.
(2
Light
overall process:
•
it
+602
6C0 +12H,O ~ C.H,,0 + 6H20
2
6
,lants comes from H O and no·
2
inferred that 0 evolved by reen
and ,L!21 0 2• Hence it was
oxidised to 0 2 •
oxidation product sulphui)er
l sulphat$vn purple & green sulphur
green sulphur bacteria. ~o. the
hydrogen donor in green plants is
reduce{CO, to carbohydrates. \
~ i s hydrogendonorf~&
ornelius van Niel
~monstrated that photosynthesis
is essentially a light dependent
reaction in which hydrogen from
su1ta~e oxidisable compound
at glucose is made in gree
IH!
rts and stored as starch.
a,P"TU
gelma~
Using a prism.Jeep alga
and .gerobic bacteria, described the
action spectrum of photosynthesis,
which rougnly resembles the
absorption spectrum of chlorophyn(a
!
CIJDhd
photosynthesis in Higher Plants
G) INTRODUCTION
~ n plants synthesise the food they
need, by photosynthesis and all other
depend on them for their
n?•
0 rganisms
Vf'h.O!~ynthesis l_s aJ>hvslco-chemiCijl\
process by which plants use light
energy to drive the synthesis of
~compounds.
use of energy from sunlight by
plants doing photosynthesis is the
~ o f life on earth.
hotosynthe~is
i important due to
two reasons :
It is the primary
source of all
on earth and@) It is
also responsible for the release of
~ en into the atmosphere.
@ WHAT DO WE KNOW?
t.
~ m e n t for starch formation on
vari~ated leaf or a leaf that was
partially covered with black paper &
exposed to light showedthat
photosynthesis occurred only in
ree~of leaves in the presence
KOH
xperiment where a part of leaf is
~ closed in a test-tube with some
soaked cotton j which absorbs
COJ, while other half is exposed to air
and set-up kept in light proved that
2
M is needed foJ photosynthesis.
EARLY EXPERIMENTS
mo.use.a©
closed
h Priestley f;'i
G)
Using bumin candle, a
plant an a e a or
space,
hypothesi
a plants restore to the
al_r whatever burning candies or
br_eaffi1ng a,t1imals r~i'riQve.
DOES PHOTOSYNTHESIS TAKE
- PLACE
t
gua, 'H\Y u,
_ _._
. a_rts
_ of the plants, mainly in the mesoph
·· e leaves, which have large number
e chloroplasts align them
~-·-r·-~ts.
·· ··
walls c)f mesophyll ~lls to get aptimum
.-?
the incident light.
I
( PERPENDICULAR \
*
CHLOROPLAST ALIGNMENT
•
\ PARALLEL \
i?NJ
*
;;:a,
oooto-oxjdatj~.
I
10
Chapter·
@ HOW MANY TYPES OF
PIGMENTS ARE INVOLVED
IN PHOTOSYNTHESIS
rtog~Qh¥
'-pigments of any green pl
be separated through
colourn leaves is due
,ents, that have the ablltty to
sorb light , !.l..!leclflc
,velengths.
ijpght or bJY@
COLOUR OF THE PIGMENTS
IN THE CHROMATOGRAM
~orophyll-a =
cuaia.
of light in nanomalres
,e klt':SI Yl\d'!'P'"· ""~---·¥':'"
with photosynthesis.
•
wavelength of light at
Is maximum absorption by 1;
mr:t!!:! I.e .• in _bl\lft aod red
O§ , also shows higher rate of
,ynthesls.
,,•
n
optimum l!S_!lt~ extremely high ,uu,.,v,uorophyll-b =C
:9me0
,thophyll =~
jnteru;ity lo gft! maxjm1 IS'
light intensity to jlVOid
~tenoids = Yel1ow to Y@JIWI·
tncklentli9!!!
CHLOROPLAST
l
NADPH)
DARK REACTlONS
(Carbon reactions)
~convention called
*
of Jjght reacfioos ~ATP &
~matic reactions to
synthesise sugar, which
in tum forms starch,
!!!-es place •
~Dependent on products
SJROMA
l,
There is a c l e a - e
chlorop!ast.
•
'
MEMBRANQIIS SYSI&lft
na + Stroma
iiae). nsible for ~
sy~
. . . _ADEfi.
light driven
--EACJJON
____ c ___ ,
(phot@ernk:ftl
'ever, this should not be construed to mean
that the dark reaction occur in darkness or ttJat
they are not ljghl-dependent.
.
SPLITTING OF WATER
,iffing complex is associ,d ; ~
.Uy klcated 1
inqe si
.
S lli,
, one of thi];9l-~
1fr
PHOTO-PHOSPHORYLATION
@ CYCLIC ANO NON-CYCLIC
en.
of
PS-I and PS-II are involved, the
non-cyclic, producing ge,
W
hich lack PS-II andNADP
location for lcvclic flow is the stroma \
nctional, cyclic flow takes
produce only ATP.
