Sharing One Of The Most Beautiful Creations Of Allah

SHARING ONE OF THE MOST BEAUTIFUL CREATIONS OF ALLAH

PHOTOSYNTHESIS

BRIEF HISTORY OF PHOTOSYNTHESIS • 1640: Jean Baptiste van Helmont – study the growth of plants. (plants grew mainly from water not soil) • 1772: Joseph Priestley – green plants restore oxygen which can support combustion (candle in an upturned glass jar) • Jan Ingenhousz: Plants only release oxygen in the presence of sunlight

BRIEF HISTORY OF PHOTOSYNTHESIS • 1780s: Jean Senebier – carbon dioxide was taken by plants during photosynthesis. • 1796: Ingenhousz verified that carbon dioxide is the source of carbon for photosynthesis • 1804: de Saussure – water required for photosynthesis • 1845: Robert Mayer – plants convert photo energy into chemical energy during photosynthesis.

BRIEF HISTORY OF PHOTOSYNTHESIS • 1905: Blackman – photosynthesis involves 2 principal reactions (photochemical and biochemical). Photochemical is lightdependent, biochemical is lightindependent • 1937: Robert Hill – chloroplasts are able to produce oxygen by splitting water molecules in the absence of carbon dioxide.

LEAF STRUCTURE & FUNCTION

CROSS SECTION OF LEAF

LEAF STRUCTURE & FUNCTION • Xylem: transports water • Phloem: transports organic products of photosynthesis • Epidermis: protective layer on the upper and lower surfaces of the leaf • Cuticle: waterproof layer which reduce excessive water lost • Stomata: allowing exchange of gases between the internal part of the leaf and the environment • Guard cells: regulate the size of the pore.

STRUCTURE OF CHLOROPLAST

PHOTOSYNTHESIS – LIGHT REACTION • Takes place in the grana • The raw material needed is water • During light reaction, chlorophyll captures light energy which excites the electrons of chlorophyll molecules • Light energy is also used to split water molecules into hydrogen ions (H+) and hydroxyl ions (OH-): PHOTOLYSIS

PHOTOSYNTHESIS – LIGHT REACTION • The hydrogen ions then combine with the electrons released by chlorophyll to form hydrogen atoms. • Energy released from the excited electrons is used to form energy rich molecules of ATP • At the same time, each hydroxyl ion loses an electron to form hydroxyl group. Hydroxyl groups combine to form water and gaseous oxygen. Oxygen is released into atmosphere

PHOTOSYNTHESIS – LIGHT REACTION • 24H2O

LIGHT CHLOROPYLL

24H+ + 24OH-

• 24H+ + 24e-

24 H (hydrogen atoms)

• 24 OH-

24OH + 24 e-

• 24 OH

12H2O + 6O2

PHOTOSYNTHESIS – DARK REACTION • The ATP molecules and hydrogen atoms move to the stroma to provide energy • Hydrogen atoms are used to fix carbon dioxide in a series of reactions catalysed by photosynthetic enzymes. • Overall reaction results in the reduction of carbon dioxide into glucose.

PHOTOSYNTHESIS – DARK REACTION

• 6CO2 + 24H • 6 (CH2O)

6(CH2O) + 6 H2O C6H12O6

PHOTOSYNTHESIS • Glucose monomers then undergo condensation to form starch which is temporarily stored as starch granules in the chloroplasts. • The entire process of photosynthesis can be represented by the following chemical equation: • 12H2O + 6CO2

LIGHT CHLOROPYLL

C6H12O6 + 6O2 +6H2O

EVALUATION • Work in groups. Review the mechanism of photosynthesis which has been discussed and list out the comparison between light and dark reaction. Light Reaction

Differences •Light energy required • Site of reaction • Substances required for reaction •Products of reaction

Dark Reaction