HOTS Questions: Diversity in Living Organisms - UPSC MCQ

The correct answer is B: Nucleus.
The cytoplasm is the fluid-filled region of a cell that surrounds the organelles. It is responsible for various cellular processes and contains numerous structures. However, the nucleus is not considered part of the cytoplasm. Here's why:
1. Ribosome: Ribosomes are small, spherical structures found in the cytoplasm. They are responsible for protein synthesis and can be free-floating or attached to the endoplasmic reticulum.
2. Mitochondrion: Mitochondria are double-membraned organelles found in the cytoplasm. They are often referred to as the "powerhouses" of the cell as they generate energy through cellular respiration.
3. Microtubule: Microtubules are long, cylindrical structures made of protein tubulin. They function in cell division, cell shape maintenance, and intracellular transport. They are part of the cytoskeleton, which supports the cell's structure.
4. Nucleus: The nucleus is a membrane-bound organelle that contains the cell's genetic material. It controls the cell's activities and is involved in processes such as DNA replication and gene expression. However, it is not considered part of the cytoplasm.
In summary, while ribosomes, mitochondria, and microtubules are all part of a cell's cytoplasm, the nucleus is not.

Answer:
The brain of the cell is called the nucleus. Here's a detailed explanation:
Nucleus:
- The nucleus is a membrane-bound organelle found in eukaryotic cells.
- It is often referred to as the "brain of the cell" because it controls most of the cell's activities and contains the genetic material.
- The nucleus houses the DNA, which carries instructions for the cell's functioning and development.
- It regulates gene expression and controls the synthesis of proteins through the process of transcription and translation.
- The nucleus also plays a crucial role in cell division, as it directs the replication and distribution of genetic material during mitosis and meiosis.
Other options and their roles:
Mitochondria:
- Mitochondria are known as the "powerhouses" of the cell because they generate energy in the form of ATP through cellular respiration.
- They are involved in various metabolic processes and play a crucial role in cell survival.
Ribosomes:
- Ribosomes are responsible for protein synthesis.
- They read the messenger RNA (mRNA) and assemble amino acids into polypeptide chains according to the instructions encoded in the mRNA.
Plasma membrane:
- The plasma membrane, also known as the cell membrane, encloses the cell and regulates the movement of substances in and out of the cell.
- It helps maintain the cell's internal environment and provides protection and support.
In conclusion, the nucleus is called the brain of the cell because it controls most of the cell's activities and contains the genetic material.

The Nucleus and its Components:
The nucleus is a membrane-bound organelle found in eukaryotic cells. It contains the cell's genetic material and is responsible for controlling cell activities. The nucleus consists of several components, including:
1. Chromatin: Chromatin is a complex of DNA, RNA, and proteins. It is the genetic material of the cell and is responsible for the transmission of genetic information. Chromatin is present in the nucleus and undergoes condensation to form chromosomes during cell division.
2. Nucleolus: The nucleolus is a dense structure within the nucleus. It is involved in the production and assembly of ribosomes, which are responsible for protein synthesis. The nucleolus contains ribosomal DNA and various proteins.
3. Centrosome: The centrosome is not a part of the nucleus. It is located near the nucleus and consists of two centrioles. The centrosome plays a crucial role in cell division by organizing the microtubules that form the spindle apparatus.
4. Nucleoplasm: Nucleoplasm is the fluid-like substance present within the nucleus. It contains various enzymes, ions, and other molecules necessary for nuclear processes. The nucleoplasm provides a medium for the movement of molecules within the nucleus.
Answer: C. Centrosome is not a part of the nucleus.

Common Features of Nucleus, Chloroplast, and Mitochondrion:
- DNA: All three organelles contain DNA, which is responsible for encoding genetic information.
- Lamellae: None of these organelles have lamellae. Lamellae are found in structures like chloroplasts and are involved in photosynthesis.
- Cristae: Only mitochondria have cristae. Cristae are the folds in the inner membrane of mitochondria that increase the surface area for cellular respiration.
- All of these: The correct answer is option A. All three organelles (nucleus, chloroplast, and mitochondrion) share the common feature of containing DNA.
So, the correct answer is A: DNA.

