Cell

51. Which one of the following structures or components is not always pr

Which one of the following structures or components is not always present in living cells ?

Cell wall
Plasma membrane
Cytoplasm
Genetic material
This question was previously asked in
UPSC NDA-1 – 2023
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The correct answer is A) Cell wall.
While the plasma membrane, cytoplasm, and genetic material (DNA or RNA) are fundamental components found in *all* living cells (both prokaryotic and eukaryotic), the cell wall is not universally present.
A cell wall is a rigid outer layer found in plant cells, fungal cells, bacterial cells, and some protists. However, animal cells, which are also living cells, lack a cell wall. Therefore, the cell wall is not always present in living cells.

52. In a plant cell, which one of the following contains their own DNA ?

In a plant cell, which one of the following contains their own DNA ?

Nucleus and Endoplasmic Reticulum
Ribosome and Golgi apparatus
Mitochondria and Chloroplast
Chloroplast and Vacuoles
This question was previously asked in
UPSC NDA-1 – 2023
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The correct answer is C) Mitochondria and Chloroplast.
In a plant cell (which is a eukaryotic cell), the majority of the genetic material (DNA) is located in the nucleus. However, some organelles within the plant cell also contain their own DNA. These are mitochondria and chloroplasts (which are a type of plastid). Both mitochondria and chloroplasts are thought to have originated from endosymbiotic events and retain their own small, circular DNA molecules (mtDNA and cpDNA, respectively), as well as their own ribosomes (70S type, similar to prokaryotes), allowing them to synthesize some of their own proteins. The Endoplasmic Reticulum, Ribosomes (cytoplasmic), Golgi apparatus, and Vacuoles are all organelles found in plant cells, but they do not contain their own DNA. Ribosomes themselves are not organelles in the sense of being membrane-bound structures, and while they are involved in protein synthesis, they don’t contain the genetic code (DNA) for those proteins.
The presence of independent DNA in mitochondria and chloroplasts supports the endosymbiotic theory, which posits that these organelles originated from free-living prokaryotic organisms that were engulfed by ancestral eukaryotic cells. This DNA allows for some degree of semi-autonomy for these organelles within the cell.

53. Which one of the following structures is not present in a prokaryoti

Which one of the following structures is not present in a prokaryotic cell ?

Cell wall
Ribosomes
Nucleus
Plasma membrane
This question was previously asked in
UPSC NDA-1 – 2023
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The correct answer is C) Nucleus.
Prokaryotic cells (like bacteria and archaea) are characterized by the absence of membrane-bound organelles. The nucleus is a membrane-bound organelle that houses the genetic material in eukaryotic cells. In prokaryotic cells, the genetic material (usually a single circular chromosome) is located in a region called the nucleoid, but it is not enclosed within a membrane. Cell walls are typically present in most prokaryotes, providing structural support. Ribosomes are present in prokaryotic cells and are essential for protein synthesis (prokaryotic ribosomes are smaller, 70S, compared to eukaryotic 80S). The plasma membrane (cell membrane) is a fundamental component present in all types of cells, both prokaryotic and eukaryotic, enclosing the cytoplasm.
Other membrane-bound organelles absent in prokaryotes include mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles. This structural simplicity is a defining characteristic of prokaryotic life.

54. Consider the following statements regarding cell wall composition :

Consider the following statements regarding cell wall composition :

  • Bacterial cell wall is made of peptidoglycan.
  • Fungal cell wall is made of cellulose.
  • Animals lack cell wall and have extracellular matrix made up of sugar and proteins.

Select the correct answer using the code given below :

2 only
1 and 2
1 and 3
1, 2 and 3
This question was previously asked in
UPSC NDA-1 – 2023
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The correct answer is C) 1 and 3.
Statement 1 is correct. The cell wall of most bacteria is primarily composed of peptidoglycan, a polymer consisting of sugars and amino acids, which provides structural support and protection. Statement 2 is incorrect. Fungal cell walls are mainly composed of chitin, a tough polysaccharide, although other components like glucans are also present. Plant cell walls are made of cellulose. Statement 3 is correct. Animal cells do not possess a rigid cell wall. Instead, animal tissues have an extracellular matrix (ECM) which is a complex network of secreted molecules, including various proteins (like collagen, elastin) and glycoproteins (like proteoglycans, which are composed of protein and carbohydrate chains), providing support, adhesion, and signaling functions.
The presence or absence and composition of the cell wall are key distinguishing features between different kingdoms of life. Bacteria, fungi, and plants all have cell walls, but their composition differs significantly. Animals do not have cell walls, which allows for greater flexibility and mobility of their cells and tissues.

55. A cell is unable to synthesize lipids. Which of its cell organelles mi

A cell is unable to synthesize lipids. Which of its cell organelles might be defective?

Smooth endoplasmic reticulum
Golgi bodies
Lysosomes
Mitochondria
This question was previously asked in
UPSC NDA-1 – 2022
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The correct option is A.
The smooth endoplasmic reticulum (SER) is a major site for lipid synthesis in eukaryotic cells.
The smooth endoplasmic reticulum synthesizes various lipids, including phospholipids, steroids, and oils. It is also involved in the detoxification of drugs and poisons, and the storage of calcium ions. Golgi bodies are involved in protein and lipid modification and packaging. Lysosomes contain hydrolytic enzymes for intracellular digestion. Mitochondria are primarily involved in energy production through cellular respiration.

