Photosynthesis & Cellular Respiration

1. Photosynthesis & Cellular Respiration Chapters 8 and 9

2. Remember... • Autotrophs: • can generate their own food • are the base of many food chains • include plants, bacteria, etc.

3. 8-1 Energy and Life • Autotrophs are any organism that can make their own energy. • Photoautotrophs undergo photosynthesis which changes light energy to chemical energy. – Ex. Plants and cyanobacteria • Chemoautotrophs undergo chemosynthesis which changes inorganic chemicals such as hydrogen sulfate into chemical energy. – Ex. Nitrobacteria

4. Chemical Energy • We use Adenosine Triphosphate (ATP) • Contains adenine, ribose, and 3 phosphate groups. • When ATP loses a phosphate, it becomes ADP (only has 2 phosphates) and energy is released • What does ATP do? • Movement in the cell (organelles) • Moves ions across membranes (sodium and potassium for many reactions)

5. Energy • Most cells only contain small amounts of ATP, they can’t store large amounts • Get new ATP from carbohydrates Where do the carbohydrates get the stored energy?

6. Properties of Light • White light from the sun is composed of a range of wavelengths. • Only 1-3% of light energy is harvested by plants = not very efficient • James Clerk Maxwell- 1st person to recognize electromagnetic spectrum

7. Photosynthesis & Plant parts Chloroplast: Site of photosynthesis in eukaryotic cells. • Thylakoids: Disk shaped membranes containing photosynthetic pigments. Site of light dependent reactions. • Grana: Stacks of thylakoids. • Stroma: Fluid filled space surrounding grana. Site of light independent reactions.

8. Light Collection • Use antenna complexes found in the thylakoid membranes • Chlorophyll is the main pigment that absorbs sunlight. – Chlorophyll absorbs blue light and red light. – It doesn’t absorb green light hence its intense green color. • Accessory Pigments (mop up) Ex: carotenoids (red, blue, black) xanthrophyll (yellow, red) beta carotene (reddish-yellow) *animals don’t make, but can absorb ex: flamingos from shrimp

9. Photosynthesis • Occurs in two stages. – The light-dependent reactions require light to work = Light Reaction – The light-independent reactions do not require light= Dark Reaction

10. Two Main Parts of the Light Dependent Reactions: • Cyclic Photophosphorylation: Excited electrons are cycled through a series of electron acceptors to make ATP. • Noncyclic Photophosphorylation: • Light energizes chlorophyll, which splits H2O (photolysis). The O2 is released to air. • More light energizes another chlorophyll which releases energy to make 2 ATP. • A different wavelength of light energizes another chlorophyll, which then releases energy to make 2 NADPH.

11. Light Dependent ReactionsThylakoid membrane • Plant pigments are organized as photosystems (Pigments surrounding a central chlorophyll a molecule....the reaction center). • Each pigment absorbs a different wavelength of light & transfers its energy to the reaction center which in turn energizes an electron. • The energized electron is then used elsewhere to make ATP or NADPH. • E- that are moving must be replaced by splitting H2O molecules

12. Electron Transport Chain

13. Light Independent Reactions Stroma of Chloroplast • Also known as the Calvin Cycle • They occur whether or not light is present. • The purpose of the reactions is to take the energy from ATP and energized ions from NADPH and add them to carbon dioxide to make glucose or sugar. • uses 6 carbon dioxide molecules to make a single 6-carbon sugar

14. Photosynthesis

15. Photorespiration • Dark Reaction can’t tell difference between oxygen and carbon dioxide. If it uses Oxygen = waste • It is only 30% efficient

16. Factors that Affect Rates- light • At low light intensity, photosynthesis occurs slowly because only a small quantity of ATP and NADPH is created by the light dependent reactions. • As light intensity increases, more ATP and NADPH are created, thus increasing the photosynthetic rate. • At high light intensity, photosynthetic rate levels out, not due to light intensity but due to other limiting factors, including competition between oxygen and carbon dioxide for the active site on RUBP carboxylase.

17. Factors that Affect Rates- carbon dioxide • At high concentrations, the rate of photosynthesis begins to level out due to factors not related to carbon dioxide concentration. • One reason might be that some of the enzymes of photosynthesis are working at their maximum rate. • In general, carbon dioxide is found in low concentration in the atmosphere, and so atmospheric carbon dioxide levels may be a major limiting factor on photosynthesis when at low levels.

18. Factors that Affect Rates- temperature • As temperature increases above freezing, the rate of photosynthesis increases. This occurs because molecules are moving more quickly and there is a greater chance of a collision resulting in a chemical reaction. • At some point, a temperature is reached that is an optimum temperature. The photosynthetic reaction rate is at its quickest rate at this point. • Above that temperature, the enzymes begin to denature, slowing the rate of photosynthesis until a temperature is reached where photosynthesis does not occur at all.

19. Cellular Respiration and Glycolysis • Energy arrives from the sun and is captured by green photosynthetic plants, and stored in the chemical bonds of glucose. • Non‐photosynthetic organisms must obtain their energy by the breakdown of these energy rich storage molecules in order to release the energy for their use. • Photosynthesis stores this energy in glucose; glycolysis and cellular respiration release it. • These are the processes by which cells can "burn" or breakdown glucose into CO2 and H2O and transfer most of the energy to the phosphate bonds of ATP.

20. Cellular Respiration • Glucose > ATP • Anaerobic- w/o O2 • Aerobic- w O2 • C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP

21. Cellular Respiration Fermentation- anaerobic 1. Lactic Acid- muscles don’t have enough O2 Turns pyruvate into lactic acid 2. alcoholic Fermentation- pyruvate into ethanol & CO2