Photosynthesis

Energy and Life• Plants and some other types of organisms are able to use

light energy from the sun to produce food.• Autotrophs: organisms such as plants, which make their

own food• Heterotrophs: obtain energy from the foods they consume• All living organisms must be able to produce energy from

the environment in which they live, store energy for future use, and use energy in a controlled manner.

Autotrophs

Heterotrophs

Chemical Energy and ATP

• A quick source of energy that is stored in the chemical bonds of a molecule that can be used quickly and easily by the cell is called adenosine triphosphate (ATP).– ATP is an energy molecule– The energy of ATP becomes available when the

molecule is broken down.– The addition and release of a phosphate group on

adenosine diphosphate creates a cycle of ATP formation and breakdown. This means the cell doesn’t have to store all the ATP it needs.

ATP Continued• Cells use this energy to make new cells, maintain

homeostasis, and to power functions (like movement).• The characteristics of ATP make it exceptionally useful as the

basic energy source of all plant cells.

Adenine Ribose 3 Phosphate groups

ATP

ADP ATP

Energy

EnergyAdenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP)

Partiallychargedbattery

Fullychargedbattery

Comparison of ADP and ATP to a Battery

ADP ATP

Energy

EnergyAdenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP)

Partiallychargedbattery

Fullychargedbattery

Comparison of ADP and ATP to a Battery

Photosynthesis• Photosynthesis: Plants use energy from the sun to convert

water and carbon dioxide into high energy carbohydrates (sugars and starches) and give off oxygen as a waste product.

• Photosynthesis happens in 2 phases: light-dependent reactions and light-independent reactions.

• In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts.

Photosynthesis Equation

•

Light Energy

Chloroplast

CO2 + H2O Sugars + O2

Photosynthesis: Reactants and Products

Light and Pigments• Plants gather the sun’s energy with light absorbing molecules

called pigments. The plants’ principal pigment is chlorophyll.• 2 types of chlorophyll: Chlorophyll a and Chlorophyll b• Chlorophyll absorbs light very well in the blue-violet and red

regions of the visible spectrum. However, chlorophyll does not absorb light very well in the green region of the spectrum. Green is reflected by leaves, which is why plants look green.

Absorption of Light byChlorophyll a and Chlorophyll b

V B G Y O R

Chlorophyll b

Chlorophyll a

Chlorophyll Light Absorption

The Reactions of Photosynthesis

• Photosynthesis takes place inside the chloroplasts• The Chloroplasts contain saclike photosynthetic membranes

called thylakoids, which are arranged in stacks known as grana. The space outside of the grana is called the stroma.

• Proteins in the thylakoids membrane organize chlorophyll and other pigments into clusters known as photosystems, which are the light collecting units of chloroplasts.

Chloroplasts

• Light-dependent reaction: uses light energy to produce oxygen and convert ADP and NADP+ into energy carriers ATP and NADPH

• The light dependent reactions take place within the thylakoid membranes (granum) of chloroplasts.

Light Dependent Reactions

HydrogenIon MovementPhotosystem II

InnerThylakoidSpace

ThylakoidMembrane

Stroma

ATP synthase

Electron Transport Chain Photosystem I ATP Formation

Chloroplast

Light-Dependent Reactions

Calvin Cycle• Calvin Cycle: uses the energy carriers ATP and NADPH from

the light-dependent reactions to produce high-energy sugars. (Calvin cycle is also called the light independent reaction)

• Calvin Cycle takes place in the stroma, outside the grana.

ChloropIast

CO2 Enters the Cycle

Energy Input

5-CarbonMoleculesRegenerated

Sugars and other compounds

6-Carbon SugarProduced

Calvin Cycle

Factors Affecting Photosynthesis

• Water, light, and temperature all affect photosynthesis

Photosynthesis

includes

of

take place intakes place in uses

to produce to produce

use

Light-dependentreactions

Calvin cycle

Thylakoidmembranes Stroma NADPHATPEnergy from

sunlight

ATP NADPH O2 Chloroplasts High-energysugars

Photosynthesis Concept Map

ChloroplastLight and Water

O2

Sugars

CO2

Light-Dependent Reactions

CalvinCycle

NADPHATP

ADP + PNADP+Chloroplast

Photosynthesis: An Overview