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PHOTOSYNTHESIS. Photosynthesis process by which green plants & some organisms –s–seaweed, algae & certain bacteria use light energy to convert CO 2 +

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Presentation on theme: "PHOTOSYNTHESIS. Photosynthesis process by which green plants & some organisms –s–seaweed, algae & certain bacteria use light energy to convert CO 2 +"— Presentation transcript:


2 Photosynthesis process by which green plants & some organisms –s–seaweed, algae & certain bacteria use light energy to convert CO 2 + water glucose all life on Earth, directly or indirectly, depends on photosynthesis as source of food, energy & O 2


4 Autotrophs self feeders –organisms that make their own organic matter from inorganic matter –producers need inorganic molecules such as CO 2, H 2 O & minerals to make organic molecules

5 Heterotrophs consumers –other feeders depend on glucose as energy source –cannot produce it obtained by eating plants or animals that have eaten plants

6 Carbon and Energy Flow CO 2 + H 2 O Carbs Proteins Lipids + O 2 Photosynthesis Cellular (Aerobic) Respiration ( ATP Produced )

7 Food Chain byproduct of photosynthesis is O 2 humans & other animals breathe in oxygen used in cellular respiration

8 Other Benefits of Photosynthesis humans depend on ancient products of photosynthesis fossil fuels –natural gas, coal & petroleum –for modern industrial energy represent remains of organisms that relied on photosynthesis millions of years ago

9 Photosynthesis plants produce more glucose than they use Stored –starch & other carbohydrates in roots, stems & leaves

10 Sites of Photosynthesis leaves & green stems cell organelles –chloroplasts concentrated in green tissue of leaf mesophyll green due to presence of green pigment chlorophyll

11 Chloroplasts each cell has chloroplasts –oval-shaped structures with double membrane inner membrane encloses compartment filled with stroma suspended in stroma are disk- shaped compartments- thylakoids –arranged vertically like stack of plates one stack-granum (plural, grana) embedded in membranes of thylakoids are hundreds of chlorophyll molecules

12 Chlorophyll light- trapping pigment

13 How Photosynthesis Works Requires –CO 2 –Water –Sunlight Makes –O2–O2 –Glucose

14 How Photosynthesis Works CO 2 enters plant via pores- stomata in leaves water-absorbed by roots from soil membranes in chloroplasts provide sites for reactions of photosynthesis chlorophyll molecules in thylakoids capture energy from sunlight chloroplasts rearrange atoms of inorganic molecules into sugars & other organic molecules

15 Photosynthesis redox reaction 6CO H 2 O C 6 H 12 O 6 + 6O 2 + 6H 2 O in presence of light must be an oxidation & a reduction water is oxidized –loses electrons & hydrogen ions carbon dioxide is reduced –gains electrons & hydrogens

16 Photosynthesis relies on a flow of energy & electrons initiated by light energy light energy causes electrons in chlorophyll pigments to boost electrons up & out of orbit hydrogens along with electrons are transferred to CO 2 sugar requires that H 2 O is split into H & O 2 –O 2 escapes to air light drives electrons from H 2 O to NADP + which is oxidized NADPH which is reduced


18 Photosynthesis 2 stages light-dependent reactions –chloroplasts trap light energy –convert it to chemical energy –contained in nicotinamide adenine dinucleotide phosphate-(NADPH) & ATP –used in second stage light-independent reactions –Calvin cycle –formerly called dark reactions –NADPH (electron carrier) provides hydrogens to form glucose ATP provides energy

19 Light Dependent Reactions convert light energy to chemical energy & produce oxygen takes place- thylakoid membranes solar energy absorbed by chlorophyll ATP + NADPH

20 Light Energy for Photosynthesis sun energy is radiation –electromagnetic energy travels as waves distance between 2 waves- wavelength light contains many colors each has range of wavelengths measured in nanometers range of wavelengths is electromagnetic spectrum part seen by humans –visible light

21 Pigments light absorbing molecules built into thylakoid membranes absorb some wavelengths & reflect others plants appear green because chlorophyll-does not absorb green light –reflected back. as light is absorbed energy is absorbed chloroplasts contain several kinds of pigments different pigments absorb different wavelengths of light red & blue wavelengths are most effective in photosynthesis other pigments are accessory pigments absorb different wavelengths enhance light-absorbing capacity of a leaf by capturing a broader spectrum of blue & red wavelengths along with yellow and orange wavelengths

22 Pigment Color & Maximum Absoption Violet: nm Indigo: nm Blue: nm Green: nm Yellow: nm Orange: nm Red: nm

23 Chlorophylls Chlorophyll A –absorbs blue-violet & red light –reflects green –participates in light reactions Chlorophyll B –absorbs blue & orange light –reflects yellow-green –does not directly participate in light reactions –broadens range of light plant can use by sending its absorbed energy to chlorophyll A

24 Carotenoids yellow-orange pigments absorb blue-green wavelengths reflect yellow-orange pass absorbed energy to chlorophyll A protective function –absorb & dissipate excessive light energy that would damage chlorophylls

25 Light Energy light behaves as discrete packages of energy called photons fixed quantity of energy

26 when pigment absorbs a photon pigments electrons gains energy electrons are excited unstable electrons do not stay in unstable state fall back to original orbits as electrons fall back to ground heat is released absorbed energy is passed to neighboring molecules