Explanation:
The nuclear envelope is a double membrane that surrounds the nucleus of a cell. It consists of an outer and inner membrane, with a small space between them called the perinuclear space. The nuclear envelope separates the nucleus from the surrounding cytoplasm and controls the movement of substances in and out of the nucleus.
Key points:
- The nuclear envelope is double-layered, consisting of an inner and outer membrane.
- The two membranes are separated by a space called the perinuclear space.
- The outer membrane is continuous with the endoplasmic reticulum, a network of membranes involved in protein synthesis and lipid metabolism.
- The nuclear envelope contains nuclear pores, which are protein-lined channels that allow for the exchange of materials between the nucleus and cytoplasm.
- The nuclear envelope is selectively permeable, meaning it regulates the passage of molecules and ions in and out of the nucleus.
- The double-layered structure and presence of nuclear pores make the nuclear envelope porous, allowing for the movement of certain molecules and ions.
Conclusion:
The correct answer is B: Double and porous.

Nucleoplasm is continuous with cytoplasm through nuclear pores.
- Nucleoplasm is the fluid-like substance present within the nucleus of a cell.
- Cytoplasm is the fluid-like substance present outside the nucleus, within the cell.
- The nucleus is separated from the cytoplasm by the nuclear envelope, which consists of two membranes and is perforated by nuclear pores.
- These nuclear pores serve as channels for the exchange of molecules between the nucleus and the cytoplasm.
- The nuclear pores are large protein complexes that allow the selective movement of molecules such as RNA, proteins, and other macromolecules.
- These pores are essential for the regulation of gene expression, as they control the movement of transcription factors, RNA molecules, and other regulatory proteins.
- Thus, the nucleoplasm is continuous with the cytoplasm through these nuclear pores, facilitating the exchange of molecules and maintaining cellular homeostasis.
In summary:
- Nucleoplasm is the fluid-like substance within the nucleus.
- Cytoplasm is the fluid-like substance outside the nucleus.
- The nuclear envelope separates the nucleus from the cytoplasm.
- Nuclear pores are channels in the nuclear envelope that allow the exchange of molecules between the nucleus and the cytoplasm.
- The nucleoplasm is continuous with the cytoplasm through these nuclear pores.

Felice Fontana

An Italian scientist named Felice Fontana discovered the nucleolus in eel cells in the year 1774. In 1964, John Gurdon and Donald Brown discovered cell nucleoli in Xenopus laevis (African clawed frog) eggs.

The function of the nucleolus in the cell is:

• Synthesis of RNA and ribosomes: The nucleolus is responsible for synthesizing ribosomal RNA (rRNA) and assembling ribosomes, which are essential for protein synthesis.

Explanation:
The nucleolus is a distinct structure within the nucleus of a cell. It plays a crucial role in the production of ribosomes, the cellular machinery responsible for protein synthesis. Here is a detailed explanation of the nucleolus' function:
1. Synthesis of RNA: The nucleolus is primarily involved in the synthesis of ribosomal RNA (rRNA), which is a key component of ribosomes. It contains specialized regions called nucleolar organizer regions (NORs) that contain the genes responsible for producing rRNA.
2. Assembly of ribosomes: In addition to rRNA synthesis, the nucleolus also facilitates the assembly of ribosomes. It contains proteins and other molecules necessary for ribosome formation. These components, along with the rRNA synthesized in the nucleolus, combine to form the two subunits of ribosomes, which are later exported to the cytoplasm.
3. Regulation of ribosome production: The nucleolus also plays a role in regulating ribosome production in response to the cell's needs. It can adjust the rate of rRNA synthesis and ribosome assembly based on signals from the cell's environment, such as nutrient availability and growth factors.
Overall, the nucleolus is vital for the production and assembly of ribosomes, which are essential for protein synthesis in cells. Its function in synthesizing rRNA and facilitating ribosome formation makes it a crucial component of cellular processes.

