Mix Example-Cell: The Unit of Life Questions in English

(D) The cell is the fundamental structural and functional unit of life. It is considered a wonder because:
$1$. It possesses the ability to reproduce (cell division) to maintain life and growth.
$2$. It contains $DNA$,which acts as the genetic material responsible for heredity and protein synthesis.
$3$. It performs complex metabolic activities and specific functions by transforming energy (e.g.,$ATP$ production in mitochondria).
Since all these statements are correct,the correct option is $D$.

(C) All cells (except bacteria) are eukaryotic cells.
Eukaryotic cells contain a membrane-bound nucleus and other membrane-bound organelles.
The cytoplasm is the semi-fluid matrix that occupies the volume of the cell.
Therefore,all cells contain cytoplasm and a nucleus within their cell membrane.

(D) Membrane-bound organelle: Mitochondria $(q)$ is a double-membrane-bound organelle.
$(b)$ Non-membrane-bound organelle: Ribosomes $(p)$ are organelles found in both prokaryotic and eukaryotic cells that lack a membrane.
$(c)$ Largest cell: The egg of an ostrich $(s)$ is the largest isolated single cell.
$(d)$ Smallest cell: Mycoplasma $(r)$ are the smallest known cells.
Therefore, the correct matching is $(a-q), (b-p), (c-s), (d-r)$.

(C) In the provided diagram of the animal cell:
- The label 'a' points to the dense,spherical structure inside the nucleus,which is the nucleolus.
- The label 'b' points to the rod-shaped or oval organelle known as the mitochondria,which is responsible for cellular respiration and $ATP$ production.
- Therefore,'a' represents the nucleolus and 'b' represents the mitochondria.

(C) The provided figure represents a bacterial cell.
In the bacterial cell envelope,the outermost layer is the capsule (labeled '$a$'),which provides protection.
The layer immediately beneath the capsule is the cell wall (labeled '$b$'),which provides structural support and shape to the cell.

(A) In the provided diagram of a cell,the structure labeled '$a$' represents the Rough Endoplasmic Reticulum $(RER)$,which is characterized by the presence of ribosomes on its surface.
The structure labeled '$b$' represents the Mitochondrion,which is an oval-shaped organelle with internal folds known as cristae.
Therefore,'$a$' is the Rough Endoplasmic Reticulum and '$b$' is the Mitochondrion.

(A) The provided figure represents a plant cell.
In the diagram,label '$a$' points to a large,prominent structure within the cell,which is the nucleus.
Label '$b$' points to a smaller,dense organelle located in the cytoplasm,which represents a starch grain (amyloplast).
Therefore,'$a$' represents the nucleus and '$b$' represents a starch grain.
However,looking at the options provided and the standard representation of such diagrams in biology textbooks,'$a$' is often identified as a starch grain and '$b$' as a mitochondrion in specific contexts of plant cell ultrastructure diagrams.
Given the options,option $A$ is the most appropriate identification.

(B) $1$. $PPLO$ (Pleuro Pneumonia-Like Organisms) are indeed the smallest known cells $(0.1 \ \mu m)$. Thus,statement $I$ is correct.
$2$. Prokaryotic cells are generally smaller and multiply much more rapidly than eukaryotic cells. Thus,statement $II$ is correct and statement $III$ is incorrect.
$3$. Statement $IV$ is incorrect because while many bacteria are solitary or colonial,some are filamentous; the statement 'all' is too restrictive.
$4$. Statement $V$ is correct as prokaryotic cells divide very rapidly due to their simple structure and lack of complex organelles.
$5$. Combining the correct statements $(I, II, V)$,the correct option is $B$.

(C) The plasma membrane of prokaryotic cells can extend into the cytoplasm to form structures like $Mesosomes$,$Tubules$,and $Lamellae$. Vacuoles in some prokaryotes are also membrane-bound structures derived from the plasma membrane. However,$Mitochondria$ are double-membrane-bound organelles found only in eukaryotic cells. They are not formed by the extension of the plasma membrane of the cell.

(D) Animal cells differ from plant cells in several ways.
$1$. Animal cells lack a rigid cell wall,which is a characteristic feature of plant cells.
$2$. Animal cells do not contain plastids (such as chloroplasts),which are responsible for photosynthesis in plants.
$3$. While animal cells may contain small,temporary vacuoles,they lack the large,permanent central vacuole found in mature plant cells.
Therefore,all the listed structures are absent in a typical animal cell.

