PHOTOSYNTHESIS. blshpbsu

Transcription

1 PHOTOSYNTHESIS blshpbsu

2 Energy needs of life All life needs a constant input of energy Heterotrophs (Animals) get their energy from eating others eat food = other organisms = organic molecules make energy through respiration Autotrophs (Plants) produce their own energy (from self ) convert energy of sunlight build organic molecules (CHO) from CO 2 make energy & synthesize sugars through photosynthesis

3 PHOTOSYNTHESIS

4 Photosynthesis Involves the Use Of light Energy to convert: Water (H 2 0) and Carbon Dioxide (CO 2 ) into Oxygen (O 2 ) and High Energy Carbohydrates (sugars, e.g. Glucose) & Starches 4

5 The Photosynthesis Equation 5

6 PHOTOSYNTHESIS HAPPENS IN CHLOROPLASTS THYLAKOIDS = sac-like photosynthetic membranes inside chloroplast GRANUM (pl. grana) = stack of thylakoids

7 THYLAKOID SPACE Gel-filled space Inside the thylakoid sac SPACES STROMA Gel-filled space inside chloroplast surrounding thylakoid sac cytoplasm Gel-filled space OUTSIDE chloroplast but inside the cell membrane

8 PHOTOSYNTHESIS HAPPENS IN CHLOROPLASTS Proteins that are part of the thylakoid membrane organize Light absorbing PIGMENTS into clusters called PHOTOSYSTEMS

9 Light Light energy from the sun must be captured for photosynthesis to occur. Sunlight is white light actually a mixture of different wavelengths.

10 Chlorophyll Photosynthetic organisms capture energy from sunlight with pigments principally with chlorophyll.

11 Light and Pigments Light contains a mixture of wavelengths Different wavelengths have different colors 11

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13 Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of light chlorophyll a absorbs best in red & blue wavelengths & least in green accessory pigments with different structures absorb light of different wavelengths chlorophyll b, carotenoids, xanthophylls Why are plants green?

14 An Overview of Photosynthesis Photosynthesis uses the energy of sunlight to convert water and carbon dioxide (low-energy reactants) into high-energy sugars and oxygen (products). light Carbon dioxide + Water Sugars + Oxygen 6CO 2 6H 2 O C 6 H 12 O 6 6O 2 + light +

15 Photosynthesis and Light Photosynthesis involves two sets of reactions: Light-dependent reactions Light-independent reactions

16 Light-Dependent Reactions (in Thylakoids!) Light-dependent reactions require the direct involvement of light and light-absorbing pigments. Water: source of electrons Oxygen: byproduct

17 Light-Independent Reactions (in the stroma) Light-independent reactions use ATP and NADPH molecules produced in the light-dependent reactions to produce high-energy sugars from carbon dioxide Carbon Dioxide Sugars and Other carbohydrates

18 Interdependence of Reactions Light-dependent and light-independent reactions have an interdependent relationship.

19 4 Factors that Affect Photosynthesis 1. Carbon Dioxide (CO 2 ) Without CO 2, the plant would not have one of the raw materials needed in the photosynthesis equation CO 2 is used in the first step of the Calvin Cycle 2. Temperature The temperature must be in the appropriate range for the plant in order for photosynthesis to properly occur

20 4 Factors that Affect Photosynthesis 3. Intensity of Light If the intensity of light is lower, the available energy for photosynthesis is lower. In a greenhouse, if the light source is further away, intensity is lower and less photosynthesis can occur If light is not available at all, the light-dependent reactions cannot occur (nor can they provide the materials used in the light-independent reactions)

21 4 Factors that Affect Photosynthesis 4. Water: A shortage of water can slow or stop photosynthesis. Desert plants and conifers that live in dry conditions have a waxy coating on their leaves to prevent water loss.

22 C3, C4 and CAM Plants Do you have friends with bad habits? Maybe they procrastinate a lot, forget your birthday, or never remember to brush their teeth. You wouldn't stop being friends with them for these reasons, yet from time to time, you might find yourself wishing they would clean up their act.

23 C3, C4 and CAM Plants All photosynthetic plants need carbon to build sugars, and all get their carbon from CO 2 in the air. C3 Pathway (most plants): carbon fixation occurs when CO 2 reacts with a five-carbon compound called RuBP (ribulose 1,5-bisphosphate). The product splits immediately to form a pair of three-carbon compounds. C4 and CAM plants are plants that use certain special compounds to gather carbon dioxide (CO 2 ) during photosynthesis. Using these compounds allows these plants to extract more CO 2 from a given amount of air, helping them prevent water loss.

