Structural Organisation of a Cell Questions in English

(N/A)

Plasma Membrane	Cell Wall
$(1)$ It is made up of lipids and proteins.	$(1)$ It is made up of cellulose.
$(2)$ It is a living structure.	$(2)$ It is a dead structure.
$(3)$ It is present in both plant and animal cells.	$(3)$ It is found exclusively in plant cells.

(N/A) Two biologically important compounds containing nitrogen are:
$1$. Proteins: These are complex organic molecules made up of amino acids,which contain nitrogen in their amino group $(-NH_2)$.
$2$. Nucleic Acids ($DNA$ and $RNA$): These are the genetic materials of living organisms,and their nitrogenous bases (adenine,guanine,cytosine,thymine,and uracil) contain nitrogen.

(N/A)
$(i)$ Respectful attitude towards teachers.
$(ii)$ Attentiveness and curiosity.
$(iii)$ Good observation skills.
$(b)$ $A$ cell is called the structural and functional unit of life because:
$(i)$ It is the basic building block of all living organisms (structural unit).
$(ii)$ It contains specialized organelles that perform all essential life processes like respiration,nutrition,and excretion,which are necessary for the survival of the organism (functional unit).

(N/A) The qualities shown by Ria's mother are:
$(i)$ In-depth knowledge of biological concepts.
$(ii)$ Care,concern,and patience in guiding her daughter.
$(b)$ $DNA$ is primarily found in the nucleus of a cell. Its function is to store and transmit hereditary information from parents to offspring and to provide instructions for constructing and organizing cells.

(N/A) Unicellular organisms: These are organisms made up of a single cell only.
Examples: $Chlamydomonas$,$Amoeba$,$Bacteria$,$Paramecium$ (any two).
$(b)$ Multicellular organisms: These are organisms in which many cells group together in a single body to perform different functions and form various body parts.
Examples: Fungi,plants,and animals (any two).

(A)

$(i)$ Type of Cell	Characteristic Feature
Plant cell	Presence of a large central vacuole that occupies most of the cell volume,pushing the nucleus to the periphery.
$(ii)$ Type of Cell	Characteristic Feature
Plant cell	The rigid cell wall provides structural support and prevents the cell from bursting due to osmotic pressure in a hypotonic (dilute) medium.
$(iii)$ Type of Cell	Characteristic Feature
Prokaryotic cell	The nuclear region is not surrounded by a nuclear membrane and is referred to as the nucleoid; membrane-bound organelles are absent.

(N/A) $(i)$ Cells are the smallest units that constitute the body of all living organisms and perform basic life processes essential for survival. Therefore,the cell is known as the structural and functional unit of life.
$(ii)$ The plasma membrane is called a selectively permeable membrane because it allows the movement of only certain selected substances into and out of the cell,while restricting the movement of others.
$(iii)$ The concentration of dissolved substances (solutes) in the water determines the movement of water across the plasma membrane,a process known as osmosis.

(N/A) Differences:

Plant Cell	Animal Cell
$(i)$ Presence of cell wall.	$(i)$ Cell wall is absent.
$(ii)$ Large central vacuole is present.	$(ii)$ Vacuoles are small or absent.
$(iii)$ Plastids are present.	$(iii)$ Plastids are absent.

Similarities:
$(i)$ Both possess a cell membrane.
$(ii)$ Both contain a nucleus.
$(iii)$ Both contain cytoplasm and various cell organelles.
$(b)$ When an animal cell is placed in distilled water (a hypotonic solution),water enters the cell through the process of osmosis. As a result,the cell will swell and eventually burst because animal cells lack a rigid cell wall to withstand the internal turgor pressure.

(N/A)

Nuclear region of a bacterial cell	Nuclear region of an animal cell
$(i)$ Poorly defined and lacks a nuclear membrane.	$(i)$ Well-defined and membrane-bound.
$(ii)$ Contains a single chromosome.	$(ii)$ Contains more than one chromosome.

$(b)$ The structure present in the nuclear region that bears genes is the $DNA$ (Deoxyribonucleic acid) molecule,which is organized into chromosomes.

(N/A)

Parameter	Prokaryotic Cell	Eukaryotic Cell
$(i)$ Nuclear region	Poorly defined due to the absence of a nuclear membrane; known as nucleoid.	Well-defined and surrounded by a nuclear membrane.
$(ii)$ Cell organelles	Membrane-bound cell organelles are absent.	Membrane-bound cell organelles are present.
$(iii)$ Chlorophyll	Associated with membranous vesicles (bag-like structures),not with plastids.	Associated with plastids (chloroplasts).

(N/A) $(i)$ The cell will lose water by osmosis; therefore,the cell will shrink. This occurs in a hypertonic solution.
$(ii)$ The cell will gain water by osmosis; therefore,the cell will swell up. This occurs in a hypotonic solution.
$(iii)$ In the case of equal concentration,there will be no net movement of water; therefore,the cell will stay at the same size. This occurs in an isotonic solution.
$(b)$ The cell membrane is composed of lipids and proteins.
The cell wall is composed of cellulose.

