Photosynthesis is the process by which plants synthesize food from sunlight, water and carbon dioxide. It occurs in the chloroplasts of plant leaves. There are two key stages - the light-dependent reactions where ATP and NADPH are produced, and the light-independent Calvin cycle where carbohydrates are produced. The light reactions take place in the thylakoid membranes of chloroplasts and utilize chlorophyll to drive the electron transport chain and create the proton gradient needed for ATP production. Oxygen is released as a byproduct of splitting water. The Calvin cycle then uses ATP and NADPH to fix carbon from carbon dioxide into glucose.

1. PHOTOSYNTHESIS
By Ruchi Choudhary
B.Sc (bt) 2nd year

2. DEFINITION AND SITE
• It is a complex process by which green plants synthesize their own
food with the help of sunlight and chlorophyll in the presence of
water and carbon dioxide and oxygen given out as a bi product.
OR
• It is conversion of solar energy into chemical energy to fix carbon and
form ATP.

3.  6CO2 + 12H20----------------- C6H12O6 + 6H2O + 6O2
Librated oxygen is release from the H2O molecule.
Only 0.2% of light is used by green plants for photosynthesis

4. • Photosynthesis occurs in a green part of the plant(leaf) where a
mesophyll cells are present in which chloroplast is present in a
palisade parenchyma.
SITE OF PHOTOSYNTHESIS

5.  There is 2 type of chemical reaction takes place inside the chloroplast.

6. Pigments involve in photosynthesis.
• Pigments are the substance that impart color to the leaf and have an
ability to absorb light, at specific wavelength.
• In leaves there is so many shades of green color present which is not
because of the single pigment 4 pigments are involved in that.
• Chlorophyll a – bright or blue green
• Chlorophyll b –yellow green
• Xanthophylls -yellow
• Caratenoids- yellow to yellow orange

7. • Chlorophyll a & chl b absorb maximum wavelength of light therefore
showing high rate of photosynthesis at blue & red region

8. Light & wavelengths
• Maximum photosynthesis occurs at red light.
• Chlorophyll a –red light maximum
• Chlorophyll b –blue light maximum
SUN lIGHT
Invisible light (eg-UV rays)
Cosmic rays, x rays
0-400 nm
 Visible light
 ( infrared radition)
 Photosynthetic Active
Radiation(PAR)
 400-700 nm

9. Emersion red drop effect
• Emerson effect. The Emerson effect is the increase in the rate of photosynthesis
after chloroplasts are exposed to light of wavelength 670 nm (deep red spectrum)
and 700 nm (far red spectrum).
• The effect was early evidence that two photosystems, processing different
wavelengths, cooperate in photosynthesis
• Maximum photosynthetic occurs at 700 nm wavelength of light but
when wavelength exceeds before it suddenly a drop occurs in
reaction called emersion red drop effect.
• Its name is emersion red drop because of the drop occurs at the red light

11. z- scheme

12. Z- SCHEME
• Pheophytin quinine is the first electron acceptor in PS 2.
• First ATP production in PS 2 occurs between cytochrome-b6 &
cytochrome f.
• NADH2 act as reducing agent in PS 1.
• PS 1- cyclic phosphorylation/ non- cyclic phosphorylation.
• In PS 2 only ATP formation occurs while in PS 1 both NADPH2 & ATP
formation occurs.

13. Water splitting
• The electrons that were moved from photosystem 2 must be
replaced, this is achieved due to splitting of water.
• The splitting of water associated with the PS2; water split into H ions ,
oxygen, electrons. this creates oxygen , one of the net product of
photosynthesis.
• The electrons needed to replace those removed from photosystem 1
are provided by photosystem 2
• 4H2O-------------------- 4H + O2 + 4e-

14. PRODUCTS OF WATER SPLITTING
• 2 molecules of oxygen- librated oxygen
• 2 molecules of water -transpirated water
• 4 H+ and 4 e- -used in phosphorylation process

15. Chemiosmotic hypothesis

16. Chemiosmotic hypothesis
• The chemiosmotic hypothesis suggests that the action of ATP
synthase is coupled with that of a proton gradient.
• It is the action of the proton gradient that causes a proton motive
force that allows ATP synthase to phosphorylate ADP and inorganic
phosphate to ATP.
• All this occurs in grana in the presence of light that’s why it is called
light reaction.
• Thylakoid membrane impermeable for hydrogen ions.
• When protons released from F1 than they release ATP energy.
•

17. Calvin cycle
• The Calvin cycle (also known as the Calvin–Bensoncycle) is
the set of chemical reactions that take place in chloroplasts
during photosynthesis.
• The cycle is light-independent because it takes place after
the energy has been captured from sunlight

19. C4 Pathway
• C4 carbon fixation pathway is a metabolicpathway where CO2 is first added to
phosphoenolpyruvate by the enzyme, PEP carboxylase, producing the four-
carbon compound within mesophyll cells that is later transported to the bundle
sheath cells where the CO2 is to be released for use in the Calvin cycle.
• Plant that are adapted to dry tropic region have the C4 pathway.
• This pathway best works in high CO2 concentration and high temperature.
• In bundle sheath cell no chlorophyll is present ;no light reaction occurs.

21. THANK YOU

22. QUESTIONS ?