Lesson 2- Photosynthetic Pigments And Chromatography Flashcards
What is photosynthetic pigment ?
Coloured molecules that absorb the light energy needed for photosynthesis
Where are the photosynthetic pigments found
In the thylakoid membrane
How are the photosynthetic pigments arranged ?
Into photo systems in the thylakoid membrane
What is the main photosynthetic pigment ?
Chlorophyll
Why do photosystems contain accessory pigments
To help absorb the wavelengths of light that are not easily absorbed by chlorophyll (maximise light absorption)
Why does chlorophyll appear green ?
It absorbs light at 2 wavelengths 430nm (blue) and 662nm (red). It reflects green light strongly so it appears green.
Why is it important to use an organic (non-polar) solvent and not a polar one like water?
A polar solvent could compete with the dissolved molecules for space on the stationary phase and could cause them to move further than they should do, giving the incorrect Rf value
Why is it important to mark positions in pencil rather than pen ( particularly the starting position of the concentrated extract)
Ink may dissolve in the solvent move up the stationary phase. Colours could affect the results and there will be no visible start line to measure Rf value from.
Why is it important that the spot of the plant extract is above the surface of the solvent when the chromatography plate is placed in the vial ?
To ensure the pigments are carried up by the solvent and don’t just dissolve out into the solvent at the bottom
Why is repeated application of the plant extract onto the same spot required ?
To increase the concentration of pigments
Why is it important that the chromatogram is stopped before the solvent front reaches the top?
So that the distance travelled by the solvent (solvent front) can be identified and drawn - needed for the Rf value calculation
Why is it important to mark the solvent front quickly?
The solvent is volatile and will evaporate quickly, once dry it can’t be seen
Why is it useful to mark the positions of the pigment spots or take a photograph of the chromatogram soon after it has been run ?
Light can cause them to fade
