1 1 Algal Physiology I. Photosynthesis in algae II. Characteristics to distinguish algal divisions 2 I. Photosynthesis 3 Light reactions: solar energy is harvested and transferred into the chemical bonds of ATP and NADPH “PSU” : Photosynthetic Unit = Antennae + rxn center 4
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Algal Physiology
I. Photosynthesis in algae II. Characteristics to distinguish algal
divisions
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I. Photosynthesis
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Light reactions: solar energy is harvested and transferred into the chemical bonds of ATP and NADPH
“PSU” : Photosynthetic Unit = Antennae + rxn center
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Calvin Cycle: C fixation from CO2 to sugar using energy from ATP and NADPH
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Chloroplasts
Thylakoid – flattened vesicles or sacks; thylakoid membrane is where the pigments are Stroma - space between inner membrane and thylakoids Granum (pl: grana) – stacks of thylakoids Pyrenoid – holds enzyme ribulose bisphospate carboxylase (Rubisco) used in Calvin cycle
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Pigment Location
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What light can be used for photosynthesis?
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What light can be used for photosynthesis? PAR = photosynthetically active radiation = 400-700 nm
Must also deal with UV light (280-320 nm); damage DNA, proteins - B-carotene, aromatic amino acids absorb UVB
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Pigments: Primary 1. Chlorophylls – green pigments, embedded in thylakoid
membrane. Chl a is the main player: used in all algae and land plants.
Chl a absorbs light primarily in the blue and far-red regions
Reflects green why most plants appear green
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What’s wrong with this picture?
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What’s wrong with this picture?
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Algae have accessory pigments: Allow harvesting of light at “middle” wavelengths, then channel energy to Chl a
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Algae have accessory pigments: Allow harvesting of light at “middle” wavelengths, then channel energy to Chl a
“PSU” : Photosynthetic Unit = Antennae + rxn center
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2. Carotenoids – brown, yellow, or red pigments. Hydrocarbons with or without an oxygen molecule = carotenes and xanthophylls.
3. Phycobilins – red or blue pigments. Water soluble. Located on the surface of thylakoids in red algae, associated with proteins to form phycobilisomes
Algal accessory pigments:
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How we study photosynthesis: The Ps/I curve
1. Pmax = Maximum production
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How we study photosynthesis: The Ps/I curve
1. Pmax = Maximum production 2. Ik= Saturating irradiance (where initial slope meets Pmax)
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2.
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How we study photosynthesis: The Ps/I curve
1. Pmax = Maximum production 2. Ik= Saturating irradiance 3. Gross photosynthesis = Total production
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How we study photosynthesis: The Ps/I curve
1. Pmax = Maximum production 2. Ik= Saturating irradiance 3. Gross photosynthesis = Total production 4. Net photosynthesis = Gross production – Respiration
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How we study photosynthesis: The Ps/I curve
1. Pmax = Maximum production 2. Ik= Saturating irradiance 3. Gross photosynthesis = Total production 4. Net photosynthesis = Gross production – Respiration 5. Ic = Compensation point: When photosynthesis equals respiration
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How we study photosynthesis: The Ps/I curve
1. Pmax = Maximum production 2. Ik= Saturating irradiance 3. Gross photosynthesis = Total production 4. Net photosynthesis = Gross production – Respiration 5. Ic = Compensation point: When photosynthesis equals respiration 6. Initial slope (alpha) = Indicative of photosynthetic efficiency
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How we study photosynthesis: The Ps/I curve
1. Pmax = Maximum production 2. Ik= Saturating irradiance 3. Gross photosynthesis = Total production 4. Net photosynthesis = Gross production – Respiration 5. Ic = Compensation point: When photosynthesis equals respiration 6. Initial slope (alpha) = Indicative of photosynthetic efficiency 7. Photoinhibition = Damage to photosystems due to high irradiance
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How we study photosynthesis: The Ps/I curve
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4.3.
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4.3.
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4.3.
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How we measure photosynthetic rates (primary productivity):
• With electrodes using O2= O2 meter or Chemical titration • Use Light and Dark Bottles
• Dark Bottles measure Respiration • Light Bottles measure Ps - Rs = Net photosynthesis • Light Bottle O2 + Dark Bottle O2 = Gross photosynthesis
• Photosynthetic Rate measured as O2 /g/hr
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How we measure photosynthetic rates (primary productivity):
• Important Considerations:
• Temperature • Saturating Light? • Background gasses – run blanks • Ambient primary productivity by phytoplankton when using seawater • Nutrients
• Other methods • CO2 measurement (by pH) • C14 isotope tracers • Infrared gas analysis
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II. Algal characteristics for distinguishing divisions: 1. Pigments 2. Storage products 3. Cellular/plastid structure 4. Motility (e.g. +/- flagella) 5. Life history
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1. Chlorophylls – green pigments, embedded in thylakoid membrane. Chl a is the main player: used in all algae and land plants.
2. Carotenoids – brown, yellow, or red pigments. Hydrocarbons with or without an oxygen molecule = carotenes and xanthophylls.
3. Phycobilins – red or blue pigments. Water soluble. Located on the surface of thylakoids in red algae, associated with proteins to form phycobilisomes