subject guide notes

C1.3.1—Transformation of light energy to chemical energy when carbon compounds are produced in photosynthesis

organisms hv developed the ability to absorb light energy from sun & convert it into chemical energy, in the form of glucose & other carbon compounds

this provides energy for all organisms

  • producers use photosynthesis to produce energy & carbon compounds. these are transferred to the primary consumer, then secondary consumer, then tertiary consumer

C1.3.2—Conversion of carbon dioxide to glucose in photosynthesis using hydrogen obtained by splitting water

hydrogen is needed to convert CO2 to glucose

  • water is common source for hydrogen

photolysis splits the water, so hydrogen can be accessed

  • byproduct is oxygen

C1.3.3—Oxygen as a by-product of photosynthesis in plants, algae and cyanobacteria

remember - the oxygen produced by photosynthesis comes from the splitting of water

without release of oxygen - life wouldn’t exist

C1.3.4—Separation and identification of photosynthetic pigments by chromatography

C1.3.5—Absorption of specific wavelengths of light by photosynthetic pigments

different photosynthetic pigments, such as chlorophyll a & b & xanthophyll & carotenoids, all absorb & reflect different wavelengths of light

  • the wavelengths reflected give the pigments their color

photons of light & the energy they carry, excite the electrons in the chlorophyll, which’re used to power the light-dependent stage

C1.3.6—Similarities and differences of absorption and action spectra

both these graphs involve a depiction of wavelengths

absorption spectra focus more on the wavelengths that’re absorbed by each pigment

action spectra depicts which wavelengths are most efficient for photosynthesis

C1.3.7—Techniques for varying concentrations of carbon dioxide, light intensity or temperature

experimentally to investigate the effects of limiting factors on the rate of photosynthesis

rate of photosynthesis can be limited by different limiting factors, such as:

  • CO2 concentration

  • light intensity

  • temperature

in experiments:

  • CO2 concentration can be adjusted by using sodium hydrogen carbonate

  • light intensity can be adjusted by changing the distance of the primary light source

  • temperature can be changed by using an ice bath

C1.3.8—Carbon dioxide enrichment experiments as a means of predicting future rates of photosynthesis and plant growth

these experiments help us understand how plants respond to high CO2 levels

two methods:

using enclosed greenhouses - if other conditions are controlled & there’s a control greenhouse that doesn’t hv enriched CO2, then the effect of CO2 enrichment can be measured through different ways

  • one of these ways is the total biomass produced, which could be measured through the yield of fruits or vegetables produced

does involve natural factors that aren’t considered

free-air carbon dioxide enrichment experiments (FACE) - CO2 is released in a circular area

  • pipes surround the area & continuously release CO2

  • sensors in the area monitor CO2 levels to ensure that elevated levels are maintained

is a natural way of measuring impact of high CO2 levels

but is expensive to carry out

C1.3.9—Photosystems as arrays of pigment molecules that can generate and emit excited electrons

photosynthesis begins with photosystems

photosystems are always located on membranes

in plants they’re located on the thylakoid membranes of chloroplast

occur in cyanobacteria & the chloroplasts of photosynthetic eukaryotes

chlorophyll a molecule within the photosystem functions as a reaction centre

pigments (which include chlorophyll a, b, & accessory pigments) are arranged in such a way that maximises light absorption across multiple wavelengths & energy transfer to the reaction centre

when photons of light strike the pigment molecules, they’re excited

excited electrons transferred through pigment array until they reach the reaction centre chlorophyll molecule

here, photoactivation occurs, releasing an excited electron

two types of photosystems - photosystem I & photosystem II

photosystem I is more sensitive to wavelengths of 700nm, & photosystem II is more sensitive to wavelengths of 680nm

  • this doesn’t mean they can only absorb light of this wavelength - their pigments allow them to absorb a range of wavelengths. it’s just that these wavelengths are the most effective at activating the chlorophylls & exciting electrons

photosystem II is first photosystem to be activated by light

C1.3.10—Advantages of the structured array of different types of pigment molecules in a photosystem

a single molecule of chlorophyll or pigments would not be able to complete a single part of photosynthesis

wider collection of pigments = wider range of wavelengths 3can be absorbed

if light energy was absorbed by individual pigments, there wouldn’t be enough energy generated to excite the electrons

C1.3.11—Generation of oxygen by the photolysis of water in photosystem II

release of electrons from photosystem II = creates unstable molecule in oxidised state

reaction centre is now oxidised, making it more powerful

  • this is the reason for photolysis?

photolysis also provides a continuous supply of electrons, replacing the electrons lost by photosystem II

C1.3.12—ATP production by chemiosmosis in thylakoids

photophosphorylation uses chemiosmosis to produce ATP?

excited electrons are released to the ETC

as they move, they lose energy

  • this energy is used to carry out chemiosmosis

hydrogen ions (protons) are pumped from the stroma into the thylakoid lumen

  • thylakoid membrane impermeable to protons = high buildup or concentration of protons in the thylakoid membrane

  • establishes electrochemical gradient

similar to cell resp - protons move through ATP synthase

as they flow, they release enough energy to phosphorylate ADP into ATP

photophosphorylation can be cyclic or non-cyclic

cyclic is when the electrons are lost from & return to the same photosystem

non-cyclic is when electrons are lost from photosystem II BUT return to photosystem I

C1.3.13—Reduction of NADP by photosystem I

NADP (Nicotinamide Adenine Dinucleotide phosphate) is electron carrier

accepts 2 electrons from photosystem I & one hydrogen from the stroma

C1.3.14—Thylakoids as systems for performing the light-dependent reactions of photosynthesis

thylakoid membrane contains: photosystems, ETC & ATP synthase

  • so, photolysis, ATP production via chemiosmosis & reduction of NADP occur in the membrane

small intermembrane space within the thylakoids helps create the electrochemical gradient (cu the space is so small & narrow that the H+ build up)

intermembrane space - also where water is split by photolysis, producing oxygen

grana provide lots of SA to allow for lots of ATP synthase, ETC & photosystems

C1.3.15—Carbon fixation by Rubisco

CO2 is fixed by adding it to Ribulose bisphosphate (RuBP)

  • forms 2 molecules of glycerate 3-phosphate (GP)

this reaction is catalysed by Rubisco

Calvin Cycle occurs in the stroma

  • this is where there’s a high concentration of Rubisco

many molecules of Rubisco are needed cuz it’s a relatively slow enzyme

it can also be competitively inhibited by oxygen, making it inefficient when there’s low concentrations of CO2

C1.3.16—Synthesis of triose phosphate using reduced NADP and ATP

ATP provides energy & reduced NADP provides a hydrogen

  • together, these are used to convert GP to triose phosphate

C1.3.17—Regeneration of RuBP in the Calvin cycle using ATP

regeneration of one RuBP molecule requires energy from one ATP

5 molecules of triose phosphate (3-carbon molecule) are converted to 3 molecules of RuBP (5-carbon molecule)

fixing 6 molecules of CO2 = 12 triose phosphate molecules produced

C1.3.18—Synthesis of carbohydrates, amino acids and other carbon compounds using the products of the Calvin cycle and mineral nutrients

all the carbon in photosynthesizing organisms has been fixed in the Calvin Cycle

each carbon compound is produced using its own metabolic pathway

so the carbon compounds produced through the Calvin Cycle are used to form carbs, amino acids, lipids & starch

  • the carbon compounds are also used to form nucleotides

C1.3.19—Interdependence of the light-dependent and light-independent reactions

each reaction requires each other in order to function

light-independent requires ATP & reduced NADP from light-dependent

if light-