Photosynthesis

Historical discoveries

Van Helmont’s experiment – In the 1600’s van Helmont wanted to determine if plants grew by taking material out of the soil…

The result- NO

Proved that water was responsible for the “hydrate” part of carbohydrate.

Preistley’s experiment- In the 1700’s Priestley wanted to determine what made the “carbo” part

The result – carbon dioxide

Experiment with plant growing in jar provided oxygen for flame.

Ingenhousz experiment – Later Ingenhousz showed that the effect observed by Priestly only occurred when a plant was exposed to sunlight.

The Photosynthesis Equation

6 CO2 + 6 H2O C6H12O6 + 6 O2

sunlight

Additional requirements

Aside from water, sunlight, and carbon

dioxide, plants also need chlorophyll.

Chlorophyll is a pigment , which is a substance

that absorbs and reflects light (which is the

reason plants look green)

Because light is a form of energy, any compound

that absorbs light also absorbs energy from that

light. In plants most of the energy is immediately

transferred into electrons in the chlorophyll

molecule.

Inside a Chloroplast

Photosystem – Clusters of pigments including chlorophyll in

the thylakoid membrane

Electron carriers

NADP+ NADPH

NADP+ accepts and holds 2 electrons and a

hydrogen ion

NADPH carries these electrons to places in the cell

where molecules like glucose are built.

The reactions

Light-dependent reactions

The Calvin Cycle

Light-Dependent Reactions

Use light and water to release oxygen and

make ATP and NADPH (photolysis)

Therefore ADP and NADP+ are required

ATP synthase – molecule found in the cell

membrane that lets H+ ions pass through thus

making ATP

Takes place in the thylakoid

The Calvin Cycle

Uses ATP and NADPH and CO2 to produce

high energy sugars (glucose)

ATP and NADPH can’t store energy for more than

a couple of minutes

Takes place in the stroma

2 Cycles of Photosynthesis

Light Dependent

Reactions

Occur in the

thylakoid

Use light and water

to make oxygen,

ATP and NADPH

Electron carriers

Calvin Cycle

Occurs in the stroma

Use carbon dioxide,

ATP and NADPH to

make glucose

vocabulary

Pigment- molecule that absorbs and reflects light

Chlorophyll- principal pigment of plants and other photosynthetic organisms; captures light energy

Photosynthesis- process by which plants and some other organisms use light energy to convert water and carbon dioxide into oxygen and high-energy carbohydrates such as glucose

NADP+ - one of the carrier molecules that transfers high-energy electrons from chlorophyll to other molecules.

Calvin Cycle- reactions of photosynthesis in which energy from ATP and NADPH is used to build glucose; occurs in the stroma

Light-dependent reactions – reactions of

photosynthesis that use energy from light to produce

ATP and NADPH; occurs in the thylakoid

Stroma- region outside the thylakoid membranes in

chloroplasts

Thylakoid- sac-like membranes that absorb light in

chloroplasts

ATP synthase- a large protein that allows H+ ions to

pass through the cell membrane to produce ATP

Photosystem- clusters of pigment in the thylakoid that

absorb light to begin photosynthesis

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Adenosine Diphosphate

Adenosine Triphosphate

Fig. 7.4

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