1. Photosynthesis

2. Overview Photosynthesis is the process that converts solar energy (sunlight) into chemical energy (glucose) Photosynthesis is the process that converts solar energy (sunlight) into chemical energy (glucose) –Directly or indirectly, photosynthesis nourishes almost the entire living world

3. Autotrophs make their own food Autotrophs make their own food –Live without eating anything from other organisms –Are the producers of the biosphere, producing organic molecules from CO 2 and other inorganic molecules  Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules from H 2 O and CO 2

4. Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes –These organisms feed not only themselves but also most of the living world BioFlix: Photosynthesis BioFlix: Photosynthesis Plants Multicellular alga Unicellular protist Cyanobacteria Purple sulfur bacteria

5. Heterotrophs obtain their energy from the foods they consume Heterotrophs obtain their energy from the foods they consume –Get their energy from organisms they eat –Are the consumers of the biosphere  Almost all heterotrophs, including humans, depend on photoautotrophs for food and O 2

6. How is energy obtained? How is energy obtained? –High–energy bonds break –Replaced by low–energy bonds –Extra energy is released  Some stored in ATP  Some released as heat ATP (adenosine triphosphate) ATP (adenosine triphosphate) –Used to store and release energy in the cell –Made of adenine, ribose (5-carbon sugar), and 3 phosphate groups

7. ADP (adenosine diphosphate) ADP (adenosine diphosphate) –When energy is available, small amounts are stored by adding a phosphate group to ADP  Making ATP Releasing energy when needed is the reverse reaction Releasing energy when needed is the reverse reaction –The high–energy bond is broken between the second (2 nd ) and third (3 rd ) phosphates

8. How much ATP does a cell contain? How much ATP does a cell contain? –Only a small amount of ATP is at hand  Enough for a few seconds of activity Why? Why? –An ATP molecule is good for energy transfer and NOT for storing over long periods of time What is the energy storage molecule? What is the energy storage molecule? –Glucose is the storage molecule  More than 90 times the chemical energy of ATP  Cells can regenerate ATP from ADP as needed

9. Photosynthesis Photosynthesis –Plants use sunlight (solar energy) to convert water (H 2 O) and carbon dioxide (CO 2 ) into high–energy carbohydrates (sugars: mainly glucose C 6 H 12 O 6 and starches: complex sugars) and oxygen (O 2 ) 6 CO 2 + 12 H 2 O C 6 H 12 O 6 + 6 O 2 + 6 H 2 O Sunlight (Solar energy)

10. How do plants capture solar energy? How do plants capture solar energy? –Requires chloroplasts and the chlorophyll within  Chlorophyll: a green pigment that absorbs light energy  Pigment: light–absorbing molecules

11. Our eyes see light as “white” light Our eyes see light as “white” light –Light is actually a mixture of different wavelengths  The different wavelengths your eyes can see make up the visible spectrum and produce different colors –Different pigments absorb different wavelengths –Wavelengths not absorbed are reflected/transmitted back

12. Chlorophyll is the major pigment of plants Chlorophyll is the major pigment of plants –Two types of chlorophyll  Chlorophyll a –Major photosynthetic pigment –Absorbs well in the blue-violet and red regions –Little is absorbed in the green region  Reflects back (this is why plants are green)  Chlorophyll b –Broadens the absorbing range –Another pigment is carotene  Red and orange pigments –Absorbs light in other regions

13. Any compound that absorb light absorbs the energy from the light Any compound that absorb light absorbs the energy from the light –After chlorophyll absorbs light  Much of the energy is transferred directly to electrons –Energy levels are raised making them high–energy electrons Animation: Light and Pigments Animation: Light and Pigments

14. A spectrophotometer measures a pigment’s ability to absorb various wavelengths A spectrophotometer measures a pigment’s ability to absorb various wavelengths –This machine sends light through pigments and measures the fraction of light transmitted at each wavelength

15. Leaves are the major location of photosynthesis Leaves are the major location of photosynthesis –Their green color is from the chlorophyll –Light energy absorbed by chlorophyll drives the synthesis of organic molecules (sugars) CO 2 enters and O 2 exits the leaf through microscopic pores called stomata CO 2 enters and O 2 exits the leaf through microscopic pores called stomata

16. Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf –A typical mesophyll cell has 30–40 chloroplasts Photosynthesis occurs inside chloroplasts Photosynthesis occurs inside chloroplasts –The chlorophyll is in the membranes of thylakoids found in the chloroplast  Saclike photosynthetic membranes –Newspapers –Thylakoids are arranged in columns called grana (granum: singular)  Stack of newspapers

17. Proteins within the thylakoid membrane organize pigments, including chlorophyll, into photosystems Proteins within the thylakoid membrane organize pigments, including chlorophyll, into photosystems –Photosystems are the light–collecting units Chloroplasts also contain stroma Chloroplasts also contain stroma –A dense fluid

18. Photosynthesis Reactions 2 types of reactions 2 types of reactions –Light–dependent reactions  Photo part  Requires light –Summary: uses light to produce oxygen (O 2 ) gas, ATP and NADPH –Light–independent reactions (Calvin cycle)  Synthesis part  Does not require light –Summary: uses CO 2, ATP and NADPH to produce sugar

19. All reactions occur within the chloroplast All reactions occur within the chloroplast –Light–dependent reactions: within the thylakoid membrane –Calvin cycle: in the stroma

20. Electron transport chain (ETC) Electron transport chain (ETC) –When electrons (e ─ ) gain energy from sunlight, they require a special carrier  High–energy electrons are too hot to handle  Electron transport: carrier molecules accept a pair of high–energy electrons and transfer (carry) them to other molecules –Electron carriers are the electron transport chain  NADP + (nicotinamide adenine dinucleotide phosphate) –Accepts and holds 2 high–energy e ─ s as well as a hydrogen ion (H + ) –Converts NADP + to NADPH  Traps some sunlight into chemical form NADP + NADPH 2 e ─ + H +

21. Light H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2 (sugars)

22. Light–dependent reactions Light–dependent reactions –Uses light energy to produce O 2 as a by–product and ATP and NADPH for use later –Step 1: pigments in photosytem II absorb light through electrons (increasing their energy)  These high–energy electrons are transported by the ETC  How are electrons available? –Split H 2 O molecules into 2 electrons, 2 hydrogen ions, and 1 oxygen  Oxygen is released to the atmosphere  Hydrogen ions are released inside the thylakoid membrane  Electrons released replace those electrons lost to the ETC

23. –Step 2: high–energy electrons move through the ETC from photosystem II to photosystem I  This energy is used in the ETC to transport H + ions into the inner thylakoid space

24. –Step 3: pigments in photosystem I use light energy to reenergize electrons  NADP + picks up these high–energy electrons with H + ions

25. –Step 4: as electrons pass from chlorophyll to NADP +  H + ions are pumped across the membrane –Making the inside of the membrane fill with a positive (+) charge –Making the outside of the membrane more negatively (-) charged  Differences across the membrane provides energy to make ATP

26. –Step 5: H + cross the membrane only through ATP synthase  As H + crosses, ATP synthase rotates –As it rotates, ATP synthase binds ADP and a phosphate group to make ATP

27. Calvin cycle Calvin cycle –Uses the energy of ATP and NADPH (short – term storage) to build high – energy compounds (sugars) for long time storage –Step 1: 6 CO 2 enter from the atmosphere combine with 3 – carbon (C) molecules to produce 12 3 – C molecules –Step 2: 12 3 – C molecules converted to high – energy forms through ATP and NADPH –Step 3: 2 3 – C molecules are removed from the 12 3 – C molecules  Used to make sugars among other compounds need by the plant for growth and metabolism –Step 4: 10 3 – C molecules converted back to the 6 5 – C molecules –The cycle continues The sugars made The sugars made –Used to meet the energy needs of the plant –Used to build complex macromolecules such as cellulose and starch 6 CO 2 6 C-C-C-C-C 12 C-C-C 2 C-C-C 10 C-C-C C-C-C-C-C-C glucose (sugar) 12 ATP 12 ADP 12 NADPH 12 NADP + 6 ATP 6 ADP

28. Rate of photosynthesis Rate of photosynthesis –Water shortage  May slow or even stop photosynthesis  Adaptations: waxy coating to reduce water loss –Temperature  Too low or high: slows down photosynthesis –Enzymes function best between 0°C and 35°C –Light intensity  Increasing light = increased photosynthesis –Until photosynthesis rate is maximized (highest it can go)