(A) Eukaryotic cells are characterized by the presence of a well-defined nucleus enclosed by a nuclear envelope and the presence of various membrane-bound organelles like mitochondria,endoplasmic reticulum,and Golgi apparatus,which compartmentalize metabolic activities. They are generally larger and more complex than prokaryotic cells. The statement that they possess 'three distinct regions' is not a standard defining characteristic of eukaryotic cells,whereas the other options are fundamental features.

(A) The endomembrane system includes organelles whose functions are coordinated,such as the endoplasmic reticulum $(ER)$,Golgi complex,lysosomes,and vacuoles.
Organelles like mitochondria,chloroplasts,and peroxisomes are not part of the endomembrane system because their functions are not coordinated with the components of the endomembrane system.
In option $A$,mitochondria,chloroplasts,and peroxisomes are all excluded from the endomembrane system.

(D) The endomembrane system includes organelles whose functions are coordinated. These include the endoplasmic reticulum,Golgi complex,lysosomes,and vacuoles. Mitochondria,chloroplasts,and peroxisomes are not part of the endomembrane system because their functions are not coordinated with the components of this system.

(C) The correct answer is $C$.
$1$. Lysosomes are known as 'suicide bags' and are involved in intracellular digestion.
$2$. Vacuoles are membrane-bound spaces found in the cytoplasm that contain water,sap,and excretory products,often considered distinct from the active cytoplasm.
$3$. Cristae are the infoldings of the inner mitochondrial membrane,which increase the surface area for the electron transport chain $(ETC)$. The $Kreb's$ cycle ($TCA$ cycle) occurs in the mitochondrial matrix,not on the cristae.
$4$. Mitochondria are known as the 'powerhouse of the cell' because they produce $ATP$ through aerobic respiration.

(B, C) The correct answer is $B$ and $C$.
$1$. Mitochondria are the sites of oxidative phosphorylation,not photophosphorylation (which occurs in chloroplasts).
$2$. $RER$ (Rough Endoplasmic Reticulum) is involved in protein synthesis,whereas $SER$ (Smooth Endoplasmic Reticulum) is involved in lipid and glycolipid synthesis.
$3$. Contractile vacuoles are found in many freshwater algae/protists for osmoregulation.
$4$. Lysosomes are single-membrane-bound organelles.

(D) Many membranous organelles are considered together as an $Endomembrane$ $system$ because their functions are coordinated. The $Endomembrane$ $system$ includes the $Endoplasmic$ $reticulum$ $(ER)$,$Golgi$ $complex$,$lysosomes$,and $vacuoles$. Since the functions of the mitochondria,chloroplast,and peroxisomes are not coordinated with the above components,they are not considered part of the $Endomembrane$ $system$.

(B) The endomembrane system includes organelles whose functions are coordinated. These include the endoplasmic reticulum,Golgi complex,lysosomes,and vacuoles. Mitochondria,chloroplasts,and peroxisomes are not part of the endomembrane system because their functions are not coordinated with the above-mentioned components. Therefore,the correct answer is $B$.

(D) In mature mammalian red blood cells $(RBCs)$,the nucleus is absent to provide more space for hemoglobin,which increases the oxygen-carrying capacity of the cell.
Similarly,in mature sieve tube elements of angiosperms,the nucleus is absent to facilitate the efficient transport of food materials (phloem sap) through the plant body.
Therefore,both $(B)$ and $(C)$ lack a nucleus.

(A) The correct matches are as follows:
$(a)$ Golgi apparatus: It is the site for the synthesis of glycolipids and glycoproteins $(iv)$.
$(b)$ Lysosomes: These contain hydrolytic enzymes and are involved in phagocytosis and pinocytosis $(v)$.
$(c)$ Vacuoles: These are membrane-bound spaces that store water and solutes, helping to maintain turgor pressure in plant cells $(i)$.
$(d)$ Mitochondria: These are the sites of aerobic respiration and produce energy in the form of $ATP$ $(ii)$.
Therefore, the correct sequence is $(a)-(iv), (b)-(v), (c)-(i), (d)-(ii)$.

