Photosynthesis in Higher Plants Class 11 Notes Biology Chapter 13

 Page 1


Points To Remember
Photosynthesis : Photosynthesis is an enzyme regulated anabolic process of 
manufacture of organic compounds inside the chlorophyll containing cells from 
carbon dioxide and water with the help of sunlight as a source of energy.
2 2 6 12 6 2 2
Sun Light
6CO 12H O C H O 6H O 6O
Chlorophyll enzymes
+ + +?
+
Historical Perspective
Josheph Priestley (1770) : Showed that plants have the ability to take up 
CO
2
 from atmosphere and release O
2
. (Candle with bell jar and mouse expt.)
Jan Ingenhousz (1779) : Release of O
2
 by plants was possible only in sun-
light and only by the green parts of plants. (Expt. with aquatic plant in light & dark)
Theodore de Saussure (1804) : Water is an essential requirement for 
photosynthesis to occur.
Julius Von Sachs (1854) : Green parts in plant produce glucose which is 
stored as starch.
T.W. Engelmann (1888) : The effect of different wavelength of light on 
photosynthesis and plotted the first action spectrum of photosynthesis.
C.B. Van Niel (1931) : Photosynthesis is essentially a light dependent 
reaction in which hydrogen from an oxidisable compound reduces CO
2
 to form 
sugar. He gave a simplified chemical equation of photosynthesis.
2 2 22
Sun Light
2HACO 2ACHOHO + ++
Hill (1937) : Evolution of oxygen occurs in light reaction.
Calvin (1954-55) : Traced the pathway of carbon fixation.
Page 2


Points To Remember
Photosynthesis : Photosynthesis is an enzyme regulated anabolic process of 
manufacture of organic compounds inside the chlorophyll containing cells from 
carbon dioxide and water with the help of sunlight as a source of energy.
2 2 6 12 6 2 2
Sun Light
6CO 12H O C H O 6H O 6O
Chlorophyll enzymes
+ + +?
+
Historical Perspective
Josheph Priestley (1770) : Showed that plants have the ability to take up 
CO
2
 from atmosphere and release O
2
. (Candle with bell jar and mouse expt.)
Jan Ingenhousz (1779) : Release of O
2
 by plants was possible only in sun-
light and only by the green parts of plants. (Expt. with aquatic plant in light & dark)
Theodore de Saussure (1804) : Water is an essential requirement for 
photosynthesis to occur.
Julius Von Sachs (1854) : Green parts in plant produce glucose which is 
stored as starch.
T.W. Engelmann (1888) : The effect of different wavelength of light on 
photosynthesis and plotted the first action spectrum of photosynthesis.
C.B. Van Niel (1931) : Photosynthesis is essentially a light dependent 
reaction in which hydrogen from an oxidisable compound reduces CO
2
 to form 
sugar. He gave a simplified chemical equation of photosynthesis.
2 2 22
Sun Light
2HACO 2ACHOHO + ++
Hill (1937) : Evolution of oxygen occurs in light reaction.
Calvin (1954-55) : Traced the pathway of carbon fixation.
Site for photosynthesis : Photosynthesis takes place only in green parts of 
the plant, mostly in leaves. Within a leaf, photosynthesis occurs in mesophyll cells 
which contain the chloroplasts. Chloroplasts are the actual sites for photosynthesis. 
The thylakoids in chloroplast contain most of pigments required for capturing solar 
energy to initiate photosynthesis : The membrane system (grana) is responsible for 
trapping the light energy and for the synthesis of A TP and NADPH. Biosynthetic 
phase (dark reaction) is carried in stroma.
(Refer figure 13.2, Page 209, NCERT Text Book of Biology, Class XI)
Importance of Photosynthesis—(1) Synthesis of organic compounds (2) 
Change of radiant energy into chemical energy (3) Useful products are obtained 
from plants gums, oils timber fire wood, resins rubber, fibers and drugs, etc. (4) 
Balance the percentage of O
2
 and CO
2
 in atmosphere (5) Fossil fuels like coal, 
natural gas and petroleum have been formed inside the earth indirectly as a product 
of photosynthesis.
