Mix Example - THE FUNDAMENTAL UNIT OF LIFE Questions in English

(A) Unlike the other options,a virus is not a cell. $A$ virus consists of genetic material ($DNA$ or $RNA$) enclosed within a protein coat called a capsid. Because of this simple structure,viruses can be crystallized and stored like non-living chemicals,a property first demonstrated by Wendell Stanley in $1935$.

(B) If the concentration of water molecules in the surrounding medium is higher than the concentration of water molecules in the cell,the cell is placed in a hypotonic solution.
According to the process of osmosis,water molecules move from a region of higher water concentration to a region of lower water concentration through a semi-permeable membrane.
Therefore,water will move into the cell,causing it to swell up.

(C) Chromosomes are composed of $DNA$ and proteins. In eukaryotic cells,$DNA$ is tightly coiled around histone proteins to form structures called nucleosomes,which further condense to form chromosomes.

(D) Ribosomes are the sites of protein synthesis in the cell.
Since enzymes are primarily proteinaceous in nature,ribosomes are involved in their synthesis.
However,most hormones are either steroids (lipids) or proteins. While some protein-based hormones are synthesized by ribosomes,many hormones are not. More importantly,starch is a carbohydrate (polysaccharide) synthesized by plastids (like amyloplasts) in plants,not by ribosomes.
Therefore,$(iii)$ and $(iv)$ are not considered primary functions of ribosomes in the context of general cellular biology.

(A) The endoplasmic reticulum $(ER)$ is involved in the synthesis,folding,modification,and transport of proteins and lipids. It does not generate energy. Energy generation in the form of $ATP$ is the primary function of mitochondria,which are known as the powerhouses of the cell.

(B) Osmosis is defined as the spontaneous net movement of solvent molecules (usually water) through a selectively permeable membrane into a region of higher solute concentration (which is equivalent to a region of lower solvent concentration) in the direction that tends to equalize the solute concentrations on the two sides. Therefore,the movement of water molecules from a region of higher water concentration to a region of lower water concentration through a semipermeable membrane is the correct definition.

(C) Plasmolysis is the process where the cytoplasm of a plant cell shrinks away from the cell wall.
This occurs when the cell is placed in a hypertonic solution (a solution with a higher solute concentration than the cell sap).
Due to the concentration gradient,water moves out of the cell through the process of exosmosis.
As water leaves the cell,the protoplast shrinks,causing the cytoplasm to pull away from the cell wall.

(C, D) In the given options, $Mitochondria$ and $Plastids$ are double-membrane bound organelles. $Lysosomes$ and $Vacuoles$ are single-membrane bound organelles. Therefore, both $C$ and $D$ are correct as they are covered by a single membrane.

(D) Statement $I$ is true because lysosomes are formed by the budding of vesicles from the Golgi apparatus.
Statement $II$ is false because although the nucleus,mitochondria,and plastids contain $DNA$,they do not synthesize all their own structural proteins. The nucleus directs protein synthesis,but the actual synthesis occurs on ribosomes in the cytoplasm. Mitochondria and plastids are semi-autonomous and synthesize only some of their proteins.
Statement $III$ is true because mitochondria generate energy in the form of $ATP$,earning them the title of the cell's powerhouse.
Statement $IV$ is false because protoplasm is the living content of the cell,which includes both the cytoplasm and the nucleus,not just the cytoplasm.
Therefore,statements $II$ and $IV$ are false.

(B) $RER$ (Rough Endoplasmic Reticulum) has ribosomes on its surface,which are responsible for protein synthesis. Since lysosomal enzymes are proteins,they are synthesized by $RER$. Thus,option $b$ is correct.
Option $a$ is incorrect because $RER$ produces proteins and $SER$ (Smooth Endoplasmic Reticulum) produces lipids.
Option $c$ is incorrect because the endoplasmic reticulum is involved in the synthesis of membrane components,not their destruction.
Option $d$ is incorrect because a nucleoid is the undefined nuclear region found in prokaryotes,not in the nucleoplasm of eukaryotic nuclei.

(C) In the liver cells of vertebrates,the $SER$ (Smooth Endoplasmic Reticulum) plays a crucial role in detoxifying many poisons and drugs. The enzymes present in the $SER$ membrane help in the metabolic breakdown of toxic substances,thereby protecting the cell.

