Scientists have contributed to understanding photosynthesis through experiments over centuries. Van Helmont concluded in 1643 that a plant's mass came from water, not soil, by growing a willow for 5 years. In 1771, Priestley found that plants released oxygen, necessary for burning, by leaving mint in a closed jar. Ingenhousz repeated this in 1779 and showed oxygen release only occurred with sunlight. Photosynthesis uses light energy and carbon dioxide to produce glucose and oxygen through light-dependent and light-independent reactions in the chloroplast. The goal is to synthesize glucose by reducing carbon dioxide using the energy from light absorption.

2. History Of Photosynthesis

3. History Of Photosynthesis
What does Photosynthesis
Means?
Site Of Photosynthesis
Light & Dark Reaction
Goal Of Photosynthesis

4. Investigating Photosynthesis
•Many Scientists Have Contributed
To Understanding Photosynthesis
•Early Research Focused On The
Overall Process
•Later Researchers Investigated The
Detailed Chemical Pathways

5. Van Helmont’s Experiment 1643
• Van Helmont planted a seed
into a pre-measured amount
of soil and watered for 5
years
• He weighed plant & soil.
Plant was 75 kg, soil the
same.
• He concluded that “Mass
Came From Water”

6. Priestley’s Experiment 1771
• He burned candle in Bell
Jar Until it went out.
• Placed sprig of Mint in Bell
Jar for a Few Days.
• Candle could be relit and
burnt.
• He concluded that “Plants
released substance (O2)
necessary for burning.”

7. Ingenhousz’s Experiment 1779
Ingenhousz repeated Priestly experiment with & without
sunlight

8. Results of Ingenhousz’s
Experiment
• He showed that Priestley’s
results occurred only in the
presence of Sunlight.
• “Light was necessary for
plants to produce the
‘Burning Gas’ or Oxygen.”

9. What does Photosynthesis means?
– Photosynthesis is the process by which certain
organisms use light energy
• To make sugar and oxygen gas from carbon
dioxide and water
Light
energy
PHOTOSYNTHESIS
6 CO2 6+ H2O
Carbon dioxide Water
C6H12O6 6+ O2
Glucose Oxygen gas

10. • Photosynthesis is a chemical process in
which energy from light is harvested to
provide carbohydrates.
• It is the major path through which Carbon
reenters the biosphere (from CO2).
• Photosynthesis is also the major source
of Oxygen in the earth's atmosphere
What does Photosynthesis means?

11. • Chloroplast is the
place where
Photosynthesis
occurs.
• Photosynthesis occurs
in the following parts of
Chloroplast:-
 Grana
 Stroma
Site Of Photosynthesis

12. Grana:- They are sac like structures
present in the chloroplast. The light
reaction takes place in grana.
Stroma:- They are the spaces
surrounding the Grana. They are site for
dark reaction. They are aqueous &
contain RNA, DNA & Ribosomes.
Grana & Stroma

13. The capturing of light energy occurs within
the chloroplasts, primarily located in the
mesophyll cells of the leaf.
The major light absorbing pigments on
thylakoid membrane is chlorophyll.
Light Harvesting Pigments

14. Light & Dark Reaction

15. • Light-dependent reactions
occur on the thylakoid
membranes.
– Light and water are
required for this process.
– Energy storage molecules
are formed. (ATP and
NADPH)
– Oxygen gas is made as a
waste product.
Light Reaction

16. • New electron need to be taken from
water to allow the process to continue.
• 4 electrons are removed from 2 water
molecule leaving 4H+ ion and 2 oxygen
atom.
• The 2 oxygen atom from O2 gas that is
released into the air to be consumed by
the heterotrophs and used in cellular
respiration.
Oxygen Production

17. • From the chlorophyll , electrons are
passed from one molecule to another
down an electron transport chain.
• The light energy electrons end up at
the electron carrier molecule NADP+
• Converting it into NADPH.
• This energy storing molecule will be
used in dark reaction.
Electron Transport

18. ATP and NADPH, generated by light
reaction are used to fix and reduce CO2
to form carbohydrate.
ATP + NADPH +H++ CO2 C6H12O6
Enzymes and intermediates of the cycle
are located in the chloroplast stroma.
Dark Reaction (Calvin Cycle)

19. • From the splitting of water, the H+ ions
left behind create a difference in charge
across the photosynthesis membrane.
• The inside of the membrane is positive
and outside is negative.
• A proton pump called ATPsynthase
make ATP (to be used in dark reaction)
by attaching H+ ions to ADP.
• This process is called Chemiosmosis.
Formation Of ATP

20. • Reduction of carbon
dioxide into carbohydrate
via the oxidation of energy
carriers (ATP, NADPH)
• Light reactions energize
the carriers
• Dark reactions (Calvin
Cycle) produce PGAL
(phosphoglyceraldehyde)
Photosynthesis
6CO2 +6H20 + light  C6H1206 +
6O2
Photosynthesis Equation

21. • The “goal” of photosynthesis is to
synthesize glucose.
–Carbon dioxide is reduced to glucose
(see equation below).
–The electrons needed for this reduction
come from water.
–The energy needed for this reduction
comes from light (ATP, NADPH).
–The equation is:
Energy + 6CO2 + 6H2O  C6H12O6 + 6O2
Goal Of Photosynthesis

22. • Photosynthesis does NOT supply
energy to the cell. Photosynthesis
USES light energy to make organic
compounds.
• To get energy for the cell, plant cells
must use cellular respiration to break
down glucose and make ATP.
Important Note On Photosynthesis