Pigments involved in photosynthesis :
Chlorophyll a : (Bright or blue green in chromatograph). Major pigment, 
act as reaction centre, involved in trapping and converting light into chemical 
energy. It is called universal photo-synthetic pigment.
Chlorophyll b : (Yellow green)
Xahthophylls : (Yellow)
Carotenoids : (Yellow to yellow-orange)
? In the blue and red regions of spectrum shows higher rate of photosynthesis.
Light Harvesting Complexes (LHC) : The light harvesting complexes are 
made up of hundreds of pigment molecules bound to protein within the photosystem 
I (PS-I) and photosystem II (PS-II). Each photosystem has all the pigments except 
one molecule of chlorophyll ‘a’ forming a light harvesting system (antennae). The 
reaction centre (chlorophyll a) is different in both the photosystems. (Refer fig. 
13.4, Page 211, NCERT-Biolog y).
Page 3


Points To Remember
Photosynthesis : Photosynthesis is an enzyme regulated anabolic process of 
manufacture of organic compounds inside the chlorophyll containing cells from 
carbon dioxide and water with the help of sunlight as a source of energy.
2 2 6 12 6 2 2
Sun Light
6CO 12H O C H O 6H O 6O
Chlorophyll enzymes
+ + +?
+
Historical Perspective
Josheph Priestley (1770) : Showed that plants have the ability to take up 
CO
2
 from atmosphere and release O
2
. (Candle with bell jar and mouse expt.)
Jan Ingenhousz (1779) : Release of O
2
 by plants was possible only in sun-
light and only by the green parts of plants. (Expt. with aquatic plant in light & dark)
Theodore de Saussure (1804) : Water is an essential requirement for 
photosynthesis to occur.
Julius Von Sachs (1854) : Green parts in plant produce glucose which is 
stored as starch.
T.W. Engelmann (1888) : The effect of different wavelength of light on 
photosynthesis and plotted the first action spectrum of photosynthesis.
C.B. Van Niel (1931) : Photosynthesis is essentially a light dependent 
reaction in which hydrogen from an oxidisable compound reduces CO
2
 to form 
sugar. He gave a simplified chemical equation of photosynthesis.
2 2 22
Sun Light
2HACO 2ACHOHO + ++
Hill (1937) : Evolution of oxygen occurs in light reaction.
Calvin (1954-55) : Traced the pathway of carbon fixation.
Site for photosynthesis : Photosynthesis takes place only in green parts of 
the plant, mostly in leaves. Within a leaf, photosynthesis occurs in mesophyll cells 
which contain the chloroplasts. Chloroplasts are the actual sites for photosynthesis. 
The thylakoids in chloroplast contain most of pigments required for capturing solar 
energy to initiate photosynthesis : The membrane system (grana) is responsible for 
trapping the light energy and for the synthesis of A TP and NADPH. Biosynthetic 
phase (dark reaction) is carried in stroma.
(Refer figure 13.2, Page 209, NCERT Text Book of Biology, Class XI)
Importance of Photosynthesis—(1) Synthesis of organic compounds (2) 
Change of radiant energy into chemical energy (3) Useful products are obtained 
from plants gums, oils timber fire wood, resins rubber, fibers and drugs, etc. (4) 
Balance the percentage of O
2
 and CO
2
 in atmosphere (5) Fossil fuels like coal, 
natural gas and petroleum have been formed inside the earth indirectly as a product 
of photosynthesis.
Pigments involved in photosynthesis :
Chlorophyll a : (Bright or blue green in chromatograph). Major pigment, 
act as reaction centre, involved in trapping and converting light into chemical 
energy. It is called universal photo-synthetic pigment.
Chlorophyll b : (Yellow green)
Xahthophylls : (Yellow)
Carotenoids : (Yellow to yellow-orange)
? In the blue and red regions of spectrum shows higher rate of photosynthesis.
