Cell membrane Questions in English

(D) membrane that allows the passage of certain substances more readily than others is known as a selectively permeable membrane.
This type of membrane controls the movement of molecules based on their size,solubility,and charge.
Examples include the plasma membrane,the tonoplast of the vacuole,and the membrane of root hairs.
Unlike a semipermeable membrane,which only allows the passage of solvent molecules,a selectively permeable membrane actively regulates the transport of specific solutes.

(A) The $Na^+/K^+$-ATPase pump is a primary active transport mechanism found in the plasma membrane of animal cells.
It functions by hydrolyzing $ATP$ to provide energy for the active transport of ions against their concentration gradients.
Specifically,for every molecule of $ATP$ hydrolyzed,the pump moves $3$ $Na^+$ ions out of the cell and $2$ $K^+$ ions into the cell.
Therefore,it facilitates the inward transport of $K^+$ and the outward transport of $Na^+$.

(B) The ultrafiltration theory was proposed by $W. Ruhland$ $(1912)$ and $Hoffman$ $(1925)$.
According to this theory,the cell membrane acts as a molecular sieve.
It suggests that small pores are present on the membrane.
Only those molecules that are smaller in size than the pores of the membrane can pass through it.
Therefore,the correct option is $B$.

(C) The theory of lipid solubility,also known as the Overton's concept,was proposed by Charles Ernest Overton in $1899$.
He observed that substances soluble in lipids (fats) penetrate the cell membrane more rapidly than those that are not.
This observation led to the conclusion that the cell membrane is composed of a lipid layer,which acts as a barrier to the entry of water-soluble substances.

(D) In secondary active transport,such as the symport of sugars or amino acids across the cell membrane,the transport protein utilizes the electrochemical gradient of $Na^+$ ions.
Specifically,$Na^+$ ions move into the cell down their concentration gradient (from a region of higher concentration outside to a region of lower concentration inside).
This movement of $Na^+$ ions provides the energy required to transport sugar or amino acid molecules against their own concentration gradient into the cell.
Therefore,$Na^+$ ions move in the direction of their concentration gradient.

(A) The plasma membrane is a selectively permeable membrane that maintains the integrity of the cell contents.
At room temperature (cold water),the membrane remains intact and prevents the leakage of pigments like anthocyanins from the cell.
When the water is boiled,the high temperature causes the denaturation of proteins and the destruction of the lipid bilayer of the plasma membrane.
This loss of semi-permeability allows the pigments to leak out into the surrounding water,causing the water to change colour.

(B) The Nobel Prize in Physiology or Medicine in $1991$ was awarded to Erwin Neher and Bert Sakmann for their discoveries concerning the function of single ion channels in cells.
They developed the patch-clamp technique,which allows for the measurement of the tiny electrical currents that flow through individual ion channels in the cell membrane.

(D) The cell membrane is composed of a lipid bilayer that is hydrophobic in nature,making it difficult for water-soluble substances to pass through directly.
Channel proteins are specialized integral membrane proteins that form hydrophilic pores or channels across the membrane.
These channels allow water-soluble molecules and ions to pass through the membrane via facilitated diffusion,bypassing the hydrophobic lipid core.

(C) . Pinocytosis is the bulk transport of fluid matter and substances across the cell membrane by forming minute detachable vesicles of $100-200 \ nm$ diameter. Pinocytosis is also known as cell drinking.

(C) The sodium-potassium pump is a transmembrane protein complex that actively transports ions across the cell membrane.
It functions as a carrier protein that uses energy from $ATP$ hydrolysis to move $3$ $Na^+$ ions out of the cell and $2$ $K^+$ ions into the cell against their respective concentration gradients.
Therefore,it is classified as a protein carrier (specifically an ion pump).

(C) Porins are large transport proteins that form large pores in the outer membranes of plastids,mitochondria,and some bacteria. These pores allow molecules up to the size of small proteins to pass through the membrane. Since they are composed of amino acid chains,they are classified as proteins.

(C) The cell membrane is composed of a lipid bilayer,which is hydrophobic in nature.
Hydrophilic (water-loving) substances cannot pass through this lipid bilayer easily.
Specialized membrane proteins,known as transport proteins or channel proteins,are embedded within the lipid bilayer.
These proteins provide specific sites and facilitate the movement of hydrophilic substances across the membrane,often through facilitated diffusion or active transport.

(A) The plasma membrane (also known as the cell membrane) is a selectively permeable membrane.
It allows only certain molecules or ions to pass through it by active or passive transport,while restricting others.
In contrast,the cell wall is generally freely permeable to water and solutes.
While mitochondrial and chloroplast membranes are semi-permeable,the plasma membrane is the primary biological example of a selectively permeable membrane in the context of cellular transport.

