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Chapter 7 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Photosynthesis and Life. During photosynthesis Organisms use the energy of light to build high-energy organic molecules. Plants, algae and some bacteria can do this. - PowerPoint PPT Presentation
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7-1
Chapter 7
Lecture OutlineSee PowerPoint Image Slidesfor all figures and tables pre-inserted intoPowerPoint without notes.
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Photosynthesis and Life
During photosynthesis– Organisms use the energy of light to build
high-energy organic molecules.– Plants, algae and some bacteria can do
this. Can make their own food using light Called photosynthetic autotrophs
99.9% of all life on earth relies on photosynthesis for their energy.– Heterotrophs eat autotrophs.
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An Overview of Photosynthesis
Photosynthesis occurs in– Chloroplasts
Contain the pigment that captures the energy in light– Chlorophyll– Found in membranous sacs called thylakoids– A stack of thylakoid is called a granum (pl. grana).– Grana are suspended in a fluid-filled space called
the stroma. During photosynthesis
– The energy in light is used to make ATP.– The energy in ATP is used to make organic
molecules such as glucose.
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Photosynthesis, Chloroplasts, and the Structure of a Leaf
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An Overview of Photosynthesis
The chemical equation of photosynthesis:Light energy + carbon dioxide + water glucose and oxygen
The three events of photosynthesis Light-capturing events
– The pigment chlorophyll absorbs certain wavelengths of light and some of its electrons become excited.
Light-dependent reactions– These reactions use the energy in the excited electrons to
make ATP and NADPH. Light-independent reactions
– ATP and NADPH from the light reactions is used to reduce carbon dioxide to make glucose.
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An Overview of Photosynthesis
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Light-capturing Events: Fundamental Concepts Visible light
– Combinations of different wavelengths of light– Can be seen as different colors
Pigments are molecules that absorb light.– Each pigment absorbs certain wavelengths of light.– The wavelengths that they do not absorb, they reflect.
This is the color we see.– In photosynthesis, only the wavelengths that are absorbed can be
used to do work. Chlorophyll: The main photosynthetic pigment
– Two forms; a and b– Absorb light in the blue and red portions of the spectrum– Reflect green wavelengths
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The Electromagnetic Spectrum, Visible Light and Chlorophyll
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Other Types of Pigments Accessory pigments
– Include carotenoids Absorb blue and green wavelengths Reflect orange and yellow Found in leaves, masked by chlorophyll
– In the autumn, when chlorophyll disintegrates, accessory pigments show through (fall colors).
Chlorophyll + accessory pigments– Organized into photosystems that harvest the energy from
many wavelengths of light– Found in thylakoids of the chloroplasts
When pigments absorb light– Some of their electrons become “excited”
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Light-dependent Reactions: Fundamental Concepts The excited electrons from chlorophyll
– Are passed through an electron transport chain– The energy released is used to pump protons up their
concentration gradient.– When protons diffuse through ATP synthase, ATP is made.
Excited electrons passed to NADP+ to make NADPH Water is split
– Electrons are donated to chlorophyll to replace the donated electrons.
– Oxygen is produced. Occurs in the thylakoid membrane
– ATP and NADPH move to the stroma to be used in the dark reactions.
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Light-independent Reactions: Fundamental Concepts The ATP and NADPH from the light-dependent
reactions – Provide the energy and electrons needed to build sugar
from carbon dioxide CO2 is captured by an enzyme called RuBisCO
– Combines CO2 with ribulose to form a 6-carbon molecule This is immediately split into two 3-C molecules.
NADPH is used to reduce these molecules. Glyceraldehyde-3-phosphate is formed.
– Can be used to make sugars, proteins or fats
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Photosynthesis: Fundamental Description
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Light-capturing Events: The Details
Light– Packaged as photons– Each photon has a distinct wavelength.– The energy in a photon is related to its
wavelength.– When a photon hits a pigment molecule, electrons
are excited. This means that the electrons jump up to a higher
energy level.
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Light-capturing Events: The Details Continued
Photosystems– Structures in which the light-capturing events take
place– Found in the thylakoid membranes– Made up of antenna complexes and a reaction center
Networks of chlorophyll and accessory pigments Capture the energy in many different wavelengths of
light and pass it to the reaction center– The reaction center is a special chlorophyll molecule that
passes its excited electrons to an electron acceptor.– There are two photosystems, I and II.
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Light Dependent Reactions: The Details
Photosystem II (PSII)– Occurs first– Donates its excited electrons to the electron transport chain– Splits water to replace the electrons it donated
O2 is released. Photosystem I (PSI)
– Occurs second– Donates its excited electrons to NADP+ to form NADPH
NADPH released into the stroma– Accepts electrons from the electron transport chain to
replace the electrons it donated PS I and II are in the thlyakoid membrane.
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The Electron Transport Chain
and ATP Synthesis
Between PSII and PSI– Electrons are passed through an electron
transport chain (ETC). This releases energy. This energy is used to pump protons from the stroma
into the thylakoid space. This creates a proton concentration gradient. Protons diffuse through ATP synthase. ATP synthase makes ATP that is released into the
stroma.
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PS II and I: How They Interact
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Light Independent Reactions: The Details
Takes place in the stroma of the chloroplast Uses
– CO2 (from the atmosphere)– ATP and NADPH (from the light-independent
reactions) – Ribulose (recycled)
Also called the dark reactions Also called the Calvin cycle
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Carbon Fixation and Sugar Formation
Carbon dioxide gas is combined with a 5-carbon sugar called ribulose.
Accomplished with an enzyme called ribulose bisphospate carboxylase (RuBisCO)
Forms a 6-carbon molecule– Immediately broken down into two 3-carbon molecules– These 3-carbon molecules are
Energized by ATP Reduced by NADPH
Glyceraldehyde-3-phosphate is formed.
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The Calvin Cycle
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Glyceraldehyde-3-phosphate: The Product of Photosynthesis Glyceraldehyde-3-
phosphate can be used for many things.
– Used to make glucose– Used to recycle ribulose for
the Calvin cycle– Used to make the sugars
needed to build ATP, DNA and RNA
– Can be converted into lipids– Can be converted into
amino acids to make proteins
– Can be broken down in glycolysis
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Other Aspects of Plant Metabolism
Plant cells can use the organic molecules produced in photosynthesis to make– Fats, proteins and other carbohydrates– Toxins for their protection
Many of these are useful medicines. Some can be used as natural insecticides.
– Vitamins Molecules that we cannot make, but that we need
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Interrelationships Between Autotrophs and Heterotrophs Autotrophs use the energy in light to make food.
– Autuotrophs use the food they make in cellular respiration. Plants use the sugar they make! Plants use the oxygen they make!
Heterotrophs eat the autotrophs.– Then use the food from the autotrophs to fuel cellular respiration– They also use the excess oxygen given off by autotrophs.
All organisms respire! The circle of life:
– Animals get sugar, oxygen, amino acids, fats and vitamins from plants.
– Plants get carbon dioxide, water and nitrogen from animals.
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The Relationship between Photosynthesis and Cellular Respiration
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