PHOTOSYNTHESISMolecular Biology

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______________________________________________Chemical Energy and ATP

ADP ATP

Energy

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

Partially charged battery

Fully charged battery

• Adenosine Triphosphate (ATP) is a short term energy storage molecule.

______________________________________________Chemical Energy and ATP

Examples of how ATP is used: – active transport (Na+ and K+ pumps) – movement of motor proteins – protein synthesis – photosynthesis

______________________________________________Energy Flow

Autotrophs - convert light energy from the sun into stored chemical energy (sugar)

______________________________________________What are plants made of?

• Plants are mainly carbohydrates. sugar C H O 6 12 62

• Where does the H2O come from?

• Where does the Carbon come from?

=

______________________________________________Photosynthesis

Photo = Light

Photosynthesis a process that uses the energy of sunlight to combine water and carbon dioxide into sugar and oxygen.

Synthesize = Combine together.

______________________________________________Photosynthesis

Light Energy

Chloroplast

CO2 + H2O Sugars + O2

______________________________________________Understanding Photosynthesis

Jan van Helmont Experiment (1643) – weighed a seedling and soil – watered for 5 years

Results – tree gained 75 kg – mass of soil was unchanged.

Conclusion – tree mass must have come from the water.

______________________________________________Understanding Photosynthesis

Joseph Priestly Experiment (1771) – candle under a bell jar – candle and mint plant

Results – candle with plant burned longer

Conclusion – Plants release oxygen

______________________________________________Understanding Photosynthesis

Jan Ingenhousz Experiment (1779) – aquatic plants in light – aquatic plants in dark

Results – aquatic plants in light produce bubbles

Conclusion – plants need sunlight to produce oxygen.

______________________________________________Understanding Photosynthesis

Theodor Engelmann Experiment (1882) – used prism to divide light into component colors – exposed photosynthetic algae to the light

Results – oxygen-requiring bacteria concentrated where

oxygen levels were highest Conclusion – red and violet colors of light

drive photosynthesis

______________________________________________Light & Pigments

Absorption of Light by Chlorophyll

Chlorophyll b

Chlorophyll a

• Chlorophyll a most common pigment in plants, protists, and bacteria.

Green Reflected

Red & Violet Absorbed

______________________________________________Chloroplast

• The chloroplast is the organelle that specializes in photosynthesis. – DNA – Ribosomes – Thylakoid (folded inner membrane) chloroplasts

in plant cell

cross sectionof leaf

chloroplasts contain

chlorophyll

______________________________________________Inside a Chloroplast

• Chloroplast structure – stroma

• fluid-filled interior – thylakoid

• contains chlorophyll • light reactions

– grana • stacks of thylakoids

______________________________________________Photosynthesis

light energy

water carbon dioxide glucose oxygen

______________________________________________Photosynthesis

• Photosynthesis occurs in two stages. – light-dependent reactions

• driven by light • occurs at the thylakoid membrane

– light-independent reactions • light does not power these reactions • occurs in the stroma

______________________________________________Light-Dependent Reactions

• Light-Dependent Reactions use sunlight energy to form ATP (cellular energy).

______________________________________________Light-Independent Reactions

• Light-Independent Reactions or Calvin Cycle, uses ATP and electrons captured from the sun to form sugar compounds.

• Glucose C6H12O6

The calvin cycle was named after Melvin Calvin who traced the chemical path that carbon follows to form glucose.

______________________________________________Photosynthesis: Big Picture

Photosynthetic Sea Slug

The green sea slug is the first animal shown to make chlorophyll like a plant.