Light Harvesting Complexes (LHC) : The light harvesting complexes are 
made up of hundreds of pigment molecules bound to protein within the photosystem 
I (PS-I) and photosystem II (PS-II). Each photosystem has all the pigments except 
one molecule of chlorophyll ‘a’ forming a light harvesting system (antennae). The 
reaction centre (chlorophyll a) is different in both the photosystems. (Refer fig. 
13.4, Page 211, NCERT-Biolog y).
Light Harvesting Complex
Photosystem I (PS-I) : Chlorophyll ‘a’ has an absorption peak at 700 nm 
(P700).
Photosystem II (PS-II) : Chlorophyll ‘a’ has absorption peak at 680 nm 
(P680),
Process of photosynthesis : It includes two phases-Photochemical phase 
and biosynthetic phase. (Formerly known as Light reaction and dark reaction)
(i) Photochemical phase (Light reaction) : This phase includes-light 
absorption, splitting of water, oxygen release and formation of A TP and NADPH. 
It occurs in grana region of chloroplast. 
(ii) Biosynthetic phase (Dark reaction) : It is light independent phase, 
synthesis of food material (sugars). (Calvin cycle). It occurs in stroma region of 
chloroplast.
Photophosphorylation : The process of formation of high-energy chemicals 
(ATP and NADPH) in presence of light.
Non-Cyclic photophosphorylation : Two photosystems work in series–First 
PSII and then PSI. These two photosystems are connected through an electron 
transport chain (Z. Scheme). Both A TP and NADPH + H
+
 are synthesised by this 
process. PSI and PSII are found in lamellae of grana, hence this process is carried 
here. (Fig. 13.6) Page 213, NCERT-BIOLOGY . Class-XI.
Page 4


Points To Remember
Photosynthesis : Photosynthesis is an enzyme regulated anabolic process of 
manufacture of organic compounds inside the chlorophyll containing cells from 
carbon dioxide and water with the help of sunlight as a source of energy.
2 2 6 12 6 2 2
Sun Light
6CO 12H O C H O 6H O 6O
Chlorophyll enzymes
+ + +?
+
Historical Perspective
Josheph Priestley (1770) : Showed that plants have the ability to take up 
CO
2
 from atmosphere and release O
2
. (Candle with bell jar and mouse expt.)
Jan Ingenhousz (1779) : Release of O
2
 by plants was possible only in sun-
light and only by the green parts of plants. (Expt. with aquatic plant in light & dark)
Theodore de Saussure (1804) : Water is an essential requirement for 
photosynthesis to occur.
Julius Von Sachs (1854) : Green parts in plant produce glucose which is 
stored as starch.
T.W. Engelmann (1888) : The effect of different wavelength of light on 
photosynthesis and plotted the first action spectrum of photosynthesis.
C.B. Van Niel (1931) : Photosynthesis is essentially a light dependent 
reaction in which hydrogen from an oxidisable compound reduces CO
2
 to form 
sugar. He gave a simplified chemical equation of photosynthesis.
2 2 22
Sun Light
2HACO 2ACHOHO + ++
Hill (1937) : Evolution of oxygen occurs in light reaction.
Calvin (1954-55) : Traced the pathway of carbon fixation.
Site for photosynthesis : Photosynthesis takes place only in green parts of 
the plant, mostly in leaves. Within a leaf, photosynthesis occurs in mesophyll cells 
which contain the chloroplasts. Chloroplasts are the actual sites for photosynthesis. 
The thylakoids in chloroplast contain most of pigments required for capturing solar 
energy to initiate photosynthesis : The membrane system (grana) is responsible for 
trapping the light energy and for the synthesis of A TP and NADPH. Biosynthetic 
phase (dark reaction) is carried in stroma.
(Refer figure 13.2, Page 209, NCERT Text Book of Biology, Class XI)
Importance of Photosynthesis—(1) Synthesis of organic compounds (2) 
Change of radiant energy into chemical energy (3) Useful products are obtained 
from plants gums, oils timber fire wood, resins rubber, fibers and drugs, etc. (4) 
Balance the percentage of O
2
 and CO
2
 in atmosphere (5) Fossil fuels like coal, 
natural gas and petroleum have been formed inside the earth indirectly as a product 
of photosynthesis.
