Extra 30 short questions and answers from the chapter:5 "The Fundamental Unit of Life" for Class 9 CBSE Science:-
1. Why is the cell called the structural and functional unit of life?
Answer:
The cell is the
smallest unit
of life that can perform all biological activities.
It provides
structure
to organisms (e.g., tissues and organs are made of cells).
It carries out
life functions
like respiration, digestion, and reproduction.
All organisms are either
unicellular or multicellular
, proving its fundamental role.
2. Explain the structure and function of the plasma membrane.
Answer:
The
plasma membrane
is the
outer covering
of a cell.
It is
selectively permeable
, allowing only certain substances to pass.
It is made of a
phospholipid bilayer
with embedded proteins.
Functions:
Regulates transport
(osmosis, diffusion) and
protects the cell
.
3. What is osmosis? Give an example.
Answer:
Osmosis
is the movement of
water molecules
from a region of higher water concentration to lower water concentration through a
semi-permeable membrane
.
Example:
If a
raisin is placed in water
, it swells up due to osmosis.
Plant root cells
absorb water from soil through osmosis.
4. What is diffusion? How is it different from osmosis?
Answer:
Diffusion
is the movement of molecules (gases, liquids) from
higher concentration to lower concentration
without a membrane.
Osmosis
is the movement of
water molecules
across a
semi-permeable membrane
.
Example of diffusion:
Perfume spreading in a room
.
Example of osmosis:
Water moving into plant cells
.
5. What happens when a cell is placed in a hypertonic solution?
Answer:
A
hypertonic solution
has a
higher solute concentration
than the cell.
Water moves
out of the cell
due to osmosis.
The cell
shrinks
(plasmolysis in plant cells).
Example: A plant cell placed in a
high salt solution loses water
and shrinks.
6. What is plasmolysis? Give an example.
Answer:
Plasmolysis
is the shrinking of the
cytoplasm
when water moves out of the cell.
This occurs when a cell is placed in a
hypertonic solution
.
Example: A
plant cell loses water
in a highly concentrated salt solution.
It makes plants
wilt
.
7. Explain endocytosis and exocytosis.
Answer:
Endocytosis
: The process by which a cell
engulfs solid or liquid particles
. Example:
Amoeba taking in food
.
Exocytosis
: The process by which a cell
removes waste or secretes substances
. Example:
Golgi apparatus secreting enzymes
.
8. Why is the nucleus called the control centre of the cell?
Answer:
The
nucleus contains DNA
, which controls cell activities.
It regulates
growth, metabolism, and reproduction
.
It
controls protein synthesis
by sending instructions to ribosomes.
It plays a role in
cell division
.
9. What is the function of mitochondria?
Answer:
Mitochondria are called the
powerhouse of the cell
.
They generate
ATP (energy currency)
through
cellular respiration
.
They contain their own
DNA and ribosomes
.
Active cells (muscle, nerve) have
more mitochondria
.
10. What are ribosomes? What is their function?
Answer:
Ribosomes are
small organelles
present
freely in the cytoplasm or on rough ER
.
They help in
protein synthesis
.
They are made of
RNA and proteins
.
Proteins synthesized by ribosomes are used for
growth and repair
.
11. What is the function of the Golgi apparatus?
Answer:
It is made of
flattened sacs (cisternae)
.
It
modifies, packages, and transports proteins and lipids
.
It helps in
secretion of enzymes and hormones
.
It forms
lysosomes
.
12. What are lysosomes? Why are they called suicidal bags?
Answer:
Lysosomes contain
digestive enzymes
that break down waste.
They
digest damaged cell parts
.
During cell damage, they
burst
, digesting the entire cell.
This is why they are called
suicidal bags
.
13. What is the function of the endoplasmic reticulum (ER)?
Answer:
Rough ER
: Helps in
protein synthesis
(has ribosomes).
Smooth ER
: Helps in
lipid synthesis
and detoxification.
It transports
materials within the cell
.
It forms
vesicles
for transport.
14. What is the difference between plant and animal cells?
Answer:
|
Feature |
Plant Cell |
Animal Cell |
|---|---|---|
|
Cell Wall |
Present (made of cellulose) |
Absent |
|
Vacuole |
Large central vacuole |
Small or absent |
|
Plastids |
Present (e.g., chloroplasts) |
Absent |
|
Shape |
Rectangular |
Round/irregular |
15. What are vacuoles? State their functions.
Answer:
Storage organelles
present in cells.