'ble
membranes
e~e,
u.,.,,-Cyclic photp-phosphorylation als·o ·
occurs when only light of wavelengths
b_,eyond 680 nm are available for
excitation.
he membrane or lamellae of the grana
-e_vs,both PS-f 8!!11'5:!L
HEMIOSMOTIC HYPOTHESIS
synthesis in photosynthesis is linked
to the development of a prc>ton gradient
across the membranes of ffiyiako@ and
protons accumulate in the lumen of
th-oids.
llffre
gradient is caused by:
· .·
~otons or hydrogen ions produced by
fnitting of water, accumulate in the
umen of the thyiakoids.
primary acce tor of electron
located towards outer side of
membrane transfers
e e on to an
~
r. which removes a proton from
stroma while transporting an electron
tolfiylakoidlumen.
Thylakoid
membrane
-k
Stroma
Stroma (low H')
- ··- - _ _
-
'
ATPs~@)
{Two parts)
O
*
PJQfl, a gmtnn
,·ec..4:! -
J
+
- .
ise ~TP.
GJ pt'(!!!l, a £>TOton3grad'1enl and
CF Protr
ya oid m
faces strom~
liI -----
l AJP 5¥Dtba;;\
•~nem10Smos1s
· · [8qu1res
· - Ul@ffi
CF Embedded in the thyt gid
m~mtrtne. Atransme.mbrane fflannel
for facilitated diffusion of protons
+
\
the membrane to the stroma through transmembrane channel of the CFOof the ATP_
· synthase.
ithin chloroplast, protons decroose
and 5cumulate in lumen. Thi,
creates a proton-gradient across thylakoid membrane as well as a measuralle,
d~ase in pH in the lumen.
reakdown of this gradient leads to synthesis of ATP, when protons move aCIOSI
jn stmma
ATP synthesis through chemiosmosis
ADP+PG
I
-~~-,.=•--··•""______.
d n stroma side of membrane,
+ ·
te
t
(-,_,,
~
..
.
r enzymewhile
locareducing
NA
o
-----=---============-=
~=
_,-._,.-..,.,.---==( /The
..,,.DP
reductase
.
~
' =----::=:--=~~JG,
- - -=
removes
•~ Protonsfrom~
NAO - + H. -NADPH
@
tinuously supplies electrons which
8
available by splitting of water.
-
...
·-· --·-----· -· •·-·· ,,d.
=-... · · -- ·* ·-i&~lectrons.
= ·-- ~- - -·~~,J-b, carotenolds and µpthgphyfl
~ re accessor i@igments. Th
absorb light an
nsfer lfie en
to Chi-a. They enaoTe a WIOOr r,
.
of wavelength of incomi- - "
!••
@ WHAT IS LIGHT REACTION?
e
PHOTOSYSTEM
[
(Hundreds of pigments)
One moleaJle
of Chi-a
LH
'1:ight reactions or the photochemical
r
phase include:
~ghtabsorption
~atersplitting
~nrelease,and
1,(~
and NADPH formation
everal protein complexes
involved In the process.
pigments are organised into two
photosystems
-
- -----ireion]
-
mnm@
JtSCOv
rption peak
~
ti,
at 680 nm
ed in the sequence of their
the sequence of their function~
poteptial
7) THE ELECTRON TRANSPORT
e whole scheme of transfer of electrons
starting from .f§:!1 uphill to the acceptor
down the ETC to PS-I Excitation of electrons
transfer to another acceptor
finally
to.NADPreducing it to NADPH
+ H° is ~ed the z-scheme. due to its
J:!!aracten
sfiag,e.
·_
his shape Is to"'1«1 when all the carriers are pltl_ced In a sequence on a redoJC
scale.
1?=:---- o
·
p;Q)Q§Yffii
AJ8 &!12 NApptl
are
- -- • - -
__.;&,;;.,;_..,
-------=-4
~e
BUNDLESHEATH CELLS
ic Acid/Aspartic
Acid
J.
L
, ransported to
~I&
ch in RuBisCO_.
-
converted to PEP
- Calvin cycle a
common to al
TI
~
.!tut lack PEPcase.
enWn:~
@ PHOTORESPIRATION
RuBisCo, the {most abundagt
in the
world , has the actiVe site that canind to both
CO2 and 0 2 . This binding is competitive. It is.the
relative concentration of 0 2 and CO 2 that
determines which of the two will bind to the
enzyme.
tiBis,
has a much greater affinity for CO2 ,
when th CO2: ol_is near1y_Ei<Jual than for 0 2•
~
rimaryCO,
acceptor is a 3-C
mpoundPE f
nzyme for this
fixation is E'EP~ se.
'acks RuBisC
{-acid formed is
QAA; which forms
mallc acjg or
q.spartic acid and
transported to
bundle sheath cells.
~
~
I >
f.[
i!;.E
-a.
'S
la:
B
s
C
~ Q ..
I
tttott ·
a
.tft::\,l:
'
respond
plants s'
saturation is seen a
greenhouse crops lik:e '9matoes
II arwr show higher yield~
.
nri
atmosphere .