24 C3 Plants Rubisco has a major flaw: instead of always using CO 2 as a substrate, it sometimes picks up O 2 instead. This side reaction initiates a pathway called photorespiration, which, rather than fixing carbon, actually leads to the loss of already-fixed carbon as CO 2. Photorespiration wastes energy and decreases sugar synthesis, so when rubisco initiates this pathway, it's committing a serious molecular faux pas.

25 C4 and CAM Plants C4 plants and CAM plants bind carbon dioxide using a much more efficient enzyme, which allows for a more efficient harvest of CO 2. C4 Plants: hot, dry climates (angiosperms!) Ex: sugar cane, corn CAM Plants: hot, cry climates Ex: cacti, pineapple

26 DAY 2

27 Photosynthesis Light reactions light-dependent reactions energy conversion reactions convert solar energy to chemical energy ATP & NADPH Calvin cycle light-independent reactions sugar building reactions uses chemical energy (ATP & NADPH) to reduce CO 2 & synthesize C 6 H 12 O 6

28 Photosystems (Light Reactions) of photosynthesis 2 photosystems in thylakoid membrane collections of chlorophyll molecules act as light-gathering molecules Photosystem II chlorophyll a P 680 = absorbs 680nm wavelength red light Photosystem I chlorophyll b P 700 = absorbs 700nm wavelength red light reaction center antenna pigments

29 Light reactions chloroplast H +H+ H + H + H +H+ H + H + H+ H + thylakoid H + Electron Transport Chain proteins in organelle membrane NADPH = electron acceptors proton (H + ) gradient across inner membrane + charge on the inside find the double membrane! ATP synthase enzyme ATP H +H+ H + H + H +H+ H + H + H+ H + H +

30 ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP use electron carrier NADPH generates O 2

31 Photosystem II chlorophyll a Photosystem I ETC of Photosynthesis chlorophyll b

32 WHY DOES PHOTOSYSTEM II COME BEFORE PHOTOSYSTEM I? It was discovered and named 1st PHOTOSYSTEM II PHOTOSYSTEM I

33 Experimental evidence Where did the O 2 come from? radioactive tracer = O 18 Experiment 1 6CO 2 + 6H 2 O + light C 6 H 12 O 6 6O energy + 2 Experiment 2 6CO 2 + 6H 2 O + light C 6 H 12 O 6 6O energy + 2 Proved O 2 came from H 2 O not CO 2 = plants split H 2 O!

34 Light-Independent Reactions The second phase of photosynthesis does not require light and is called the Calvin Cycle. The Calvin Cycle occurs in the stroma of the chloroplast.

35 Light-independent Reactions The Calvin Cycle uses the ATP and NADPH that was built during the light-dependent reactions

36 CALVIN CYCLE (OCCURS IN THE STROMA) Calvin Cycle: Series of steps that build up compounds using carbon dioxide from the air. 1. Electrons and ATP from light reaction get dumped into the Calvin Cycle to run it. 2. Energy from ATP and Hydrogen from NADPH combine to form glucose.

37 Calvin Cycle (8E) Click the image to play the video segment.

38 Photosynthesis Equation Light Energy 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 chlorophyll Carbon Dioxide from the air Used in the Calvin Cycle during the Dark Reactions Water Split during Photolysis in the Light Reactions Glucose Made in the Calvin Cycle during the Dark Reactions Oxygen Released during Photolysis in the Light Reactions Plants can use this glucose molecule for energy during Cellular Respiration. Plants can also convert this glucose molecule into other organic compounds such as proteins and fats/lipids or other carbohydrates like starch and cellulose

39 What goes in and out

40 So what do plants do with all the stored glucose (starch)? Growth Repair Reproduction

41 3 Factors that Affect Photosynthesis 1. Carbon Dioxide (CO 2 ) Without CO 2, the plant would not have one of the raw materials needed in the photosynthesis equation CO 2 is used in the first step of the Calvin Cycle 2. Temperature The temperature must be in the appropriate range for the plant in order for photosynthesis to properly occur

42 3 Factors that Affect Photosynthesis 3. Intensity of Light If the intensity of light is lower, the available energy for photosynthesis is lower. In a greenhouse, if the light source is further away, intensity is lower and less photosynthesis can occur If light is not available at all, the lightdependent reactions cannot occur (nor can they provide the materials used in the lightindependent reactions)

43 Concept Map Section 8-3 Photosynthesis includes use take place in takes place in uses to produce of to produce

44 Concept Map Section 8-3 Photosynthesis includes use Lightdependent reactions take place in takes place in Calvin cycle uses Energy from sunlight Thylakoid membranes Stroma ATP NADPH to produce of to produce ATP NADPH O 2 Chloroplasts High-energy sugars