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Chapter 8: Photosynthesis Mr. Wilmot. Part I- Photosynthetic structures And Overview 1.Where it takes place 2.What structures are involved and what are.

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Presentation on theme: "Chapter 8: Photosynthesis Mr. Wilmot. Part I- Photosynthetic structures And Overview 1.Where it takes place 2.What structures are involved and what are."— Presentation transcript:

1 Chapter 8: Photosynthesis Mr. Wilmot

2 Part I- Photosynthetic structures And Overview 1.Where it takes place 2.What structures are involved and what are the raw material and products

3 Photosynthesis takes place in the mesophyll cells of the leaf Mesophyll

4 Each Mesophyll Cell contains many Chloroplasts Also, CO 2 comes into, and O 2 Leaves the cell through the stoma. Water gets to, and Glucose leaves through the Xylem and Phloem CO 2 O2O2 Water Glucose

5 The Chloroplast- Contains Chlorophyll- a light absorbing pigment Chlorophyll is actually located on the membrane of the thylakoid ___________ (Stack of Thylakoid) ____________________ Aqueous Place Inside Chloroplast GranumThylakoidStroma

6 Chlorophyll and Chloroplasts 1.Light- energy from the sun that travels to earth comes in different wavelengths a. The visible part of this spectrum appears as different colors

7 Pigments- light absorbing molecules that captures energy from the sun Chlorophyll- the plants principle pigment  Include Chlorophyll A and Chlorophyll B  There are other accessory pigment that augment the primary pigment allowing for more energy to be absorbed  Include carotenoids and xanthophylls

8 Chlorophyll absorbs light very well in the blue-violet and red wavelengths It does not absorb green wavelengths, instead it reflects these wavelengths

9 Chloroplasts- site of photosynthesis a.Thylakoids- sac-like photosynthetic membranes Arranged in stacks called Grana Contain pigments- chlorophyll b. Stroma- the fluid inside the chloroplast Chloroplast Anatomy

10 Energy Collection Light is energy Pigments absorb light and energy Light energy is transferred directly to electrons in the chlorophyll molecule The raising of energy levels of electrons is the driving force of photosynthesis

11 High Energy Electrons Chemically, the high energy electrons produced by chlorophyll require a special carrier Analogy: Hot potato, oven mitt = special carrier Electron carriers are the so called oven mitt, transferring these electrons from the chlorophyll to other molecules

12 NADP+: is an electron carrier Function- accepts and holds two high energy electrons along with a hydrogen ion (H+). This converts NADP+ to NADPH Used to help build carbohydrates

13 An Overview of Photosynthesis

14 Light-Dependent Reactions Equation is a simplified form of photosynthesis; actually requires many steps to get from light to carbohydrates Actually involves 2 sets of reactions – Light depedendent – Light independent

15 Light dependent- set of reactions in photosynthesis that use energy from light to produce ATP and NADPH Require light and light absorbing pigments These reactions take place within the thylakoids of chloroplasts Water is need for these reactions as a source of electrons and H+ Oxygen is released as a bi-product Light phase reactions animation Confused? Check this out…..

16 Light Independent Reactions – a.k.a. “The Dark Side”, er Phase a. Plants absorb CO 2 from the atmosphere and complete the process of photosynthesis b. ATP and NADPH produced in the “light phase” reactions are used to produce high energy sugars…. with the addition of CO2. Dark Phase Animation

17 c. No light is required d. Reactions occur in the stroma (liquid outside of thylakoid) e. Reliant on the light phase for materials f. Both light and dark phases work together to create energy-rich carbohydrates

18 End of Part 1

19 The Process of Photosynthesis Light-Dependent Reactions: Generating ATP and NADPH Summary: The light dependent reactions use energy from sunlight to produce oxygen and convert ADP and NADP+ into the energy carriers ATP and NADPH These carriers provide energy needed to build high-energy sugars from low-energy carbon dioxide

20 The Light-Dependent Reaction Takes Place on the membrane of the Thylakoid

21 Light-Dependent Reactions It happens in two parts called photosystems: 1- Photosystem 2 2- Photosystem 1

22 Light-Dependent Reactions a. Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level. Photosystem II

23 Light-Dependent Reactions These high-energy electrons are passed on to the electron transport chain. Photosystem II Electron carriers High-energy electron

24 Light-Dependent Reactions b. Enzymes on the thylakoid membrane break water molecules into: Copyright Pearson Prentice Hall Photosystem II 2H 2 O Electron carriers High-energy electron

25 Light-Dependent Reactions – hydrogen ions – oxygen atoms – energized electrons Photosystem II 2H 2 O + O 2 Electron carriers High-energy electron

26 Light-Dependent Reactions Photosystem II 2H 2 O + O 2 c. The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain. High-energy electron

27 Light-Dependent Reactions Photosystem II 2H 2 O d. As plants remove electrons from water, oxygen is left behind and is released into the air. + O 2 High-energy electron

28 Light-Dependent Reactions Photosystem II 2H 2 O e. The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane. + O 2 High-energy electron

29 Light-Dependent Reactions Photosystem II 2H 2 O f. Energy from the electrons is used to transport H + ions from the stroma into the inner thylakoid space. + O 2 Outside Thylakoid Inside Thylakoid

