of the following combinations correctly represents the genetic materials in prokaryotes and eukaryotes respectively?

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Nucleoid and Chromatin
Chromatin and Nucleoid
Nucleoid and Nucleolus
Nucleolus and Chromatin
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UPSC CAPF – 2022
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The correct answer is A) Nucleoid and Chromatin.
Prokaryotes (like bacteria) lack a membrane-bound nucleus. Their genetic material (usually a single circular chromosome) is located in a region of the cytoplasm called the nucleoid. Eukaryotes (like plants and animals) have a membrane-bound nucleus containing their genetic material, which is organized into multiple linear chromosomes composed of DNA wrapped around proteins (histones) forming a structure called chromatin.
The nucleolus is a dense structure found within the eukaryotic nucleus, involved in ribosome synthesis, not the primary form of the entire genetic material itself. Chromatin is the complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells.

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16. Which one of the following statements about life processes in single-c

Which one of the following statements about life processes in single-celled organisms is not correct?

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They require separate organ for food uptake.
Separate organ is not needed for respiration.
Waste of excretory material is produced by these organisms.
They remain in contact with external environment.
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UPSC CAPF – 2021
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Single-celled organisms are prokaryotic or eukaryotic organisms consisting of a single cell. All necessary life processes, such as nutrition, respiration, excretion, and reproduction, occur within this single cell.
Unlike multicellular organisms which have specialized organs for specific functions, single-celled organisms perform all functions through the mechanisms available within that single cell. Food uptake in organisms like Amoeba occurs through processes like phagocytosis or pinocytosis across the cell membrane, not through a separate organ. Gaseous exchange for respiration and elimination of waste materials occur directly through diffusion across the cell surface, which is in direct contact with the external environment.
The large surface area to volume ratio in single-celled organisms facilitates efficient exchange of materials, nutrients, gases, and waste products directly with their surroundings, making specialized organs unnecessary.

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17. Which one of the following is not a breakdown product of glucose dur

Which one of the following is not a breakdown product of glucose during respiration?

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Ethanol
Lactic acid
Water
Methanol
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UPSC CAPF – 2021
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The correct answer is D) Methanol.
Cellular respiration is the process by which glucose is broken down to release energy. This process begins with glycolysis, which converts glucose into pyruvate. Depending on the presence of oxygen, pyruvate can be further metabolized:
1. Aerobic respiration (in the presence of oxygen): Pyruvate is completely oxidized to carbon dioxide (CO₂) and water (H₂O).
2. Anaerobic respiration (fermentation, in the absence of oxygen): Pyruvate is converted into products like ethanol and carbon dioxide (in yeast and plants) or lactic acid (in muscle cells and some bacteria).
Ethanol, lactic acid, and water are all potential breakdown products of glucose during respiration. Methanol is not produced during the standard biological breakdown of glucose.
Methanol (CH₃OH) is a simple alcohol. It is produced industrially or by anaerobic metabolism of certain bacteria, but not as a standard product of glucose respiration in humans or most common organisms.

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18. Which one of the following organelles is not found in animal cells?

Which one of the following organelles is not found in animal cells?

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Cell membrane
Endoplasmic reticulum
Cell wall
Lysosome
This question was previously asked in
UPSC CAPF – 2021
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The question asks which of the listed organelles is *not* found in animal cells. Let’s review each option:
A) Cell membrane: The cell membrane is the outer boundary of animal cells and is present in all eukaryotic cells, including plant cells (where it is inside the cell wall).
B) Endoplasmic reticulum: The endoplasmic reticulum (ER) is a network of membranes involved in protein synthesis (rough ER) and lipid synthesis (smooth ER). It is found in both animal and plant cells.
C) Cell wall: The cell wall is a rigid outer layer that provides structural support, protection, and shape to the cell. Cell walls are present in plant cells (made primarily of cellulose), fungi, bacteria, and some protists, but they are *absent* in animal cells.
D) Lysosome: Lysosomes are membrane-bound organelles containing digestive enzymes. They are primarily found in animal cells, where they are involved in breaking down waste materials and cellular debris. While some plant cells may have vacuoles with lytic activity similar to lysosomes, dedicated lysosomes as found in animal cells are generally considered absent in plant cells. However, the cell wall is definitively absent in animal cells, making it the correct answer.
– Recall the key organelles found in typical animal and plant cells.
– Note the distinguishing features between plant and animal cells, such as the presence of a cell wall, chloroplasts, and large central vacuoles in plants, and lysosomes and centrioles typically in animals.
– The cell wall is a defining feature of plant cells that is absent in animal cells.
Other organelles typically found in animal cells but not in plant cells include centrioles. Organelles typically found in plant cells but not in animal cells include cell walls (as mentioned), chloroplasts, and often a large central vacuole. Both cell types have cell membranes, nuclei, mitochondria, endoplasmic reticulum, Golgi apparatus, and ribosomes.

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19. Which one of the following statements is correct ?

Which one of the following statements is correct ?

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Glucose breaks down to CO₂, H₂O and energy in all organisms
Glucose breaks down into ethanol, CO₂ and energy in our muscle cells
Glucose breaks down into CO₂, H₂O and energy in all aerobic tissues
Glucose breaks down into lactate and energy in yeast
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UPSC CAPF – 2020
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In aerobic respiration, which occurs in the presence of oxygen, glucose is completely broken down into carbon dioxide (CO₂), water (H₂O), and a large amount of energy (ATP). This process occurs in aerobic tissues of organisms, including humans. Option A is incorrect because not all organisms perform aerobic respiration (e.g., anaerobic bacteria, yeast under anaerobic conditions). Option B is incorrect because muscle cells produce lactate during anaerobic conditions, not ethanol and CO₂. Option D is incorrect because yeast produces ethanol and CO₂ during alcoholic fermentation, not lactate.
Aerobic respiration yields the maximum amount of energy from glucose and results in CO₂ and H₂O as final products. Anaerobic respiration (fermentation) yields less energy and produces different products like lactate or ethanol.
The overall equation for aerobic respiration is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP). This process involves glycolysis (cytoplasm), the Krebs cycle (mitochondrial matrix), and the electron transport chain (inner mitochondrial membrane).

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20. In which part of the cell, the glucose is converted into pyruvate ?

In which part of the cell, the glucose is converted into pyruvate ?

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Mitochondria
Nucleus
Cytoplasm
Endoplasmic reticulum
This question was previously asked in
UPSC CAPF – 2020
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The metabolic pathway in which glucose is converted into pyruvate is called glycolysis. This process occurs in the cytoplasm (cytosol) of the cell, both in prokaryotes and eukaryotes.
Glycolysis is the first stage of cellular respiration and occurs in the cytoplasm. It breaks down a molecule of glucose (a 6-carbon sugar) into two molecules of pyruvate (a 3-carbon molecule), producing a net gain of ATP and NADH.
Pyruvate then enters the mitochondria (in aerobic respiration) for further oxidation via the Krebs cycle and electron transport chain, or is converted to lactate or ethanol in anaerobic conditions (fermentation), also in the cytoplasm.

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