27 Photosynthesis Pigments Absorb light Excites electrons Energy passed to sites in cell Energy used to make glucose

28 Photosystems chlorophyll & other pigments are found clustered next to one another in a photosystem two participate in light reactions

29 Photosystems photosystem I & II each has specific chlorophyll at reaction center photosystem II –chlorophyll P680 photosystem I –chlorophyll P700 named for type of light they absorb best P700 absorbs light in far red region of electromagnetic spectrum

30 Reaction Center when photon strikes one pigment molecule energy jumps from pigment to pigment until arrives at reaction center electron acceptor traps a light excited electron from reaction center chlorophyll passes it to electron transport chain which uses energy to make ATP & NADPH

31 Reaction Center

32 Light Reactions during process of making ATP & NADPH electrons are removed from molecules of water passed from photosystem II to photosystem I to NADP +

33 Photosystem II water is split oxygen atom combines with oxygen from another split water forming molecular oxygen-O 2 each excited electron passes from photosystem II to photosystem I via electron transport chain


35 Photosystem I primary electron acceptor captures an excited electron excited electrons are passed through short electron transport chain to NADP + reducing it to NADPH NADP + is final electron acceptor electrons are stored in high state of potential energy in NADPH molecule NADPH, ATP and O 2 are products of light reactions

36 ATP Formation- Chemiosmosis uses potential energy of hydrogen ion concentration gradient across membrane gradient forms when electron transport chain pumps hydrogen ions across thylakoid membrane as it passes electrons down chain that connects two photosystems

37 ATP Formation-Chemiosmosis ATP synthase (enzyme) uses energy stored by H gradient to make ATP ATP is produced from ADP & P i when hydrogen ions pass out of thylakoid through ATP synthase photophosphorylation

38 Chemiosmosis H+H+ H+H+ pH 7 pH 8

39 Substrate-level Phosphorylation

40 Calvin Cycle light independent reactions depend on light indirectly to obtain inputs for cycle-ATP & NADPH takes place in stroma of chloroplast cycle of reactions makes sugar from CO 2 & energy ATP provides chemical energy NADPH provides high energy electrons for reduction of CO 2 to sugar

41 Steps of Calvin Cycle starting material-ribulose bisphosphate (RuBP) first step-carbon fixation rubisco (an enzyme) attaches CO 2 to RuBP Next-reduction reaction takes place NADPH reduces 3-phosphoglyceric acid (3-PGA) to glyceraldehye 3- phosphate (G3P) with assistance of ATP to do this cycle uses carbons from 3 CO 2 molecules to complete cycle must regenerate beginning component-RuBP for every 3 molecules of CO 2 fixed, one G3P molecule leaves cycle as product of cycle remaining 5 G3P molecules are rearranged using ATP to make 3 RuBP molecules


43 Calvin Cycle regenerated RuBP is used to start cycle again process occurs repeatedly as long as CO 2, ATP & NADPH are available thousands of glucose molecules are produced used by plants to produce energy in aerobic respiration used as structural materials stored

44 Photosynthesis Variations plants vary in the way they produce glucose and when

45 C3 Plants use CO 2 directly from air first organic compound produced is a 3 carbon compound 3-PGA reduce rate of photosynthesis in dry weather CO 2 enters plants through pores in leaves on hot days stomata in leaves close partially to prevent escape of water with pores slightly open, adequate amounts of CO 2 cannot enter leaf Calvin cycle comes to a halt no sugar is made in this situation rubisco adds O 2 to RuBP 2-carbon product of this reaction is broken down by plant cells to CO 2 + H 2 0 Photorespiration provides neither sugar nor ATP

46 C4 Plants have special adaptations allowing them to save water without shutting down photosynthesis corn, sugar cane & crabgrass evolved in hot, dry environments when hot & dry stomata are closed saves water sugar is made via another route developed way to keep CO 2 flowing without capturing it directly from air

47 C4 Plants have enzymes that incorporate carbon from CO 2 into 4-C compound enzyme has an intense desire for CO 2 can obtain it from air spaces even when levels are very low 4-C compound acts as a shuttle transfers CO 2 to nearby cells - bundle-sheath cells found in vast quantities around veins of leaves CO 2 levels in these cells remain high enough for Calvin cycle to produce sugar

48 CAM Plants pineapple, some cacti & succulent plants conserve water by opening stomata & letting CO 2 in at night CO 2 is fixed into a 4-C compound saves CO 2 at night & releases it in the day photosynthesis can take place without CO 2 needing to be admitted during the day when conditions are hot and dry

49 Environmental Consequences of Photosynthesis CO 2 makes up 0.03% of air provides plants with CO 2 to make sugars important in climates retains heat from sun that would otherwise radiate from Earth warms the Earth greenhouse effect

50 Global Warming CO 2 traps heat warms air maintains average temperature on Earth about 10 degrees C warmer than without it. Earth may be in danger of overheating because of this greenhouse effect CO 2 in air is increasing because of industrialization when oil, gas and coal are burned CO 2 is released levels in atmosphere have increased 30% since 1850 increasing concentrations have been linked to global warming slow & steady rise in surface temperature of Earth could have dire consequences for all life forms on Earth

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