30 Light-Dependent Reactions Photosystem II 2H 2 O g. High-energy electrons move through the electron transport chain from photosystem II to photosystem I. + O 2 Photosystem I

31 Light-Dependent Reactions 2H 2 O h. Pigments in photosystem I use energy from light to re-energize the electrons. + O 2 Photosystem I

32 Light-Dependent Reactions 2H 2 O i. NADP + then picks up these high-energy electrons, along with H + ions, and becomes NADPH. + O 2 2 NADP + 2 NADPH 2

33 Light-Dependent Reactions 2H 2 O j. As electrons are passed from chlorophyll to NADP +, more H + ions are pumped across the membrane. + O 2 2 NADP + 2 NADPH 2

34 Light-Dependent Reactions 2H 2 O k. Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged. + O 2 2 NADP + 2 NADPH 2

35 Light-Dependent Reactions 2H 2 O The difference in charges across the membrane provides the energy to make ATP. + O 2 2 NADP + 2 NADPH 2

36 Light-Dependent Reactions 2H 2 O H + ions cannot cross the membrane directly. + O 2 ATP synthase 2 NADP + 2 NADPH 2

37 Light-Dependent Reactions 2H 2 O The cell membrane contains a protein called ATP synthase that allows H + ions to pass through it. + O 2 ATP synthase 2 NADP + 2 NADPH 2

38 Light-Dependent Reactions 2H 2 O l. As H + ions pass through ATP synthase, the protein rotates. + O 2 ATP synthase 2 NADP + 2 NADPH 2

39 Light-Dependent Reactions 2H 2 O m. As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP. + O 2 2 NADP + 2 NADPH 2 ATP synthase ADP

40 Light-Dependent Reactions 2H 2 O Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well. + O 2 ATP synthase ADP 2 NADP + 2 NADPH 2

41 2H 2 O + O 2 ATP synthase ADP 2 NADP + 2 NADPH 2

42 End of Part 2

43 B. The Calvin Cycle Also called the light independent (aka Calvin cycle, aka “dark phase”)reactions ATP and NADPH formed by the light- dependent reactions contain an abundance of chemical energy, but they are not stable enough to store that energy for more than a few minutes. 3. During the Calvin cycle plants use the energy that ATP and NADPH contain to build high-energy compounds that can be stored for a long time.

44 The Calvin Cycle

45 a. Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5- carbon molecules. CO 2 Enters the Cycle

46 b. The result is twelve 3-carbon molecules, which are then converted into higher- energy forms.

47 The Calvin Cycle The energy for this conversion comes from ATP and high-energy electrons from NADPH. 12 NADPH ADP 12 NADP + Energy Input

48 c. Two of twelve 3-carbon molecules are removed from the cycle. Energy Input 12 NADPH ADP 12 NADP +

49 The 2 removed molecules are used to produce sugars, lipids, amino acids and other compounds. 12 NADPH ADP 12 NADP + 6-Carbon sugar produced Sugars and other compounds

50 d. The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle. 12 NADPH ADP 12 NADP + 5-Carbon Molecules Regenerated Sugars and other compounds 6 6 ADP

51 The Calvin Cycle – The two sets of photosynthetic reactions work together. a. The light-dependent reactions trap sunlight energy in chemical form. b. The light-independent reactions use that chemical energy to produce stable, high- energy sugars from carbon dioxide and water.

52 C. Factors Affecting Photosynthesis 1. Temperature, Light, and Water a.Temperature – Among most important factors that affect photosynthesis are temperature, light intensity, and availability of water.

53 – Reactions made possible by enzymes that function best b/w 0 o C and 35 o C – Above or below these temps could slow down rate of photosynthesis – Low temps, may stop entirely

54 b. Light – Intensity of light affects rate of photosynthesis – High light intensity increases rate of photosynthesis – After intensity reaches a certain level, plant reaches maximum rate of photosynthesis

55 c. Water – Water is one of raw materials of photosynthesis – Shortage of water can slow or stop photosynthesis – Water loss can damage plant tissues – Plants that live in dry conditions often have waxy coatings on leaves to reduce water loss – May also have biochemical adaptations that make photosynthesis more efficient under dry conditions

56 2. Photosynthesis Under Extreme Conditions a. To conserve water: plants in bright, hot conditions close small openings in leaves that normally admit carbon dioxide – Keeps plants from drying out – Causes carbon dioxide w/in leaves to fall to very low levels – Photosynthesis slows down or stops

57 3. C4 Photosynthesis a. Specialized chemical pathway that allows them to capture very low levels of carbon dioxide to pass it on to Calvin cycle 1 st compound formed in pathway contains 4 carbon atoms c. Enables photosynthesis to keep working under intense light and high temperatures d. Requires extra energy in form of ATP to function e. Examples: corn, sugar cane, sorghum Animation

58 4. CAM Plants a. Carbon dioxide becomes incorporated into organic acids during photosynthesis – Process called Crassulacean Acid Metabolism b. Admit air into leaves only at night c. In cool darkness, carbon dioxide is combined w/ existing molecules to produce organic acids, “trapping” carbon w/in leaves d. During daytime, leaves tightly sealed to prevent loss of water  compounds release carbon dioxide  enable carbohydrate production Examples: pineapple, cacti, “ice plants” (near freeways along west coast to retard brush fires and prevent erosion)


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