(N/A) The plasma membrane is primarily composed of lipids and proteins,while the cell wall is mainly made up of cellulose.
Functions:
- Plasma membrane: It regulates the movement of substances into and out of the cell (selectively permeable) and provides protection.
- Cell wall: It provides structural support,shape,and protection to the plant cell.

Cell wall	Plasma membrane
$1$. It is non-living.	$1$. It is living.
$2$. It is permeable.	$2$. It is semipermeable.
$3$. It is found only in plant cells.	$3$. It is found in both plant and animal cells.
$4$. It is rigid.	$4$. It is flexible.

(N/A) $(i)$ The diagram of a prokaryotic cell is provided in the image.
$(ii)$ In bacteria,the nuclear region is poorly developed or undefined because it lacks a nuclear membrane. Such an undefined nuclear region,which contains only nucleic acids,is called a nucleoid. Organisms that possess such cells with an undefined nuclear region are called prokaryotes (pro = primitive,karyote = nucleus).

(N/A)

Prokaryotic Cell	Eukaryotic Cell
$1$. Size is generally small $(0.5-10 \mu m)$.	$1$. Size is generally larger $(1-100 \mu m)$.
$2$. Nuclear region is not surrounded by a nuclear membrane.	$2$. Nuclear region is surrounded by a nuclear membrane.
$3$. Membrane-bound organelles such as mitochondria,lysosomes,and endoplasmic reticulum are absent.	$3$. All membrane-bound organelles are present.
$4$. Nucleolus is absent.	$4$. Nucleolus is present.
$5$. Cell division occurs by fission or budding (no mitosis).	$5$. Cell division is mitotic or meiotic.
$6$. They always have a single chromosome.	$6$. They have more than one chromosome.
$7$. $DNA$ is circular and lies free in the cytoplasm (no true nucleus).	$7$. $DNA$ is linear and contained within a nucleus.
$8$. $DNA$ is naked (not associated with histones). e.g.,$PPLO$,bacteria,and blue-green algae.	$8$. $DNA$ is associated with proteins (histones) to form chromosomes. e.g.,Plants and animals.

Activity to show endosmosis and exosmosis:
Put dried raisins in plain water and leave them for some time. Then,place these swollen raisins into a concentrated salt solution.
Observation:
$(i)$ When dried raisins are placed in plain water,they swell up due to the osmotic entry of water into the raisins. Plain water acts as a hypotonic medium for the raisins.
$(ii)$ When the swollen raisins are transferred to a concentrated salt solution,they shrink again. The concentrated solution acts as a hypertonic medium for the swollen raisins. Exosmosis occurs,and the raisins lose water.

(D) $(i)$ The stain commonly used for onion peel is $Iodine$ solution,and for cheek cells,$Methylene$ $blue$ is typically used. $Safranin$ is also used for plant tissues.
$(ii)$ Stains are necessary because they provide contrast to the transparent or colorless cellular components,making them clearly visible under a microscope.
$(iii)$ No,all organelles do not absorb stain equally. The absorption of stain depends on the chemical composition and density of the specific organelle.

(N/A) $(i)$ Proteins and lipids provide structural flexibility and integrity to the plasma membrane.
$(ii)$ The plasma membrane is called selectively permeable because it regulates the entry and exit of specific substances while preventing the movement of others.
$(iii)$ Cellulose provides structural strength and rigidity to the plant cell wall. It also helps in water retention,preventing the desiccation of the cell.
$(iv)$ Plasmolysis is the phenomenon where a living plant cell loses water through osmosis,causing the cell contents to shrink away from the cell wall.
$(v)$ The flexibility of the cell membrane allows the cell to engulf food and other materials from its external environment through a process called endocytosis,which is essential for organisms like $Amoeba$.
$(vi)$ The process is known as diffusion.

(N/A) Diffusion: This is a phenomenon of the spontaneous movement of molecules from a region of higher concentration to a region of lower concentration. This process is faster in the gaseous phase than in liquids and solids. This process leads to a uniform concentration within a cell.
Importance: Substances (molecules,ions) such as $CO_2, O_2, H_2O$,etc.,can move across the plasma membrane by the process of diffusion.
$(b)$ Osmosis: It involves the movement of water molecules (solvent particles) from a region of their higher concentration to a region of lower concentration through a semipermeable membrane.
Importance: It is a purely mechanical diffusion process by which cells absorb water without spending any metabolic energy.