Phenomena referred to as 'cell drinking' is:

Pinocytosis
Pinocytosis is a cellular process in which cells take in extracellular fluid and associated solutes. It is commonly referred to as 'cell drinking' because the cells engulf small droplets of fluid from their surroundings.
Explanation:
Pinocytosis involves the following steps:
1. Formation of vesicles: The plasma membrane invaginates, forming small vesicles called pinocytic vesicles.
2. Ingestion of fluid: The pinocytic vesicles engulf the extracellular fluid along with dissolved substances.
3. Transportation: The pinocytic vesicles move into the cytoplasm of the cell.
4. Processing and utilization: The vesicles fuse with lysosomes, where the ingested materials are broken down and processed for utilization by the cell.
Pinocytosis is a non-specific process and occurs in various cell types. It plays a role in nutrient uptake, immune responses, and maintenance of cellular homeostasis. Unlike phagocytosis, which involves the engulfment of large particles, pinocytosis is characterized by the intake of liquid and dissolved substances.
Therefore, the correct answer is B: Pinocytosis.

The cell organelle taking part in photorespiration is the peroxisome.
- Photorespiration is a metabolic pathway that occurs in plants when they fix oxygen instead of carbon dioxide during the process of photosynthesis.
- This process takes place in the peroxisome, which is a specialized organelle found in eukaryotic cells.
- The peroxisome contains enzymes called photorespiratory enzymes that are responsible for carrying out the photorespiration process.
- These enzymes help convert toxic compounds produced during photorespiration into less harmful substances.
- The peroxisome also plays a role in other cellular processes, such as fatty acid metabolism and detoxification of harmful substances.
- Other organelles, such as the chloroplast and mitochondria, are involved in photosynthesis and respiration, respectively, but the peroxisome specifically participates in photorespiration.
- The peroxisome is involved in the breakdown of hydrogen peroxide, a byproduct of photorespiration, into water and oxygen.
- Without the peroxisome, the photorespiration process would not be able to occur efficiently, leading to negative effects on plant growth and development.
In conclusion, the peroxisome is the cell organelle that takes part in photorespiration, playing a crucial role in converting toxic compounds and maintaining the overall balance of cellular processes.

Endoplasmic Reticulum and its Components
The endoplasmic reticulum (ER) is an important organelle found in eukaryotic cells. It plays a crucial role in various cellular processes, including protein synthesis, lipid metabolism, and calcium storage. There are two types of ER: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).
1. Rough Endoplasmic Reticulum (RER)
- RER is characterized by the presence of ribosomes attached to its surface, giving it a rough appearance under a microscope.
- Ribosomes are responsible for protein synthesis. They read the genetic instructions from the messenger RNA (mRNA) and assemble amino acids into proteins.
- Thus, RER contains ribosomes, making option A (Ribosomes) the correct answer.
2. Smooth Endoplasmic Reticulum (SER)
- Unlike RER, SER does not have ribosomes attached to its surface.
- SER is involved in various functions, including lipid metabolism, detoxification of drugs and toxins, and calcium storage.
- SER synthesizes lipids, such as phospholipids and steroids, which are important components of cell membranes.
- It also detoxifies harmful substances by modifying them into more water-soluble compounds that can be excreted from the cell.
- Additionally, SER stores calcium ions, which are crucial for cell signaling and muscle contractions.
Conclusion:
In conclusion, the endoplasmic reticulum (ER) contains ribosomes, which are responsible for protein synthesis. Therefore, option A (Ribosomes) is the correct answer. Lysosomes, Golgi bodies, and none of these are not components of the ER.