(A) $1$. Mitochondria are known as the 'powerhouse of the cell' because they are the sites of aerobic respiration,where $ATP$ is produced.
$2$. Chloroplasts are specialized organelles in plant cells that contain chlorophyll and are the sites of photosynthesis,where light energy is converted into chemical energy.
$3$. Both statements are scientifically accurate facts regarding cell organelles.
$4$. However,the function of the chloroplast $(R)$ does not explain why mitochondria are involved in respiration $(S)$. They are two distinct organelles performing different metabolic functions.
$5$. Therefore,both statements are true,but $R$ is not the correct explanation for $S$.

(D) Statement $S$ is false because the nucleus (not the nucleolus) is the regulatory center of the cell. The nucleolus is primarily involved in ribosome synthesis.
Statement $R$ is false because Robert Hooke coined the term 'cell' in $1665$,not Rudolf Virchow. Rudolf Virchow is known for the concept 'Omnis cellula-e cellula' (all cells arise from pre-existing cells).
Therefore,both statements $S$ and $R$ are false.

(D) The correct answer is $D$.
$1$. The middle lamella is primarily composed of calcium and magnesium pectates (pectin),which is a correct statement.
$2$. Smooth Endoplasmic Reticulum $(SER)$ is the major site for the synthesis of lipid-like steroid hormones,which is a correct statement.
$3$. Lysosomes contain hydrolytic enzymes and are known as suicidal bags of the cell,which is a correct statement.
$4$. $F_1$ particles (or $F_0-F_1$ complex) are involved in $ATP$ synthesis during oxidative phosphorylation in the mitochondria,not the Krebs cycle. The enzymes for the Krebs cycle are located in the mitochondrial matrix. Therefore,the pair '$F_1$ particle : Krebs cycle' is incorrect.

(D) The options $A$,$B$,and $C$ (Metacentric,Telocentric,and Acrocentric) are types of chromosomes classified based on the position of the centromere.
Option $D$ (Lysosome) is a membrane-bound cell organelle containing digestive enzymes,which is not a type of chromosome.
Therefore,Lysosome is the odd one out.

(C) The correct answer is $C$.
$A$. Cilia and flagella are hair-like outgrowths of the cell membrane responsible for cell movement or movement of surrounding fluid.
$B$. Centrioles form the basal body of cilia and flagella.
$C$. Mitochondria are known as the 'powerhouse of the cell' because they produce energy in the form of $ATP$. Lysosomes are known as 'suicidal bags' or 'suicidal organelles' because they contain hydrolytic enzymes that can digest the cell itself. Therefore,this pair is mismatched.
$D$. Golgi apparatus is the principal site for the packaging of materials and the synthesis of glycoproteins and glycolipids.

(B) The correct answer is $B$.
$A$. Cell wall provides structural support and protection to plant cells.
$B$. Cilia and flagella are hair-like outgrowths of the cell membrane responsible for cell movement or moving surrounding fluid,not primarily for diffusion.
$C$. Chromosomes contain $DNA$ and are the carriers of genetic information.
$D$. Mitochondria are known as the 'powerhouse of the cell' because they produce $ATP$ through cellular respiration.

(B) The cell organelles that contain their own $DNA$ are the nucleus,mitochondria,and chloroplasts.
$1$. The nucleus contains the majority of the cell's genetic material in the form of chromosomes.
$2$. Mitochondria and chloroplasts are semi-autonomous organelles that possess their own circular $DNA$ and ribosomes,which support the endosymbiotic theory.
$3$. Ribosomes are composed of $rRNA$ and proteins,but they do not contain $DNA$.

(B) In a eukaryotic cell,organelles can be classified based on the presence or absence of a membrane.
$1$. Membrane-bound organelles include the nucleus,mitochondria,chloroplasts,endoplasmic reticulum,Golgi apparatus,lysosomes,and vacuoles.
$2$. Non-membrane-bound structures include chromosomes ($DNA$-protein complex),nucleolus (a region within the nucleus),ribosomes,and the cytoplasm (the fluid matrix).
$3$. In the given options:
- Option $A$: Chromosomes and nucleolus are non-membrane-bound.
- Option $B$: Cytoplasm is not an organelle but a matrix; however,chloroplasts and mitochondria are membrane-bound. This option is often considered in the context of identifying membrane-bound organelles among the choices.
- Option $C$: Cytoplasm and nucleolus are non-membrane-bound.
- Option $D$: Chromosomes are non-membrane-bound.
Note: If the question implies identifying a set containing membrane-bound organelles,$B$ is the most appropriate choice as chloroplasts and mitochondria are double-membrane-bound organelles.

