Photosynthesis is an inevitable process that keeps us alive.It is the main source for food and it's byproduct keeps us breathing. This ppt is the detailed explanation of photosynthesis and the components involved in it. Here you can easily understand the concept and you are able to strengthen your grip on this topic.

1. PHOTOSYNTHESIS
YOGESH THILAK
23PBT819

2. Table of Contents
 Introduction : Photosynthesis
 Type of photosynthesis
 Site of photosynthesis
 Photosynthetic pigments
 Photosystems
 PHOTOSYNTHESIS in green plants
 Light reaction
 Carbon fixation reaction

3. PHOTOSYNTHESIS
 Photosynthesis is a process by which phototrophs convert light energy into
chemical energy, which is later used to fuel cellular activities.
 Occurs in plants , algae and some prokaryotes.
 Photosynthesis reaction involves two reactants, carbon dioxide and water.
These two reactants yield two products, namely, oxygen and glucose.
 Hence, the photosynthesis reaction is considered to be an endothermic
reaction.
 Overall photosynthetic process can be written as
6CO2 + 6H2O —> C6H12O6 + 6O2

4.  Photosynthesis is carried out by many different organisms (termed
photosynthetic organisms), ranging from photosynthetic bacteria to green
plants.
 These photosynthetic organisms may be oxygenic or anoxygenic, on the basis
of generation of oxygen during photosynthesis.
 In anoxygenic photosynthesis, light energy is captured and converted into ATP,
without the production of oxygen. Water is, therefore, not used as an
electron donor.
 In oxygenic photosynthesis, light energy is captured and converted into ATP,
with the production of oxygen. Here, synthesis of oxygen occurs due to photo
oxidation or photolysis of water.
 Oxygenic photosynthetic organisms include both eukaryotes as well as
prokaryotes whereas anoxygenic photosynthetic organisms include only
prokaryotes.
OXYGENIC AND ANOXYGENIC
PHOTOSYNTHESIS

5. LEAVES : SITE OF PHOTOSYNTHESIS
 Photosynthesis occurs in chloroplasts, Organelle in Certain plants.
 All green plants parts have chloroplasts and carry out photosynthesis.
 The leaves have the most chloroplasts.
 The green colour comes from chlorophyll which is present in the chloroplast.
 The pigments absorbs light energy.
 A chloroplant contains:
✓ Stroma, a fluid.
✓ Grana, Stacks of thylakoids.
 The thylakoids contain chlorophyll.
→ Chlorophyll is the green pigment that captures light for
photosynthesis.

6. PHOTOSYNTHETIC PIGMENTS
 Plant cells have green chloroplast.
 The thylakoid membrane of the chloroplast is impregnated with
photosynthetic pigments (chlorophylls , Carotenoids).
 Plants are green because the green wavelength is reflected,not absorbed.
Why plants are green ?
 The light energy required for photosynthesis is captured by photosynthetic
pigment molecules.
 Different types of photosynthetic pigments participate in this process.
 Three types of photosynthetic pigments are present in oxygenic photosynthetic
organisms.
 These pigments are chlorophylls, carotenoids and phycobilins.

7. STRUCTURE OF CHLOROPHYLL
Chlorophyll a – CH3
Chlorophyll b - CHO

8. PHOTOSYSTEM
 In all natural photosynthetic systems, pigment molecules are
bound to proteins forming pigment-protein complexes called
pigment system (or photosystem).
 The pigment systems have two components: Photochemical
reaction center and antenna complex
 Photochemical reaction center is a protein-pigment
complex that carries out photochemical reaction.
 There are two types of photochemical reaction centers - Fe-
S type reaction center (or type I) and Pheophytin-quinone
type reaction center (or type II)

9. • Antenna complex (or light-harvesting complex)
consists of a number of distinct pigment-protein
complexes.
• It has two components - core or inner antenna and
peripheral or outer antenna .
• The antenna complex captures light energy and feeds it to
the reaction center by a process called resonance energy
transfer.
• The size of the antenna complex varies considerably in
different organisms, generally 200 to 300 chlorophylls per
reaction center in higher plants.
• All photosynthetic organisms, with the exception of
Hellobacteria, possess an antenna complex.