(D) The endoplasmic reticulum $(ER)$ is responsible for the synthesis of both proteins and lipids.
Specifically,the Rough Endoplasmic Reticulum $(RER)$ contains ribosomes on its surface and is primarily involved in protein synthesis.
The Smooth Endoplasmic Reticulum $(SER)$ lacks ribosomes and is primarily involved in the synthesis of lipids.
These molecules are then used for membrane biogenesis,which is the process of building the cell membrane.

(A) In prokaryotic cells,the genetic material is not enclosed by a nuclear membrane. This undefined nuclear region,which contains only nucleic acids,is called the nucleoid.

(B) The $Golgi$ apparatus is the cell organelle responsible for the modification,packaging,and transport of proteins and lipids. It is also involved in the synthesis of complex sugars from simple sugars.

(C) Vacuoles are membrane-bound organelles found in the cytoplasm of plant and animal cells.
They perform various functions such as storage of nutrients,water,and waste products.
In plant cells,they provide turgidity and rigidity by maintaining cell pressure.
Locomotion is not a function of vacuoles; it is typically carried out by specialized structures like cilia,flagella,or pseudopodia.

(D) The term endocytosis is composed of two parts: 'endo' means towards the inside and 'cytosis' means movement related to the cell. Amoeba uses its flexible cell membrane to engulf food particles from its external environment,a process known as endocytosis (specifically phagocytosis).

(A) The cell walls of plants like $Hydrilla$,$Mango$ $tree$,and $Cactus$ are primarily composed of cellulose. In contrast,the cell wall of $Bacteria$ is composed of $peptidoglycan$ (also known as $murein$).

(B) Camillo Golgi developed a staining technique known as the 'black reaction',which involved the use of silver nitrate.
This technique allowed for the visualization and detailed study of the Golgi apparatus and individual nerve cell structures.

(C) Mitochondria and chloroplasts are semi-autonomous organelles that contain their own $DNA$ and ribosomes. Because they possess their own $DNA$,they have the capability of self-replication,independent of the nuclear $DNA$.

(D) In plant cells,food is synthesized through the process of photosynthesis,which occurs within specialized organelles called chloroplasts. Because they are the sites of food production,chloroplasts are referred to as the kitchen of the cell.

(A) The smooth endoplasmic reticulum $(SER)$ is responsible for the synthesis of lipids,including steroids and phospholipids,within the cell. In contrast,the rough endoplasmic reticulum $(RER)$ is primarily involved in protein synthesis due to the presence of ribosomes on its surface.

(B) The concept that 'all cells arise from pre-existing cells' was proposed by Rudolf Virchow in $1855$. This statement,known as 'Omnis cellula-e cellula',provided a significant addition to the cell theory originally proposed by Schleiden and Schwann,which did not explain how new cells were formed.

(C) The cell theory was proposed by Matthias Schleiden and Theodor Schwann in $1838$ and $1839$ respectively.
They stated that all plants and animals are composed of cells and that the cell is the basic unit of life.

(D) Prokaryotic cells lack membrane-bound organelles such as mitochondria,lysosomes,and plastids.
Ribosomes are the only organelles present in prokaryotic cells,which are non-membrane-bound and are responsible for protein synthesis.

(A) Ribosomes are non-membrane-bound organelles found in both prokaryotic and eukaryotic cells. They are composed of ribosomal $RNA$ $(rRNA)$ and proteins. In contrast,organelles like the Golgi apparatus,chloroplasts,and the nucleus are membrane-bound structures.

(B) The prefix $\mu$ (micro) represents a factor of $10^{-6}$. Therefore,$1 \, \mu m$ (micrometer) is equal to $10^{-6} \, m$ (meters). This unit is commonly used in biology to measure the size of cells and organelles.

(C) Lysosomes are membrane-bound cell organelles that contain digestive enzymes. They are formed by the process of packaging in the Golgi apparatus. The enzymes within lysosomes are synthesized by the rough endoplasmic reticulum,transported to the Golgi apparatus for modification and sorting,and then pinched off as vesicles to form lysosomes.

(D) Robert Hooke was the first to observe cells in $1665$,but he observed dead cells from a cork slice.
It was Antonie van Leeuwenhoek who,with the help of an improved microscope,was the first to observe and describe free-living cells such as bacteria and protozoa in pond water.

