Textbook - THE FUNDAMENTAL UNIT OF LIFE Questions in English

(N/A) The cell was discovered by $Robert \ Hooke$ in $1665$ using a self-designed microscope.
He examined a thin slice of cork under the microscope.
He observed that the cork resembled the structure of a honeycomb,consisting of many small,box-like compartments which he termed as 'cells'.

(N/A) The cell is considered the structural unit of life because all living organisms are composed of cells,which provide the basic framework and organization for the body.
It is called the functional unit of life because all metabolic activities and physiological processes necessary for survival,such as respiration,protein synthesis,and waste excretion,occur within the cell.
These activities are carried out by specialized structures known as cell organelles,which perform specific tasks like energy production,transportation,and synthesis of materials.
Therefore,the cell is the smallest unit capable of performing all life processes independently.

(N/A) Substances like $CO_2$ move in and out of the cell through the process of diffusion. When $CO_2$ accumulates in high concentration inside the cell,a concentration gradient is created between the internal and external environment. $CO_2$ moves from a region of high concentration to a region of low concentration outside the cell via diffusion. Similarly,water moves in and out of the cell through a specialized process called osmosis,which is the movement of water molecules from a region of higher water concentration to a region of lower water concentration through a selectively permeable membrane.

(N/A) The plasma membrane is called a selectively permeable membrane because it selectively allows the movement of certain substances into and out of the cell. It permits the passage of specific molecules while preventing the movement of others,thereby maintaining the internal environment of the cell.

(N/A) The completed table is as follows:

< strong>Prokaryotic Cell	< strong>Eukaryotic Cell
$1.$ Size: generally small $(1-10 \,\mu m)$	$1.$ Size: generally large $(5-100 \,\mu m)$
$2.$ Nuclear region: poorly defined due to the absence of a nuclear membrane,known as nucleoid	$2.$ Nuclear region: well defined and surrounded by a nuclear membrane
$3.$ Chromosome: single	$3.$ More than one chromosome
$4.$ Membrane-bound cell organelles absent	$4.$ Membrane-bound cell organelles (e.g.,mitochondria,plastids) are present

(B) The two organelles that contain 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.

(B) The cell is the fundamental structural and functional unit of life. Its organization is maintained by various organelles and biochemical processes. If this organization is destroyed due to physical or chemical influence,the cell loses its ability to perform essential life processes such as respiration,nutrition,and waste excretion. Consequently,the cell will not be able to perform its basic functions and will die after some time.

(N/A) Lysosomes contain very powerful hydrolytic enzymes that are capable of breaking down organic matter.
When a cell gets damaged or its metabolic processes are disturbed,lysosomes may burst,and these enzymes digest their own cell.
Because of this self-digesting action,lysosomes are known as the 'suicide bags' of the cell.

(B) Ribosomes are the sites of protein synthesis within the cell. They are small,granular structures found either floating freely in the cytoplasm or attached to the surface of the Rough Endoplasmic Reticulum $(RER)$.

(N/A) Comparison of plant cell and animal cell:
$1$. Cell Wall: Plant cells possess a rigid cell wall outside the plasma membrane,whereas animal cells lack a cell wall.
$2$. Shape: Plant cells generally have a fixed,regular shape due to the cell wall,while animal cells are generally irregular or flexible in shape.
$3$. Size: Plant cells are typically larger in size compared to animal cells.
$4$. Plastids: Plant cells contain plastids (like chloroplasts) for photosynthesis,which are absent in animal cells (except in some protists like $Euglena$).
$5$. Vacuoles: Plant cells contain a single,large,permanent central vacuole,whereas animal cells have many small,temporary vacuoles.