11. PHOTOSYNTHESIS IN GREEN PLANTS
 Photosynthesis is a two-stage process: one stage involves light reactions which
directly dependent on the light and other carbon-fixation reactions.
 The light reactions (light-dependent photochemical reactions) occur in the
thylakoid of chloroplast, and require the direct energy of light to make
NADPH and ATP that are used in the carbon-fixation reactions.
 Light reactions are also known as the thylakoid reactions because almost all
the reactions takes place within the thylakoids.
 A process of formation of ATP from ADP and inorganic phosphate during light
reaction by utilizing light energy is called photophosphorylation.
 It involves of Photosystems (1 and 2) and in green plants the flow of electron
is of two types :
1. Non-cyclic photophosphorylation.
2. Cyclic photophosphorylation.

12.  The carbon-fixation reactions (sometimes misleadingly called the dark
reactions), occur in the stroma of the chloroplasts and driven by the
products of the light reactions, ATP and NADPH, to make
glyceraldehyde 3-phosphate (a triose phosphate) from reduction of
carbon dioxide.
 The carbon fixation and reduction reactions are also called the
stroma reactions because the carbon reduction reactions take place in
the aqueous region of the chloroplast, the stroma.

14. LIGHT REACTION
 It is also known as Photochemical reaction.
 Takes place in thylakoids.
 Requires light.
 Converts light energy into chemical energy.
 Carbon fixation reaction depends on the end products ( reduced NADP+ and
ATP ) of light reaction.

15. Z – SCHEME

16. CARBON FIXATION REACTION
 Carbon fixation cycle is the CO2 reduction and fixation cycle also
known as C3 cycle.
 In Eukaryotes , it occurs in the stroma of chloroplasts whereas in
prokaryotes, it oocurs in cytosol.
 It was elucidated by Melvin Calvin and Andy Benson thus the cycle Is
also know as Calvin cycle
 Takes place in the stroma of the chloroplast.
 No light required but need the end products (reduced NADP+ and ATP)
of light dependent reaction to produce simple sugars.
 Need an enzyme RUBISCO (Ribulose Bisphosphate Carboxylase and
Carbon dioxide).

17.  The Calvin cycle has three phases:
- Carbon fixation (catalyzed by rubisco)
- Reduction
- Regeneration of the CO₂ acceptor (RuBP).
 Phase 1 – Fixation of CO₂
•CO₂ is added to ribulose 1,5-bisphosphate 2 (RuBP).
• Ribulose bisphosphate carboxylase/oxygenase (rubisco) catalyzes
the reaction.
•A 6-carbon molecule results, which quickly breaks into two 3-
carbon molecules: 3- phosphoglycerate (3PG).

18.  Phase 2 – Reduction
3PG is reduced to form glyceraldehyde 3-
phosphate (G3P).
 Phase 3 –Regeneration of CO₂
• The CO, acceptor, RuBP, is regenerated from
G3P.
• Some of the extra G3P is exported to the cytosol
and is converted to hexoses (glucose and fructose).
• When glucose accumulates, it is linked to form
starch, a storage carbohydrate.

20. What is the energy expenditure for
synthesizing a glucose?
 Six rounds of the Calvin cycle are required for synthesis of a glucose, because
one carbon atom is reduced in each round.
 Twelve molecules of ATP are expended in phosphorylating 12 molecules of 3-
phosphoglycerate to 1,3-bisphosphoglycerate, and 12 molecules of NADPH are
consumed in reducing 12 molecules of 1,3-bisphosphoglycerate to
glyceraldehyde 3-phosphate.
 An additional six molecules of ATP are spent in regenerating RuBP. Hence,
total 18 ATP and 12 NADPH are required for synthesis of a glucose molecule.

21. Thank you !