Chapter 8 - Photosynthesis Energy

1. CHAPTER 8 - PHOTOSYNTHESIS

3. ENERGY Energy is the ability to do work. • All living things depend on energy. • Energy comes in the form of light, heat, electricity, or sound. • Energy can be stored in chemical compounds.

4. ATP • ATP (adenosine triphosphate) is the energy currency of cells. • Used to store and release energy in cells. • Consists of adenine (a nucleotide), ribose (a sugar or carbohydrate), and three phosphate groups. • Release of energy – by breaking the chemical bonds to convert ATP into ADP. • Storage of energy – by creating a chemical bond between ADP and P to create ATP. • Energy used for active transport, protein synthesis, homeostasis, etc.

5. Autotrophs and Heterotrophs • Autotrophs are organisms that make their own food. • Use light energy from the sun to produce food • Plants are examples of autotrophs. • Heterotrophs obtain energy from the food they consume. • Unable to directly use the sun’s energy. • Must consume other organisms either by ingesting (eating) them or decomposing them. • Animals are examples of heterotrophs.

6. The Photosynthesis Equation • Photosynthesis is the process whereby plants use the energy of sunlight to convert water and carbon dioxide into oxygen and high-energy carbohydrates. • Carbon dioxide +water  sugar and oxygen • In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts.

7. The Photosynthesis Equation 3 Requirements for Photosynthesis: Sunlight Pigments Energy storing compounds

8. 1. LIGHT • Light travels to the Earth in the form of sunlight • We perceive sunlight as white light, but is really a mixture of many different wavelengths of light • Wavelengths of light that are visible to us are known as the visible light spectrum

9. 2. PIGMENTS • Pigments are light absorbing molecules that help plants gather the sun’s energy • The main pigment found in plants is chlorophyll • Chlorophyllabsorbs red and blue wavelengths of light, but it reflects green making the plant appear green • When the pigments absorb light they are also absorbing the energy in that light, producing more energy for the cell

10. INSIDE A CHLOROPLAST • Photosynthesis takes place in chloroplasts. • Chloroplasts contain saclike photosynthetic membranes called thylakoids. • Thylakoids contain clusters of chlorophyll and other pigments and proteins known as photosystems that are able to capture sunlight. • Light dependent reactions take place here. • Thylakoids are arranged in stacks known as grana. • The region outside the thylakoid membrane is called the stroma. • Light independent (dark) reactions take place here.

12. 3. Energy Storing Compounds • Used to trap high energy electrons into chemical bonds. • Occurs in 2 ways: • 1. Electron carrier NADP+ accepts a pair of high energy electrons and gets converted to NADPH. • 2. AMP is converted to ADP which is then converted to ATP. • NOTE: The energy stored in these molecules is released by breaking chemical bonds to generate things the cell needs, like glucose!

13. Light and Dark Rxns • Light-dependent reactions produce oxygen and make energy storing compounds (ATP and NADPH). • Occurs by converting ADP and NADP+ into ATP and NADPH. • These reactions REQUIRE light. • Light-independent (dark) reactions use the energy stored in NADPH and ATP to make glucose. • Glucose is more stable and can store up to 100 times more energy than NADPH and ATP. • These reactions do not require light.

14. Light Dependent Rxns • Photosynthetic membranes of chloroplast (thylakoids) contain chlorophyll. • This is where the light reactions occur. • The light reactions are divided into 4 processes: • 1. Light absorption • 2. Electron transport • 3. Oxygen production • 4. ATP production

15. 1. Light Rxns - Light absorption • Green plants contain photosystems. • Clusters of pigment molecules that absorb energy from sunlight. • High energy electrons move through the photosystems and are then released to electron carriers.

16. 2. Light Rxns - electron transport • During electron transport, high energy electrons are passed along electron carriers in the photosynthetic membrane. • These carriers are called the electron transport chain. • At the end of the chain, high energy electrons are passed to NADP+ converting it to NADPH.

17. 3. Light Rxns - Oxygen Production • Electrons are getting used up by chlorophyll and must be replaced! • This occurs by taking electrons from water to replace those used by chlorophyll. • Electrons are removed from water molecules leaving H+ ions and oxygen. • Oxygen is a by-product of the splitting of water by is NEEDED by us!

18. 4. Light Rxns - ATP production • Because hydrogen (H+) ions were released inside the thylakoid membrane as a product of the splitting of water molecules, the inside of the membrane becomes positively charged, while the outside is negatively charged. • This difference in charges creates a gradient that provides the energy to make ATP from ADP. • ATP synthase – enzyme in thylakoid membrane that binds a P to ADP to create ATP.

19. Light Rxns - SUMMARY • The light reactions USE: water, light energy, chlorophyll pigments • The light reactions PRODUCE: oxygen, NAPDH, ATP

20. Dark Rxns -The Calvin Cycle • ATP and NADPH can hold large amounts of chemical energy, but only for a few minutes. • The Calvin Cycle uses CO2as well as ATP and NADPH from the light-dependent reactions to produce glucose that can be stored in the plant for long periods of time. • This process does not require light, but often takes place while the sun is shining.

21. Calvin Cycle • Carbon dioxide molecules enter the cycle from the atmosphere. • The carbon dioxide molecules combine with 5-carbon molecules. • This reaction is catalyzed by the enzyme rubisco. • The result is 3-carbon molecules.

22. Calvin Cycle • The energy from breaking ATP into ADP and NADPH into NADP+ is used to convert the 3-carbon molecules into PGAL. • Most PGAL is recycled. • 1 of 6 PGAL molecules formed is used to make glucose. • Plants use glucose for energy. • Organisms that eat plants indirectly also use this energy from glucose.

23. Calvin Cycle - SUMMARY • Calvin Cycle USES: NADPH, ATP ,CO2 • Calvin cycle PRODUCES: glucose (C6H12O6)

24. 3 factors affect photosynthesis • 1. Temperature – enzymes that control the reactions of photosynthesis work best at 0-35 degrees C. • 2. Light – higher is better. • 3. Water – a raw material; shortage slows or stops photosynthesis and damages plant tissues.