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Chapter 10: Photosynthesis. Essential Knowledge u 2.a.1 – All living systems require constant input of free energy (10.1-10.3). u 2.a.2 – Organisms capture.

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Presentation on theme: "Chapter 10: Photosynthesis. Essential Knowledge u 2.a.1 – All living systems require constant input of free energy (10.1-10.3). u 2.a.2 – Organisms capture."— Presentation transcript:

1 Chapter 10: Photosynthesis

2 Essential Knowledge u 2.a.1 – All living systems require constant input of free energy (10.1-10.3). u 2.a.2 – Organisms capture and store free energy for use in biological processes (10.1-10.3).

3 Photosynthesis u Process by which plants use light energy to make food u A reduction process that makes complex organic molecules from simple molecules

4 Ps General Equation 6 CO 2 + 6 H 2 O  C 6 H 12 O 6 + 6 O 2 u Requires:♦Notice: u Chlorophyll This is VERY u Light similar to the cell resp eq.

5 Ps: a redox process u Hydrogens are added to Carbons-reduces CO 2 to sugar u Water is split; becomes source of hydrogens u Complex covalent bonds made u Requires energy

6 Ps u Has two chemical reactions: 1. Light Reaction 2. Dark Reaction u Names are from “light” as a requirement, not where or when they occur

7 Light u A form of electromagnetic radiation/energy u Visible light has the right energy for use in Ps u Travels in waves

8 Too Hot Too Cold Just Right Detected by our eye-hence the term visible


10 Action Spectrum u Not all colors are useable to the same degree for Ps u RedBlue u Red and Blue light - absorbed and used in Ps u Green u Green light - reflected or transmitted


12 Comment red u In oceans, red light is lost or filtered out early because it has lower energy blue u Only blue light which has higher energy can reach the lower depths

13 Result u Many deep ocean fish are bright red in color. u Why? red u They can’t be seen because there is no red light to reflect their color

14 Photosynthesis Pigments u Pigment: absorb light u Different pigments absorb different wavelengths u Types: u Chlorophylls (a and b) u Accessory Pigments (carotenoids)

15 Chlorophylls u Have C,H,O,N and Mg u Two major types: a, b u Molecule has a lipophilic tail (allows it to dissolve into membranes) u Contains Mg in a reaction center.


17 Accessory Pigments u Absorb light energy and transfer it to chlorophyll u Various shades of yellow/orange u Function: photoprotection u Ex: Carotene (orange) Xanthophyll (yellow)

18 Fall Leaf Colors u Chlorophyll breaks down u N and Mg salvaged and moved into the stem for next year u Accessory pigments remain behind, giving the various fall leaf colors

19 Parts of Plant: Ps function u Stomata u Roots u Mesophyll u Veins


21 Site of Ps u Chloroplast u Contain chlorophyll pigment u All green parts of plants contain chloroplasts u Most are found in leaves u Why? Larger surface area

22 Chloroplast Structure u Double outer membrane u Inner membrane folded and stacked into grana u Stroma - liquid that surrounds the thylakoid membranes


24 Photosystems u Collection of pigments that serve as a light trap u Made of chlorophyll and the accessory pigments u Two types known: u PSI & PSII


26 Parts of Photosystem u 1) Rxn center/e- acceptor u Chlorophyll uses light energy to move e- to next energy level u 2) Pigment u Light absorption, photon acceptor u 3) Light-harvesting complex u Proteins, contain pigment


28 Light Reaction u Same thing as Noncyclic Photophosphorylation u Location - grana of the chloroplast u Function - to split water and produce ATP and NADPH (provide chem energy for next cycle)


30 Light Reaction Requirements: u Light u Water u ADP + Pi u NADP + Products: uO2uO2 u ATP u NADPH

31 Chemiosmosis Model u The chloroplast produces ATP in the same manner as the mitochondria in Rs u Light energy is used to pump H + across a membrane u When the H + diffuses back, ATP is generated