Ribosomes are composed of 2 subunits

Here is a detailed explanation of the composition of ribosomes:
1. Structure of Ribosomes:
- Ribosomes are cellular organelles responsible for protein synthesis.
- They consist of two subunits, a large subunit, and a small subunit, which come together during protein synthesis but can also exist separately.
- The large subunit is responsible for peptide bond formation, while the small subunit helps in mRNA decoding.
2. Composition of Ribosomal Subunits:
- Both the large and small subunits of ribosomes are composed of RNA and proteins.
- The small subunit contains one RNA molecule called ribosomal RNA (rRNA) along with associated proteins.
- The large subunit contains three rRNA molecules and a larger number of proteins compared to the small subunit.
3. RNA Component:
- The ribosomal RNA (rRNA) molecules play a crucial role in the structure and function of ribosomes.
- They provide a scaffold for the assembly of ribosomal proteins and help in catalyzing the formation of peptide bonds during protein synthesis.
4. Protein Component:
- The protein component of ribosomes helps stabilize the overall structure of the ribosomal subunits.
- These proteins are involved in various functions, such as providing binding sites for mRNA and tRNA, facilitating the movement of the ribosome along the mRNA, and promoting protein folding.
5. Assembly of Ribosomes:
- The two subunits of ribosomes are assembled separately in the nucleolus of the cell.
- The small and large subunits are then exported to the cytoplasm, where they come together to form a functional ribosome during protein synthesis.
In conclusion, ribosomes are composed of two subunits, a large subunit, and a small subunit, each containing a combination of ribosomal RNA (rRNA) molecules and associated proteins. These subunits come together during protein synthesis to form a functional ribosome.

The green pigment chlorophyll is located within the thylakoid membrane, and the space between the thylakoid and the chloroplast membranes is called the stroma

The sedimentation coefficient of a molecule is a measure of its size and shape. It is expressed in Svedberg units (S), which are based on the speed at which the molecule sedimentates in a centrifugal field. The sedimentation coefficient of the complete ribosome in a bacterial cell is 70S.
Here is a detailed explanation:
Definition of sedimentation coefficient:
The sedimentation coefficient is a measure of the rate at which a molecule moves through a centrifugal field during sedimentation. It is influenced by the size, shape, and mass of the molecule.
Sedimentation coefficient of ribosomes:
Ribosomes are involved in protein synthesis and are composed of two subunits, the large subunit (LSU) and the small subunit (SSU). The sedimentation coefficient of ribosomes is determined by the combination of these subunits.
In bacterial cells, the complete ribosome consists of a 50S large subunit and a 30S small subunit. When these subunits combine, they form a 70S ribosome.
Explanation of the answer:
The sedimentation coefficient of 70S indicates that the complete ribosome in a bacterial cell has a sedimentation rate equivalent to 70 times that of a standard sedimentation unit.
- Option A: 70S - This is the correct answer as explained above.
- Option B: 80S - The sedimentation coefficient of 80S is typically found in eukaryotic cells, not bacterial cells.
- Option C: 78S - This is not the correct answer as the sedimentation coefficient of the complete ribosome in bacterial cells is 70S.
- Option D: 60S - This is not the correct answer as the sedimentation coefficient of the complete ribosome in bacterial cells is 70S, not 60S.
In conclusion, the sedimentation coefficient of the complete ribosome in a bacterial cell is 70S, which indicates the combined sedimentation rate of the 50S large subunit and the 30S small subunit.

Common Features in Plant and Animal Cells:
There are several structures and components that are common in both plant and animal cells. One such feature is the mitochondria. Here is a detailed explanation of the common features:
Mitochondria:
- Mitochondria are double-membraned organelles found in the cytoplasm of both plant and animal cells.
- They are often referred to as the "powerhouse" of the cell because they are responsible for producing energy in the form of ATP through cellular respiration.
- Mitochondria have their own DNA and can self-replicate.
- They are involved in various cellular processes, including metabolism and apoptosis (programmed cell death).
- Mitochondria have an inner membrane that is folded into structures called cristae, which increase the surface area for ATP production.
Other Features:
Although mitochondria are a common feature, there are other structures and components that differ between plant and animal cells. These include:
Chloroplasts:
- Chloroplasts are found only in plant cells and are responsible for photosynthesis.
- They contain a pigment called chlorophyll that captures light energy and converts it into chemical energy.
- Chloroplasts have their own DNA and can self-replicate, similar to mitochondria.
Centrioles:
- Centrioles are found only in animal cells and are involved in cell division.
- They play a crucial role in the formation of spindle fibers, which help separate chromosomes during mitosis.
Cell Wall:
- The cell wall is a rigid structure found in plant cells, bacteria, fungi, and some protists.
- It provides structural support and protection to the cell.
- Animal cells do not have a cell wall; instead, they have a flexible cell membrane.
In conclusion, while mitochondria are common in both plant and animal cells, chloroplasts and cell walls are specific to plants, and centrioles are specific to animal cells.