'>erature : Dark reactions being
enzymatic are \2mpe ratu re contrg~ed
Light reactions are also tempera ure
sensitlvie. C 4 -plants show higher yield at
high temperature while C ,-plants have a
ral ure optlrmnn.
ater: Effect of water as a fact.or i~
through its effect on the plant rather than
d!'ectt-, u,:, pnotosynmesls. Wamr stress
causes t e stomata to close hence
reducing CO2 availability. Water stress also
makes leaves wilt._Jtlus, reducing the
surface area of leaves and their metabolic
S ffiitV 8$ 161..@ll
E
,w Ii
Blackman'sLawofLlmltlngfactor
\
If a chemical process is affected by more
than one factor, then its rate will be ·
determinedby thefactor whichlaneareatto
j1§ minjmal yalye, It is the , __.__ ...L t- c.
directly affects the
C
ged.
ight: Light saturatlo
full sunlight. Except
dense forests, liibt is rat11\Y IIITl lllllQ ,octv, I
innat
"""
~ e is a linear relatlonshlo between
incidentlight&CO, flxatlonrates
II ht inten i i s .
t 1g er light Intensities, gradually the
rate does not show further, Increase as
otherfactorsbecom~lim~ti~g .
,
0 concentration: l tv1a1or hm1tin9 factor\
2
The concenu tion
very low in the
h
03 o o o "
increase In
atmosp ere
.
_ ---·
concentrat
increase in_
" can
""4-t.t:O~HQ.N-£>-R~l-t-l
k
@ FACTORS A FFECTING
PHOTOSYNTHESIS
,thesis is under the influence
ral factors, both internal (plant)
nal.
actors:
,lant factors include the ~umber,
aQ!L! orientation of eaves,
hyll cens.. and ch loroplasts .
,.. ,,.al CO 2 concentratio n & the
~untof chlorophyll.
·actors are
,etic
--.------·· & g'rowiii'o1 the plant.
mai factors: indude availabiliW
>f sunlight, tem p er a ture. CO 2
concentration and water.
co,
lr
@ wHEREARETHEATP
'1J' THE
_..,o;#'!,---'-:---~
.
AN D NADPH USED?
c.-PATHWAY
nts
me 02 does bind to
ft._ adapted to Q!Y tropical regions have
co, and hence CO2 fixation is
,way.
eased , due
t
·
NADPH and 02, Aa ditfitses gut of
ants are special· They have special type
· n.
.
- -~ ~ chloroplast while ATE.and NADPH are
-=--==;.:.; y, tole~te hi@her te~eratur
) + 02 RuBisC
used to synthesise sug ars in the
lo high Ii hJ Tutens)ies,
I> OS
I
b"iiisynthetic phasetg
at1on and have great
a~
C
.
.
•
.
is called photo-resp1ratipn
.
14
Melvin Calvin use ra; oacbv~
~~ ....:::~lll,l,l;LLLI""' have leaves sho .
n photerrespiration there is neither
!!i2,!...Photosynthes1s studies to
ANATOM theparticul
~~ll"tl!I~
synthesis of sugars, no~ of ~TP._ It
disCOver the first CO 2 fixatjon product
vascular bundles,
results ir{i-e~ase pf
with 111ll!sal!~
the 3-C or g anic acid { 3 - PGA \
and are called~-.ii!i=~:;;!iii:"!!!'!!!!ii~ ~ ~ ,.,,,- .,.E_->
Mlt-o C ln°"ctvt
th a )
characterised by
The biologica fun~
_of
(~ w Y ·
chloroplasts thick
photorespiration i~
nown yet.*
_aL~ther group of plants, the first
ange a~d no in
n c ,-plants photerrespiration does n9t
stable p_rod ~ ct was (I)carbo~
pathway 15 cyclic & called the Hatch and
~ r, as they have a m~ anism that
o~alo,.Pcetic aeiJ3?,· e2thway).
:21ack Pathway. It is partly completed in
increases the con~ ntration of CO2 at
··· · · phyll & partly in bundle sheath cell.
the enzyme s~. This ensure~~~he
R1;1~•s~~ functions as a ca
xy se
m1mm1sing theoxygenaseactivity.
, W THE CALVIN CYCLE
Cl!lvin cycle occurs in all
photosynthetic plants; whether theX,
have C 3 or c, (or any other)
crucial*
n cycle can be described under
three stages:
,pa~ .
~
A Rsoxv LAT 10N1 Most
.teQUW
step. ~
RuBP RuBis
~
"'x '""3,...-"'"""'
PG
=-A
.,....,\
(5C)
c_;J...c)
(3C) +:'i~ =~
0 2 + H20
~
UCTION : A series of reactions
that lead to formation of glucose.
Utilises, 2 ATE and 2 NADPffer COrlj1_
(The fixation of 6C02 and 6 turns of the
cycle are needed to form one molecule
of wi-ose from the pathway).
GENERATION : Regeneration of
RUBP is crucial for t e
to
continue. Thisste r uir oneATP.
So, t o pro uce one mo ecu e of
in Calvin cycle an ~ ut of
~
II t§ii
._1,a