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Frequently Asked Questions (FAQ’S)
Q1. What are peroxisomes?
Ans: peroxisomes are organalles that contains the
enzymes for certain oxidative reactions like βoxidation.
Q2.
What
differes
peroxisomes
from
mitochondria and chloroplast?
Ans:
Peroxisomes differ from mitochondria and
chloroplasts in having a single membrane (instead
of a double membrane) and they do not contain
DNA or ribosomes.
Q3. How peroxisome helps in removal of O2
and production of H2O2?
Ans:
Peroxisomes contain enzymes that use
molecular
organic
oxygen
to
substances
remove
and
hydrogen
produce
from
hydrogen
peroxide. This H2O2 is utilized by catalase to
oxidise a variety of substances including phenols,
formic acid, formaldehyde, and alcohol.
Catalase
also converts excess H2O2 into H2O.
Q4. How break down of fatty acids takes
place in peroxisomes.
Ans: Peroxisomes achieve breakdown of fatty acid
molecules by a process called 'β oxidation'. In this
process, alkyl chains of fatly acids are removed
sequentially by blocks of two carbon atoms at a
time, and are converted into acetyl CoA. The
acetyl CoA produced during β-oxidation is exported
from peroxisomes to the cytosol for reuse in
biosynthetic pathways. In animals, this P oxidation
occurs both in mitochondira and peroxisomes,
while in yeast and plant cells, it occurs only in
peroxisomes.
Q5. Are peroxisomes responsible for human
diseases
Ans: Peroxisomes are also responsible for certain
diseases. These are, diseases due to deficiency
e.g. ALD (adrenoleukodystrophy) and diseases due
to defects in the formation of the organelle e.g
zellweger syndrome.
Q6. What are the proteins associated with the
peroxisomes?
Ans: There are more than 100 proteins that are
either targeted to peroxisomal membrane, or are
transposted across this membrane. Of these, large
number constitute peroxisome membrane proteins
(PMPs)
and
at
least
32
known
peroxisomal
proteins, called peroxins, which participate in the
process of peroxisome assembly.
Q7.
How
peroxisomes
are
related
to
photorespiration and glyoxylate cycle.
Ans: In plants two types of peroxisomes perform
following two different but important functions: (i)
In
leaves,
leaf-type
peroxisomes
help
in
photorespiration (involving oxidation of a side
product of photosynthesis) in which O2 is used and
CO2 is liberated; (ii) In germinating seeds, they
convert fatty acids into sugars (needed for the
growth of the young plant) by a series of reactions
known
as
glyoxylate
cycle,
so
that
these
peroxisomes are called glyoxysomes.
Q8. What is nucleoid?
Ans: peroxisomes contain a fine granular
substance condensing in the centre to form
an
opaque
homogeneous
core
known
as
nucleoid.
Q9. What are vacuoles?
Ans:
Vacuoles are small, spherical, membrane-
bound organelles containing a fluid with dissolved
molecules. They are used for storage or digestion
purposes in different kinds of cells. Plant cells
often contain a large central vacuole that stores
water, proteins, and waste materials.
Q10. What is the pH of the sap of plant
vacuoles?
Ans: The pH of plant vacuoles may be as high as 9
to 10 due to large quantities of alkaline substances
or as low as 3 due to the accumulation of
quantities of acids (e.g., citric, oxalic and tartaric
acids).
Q11. What are contractile vacuoles?
Ans: These are small vacuoles found in many
fresh water organisms. These vacuoles periodically
expand within the cell, filling with water (from
cytoplasm) and then suddenly contract, expelling
its content to the exterior of the cell. This
mechanism probably removes the water which
continually enters the cell by osmosis from the
environment, or with the food.
Q12. Why vacuoles do not have definite size
and shape?
Ans: The vacuoles are usually formed by the
fusion of many membrane vesicles and because of
this reason, a vacuole does not have any specific
size or shape.
Q13. How vacuoles maintain the turgour
pressure of the cell?
Ans: The vacuoles are large and it pushes the
contents of the cell to the borders, near the cell
wall
and
cell
membrane
and
thus, helps
to
maintain the turgour pressure of the cell.
Q14. What is diastole and systole and with
which organelle these are associated?
Ans: Diastole is the swelling of the contractile
vacuole by the passage of substances in to it and
systole is the removal of substances from the
contractile vacuole due to which it collapses. The
diastole
and
systole
are
associated
with
the
vacuole of the cell.
Q15. What are the functions of tonoplast?
Ans: The tonoplast helps to separate the contents
of
the
vacuole
from
those
floating
in
the
cytoplasm. Thus, this membrane does not allow
harmful substances present in the vacuole from
entering and harming the rest of the cell. As the
tonoplast is selectively permeable in nature, it also
tends to maintain the pH and ionic concentration of
the cell, by regulating what travels in and out of
the vacuole.