Photosynthetic Pigments

Bellwork Plants grown in the shade often produce larger leaves than plants grown in full sunlight. Propose a hypothesis to explain this observation.

Learning Objectives List the stages of photosynthesis Identify the site of photosynthesis in eukaryotes and prokaryotes Identify the part of the visible light spectrum that chlorophyll and cartenoids absorb Explain how paper chromatography separates photosynthetic pigments in a leaf extract

Key Terminology Photosynthetic pigments Paper chromatography Stationary phase Mobile phase

Photosynthesis Chemical Reaction CO2 + H20 + light C6H12O6 + O2

Stages of Photosynthesis Absorption of sunlight Stage 2 Conversion of light energy to chemical energy in the form of ATP and NADPH Light-dependent reactions Stage 3 Synthesis of organic compounds, with CO2 as carbon source light-independent reactions

Cellular site of photosynthesis Chloroplasts plant cells and algae (eukaryotes) Plasma membrane photosynthetic bacteria (prokaryotes)

PROPERTY OF PIMA COUNTY JTED, 2010 Think-Pair-Share Explain why the site of photosynthesis is the plasma membrane not chloroplasts in photosynthetic bacteria. 3. Think-pair-share teacher presents a question teacher gives wait time for student to form answer teacher instructs students to share their answer with a partner teacher calls on non-volunteers to share with the class PROPERTY OF PIMA COUNTY JTED, 2010 3 8

Stage 1: Absorption of Light How does a leaf absorb light? Through light-absorbing substances called pigments

Light Spectrum Visible Spectrum Part of the spectrum that we see with our eyes Photosynthetic pigments absorb in the visible spectrum

Classification of Pigments Two Major Groups Chlorophyll primary photosynthetic pigment absorb in red and blue region of visible light spectrum Reflects green Carotenoids absorb light of blue and blue-green wavelengths reflects yellow, orange and red aid chlorophyll in the absorption of light

PROPERTY OF PIMA COUNTY JTED, 2010 Think-Pair-Share Why does a red rose appear the color red to your eyes? 3. Think-pair-share teacher presents a question teacher gives wait time for student to form answer teacher instructs students to share their answer with a partner teacher calls on non-volunteers to share with the class PROPERTY OF PIMA COUNTY JTED, 2010 3 12

Identification of Plant Pigments Photosynthetic pigments identified by a laboratory procedure known as paper chromatography.

Purpose of Chromatography Separate components of a mixture through interaction with a stationary and mobile phase Use paper chromatography to separate the photosynthetic pigments

Paper Chromatography Stationary phase – paper Mobile phase - solvent

How paper chromatography works Place mixture at the origin of paper (Black dot) Place the tip of the paper in a solvent Solvent migrates up paper (solvent front) Components that are soluble in the solvent will move with the solvent up the paper

Demonstration with Black Washable Marker In the demonstration, identify the stationary phase, mobile phase Identify which color was most soluble in the solvent, least soluble in the solvent

How components of mixture separate Depends on their attraction to paper versus their solubility in the solvent Example: Non-polar solvent A component that carries a charge will be more attracted to the charged molecules (i.e. cellulose) in the paper than the solvent. Consequently, it will stay close to the origin where the mixture was applied to the paper.

Demonstration with Black Washable Marker Which color was most attracted to the chromatography paper? Explain.

Separation, therefore, depends on: Solubility in the solvent (more soluble more it will move up the paper) Attraction to the cellulose in the paper (more attracted to the paper will stay close to the origin)

Components of mixture identified by its Rf Value Rf value = distance from origin to spot divided by distance from origin to solvent front Rf value important when comparing chromatographs because that value stays constant for a particular component

Chromatogram

Calculation of Rf value The solvent migrated 10 mm Xanthophyll pigment migrated 4 mm What was its Rf value? So this pigment moved 0.4 as far as the solvent

Write a “snapshot” of today’s learning in 25 to 50 words. teacher provides a prompt from the lesson students must write a “snapshot” of the lesson in 25 words or less teacher uses a strategy to check all 24