y5 bio: cluster 4 (photosynthesis)

what happens when you take CO2 + H and remove excess O?

glucose

equation for ‘splitting water forms hydrogen’

12H2O-> 24H+6O2

equation for ‘glucose synthesis, where half H atoms enter glucose and other half removes O from CO2

6CO2+24H -> C6H12O6 + 6H2O

chemical equation for photosynthesis

6CO2 + 6H2O + light -> C6H12O6 + 6O2

regarding chromatography of photosynthetic pigments, what do they use to dissolve pigments?

acetone/propanone

regarding chromatography of photosynthetic pigments, how to identify chlorophyll A and B from the Rf values?

their Rf values are always very close to each other (e.g. A - 0.65 and B - 0.60)

Rf value equation

distance moved by spot/distance moved by solvent

what does a higher/lower Rf value mean?

higher Rf = more attracted to hydrophobic running solvent, lower Rf = more attracted to hydrophilic chromatography strip

what can we use to determine the wavelengths of light absorbed in photosynthesis?

absorption spectrum, a graph of absorbance at each wavelength

what does high energy photon tell you about its wavelenght?

its shorter wavelength

when does chlorophyll A and chlorophyll B peak?

A - 430nm (blue), 662nm (red) AND B - 453nm (blue), 642nm (red)

blue and red light, which has shorter wavelength?

blue is shorter WL, red is longer WL

absorption VS action spectra (3 diff)

1. absorption spectra shows wavelengths absorbed by pigments, but action spectra shows relative relative rates of photosynthesis at each wavelength 2. absorption spectrum measures directly from pigment solutions, but action spectra measures O2 produced or CO2 consume per wavelength 3. at green (550nm), absorption spectra for chlorophyll pigment has a deep trough but action spectra still has some activity at green wavelengths as some accessory pigments absorb blue-green wavelengths that chlorophyll does not

when light is not absorbed by pigments, they’re instead being…

reflected! thats what happening to the light when light absorbance for chlorophyll A and B are very low from 500 to 600 WL, green and orange light

what are the 3 limiting factors (+ one bonus!) of photosynthesis?

temperature, light intensity and CO2 concentration (and amount of chlorophyll)

how to vary these 3 limiting factors of photosynthesis?

temp - thermostatically controlled water bath, light intensity - move light source, use lux meter, where intensity is directly proportionate to 1/distance^2, CO2 conc. - add NaHCO3 to water to get around 50mmol/dm3

what are CO2 enrichment experiments and examples of them?

CO2 enrichment tests effects of elevated CO2 conc on photosynthesis and plant growth. some examples are greenhouse experiments and ‘free air CO2 enrichment’ experiments

what are photosystems and what do they contain?

molecular arrays of chlorophyll + accessory pigments. they contain antenna complexes to harvest light + funnels energy to reaction centre AND reaction centres, that contain special chlorophyll, which receives energy and emit excited electrons.

what are photosystems found?

they are always found in thylakoid membranes

where are photosystems I and II found?

PSI is positioned when thylakoid membrane faces the stroma, and PSII does not ended to be in contact with the stroma

3 advantages of photosystems

1. greater light capture 2. broader wavelength absorption 3. efficient energy transfer (TLDR for understanding: a single chlorophyll molecule CANNOT perform photosynthesis alone, the structured array is essential for function)

important structures of chloroplast

1. thylakoids (a stack of them = granum)

2. thylakoid membranes

3. thylakoid spaces

4. stroma

5. starch grain

function of stroma’s adaptation

stroma contains all the enzymes and substrates needed for the Calvin cycle, for example Rubisco. this optimizes the conditions for the light dependent reaction to occur

function of thylakoid’s adaptation (includes membrane and lumen)

thylakoid has:

1. membrane - provides a large total surface area for light absorbing photosystems. provides a site for electron flow

2. space (lumen) - small volume so steep proton conc gradient builds up even after relatively few photons of light have been absorbed

P680 definition

a special chlorophyll in PS II reaction centre that absorbs 680nm light

whats a lamella?

a very long thylakoid…

examples of LIR and LDR (main processes and locations)

LIR - takes place within thylakoid membrane, LDR - calvin cycle, takes place within stroma

calvin cycle, LIR or LDR, and done where?

LIR, done at stroma (now visualise the diagram in your head)

whats the key exit product of calvin cycle?

triose phosphate (TP)

purpose of combination of TP intermediates from calvin cycle (TP + TP, GP/TP, GP/TP + N/S ions, TP intermediates)

TP+TP = glucose, which forms sucrose, starch and cellulose. GP/TP = fatty acids, which forms lipids/phospholipids. GP/TP + N/S ions = amino acids, which forms proteins