Pigments involved in photosynthesis :
Chlorophyll a : (Bright or blue green in chromatograph). Major pigment, 
act as reaction centre, involved in trapping and converting light into chemical 
energy. It is called universal photo-synthetic pigment.
Chlorophyll b : (Yellow green)
Xahthophylls : (Yellow)
Carotenoids : (Yellow to yellow-orange)
? In the blue and red regions of spectrum shows higher rate of photosynthesis.
Light Harvesting Complexes (LHC) : The light harvesting complexes are 
made up of hundreds of pigment molecules bound to protein within the photosystem 
I (PS-I) and photosystem II (PS-II). Each photosystem has all the pigments except 
one molecule of chlorophyll ‘a’ forming a light harvesting system (antennae). The 
reaction centre (chlorophyll a) is different in both the photosystems. (Refer fig. 
13.4, Page 211, NCERT-Biolog y).
Light Harvesting Complex
Photosystem I (PS-I) : Chlorophyll ‘a’ has an absorption peak at 700 nm 
(P700).
Photosystem II (PS-II) : Chlorophyll ‘a’ has absorption peak at 680 nm 
(P680),
Process of photosynthesis : It includes two phases-Photochemical phase 
and biosynthetic phase. (Formerly known as Light reaction and dark reaction)
(i) Photochemical phase (Light reaction) : This phase includes-light 
absorption, splitting of water, oxygen release and formation of A TP and NADPH. 
It occurs in grana region of chloroplast. 
(ii) Biosynthetic phase (Dark reaction) : It is light independent phase, 
synthesis of food material (sugars). (Calvin cycle). It occurs in stroma region of 
chloroplast.
Photophosphorylation : The process of formation of high-energy chemicals 
(ATP and NADPH) in presence of light.
Non-Cyclic photophosphorylation : Two photosystems work in series–First 
PSII and then PSI. These two photosystems are connected through an electron 
transport chain (Z. Scheme). Both A TP and NADPH + H
+
 are synthesised by this 
process. PSI and PSII are found in lamellae of grana, hence this process is carried 
here. (Fig. 13.6) Page 213, NCERT-BIOLOGY . Class-XI.
Cyclic photophosphorylation : Only PS-I works, the electron circulates 
within the photosystem. It happens in the stroma lamellae (possible location) 
because in this region PSII and NADP reductase enzyme are absent. Hence only 
ATP molecules are synthesised. It occurs when only light of wavelengths beyond 
680 nm are available for excitation.
The electron transport (Z-Scheme) : In PS II, reaction centre (chlorophyll 
a) absorbs 680 nm wavelength of red light which make the electrons to become
excited. These electrons are taken up by the electron acceptor that passes them to 
an electron transport system (ETS) consisting of cytochromes. The movement of 
electron is down hill. Then, the electron pass to PS I and move down hill further. 
(Fig. 13.5) Page 212, NCERT-BIOLOGY -Class XI
The splitting of water : It is linked to PS II. Water splits into H
+
, [O] and 
electrons.
2H
2
O ? 4H
+
 + O
2
 + 4e
–
Chemiosmotic Hypothesis : Chemiosmotic hypothesis explain the 
mechanism of ATP synthesis in chloroplast. In photosynthesis, ATP synthesis 
is linked to development of a proton gradient across a membrane. The protons 
are accumulated inside of membrane of thylakoids (in lumen). ATPase enzyme 
has a channel of that  allow diffusion of protons back across the membrane. This 
release energy to activate ATPase enzyme that catalyses the formation of ATP. 
(Fig. 13.7). Page 214
Page 5


Points To Remember
Photosynthesis : Photosynthesis is an enzyme regulated anabolic process of 
manufacture of organic compounds inside the chlorophyll containing cells from 
carbon dioxide and water with the help of sunlight as a source of energy.
2 2 6 12 6 2 2
Sun Light
6CO 12H O C H O 6H O 6O
Chlorophyll enzymes
+ + +?
+
Historical Perspective
Josheph Priestley (1770) : Showed that plants have the ability to take up 
CO
2
 from atmosphere and release O
2
. (Candle with bell jar and mouse expt.)
