Cell

1. Which one of the following human cells is devoid of a nucleus?

Which one of the following human cells is devoid of a nucleus?

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Nerve cell
Bone cell
Red blood cell
White blood cell
This question was previously asked in
UPSC CISF-AC-EXE – 2024
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Mature mammalian red blood cells (erythrocytes) are unique among human cells in that they lack a nucleus, as well as other organelles like mitochondria, ribosomes, and endoplasmic reticulum. This adaptation allows them to maximize the space available for hemoglobin, the protein responsible for oxygen transport, and also makes them more flexible to squeeze through narrow capillaries.
Mature red blood cells are anucleated, meaning they are devoid of a nucleus.
While mature red blood cells in mammals lack a nucleus, this is not the case for red blood cells in birds, reptiles, amphibians, and fish, which retain their nuclei. Nerve cells, bone cells, and white blood cells are all nucleated cells that perform various functions in the body, such as transmitting electrical signals, providing structural support, and fighting infections, respectively.

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2. Consider the following statements about stem cells : 1. Stem cells h

Consider the following statements about stem cells :

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  • 1. Stem cells have the potential for self-renewal via mitotic cell division.
  • 2. In 1908, James Thomas and his colleagues first derived human embryonic stem cells from donated blastocysts through in vitro fertilization.

Which of the statements given above is/are correct?

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1 only
2 only
Both 1 and 2
Neither 1 nor 2
This question was previously asked in
UPSC CISF-AC-EXE – 2024
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The correct answer is A) 1 only.
Statement 1 is correct: Stem cells possess the unique ability to divide and renew themselves through mitotic cell division, maintaining the stem cell population. Statement 2 is incorrect: Human embryonic stem cells were first successfully derived in 1998 by James Thomson and his colleagues at the University of Wisconsin-Madison, not in 1908 by James Thomas.
Stem cells are undifferentiated cells that can differentiate into specialized cell types and can self-renew. There are different types, including embryonic stem cells (derived from blastocysts) and adult stem cells (found in various tissues). Their discovery and potential applications in regenerative medicine are significant areas of research.

3. Which one of the following cell organelles is not lined by membrane ?

Which one of the following cell organelles is not lined by membrane ?

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Lysosome
Ribosome
Nucleus
Golgi Apparatus
This question was previously asked in
UPSC CISF-AC-EXE – 2022
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Cell organelles in eukaryotic cells are often enclosed by membranes. The question asks which of the listed organelles is not lined by a membrane.
– Lysosome: Lined by a single membrane.
– Ribosome: Composed of ribosomal RNA (rRNA) and proteins, not enclosed by a membrane.
– Nucleus: Enclosed by a double membrane (the nuclear envelope).
– Golgi Apparatus: Composed of membrane-bound sacs (cisternae), lined by a single membrane.
Ribosomes are responsible for protein synthesis and are found in both prokaryotic and eukaryotic cells (though they differ in size/structure). Their lack of a membrane is a key structural feature that distinguishes them from many other organelles in eukaryotic cells. Other non-membrane-bound structures in eukaryotic cells include the nucleolus, centrioles, and components of the cytoskeleton.

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4. In a mammalian cell, the protein is synthesized by

In a mammalian cell, the protein is synthesized by

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Ribosome.
Golgi.
Lysosome.
Smooth endoplasmic reticulum.
This question was previously asked in
UPSC CISF-AC-EXE – 2021
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Ribosomes are small organelles found in the cytoplasm of all cells (prokaryotic and eukaryotic), as well as attached to the endoplasmic reticulum in eukaryotic cells. They are the cellular machinery responsible for protein synthesis, a process called translation, where messenger RNA (mRNA) is decoded to build a protein chain.
Protein synthesis involves two main steps: transcription (DNA to mRNA) and translation (mRNA to protein). Translation occurs on ribosomes. Ribosomes are composed of ribosomal RNA (rRNA) and proteins and consist of two subunits, a large one and a small one, which come together during translation.
The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles. Lysosomes contain hydrolytic enzymes for digesting waste materials and cellular debris. The smooth endoplasmic reticulum is involved in lipid synthesis, detoxification, and calcium storage, but not protein synthesis (which occurs on rough ER due to attached ribosomes, or free in the cytoplasm).

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5. Which of the following organelle(s) in an animal cell would have DNA a

Which of the following organelle(s) in an animal cell would have DNA and RNA?

