chromatography Flashcards
chloroplasts contain…
several different photosynthetic pigments within the thylakoids
what do photosynthetic pigments do?
absorb different wavelengths of light
where does the LDS occur?
thylakoid membranes and the thylakoid spaces
what does the thylakoid membrane system do?
provides many pigment molecules in an arrangement that ensures as much light as necessary is absorbed
how are pigments molecules arranged?
in light-harvesting clusters (photosystems)
how are pigments molecules arranged in a photo system?
-in funnel-like structures
-each pigment molecule passes energy down to the next pigment molecule in the cluster until it reaches the primary pigment reaction centre
how many groups of pigments are there and what are they?
two groups:
primary pigments → chlorophylls
accessory pigments → carotenoids
what are the primary pigments in each photosystem?
photosystem I = chlorophyll a
photosystem II = chlorophyllb
where are accessory pigments?
they surround the primary pigment
what do accessory pigments do?
-absorb both similar and different wavelengths of light to chlorophyll
-this expands the wavelength range that can be absorbed from light for use in photosynthesis
chlorophyll colours:
chlorophyll a → blue-green
chlorophyll b → yellow-green
carotenoid colours:
β carotene - orange
xanthophyll - yellow
what do chlorophylls absorb & reflect?
-they absorb wavelengths in the blue-violet and red regions of the light spectrum
-they reflect green light, causing plants to appear green
what do cartenoids absorb?
absorb wavelengths of light mainly in the blue-violet region of the spectrum
what is chromatography?
an technique that is used to separate a mixture by dissolving it in a solvent (the mobile phase) and passing it through a solid (the stationary phase)
principles of chromatography:
-dfferent components within the mixture travel through the material at different speeds
-this causes the different components to separate
-an rf value can be calculated for each component of the mixture
most common chromatography techniques:
-paper chromatography
-thin-layer chromatography
what is paper chromatography?
the mixture of pigments is passed through paper
what is thin layer chromatography?
the mixture of pigments is passed through a thin layer of adsorbent, through which the mixture travels faster and separates more distinctly
equipment of chromatography practical:
-leaf
-distilled water
-pestle and mortar
-filter paper
-capillary tube
-chromatography solvent
-acetone
-pencil & ruler
method of chromatography practical:
1) draw a straight line in pencil approx 1cm above the bottom of the filter paper being used
2) cut a section of leaf and place it in a mortar
3) add 20 drops of acetone and use the pestle to grind up the leaf sample and release the pigments
4) extract some of the pigment using a capillary tube and spot it onto the centre of the pencil line you have drawn
5) suspend the paper in the chromatography solvent so that the level of the solvent is below the pencil line
6) leave the paper until the solvent has reached the top of the paper
7) remove the paper from the solvent and draw a pencil line marking where the solvent moved up to
8) the pigment should have separated out and there should be different spots at different heights above the pencil line, these are the separate pigments
9) calculate the Rf value for each spot
what is the mobile phase?
-the solvent that moves up the paper
-it carries any soluble molecules with it as it moves
mobile phase: speed
the greater the affinity a molecule has in the mixture has in the mobile phase, the faster it will travel
what is the stationary phase?
is contained on the paper and does not move through it
