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21st SYNOPTIC > chromatography > Flashcards

chromatography Flashcards

1
Q

chloroplasts contain…

A

several different photosynthetic pigments within the thylakoids

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2
Q

what do photosynthetic pigments do?

A

absorb different wavelengths of light

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3
Q

where does the LDS occur?

A

thylakoid membranes and the thylakoid spaces

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4
Q

what does the thylakoid membrane system do?

A

provides many pigment molecules in an arrangement that ensures as much light as necessary is absorbed

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5
Q

how are pigments molecules arranged?

A

in light-harvesting clusters (photosystems)

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6
Q

how are pigments molecules arranged in a photo system?

A

-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

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7
Q

how many groups of pigments are there and what are they?

A

two groups:
primary pigments → chlorophylls
accessory pigments → carotenoids

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8
Q

what are the primary pigments in each photosystem?

A

photosystem I = chlorophyll a
photosystem II = chlorophyllb

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9
Q

where are accessory pigments?

A

they surround the primary pigment

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10
Q

what do accessory pigments do?

A

-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

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11
Q

chlorophyll colours:

A

chlorophyll a → blue-green
chlorophyll b → yellow-green

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12
Q

carotenoid colours:

A

β carotene - orange
xanthophyll - yellow

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13
Q

what do chlorophylls absorb & reflect?

A

-they absorb wavelengths in the blue-violet and red regions of the light spectrum

-they reflect green light, causing plants to appear green

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14
Q

what do cartenoids absorb?

A

absorb wavelengths of light mainly in the blue-violet region of the spectrum

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15
Q

what is chromatography?

A

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)

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16
Q

principles of chromatography:

A

-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

17
Q

most common chromatography techniques:

A

-paper chromatography
-thin-layer chromatography

18
Q

what is paper chromatography?

A

the mixture of pigments is passed through paper

19
Q

what is thin layer chromatography?

A

the mixture of pigments is passed through a thin layer of adsorbent, through which the mixture travels faster and separates more distinctly

20
Q

equipment of chromatography practical:

A

-leaf
-distilled water
-pestle and mortar
-filter paper
-capillary tube
-chromatography solvent
-acetone
-pencil & ruler

21
Q

method of chromatography practical:

A

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

22
Q

what is the mobile phase?

A

-the solvent that moves up the paper
-it carries any soluble molecules with it as it moves

23
Q

mobile phase: speed

A

the greater the affinity a molecule has in the mixture has in the mobile phase, the faster it will travel

24
Q

what is the stationary phase?

A

is contained on the paper and does not move through it

25
Q

stationary phase: speed

A

the greater the affinity (attraction) the molecule in the mixture has in the stationary phase, the slower it will move with the mobile phase

26
Q

different components & their phases:

A

-the different dissolved substances in a mixture are attracted to the two phases in different proportions
-this causes them to move at different rates through the paper

27
Q

how to calculate the rf value:

A

distance travelled by pigment ÷ distance travelled by the solvent

28
Q

which part of the pigment should you measure ?

A

always measure to the centre of each spot

29
Q

what are chromatography results used to do?

A

identify chloroplast pigments that have been extracted from a leaf as each pigment will have a unique rf value

30
Q

what does the rf value demonstrate?

A

how far a dissolved pigment travels through the stationary phase

how easy it was for that substance to dissolve and move up the paper

31
Q

what does a small rf value mean?

A

the molecule has a higher affinity to the stationary phase

32
Q

what does a large rf value mean?

A

the molecule has a higher affinity for the mobile stage (more soluble)

33
Q

rf value of cartenoids, chlorophyll and & b?

A

-carotenoids have the highest rf values (usually close to 1)

-chlorophyll b has a much lower rf value

-chlorophyll a has an rf value somewhere between carotenoids and chlorophyll b

(xanthophyll is very low)

34
Q

what does a small rf value suggest about the pigment?

A

the pigment is less soluble and/or larger in size

35
Q

limitations of paper chromatography:

A

paper chromatography is not as specific as other chromatography techniques
→ It is sufficient to separate and distinguish different pigments and to calculate their rf value

36
Q

limitations of general chromatography:

A

chromatography does not give data on the amount of each pigment present or the wavelengths that they absorb

37
Q

why isn’t a pen used for chromatography?

A

the ink will separate into pigments within the experiment and obscure the results

38
Q

what type of leaf must be chosen?

A

it’s important to choose a healthy leaf that has been in direct sunlight so you can be sure it contains many active photosystems

21st SYNOPTIC (9 decks)

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