(A) Option $A$ is the odd one out because it is a false statement. Plant cell membranes are primarily composed of lipids and proteins,not chitin. Chitin is a structural polysaccharide found in the cell walls of fungi and the exoskeletons of arthropods,not in plant plasma membranes. Options $B$,$C$,and $D$ are scientifically accurate descriptions of membrane composition and transport properties.

(C) Lysosomes are known as 'suicide-bags' because they contain powerful digestive enzymes. When the cell gets damaged or its metabolism is disturbed,lysosomes may burst,and the released enzymes digest their own cell.

(N/A) Yes,$I$ agree with the statement that '$A$ cell is a building unit of an organism'.
This is because all living organisms are composed of cells,which are the fundamental structural and functional units of life.
Just as bricks are the building blocks of a building,cells are the basic units that organize to form tissues,organs,and organ systems,ultimately constituting the entire organism.
Furthermore,a cell is the smallest independent unit capable of performing all essential life processes,such as metabolism,growth,and reproduction.

(B) When you wash clothes for a long time,the soap solution acts as a hypertonic solution relative to the cells of your skin.
According to the process of osmosis,water moves from a region of higher water concentration to a region of lower water concentration through a semi-permeable membrane.
Since the soap solution is more concentrated (hypertonic) than the cytoplasm of your skin cells,water moves out of the finger cells into the soap solution.
This loss of water causes the skin cells to shrink,resulting in the wrinkled appearance of your fingers.

(N/A) Endocytosis is the process by which cells engulf materials from their surroundings by forming vesicles from the plasma membrane.
In animal cells,the plasma membrane is the outermost boundary because a rigid cell wall is absent.
This flexibility allows the plasma membrane to fold inward and engulf external substances.
In contrast,plant cells possess a rigid,protective cell wall outside the plasma membrane,which prevents the membrane from invaginating or engulfing large particles,thus making endocytosis impossible in plant cells.

(N/A) The phenomenon responsible for this situation is $Exosmosis$. When a person consumes a concentrated salt solution (a hypertonic solution),the concentration of salt outside the cells of the alimentary canal becomes much higher than inside the cells. Due to the difference in concentration,water moves out of the cells into the surrounding medium through the process of $Exosmosis$. This leads to severe dehydration of the cells lining the digestive tract,which triggers the body's protective reflex to expel the irritant,resulting in vomiting.

(N/A) non-membranous cell organelle is a structure within the cell that is not enclosed by a lipid bilayer membrane. The most prominent example of a non-membranous organelle is the $Ribosome$. Other examples include the $Centrosome$ and $Cytoskeleton$.

(B) The absorption of digested food nutrients (like glucose and amino acids) primarily occurs through diffusion (simple or facilitated) and active transport across the intestinal epithelium.
Water is absorbed primarily through the process of osmosis,which is the movement of water molecules from a region of higher water potential to a region of lower water potential across a semi-permeable membrane.

(B) When salt is added to vegetables,the concentration of the surrounding medium becomes hypertonic compared to the cytoplasm of the vegetable cells.
Due to this concentration gradient,water moves out of the vegetable cells into the surrounding medium through the cell membrane.
This process of movement of water from a region of higher water potential (inside the cell) to a region of lower water potential (outside the cell) through a semi-permeable membrane is known as $Exosmosis$.

(C) Both $(a)$ and $(b)$ are correct. When the surrounding medium is hypotonic,water moves into the cells due to osmosis. This results in the swelling of the cells. $RBCs$ (Red Blood Cells) lack a cell wall,making them susceptible to bursting under osmotic pressure. In contrast,the presence of a rigid cell wall in onion peel cells provides structural support,preventing them from bursting.

(A) In photoautotrophic bacteria,photosynthesis occurs in specialized structures called chromatophores.
These are small,membrane-bound vesicles or lamellae that are extensions of the plasma membrane.
These structures contain photosynthetic pigments (like bacteriochlorophyll) that trap solar energy to synthesize food.