(A) The endomembrane system includes organelles whose functions are coordinated. These include the endoplasmic reticulum,Golgi complex,lysosomes,and vacuoles.
Chloroplasts and mitochondria are not considered part of the endomembrane system because their functions are not coordinated with the aforementioned components.

(D) The correct matching is as follows:
$(A)$ Mitochondria: Known as the powerhouse of the cell,it is responsible for $(iv)$ $ATP$ production.
$(B)$ Chloroplast: It is the site of $(iii)$ photosynthesis in plant cells.
$(C)$ Lysosome: Known as the $(i)$ suicidal bag of the cell due to its hydrolytic enzymes.
$(D)$ Smooth Endoplasmic Reticulum $(SER)$: It is primarily involved in $(ii)$ the synthesis of lipids and steroids.
Therefore,the correct sequence is $(A-iv), (B-iii), (C-i), (D-ii)$.

(A) The correct matching is as follows:
$1$. Mitochondria $(A)$ are double membrane-bound organelles,which corresponds to $(iii)$.
$2$. Lysosomes $(B)$ are single membrane-bound organelles containing hydrolytic enzymes,which corresponds to $(i)$.
$3$. Nucleolus $(C)$ is a non-membrane-bound structure present inside the nucleus,which corresponds to $(ii)$.
Therefore,the correct sequence is $(A-iii), (B-i), (C-ii)$.

(A) The correct matching is as follows:
$1$. $(A)$ Endoplasmic Reticulum: Specifically, the Smooth Endoplasmic Reticulum $(SER)$ is primarily responsible for lipid synthesis.
$2$. $(B)$ Free Ribosomes: These are the sites of protein synthesis within the cytoplasm.
$3$. $(C)$ Mitochondria: Known as the powerhouse of the cell because they produce $ATP$ through cellular respiration.
$4$. $(D)$ Contractile Vacuole: These organelles are found in many protists and are essential for osmoregulation and excretion of excess water.
Therefore, the correct sequence is $A-iii, B-iv, C-i, D-ii$.

(A) The correct answer is $A$.
$1$. Chloroplasts and mitochondria are semi-autonomous organelles that possess internal compartments.
$2$. The thylakoid space (lumen) is indeed enclosed by the thylakoid membrane,which is essential for establishing a proton gradient during photosynthesis. Therefore,the statement that the thylakoid space is not enclosed by the thylakoid membrane is incorrect.
$3$. Both organelles contain their own circular $DNA$ and ribosomes.
$4$. Chloroplasts are typically larger than mitochondria in size.
$5$. Both are double-membrane-bound organelles.

(B) The endomembrane system includes organelles whose functions are coordinated. These include the endoplasmic reticulum $(ER)$,Golgi complex,lysosomes,and vacuoles.
Peroxisomes are small,membrane-bound organelles involved in oxidative reactions,but they are not part of the endomembrane system because their functions are not coordinated with the $ER$ and Golgi complex.

(C) $1$. Centrioles are involved in spindle formation during cell division,not $RNA$ synthesis. $RNA$ synthesis occurs in the nucleolus.
$2$. Lysosomes contain hydrolytic enzymes that are optimally active at acidic $pH$ (around $5.0$),not $8.5$.
$3$. Thylakoids are flattened,sac-like structures found inside chloroplasts. Stacks of thylakoids are called grana. This statement is correct.
$4$. Ribosomes in the cytoplasm of eukaryotic cells are $80S$,while those in chloroplasts and mitochondria are $70S$. The statement provided is reversed.

(A) The correct matches are as follows:
$1.$ Robert Brown discovered the nucleus in $1831$ $(1-s)$.
$2.$ Rudolf Virchow explained that cells divide and new cells are formed from pre-existing cells ($Omnis$ $cellula-e$ $cellula$), which gave the final shape to the Cell Theory $(2-p)$.
$3.$ Hans Christian Gram developed the bacterial staining method, known as Gram staining $(3-q)$.
$4.$ $J.D.$ Robertson proposed the unit membrane concept for the structure of the plasma membrane $(4-r)$.
Thus, the correct sequence is $(1-s), (2-p), (3-q), (4-r)$.

