2. Overview: The Process That Feeds the
Biosphere
Photosynthesis is the process that converts solar energy into chemical
energy. Or we can say in different word,
Photosynthesis is the process a plant uses to make food and grow.
Directly or indirectly, photosynthesis nourishes almost the entire living
world.
Photosynthesis occurs in plants, algae, certain other protists, and some
prokaryotes.
These organisms feed not only themselves but also the entire living world.
3. Autotrophs are the producers of the biosphere, producing organic molecules from CO2
and other inorganic molecules.
Almost all plants are photoautotrophs, using the energy of sunlight to make organic
molecules from water and carbon dioxide
Heterotrophs obtain their organic material from other organisms
Heterotrophs are the consumers of the biosphere
Almost all heterotrophs, including humans, depend on photoautotrophs for food and
oxygen
5. • 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
6. 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)
7. Chloroplasts absorb light energy and convert it
to chemical energy
Light
Reflected
light
Absorbed
light
Transmitted
light
Chloroplast
The color of light seen is the color not absorbed
8. Four things are needed for photosynthesis:
Travels up
from the roots
WATER
CARBON DIOXIDE
Enters the leaf through small holes on
the underneath
SUNLIGHT
Gives the plant energy
CHLOROPHYLL
The green
stuff where
the chemical
reactions
happen
9. Chloroplasts: The Sites of Photosynthesis
Leaves are the major locations of photosynthesis
Their green color is from chlorophyll, the green pigment within chloroplasts
Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the
chloroplast
Through microscopic pores called stomata, CO2 enters the leaf and O2 exits .
Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf
A typical mesophyll cell has 30-40 chloroplasts
The chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast);
thylakoids may be stacked in columns called grana
Chloroplasts also contain stroma, a dense fluid
10. The location and structure of chloroplasts
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outer
membrane
Inner
membrane
Thylakoid
compartmentThylakoidStroma
Granum
StromaGrana
13. Photosynthesis is the process by which autotrophic organisms use light energy to make
sugar and oxygen gas from carbon dioxide and water.
Photosynthesis is a redox process in which water is oxidized and carbon dioxide is
reduced
An overview of photosynthesis
Carbon
dioxide
Water Glucose Oxygen
gas
PHOTOSYNTHESIS
14. The word and chemical equations for photosynthesis:
Carbon dioxide + water glucose + oxygen
6CO2 + 6H20 C6H12O6 + 6O2
Sunlight
Chlorophyll
Sunlight
Chlorophyll
15. Stages of Photosynthesis
Light reactions (the photo part)
Occur in the thylakoids
Split water,
Release O2,
Produce ATP, NADPH
Calvin cycle (the synthesis part)
Occur in the stroma
Forms sugar from CO2,
Using ATP and NADPH
Begins with carbon fixation,
Incorporating CO2 into organic molecules
18. • The action spectrum of photosynthesis was first demonstrated in 1883 by
Thomas Engelmann
• In his experiment, he exposed different segments of a filamentous alga to
different wavelengths
• He used aerobic bacteria clustered along the alga as a measure of O2 production
19. A Photosystem: A Reaction Center Associated with Light-
Harvesting Complexes
A photosystem consists of a reaction center surrounded by light-harvesting
complexes
The light-harvesting complexes (pigment molecules bound to proteins) funnel
the energy of photons to the reaction center.
