Download 1. By looking at a plant externally can you tell whether a plant if C 3

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1. By looking at a plant externally can you tell whether a plant if C3 of C4? Why and how?
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Solution:
As compared to C3 plants, C4 plants are adapted to dry tropical regions. Such plants are able to
tolerate high temperatures and show marked responses towards high light intensities. Also C4 plants
have a greater productivity of biomass.
2. By looking at which internal structure of a plant can you tell whether a plant is C3 or
C4? Explain.
Solution:
By studying the anatomical details of the leaf. We can tell whether a plant is C3 or C4.
C4 plants show typical Kranz anatomy.
The vein of the leaf is surrounded by bundle sheath which contains numerous chloroplast of
mesophyll cells have well developed grana, while chloroplasts of bundle sheath have peripheral
reticulum.
3. Even though a very few cells in a C4 plant carry out the biosynthetic Calvin pathway,
yet they are highly productive. Can you discuss why?
Solution:
Even though very few cells in a C4 plant carry out the biosynthetic – Calvin pathway, yet they are
highly productive. This is because of the following reasons:
(a) C4 plants have a high value of net assimilation at high temperatures.
(b) Their rate of carbon assimilation is quite rapid.
(c) C4 plants perform photosynthesis even when stomata are closed.
(d) Their rate of net photosynthesis at full sunlight is as high as 40-80 mg CO2/ dm2/hr.
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4. Rubisco is an enzyme that acts both as a carboxylase and oxygenase. Why do you
think Rubisco carries out more carboxylation in C4plants?
Solution:
Rubisco, i.e., ribulose biphophate carboxylase and oxygenase. This is because its active site can bind
to both CO2 and O2. But actually rubisco has much greater affinity for CO2, than O2. The relative
concentration of CO2 and O2 determines which of the two will bind to the enzyme. In case of
C4plants, since there is a high concentration of CO2 plants, at the enzyme site, photorespiration does
not occur. Therefore rubisco carries out more carboxylation in C4 plants.
5. Suppose there were plants that had a high concentration of chlorophyll b, but lacked
chlorophyll a, would it carry out photosynthesis? Then why do plants have chlorophyll and
other accessory pigments?
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CONTACT FOR MATHEMATICS GROUP/HOME COACHING FOR CLASS 11TH 12TH BBA,BCA,
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CONTACT FOR COACHING MATHEMATICS FOR 11TH 12TH NDA DIPLOMA SSC CAT SAT CPT
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Solution:
If there were complete absence of chlorophyll a in a plant, it would not carry out photosynthetic
activity at all because chlorophyll a is the chief pigment associated with photosynthesis as it traps
light. Other accessory pigments like chlorophyll b, santhophylls and carotenoids are equally essential
as they also absorb light and transfer energy to chlorophyll a. They also enable a wider range of
wavelength of incoming light to be utilised for photosynthesis and protect chlorophyll a from photooxidation.
6. Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which
pigment do you think is more stable?
Solution:
The colour of leaf kept in dark frequently changes because of absence of chlorophyll in darkCarotenoids and Xanthophyll pigments are more stable.
7. Look at leaves of the same plant on the shady side and compare it with the leaves on
the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade.
Which of them has leaves that are darker green? Why?
Solution:
The plants placed in light will have darker leaves as compared to leaves of a plant placed in shade. It
is due to the fact that chlorophyll pigments will be more in light.
8. Compare the following:
(a) C3 and C4 pathways
(b) Cyclic and non- cyclic photophophorylation
(c) Anatomy of leaf in C3 and C4 plants
Solution:
(a) C3 and C4 pathways.
Characters
1. CO2 acceptor
2. First stable product
3. Type of chloroplast
C4 plants
The CO2 acceptor is ribulose 1.5
diphosphate.
The fist stable product is
phosphoglyceric acid.
All cells participating in
photosynthesis have one type
not chloroplast.
The CO2 acceptor is phosphoenolpyruvate.
Oxaloacetate is the first stable
product.