Jan Ingenhousz (1779) : Release of O
2
 by plants was possible only in sun-
light and only by the green parts of plants. (Expt. with aquatic plant in light & dark)
Theodore de Saussure (1804) : Water is an essential requirement for 
photosynthesis to occur.
Julius Von Sachs (1854) : Green parts in plant produce glucose which is 
stored as starch.
T.W. Engelmann (1888) : The effect of different wavelength of light on 
photosynthesis and plotted the first action spectrum of photosynthesis.
C.B. Van Niel (1931) : Photosynthesis is essentially a light dependent 
reaction in which hydrogen from an oxidisable compound reduces CO
2
 to form 
sugar. He gave a simplified chemical equation of photosynthesis.
2 2 22
Sun Light
2HACO 2ACHOHO + ++
Hill (1937) : Evolution of oxygen occurs in light reaction.
Calvin (1954-55) : Traced the pathway of carbon fixation.
Site for photosynthesis : Photosynthesis takes place only in green parts of 
the plant, mostly in leaves. Within a leaf, photosynthesis occurs in mesophyll cells 
which contain the chloroplasts. Chloroplasts are the actual sites for photosynthesis. 
The thylakoids in chloroplast contain most of pigments required for capturing solar 
energy to initiate photosynthesis : The membrane system (grana) is responsible for 
trapping the light energy and for the synthesis of A TP and NADPH. Biosynthetic 
phase (dark reaction) is carried in stroma.
(Refer figure 13.2, Page 209, NCERT Text Book of Biology, Class XI)
Importance of Photosynthesis—(1) Synthesis of organic compounds (2) 
Change of radiant energy into chemical energy (3) Useful products are obtained 
from plants gums, oils timber fire wood, resins rubber, fibers and drugs, etc. (4) 
Balance the percentage of O
2
 and CO
2
 in atmosphere (5) Fossil fuels like coal, 
natural gas and petroleum have been formed inside the earth indirectly as a product 
of photosynthesis.
Pigments involved in photosynthesis :
Chlorophyll a : (Bright or blue green in chromatograph). Major pigment, 
act as reaction centre, involved in trapping and converting light into chemical 
energy. It is called universal photo-synthetic pigment.
Chlorophyll b : (Yellow green)
Xahthophylls : (Yellow)
Carotenoids : (Yellow to yellow-orange)
? In the blue and red regions of spectrum shows higher rate of photosynthesis.
Light Harvesting Complexes (LHC) : The light harvesting complexes are 
made up of hundreds of pigment molecules bound to protein within the photosystem 
I (PS-I) and photosystem II (PS-II). Each photosystem has all the pigments except 
one molecule of chlorophyll ‘a’ forming a light harvesting system (antennae). The 
reaction centre (chlorophyll a) is different in both the photosystems. (Refer fig. 
13.4, Page 211, NCERT-Biolog y).
Light Harvesting Complex
Photosystem I (PS-I) : Chlorophyll ‘a’ has an absorption peak at 700 nm 
(P700).
Photosystem II (PS-II) : Chlorophyll ‘a’ has absorption peak at 680 nm 
(P680),
Process of photosynthesis : It includes two phases-Photochemical phase 
and biosynthetic phase. (Formerly known as Light reaction and dark reaction)
(i) Photochemical phase (Light reaction) : This phase includes-light 
absorption, splitting of water, oxygen release and formation of A TP and NADPH. 
It occurs in grana region of chloroplast. 
(ii) Biosynthetic phase (Dark reaction) : It is light independent phase, 
synthesis of food material (sugars). (Calvin cycle). It occurs in stroma region of 
chloroplast.
Photophosphorylation : The process of formation of high-energy chemicals 
(ATP and NADPH) in presence of light.
Non-Cyclic photophosphorylation : Two photosystems work in series–First 
PSII and then PSI. These two photosystems are connected through an electron 
transport chain (Z. Scheme). Both A TP and NADPH + H
+
 are synthesised by this 
process. PSI and PSII are found in lamellae of grana, hence this process is carried 
here. (Fig. 13.6) Page 213, NCERT-BIOLOGY . Class-XI.