(N/A) Osmosis is the spontaneous net movement of water molecules from a region of higher water potential to a region of lower water potential through a selectively permeable membrane,such as the plasma membrane. This is a passive process,meaning it does not require the expenditure of cellular energy.
Examples where osmosis is helpful:
$(i)$ Freshwater organisms like $Amoeba$ and $Paramecium$ maintain their internal water balance through osmosis.
$(ii)$ The movement of water into and out of plant cells occurs primarily due to osmosis.
$(iii)$ Absorption of water from the soil by root hairs is facilitated by osmosis.
$(iv)$ It plays a crucial role in the opening and closing of stomata by regulating the turgor pressure of guard cells.
$(v)$ It is responsible for the seismonastic movements (thigmonasty) in the 'touch-me-not' plant ($Mimosa$ $pudica$).
$(vi)$ This process helps plant cells,tissues,and soft organs like leaves,young shoots,and flowers maintain turgidity and structural integrity.

(N/A) $(i)$ Endocytosis: It is the process of ingestion of material by the cells through the plasma membrane.
$(ii)$ Phagocytosis: It is a common method of feeding in some organisms such as $Amoeba$ and sponges. Biologically, it means "cell eating". The $WBCs$ engulf cell debris and microbes with the help of this process.
$(iii)$ Exocytosis: It is the process by which the plasma membrane removes its contents to the surrounding medium.

(A) Viruses are considered to be at the border of living and non-living organisms. Unlike bacteria,amoebae,or sperm cells,which are cellular organisms,viruses consist of genetic material ($DNA$ or $RNA$) enclosed in a protein coat called a capsid. Because they lack cellular machinery and metabolic processes,they can be crystallized and stored like chemical substances,a property characteristic of non-living matter. Therefore,the correct answer is $A$.

(B) cell swells up when it is placed in a hypotonic solution.
In a hypotonic solution,the concentration of water molecules in the surrounding medium is higher than the concentration of water molecules inside the cell.
Due to the process of osmosis,water molecules move from the region of higher water concentration (outside) to the region of lower water concentration (inside the cell) through the semi-permeable plasma membrane.
This net movement of water into the cell causes it to swell.

(C) Chromosomes are thread-like structures located inside the nucleus of animal and plant cells.
Each chromosome is made of protein and a single molecule of deoxyribonucleic acid $(DNA)$.
These components are essential for the packaging of genetic material within the cell nucleus.

(A) Plasmolysis is the process in which cells lose water in a hypertonic solution.
When a plant cell is placed in a hypertonic solution (a solution with a higher solute concentration than the cell sap),water moves out of the cell due to osmosis.
As water leaves the cell,the cytoplasm shrinks away from the cell wall.
This phenomenon is known as plasmolysis.

(A) The functional segments of $DNA$ are known as genes.
Genes are the basic units of heredity and are responsible for the transmission of traits from parents to offspring.
Each gene contains the instructions required to synthesize a specific protein or functional $RNA$ molecule.

(B) The correct answer is $B$.
$A$ is correct: Osmosis is the movement of water across a semipermeable membrane,which depends on the solute concentration.
$B$ is incorrect: Plasma membranes in plants are composed of lipids and proteins; they do not contain chitin. Chitin is a structural polysaccharide found in the cell walls of fungi and the exoskeletons of arthropods,not in plant plasma membranes.
$C$ is correct: Biological membranes are primarily composed of a phospholipid bilayer with embedded proteins.
$D$ is correct: Since the membrane is lipid-based,substances that are lipid-soluble (soluble in organic solvents) can diffuse through the membrane easily.

(A) In prokaryotic cells,the nuclear region is not well-defined because it lacks a nuclear membrane. This undefined nuclear region,which contains only nucleic acids,is called the $Nucleoid$.

(D) $Amoeba$ is a unicellular organism that captures its food using temporary finger-like extensions of its cell surface called pseudopodia.
This process of engulfing food particles from the external environment into the cell is known as endocytosis.
Once the food is inside,it is enclosed in a food vacuole where digestion occurs.
Therefore,the correct term for the acquisition of food by $Amoeba$ is endocytosis.

(A) The cell wall of plants,such as $Hydrilla$,$Mango$ $tree$,and $Cactus$,is primarily composed of cellulose,which provides structural support and rigidity.
In contrast,the cell wall of $Bacteria$ is made up of peptidoglycan (also known as murein),which consists of sugars and amino acids.
Therefore,the correct option is $A$.

(C) In a non-dividing cell,the genetic material is present in the form of chromatin material.
Chromatin is a complex of $DNA$ and proteins (histones).
It appears as an entangled mass of thread-like structures within the nucleus.
When the cell prepares to divide,this chromatin condenses into distinct,thick,rod-like structures known as chromosomes.

(D) In $1839$,the Czech physiologist $Jan$ $Evangelista$ $Purkinje$ coined the term $Protoplasm$ for the fluid substance of the cell.
$Protoplasm$ is the living content of the cell,which includes both the cytoplasm and the nucleus.
Therefore,the correct option is $D$.

(FALSE) The statement is False.
An undefined nuclear region containing only nucleic acids (and lacking a nuclear membrane) is known as the nucleoid,which is characteristic of prokaryotic cells.
$A$ nucleolus is a distinct,spherical,non-membrane-bound structure found within the nucleus of eukaryotic cells,primarily involved in ribosome synthesis.