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THE FUNDAMENTAL
UNIT OF LIFE
TEXTBOOK QUESTIONS AND THEIR ANSWERS
Q. 1.
Who discovered cells, and how?
Ans.
Cell was discovered by an English scientist, Robert
Hooke.
Hooke, in 1665, while observing a thin slice of cork,
under his crude compound microscope, observed that
the cork was composed of several box-like
compartments, forming a honey-comb structure. He
named the compartments as cells.
Q. 2.
Why is the cell called the structural and
functional unit of life?
Ans.
Each living cell has the capacity to perform certain
basic functions that are characteristic of all living
forms. Each cell has some specific components in it
known as cell organelles. Each cell acquires its
structure and ability to function because of the
organisation of its membrane and organelles in
specific ways. The cell thus has a basic structural
organisation. This helps the cell to perform functions
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like respiration, obtaining nutrition and clearing of
waste materials, or forming new proteins. Thus, the
cell is the structural and functional unit of living
organism.
Q. 3.
How do substances like CO2 and water move in
and out of the cell? Discuss.
Ans.
Movement of CO2 in and out of the cell occurs
through diffusion. When concentration of CO2 is
higher inside the cell in comparison to the cell’s
external environment, then this difference in
concentration of CO2 in and out of the cell leads to
diffusion. Thus, CO2 moves out of the cell from a
region of its high concentration to a region of its low
concentration outside the cell.
Movement of water molecules occurs due to
osmosis. Concentration of water depends on the
dissolved materials present in it. Here, water moves
through a selectively permeable membrane from
lower concentration to higher concentration of
solution.
Q. 4.
Why is the plasma membrane called a selectively
permeable membrane?
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Ans.
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Plasma membrane is a living, delicate membrane. It
regulates the movement of molecules inside and
outside the cell. It allows the entry or exit of some
molecules in and out of the cell and simultaneously it
also prevents the movement of some other
molecules. Thus, it is called selectively permeable
membrane.
Q. 5.
Fill in the gaps in the following table illustrating
differences between prokaryotic and eukaryotic
cells.
Prokaryotic
Eukaryotic Cell
1. Size : Generally small
(1-10 μ m) 1 μ m = 10–6m
1. Size : generally large
(5-100 μ m)
2. Nuclear region :
___________________
___________________
2. Nuclear region : we
defined and surrounding
by a nuclear membrane
and known as ___
3. More than one
3. Chromosome :
single
chromosome
4. ____________________
4. Membrane-bound cell
organelles absent.
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____________________
____________________
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Ans.
Prokaryotic Cell
Eukaryotic Cell
(a) Size : generally small (1 -
(a) Size : generally large (5-
10 μm) 1 μm = 10–6 m
100 μm)
(b) Nuclear region : well
(b) Nuclear region :
defined and surrounded by
undefined nuclear region
a nuclear membrane
containing genetic material,
known as nucleoid.
(c) More than one chromosome
(c) Chromosome : single
(d) Membrane bound cell
(d) Membrane-bound cell
organelles present.
organelles absent
Q. 6.
Can you name the two organelles we have studied
that contain their own genetic material?
Ans.
The cell organelles like mitochondria and chloroplast
have their own genetic material.
Q. 7.
If the organisation of a cell is destroyed due to
some physical or chemical influence, what will
happen?
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Ans.
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Each living cell has the capacity to perform certain
basic functions because of its organisation. All the
cellular organelles, together plays an important role
in the cellular organisation. If this organisation is
destroyed, the cell can’t perform like before and it
will die ultimately.
Q. 8.
Why are lysosomes known as suicide bags?
Ans.
During the disturbance in cellular metabolism,
lysosomes are capable of digesting or lysing the
entire cell by releasing their own enzymes. For this
reason, lysosomes are called suicide bags.
Q. 9.
Where are proteins synthesised inside the cell?
Ans.
Ribosomes are the sites of protein synthesis inside
the cell.
Q 10.
Make a comparison and write down ways in
which plant cells are different from animal cells.
Ans.
Plant and animal cells differ in their sizes, presence
and absence of structural components as well as
shape, and number of cellular organelles.
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Major difference between plant and animal cells
are —
Plant Cell
Animal Cell
(a) Cells comparatively larger (a) Cells usually smaller in
in size.
size.
(b) Cell wall is present.
