photosynthesis chap 2 photosynthetic pigments

State two adaptations of palisade mesophyll cells and explain how this allows them to carry out their function (2)

They are densely packed with chloroplasts to increase harvesting of light (1)

They are long and thin, with tiny gaps between them to increase surface area for CO₂ to diffuse in (1)

They are densely packed to maximise harvesting of sunlight (1)

1. Give two examples of coenzymes formed in the light dependent reaction

 Reduced NADP and ATP

wat is the priamry pigment in plants

chlorophyll a

what are the accessory pigments & colours

xanthophyll-yellow carotenoids - orange and cholorophyll b - blue green

Photosynthesis is an endothermic reaction. Explain why.

 Overall, energy is absorbed from the surroundings to enable the reaction to occur (from light)

Give three reasons why most of the energy from light hitting a leaf is not transferred via photosynthesis to make glucose

Some light is reflected (wavelengths for green light). (1)

Some light is transmitted through the leaf / does not hit a chloroplast (1) 

Some energy from light cannot be harnessed if another factor (e.g. CO₂) is limiting (1)

Leaves can be crushed, and thin layer chromatography can be used to separate pigments. Why is water not used as the solvent?

pigments are insoluble / less soluble in water so would not dissolve and move up the chromatography plate

How can the data from chromatography be used to identify a specific pigment?

Measure the distance from origin to solute  (1)

Measure distance from origin to solvent front (1)

Divide the first distance by the second to get an Rf value that is 1.0 or less. (1)

Compare the Rf value to a set of known Rf values to identify the pigment (1)

Explain why different pigments would separate using chromatography

 pigments differ in polarity and solubility

They have different interactions with the solvent (mobile phase) and chromatography plate (stationary phase) thus move up at different rates

Give four steps taken to ensure the results of thin layer chromatography are accurate

a. Draw origin line in pencil to avoid it dissolving and moving

b. Don’t allow solvent to reach the top of the plate, as a reliable distance moved by solvent cannot be measured

c. Don’t allow thin layer plate to touch sides of the container (adhesion will draw up solvent faster on the sides)

d. Don’t touch the plate as oil will contaminate sample – wear gloves, only touch the sides

e. Ensure the solute is below the origin line so it diffuses up the plate

how to convert between nm to mm

divide by 10⁶

Explain why it would be harmful for a plant if it didn’t produce Chlorophyll b or beta carotene

wavelengths of light that can be absorbed by the plant would be reduced, so less energy can be transferred to form biomass (1). Thus the plant would produce less biomass for respiration (1)

where ate the photo systems embedded

thylakoid membrane

what does the photosystem consist of

antenna complex and reaction centre

what does the antenna complex have

contains hundreds of diff accessory pigments molecules that absorbs diff wavelengths of light to max transfer of energy

what does the reaction centre have and what does it do

contains proteins and chlorophyll a (primary pig) energy funnelled from antenna complex to reaction centre exciting a pair of e-. when enough energy is transferred the e- can break away from chlorophyll a ionising it. e- donated to e- transport chain across membrane

Suggest what might happen if there were no accessory pigments surrounding the reaction centre

A narrower range of wavelengths of light would be harvested. (1)

Therefore less energy is transferred to Chlorophyll a / the reaction centre (1)

Therefore electrons aren’t excited enough to cause them to enter the ETC, so photosynthesis cannot occur (1)

What would the charge be on a Chlorophyll a ion once formed?

2+ as 2 neg e- are lost

What is the chemical term for what happens to Chlorophyll a when it transfers electrons to the electron transport chain?

oxidation as e- are lost to the etc (electron transport chain)

Why is it important for thylakoids to have large surface areas, with reference to the above information?

Large surface areas provide space for many photosystems. This increases the amount of light harvested to transfer more energy

Explain how the primary pigment differs from the accessory pigments in function

The primary pigment can donate excited electrons to the ETC (as it is within the reaction centre), but accessory pigments only transfer energy to the primary pigment without donating electrons.