32 Chemiosmosis u H + are pumped into the thylakoid space u ATP and NADPH are made when the H + diffuse into the stroma u Both Rs and Ps use ETC to pump H +

33 Light Rxn Tutorial

34 Dark Reactions u How plants actually make food (carbohydrates) u Don't require light directly to run u Also known as the Calvin cycle or C3 Ps

35 Calvin cycle/Dark reaction u Anabolic – builds sugars from smaller molecules u Function - use ATP and NADPH to build food from CO 2 u Location - stroma of the chloroplast Calvin Cycle movie Calvin Cycle movie

36 Rubisco u Ribulose BisPhosphate Carboxylase u Enzyme that adds CO 2 to an acceptor molecule u Most important enzyme on earth u Catalyzes first step of dark rxn

37 C3 Ps u C3 plants are plants that DO use Rubisco enzyme “normally” u Keep stomata open during day u MOST plants are C3 plants u When you “think of Ps”, you think of a C3 plant performing Ps u Adaptive value: Require less u Less enzyme activity, no specialized organs/anatomy

38 Photorespiration u When Rubisco accepts O 2 instead of CO 2 as the substrate u Generates no ATP u Actually uses ATP u Decreases Ps output by as much as 50%

39 Photorespiration u May reflect a time when O 2 was less plentiful and CO 2 was more common u Important to evolution of autotrophs u Photo=occurs in light u Respiration=consumes oxygen while producing CO 2

40 Alternate Ps Methods 1. C4 Ps 2. CAM Ps

41 Intro to C4 and CAM u Remember: MOST plants are C3 plants that performs Ps “normally” u Both are adaptations to arid conditions u CAM plants “idle” and save energy while C4 plants go through Ps faster

42 C4 Ps u Uses a different enzyme to initially capture CO 2 u Separates CO 2 capture from carbon fixation into sugar u Still uses C3 Ps to make sugar, but only does so in the bundle sheath cells

43 C4 Ps u Found in 19 plant families u Characteristic of hot regions with intense sunlight u Examples - sugarcane, Bermuda grass, crab grass

44 C3 Ps vs C4 Ps u Can use photorespiration u Shade to full sun u High water use u Cool temperatures u Slow to moderate growth rates u Cool season crops u No Photorespiration u Full sun only u Moderate water use u Warm temperatures u Very fast growth rates u Warm season crops

45 CAM plants u Found in plants from arid conditions (where water stress is a problem) u Avoid H 2 O stress by keeping stomates closed during the day u Generally have slow growth u Ex: pineapple, cacti, orchids

46 CAM Plants, cont. u Store CO 2 as C4 acid u During the day, the acid is broken down and CO 2 is made into sugar.


48 Ps:Rs Ratios u Reflect a plant’s balance in making food and using food 1. Ps > Rs, energy available for growth and reproduction 2. Ps = Rs, no growth, but don’t die either 3. Ps < Rs, death by starvation

49 Comments - Ps:Rs u Rs happens 24 hours a day u Ps only in light u Plants overwinter on stored food when Ps > Rs u If Ps < Rs, best solution is to increase the amount of light

50 Factors Affecting Ps 1. Light - quantity and quality 2. Temperature - too hot or too cold 3. CO 2 - often limits C3 plants 4. Minerals - especially NPK and Mg

51 Importances of Ps 1. Food - either directly or indirectly comes from plants 2. Oxygen in the air 3. CO 2 balance 4. Plant products 5. Life on Earth

52 Summary u Identify the basic equation of photosynthesis. u Identify the main reactions of photosynthesis. u Recognize the function, location, requirements and products of the photosynthesis reactions. u Recognize the role of light and pigments in the photosynthesis process. u Recognize the effects and importance of photorespiration. u Recognize various types of photosynthesis and their importance. u Identify the biological and economic importance of photosynthesis.


54 Exclusion Statements u You do NOT need to memorize the steps in the Calvin Cycle, the structure of the molecules, and the names of the enzymes (except ATP synthase).

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