practical 7 Flashcards
Use of chromatography to investigate the pigments isolated from leaves of different plants eg leaves from shade-tolerant and shade intolerant plants or leaves of different colours.
An Investigation of pigments present in leaves
In plants, chlorophyll is the main pigment that absorbs light energy during photosynthesis. Most plants have other photosynthetic pigments as well and these are not green. You will be using a technique called chromatography to separate chlorophyll and other pigments from two different leaves, A and B.
- Students carried out similar investigations to you with green leaves and yellow leaves. The students stopped each chromatogram when the solvent front had run exactly the same distance. They then measured the distance moved by the pigment nearest the origin.
Q)Give your choice of statistical test and Give a reason for your choice of statistical test.
Student T TEST
Comparing the difference between 2 means
You were told to use a pencil to mark the origin. It was important not to use a pen to mark this line. Suggest why.
Ink would dissolve in solvent / ink would be confused with substances on chromatogram / ink will run;
Use of chromatography to investigate the pigments isolated from leaves of different plants eg leaves from shade-tolerant and shade intolerant plants or leaves of different colours.
An Investigation of pigments present in leaves
In plants, chlorophyll is the main pigment that absorbs light energy during photosynthesis. Most plants have other photosynthetic pigments as well and these are not green. You will be using a technique called chromatography to separate chlorophyll and other pigments from two different leaves, A and B.
- Students carried out similar investigations to you with green leaves and yellow leaves. The students stopped each chromatogram when the solvent front had run exactly the same distance. They then measured the distance moved by the pigment nearest the origin.
Q)You were told not to move the bottle once you had put the TLC paper in it.
Suggest why this is important.
Pigments / solvent would not run straight / would run off side of paper / pigments could wash off paper;
Use of chromatography to investigate the pigments isolated from leaves of different plants eg leaves from shade-tolerant and shade intolerant plants or leaves of different colours.
An Investigation of pigments present in leaves
In plants, chlorophyll is the main pigment that absorbs light energy during photosynthesis. Most plants have other photosynthetic pigments as well and these are not green. You will be using a technique called chromatography to separate chlorophyll and other pigments from two different leaves, A and B.
- Students carried out similar investigations to you with green leaves and yellow leaves. The students stopped each chromatogram when the solvent front had run exactly the same distance. They then measured the distance moved by the pigment nearest the origin.
Q)You could use Rf values to find out if a pigment on your chromatogram was the same as a pigment on another student’s chromatogram. Explain why it would be better to use the Rf value to do this and not the distances moved by the pigment spots.
1 The solvent / pigment moves different distances;
2 Rf value is distance moved (by spot) divided by distance moved by solvent front / Rf value is a ratio of distance moved (by spot) to distance moved by solvent front/Rf is a proportion;
3 Rf value constant (for the same pigment) / Rf values can be compared;
You were told to draw a line to show the solvent front before the filter paper dried.
Explain why it was necessary to draw the line before the filter paper dried.
Cannot see (solvent);
You were told to find the distance moved by the pigment by measuring to the centre of the pigment spot. Explain why you should measure to the centre of the pigment spot.
1 Would standardise readings;
2 Allow comparisons to be made;
3 Pigment is spread out / moves different distances;
4 It is the mean / average distance moved by the pigment
Use of chromatography to investigate the pigments isolated from leaves of different plants eg leaves from shade-tolerant and shade intolerant plants or leaves of different colours.
An Investigation of pigments present in leaves
In plants, chlorophyll is the main pigment that absorbs light energy during photosynthesis. Most plants have other photosynthetic pigments as well and these are not green. You will be using a technique called chromatography to separate chlorophyll and other pigments from two different leaves, A and B.
- Students carried out similar investigations to you with green leaves and yellow leaves. The students stopped each chromatogram when the solvent front had run exactly the same distance. They then measured the distance moved by the pigment nearest the origin.
The technique you used to extract pigments from the leaves may not produce good results if it is used with the leaves of xerophytic plants. to suggest why. 2
1 Thick cuticle;
2 Prevents pigments penetrating / prevent pigment being transferred to paper;
OR
1 Thicker / stronger leaves;
2 Lower concentration of pigment / lower amount of pigment / more cells without pigment / more tissue without pigment / harder to crush;
OR
1 Leaves are spines;
2 Have little / no pigment;
Leaves change colour in the Autumn. This is partly due to loss of chlorophyll. Describe how you could use chromatography to show that chlorophyll is lost. 2
1 Carry out chromatography at different times;
2 Find Rf for chlorophyll;
3 Look for substance at predicted position / look for green substance;
Holly usually has dark green leaves. Some cultivated varieties of holly have yellow leaves. Explain why these cultivated varieties grow more slowly than holly with dark green leaves. 3
1 Yellow leaves have less / no chlorophyll;
2 Less / no photosynthesis;
3 Products of / named product of photosynthesis needed for growth / synthesis;
Describe what happens during photoionisation in the LDR 2
Chlorophyll absorbs light
OR
Light excites/moves electrons in chlorophyll;
Ignore photosystems.
2. Electron/s are lost
OR
(Chlorophyll) becomes positively charged
describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin 2
Level of solvent below origin/line;
Reject water or any named aqueous solution.
Accept named organic solvent.
2. Remove/stop before (solvent) reaches top/end;
a suspension of chloroplast was isolated from an aquatic plant and a reagent was added. the reagent is blue when oxidised and is colourless when reduced.
the suspension of chloroplast in blue reagent was exposed to sunlight. use your knowledge of LDR of photosynthesis to explain why
(i) chlorophyll excited / reduced NADP formed;
electrons from chlorophyll / reduced NADP changes the dye colour;
a suspension of chloroplast was isolated from an aquatic plant and a reagent was added. the reagent is blue when oxidised and is colourless when reduced.
the suspension of chloroplast in blue reagent was exposed to sunlight.
another suspension of chloroplast was set up as this. small quantities of ADP and phosphate ions were added and then the tube was exposed to light. The blue colour disappeared more quickly. explain why
ADP and phosphate needed to produce ATP / ATP is a product of
the light dependent reactions;
ADP levels are a limiting factor;
(must explain the idea of limiting factors – do not
credit answers like more ADP causes more
photosynthesis)
the pigments in leaves are different colours, suggest and explain the advantage of different coloured pigments 1
(Absorb) different/more wavelengths (of light) for photosynthesis;
Accept wider/larger range of wavelengths.
Accept frequency for wavelength