Cyclic photophosphorylation : Only PS-I works, the electron circulates 
within the photosystem. It happens in the stroma lamellae (possible location) 
because in this region PSII and NADP reductase enzyme are absent. Hence only 
ATP molecules are synthesised. It occurs when only light of wavelengths beyond 
680 nm are available for excitation.
The electron transport (Z-Scheme) : In PS II, reaction centre (chlorophyll 
a) absorbs 680 nm wavelength of red light which make the electrons to become
excited. These electrons are taken up by the electron acceptor that passes them to 
an electron transport system (ETS) consisting of cytochromes. The movement of 
electron is down hill. Then, the electron pass to PS I and move down hill further. 
(Fig. 13.5) Page 212, NCERT-BIOLOGY -Class XI
The splitting of water : It is linked to PS II. Water splits into H
+
, [O] and 
electrons.
2H
2
O ? 4H
+
 + O
2
 + 4e
–
Chemiosmotic Hypothesis : Chemiosmotic hypothesis explain the 
mechanism of ATP synthesis in chloroplast. In photosynthesis, ATP synthesis 
is linked to development of a proton gradient across a membrane. The protons 
are accumulated inside of membrane of thylakoids (in lumen). ATPase enzyme 
has a channel of that  allow diffusion of protons back across the membrane. This 
release energy to activate ATPase enzyme that catalyses the formation of ATP. 
(Fig. 13.7). Page 214
Biosynthesis phase in C
3
 plants :
A TP and NADPH, the products of light reaction are used in synthesis of food. 
The first CO
2
 fixation product in C
3
 plant is 3-phosphoglyceric acid or PGA. The 
CO
2
 acceptor molecule is RuBP (ribulose bisphosphate). The cyclic path of sugar 
formation is called Calvin cycle on the name of Melvin Calvin, the discover of 
this pathway. Calvin cycle proceeds in three stages. 
(1) Carboxylation : CO
2
 combines with ribulose 1, 5 bisphosphate to form 
3 PGA in the presence of RuBisCo enzyme (present in stroma)
(2) Reduction : Carbohydrate is formed at the expense of A TP and NADPH.
It involves 2A TP for phsophorylation and 2NADH
2
 for reduction per CO
2
 
molecule fixed.
(3) Regeneration : The CO
2
 acceptor ribulose 1, 5-bisphosphate is formed 
again.
6 turns of Calvin cycles and 18 ATP molecules are required to synthesize 
one molecule of glucose. (Fig. 13.8)
6CO
2
 + 6 RuBP + 18ATP + 12NADPH ?C
6
H
12
O
6
 + 6RuBP + 18ADP + 
18Pi + 12NADP
Input Output
6CO
2
 — One Glucose
18 ATP — 18 ADP
18NADPH — 12 NADP
The C4 pathway : C
4
 plants such as maize, sorghum, sugarcane have 
special type, of leaf anatomy, they tolerate higher temperatures. In this pathway, 
oxaloacetic acid (OAA) is the first stable product formed. It is 4 carbon atoms 
compound, hence called C
4
 pathway (Hatch and Slack Cycle). The leaf has two 
types of cells : mesophyll cells and Bundle sheath cells (Kranz anatomy). Initially 
CO
2
 is’ taken up by phosphoenol pyruvate (PEP) in mesophyll cell and changed 
to oxaloacetic acid (OAA) in the presence of PEP carboxylase. Oxaloacetate is 
reduced to maltate/asparate that reach into bundle sheath cells.
The decarboxylation of maltate/asparate occurs with the release of CO
2
 and 
formation of pyruvate (3C). In high CO
2
 concentration RuBisCO carboxylase and 
not as oxygenase, hence the photosynthetic losses are prevented. RuBP operates 
now under Calvin cycle and pyruvate transported back to mesophyll cells and 
changed into phosphoenol pyruvate (PEP) to keep the cycle continue. (Fig., 13.9) 
Page 219, NCERT BIOLOGY.