Photosynthesis

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Photosynthesis!
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Plant questions?

• How do plants obtain energy?
• Why do plants need light?
• Why do plants need water?
• Why are plants green?
• http//fig.cox.miami.edu/cmallery/150/phts/phts.h
  tm

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• The best known form of photosynthesis is the one
  carried out by higher plants and algae, as well
  as by cyanobacteria and their relatives, which
  are responsible for a major part of
  photosynthesis in oceans.

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The very basics

• Energy from light is used to convert CO2, H2O
  into sugar
• O2 is a byproduct or leftover and is released
• Photosynthesis
• In 6CO26H2OEnergy
• Out C6H12O66O2

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Anatomy of a leaf (photosynthetic organ)

• Leaf functions
• Trap sunlight
• Perform photosynthesis
• Move food to storage areas in the plant
• Absorb CO2 from the air
• Minimize water loss from evaporation
• Leaf structure is related to function

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Why are leaves green?
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Because.

• Their cells are full of chloroplastswhich
  contain chlorophylla pigment that reflects green
  lightwhich we see.so leaves are green

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Summary of chloroplast structure

• Enclosed in a double membrane
• Contain Thylakoid disks called grana (pigments
  embedded in Thylakoid membrane)
• The liquid part of chloroplasts is the Stroma
• Stroma contains
• Electron Transport System
• Loose enzymes

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Photosynthesis takes place in 2 stages each
made up of a set of reactions

• Light Dependent Reactions
• Convert light energy to chemical energy in the
  form of ATP NADPH
• Light Independent Reactions (Calvin-Benson Cycle)
• Convert chemical energy from ATP NADPH to long
  term storage form glucose/starch

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Where does the light come from?

• What are photons?
• Light particles
• No mass
• Travel as a wave
• Photons Energy
• The smaller the wavelength, the higher the energy
  per photon

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Sunlight is a mixture of the colors of the
rainbow
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Photosynthetic Pigments Light energy captors

• Photosynthetic plant pigments
• Embedded in membranes of thylakoid disks
• Consist of different varieties of chlorophylls
  and other accessory pigments such as
  beta-carotene

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Pigments

• Pigments absorb light energy and convert it to
  chemical energy.
• Chlorophyll GREEN (most important in
  photosynthesis)
• Carotenoids YELLOW, ORANGE RED.
• Photosynthesis only takes place when chlorophyll
  is present.

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Photosynthetic pigments absorb the energy in
specific colors of light
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What colors are absorbed?What colors
reflected?Different pigments absorb different
colors of lightThis allows plants to use most of
the available light
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1. Light Reaction

• needs light energy
• takes place in the thylakoids
• needs water (H2O), which is divided into
  electrons and oxygen (which is liberated)
• uses 2 photosystems to capture the suns energy
• produces ATP which is used in the dark rx
  (Calvin-Benson cycle)

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The Light Reaction

• Two Steps
• 1. Trapping Energy from the Sun.
• 2. Splitting of Water

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Animation of the Light Reaction http//www.biolog
y4all.com/resources_library/source/61a.swf
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LIGHT REACTION PRODUCTS

• Energy
• ATP
• NADPH
• Oxygen (which is released into the atmosphere)

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2.The Dark Reaction (Calvin cycle)
- uses CO2 to make glucose (fixation of carbon
dioxide)
- takes place in the stroma of the chloroplast
- also known as C3 bc of the 3 carbon molecule
(PGA) that is formed
- there are 2 other methods that plants may use
to make glucose C4 and CAM
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Calvin Cycle the synthesis
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The rate of photosynthesis
- which factors affect the rate of fixed
glucose?
1) The rate of photosynthesis can be limited by
physical factors such as temperature. The lower
the temperature, the slower the photosynthesis.
2) The availability of light is a factor that
limits the rate of photosynthesis. When the
amount of light decreases, the rate of
photosynthesis also decreases
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The C4 CAM plants
The Calvin cycle and the C4 Plants
- in certain climates, the sun is too abundant,
and it never limits photosynthesis
- however, these climates are also very try and
hot
- here, its the CO2 that limits photosynthesis
- we can think of it as the availability and the
loss of water (H2O)
- when the plant photosynthesises in the sun, the
CO2 must enter the leaves through the stomatas
(little holes under the leaves)
- but, when these holes are open, H2O is lost and
the plant dehydrates
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- if you close the stomatas, CO2 cannot enter so
this limits photosynthesis
- in C4 plants, the stomatas are only partially
opened during the day
- these plants have an enzyme that can transform
the CO2 into a 4-carbon molecule
- these molecules are stored in the different
cells and the CO2 can be released when the plant
lacks any
Examples of C4 plants are corn, sugar canes
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Crassulacean Acid Metabolism (CAM)
- the ultimate prevention of CO2 loss is found in
desert plants like the cactus
- in these plants, the stomatas are only opened
at night
- the plants fixes the CO2 into 4-carbon
molecules during the night and transfer the
carbon to the Calvin cycle during the day
- in the day, the stomatas are completely closed
and there is no water loss
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Comparison between photosynthesis and aerobic
resp.
Global rx of photosynthesis
6CO2 6H2O light energy ? C6H12O6
6O2
Global rx of aerobic cellular resp
C6H12O6 6O2 38 ADP 38 P ? 6CO2
6H2O 38 ATP
- in a way, photosynthesis is the opposite of
aerobic resp.
- the products of photosynthesis are the raw
materials (reactants) of resp.
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• PHOTOSYNTHESIS RESPIRATION
• Where? In cholorophyll-bearing cells In all
  cells
• When? In the presence of light All the time
• Input? Carbon dioxide and water Reduced carbon
  compounds and oxygen
• Output? Reduced carbon compounds, Carbon dioxide
  and water
• oxygen, and water
• Energy sources? Light Chemical bonds
• Energy result? Energy stored Energy released
• Reaction ? Reduction of carbon Oxidation of
  carbon compounds compounds
• Energy carrier(s) NADP NAD and FAD