(B) Porins are channel proteins present in the outer membranes of mitochondria,plastids (like chloroplasts),and some bacteria.
These proteins form large channels or pores that allow the passage of molecules up to the size of small proteins.
Therefore,molecules as large as proteins can pass through these pores.

(C) Porins are proteins that form large channels in the outer membranes of Gram-negative bacteria,some Gram-positive bacteria,mitochondria,and chloroplasts.
These channels allow the passive diffusion of molecules,such as small proteins and other solutes,across the membrane.
Therefore,porins are responsible for creating large pores in the outer membrane of bacteria.

(A) The cell membrane is a selectively permeable membrane. Under normal conditions or when kept in cold water/ice,the membrane remains intact and maintains its selective permeability,preventing the leakage of large molecules like anthocyanin pigments from the vacuole. If the beetroot were boiled or treated with chemicals,the membrane would lose its integrity and become permeable,causing the pigment to leak out. Therefore,the lack of leakage indicates that the membrane remains impermeable to anthocyanin under these conditions.

(B) The Donnan equilibrium refers to the behavior of charged particles (ions) near a semi-permeable membrane that fails to distribute evenly across the two sides of the membrane.
This phenomenon occurs because one side of the membrane contains charged particles (like proteins or fixed ions) that cannot pass through the membrane, leading to an unequal distribution of diffusible ions.
In biological systems, this process primarily takes place at the $Plasma \text{ } membrane$ (cell membrane), which acts as the semi-permeable barrier regulating the movement of ions between the cytoplasm and the extracellular environment.

(D) Ion channels are specialized transmembrane proteins that allow the passage of specific ions across the cell membrane. These channels are embedded within the lipid bilayer of the plasma membrane,facilitating the selective transport of ions like $Na^+$,$K^+$,$Ca^{2+}$,and $Cl^-$ into or out of the cell. Therefore,the correct location for ion channels is the plasma membrane.

(B) Specific proteins embedded in the cell membrane act as ion channels. These channels are highly selective and allow the passage of specific ions across the membrane,which is essential for maintaining the electrochemical gradient and cellular homeostasis. Therefore,the correct option is $B$.

(C) The cell membrane of bacteria (prokaryotes) is a selectively permeable membrane that is structurally similar to the eukaryotic cell membrane.
It is primarily composed of a phospholipid bilayer embedded with various proteins.
Therefore,the correct composition is lipid and protein.

(B) $E. coli$ is a prokaryotic organism,while $Chlamydomonas$ is a eukaryotic organism.
$1$. Cell wall: $E. coli$ has a peptidoglycan cell wall,whereas $Chlamydomonas$ has a cellulosic cell wall.
$2$. Cell membrane: Both prokaryotic and eukaryotic cells possess a plasma membrane (cell membrane) composed of a lipid bilayer with embedded proteins,which is structurally and functionally similar in both.
$3$. Ribosomes: $E. coli$ has $70S$ ribosomes,while $Chlamydomonas$ has $80S$ ribosomes in the cytoplasm.
$4$. Chromosomal organization: $E. coli$ has a single circular $DNA$ molecule without histones,whereas $Chlamydomonas$ has linear $DNA$ organized into chromosomes with histones.
Therefore,the cell membrane is the structure that does not differ significantly between the two.

(C) The cell membrane is primarily composed of a phospholipid bilayer.
Lecithin is a common type of phospholipid found in cell membranes.
Therefore,both phospholipid and lecithin are lipids found in the cell membrane.
Thus,the correct option is $(C)$.

(A) In animal cells,the concentration of ions is maintained by the $Na^+-K^+$ pump.
$Na^+$ ions are found in high concentrations in the extracellular fluid (outside the cell).
Conversely,$K^+$ ions are found in high concentrations inside the cell (intracellular fluid).
Therefore,$Na^+$ is the element found in abundance on the outside of an animal cell.

(B) Robertson proposed the Unit Membrane model,which suggests that the cell membrane consists of a phospholipid bilayer sandwiched between two layers of globular proteins.
In contrast,Singer and Nicolson proposed the Fluid Mosaic model,which suggests that proteins are not arranged in continuous layers but are embedded within or attached to the surface of the phospholipid bilayer in a mosaic pattern.
Therefore,the primary difference lies in the arrangement of proteins.

(B) The cell membrane is called a selectively permeable membrane.
It regulates the movement of substances in and out of the cell by allowing only specific molecules to pass through based on the cell's requirements,using mechanisms like protein channels and active transport.

