PHOTOSYNTHESIS

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PHOTOSYNTHESIS

• Using light to make food

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PHOTOSYNTHESIS
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• Autotrophs are the producers of the biosphere
• Plants are autotrophs
• Producing their own food and sustaining
  themselves without eating other organisms
• What are we?
• We are heterotrophs

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• Plants, algae, and some bacteria are
  photoautotrophs
• Producers of food consumed by virtually all
  organisms

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• PLANTS USE ENERGY FROM THE SUN TO TRANSFORM CO2
  AND WATER INTO ENERGY RICH CARBOHYDRATES(glucose).
  
• Plants are AUTOTROPHS make their own food
• Plants supply all the energy (food) for life on
  earth and the oxygen that most
• organisms need

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How old is photosynthesis? How important is it?

• Evidence of photosynthesis exists in rocks 3.5
  billion years old.
• Photosynthesis is the largest biochemical
  process on earth.
• Importance?
• Photosynthesis supplies OXYGEN to earth
  atmosphere and FOOD to all organisms

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• Photosynthesis is the process by which certain
  organisms use light energy to make sugar and
  oxygen gas from carbon dioxide and water.

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Where in the plant does photosynthesis occur?

• In the CHLOROPLAST. The leaf is a food factory.
  The light trapping pigments are inside the
  chloroplasts embedded in the thylakoid membranes.
• STOMATA or STOMA are openings on the leaf surface
  through which CO2 and O2 as well as water vapor
  go in and out of leaves.

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• Where does it occur?
• Photosynthesis occurs in chloroplasts
• Occurs primarily in the leaves, in the
  chloroplasts, which contain stroma, and stacks of
  thylakoids called grana

Figure 7.2
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ENERGY-CONVERTING ORGANELLES

• Chloroplasts conver t solar energy to chemical
  energy (in sugars).
• . Found in plants and some protists. This is
  where PHOTOSYNTHESIS takes place

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Sites to check

• http//www.mhhe.com/biosci/esp/2001_gbio/folder_st
  ructure/ce/m6/s1/index.htm
• http//www.tvdsb.on.ca/westmin/science/Biology12/M
  etabolic20Processes/stoma.htm
• http//www.tvdsb.on.ca/westmin/science/Biology12/M
  etabolic20Processes/chloro.htm
• http//www.mhhe.com/biosci/esp/2001_gbio/folder_st
  ructure/ce/m6/s3/index.htm

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ENERGY-CONVERTING ORGANELLES

• Chloroplasts conver t solar energy to chemical
  energy (in sugars).
• . Found in plants and some protists. This is
  where PHOTOSYNTHESIS takes place

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Thylakoids

• Thylakoids are membranes that look like green
  flattened sacs stacked upon each other.
• Granum is a stack of these sacs
• The STROMA is the fluid between the membranes.

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• Plants produce O2 gas by splitting water
• The O2 liberated by photosynthesis
• Is made from the oxygen in water

Figure 7.3AC
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• Photosynthesis is a redox process, as is cellular
  respiration
• In photosynthesis
• H2O is oxidized and CO2 is reduced

Figure 7.4A, B
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PHOTONS AND PIGMENTS

• PHOTONS are packets of light energy
• Light electromagnetic energy waves that travel
  in waves of different lengths
• PIGMENTS are molecules that absorb light energy
  (photons)
• CHLOROPHYLL is the main pigment in plants.
  Absorbs the blue and red portions of the visible
  light spectrum and scatters or reflects back the
  green wave length. This is why plants look green.
• CAROTENOIDS reflect the reds and yellows

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THE LIGHT REACTIONS CONVERTING SOLAR ENERGY TO
CHEMICAL ENERGY
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• wavelengths of visible light (red,blue),
  absorbed by pigments drive the light reactions of
  photosynthesis

Figure 7.6A, B
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• Overview Photosynthesis occurs in two stages
  linked by ATP and NADPH
• The complete process of photosynthesis consists
  of two linked sets of reactions
• The Light Dependent Reactions and
• The Calvin Cycle (discovered by Calvin and
  Benson)

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Photosynthesis

• H2O CO2 ? ? O2 C6H12O6 H2O
• water carbon light
  oxygen glucose water vapor
• dioxide energy

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STEPS OF PHOTOSYNTHESIS

• capture sun light
• use light energy to make ATP
• use ATP to make carbohydrate molecules from
  CO2(carbon dioxide) and H2O (water)

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LIGHT DEPENDENT REACTIONS

• is the first stage of photosynthesis.
• It takes place in the thylakoid membranes.
• Oxygen is released, Water molecules are split.
  Oxygen gas diffuses out
• ATP and electrons are carried to the next stage.
  Electrons are used to make ATP.

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Light Dependent Reactions (In thylakoids of
chloroplasts)

• This is where light energy is converted to a form
  that can be used by plants to build Carbon
  compounds (sugars)
• 1.The energy of sunlight hits the photosystems
  (cluster of pigment molecules) and excites
  chlorophyll (pigment) electrons to a higher
  energy state. Light energy is absorbed by the
  photosystems
  
  
  
  
• 2. Water molecules split, oxygen is released.
• Light energy is converted to chemical energy (ATP
  formation)
• NADPH electron carrier take electrons from
  chlorophyll to the Calvin Cycle.