The correct answer is option A: Vacuoles.
Explanation:
A nonliving cell inclusion refers to a structure or component found within a cell that is not considered a living entity. Let's examine each option to determine which one fits the description:
- Vacuoles: Vacuoles are membrane-bound sacs found in plant and animal cells. They serve various functions, including storage of water, nutrients, and waste products. Vacuoles are considered nonliving cell inclusions because they are not considered living entities.
- Ribosomes: Ribosomes are small structures found in the cytoplasm of cells. They are responsible for protein synthesis and are considered living entities as they contain RNA and proteins.
- Centrosomes: Centrosomes are structures found in animal cells near the nucleus. They play a role in cell division and contain centrioles. Centrosomes are considered living entities.
- Golgi complex: The Golgi complex, also known as the Golgi apparatus, is a stack of flattened membranes found in eukaryotic cells. It is involved in the processing, packaging, and distribution of molecules within the cell. The Golgi complex is considered a living entity.
Therefore, the nonliving cell inclusion among the given options is vacuoles (option A).

Cell Vacuole Contains:
- Water: The vacuole is filled with water, which makes up the majority of its volume. Water is essential for maintaining the turgidity and shape of the cell.
- Dissolved Substances: Along with water, the vacuole contains various dissolved substances such as sugars, salts, organic acids, and enzymes. These substances play important roles in cellular processes and can act as storage for nutrients and waste products.
- Metabolic Gases: The vacuole may also contain metabolic gases such as oxygen and carbon dioxide. These gases are involved in cellular respiration and photosynthesis, respectively.
- Cytoplasm: The vacuole is surrounded by the cytoplasm, the gel-like substance that fills the cell. The cytoplasm contains various organelles and is involved in many cellular functions.
The vacuole is an important organelle in plant cells, providing structural support, regulating cell volume, storing substances, and facilitating cellular processes. Its contents contribute to the overall functioning and survival of the cell.

- Centrioles play a crucial role in cell division in animal cells.
- They are involved in the formation of the spindle apparatus, which is essential for separating chromosomes during mitosis and meiosis.
- Spindle fibers, which originate from the centrosomes (where centrioles are located), attach to chromosomes and help pull them apart to opposite poles of the cell.
- Thus, centrioles are directly involved in spindle formation, making option D the correct answer.

Answer:
The correct answer is B: Ribosome.
A ribosome is an organelle within an organelle because it is found within the cytoplasm of a cell, which is itself an organelle within the cell. Ribosomes are responsible for protein synthesis and are found in all living cells. Here is a detailed explanation:
- Ribosome: A ribosome is a small, spherical organelle found in the cytoplasm of a cell. It is composed of RNA and protein and is responsible for protein synthesis. Ribosomes can be found freely in the cytoplasm or attached to the endoplasmic reticulum.
- Organelle within an organelle: An organelle is a specialized structure within a cell that has a specific function. In the case of ribosomes, they are considered "organelles within organelles" because they are found within the cytoplasm, which itself is an organelle within the cell.
- Plastid: Plastids are a group of organelles found in plant cells. They include chloroplasts, which are responsible for photosynthesis, as well as other types of plastids such as leucoplasts and chromoplasts. Plastids are not considered "organelles within organelles."
- Lysosome: Lysosomes are organelles responsible for the digestion and recycling of cellular waste. They contain enzymes that break down molecules and are involved in various cellular processes. However, lysosomes are not considered "organelles within organelles."
- Microsome: Microsomes are small vesicles derived from the endoplasmic reticulum. They are involved in lipid metabolism and protein synthesis. However, microsomes are not considered "organelles within organelles."
In conclusion, a ribosome is called "an organelle within an organelle" because it is found within the cytoplasm, which itself is an organelle within the cell.