• There are two types of photosystems in the thylakoid membrane
• Photosystem II functions first (the numbers reflect order of discovery) and is best at
absorbing a wavelength of 680 nm
• Photosystem I is best at absorbing a wavelength of 700 nm
• The two photosystems work together to use light energy to generate ATP and
NADPH
21. Photophosphorylation
Two types of Photophosphorylation
Cyclic
Photosystem1 (best work at 700nm)
produces only ATP
Non-cyclic
Photosystem2 (best work at 680nm) and photosystem1 (best work at
700nm)
produces only ATP and NADPH
22. Cyclic Photophosphorylation
Process for ATP generation associated with some Photosynthetic Bacteria
Reaction Center => 700 nm
Cytochrome
complex
Fd
Pc
Primary
acceptor
Photosystem I
ATP
25. Chemiosmosis powers ATP synthesis in the light reactions
The electron transport chains are arranged with the photosystems in the thylakoid
membranes and pump H+ through that membrane
The flow of H+ back through the membrane is harnessed by ATP synthase to make ATP
In the stroma, the H+ ions combine with NADP+ to form NADPH
26. 2 H + 1/2
Water-splitting
photosystem
Reaction-
center
chlorophyll
Light
Primary
electron
acceptor
Energy
to make
Primary
electron
acceptor
Primary
electron
acceptor
NADPH-producing
photosystem
Light
NADP
1
2
3
How the Light Reactions Generate ATP and NADPH
27. The production of ATP by chemiosmosis in
photosynthesis
Thylakoid
compartment
(high H+)
Thylakoid
membrane
Stroma
(low H+)
Light
Antenna
molecules
Light
ELECTRON TRANSPORT
CHAIN
PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE
28. The Calvin cycle uses ATP and NADPH to convert CO2 to
sugar
The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules
enter and leave the cycle
The cycle builds sugar from smaller molecules by using ATP and the reducing power of
electrons carried by NADPH
Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde-3-phospate
(G3P)
For net synthesis of one G3P, the cycle must take place three times, fixing three molecules
of CO2
29. The Calvin cycle has three phases:
Carbon fixation (catalyzed by rubisco)
Reduction
Regeneration of the CO2 acceptor (RuBP)
30. LE 10-18_3
[CH2O] (sugar)O2
NADPH
ATP
ADP
NADP+
CO2
H2O
LIGHT
REACTIONS
CALVIN
CYCLE
Light
Input
CO2
(Entering one
at a time)
Rubisco
3 P P
Short-lived
intermediate
Phase 1: Carbon fixation
6 P
3-Phosphoglycerate
6 ATP
6 ADP
CALVIN
CYCLE
3
P P
Ribulose bisphosphate
(RuBP)
3
6 NADP+
6
6 NADPH
P i
6 P
1,3-Bisphosphoglycerate
P
6 P
Glyceraldehyde-3-phosphate
(G3P)
P1
G3P
(a sugar)
Output
Phase 2:
Reduction
Glucose and
other organic
compounds
3
3 ADP
ATP
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP) P5
G3P
31. Summary
Light
CO2
H2O
Light reactions Calvin cycle
NADP+
RuBP
G3PATP
Photosystem II
Electron transport
chain
Photosystem I
O2
Chloroplast
NADPH
ADP
+ P i
3-Phosphoglycerate
Starch
(storage)
Amino acids
Fatty acids
Sucrose (export)
33. kinetics
Energy transfer to chlorophyll----1 femtosecond to 1 picosecond.
Transfer of electron to centre------ 1 picosecond to 1 nanosecond.
ETC and ATP synthesis ------------- 1 microsecond to 1 millisecond.
Carbon fixation and export of stable products----- 1 millisecond.
34. plateau
At low CO2 concentration, rate is
positively correlated with concentration
CO2 is a substrate in an
enyme-catalysed light-
dependent reaction.
35. At low light intensity, rate of photosynthesis is
proportional to light intensity.
plateau
36. Increased temp.
gives increased
energy and
increased rate of
photosynthesis
Optimum
temperature
Above the
optimum temp.,
enzymes are
denatured and
rate drops steeply.
Which enzymes are
used in respiration?
Editor's Notes
CO2 affects rate of photosynthesis. CO2 is the substrate in carbon fixation (Calvin cycle) – rubisco is the enzyme.
Light intensity affects rate of photosynthesis.
Temperature affects the rate of photosynthesis. Remember enzyme theory. Enzymes used in respiration: rubisco is the main one. ATP synthase can also be denatured.