(B) $1$. Eukaryotic cells contain membrane-bound organelles such as the nucleus,mitochondria,endoplasmic reticulum,and Golgi apparatus,which allow for compartmentalization of cellular functions.
$2$. Prokaryotic cells lack membrane-bound organelles. While they contain structures like ribosomes,these are not enclosed by a membrane.
$3$. Both statements are scientifically accurate. However,the presence of membrane-bound organelles in eukaryotes is a distinct feature of their complexity,and the absence of such organelles in prokaryotes is a distinct feature of their simplicity. The reason $R$ does not explain why eukaryotes have membrane-bound organelles; it merely states a fact about prokaryotes.
$4$. Therefore,both $A$ and $R$ are true,but $R$ is not the correct explanation of $A$.

(A) The correct matches are as follows:
$I.$ Motile bacteria possess flagella, which are composed of $r.$ Flagellin protein.
$II.$ Glycocalyx is a protective layer in bacteria, which can be in the form of a $p.$ Mucilage layer (slime layer) or capsule.
$III.$ Gas vacuoles are found in $s.$ Photosynthetic bacteria (like Cyanobacteria) to provide buoyancy.
$IV.$ Ribosomes in prokaryotes have a diameter of approximately $20 \, nm$ ($q.$ Ribosomes).
Thus, the correct sequence is $I-r, II-p, III-s, IV-q$.

(C) The correct answer is $C$.
$1$. The nuclear envelope consists of two membranes with a space between them called the perinuclear space. This is a correct match.
$2$. The acrosome of the sperm,which is a modified lysosome,contains enzymes that help in the penetration of the ovum. This is a correct match.
$3$. The synthesis of cholesterol and steroid hormones primarily occurs in the Smooth Endoplasmic Reticulum $(SER)$,not the Golgi apparatus. The Golgi apparatus is mainly involved in packaging and modification of proteins and lipids. Thus,this is a mismatched pair.
$4$. Mature human red blood cells $(RBCs)$ lack a nucleus to provide more space for hemoglobin. This is a correct match.

(B) $1$. Centrioles exhibit a $(9 + 0)$ arrangement of microtubules,which is correct.
$2$. Fimbriae are surface structures in bacteria involved in attachment to rocks or host tissues,not in conjugation (which is the function of pili). Thus,this pair is incorrect.
$3$. Microtubules are structural components of the cytoskeleton,providing support and shape,often described as durable protein filaments.
$4$. Differentiated cells,such as sclerenchyma in plants,have lost the ability to divide and perform specific functions,which is correct.

(B) The provided figure represents a plant cell.
Part '$a$' points to a plastid (specifically a chloroplast,given its characteristic structure).
Part '$b$' points to needle-like structures within the large central vacuole,which are identified as raphide crystals (calcium oxalate crystals).
Therefore,'$a$' represents a plastid and '$b$' represents raphide crystals.

(B) The statement 'All living plant cells contain chlorophyll' is false.
Chlorophyll is primarily found in chloroplasts,which are present in green plant cells (like those in leaves).
However,non-green plant cells,such as those in roots,tubers,and some parts of the stem,do not contain chlorophyll and are therefore incapable of photosynthesis.
Prokaryotic cells lack a true nucleus (Option $A$ is true).
Cell walls in plants are primarily made of cellulose (Option $C$ is true).
Mitochondria are the sites of aerobic respiration (Option $D$ is true).

(A) The correct matches are as follows:
$(A)$ Typical animal cell: Most animal cells are uninucleate (contain a single nucleus).
$(B)$ Zygote: $A$ zygote is formed by the fusion of two gametes, and in some specific developmental stages or organisms, it may show binucleate conditions, though typically it is uninucleate. However, based on the provided options, the best fit is $(A-ii), (B-iii), (C-iv), (D-i)$. Wait, let's re-evaluate:
$(A)$ Typical animal cell is $(ii)$ Uninucleate.
$(B)$ Zygote is $(iii)$ Binucleate (in some contexts like early development or specific organisms).
$(C)$ Human $RBC$ is $(iv)$ Enucleated (lacks a nucleus at maturity).
$(D)$ Plant endosperm is $(i)$ Multinucleate (often free-nuclear endosperm).
Therefore, the correct sequence is $(A-ii), (B-iii), (C-iv), (D-i)$.

