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A- Level Biology - Photosynthesis > Photosynthesis Experiments > Flashcards

Flashcards in Photosynthesis Experiments Deck (38)
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What are different about all plants?

Different photosynthetic pigments in their leaves

Each pigment absorb different wavelength of light 

so more than one type of pigment increases range of wavelength of light the plant can absorb


Why do pigments play an essential role other than photosynthetic pigments?

Protecting leaves from excessive UV radiation


What do different species of plant contain?

Different proportion and mixture of pigments


How to experiment the different pigments presented in leaves?


(Thin layer chromatography)


What does TLC involve?

  • Mobile phase
  • Stationary phase


What is mobile phase?

Where molecules can move

in TLC this is a liquid solvent


What is stationary phase?

Where molecules move

TLC consist of solid (e.g glass plate)

plate with a thin layer of gel (e.g silica gel) on top


Why does TLC help?

A sample of pigments can be extracted from a plant and put onto the TLC plate

When a plate is placed vertically in solvent, solvent move upwards through the gel carrying the dissolved pigments through it

Some pigments travel faster or further through the gel than others making them separated


How to identify a certain pigment?

Calculating its R1 value and looking up in database 

R1 is the distance a substance has moved through the gel in relation to solvent

Each pigment has a specific R1 value


How to investigate using TLC?

Compare pigments present in shade-tolerant plants and shade-intolerant plants


What are the safety factors in TLC investigation?

Wear lab coat, eye protection , gloves

Because of chemicals involed are toxic and highly flammable


What are the first step of TLC

Grind up several leaves from shade tolerant plant you are investigating with some andydrous sodium sulfate

Add few drops of propane


What are the second step of TLC?

Transfer liquid to a test tube add some petroleum ether and gently shake the tube

Two distinct layers will form in liquid

Top layer is the pigments mixed in with petroleum ether


How to do the step 2 efficiently and 5?

In a fume cupboard as chemicals are volatile

they evporate easily and vapours are hazardous


What is step 3?

Transfer some of the liquid from top layer into second test tube with some anhydrous sodium sulfate


What is the fourth step?

Draw a horizontal pencil line near the bottom of TLC plate

Build up a concentrated spot from liquid from step 3 on line by applying several drops and ensuring one is dry before adding another

This is point of origin


What is the fifth step?

  • Once point of origin is dry
  • Put plate in small glass containor with prepared solvent (point of origin should be above solvent)
  • Put lid in containor and leave to develop


What happens as solvent spreads up plate?

Different pigments move with it at different rates so they separate


What is seventh step?

When solvent nearly reached the top, take plate out and mark the solvent front (furherest point the solvent has reached with pencil)


Leave the plate to dry in well-ventialted plate


What is the eighth step of TLC?

  • Repeat process for shade-intolerant and compare pigments


How to calculate Rf value?

B/A = Distance travelled by spot/Distance travelled by solvent


What do you do after the Rf value?

Look up in a database and identify the pigments


How is the pigments of leaf in shade-tolerant plant different from shade intolerant plants?

Shade tolerant

  • Adapt to light conditions by possessing different proportion of photosynthetic pigments allowing plant to make best use of light available
    • Mixture of non-photosynthetic pigments are different
  • e.g shade tolerant plants are adapted for photosynthesis in low light condition but really sensitive for higher levels of light
  • These plants produce dark red and purple pigments called anthocyanins , protect chloropladts from brieg exposure to higher levels of light


What reaction is catalysed by dehyrogenase enzyme?


NADP acts as a electron accept and it is reduced


How to measure activity of dehyrogenase enzyme?

Adding redox indicator dye to extract of chloroplasts

Dye acts as an electron accept (e.g NADP) and gets reduced by dehydrogenase in chloroplasts

As dye gets reduced - see colour change

e.g DCPIP changes from blue to colourless being reduced


How to measure the rate of dehygrongenase activity?

Measuring the rate at which DCPIP loses its blue colour

Need a colorimeter

Measure how much light a solution absorbs when light source shoen directly through

A coloured solution absorb more than colourless solution


What things does investigating effect of light intensity on dehydrogenase activity in extract in chloroplasts use?

  • A bench lamp as a light source and involve placing tubes of chloroplast extract mixed with DCPIP at range of different distance from light source
  • Light intensity should decrease with increasing distance from lamp


What is the first step of effect of light intensity on dehydorgenase activity in extract of chloroplast?

Cut a few leaves (spinach) into pieces and remove any tough stalks


What is the second step of effect of light intensity on dehydorgenase activity in extract of chloroplast?

Use pestle and mortar , grind up the leaf pieces with chilled isolation solution (sucorse, potassium chloride and phosphate buffer at pH7)

Filter the liquid you make into beaker througha funnel lined with muslin cloth


What is the third step of effect of light intensity on dehydorgenase activity in extract of chloroplast?

Transfer liquid to centrifuge tubes and centrifuge them at high speed for 10 minutes

Make chloroplasts gather at bottom - pellet