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• The light reactions
• Convert light energy to chemical energy and
  produce O2
• The Calvin cycle assembles sugar molecules from
  CO2
• Using ATP and NADPH from the light reactions

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THE CALVIN CYCLE CONVERTING CO2 TO SUGARS

• ATP and NADPH power sugar synthesis in the Calvin
  cycle
• The Calvin cycle occurs in the chloroplasts
  stroma
• Consists of carbon fixation, reduction, release
  of G3P, (glyceraldehyde 3-phosphate)and
  regeneration of RuBP

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LIGHT INDEPENDENT REACTIONS-CALVIN CYCLE

• (In stroma of chloroplasts ) This is a cyclic
  pathway where the final products are also the
  first reactants on the cycle
• The Calvin Cycle uses the energy in ATP and NADPH
  to synthesize carbohydrates.
• Carbon enters the cycle as a molecule of CO2

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LIGHT INDEPENDENT REACTION or CALVIN CYCLE

• Takes place in the stroma of the chloroplasts.
• This is the synthesis part of photosynthesis.
  Making food (glucose) and trapping CO2 to
  incorporate carbon into living things.

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CALVIN CYCLE- making glucose

• The energy from ATP and NADPH go into the bonds
  of a glucose molecule.
• Electrons ( hydrogens) from the carrier molecule
  are put together with CO2 to make glucose.
• An enzyme called RUBISCO fixes the CO2 ( from the
  air) by bringing together the CO2 and the sugar.

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LIGHT INDEPENDENT REACTIONS-CALVIN CYCLE

• Fixes Carbon (from CO2) using the enzyme rubisco.
  This enzyme catalizes the binding of carbon from
  CO2 to RuBP ( ribulose bisphosphate). This is how
  all carbon enters the world of life.
• Put together sugars using ATP and NADPH as energy
  sources.
• The final product is a three carbon sugar called
  G3P (glyceraldehyde 3-phosphate)
• G3P is a sugar phosphate that can be modified to
  form glucose

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PHOTOSYNTHESIS REVIEWED

• Review Photosynthesis uses light energy to make
  food molecules

Figure 7.11
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C3 PLANTS

• Plants that use CO2 directly from the air are
  called C3 plants. Soybeans, oats wheat and rice
  are C3 plants.
• In hot dry weather these plants close their
  stomata ( pores in underside of leaves) to reduce
  water loss. Since no CO2 can enter, the rate of
  photosynthesis is reduced and your crop
  productivity is poor.

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• In C3 plants a drop in CO2 and rise in O2 when
  stomata close on hot dry day divert the Calvin
  cycle to photorespiration
• ( Rubisco can bind oxygen in place of CO2 as CO2
  becomes scarce. When Oxygen enters the Calvin
  cycle instead of CO2 so it cannot produce sugars
  )
• C4 and CAM plants have special adaptations that
  save water

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CAM PLANTS

• CAM PLANTS
• In hot and very dry climates. (deserts)
• Examples pineapple, cactus, orchids all the
  succulent plants such as Aloe and Jade plants
• When stoma opens to get CO2 the water can get
  out. Survival depends on water retention.
• Adaptation Stoma is closed during the day and
  open at night. Co2 is taken in at night and
  banked until the next day when it is given to the
  Calvin cycle to make carbohydrates.
• The CO2 taken in at night stays banked until
  the suns energy comes in the next day.

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• CAM plants open their stomata at night
• Making a four-carbon compound used as a CO2
  source during the day

CO2
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C4 PLANTS

• Have special adaptations to save water without
  shutting down photosynthesis
• In hot climates.
• Examples grasses , corn, sugarcane
• In hot climates the stoma closes to keep water
  in. It also keeps CO2 out and oxygen builds up
  inside the leaves. Since there is not enough CO2
  the enzyme rubisco (that normally binds CO2)
  binds oxygen and the plants would not grow well.
• Adaptation It continues to make sugars with
  closed stomata.
• How? These plants use a different enzyme to bind
  CO2.This enzyme fix carbon twice to produce a 4
  carbon compound which can then donate the C to
  the Calvin cycle

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• C4 plants first fix CO2 into a four-carbon
  compound
• That provides CO2 to the Calvin cycle

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ENVIRONMENTAL IMPACT OF PHOTOSYNTHESIS

• Food. Photosynthesis is the source of all the
  food that gives us energy ( from the sun)
• Oxygen production
• CO2 is the gas plants use to make sugars.
• CO2 in the atmosphere retains heat from the sun
  that would otherwise radiate back into space

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PHOTOSYNTHESIS, SOLAR RADIATION, AND EARTHS
ATMOSPHERE CONNECTION

• Photosynthesis moderates global warming
• Greenhouses used to grow plants trap solar
  radiation, raising the temperature inside

Figure 7.13A
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Global warming and the Greenhouse effect

• Global warming is the slow and steady rise in
  Earth surface temperatures.
• Warming is caused by CO2 and other greenhouse
  gases.
• It is called the green house effect because CO2
  traps heat and keeps it warm near the earth
  surface.
• When this occurs in moderation it is a good
  thing, otherwise the planet would be about 10
  degrees colder all the time. The trouble is that
  we get overheating.

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What are greenhouse gases?

• All the cars and industries that burn fossil fuel
  produce so much CO2 that we now have 30 more
  than ever before. This causes global warming.
• Some greenhouse gases are carbon dioxide CO2,
  methane CH4, water vapor and others
• http//www.net.org/globalwarming/sea_level/

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Web sites to check

• http//www.fw.vt.edu/dendro/forestbiology/photosyn
  thesis.swf
• http//highered.mcgraw-hill.com/sites/0072437316/s
  tudent_view0/chapter10/animations.html
• http//www.sumanasinc.com/webcontent/anisamples/ma
  jorsbiology/harvestinglight.swf