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Nucleus only
Nucleus and mitochondria only
Nucleus, mitochondria and ribosomes
Mitochondria only
This question was previously asked in
UPSC CISF-AC-EXE – 2020
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In an animal cell, the Nucleus and mitochondria only would have DNA and RNA.
– DNA (Deoxyribonucleic Acid) is the primary genetic material in most organisms. In eukaryotic cells, the majority of DNA is found in the nucleus (nuclear DNA), forming chromosomes.
– Eukaryotic cells also contain DNA in certain organelles: mitochondria (mitochondrial DNA or mtDNA) and, in plant cells and some other eukaryotes, chloroplasts (chloroplast DNA or cpDNA). Animal cells lack chloroplasts.
– RNA (Ribonucleic Acid) is involved in protein synthesis and other cellular processes. Various types of RNA (mRNA, tRNA, rRNA) are transcribed from DNA.
– In animal cells:
– Nucleus: Contains the main genome (DNA) and is where transcription occurs, producing various types of RNA. Thus, the nucleus has both DNA and RNA.
– Mitochondria: Contain their own circular DNA (mtDNA) and also have ribosomes (mitoribosomes) made of ribosomal RNA (mt-rRNA) and proteins, and produce their own mRNA and tRNA. Thus, mitochondria have both DNA and RNA.
– Ribosomes: Are complex molecular machines responsible for protein synthesis. They are composed of ribosomal RNA (rRNA) and proteins. Ribosomes themselves do not contain DNA. They read mRNA to build proteins.
– Therefore, in an animal cell, the nucleus and mitochondria are the organelles that contain both DNA and RNA.
While RNA is widely present in the cytoplasm (as mRNA being translated, tRNA carrying amino acids, and ribosomes containing rRNA), the question asks about *organelles* that contain both DNA and RNA. Ribosomes are technically organelles (or macromolecular machines depending on definition), but they lack DNA. The nucleus and mitochondria fit the criteria.

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6. Which one of the following cell organelles synthesizes its own protein

Which one of the following cell organelles synthesizes its own proteins involving genes present in its DNA?

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Endoplasmic reticulum
Plasma membrane
Plastid
Lysosome
This question was previously asked in
UPSC CISF-AC-EXE – 2019
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Plastids (like chloroplasts) contain their own DNA and ribosomes and can synthesize some of their own proteins.
Mitochondria and plastids are unique among eukaryotic organelles because they possess their own circular DNA (similar to bacterial DNA) and ribosomes (70S type). This allows them to synthesize some of the proteins required for their function, independently of the cell’s nucleus and cytoplasmic ribosomes.
The endoplasmic reticulum is involved in protein synthesis and modification but relies on ribosomes attached to it or free in the cytoplasm. The plasma membrane is a structural component. Lysosomes contain enzymes synthesized elsewhere in the cell.

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7. Which of the following statements are correct regarding the general di

Which of the following statements are correct regarding the general difference between plant and animal cells ?

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  • 1. Plant cells have cellulose cell walls whilst animal cells do not.
  • 2. Plant cells do not have plasma membrane unlike animal cells which do.
  • 3. Mature plant cell has one large vacuole whilst animal cell has many small vacuoles.

Select the correct answer using the code given below :

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1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3
This question was previously asked in
UPSC IAS – 2020
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Statement 1 is correct: Plant cells have a rigid outer cell wall made primarily of cellulose, which provides structural support and protection. Animal cells lack a cell wall. Statement 3 is correct: Mature plant cells typically have a single, large central vacuole that can occupy a significant portion of the cell volume, maintaining turgor pressure. Animal cells may have several small vacuoles, but not a large central one.
The presence of a cellulose cell wall and the nature of vacuoles are key distinguishing features between plant and animal cells.
Statement 2 is incorrect: Both plant cells and animal cells have a plasma membrane (also called the cell membrane). The plasma membrane is an essential boundary that encloses the cytoplasm in all living cells, regulating the passage of substances in and out. In plant cells, the plasma membrane is located just inside the cell wall.

8. Which one of the following structure is NOT found in prokaryotes ?

Which one of the following structure is NOT found in prokaryotes ?

