Photosynthesis

ContentsWhat is photosynthesis?OverviewWhere does photosynthesis occur?(Leaf)Structure of leafWhy do plants need photosynthesis?Requirements Photosynthesis: the chemical processBenefits of photosynthesis

What is photosynthesis? The biochemical process in which

sun light fixes carbon dioxide into glucose in the

presence of water is

called photosynthesis.

Photosynthesis in Overview• Process by which plants and other autotrophs

store the energy of sunlight into sugars.• Requires sunlight, water, and carbon dioxide.• Overall equation:

6 CO2 + 6 H20 + sunlight C6H12O6 + 6 O2

• Occurs in the leaves of plants in organelles called chloroplasts.

Where does photosynthesis occur?

• Photosynthesis occurs in the leaves of a plant.

Leaf Structure• Most photosynthesis occurs in the palisade layer.• Gas exchange of CO2 and O2 occurs at openings called

stomata surrounded by guard cells on the lower leaf surface.

Palisade

Spongy

Chloroplast Structure• Inner membrane

called the thylakoid membrane.

• Thickened regions called thylakoids. A stack of thylakoids is called a granum. (Plural – grana)

• Stroma is a liquid surrounding the thylakoids.

Pigments

• Chlorophyll A is the most important photosynthetic pigment.

• Other pigments called antenna or accessory pigments are also present in the leaf.– Chlorophyll B

– Carotenoids (orange / red)

– Xanthophylls (yellow / brown)

• These pigments are embedded in the membranes of the chloroplast in groups called photosystems.

Why do plants need photosynthesis?

• Glucose is the food for the plant. It gives the plant energy to grow.

• They do photosynthesis to gain energy.

Requirements for photosynthesis to occur.

• Light

• Carbon Dioxide

• Water

• But the most important among these is sunlight

Photosynthesis: The Chemical Process

• Photosynthesis is a chemical process.• It occurs in two main phases.

– Light reactions– Dark reactions (the Calvin Cycle)

Light Reactions

• Light-dependent reactions occur on the thylakoid membranes.– Light and water are required for this

process.– Light reactions are the “photo” part of

photosynthesis. – Light is absorbed by pigments and is

transformed into ATP and NADPH molecules

Dark Reactions• Dark reactions (light-independent) occur in the

stroma. – Dark reactions are the synthesis parts of

photosynthesis– Trapped energy by pigments is converted

into chemical ennergy– Carbon dioxide is “fixed” into glucose– ATP and NADPH molecules created during

the reaction is responsible for production of this glucose

EQUATIONEQUATION FORFOR PHOTOSYNTHESISPHOTOSYNTHESIS

6CO6CO22 + + 6H6H22OO + +ENERGYENERGY CC66HH1212OO66 + + 6O6O22 CARBONCARBON DIOXIDEDIOXIDE

WATERWATER

GLUCOSEGLUCOSE

OXYGENOXYGEN

How much glucose does a plant make?

• Plants make enough glucose to be used during the night and on cloudy days when they don’t get sunlight

• The extra glucose is stored in the plant’s leaves and other parts.

Advantages

Basic source of energy for all livingsProduction of oxygenHealthy environmentLessen global warming

PHOTOSYNTHESIS AND LIFE

• During the process of photosynthesis, oxygen is produced. We use this oxygen to breathe.

photosynthesis and photosynthesis and respirationrespiration

PHOTOSYNTHESISPHOTOSYNTHESIS CELLCELLACTIVITIESACTIVITIES

RESPIRATIONRESPIRATION

SUNSUN

RADIANTRADIANT ENERGYENERGY

GLUCOSEGLUCOSE ATP(ENERGY)ATP(ENERGY)

Photosynthesis andPhotosynthesis and RespirationRespiration

CC66HH1212OO66 + +

GLUCOSEGLUCOSE

6O6O22

OXYGENOXYGEN

6CO6CO22 ++

CARBON CARBON DIOXIDEDIOXIDE

6H6H22OO + +ENERGYENERGY

WATERWATER

ATPATP