(D) The cell membrane is primarily composed of lipids (mainly phospholipids) and proteins.
In addition to these,the cell membrane also contains carbohydrates.
According to the fluid mosaic model,the membrane consists of a phospholipid bilayer with proteins embedded within it,and carbohydrate chains attached to the outer surface of the membrane.

(C) The fluid mosaic model,proposed by $Singer$ and $Nicolson$ in $1972$,describes the cell membrane as a fluid structure.
It consists of a phospholipid bilayer in which protein molecules are embedded.
These proteins are categorized into two types based on their ease of extraction: integral (intrinsic) proteins,which are partially or totally buried in the membrane,and peripheral (extrinsic) proteins,which lie on the surface of the membrane.
Therefore,the cell membrane is composed of phospholipids,extrinsic proteins,and integral proteins.

(D) The unit membrane concept was proposed by $J.D. \, Robertson$ in $1959$.
According to this concept,all cellular membranes (plasma membrane,nuclear membrane,etc.) have a similar structure consisting of a bimolecular lipid layer sandwiched between two protein layers.
This model was based on electron microscopic studies and suggested a universal structure for all biological membranes.

(B) The process by which cells ingest large particles or molecules from their surroundings by engulfing them in a vesicle formed from the plasma membrane is known as $Endocytosis$.
$Diffusion$ is the movement of molecules from a region of higher concentration to lower concentration.
$Exocytosis$ is the process of exporting materials out of the cell.
$Osmosis$ is the movement of water molecules across a semi-permeable membrane.
Therefore,the correct answer is $Endocytosis$.

(A) The cell membrane is composed of a lipid bilayer which is hydrophobic in nature.
Non-polar and hydrophobic molecules can easily pass through the lipid bilayer due to their lipid-soluble nature.
However,polar molecules (hydrophilic) cannot pass through the non-polar lipid bilayer easily.
Therefore,they require specific membrane proteins,known as carrier proteins or channel proteins,to facilitate their transport across the membrane. This process is called facilitated diffusion.

(B) The process of engulfing solid food particles by the cell membrane is called $Phagocytosis$.
$Phagocytosis$ is a type of endocytosis where the cell membrane invaginates to form a vesicle around solid particles.
$Pinocytosis$ refers to the ingestion of liquid droplets.
$Endosmosis$ is the movement of water into a cell.
$Cytokinesis$ is the division of the cytoplasm during cell division.

(D) The cell membrane is primarily composed of lipids and proteins. The lipids in the cell membrane are mainly arranged in a bilayer. The most abundant lipids are phosphoglycerides. These molecules have a polar hydrophilic head and two non-polar hydrophobic tails,which allows them to form the structural framework of the membrane.

(D) In $1972$,$Singer$ and $Nicolson$ proposed the $Fluid$ $Mosaic$ $Model$ for the structure of the cell membrane.
According to this model,the cell membrane consists of a lipid bilayer with proteins embedded within it,which can move laterally,giving it a fluid nature.
This model is widely accepted as it explains both the structural and functional properties of the cell membrane.

(D) The cell membrane is composed of a lipid bilayer. In this structure,the lipid molecules are arranged in two layers. Within each layer,the hydrophobic tails face inward,while the hydrophilic heads face outward. The lipid molecules are arranged parallel to each other,forming a stable bilayer structure that provides fluidity and integrity to the membrane.

(D) The light microscope has a limited resolution (about $0.2 \ \mu m$) due to the wavelength of visible light.
Many small organelles or fine structures like the nuclear envelope (the membrane separating the nucleus from the cytoplasm) are too thin or small to be resolved clearly under a light microscope.
An electron microscope uses a beam of electrons with a much shorter wavelength,allowing for a much higher resolution (up to $0.1 \ nm$),which makes it possible to visualize the fine structure of the nuclear membrane and other sub-cellular components that appear invisible or as mere dots under a light microscope.

(D) Cell recognition is a critical function of the cell membrane,allowing cells to identify and interact with other cells.
This process is primarily mediated by carbohydrate chains attached to proteins (forming glycoproteins) or lipids (forming glycolipids) on the outer surface of the plasma membrane.
These molecules act as 'markers' or 'tags' that allow the immune system and other cells to recognize specific cell types.
Therefore,the correct answer is glycoproteins and glycolipids.

(D) The term $Pinocytosis$ refers to the process of cell drinking,where the cell membrane invaginates to form vesicles that engulf extracellular fluid and dissolved solutes.
This term was coined by the scientist $W.H. Lewis$ in $1931$ to describe the uptake of fluid droplets by cells.

