Cell Energy: Photosynthesis

Where Does Energy Come From?  Autotrophs: Use light energy from the sun to produce food necessary to give them energy.  Heterotrophs: Can’t use the energy of the sun, these organisms need to obtain energy from foods they consume.

Energy  Energy comes in many forms: Light, Heat, Electricity.  One source of chemical energy that living things use is adenosine triphosphate (ATP).

ATP: Adenosine Triphosphate  Consists of:  Adenosine  A 5-Carbon sugar called Ribose  3 Phosphate groups (the key to its ability to store and release energy).  Energy storage and release  Cells have the ability to store energy in small amounts (3-5 seconds)  ADP (energy source like ATP but with one less phosphate group) must add a phosphate group so the cell can store energy,  Energy will be released from that ATP when that same phosphate group is removed.  ATP powers many reactions this way (active transport, protein synthesis, muscle contraction)

Photosynthesis  The process which plants use to convert the energy of sunlight into carbohydrates (sugars and starches) they can use as an energy source.

Scientist of Photosynthesis  Van Helmont- Experimented to see if plants grew by taking materials out of soil.  He concluded that water was responsible for the majority of plant growth.  He had it ½ right, he didn’t realized that the carbon dioxide in the air was used with the water and sunlight to produce energy.

Scientist of Photosynthesis  Priestly- Experimenting with a fig plant and a candle under a jar, discovers that plants release a chemical (we now know is Oxygen) that allows the candle to burn.  Ingenhousz-Discovers that plants produce oxygen when in light but, not in the dark.

Photosynthesis  The photosynthesis reaction:  6CO 2 +H 2 O --> C 6 H 12 O 6 +6O 2 (With light present).  The photosynthesis reaction requires: Light, Water, and Carbon Dioxide.  The light used for photosynthesis to occur, is captured by a green pigment (chlorophyll) stored in the chloroplast.  Plants also contain other pigments (red, orange, yellow, etc.) that absorb light from another part of the spectrum that chlorophyll does not absorb.

Photosynthesis  Inside the Chloroplast:  Chloroplast Envelope- Made of an inside and outside membrane surrounds the chloroplast.  Thylakoids- Saclike photosynthetic membrane (location of Light Reaction).  Granum- Stack of thylakoids  Photosystems- Proteins in the thylakoids organize chlorophyll and other pigments into clusters known as photosystems, this is the light collecting unit of the chloroplast.  Stroma- Space outside of the thylakoids (location of Dark Reaction).

Photosynthesis  Light Reaction:  The first step of photosynthesis.  Requires Light.  Takes place in the Thylakoids.  Uses sunlight to produce Oxygen and convert ADP & NADP into ATP and NADPH.  Requires water (H 2 O).

Photosynthesis  The steps of a Light Reaction 1.Pigments begin to absorb light, which is used to break up water molecules into H + and O (which is released into the air). 2.Energy from electrons in the electron transport chain is used to transport H + from the stroma into the thylakoid. 3.Energy from light is used to reenergize electron. NADP picks up these electron along with H + at the outer surface of the thylakoid to become NADPH. 4.As electrons pass from chlorophyll to NADP, more H + ions are passed across the membrane, after a while the inside becomes (+) and the outside becomes (-) this difference in charge provides the energy necessary to make ATP. 5.H + use a protein called ATP synthase to help it pass through the membrane, as H + passes the membrane it rotates the protein, As it is rotating it binds ADP and a phosphate group together producing ATP.

Photosynthesis  Dark Reaction:  Also known as the Calvin Cycle, it is the second step in photosynthesis.  Takes place in the Stroma.  Uses the energy from the ATP and NADPH produced by the light reaction to make high energy sugars.  Doesn’t require light.  Requires CO 2.

Photosynthesis  The steps of a Dark Reaction: 1.6 carbon dioxide molecules enter the reaction in the stroma, they combine with 6 (5 carbon) molecules to make 12 (3 carbon) molecules. 2.Energy from ATP and high-energy electrons from NADPH are used to convert the 12 (3 carbon ) molecules into high-energy forms. 3.2 of the 12 (3 carbon ) molecules are removed from the cycle, the plant cell uses these molecules to produce; sugars, lipids, amino acids, and other molecules needed for plant metabolism and growth. 4.The remaining 10 (3 carbon) molecules are converted back to 6 (5 carbon) molecules like the cycle started with, they will be used to start the cycle over again.

Photosynthesis