56. Which one of the following statements about ‘vacuoles’ is not correct?

Which one of the following statements about ‘vacuoles’ is not correct?

In plants, there is a large central vacuole that may occupy 90% of total cell volume.
In plant cells, vacuoles provide turgidity and rigidity.
In Amoeba, vacuoles have role in nutrition.
Vacuoles are absent in animal cells.
This question was previously asked in
UPSC NDA-1 – 2022
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Statement D is incorrect. Vacuoles are indeed present in animal cells, although they are generally smaller, more numerous, and less prominent than the large central vacuole found in mature plant cells. Animal cell vacuoles can perform various functions, including storage, waste disposal, protection, and growth. Statements A, B, and C are correct descriptions of vacuole functions in plants and some protists like Amoeba.
Vacuoles are present in both plant and animal cells, but their size and primary functions differ significantly.
In plant cells, the large central vacuole helps maintain turgor pressure, provides structural support, stores water, ions, nutrients, and waste products. In Amoeba, contractile vacuoles are crucial for osmoregulation, and food vacuoles are formed during phagocytosis for digestion.

57. Which one of the following plant plastids stores starch, oil and prote

Which one of the following plant plastids stores starch, oil and protein granules?

Chloroplast
Leucoplast
Chromoplast
Xanthoplast
This question was previously asked in
UPSC NDA-1 – 2022
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Leucoplasts are colourless plastids found in plant cells. They are primarily involved in the storage of various nutrients. Different types of leucoplasts are specialized for storing specific substances: amyloplasts store starch, elaioplasts store oils or fats, and aleuroplasts (or proteinoplasts) store proteins. The question asks for a plastid that stores starch, oil, and protein granules, and leucoplast is the general category that includes these specific storage plastids.
Leucoplasts are storage plastids in plant cells, specialized for storing starch, oils, and proteins.
Chloroplasts contain chlorophyll and are the sites of photosynthesis. Chromoplasts contain carotenoid pigments (like carotenes and xanthophylls) and give colour to flowers and fruits. Xanthoplast is a type of chromoplast containing yellow pigments (xanthophylls).

58. If human blood is placed in a 2% detergent solution, what will happen

If human blood is placed in a 2% detergent solution, what will happen to the RBC?

The RBC will shrink.
The RBC will swell and become turgid.
The RBC will swell and burst.
The RBC will lyse.
This question was previously asked in
UPSC NDA-1 – 2021
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The correct answer is (D) The RBC will lyse.
Detergents are surfactants that disrupt cell membranes, which are primarily composed of lipid bilayers and proteins. Placing red blood cells (RBCs) in a detergent solution causes the detergent molecules to interact with and solubilize the lipids and proteins of the cell membrane. This disruption leads to the breakdown and disintegration of the cell membrane, a process called lysis.
While osmotic effects (swelling/bursting in hypotonic solutions or shrinking in hypertonic solutions) can cause RBCs to change shape and potentially lyse (in hypotonic conditions), the primary action of a detergent is direct chemical disruption of the membrane structure, leading to lysis regardless of simple osmosis. A 2% detergent solution is a potent cell lysing agent.

59. Transformation of meristematic cells into specific permanent tissues o

Transformation of meristematic cells into specific permanent tissues occurs by the process of

Cell differentiation.
Cell division.
Cell multiplication.
Cell regeneration.
This question was previously asked in
UPSC NDA-1 – 2021
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The correct answer is A) Cell differentiation. Cell differentiation is the process by which a less specialized cell becomes a more specialized cell type.
– Meristematic cells are undifferentiated plant cells capable of active division.
– Permanent tissues are composed of cells that have undergone differentiation and often lose the ability to divide or divide slowly, performing specific functions.
– Differentiation involves changes in cell structure and function leading to specialization.
– Cell division (or multiplication) is the process by which a parent cell divides into two or more daughter cells, increasing the number of cells but not necessarily leading to specialization.
– Cell regeneration refers to the regrowth of damaged or missing tissues or organs.

60. In mitochondria, ATP synthesizing chemical reactions take place in the

In mitochondria, ATP synthesizing chemical reactions take place in the

Outer membrane.
Matrix.
Inner membrane.
DNA of mitochondria.
This question was previously asked in
UPSC NDA-1 – 2021
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In mitochondria, ATP synthesizing chemical reactions, specifically oxidative phosphorylation, take place on the inner membrane.
The inner mitochondrial membrane contains the electron transport chain complexes and ATP synthase. The process of oxidative phosphorylation, which generates the vast majority of ATP in cellular respiration, involves creating a proton gradient across the inner membrane (protons pumped from the matrix to the intermembrane space) and then using the potential energy of this gradient as protons flow back into the matrix through ATP synthase, which catalyzes the synthesis of ATP from ADP and phosphate.
The matrix is where the Krebs cycle occurs, producing electron carriers (NADH and FADH₂) that feed electrons into the electron transport chain located on the inner membrane. The outer membrane is permeable to small molecules and ions. Mitochondrial DNA (mtDNA) is located in the matrix and encodes some of the proteins required for mitochondrial function, but not the main ATP synthesizing reactions themselves.
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