Cell

41. One of the additional functions of Smooth Endoplasmic Reticulum (SER)

One of the additional functions of Smooth Endoplasmic Reticulum (SER) is

protein synthesis
lipid synthesis
storage of biomolecules
detoxification of toxic substances
This question was previously asked in
UPSC NDA-2 – 2018
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The Smooth Endoplasmic Reticulum (SER) performs several key functions distinct from the Rough Endoplasmic Reticulum (RER), which is primarily involved in protein synthesis. These functions of SER include lipid synthesis (phospholipids, steroids), detoxification of drugs and poisons (especially in liver cells), metabolism of carbohydrates, and storage of calcium ions (critical for muscle contraction). Among the given options, detoxification of toxic substances is a well-established function of SER.
– RER has ribosomes on its surface and is involved in synthesizing and modifying proteins destined for secretion or insertion into membranes.
– SER lacks ribosomes and is involved in metabolic processes.
– Key functions of SER include lipid synthesis, detoxification, carbohydrate metabolism, and calcium storage.
For example, in hepatocytes (liver cells), the SER contains enzymes that catalyze reactions to detoxify lipid-soluble drugs and harmful metabolic products by making them more water-soluble for excretion from the body. SER is also extensive in cells that synthesize steroids (like hormone-producing cells).

42. Which one of the following groups of cellular organelles contains DNA?

Which one of the following groups of cellular organelles contains DNA?

Mitochondria, nucleus, chloroplast
Mitochondria, Golgi bodies, nucleus
Mitochondria, plasma membrane, nucleus
Chloroplast, nucleus, ribosomes
This question was previously asked in
UPSC NDA-2 – 2018
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In eukaryotic cells, DNA is primarily located in the nucleus. Additionally, mitochondria (in both plant and animal cells) and chloroplasts (in plant cells and algae) possess their own circular DNA (mtDNA and cpDNA, respectively), which contains genes essential for their function and reproduction.
– Nucleus: Contains the majority of the cell’s genetic material in the form of linear chromosomes.
– Mitochondria: Contain a small, circular genome (mtDNA) involved in cellular respiration.
– Chloroplasts: Contain a small, circular genome (cpDNA) involved in photosynthesis.
The endosymbiotic theory suggests that mitochondria and chloroplasts originated from free-living bacteria that were engulfed by early eukaryotic cells, retaining their own genetic material and ribosomes. Golgi bodies, plasma membrane (cellular membrane), and ribosomes do not contain DNA.

43. The genetic material of bacteria is found in

The genetic material of bacteria is found in

nucleus
cytoplasm
cell membrane
ribosome
This question was previously asked in
UPSC NDA-2 – 2016
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The genetic material of bacteria is found in the cytoplasm.
Bacteria are prokaryotic organisms, meaning their cells lack a membrane-bound nucleus. Their genetic material, which typically consists of a single circular chromosome, is located in a specific region within the cytoplasm called the nucleoid. Unlike eukaryotic cells, there is no nuclear envelope separating the genetic material from the rest of the cytoplasm.
In addition to the main chromosome in the nucleoid, bacteria may also contain smaller, circular DNA molecules called plasmids, which are also located in the cytoplasm. Ribosomes, also found in the cytoplasm, are the sites of protein synthesis, not the location of the primary genetic material. The cell membrane encloses the cytoplasm but does not contain the main genetic material.

44. Which one of the following is not an example of eukaryotic organism?

Which one of the following is not an example of eukaryotic organism?

Yeast
Bacteria
Plant
Human being
This question was previously asked in
UPSC NDA-2 – 2015
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The correct answer is B) Bacteria.
Eukaryotic organisms are characterized by having a membrane-bound nucleus and other membrane-bound organelles within their cells. Prokaryotic organisms, such as bacteria and archaea, lack a nucleus and most membrane-bound organelles. Yeast (a fungus), plants, and human beings (animals) are all examples of eukaryotic organisms.
The classification into prokaryotes and eukaryotes is one of the fundamental distinctions in biology. Eukaryotic cells are generally larger and more complex than prokaryotic cells.

45. Bacterial DNA is referred to as naked because it is not associated w

Bacterial DNA is referred to as naked because it is not associated with :

any scaffold
proteins
ribozymes
plasmid
This question was previously asked in
UPSC NDA-1 – 2024
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Bacterial DNA is referred to as naked because it is not associated with proteins (specifically histone proteins).
The term “naked DNA” in the context of bacteria refers to the fact that their DNA is not complexed with histone proteins to form chromatin, as is the case with eukaryotic DNA. While bacterial DNA does associate with some non-histone proteins for packaging and organization, the absence of histones is the defining characteristic leading to the term “naked”.
Eukaryotic DNA is wrapped around histone proteins to form nucleosomes, which are further folded to form chromatin. This structured packaging is absent in prokaryotes. Plasmids are extra-chromosomal DNA found in bacteria, not proteins associated with the main chromosome.

46. In most prokaryotes, the chromosome number is :

In most prokaryotes, the chromosome number is :

4
3
2
1
This question was previously asked in
UPSC NDA-1 – 2024
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In most prokaryotes, the chromosome number is 1.
Prokaryotic organisms, such as bacteria and archaea, typically possess a single, circular chromosome located in a region called the nucleoid within the cytoplasm. Unlike eukaryotes, their genetic material is not enclosed within a membrane-bound nucleus and is usually present as one primary chromosome.
While most prokaryotes have one main circular chromosome, some may have linear chromosomes or additional smaller circular DNA molecules called plasmids. Eukaryotes, in contrast, have multiple linear chromosomes located within the nucleus.

