Chapter 8 Photosynthesis

You get energy from the food you eat. 8-1 Energy and Life You get energy from the food you eat. Directly or indirectly, all of the Energy in living systems needed for Metabolism comes from the sun.

Metabolism involves either using energy To build molecules or breaking Down molecules in which energy Is stored. Photosynthesis is the process by which Light energy is converted to Chemical energy.

Autotrophs are organisms that use Energy from sunlight or Inorganic substances to make Organic compounds. Like plants use sunlight to Make glucose.

Heterotrphs are organisms that Must get energy from food instead Of directly from sunlight. We are heterotrophs because We can’t make our own food In our cells. Instead we use cellular respiration To “burn” fuel in our bodies.

Almost all of the food we eat goes To heat, but some of the energy Goes into making ATP. ATP (adenosine triphosphate) Provides cells with the energy they Need to carry out life’s processes.

8-2 Photosynthesis

In the process of Photosynthesis, plants use 6CO2 + 6H2O + Light C6H12O6 + 6O2 In the process of Photosynthesis, plants use The energy of sunlight to convert water and carbon dioxide Into high energy carbohydrate and oxygen.

In the 1600’s, the Belgian, Jan van Helmont devised an Experiment to find out if plants got their mass out of The soil. After 5 years of taking data, he decided that plants get most of their mass from water.

After more than 100 years, Joseph Priestly experimented With plants and candles. He learned that if you left a plant under a closed jar, That eventually it would be filled with oxygen. He tested for the oxygen by lighting candles under the jars.

Later, the Dutch scientist Jan Ingenhousz found that Plants only produced oxygen when exposed to light. The experiments performed by these three scientists led to work by other scientists who finally discovered that in the presence ff light, plants transform carbon dioxide and water into sugar and oxygen.

The plants principle pigment There are 2 types of chlorophyll, In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll. Plants gather the sun’s energy with light absorbing molecules called pigments. The plants principle pigment Is chlorophyll. There are 2 types of chlorophyll, a and b.

8-3 Reactions of Photosynthesis 6CO2 + 6H2O + Light C6H12O6 + 6O2

In stage 1, light energy is absorbed. 6CO2 + 6H2O + Light C6H12O6 + 6O2 In stage 1, light energy is absorbed. Structures that will absorb light Contain pigments. Chlorophyll is the primary pigment That absorbs mostly blue and red Light and reflects green and yellow.

That reflection is why plants Are green. Plants contain 2 types of chlorophyll, a and b chlorophyll. Both types of chlorophyll play a Role in photosynthesis.

The pigments that produce yellow And orange colors in fall or In fruits and vegetables Are called carotenoids.

Pigments involved in plant Photosynthesis are located in the Chloroplasts of leaf cells. Clusters of pigments are embedded In the membranes of disk Shaped structures called Thylakoids.

When chlorophyll absorbs light this causes 1 pair of chlorophyll electrons to “bounce around”

Instead of being “trapped” in a wire they are stored in chemical bonds.

These “excited” electrons that leave The chlorophyll molecules are used To produce new molecules that Temporarily store chemical energy, Including ATP. The series of molecules through which Excited electrons are passed along A thylakoid membrane are called Electron transport chains.

-accepts electrons and is converted to NADPH NADP+ (in plants) -accepts electrons and is converted to NADPH NADPH is an electron carrier that Provides the high-energy electrons Needed to make C-H bonds in stage 3.

In the 1st and 2nd stages of Photosynthesis, light energy is used To make ATP and NADPH, which Temporarily store chemical energy. In stage 3, energy is stored in Organic molecules.

In the 3rd stage of photosynthesis, Carbon atoms from the CO2 in The air are used to make Organic compounds in which Chemical energy is stored. This energy is stored in the form Of sugar… Glucose.

The transfer of carbon dioxide To organic compounds is called Carbon fixation. The most common method for Carbon fixation is the Calvin Cycle. The Calvin cycle is a series of enzyme Assisted chemical reactions that Produce 3 carbon sugars.

Photosynthesis is affected by Various types of environmental factors. The most obvious is light Then there is CO2 concentration Also temperature

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