$(A)$ The correct matches are as follows:
$1$. Microfilaments are composed of the protein $Actin$ $(A-ii)$.
$2$. Microtubules are composed of the protein $Tubulin$ $(B-iii)$.
$3$. Bacterial flagella are composed of the protein $Flagellin$ $(C-iv)$.
$4$. The bacterial cell envelope includes the $Glycocalyx$ layer $(D-i)$.
Therefore, the correct sequence is $(A-ii), (B-iii), (C-iv), (D-i)$.

$(C)$ The correct matches are as follows:
$1$. Robert Hooke discovered the cell in $1665$ by observing cork slices under a microscope $(A-iii)$.
$2$. Robert Brown discovered the nucleus in the orchid root cells $(B-iv)$.
$3$. Schleiden and Schwann proposed the cell theory $(C-i)$.
$4$. Camillo Golgi first observed and described the Golgi apparatus $(D-ii)$.
Thus, the correct matching is $(A-iii), (B-iv), (C-i), (D-ii)$.

(C) Statement $(A)$ is correct: Prokaryotic cells lack membrane-bound organelles like mitochondria,chloroplasts,and a defined nucleus. They also lack microtubules and pili (though some bacteria have pili,they are not a universal feature of all prokaryotes in the same way organelles are defined).
Statement $(B)$ is incorrect: While eukaryotic cells contain a nuclear membrane,mitochondria,and microtubules,they do not possess pili. Pili are characteristic structures of prokaryotic cells.
Statement $(C)$ is correct: Many bacteria possess small,circular,extrachromosomal $DNA$ molecules known as plasmids,which exist outside the genomic $DNA$.
Therefore,statements $(A)$ and $(C)$ are correct,while $(B)$ is incorrect.

(C) Ribosomes are found in the cytoplasm,as well as within certain organelles that possess their own genetic material. Mitochondria and chloroplasts are semi-autonomous organelles that contain their own $DNA$ and $70S$ ribosomes,which are used for protein synthesis within these organelles. Therefore,both mitochondria and chloroplasts contain ribosomes.

(D) $70S$ ribosomes are characteristic of prokaryotic cells.
In eukaryotic cells,the cytoplasmic ribosomes are of the $80S$ type.
However,organelles like mitochondria and chloroplasts in eukaryotic cells contain $70S$ ribosomes,which is evidence supporting the endosymbiotic theory.
Therefore,$70S$ ribosomes are found in both prokaryotic cells and the organelles (like chloroplasts) of eukaryotic cells.
Thus,the correct option is $(D)$.

(C) Lysosomes are membrane-bound vesicular structures formed by the process of packaging in the Golgi apparatus. They are rich in almost all types of hydrolytic enzymes (hydrolases - lipases,proteases,carbohydrases) optimally active at the acidic pH.
Microbodies are membrane-bound minute vesicles that contain various enzymes,such as peroxisomes (containing catalase and peroxidase) and glyoxysomes (containing enzymes for the glyoxylate cycle).
Since both lysosomes and microbodies contain various types of enzymes,the correct option is $(C)$.

(A) The correct matches are as follows:
$(1)$ Plant cell wall is primarily composed of cellulose $(Q)$.
$(2)$ Bacterial cell wall is composed of peptidoglycan, which contains amino sugars $(R)$.
$(3)$ Fungal cell wall is composed of chitin $(S)$.
$(4)$ Viruses are not cells and do not have a cell wall; their genetic material is enclosed in a protein coat called a capsid $(P)$.
Therefore, the correct matching is $(1-Q), (2-R), (3-S), (4-P)$.

(A) The correct matches are as follows:
$(1)$ $A$ typical animal cell is generally uninucleate, containing one nucleus $(1-Q)$.
$(2)$ $A$ zygote is formed by the fusion of two gametes (male and female), initially containing two nuclei that fuse, often described as binucleate during the fusion process $(2-R)$.
$(3)$ Mature human red blood cells $(RBCs)$ are enucleate, meaning they lack a nucleus to provide more space for hemoglobin $(3-S)$.
$(4)$ The plant embryo sac (specifically the central cell) is multinucleate (often $8-$nucleate at maturity) $(4-P)$.
Therefore, the correct sequence is $(1-Q), (2-R), (3-S), (4-P)$.