Educational info

1. Dr. Tushar Wankhede
Associate Professor
Department of Botany
Shri Shivaji Science College,
Amravati. M.S

2. UNIT - II
PHOTOSYNTHESIS
2.1 Photosynthesis – Introduction,
 Role of Light,
 Photosynthetic Apparatus and Pigments,
 Two Pigment Systems,
 Photophosphorylation,
 C3 and C4 cycle, CAM Pathway.
2.2 Respiration - Introduction,
 Mitochondria as a Respiratory centre,
 Types of Respiration - Aerobic and Anaerobic,
 Mechanism of aerobic respiration- Glycolysis, Kreb's cycle,
Electron transport system and Chemiosmotic ATP
generation,
 Respiratory Quotient (RQ)

5. FREE ENERGY
(available for work)
vs.
HEAT
(not available for work)

7. • Almost all plants are photosynthetic autotrophs, as are
some bacteria and protists
– Autotrophs generate their own organic matter through
photosynthesis
– Sunlight energy is transformed to energy stored in the form of
chemical bonds
(a) Mosses, ferns, and
flowering plants
(b) Kelp
(c) Euglena (d) Cyanobacteria
THE BASICS OF PHOTOSYNTHESIS

8. Food Chain

10. UNIT - II
PHOTOSYNTHESIS
2.1 Photosynthesis – Introduction,

Life on earth ultimately depends on energy
derived from the sun
Photosynthesis literally
means “Synthesis using light”
Light energy drives the synthesis of
carbohydrates from carbon dioxide and water
With generation of oxygen

11. UNIT - II
PHOTOSYNTHESIS
2.1 Photosynthesis – Introduction,

Van Helmonount 1648 showed it in
soil experiment
Julius Sachs 1862 showed photosynthes is
occurs in Chloroplast

12. Role of Light
Role of Light :
Light has both a wave features and particles
wavelength denoted by lambda (λ) which is a distance between successive wave crests.
The frequency represented by Greek letter nu (v) i.e. no. of crests pass in given time.
C = λv where C is speed of wave or light (3x 108 ms-1)
Here wave oscillates in both electric and
magnetic field perpendicularly.
Light is also a particle : Features as Photon.
Each photon contains an amount of energy called
Quantum or Quanta (pleural)
so energy delivered not continuously but in packets .
The energy “E” denoted by
E=hv Where h is Planks Constant (6.626 x 10-34 JS )
Hence Sun is rain of photons of different frequencies.

13. Different wavelengths of visible light are seen by
the human eye as different colors.
WHY ARE PLANTS GREEN?
Gamma
rays
X-rays UV Infrared
Micro-
waves
Radio
waves
Visible light
Wavelength (nm)

14. Role of Light

15. Role of Light

16. Sunlight minus absorbed
wavelengths or colors equals
the apparent color of an
object.
The feathers of male cardinals
are loaded with carotenoid
pigments. These pigments
absorb some wavelengths of
light and reflect others.

17. Why are plants green?
Transmitted light

18. An absorption spectrum shows all the light
typically absorbed by a leaf.

19. An action spectrum, meanwhile,
shows all the light that is actually used for photosynthesis.

25. When molecules absorbs or emits light, they change their
electronic state
Chl + h v Chl*
Absorption of blue light excites chlorophyll to higher energy
state than red light as energy of photons is higher
when wavelength is shorter
Photosynthetic pigments absorb the light that powers
photosynthesis
Photosynthesis takes place in complexes containing Light
Harvesting Antennas and photochemical reaction centers

26. Figure 10-9
Photons
Energy state of electrons in chlorophyll
e–
e–
Blue photons excite electrons to
an even higher energy state
Red photons excite electrons
to a high-energy state

28. Excited
state
e
Heat
Light
Photon
Light
(fluorescence)
Chlorophyll
molecule
Ground
state
2
(a) Absorption of a photon
(b) fluorescence of isolated chlorophyll in solution
Excitation of chlorophyll
in a chloroplast
Loss of energy due to heat
causes the photons of light to be
less energetic.
Less energy translates into
longer wavelength.
Energy = (Planck’s constant)
x (velocity of
light)/(wavelength of light)
Transition toward the red end
of the visible spectrum.
e

29. Plant Cells
have Green
Chloroplasts
The thylakoid
membrane of the
chloroplast is
impregnated with
photosynthetic
pigments (i.e.,
chlorophylls,
carotenoids).

30. LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outer
membrane
Inner
membrane
Thylakoid
compartmentThylakoidStroma
Granum
StromaGrana

32. Chloroplast
Light
Stack of
thylakoids ADP
+ P
NADP
Stroma
Light
reactions
Calvin
cycle
Sugar used for
 Cellular respiration
 Cellulose
 Starch
 Other organic compounds

33. • 2. The Calvin cycle makes
sugar from carbon dioxide
– ATP generated by the light
reactions provides the
energy for sugar synthesis
– The NADPH produced by
the light reactions
provides the electrons for
the reduction of carbon
dioxide to glucose
Light
Chloroplast
Light
reactions
Calvin
cycle
NADP
ADP
+ P
Produce ATP &
NADPH
AN OVERVIEW OF PHOTOSYNTHESIS

34. Water-splitting
photosystem
NADPH-producing
photosystem
ATP
mill

35. Primary photo-event
A photon of light is captured
An electron within the pigment is excited
Charge separation
Excitation energy is transferred to reaction center
(specialized chlorophyll pigment)
Reaction center transfer energy to electron receptor
Electron transport
Excited electron is shuttled along a series of electron
carrier molecules.
Protons are transported across the membrane
Chemiosmosis
Protons flow back through ATP synthase where
chemiosmotic synthesis of ATP takes place (just like in
aerobic respiration)

36. Light is trapped by the thylakoid membrane
involves light absorption, splitting of molecules,
oxygen release and formation of high energy
chemicals like ATP and NADPH.
Water is broken down into
hydrogen ions, electrons, and oxygen gas.
he two products of the light-dependent
reactions of photosystem are ATP and NADPH.

42. Transfer of electrons and protons in the thylakoid membrane is carried out vectorially
Stroma
Thylakoid Lumen
Protons diffuse to the site of ATP synthase
Dashed lines represent electron transfer
Solid lines represent proton movement

43. Stroma
Thylakoid Lumen

46. Melvin Ellis Calvin (April 8, 1911 – January 8, 1997)
was an American biochemist known for discovering
the Calvin cycle along with Andrew Benson and James
Bassham, for which he was awarded the 1961 Nobel Prize
in Chemistry. He spent most of his five-decade career at
the University of California, Berkeley

51. 1. Carbon fixation
A CO2 molecule combines with a five-carbon acceptor molecule,
Ribulose-1,5-Biphosphate (RuBP). This step makes a six-carbon
compound that splits into two molecules of a three-carbon
compound, 3-phosphoglyceric acid (3-PGA). Rubisco
2. Reduction
In the second stage, ATP and NADPH are used to convert the 3-PGA
molecules into molecules of a three-carbon sugar, glyceraldehyde-
3-phosphate (G3P). because NADPH donates electrons to,
or reduces, a three-carbon intermediate to make G3P.
3. Regeneration
Some G3P molecules go to make glucose, while others must be
recycled to regenerate the RuBP acceptor. Regeneration requires
ATP and involves a complex network of reactions

52. 1. Carboxylative phase
Three molecules of CO2 are accepted by 3 molecules of 5C
compound viz., ribulose diphosphate to form three molecules of an
unstable intermediate 6C compound. The three molecules of the
unstable 6 carbon compound are converted by the addition of 3
molecules of water into six molecules of 3 phosphoglyceric acid.

53. 2. Reductive phase
Six molecules of 3PGA are phosphorylated by 6 molecules of ATP
(produced in the light reaction) to yield 6 molecules of 1-3 diphospho
glyceric acid and 6 molecules of ADP. This reaction is catalyzed by the
enzyme, Kinase
Six molecules of 1, 3 diphosphoglyceric acid are reduced with the use
of 6 molecules of NADPH2 (produced in light reaction) to form 6
molecules of 3 phospho glyceraldehyde. This reaction is catalysed by
the enzyme, triose phosphate dehydrogenase.