In plants
, they store
water, minerals, and waste
.
In animals
, they are small and help in
digestion and waste removal
.
They
maintain turgor pressure
in plant cells.
16. What are prokaryotic and eukaryotic cells? Give examples.
Answer:
|
Feature |
Prokaryotic Cell |
Eukaryotic Cell |
|---|---|---|
|
Nucleus |
Absent |
Present |
|
Size |
Small |
Large |
|
Organelles |
Few or none |
Many |
|
Example |
Bacteria |
Plants, Animals |
17. Why do plant cells have a cell wall?
Answer:
Provides
shape and support
.
Protects against
mechanical stress
.
Prevents
excessive water loss
.
Made of
cellulose
, allowing permeability.
18. What is the role of plastids in plant cells?
Answer:
Chloroplasts
– Photosynthesis.
Chromoplasts
– Provide
colour
.
Leucoplasts
– Store starch and proteins.
19. What are the functions of the cytoplasm?
Answer:
Supports organelles
.
Site of biochemical reactions
.
Stores nutrients
.
Allows
movement of materials
.
20. What is the significance of ATP in the cell?
Answer:
ATP is the
energy currency
of the cell.
It provides
energy for metabolic processes
.
It is produced in
mitochondria
.
It helps in
muscle contraction and nerve function
.
21. What are the different types of plastids? Give their functions.
Answer:
Chloroplasts
– Contain
chlorophyll
and help in
photosynthesis
.
Chromoplasts
– Provide
colour
to flowers and fruits (e.g., red, yellow pigments).
Leucoplasts
–
Store starch, proteins, and oils
in roots and seeds.
22. What happens to a plant cell when placed in a hypotonic solution?
Answer:
A
hypotonic solution
has a
lower solute concentration
than the cell.
Water moves
into the cell
due to
osmosis
.
The
vacuole swells
, and the cell becomes
turgid
(firm).
This helps plants maintain their shape.
23. Why are mitochondria called semi-autonomous organelles?
Answer:
They have their own
DNA and ribosomes
.
They can
replicate
independently.
They produce
enzymes for energy production
.
They synthesize some of their
own proteins
.
24. What is the difference between permeable, semi-permeable, and impermeable membranes?
Answer:
|
Type of Membrane |
Definition |
Example |
|---|---|---|
|
Permeable |
Allows all substances to pass through |
Cell wall |
|
Semi-permeable |
Allows only selective substances to pass |
Plasma membrane |
|
Impermeable |
Does not allow any substance to pass |
Plastic sheet |
25. How do lysosomes help in cell defence?
Answer:
Contain digestive enzymes
that destroy harmful substances.
Engulf bacteria and viruses
to protect the cell.
Help in the
breakdown of damaged cell parts
.
Prevent the spread of
infection
in the cell.
26. Why do onion peel cells and human cheek cells appear different?
Answer:
Onion peel cells
have a
cell wall
(plant cell), whereas
cheek cells
do not (animal cell).
Onion cells
contain
vacuoles and plastids
, while
cheek cells
lack plastids.
Cheek cells
are
irregular
in shape, while
onion cells
are
rectangular
.
Both have a
nucleus and cytoplasm
.
27. What are the two types of endoplasmic reticulum? How do they function?
Answer:
Rough ER (RER)
– Contains
ribosomes
and helps in
protein synthesis
.
Smooth ER (SER)
– Lacks ribosomes and helps in
lipid synthesis
and
detoxification
.
RER sends proteins to the
Golgi apparatus
for modification.
SER helps in the production of
steroids and hormones
.
28. What happens if the plasma membrane ruptures?
Answer:
The
cell loses its contents
and dies.
The
exchange of materials
is disrupted.
The cell cannot
maintain homeostasis
.
Organelles stop functioning, leading to
cell death
.
29. Explain the function of the cytoskeleton.
Answer:
Provides
mechanical support
to the cell.
Helps in the
movement of organelles
.
Maintains the
shape of the cell
.
Assists in
cell division and intracellular transport
.
30. How does the cell maintain homeostasis?
Answer:
The
plasma membrane regulates transport
through osmosis and diffusion.
The
nucleus controls metabolism
and gene expression.
Mitochondria produce
ATP
for energy needs.
Lysosomes break down
waste and damaged parts
to maintain balance.