47. Consider the following statements: DNA replication takes place when

Consider the following statements:

  • DNA replication takes place when chromatin is opened up.
  • Chromatin organises itself into rod-shaped chromosomes before cell division.
  • Both prokaryotes and eukaryotes have the same process for cell division.

Which of the statements given above is/are correct ?

1 only
1 and 2 only
1, 2 and 3
3 only
This question was previously asked in
UPSC NDA-1 – 2024
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Statements 1 and 2 are correct, while statement 3 is incorrect. Thus, the correct option is B.
Statement 1 is correct: DNA replication happens during the S phase when chromatin is relatively decondensed (‘opened up’) to allow access for replication enzymes. Statement 2 is correct: Before eukaryotic cell division (mitosis or meiosis), the diffuse chromatin fibers condense and coil tightly to form discrete, visible chromosomes. Statement 3 is incorrect: Prokaryotic cell division (binary fission) is a simpler process than eukaryotic cell division (mitosis and meiosis), which involves complex stages, spindle formation, and chromosome segregation mechanisms not found in prokaryotes.
In eukaryotes, DNA replication occurs during interphase, specifically the S phase. Chromosome condensation makes it easier to accurately segregate genetic material during cell division. Prokaryotic cells have a single circular chromosome and divide rapidly through binary fission without forming complex structures like a mitotic spindle.

48. Consider the following cell types: 1. Monocyte 2. Chondrocyte 3. B

Consider the following cell types:

  • 1. Monocyte
  • 2. Chondrocyte
  • 3. Basophil
  • 4. Lymphocyte

How many of the above belong to animal cell types ?

1
2
3
4
This question was previously asked in
UPSC NDA-1 – 2024
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All four listed cell types, Monocyte, Chondrocyte, Basophil, and Lymphocyte, are types of cells found in animals. Therefore, the correct option is D.
Monocytes, Basophils, and Lymphocytes are specific types of white blood cells (leukocytes) found in the circulatory and lymphatic systems of vertebrates, which are animals. Chondrocytes are the cells that produce and maintain cartilage, a connective tissue found in many animals.
Animal cells are eukaryotic cells that form the tissues and organs of animals. The listed cell types are examples of specialized cells performing distinct functions within the animal body, such as immune response (Monocyte, Basophil, Lymphocyte) and structural support (Chondrocyte).

49. Which of the following statements regarding animal cell membrane is co

Which of the following statements regarding animal cell membrane is correct ?

They are composed of phospholipids only.
They are composed of proteins only.
They are composed of phospholipids and proteins only.
They are composed of phospholipids, proteins and cholesterol (lipid).
This question was previously asked in
UPSC NDA-1 – 2024
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The animal cell membrane is a complex structure composed of a phospholipid bilayer, various proteins embedded within or associated with the bilayer, and cholesterol. Phospholipids form the basic structural framework. Proteins perform diverse functions like transport, signaling, and recognition. Cholesterol, a type of lipid, is present in animal cell membranes and plays a crucial role in regulating membrane fluidity and stability. Therefore, the animal cell membrane is composed of phospholipids, proteins, and cholesterol.
The fluid mosaic model is the widely accepted model describing the structure of the cell membrane, depicting it as a fluid bilayer of lipids with proteins embedded or associated with it.
Plant cell membranes also have phospholipid bilayers and proteins, but they typically lack cholesterol. Instead, they contain other sterols. Cell membranes also contain carbohydrates, usually attached to proteins (glycoproteins) or lipids (glycolipids), which are involved in cell recognition and adhesion, although the options only list phospholipids, proteins, and cholesterol as primary constituents.

50. When yeast cells are O₂ starved, fermentation serves as the source of

When yeast cells are O₂ starved, fermentation serves as the source of energy. This results in the production of :

ATP + CO₂ + Ethanol
ATP + O₂ + Pyruvate
ATP + CO₂ + Lactic acid
ATP + O₂ + Acetaldehyde
This question was previously asked in
UPSC NDA-1 – 2023
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When yeast cells are deprived of oxygen, they switch from aerobic respiration to anaerobic fermentation to regenerate NAD⁺ needed for glycolysis. Glycolysis is the initial stage where glucose is broken down into pyruvate, producing a small amount of ATP. In alcoholic fermentation, pyruvate is converted into acetaldehyde and then ethanol, with the release of carbon dioxide. The net products from the glucose under oxygen-starved conditions undergoing fermentation by yeast are ATP (produced during glycolysis), CO₂, and Ethanol.
– Yeast undergoes alcoholic fermentation under anaerobic conditions.
– Fermentation allows glycolysis to continue by regenerating NAD⁺.
– Glycolysis produces ATP.
– Pyruvate is converted to acetaldehyde and then ethanol during alcoholic fermentation, releasing CO₂.
Lactic acid fermentation is another type of fermentation that occurs in muscle cells and some bacteria, producing lactic acid instead of ethanol and CO₂. The primary purpose of fermentation is not to directly produce large amounts of ATP but to regenerate the NAD⁺ consumed during glycolysis, allowing ATP production via glycolysis to continue in the absence of oxygen.
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