CBSE Class IX, NCERT Science (Biology)
Chapter 5, The
Fundamental Unit of Life
NCERT
Answers and CBSE Guide (NCERT Chapter Exercise Questions)
Question.1: Make a comparison to write down ways in which plant
cells are different from animal cells.
Answer: The cells of animals and plants have the
following differences:
|
Animal Cell
|
Plant Cell
|
|
>> Animal cells are
generally small in size.
>> Cell wall is absent.
>> Except the protozoan Euglena, no animal cell possesses
plastids.
>> Vacuoles in animal
cells are many, small and temporary.
>> Animal cells have a
single highly complex and prominent Golgi apparatus.
>> Animal cells have centrosome and centrioles.
|
>> Plant cells are larger than animal cells.
>> The plasma membrane of plant cells is surrounded
by a rigid cell wall of cellulose.
>> Plastids are present.
>> Most mature plant cells have a permanent and
large central sap vacuole.
>> Plant cells have many simpler units of Golgi
apparatus, called dictyosomes.
>> Plant
cells lack centrosome and centrioles.
|
Question.2:
How is a prokaryotic cell different
from a eukaryotic cell?
Answer: Difference between prokaryotic cell and
eukaryotic cell:
|
Prokaryotic Cell
|
Eukaryotic Cell
|
|
>> Cell size is generally
small (1 - 10 µm).
>> Nuclear region is
called nucleoid and is not surrounded by a nuclear membrane.
>> Only a single
chromosome is present.
>> Nucleolus is absent.
>> Membrane bound cell organelles
are absent.
>> Cell division by
fission or budding (no mitosis).
|
>> Cell is generally large (5 - 100 µm).
>> Nuclear material is surrounded by a nuclear
membrane.
>> More than one chromosome is present.
>> Nucleolus is present.
>> Membrane bound cell organelles.
>> Cell division mitotic or meiotic.
|
Question.3: What would happen if the plasma membrane ruptures or
breaks down?
Answer: Plasma
membrane is a selectively permeable membrane of the cell that maintains its
homeostasis, i.e., constant internal composition of the cell. If it ruptures or
breaks down the constant internal chemical composition of the cell will be lost
and it will not be able to perform its basic functions. Such a cell with
ruptured plasma membrane is killed.
Question.4: What would happen to the life of a cell if there is
no Golgi apparatus?
Answer: The materials
synthesized in the ER are stored, sorted, modified, packaged and dispatched to
various targets inside and outside the cell through the Golgi apparatus packs
products in vesicles, the secretary vesicles. In some cases complex sugars e.g.
cellulose, may be made from simple sugars in Golgi apparatus. The Golgi
apparatus is also involved in the formation of the cells which will not be
possible if Golgi apparatus is not there.
Question.5: Which organelle is known as the powerhouse of the
cell? Why?
Answer: Mitochondria are known as the powerhouse of the cell
because they contain enzymes that are needed for stepwise oxidation of food
stuffs (carbohydrate, fats and lipids) present in the cells to CO2 and water. Oxidation of food
releases energy which is used to form high-energy ATP (adenosine triphosphate) molecules. ATP is known as Energy Currency of the cell and it is
used as cellular fuel. Energy stored in ATP is used to bring about energy
requiring activities of the cell such as photosynthesis, protein synthesis and
muscle contraction.
Question.6: Where do the lipids and proteins constituting the cell membrane get synthesized?
Answer: Rough Endoplasmic Reticulum
(RER) - synthesizes proteins constituting cell membrane.
Smooth Endoplasmic Reticulum (SER)
- synthesizes lipids constituting cell membrane.
Question.7:
How does Amoeba obtain its food?
Answer: Amoeba has flexible cell membrane. It enables
amoeba to engulf in food by the process called endocytosis.
Question.8: What is osmosis?
Answer: The diffusion
of water or solvent through a semi-permeable membrane from a solution of lower
concentration of solutes to a solution of higher concentration of solutes, to
which the membrane is relatively impermeable, is called osmosis.
Easy
ReplyDelete