This presentation is help for Education purpose.

1. PHOTOSYNTHESIS
PRESENTED BY: Erum Ali Akbar
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2. LEARNING OBJECTIVES
 Photosynthesis
 Structure of chloroplast
 Stages in photosynthesis
 Light dependent reaction
 Light independent reaction and also explain Calvin Cycle

3. PHOTOSYNTHESIS
Photo means light
Synthesize means putting together
DEFINATION:
“Photosynthesis is the process by which plants
use sunlight, water, and carbon dioxide to create
oxygen and energy in the form of sugar”

4. PHOTOSYNTHESIS
 The second key process for synthesizing ATP is Photosynthesis.
 In plants, photosynthesis occurs in chloroplast, large organelles found
mainly in leaf cells.
 During photosynthesis, chloroplasts capture the energy of sunlight,
convert it into chemical energy in the form of ATP and NADPH, and then
use this energy to make complex carbohydrates cut of carbon dioxide and
water.

5. PHOTOSYNTHESIS

6. STRUCTURE OF CHLOROPLAST

7. STRUCTURE OF CHLOROPLAST

8. STAGES IN PHOTOSYNTHESIS
 Three of the four stages in photosynthesis occur only during illumination..
The photosynthesis process in plants can be divided into four stages, each
localized to a defined area of the chloroplast:
1. Absorption of light, generation of high energy electrons, and formation of O2
from H2O.
2. Electron transport leading to reduction of NADP+ to NADPH, and generation of
a proton-motive force.
3. Synthesis of ATP.
4. Conversion of CO2 into carbohydrates, commonly referred to as carbon fixation.

9. STAGES IN PHOTOSYNTHESIS

10. STAGES IN PHOTOSYNTHESIS

11. STAGES IN PHOTOSYNTHESIS

16. CHLOROPLAST CONTAIN TWO PHOTOSYSTEMS
 LIGHT DEPENDENT REACTION
 LIGHT INDEPENDENT REACTION

17. LIGHT DEPENDENT REACTION
 Linear electron flow in chloroplasts involves PSII and PSI in an obligate
series.
 The process begins with absorption of a photon by PSII, causing an
electron to move from a P680 chlorophyll a to an acceptor plastoquinone
(QB) on the stromal surface.
 The resulting oxidized P680+ strips one electron from the relatively
unwilling donor H2O, forming an intermediate in O2 formation.
 After P680 absorbs a second photon, the semiquinone Q-accepts a second
electron and picks up two protons from the stromal space, generating
QH2.

18. LIGHT DEPENDENT REACTION
 After diffusing in the membrane, QH2 binds to the Qo on a cytochrome bf
complex .
 After the cytochrome bf complex accepts electron from QH2, it transfers
them one at a time, to the Cu2+ form of the soluble electron carrier
plastocyanin ( analogue to cytochrome c), reducing it to the Cu1+ form.
 Reduced plastocyanin then diffuses n the thylakoid lumen, carrying the
electron to PSI.
 Absorption of a photon by PSI leads to removal of an electron from the
reaction center chlorophyll a, P700.
 The resulting oxidized P700+ is reduced by an electron from plastocyanin
that originated in PSII.

19. LIGHT DEPENDENT REACTION

20. LIGHT DEPENDENT REACTION
 In linear electron flow, electrons excited in PSI are transferred from
ferredoxin via the enzyme ferredoxin-NADPH+reductase (FNR).
 The linear electron flow pathway is now completed.
 F0F1 complexes in the thylakoid membrane use the photon-motive
force generated during linear electron flow to synthesize ATP on the
stromal side of the membrane.
 Thus this pathway exploits the energy from multiple photons
absorbed by both PSII and PSI and their anstennas to generate both
NADPH and ATP in the stroma of the chloroplast, where they are
used for CO2 fixation.

21. CALVIN CYCLE
LIGHT INDEPENDENT REACTION

22. CALVIN CYCLE

23. STAGES OF CALVIN CYCLE

26. SUMMARY
 The process in which green plants synthesize organic molecule from CO2 & H2O
using energy of light.
 Photosynthesis occurs in green plants protists (Algae) & some bacteria.
 ROLE OF CO2 & H2O:
 CO2: Help in the function of carbohydrates.
 H2O: Oxygen we break comes from H2O.

27. SUMMARY
 The structure of the chloroplast allows the process of photosynthesis to take place.
 Chloroplast contains chlorophyll pigment and carotenoids and is involved in
photosynthesis.
 In the light- dependent reactions, which take place at the thylakoid membrane,
chlorophyll absorbs energy from sunlight and then converts it into chemical energy
with the use of water. The Light- dependent reactions release oxygen as a byproduct as
water is broken apart.
 The Calvin Cycle is not directly dependent on light, it is indirectly dependent on light
since the necessary energy carriers (ATP and NADPH) are products of light-
independent reactions.
 So, the purpose of the Calvin Cycle is to produce organic sugars molecules as a source
of energy for aerobic cellular respiration.

28. REFERENCE
 Chapter 12 of Molecular cell biology by Lodish

29. THANK YOU