Photosynthesis

Photosynthesis is a process in which make their own food from their light and release oxygen.

Photo means light 

Photosynthesis use light energy change their chemical energy store in starch.

Photosynthetic organisms is known as photoautotrophs.

Photosynthesis is important due to to process

• food is primary source  on earth
•  release of oxygen is responsible for the atmosphere.

Feature of photosynthesis

• Physio chemical process
• Redox process
• Up hill process
• Endergonic process.

Physicochemical process

Light energy is converted into glucose/starch.

Light energy is physical form.

Starch or Glucose is chemical form.

Redox process

Light reaction is oxidation process and

 dark reaction is reduction process.

Light reaction is a splitting of water.

Dark reaction is CO2 (carbon dioxide) fixation.

Uphill process

Carbon dioxide is a weak electron acceptor.

Electron move like in upward direction.

Endergonic process

Energy in which consumption in the form of light.

Equation of photosynthesis

6C02 + 12 H2O -------------C6 H12 06 + 6 H2O + 6O2

                            Sunlight 

Photosynthesis takes place in green leaves, but it also in other green parts of the plants example sepals, herbaceous stem and unripe  greenfruits Etc.

Photosynthesis in which production of food in the form of Glucose and store in form starch.

Because Glucose is chemically reactive and soluble.

Starch is chemically inreactive and insoluble.

Photosynthesis in which involve two process light reaction and dark reaction.

Light reaction in which splitting of water and dark reaction is CO2 fixation.

 Wavelength of photosynthesis.

Wavelength of light is 400 to 700

Photosynthesis is maximum in blue and red light.

Chloroplast

Chloroplast in which  two things.

• Membranous system and
• Fluid stroma

Membranous system in which two lamellae

• Grana lamellae
• Stroma lamellae

membrane system responsible for trapping the light energy and also for the synthesis of ATP and NADPH.

Directly involved in light reaction.

Fluid stroma

In which enzymatic reaction take palace change into starch.

Directly involved in dark reaction

Pigment are involved in photosynthesis.

leaf pigment can be separated from the green plant through paper chromatography.

In which involve four pigment.

• Chlorophyll A
•  chlorophyll B
• Xanthophyll
•  carotene

Chlorophyll A

• Chlorophyll A is bright green or blue green in colour.
• Chlorophyll A  is molecular formula C55 H72 O5 N4 Mg.
• Chlorophyll A is universal photosynthetic pigment.
• Chlorophyll a primary photosynthetic pigment
• Chlorophyll a most abundant photosynthetic pigment.

Chlorophyll B

Chlorophyll B is yellow green colour

Chlorophyll B molecular formula is C55 H70 O6 N4 Mg.

Xanthophyll is yellow colour

Carotene is yellow orange colour

Action spectrum 

First action spectrum of photosynthesis is given by T.W.Engelmann.

Prism splits sunlight into spectral component of 7 colour.

He used to cladophora green algae in the experiment.

Cladophora placed in a suspension of aerobic bacteria.

The bacteria were used to detect the site of O2 evolution.

In which bacteria is used in photoautotrophs.

Observation

• At a palace of  blue and red light, bacteria are accumulated Mainly.
  
  

Mechanism of photosynthesis

Photosynthesis in two stage

1. Light reaction
2. Dark reaction

Light reaction

• Light reaction is a oxidation reaction.
• Light reaction occur in grana of chloroplast.
• Light reaction is also called hill reaction or photo chemical phase.

Light reaction involved

• light absorption
•  water splitting
•  oxygen release
• formation of high-energy chemical intermediate

         (ATP and NADPH)

Light harvesting complex made of hundred of pigment molecules 250 to 400 bond to protein.

Each photosystem has all the pigment (except one molecule of chlorophyll A) forming a light harvesting system also called antenna.

Photolysis of water

photolysis of water occur at grana that is lumen side of grana thylakoid membrane with the help of water splitting complex.

Light reaction  involves two photosystem

1. Photosystem 1 and
2.  photosystem II

Photosystem 1

1. Located at non appressed parts of grana thylakoid and stroma lamellae
2. Photosystem 1 of reaction centre is P700
3. Photosystem 1 has reducing nature
4. photosystem 1 has participate in both cyclic and noncyclic photophosphorylation.
5. Photosystem 1 is cyclic photophosphorylation

Photosystem II

1. Located at appressed parts of grana thylakoid
2. reaction centre is 680
3. Photosystem II has oxidizing nature
4. Participate only  in non cyclic photophosphorylation.
5. photosystem II is non cyclic photophosphorylation

Photophosphorylation

ATP synthesis is known as photophosphorylation.

Photophosphorylation is synthesis of ATP from ADP inorganic phosphate in the presence of light.

Cyclic photophosphorylation

• Cyclic photophosphorylation is photosystem 1 is functional.
• cyclic photophosphorylation is in the stroma lamellae because stroma lamellae lack photosystem II as well as in NADP reductase enzyme.
• Cyclic photophosphorylation also occur when light of wavelength beyond 680 nm are available for excitation.
• during cyclic photophosphorylation the excited electron does not pass on to NADP+ but cycle back to the photosystem 1 complex through the electron transport chain.

Non cyclic photophosphorylation.

• non cyclic photophosphorylation in which two photosystem work together photosystem 1 and photosystem II.

• Transfer of electron starting from photosystem II,
• Redox potential scale given shaped like Z.
• Z scheme was proposed by hill and Bendall.
• Redox potential maasured in volt all Mili volt.

Factor affecting photosynthesis

Plant factor

1. number of leaves
2. size of leaves
3. orientation of leaves
4. Mesophyll
5. No of chloroplast
6.  amount of chlorophyll 
7. age of leaves
8. Internal CO2 concentration.

External factor

1. sunlight 
2. atmospheric CO2 concentration 
3. Water
4. Temperature

Light

• Light quality
•  light intensity
•  duration of exposure of light.

Carbon dioxide concentration

Carbon dioxide major limiting factor for photosynthesis.

Carbon dioxide compensation point for C4 plant is 0-10ppm.

Carbon dioxide compensation point for C3 plant is 25-100ppm.

Temperature

Dark reaction being enzymatic is temperature control.

Water

Water stress due to stomata close and wilting of leaves.

Stomata close then reducing the carbon dioxide   availability and then decrease the photosynthesis.

Wilting of leaves

Reducing the surface area of leaves then decrease the photosynthesis.

Inhibitors

Weedicides  or herbicide.

Respiration

Enzymes

ETS cycle