(C) The correct matches are as follows:
$(a)$ Smooth endoplasmic reticulum is responsible for the detoxification of many poisons and drugs in liver cells,so $(a)-(iv)$.
$(b)$ Lysosomes are known as the suicidal bags of the cell because they contain powerful digestive enzymes,so $(b)-(v)$.
$(c)$ Nucleoid is the undefined nuclear region containing only nucleic acids found in prokaryotic organisms like bacteria,so $(c)-(iii)$.
$(d)$ Food vacuoles are temporary structures formed in organisms like Amoeba to digest food particles,so $(d)-(i)$.
$(e)$ Chromatin material and nucleolus are the components found inside the nucleus of a eukaryotic cell,so $(e)-(ii)$.
Therefore,the correct sequence is $a-(iv), b-(v), c-(iii), d-(i), e-(ii)$.

(N/A) $Chromoplast$: Found in colored parts of plants such as flowers and fruits.
$Chloroplast$: Found in green parts of plants such as leaves.
$Leucoplast$: Found in non-colored parts of plants such as roots,tubers,and seeds.

(A) Endoplasmic reticulum: It acts as a transport system for materials between various regions of the cytoplasm or between the cytoplasm and the nucleus.
$(b)$ Mitochondria: It produces energy in the form of $ATP$ (Adenosine Triphosphate),hence known as the power house.
$(c)$ Golgi body: It is involved in the packaging and dispatching of proteins and lipids synthesized in the cell.
$(d)$ Lysosome: It contains powerful digestive enzymes capable of breaking down all organic material,hence called the digestive bag or suicide bag.
$(e)$ Vacuole: These are storage sacs for solid or liquid contents.
$(f)$ Chloroplast: It contains chlorophyll,which is essential for photosynthesis,thus acting as the kitchen of the cell.
$(g)$ Nucleus: It contains the genetic material $(DNA)$ and regulates all cellular activities,acting as the control room.

(N/A) bacterial cell is a prokaryotic cell,whereas an onion peel cell is a eukaryotic plant cell. The differences are summarized below:

Bacterial Cell	Onion Peel Cell
$(i)$ Cell wall is made of peptidoglycan.	$(i)$ Cell wall is made of cellulose.
$(ii)$ Nucleus is absent (nucleoid present).	$(ii)$ Nucleus is present.
$(iii)$ Membrane-bound organelles are absent.	$(iii)$ Membrane-bound organelles are present.
$(iv)$ These are prokaryotes.	$(iv)$ These are eukaryotes.

(B) Carbon dioxide $(CO_2)$ moves in and out of the cell through the process of diffusion,which is the spontaneous movement of a substance from a region of higher concentration to a region of lower concentration.
Water $(H_2O)$ moves in and out of the cell through the process of osmosis,which is the movement of water molecules through a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.

(A) Amoeba obtains its food by forming temporary finger-like extensions of the cell surface known as pseudopodia.
These pseudopodia surround the food particle and fuse over it.
This process results in the formation of a food vacuole inside the cell,where complex substances are broken down into simpler ones.
This process of engulfing food by Amoeba is known as endocytosis.

(B) The two organelles in a plant cell that possess their own genetic material $(DNA)$ and ribosomes are mitochondria and plastids.
These organelles are considered semi-autonomous because they can synthesize some of their own proteins and replicate independently of the cell nucleus.

(B) Lysosomes contain powerful digestive enzymes that are capable of breaking down complex organic molecules,worn-out cell organelles,and foreign materials like bacteria or viruses that enter the cell.
By digesting these waste materials and cellular debris,they keep the cell clean.
Because of this cleaning function,lysosomes are commonly referred to as the 'scavengers of the cells' or 'suicide bags'.

(B) The $Nucleus$ is known as the control center of the cell. It contains the genetic material $(DNA)$ which regulates cellular activities such as metabolism, protein synthesis, and cell division by controlling gene expression.

(A) Leucoplasts are colorless plastids primarily found in the roots of plants,where they store nutrients like starch,oils,and proteins.
$(b)$ Chloroplasts are green-colored plastids containing chlorophyll,which are abundant in the leaves of plants to facilitate photosynthesis.
$(c)$ Chromoplasts are colored plastids (containing pigments like carotene and xanthophyll) that provide red,orange,or yellow colors to flowers and fruits.

(D) Plant cells possess large-sized vacuoles for the following reasons:
$1$. They store many important substances,including nutrients,water,and waste products.
$2$. They contain cell sap,which exerts turgor pressure against the cell wall,providing turgidity and structural rigidity to the plant cell.