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Nuclear envelope
Cell membrane
Ribosome
Cell wall
This question was previously asked in
UPSC CAPF – 2024
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The correct option is A. The nuclear envelope is a structure that is NOT found in prokaryotes.
– Prokaryotic cells (like bacteria and archaea) lack a true nucleus and other membrane-bound organelles.
– The genetic material (DNA) in prokaryotes is located in a region called the nucleoid, which is not enclosed by a membrane.
– The nuclear envelope is the double membrane that surrounds the nucleus in eukaryotic cells.
Cell membranes are present in all cells, prokaryotic and eukaryotic, as they define the cell boundary. Ribosomes, responsible for protein synthesis, are also present in both prokaryotes and eukaryotes, although they differ slightly in size (70S in prokaryotes, 80S in eukaryotes). Cell walls are present in most prokaryotes (like bacteria) and some eukaryotes (like plants and fungi), but not in animal cells.

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9. Both starch and glycogen are made up of glucose, however:

Both starch and glycogen are made up of glucose, however:

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starch is present in liver and glycogen is present in red blood cells.
glycogen is made in animal cells, but starch is made in plant cells.
both starch and glycogen are present in animal and plant cells.
both starch and glycogen are present in plant cells only.
This question was previously asked in
UPSC CAPF – 2023
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Starch and glycogen are both polysaccharides composed of glucose units, serving as energy storage molecules. Starch is the primary storage carbohydrate in plants, found in plastids like chloroplasts and amyloplasts. Glycogen is the primary storage carbohydrate in animals and fungi, mainly stored in the liver and muscles in animals. Therefore, glycogen is made and stored in animal cells, while starch is made and stored in plant cells.
– Both starch and glycogen are glucose polymers used for energy storage.
– Starch is found in plants.
– Glycogen is found in animals and fungi.
Starch exists in two forms: amylose (linear chain) and amylopectin (branched chain). Glycogen is highly branched, more so than amylopectin. The different structures affect their physical properties and rate of breakdown. Neither starch nor glycogen are typically found in both animal and plant cells in significant quantities; their roles are specific to different domains of life. Red blood cells in animals do not store glycogen as they lack the necessary organelles.

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10. The rate of an enzyme catalyzed reaction depends :

The rate of an enzyme catalyzed reaction depends :

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upon substrate concentration and pH, but not on temperature.
only on substrate concentration and pH, but not on temperature.
only on pH and temperature, but not on substrate concentration.
only on temperature, but not on pH and substrate concentration.
This question was previously asked in
UPSC CAPF – 2023
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The rate of an enzyme-catalyzed reaction is influenced by multiple factors. Substrate concentration is a key factor, as the rate typically increases with substrate concentration until enzyme saturation is reached (Michaelis-Menten kinetics). pH affects the ionization state of amino acid residues in the enzyme’s active site and the substrate, influencing enzyme-substrate binding and catalysis; enzymes have optimal pH values. Temperature affects the kinetic energy of molecules, increasing reaction rates with increasing temperature up to an optimum, after which the rate decreases sharply due to enzyme denaturation. Therefore, the rate depends on substrate concentration, pH, and temperature. Option A states the rate depends “upon substrate concentration and pH, but not on temperature”. While the premise that the rate does *not* depend on temperature is scientifically incorrect, among the given options, Option A acknowledges dependence on two crucial factors (Substrate concentration and pH). However, it must be stated that the rate *also* depends significantly on temperature. The phrasing of the options appears flawed as dependence on temperature is a fundamental aspect of enzyme kinetics. Assuming there is an intended correct answer among the choices, Option A includes dependencies on two critical factors, even though its exclusion of temperature is incorrect.
– Enzyme reaction rate depends on substrate concentration, pH, and temperature.
– Substrate concentration affects the frequency of enzyme-substrate collisions and active site saturation.
– pH affects the ionization states of enzyme and substrate, influencing activity.
– Temperature affects molecular kinetic energy and enzyme stability (denaturation).
The relationship between reaction rate and substrate concentration is described by models like the Michaelis-Menten equation. Temperature dependence follows the Arrhenius equation up to the optimal temperature. pH dependence is often represented by a bell-shaped curve. All three factors are interdependent and influence the overall enzyme activity and reaction rate. The provided options contain a significant scientific inaccuracy by claiming the rate does not depend on one of the listed factors. Assuming this is a question from a specific exam where A was marked correct despite the flaw, the justification focuses on the factors mentioned in A.

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