(b) Cell wall is absent.
(c) Plastids are present.
(c) Plastids are absent.
(d) Vacuoles are present, one (d) Vacuoles generally absent,
generally one large vacuole
if present they are more in
is present.
number and smaller in size.
(e) Dictyosomes (sub-units of (e) Prominent
Golgi body) present.
Golgi
bodies
present.
(f) Lysosomes are either absent (f) Lysosomes are more in
or very few in number.
number.
(g) Centrosome absent.
Q. 11.
(g) Centrosome present.
How is a prokaryotic cell different from an
eukaryotic cell?
Ans.
The
major
differences
between
prokaryotic
and
eukaryotic cells are —
Prokaryotic Cell
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Eukaryotic Cell
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(a) Prokaryotic
cells
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are (a) Eukaryotic cells are larger
generally smaller in size (1 -
in size (5 – 100 μm in
10 μm in diameter).
diameter).
(b) Nuclear region is not well- (b) Nuclear region is welldefined and genetic material
defined and surrounded by
is known as nucleoid.
a nuclear membrane.
(c) Single chromosome is
(c) More than one chromosome
present.
is present.
(d) Membrane-bound cell
(d) Membrane-bound cell
organelles absent.
organelles present
Q. 12. What would happen if the plasma membrane
ruptures or breaks down?
Ans.
As plasma membrane acts as the mechanical barrier,
if it ruptures or breaks down, the cell can not
differentiate
between
external
and
internal
environment of it and can’t protect inner cell content.
Along with these, movement of CO2, O2 and water
will also be hampered. The shape of the cell will also
be altered.
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Q. 13. What would happen to the life of a cell if there
was no Golgi apparatus?
Ans.
Golgi apparatus is an important component of cell.
In its absence packaging as well as transporting of
synthesised material outside the cell will not be
possible. Thus, materials will accumulate into the
cell. Along with this lysosomes would not be formed
without golgi body (i.e., absence of golgi apparatus
means absence of lysosome also). Thus, it is not
possible for a cell to survive without Golgi
apparatus.
Q. 14. Which organelle is known as the powerhouse of
the cell? Why?
Ans.
Mitochondria are known as the powerhouse of cell.
Mitochondria
contain
enzymes
for
catalysing
biochemical
reactions
involved
in
respiration.
Energy in the form of ATP is produced in the
process. For this reason, mitochondria are generally
called powerhouses of cell.
Q. 15. Where do the lipids and proteins constituting the
cell membrane get synthesised?
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Ans.
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Protein constituting the cell membrane is synthesised
by ribosomes situated on rough endoplasmic
reticulum (RER) whereas lipid is synthesised by
smooth endoplasmic reticulum (SER).
Q. 16. How does an Amoeba obtain its food?
Ans.
Amoeba obtains food through phagocytosis (the
process by which solid food materials are engulfed).
With the help of pseudopodia, Amoeba engulfs food
and it is enclosed within the food vacuole from
where it takes its nourishment.
Q. 17. What is osmosis?
Ans.
Osmosis is the diffusion of a solvent, usually water,
through a semi-permeable membrane from a dilute
or weaker solution into a concentrated or stronger
solution.
Q. 18. Carry out the following osmosis experiment. Take
four peeled potato halves and scoop each one out
to make potato cups. One of these potato cups
should be made from a boiled potato. Put each
potato cup in a trough containing water. Now,
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(a) Keep cup A empty
(b) Put one teaspoon sugar in cup B.
(c) Put one teaspoon salt in cup C.
(d) Put one teaspoon sugar in the boiled potato
cup D.
Keep these for two hours. Then observe the
four potato cups and answer the following :
(i) Explain why water gathers in the hollowed
portion of B and C.
(ii) Why
is
potato
A
necessary
for
this
experiment?
(iii) Explain why water does not gather in the
hollowed out portions of A and D.
Ans. (i) The water gathers in the hollowed portion of B
and C due to endosmosis since the concentration
is higher inside the cup as compared so that of
water outside.
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(ii) Potato A is necessary for this experiment as it acts
as the control set-up to compare the results with
the other three potatoes.
(iii) Water does not gather in the hollowed out portion
of A since it is empty having no concentration
at all. Potato D, which is a boiled one, loses
its semi-permeable nature to allow osmosis to
take place.
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