The first stable compound during the pathway is 4C OAA (Oxalocatic acid) compound. Hence called the C4 pathway.

1. C4 pathway, CAM
Photorespiration
Department Of Botany
Prepared by
Dr. P. B. Cholke
(Assistant Professor in Botany)
Pune District Education Association’s
Anantrao Pawar College ,Pirangut,
Tal-Mulshi, Dist-Pune- 412115

2. Kranz anatomy.
i. It is only present in C4 plants (monocot plants).
ii. Kranz means ring / wreath / neacklase.
iii. Kranz anatomy is discovered by Kortshak (1964) in the leaves
of sugar cane.
iv. Vascular bundle remain surrounded by thick walled bundle
sheath cells in a ring like manner. Hence called Kranz anatomy.
v. Thin walled more or less oval photosynthetic cells called
mesophyll cells lies towards upper and lower epidermis in leaf.
• vi. In mesophyll cells small chloroplast is present in which
only grana is present therefore called granal chloroplast.
• vii. In bundle sheath cells large chloroplast in present in which
only stroma is present therefore called Agranal chloroplast.

3. Upper epidermis
Mesophyll cells with
granal chloroplasts
Xylem
Phloem
Bundle sheath cell with
agranal chloroplasts
StomaLower epidermis
Fig. T.S. Of a leaf showing Kranz anatomy

4. C4 pathway
• i. The first stable compound during pathway
is 4C OAA (Oxalocatic acid) compound. Hence
called C4 pathway.
• ii. Details about fixation of CO2 and stable
compound worked out by hatch, slack and
kortshack hence called H.S.K. pathway

5. • Steps involved in C4 cycle :
• i. In mesophyll cells of the chloroplast the
phosphoenol pyruvic acid (PEPA) accepts CO2
and form oxaloacetic acid (OAA) (4C) with the
help of enzyme PEPA carboxylase.
• ii. OAA (4C) is reduced to malic acid after
reacting with NADPH2.

6. Fig. HSK pathway (C-4 plants)

7. • iii. Malic acid (4C) enters in chloroplast of
bundle sheath cells where it decorboxylated
to form pyruvic acid.
• iv. The CO2 released during decarboxylation
enters in C3 cycle and reacts with RUDP to
form PGA and ultimately glucose in formed.

8. Fig. HSK pathway (C-4 plants)

9. • v. The pyruvic acid (3C) enters in chloroplast
of mesophyll cells were it react with ATP to
form PEPA (3C) whichis recycled.
• vi. Experimental evidence indicate that
mesophyll cells carry out C4 pathway and
bundle sheath cells carry out C3 pathway

10. • Significance of C4 pathway.
• Ans.
• i. C4 plants can start the process of photosynthesis
in less CO2 concentration due to the avalability of
PEPA carboxylase.
• ii. The plants can also survive with less amount of
water because the vein are separated from stomata.
• iii. C4 plants can withstand at high intensity of light
and high temperature.
•

11. mechanism of photorespiration
i. The process of respiration which initiated in
chloroplast during day time only called
photorespiration.
• ii. It is process is accomplished with
chloroplast, peroxisomes and mitochondria.

12. Fig. Diagrammatic representation of photorespiration

13. • iii. In chloroplast RUBP (Ribulose-1,5-Bi-
phosphate) (5C) accepts the oxygen and forms
PGA (3C) and phosphoglycolate (2C).
• iv. PGA (3C) enters in Dark reaction and
phosphoglycolate is dephosphorylated into
glycolate (2C)
• v. This glycolate enters in peroxysomes where
oxidation of glycolate results into glycoxylate with
the release of H2O2 (Hydrogen peroxide).
• vi. Glyoxylate is converted into glycine amino
acid.

14. • vii. This glycine is transported to mitochondria
where 2 molecules of glycine is converted to
serine amino acid with the release of CO2.
• viii.This serine enters in peroxisomes when it
is converted to glycerate.
• ix. This glycerate is transferred to chloroplast
where it phosphorylated and converted to
PGA this PGA enters in dark reaction

15. Explain Crassulacean Acid Metabolism
• i. Plants which grow in dry regions as well as
plants having succulent leaves shows
opens stomata during night time and close
during day time.
• ii. Plants achieve night photosynthetic
activity.
• iii. Initially this plants are reported from the
family crassulaceae hence called CAM
plants.

16. • The process of CAM is as follows :
• A. During Night time (when stomata are open) :
• i. PEPA (3C) Phosphoenol pyruvic acid is formed
from starch.
• ii. CO2 is absorbed by PEPA with the help of
enzyme PEPA carboxylase which leads to the
formation of OAA (4C).
• iii. OAA (4C) is reduced to malic acid after
reacting with NADPH2 in the presence of
enzyme malate dehydrogenase.
• iv. This process is called acidification as CO2 is
fixed in acids.

17. • B. During Day time (When stomata are closed) :
• i. Malic acid decarboxylated to pyruvic acid with the
release of CO2.
• ii. This process is called deacidification as organic acid
concentration decreases almost of zero.
• iii. The CO2 released during decarboxylation enters in
C3 cycle to prepare carbohydrate.
• iv. Pyruvic acid (3C) is converted into carbohydrate by
reverse glycolysis.
• v. Thus, during night time organic acid concentration
of succulent increase and during day time it
decreases to almost zero.
• vi. This day and night fluctuation in acid concentration
is an essential feature of CAM plants.

18. • : Factors affecting photosynthesis
• External factors:-
• a) Light : It is the most important factor for
photosynthesis as it is used as a source of energy Normally
plants utilize sunlight, marine algae also use moon light,
photosynthesis even occurs in electric light.
• 1) Quality of light:
• The rate of photosynthesis is maximum
in red and blue light, minimum in green light
• 2) Intensity of light :
• Only 1- 4 % light is utilized in
photosynthesis, in general rate of photosynthesis as more
in intense light than diffused light.
• 3) Duration of light:
• Rate of photosynthesis is independent of
duration of light.

19. • b) Carbon - di - oxide:
• By increasing CO2 conc. 15 to 20 times ,
the rate of photosynthesis increases but after
that it decreases. Very high conc of CO2 becomes
toxic to plant.
• c) Availability of water:
• Water deficiency may decrease the rate
of photosynthesis as water the raw materials and
also may cause closure of stomata leads to low
CO2 availability.

20. • d) Temperature:
• The optimum temperature for
photosynthesis is 20 -350 C. If the temperature is
increased too high, the rate of photosynthesis is
reduced due to denaturation of enzymes.
• e) Oxygen :
• High O2 levels reduces the rate of
photosynthesis as O2 competes for active sites of
RUBP carboxylase enzyme with CO2 (Warburg’s
effect)

21. • Internal factors:
• a) Chlorophyll content :
• If all other factors are favorable,
increase in chlorophyll leads to increase in
photosynthesis.
• b) Accumulation of ends products:
• It results in decrease in rate of
photosynthesis.

22. • Law of limiting factors
• i) This was given by F.F. Blackman (1905)
• ii) It states that, “When a process is conditioned
so as to its rapidly by number of factors, then the rate of
process is limited by the pace of the lowest factor”
• iii) According to this principle, the rate of
photosynthesis controlled by several factors is only as
rapid as the slowest factor permits.
• iv) He claimed that, if all the other factors are kept
constant, the factor under consideration will affect the
rate of photosynthesis.
• v) It starts with minimum, below which no
photosynthesis takes place and optimum at which a
horizontal would be established i.e. the rate would remain
constant. (Highest rate) and a maximum value, above
which photosynthesis fails to take place.