Photosynthesis

History Of Photosynthesis

History Of Photosynthesis

What does Photosynthesis Means?

Site Of Photosynthesis

Light & Dark Reaction

Goal Of Photosynthesis

Contents

Investigating Photosynthesis

•Many Scientists Have Contributed To Understanding Photosynthesis

•Early Research Focused On The Overall Process

•Later Researchers Investigated The Detailed Chemical Pathways

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”

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.”

Ingenhousz’s Experiment 1779

Ingenhousz repeated Priestly experiment with & without sunlight

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.”

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

Lightenergy

PHOTOSYNTHESIS

6 CO2 6+ H2O

Carbon dioxide Water

C6H12O6 6+ O2

Glucose Oxygen gas

• 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?

• Chloroplast is the place where Photosynthesis occurs.

• Photosynthesis occurs in the following parts of Chloroplast:-

Grana Stroma

Site Of Photosynthesis

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

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

Light & Dark Reaction

• 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

• 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

• 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

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)

• 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

• 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)

Photosynthesis6CO2 +6H20 + light C6H1206 + 6O2

Photosynthesis Equation

• 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

• 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