The chloroplast of parenchymatous
bundle sheath is different from that of
mesophyll cells. Leaves have ‘Kranz’
type of anatomy. The bundle sheath
chloroplasts lack grana. Mesophyll cells
have normal chloroplasts.
Both C4- dicarbodylic acid and
reductive pentose phosphate cycles
are found.
In C4 plants it is 30-450C.
4. Cycles
Only reductive pentose
phosphate cycle is found.
5. Optimum temperature
The optimum temperature for
the process is 10-250C.
Oxygen present in air (= 21%
O2). markedly inhibit the
photosynthetic process as
6. Oxygen inhibition
in
C3 plants
The process of photosynthesis is not
inhibited in air as compared to an
external atmosphere containing no
2
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BADHANEDUCATION D96 MUNIRKA VILLAGE NEW DELHI 110067 & VIKAS PURI NEW DELHI
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compared to an external
atmosphere containing no
oxygen.
In each chloroplast,
Photosystems I and II are
present. Thus the Calvin cycle
occurs.
7. PS I and PS II
oxygen.
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In the chloroplasts of bundle sheath
cells, the photosystem II is absent.
Therefore, these are dependent to
mesophyll chloroplast of the supply of
NADPH + H+.
The Calvin cycle enzymes are
The calvin cycle enzymes are absent in
present in mesophyll chloroplast mesophyll chloroplasts. The cycle
occurs only in the chloroplasts of
sheath cells.
The CO2 compensation point is CO2 compensation point is 0-10 ppm.
50-150 ppm.
Photorespiration is present and Photorespiration is present only to a
easily detectable.
slight degree and difficult to detect.
Net rate of photosynthesis in full It is 40-80 mg. Of CO2 per dm2 of leaf
sunlight (10,000- 12,000 ft.c) is area per h that is photosynthetic rate
15-35 mg of CO2 per dm2 of leaf is quite high. The plants are efficient.
area per h.
The saturation intensity reached It is difficult to reach saturation even
is in the range of 100-4000 ft.c. in full sunlight.
8. Enzymes
9. Compensation point
10. Photorespiration
11. Net rate
12. Saturation intensity
(b) Differences between cyclic and non- cyclic photophosphorylation.
Characters
1. Synthesis
2. Oxygen
3. Requirement
4. Cycling
5. Performance
6. Operation
Cyclic- Photophosphorylation
Non- cyclic photophosphorylation
It synthesizes only ATP.
Oxygen is not evolved.
It forms ATP as well as NADPH2.
Oxygen is liberated due to photolysis of
water.
It requires only PS-I.
It is performed with collaboration of PS-I
and PS-II.
Electron emitted by P700 is recycled It needs external electron donor.
back and no external source of
electron is needed.
This process is operative at low
It performs best under optimum light
light intensity. Less availability of
presence of CO2 and under aerobic
CO2 and under anaerobic
conditions.
conditions.
It does not usually operate for
It is functional for normal CO2 fixation.
photosynthesis except bacteria.
C4 plants
C3 plants
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(c) Differences in Anatomy of leaf in C3 and C4 plants.
1. Chloroplasts are present in mmesophyll cells as 1. Chloroplasts are present in mesophyll cells
well as in bundle sheath cells.
only.
2. Kranz type of anatomy present.
2. Kranz type of anatomy absent.
3. Intercellular spaces between mesophyll cells
3. Intercellular spaces are larger.
are smaller.
4. Dimorphic chloroplasts are present.
4. Only one type of normal chloroplasts is
present.
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CONTACT FOR COACHING MATHEMATICS FOR 11TH 12TH NDA DIPLOMA SSC CAT SAT CPT
CONTACT FOR ADMISSION GUIDANCE B.TECH BBA BCA, MCA MBA DIPLOMA AND OTHER COURSES 09810144315
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CONTACT FOR MATHEMATICS GROUP/HOME COACHING FOR CLASS 11TH 12TH BBA,BCA,
DIPLOMA CPT CAT SSC AND OTHER EXAMS Also home tutors for other subjects in DELHI AND OTHER MAJOR CITIES
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