(C) Carrier proteins are specialized membrane proteins that facilitate the movement of specific molecules across the cell membrane.
They are essential for active transport,where ions or molecules are moved against their concentration gradient,requiring energy in the form of $ATP$.
They also participate in facilitated diffusion,which is a form of passive transport.
Among the given options,the active transport of ions is a primary function mediated by carrier proteins (pumps) that utilize energy to move ions across the membrane.

(C) The fluid mosaic model of the plasma membrane was proposed by $S.J. Singer$ and $G.L. Nicolson$ in $1972$.
According to this model,the cell membrane is composed of a lipid bilayer with proteins embedded within it,giving it a fluid-like structure.

(B) The unit membrane model,often referred to as the $Davson-Danielli$ model,describes the structure of the cell membrane.
According to this model,the cell membrane consists of a phospholipid bilayer sandwiched between two layers of globular proteins.
Therefore,the composition is represented as $Protein-Lipid-Protein$.

(C) According to the Fluid Mosaic Model proposed by Singer and Nicolson in $1972$,the cell membrane consists of a lipid bilayer with embedded proteins.
These proteins are classified into two types: extrinsic (peripheral) proteins and intrinsic (integral) proteins.
Extrinsic proteins are located on the surface of the lipid bilayer.
They are loosely associated with the membrane surface or with the integral proteins.
Due to this weak association,they can be easily extracted or separated from the membrane for study.

(D) The $Na^+/K^+$ pump is a transmembrane protein that uses energy in the form of $ATP$ to transport ions against their concentration gradient.
It pumps $3$ $Na^+$ ions out of the cell and $2$ $K^+$ ions into the cell.
Since this process requires energy to move ions from an area of lower concentration to an area of higher concentration,it is classified as active transport.

(C) The sodium-potassium pump ($Na^+/K^+$-ATPase) is a transmembrane protein that actively transports ions across the cell membrane.
It functions by pumping $3$ $Na^+$ ions out of the cell and $2$ $K^+$ ions into the cell against their respective concentration gradients.
Since it facilitates the movement of ions across the membrane,it is classified as a carrier protein or a transport protein.

(A) The scientist $J.D. Robertson$ proposed the $Unit Membrane Concept$ in $1959$.
This concept suggests that all cellular membranes (plasma membrane and organelle membranes) have a similar trilaminar structure consisting of a bimolecular lipid layer sandwiched between two protein layers.
The $Fluid-Mosaic Model$ was proposed by Singer and Nicolson in $1972$.

(D) The cell membrane (plasma membrane) is a selectively permeable membrane that encloses the cell contents,provides protection,and regulates the transport of molecules in and out of the cell.
However,the control of cellular activities is the primary function of the nucleus,which contains the genetic material $(DNA)$ that directs and regulates all metabolic processes within the cell.
Therefore,option $D$ is the correct answer as it is not a function of the cell membrane.

(D) In a plant cell,the outermost boundary is the cell wall.
Inside the cell wall,the cytoplasm is lined by the cell membrane (plasma membrane).
Therefore,the cell membrane represents the innermost boundary of the cell proper,separating the cytoplasm from the external environment or the cell wall space.
Thus,the correct option is $D$.

(D) The cell membrane is a biological membrane that separates the interior of all cells from the outside environment. It is described as selectively permeable because it allows certain molecules or ions to pass through it by means of active or passive transport. While the term 'semi-permeable' is often used interchangeably in general contexts to describe membranes that allow solvent molecules to pass but restrict solutes,in biological terminology,'selectively permeable' is the more accurate description for the cell membrane as it actively regulates the passage of specific substances. Therefore,both terms are frequently used to describe its nature in various educational contexts.

(B) membrane that allows the movement of specific molecules or ions while restricting others based on their size,solubility,or charge is called a $Selectively$ $permeable$ $membrane$.
Biological membranes,such as the plasma membrane,are selectively permeable,which is essential for maintaining cellular homeostasis.
In contrast,a semi-permeable membrane typically refers to a membrane that allows only solvent molecules (like water) to pass through,while a selectively permeable membrane allows specific solutes as well.

(B) The plasma membrane (also known as the cell membrane) is selectively permeable or semi-permeable in nature.
It allows only certain molecules to pass through it while restricting others,thereby maintaining the internal environment of the cell.
In contrast,the cell wall is generally freely permeable,and structures like the capsule and slime layer (glycocalyx) are protective layers in bacteria.

(B) The plasma membrane acts as a selectively permeable membrane or a molecular sieve. It regulates the entry and exit of substances,allowing only specific molecules to pass through while restricting others based on size,charge,and solubility. This property is essential for maintaining cellular homeostasis.