54. 3. Regenerative phase
In the regenerative phase, the ribose diphosphate is regenerated. The
regenerative phase is called as pentose phosphate pathway or hexose
monophophate shunt.
Some of the molecules of 3 phospho glyceraldehyde into Dihydroxy
Acetone Phosphate. Both 3 phospho glyceraldehyde and dihydroxy
acetone phosphate then unite in the presence of the enzyme, aldolase
to form fructose, 1-6 diphosphate.

55. 3. Regenerative phase

56. 3. Regenerative phase

57. 3. Regenerative phase

59. C4 - Cycle or Hatch and Slack Pathway
It is the alternate pathway of C3 cycle to fix CO2.
In this cycle, the first formed stable compound is a 4 carbon
compound viz., oxalo acetic acid. (OAA) Hence it is called C4 cycle.
This pathway is commonly seen in many
Grasses, Sugar cane, Maize, Sorghum Amaranthus and Chenopodium

60. C4 - Cycle or Hatch
and Slack Pathway
 The chloroplasts are
dimorphic in nature
 Vascular bundles are
surrounded by bundle
sheath of larger
parenchymatous cells with
chloroplasts
 The chloroplasts in
Mesophyll cells are smaller
and always contain grana
(Granal)
 These chloroplasts of
bundle sheath are larger,
lack grana (agranal) and
contain starch grains
C4 Plant Maize : leaf Anatomy

61. Kranz Anatomy
 The peculiar anatomy of leaves of C4 plants is called Kranz anatomy.
 The bundle sheath cells are bigger and look like a ring or wreath.
 Kranz in German means wreath and hence it is called Kranz anatomy.

63. The C4 cycle involves two carboxylation reactions,
 One taking place in chloroplasts of mesophyll cells
 Another in chloroplasts of bundle sheath cells.
There are four steps in Hatch and Slack cycle:
1. Carboxylation
2. Breakdown
3. Splitting
4. Phosphorylation.

64. 1. Carboxylation
It takes place in the chloroplasts of mesophyll cells.
Phosphoenolpyruvate, a 3 carbon compound picks up CO2 and
changes into 4 carbon oxaloacetate in the presence of water and
catalysed by the enzyme, phosphoenol pyruvate carboxylase
2. Breakdown
Oxaloacetate breaks down readily into 4 carbon Malate and Aspartate
in the presence of the enzyme, transaminase and malate dehydrogenase.
These compounds diffuse from the mesophyll cells into sheath cells.

65. 3. Splitting
In the sheath cells, malate and aspartate split enzymatically to
yield free CO2 and 3 carbon pyruvate.
The CO2 is used in Calvin’s cycle in the sheath cell.
The second Carboxylation occurs in the chloroplast of bundle
sheath cells. The CO2 is accepted by 5 carbon compound ribulose
diphosphate in the presence of the enzyme, carboxy dismutase
and ultimately yields 3 phosphoglyceric acid.
Some of the 3 phosphoglyceric acidis utilized in the formation of
sugars and the rest regenerate ribulose diphosphate.

66. 4. Phosphorylation
The pyruvate molecule is transferred to chloroplasts of mesophyll cells
where, it is phosphorylated to regenerate phosphoenol pyruvate and
catalysed by pyruvate phosphokinase and the phophoenol pyruvate
is regenerated.
 In Hatch and Slack pathway, the C3 and C4 cycles of carboxylation
are linked and this is due to the Kranz anatomy of the leaves.
 The C4 plants are more efficient in photosynthesis than the C3 plants.
The enzyme, phosphoenol pyruvate carboxylase of the C4 cycle is found
to have more affinity for CO2 than the ribulose diphosphate
carboxylase of the C3 cycle in fixing the molecular CO2 in organic
compound during Carboxylation.

81.  Glycolysis breaks a six-carbon glucose into two three-
carbon molecules
 These molecules then donate high energy electrons to
NAD+, forming NADH
 A molecule of glucose is split into two molecules of
pyruvic acid

96. Respiratory Quotient
RQ is is the measure of moles CO2 evolved to moles O2 absorbed in plant cells.
It is 1 when the substrate is carbohydrate but lower for lipids and proteins.

97. Respiratory Quotient
RQ is is the measure of moles CO2 evolved to moles O2 absorbed in plant cells.
It is 1 when the substrate is carbohydrate but lower for lipids and proteins.