Cell organelle common in Protista and Monera is Ribosome
Explanation:
- Ribosome is a cell organelle that is present in both Protista and Monera.
- It is responsible for protein synthesis in cells.
- Ribosomes are found in all living cells, including bacteria (Monera) and single-celled organisms (Protista).
- They are also present in eukaryotic cells, such as those found in plants and animals.
- Ribosomes can be found free in the cytoplasm or attached to the endoplasmic reticulum.
- They consist of a large subunit and a small subunit, which work together to assemble amino acids into proteins.
- Ribosomes are essential for the growth and maintenance of cells, and their presence in both Protista and Monera highlights their importance in basic cellular processes.
- This makes ribosomes a common organelle in these two groups of organisms.

Ribosomes lack membranes.
- Ribosomes are small, spherical organelles found in the cytoplasm of cells.
- They are responsible for protein synthesis, translating the genetic information from the nucleus into functional proteins.
- Unlike other organelles, ribosomes lack a membrane structure.
- They are composed of two subunits, a small subunit, and a large subunit, which come together during protein synthesis.
- Ribosomes can be found freely floating in the cytoplasm or attached to the endoplasmic reticulum.
- Their lack of a membrane allows them to directly interact with mRNA and tRNA during protein synthesis.
- The absence of a membrane also enables ribosomes to easily move within the cytoplasm and attach to different mRNA molecules.
- Ribosomes are found in all types of cells, both prokaryotic and eukaryotic, indicating their essential role in protein synthesis.

The correct option is C.
The other two cell wall networks are Pectic and glycoprotein other than cellulose microfibrils.

The location of the middle lamella in the plant cell wall:
The middle lamella is a layer that occurs between adjacent plant cell walls. It plays a crucial role in holding the cell walls together and providing structural support to the plant tissue. The location of the middle lamella can be described as follows:
1. Inner to primary wall:
The primary wall is the first layer that is formed around the plant cell when it is growing. The middle lamella is located inside the primary wall, forming a boundary between adjacent cells.
2. Inner to secondary wall:
In some plant cells, a secondary wall is formed inside the primary wall, providing additional strength and support. The middle lamella is present between the secondary walls of adjacent cells.
3. Outer to secondary wall:
Contrary to the above option, the middle lamella is not located outside the secondary wall. It is positioned between the secondary walls of neighboring cells.
4. Outer to primary wall:
Similarly, the middle lamella is not found outside the primary wall. It is situated inside the primary wall, separating adjacent cells.
Therefore, the correct answer is option D: Outer to primary wall. The middle lamella occurs between adjacent plant cell walls, specifically outside the primary wall.

Hydrophilic Chemical of Cell Wall: Pectin
Pectin is a hydrophilic chemical found in the cell walls of plants. It is a complex polysaccharide made up of a chain of galacturonic acid molecules. Pectin is responsible for several important functions in the cell wall, including:
1. Water Absorption: Pectin has a high water-holding capacity, allowing it to absorb and retain water in the cell wall. This helps to maintain the turgidity and rigidity of plant cells.
2. Cell Adhesion: Pectin acts as a glue-like substance, binding adjacent plant cells together. It forms a gel-like matrix that provides structural support to the cell wall and helps maintain the overall integrity of the plant tissue.
3. Regulation of Cell Wall Porosity: Pectin plays a role in controlling the permeability of the cell wall. It can form a barrier that regulates the movement of substances in and out of the cell, allowing for selective transport.
4. Plant Defense: Pectin is involved in plant defense mechanisms against pathogens. It can form a physical barrier that limits the penetration of pathogens into the plant tissue.
In conclusion, pectin is a hydrophilic chemical in the cell wall that has various functions, including water absorption, cell adhesion, regulation of porosity, and plant defense.