PHOTOSYNTHESIS
Using Light Energy to Synthesize
Reduced Carbon (Stored Energy)
Lab #6
Introduction
• Full discussion of Photosynthesis will come at
the end of the semester
• TODAY
– Molecules that absorb light to power
Photosynthesis
– Light absorbing properties of photosynthetic
molecules (pigments)
– Relationship between light intensity and
photosynthetic rate.
Nature of Light
• Generic Definition: illumination
• Scientific: Electromagnetic Radiation
– All energy emitted by the sun
Electromagnetic Radiation
• As a particle: Photon
• As a wave
– Wavelength
– Frequency
– High f / Short λ
– Low f / Long λ
Electromagnetic Spectrum
• A continuum of Electromagnetic radiation
violet blue
400nm
green yellow orange red
700nm
Today’s Experiments
• Paper Chromatographic separation of grass
pigments (1/group)
• Using a Spectrophotometer to determine the
light absorption properties of grass pigments
• Using Sarcococca sp. (“Christmas box”) to
determine the relationship between Light
Intensity and Photosynthetic Rate.
Paper Chromatography
of Grass Pigments Set-Up
• Demonstration of Set-Up (p.5 in Lab Manual)
– Large Test Tube (Chromatography Tank)
– Cork with “hook”
– Chromatography paper – WARNINGS
– Chromatography solvent – WARNINGS
– Pigment Loading
• Return solvent to flask
• STOP – all groups set up chromatograms
(15’/8pm)
Using Spectrophotometer To Determine %T of Grass Pigments (1)
• Each group at a Spectrophotometer
• You will be measuring %Transmittance (%T)
– Amount of a specific wavelength of VISIBLE
light that passes through (is transmitted) by a sample
– Computer will convert to % T to % A (absorption),
amount of light absorbed, & create % Absorption
Graph
– %T + %A = 100%
– 0 %T / 100% A = Opaque
– 100 %T / 0% A = Transparent
Using Spectrophotometer To Determine
%T of Grass Pigments (2) (pg.7)
• Review Spec parts and steps
– Laminated card
– Handout
– Explain Blanking – “teaching” the spec what to
ignore
• Enter data in Spreadsheet when finished
• Keep an eye on those Chromatograms
– Describe when Chromagraph is “done”
• 15’ – 20’
Light Intensity and Photosynthetic Rate
• Leaf morphology and basis of experiment
Light Intensity and Photosynthetic Rate p.2
• Review Set-Up and Leaf Disk prep (p.15 in Lab
Manual)
– Bowl of water for heat absorption
– Different heights
– Each group sends 1 student to cut disks
• 1 pump buffer into beaker
• Cut 10 disks
– Bring to front, Instructor adds to large flask
– CONTINUES ON NEXT SLIDE
Light Intensity Setup p.3
• Disk evacuation + Room Lights out +
Experiment Lights on
• Each group gets 3 “evacuated” disks in 20ml of
buffer + 3-4 drops of NaHCO3 (sodium bicarbonate)
• Place beaker on white platform
• Definition of “Disk has risen”
• Call out data: height & time
Discussion
• Review Leaf Disk results
–Relationship between Light
Intensity and Photosynthetic Rate
–Purpose of NaHCO3
Discussion p.2
Discussion p.3
• Provide %A data & Review Study Guide Questions
• Discuss color perception: eyes receive, brain perceives
NEXT SLIDE FOR
LAB 7 & 8 PREP
PREP FOR LAB 7 & 8
• PREP IS CRITICAL!!!!
• Review Lab 7 & 8 Study Guide on
Website