(N/A)

Prokaryotic Cell	Eukaryotic Cell
$1$. Size: Generally small $(1-10 \,\mu m)$ where $1 \,\mu m = 10^{-6} \,m$.	$1$. Size: Generally large $(5-100 \,\mu m)$.
$2$. Nuclear region: Poorly defined due to the absence of a nuclear membrane; known as nucleoid.	$2$. Nuclear region: Well-defined and surrounded by a nuclear membrane.
$3$. Chromosome: Single.	$3$. More than one chromosome.
$4$. Membrane-bound cell organelles are absent.	$4$. Membrane-bound organelles like mitochondria and plastids are present.

(B) If the plasma membrane ruptures or breaks down:
$1$. The cell will lose its structural integrity and its ability to maintain homeostasis.
$2$. All the useful substances (like proteins,ions,and nutrients) will move out of the cell.
$3$. There will be no difference between the cell content and its external environment,leading to the death of the cell.
$4$. The cell will lose its normal shape and eventually disintegrate.

(B) Effect of absence of Golgi apparatus on the life of a cell:
$(i)$ The packaging and dispatching of various proteins to different targets inside and outside the cell will be severely affected.
$(ii)$ Cellular products cannot be stored,modified,or sorted properly.
$(iii)$ The formation of lysosomes will be inhibited. This leads to the accumulation of worn-out and dead cell organelles within the cell,which may eventually cause cell death.

(N/A) The organelle $Mitochondria$ is known as the powerhouse of the cell.
This is because the process of cellular respiration takes place within the mitochondria to generate energy in the form of $ATP$ ($Adenosine$ $Triphosphate$).
This energy is essential for carrying out various chemical activities required for the life of the cell.

(A) The lipids constituting the cell membrane are synthesized in the smooth endoplasmic reticulum $(SER)$.
Membrane proteins are synthesized by the ribosomes attached to the rough endoplasmic reticulum $(RER)$.
These components are then transported to the cell membrane to facilitate membrane biogenesis.

(B) Amoeba obtains its food through a process called phagocytosis (a type of endocytosis).
When food particles come near the Amoeba,it extends its cell membrane to form finger-like projections known as pseudopodia (false feet).
These pseudopodia surround the food particle and fuse together to form a food vacuole.
Inside the food vacuole,complex substances are broken down into simpler ones,which then diffuse into the cytoplasm.

(B) Osmosis is defined as the movement of solvent molecules (typically water) from a region of their higher concentration to a region of their lower concentration through a semipermeable membrane.
During this process,water molecules are free to move across the plasma membrane in both directions,but the net movement occurs from the region of higher water concentration to the region of lower water concentration.

(N/A) $(i)$ Osmosis is the process responsible for the gathering of water in the hollowed portion of $B$ and $C$. Since the concentration of solute (sugar in cup $B$ and salt in cup $C$) is higher inside the cup as compared to the water outside,water moves from its higher concentration (outside the cup) towards the lower concentration (inside the cup) through the semipermeable membrane of the potato cells. This process of inward movement of solvent is called endosmosis.
$(ii)$ Potato $A$ acts as a control for the experiment. It is necessary to provide a baseline for comparing the results and to demonstrate that the movement of water is due to the concentration gradient of the solute.
$(iii)$ Water does not gather in the hollowed portions of $A$ and $D$ because:
In potato $A$,the hollowed portion is empty. Since there is no concentration difference (no solute),no osmosis occurs.
In potato $D$,although it contains sugar,it is boiled. Boiling kills the potato cells and destroys the semipermeable membrane,which is essential for osmosis to occur. Therefore,no water movement takes place.

(N/A) There are two main types of cell division:
$1.$ Mitosis: This is the type of cell division that results in the formation of two daughter cells,each having the same number of chromosomes as the parent cell. It is essential for the growth and repair of body tissues.
$2.$ Meiosis: This is a type of cell division that results in the formation of four daughter cells,each having half the number of chromosomes as the parent cell. It is specifically involved in the formation of gametes (sex cells) for sexual reproduction.
Therefore,mitosis is required for the growth and repair of the body,while meiosis is involved in the formation of gametes.