not a good long term energy source, due to its relative instability of the phosphate bonds, so fats and carbohydrates are better for storage
ATP is a source of immediate energy
ATP
small, moves easily in and out of organelles
soluble, energy requiring processes takes place in aqueous solutions
phosphate bonds have intermediate energy, the quantities of energy released are large enough to support cellular reactions but not so large that energy is wasted
easily regenerated
The hydrolysis of one mole of ATP generates 30.5 kj/mol
photosynthesis:
6CO2 + 6H20 = C6H1202 + 6o2
Light dependent reaction
energy from the sunlight is absorbed and ATP is formed
hydrogen from water is used to replace the co-enzyme NADP to reduced NADPH
Light independent reaction (calvin cycle)
hydrogen from reduced NADP and carbon dioxide are used to build organic molecules such as glucose
ATP from light dependent stage supplies energy
autotrophs make their own food using carbon dioxide via photosynthesis
heterotrophs assimilate energy by consuming plants and animals
chloroplasts
double membrane - has pigments of chlorophyll for light absorption
stroma - site of many chemical reactions, as it contains enzymes and the correct pH level for light independent reaction
thylakoid - Has ATP synthase for photophosphorylation, which absorbs light
granum - flat membrane stacks increase SA:V ratio for a faster rate of absorption
lamella - connects thylakoids and provides structure and supports to the chloroplast
respiration:
6o2 + C6H12o6 = 6CO2 + 6H20 + energy
Photosynthesis stages:
Capturing of light energy - pigments of chlorophyll.
Light dependent reaction - light energy converted into chemical energy.
Light independent reaction - sugars and other organic molecules are produced.
Photosynthetic pigments:
chlorophylla - main pigment that absorbs red and blue light and reflects green light
chlorophyll b - an accessory pigment mostly found with chlorophyll a in light-harvesting complex
Xanthophylls and carotenoids - absorb different wavelengths than chlorophyll, broadening the spectrum of light that can drive photosynthesis.
Light dependent stage:
takes place in thylakoid membrane
light energy absorbed by photosystems
water split by photolysis
excited electrons are passed along the electron transport chain
some ATP is produced by photophosphorylation
NADP is reduced
LDS:
light is absorbed & electrons get excited
light shines on photosystem 2
the absorbed energy leads to excitation of 2 electrons which then are accepted by the electron transport chain
LDS:
2. water is split into protons, electrons and oxygen
photosystem 2 contains an enzyme that split water in the presence of light - photolysis
the 2 electrons are used to replace the 2 excited electrons which have left chlorophyll in photosystem 2
Photolysis - splitting of water by light
photolysis equation:
2H20 = O2 + (4H+) +(4e-)
LDS:
3. high energy electrons are moved along the electron transport chain
at each stage a small amount of energy is released
electron carriers are molecules which all contain iron
energy is used to pump protons (H+) across the thylakoid membrane from stroma into thylakoid space forming a proton pump
LDS:
4. Proton gradient is used to drive the production of ATP by ATP synthase
this is chemiosmosis
Production of ATP from ADP and phosphate using light is called photophosphorylation
photophosphorylation - ATP formed using light energy
two types of photophosphorylation:
cyclic
non-cyclic
cyclic photophosphorylation:
uses only photosystem 1
excited electrons pass to an electron acceptor and back to the chlorophyll molecule
electron pass along electron transport carriers
electrons leaving return to photo stage 1
energy released is used to synthesise ATP
no NADP is formed/used
non-cyclic photophosphorylation:
involves photosystem 1 and 2
light strikes photosystem 2, excites electrons which pass along electron transport chain and energy released is used to synthesise ATP - chemiosmosis
electrons lost from ps2 are replaced from water by being broken down by photolysis
light strikes photosystem 1 and a pair of electrons are lost which travel along ETC and ATP is produced - chemiosmosis
electrons get accepted along with hydrogen ion, by NADP forming reduced NADP
Light independent reaction
builds sugars from carbon dioxide and regenerates ribulose bisphosphate (RuBP)
takes place in the stroma of the chloroplast
uses ATP and reduced NADP from the light independent stage
Light independent reaction
fixation
reduction
regeneration
Light independent reaction
fixation
the RUBISCO enzyme catalyses the combination of ribulose bisphosphate (RuBP) and carbon dioxide
RuBP is a 5-carbon compounds which forms a transient (breaks down easily) molecule
The 6-carbon immediately splits into two molecules of glycerate-3-phosphate (GP)
Light independent reaction - fixation stages as a flow chart
RuBP (5c) + Co2 (1c) (catalysed by RUBISCO) = 6c = 3c (GP) + 3C (GP)
Light independent reaction:
2. reduction
glycerate-3-phosphate (GP) is then changed into triose phosphate (TP) by the addition of phosphate (from ATP) and hydrogen (from reduced NAPD) from the light dependent reaction
Light independent reaction:
3. regeneration
5 out of every 6 molecules of triose phosphate (TP) are recyled by phosphorylation, using ATP from the light dependent reaction and the rest are used to make glucose, lipids and amino acids
Light independent reaction
some glycerate-3-phosphate (GP) is used to make amino acids and fatty acids
glucose can be isomerised to form fructose
glucose and fructose can combine to form sucrose
pairs of triose phosphate (TP) can form sugars
photosynthesis requires:
photosynthetic pigment - absorb light energy
co2 - provides carbon to make glucose
water - provides electrons and hydrogen irons
light energy - energy to split water into ATP and reduced NADP
enzymes - internal
limiting factor - factor in lowest supply and therefore limiting the rate of reaction
Light intensity:
limits the light dependent reaction
less light = less excitation of chlorophyll and electrons
less electrons pass down the electron transport chain
Light intensity:
limits the light dependent reaction and glucose-3-phosphate (GP) accumulates
ATP and reduced NADP are not produced, therefore GP cannot be reduced to triose phosphate (TP)
Light intensity:
low light intensity - limits LDS, so not much ATP and NADPH are produced. Slows LIR and photosynthesis slows.
moderate light intensity - produced more ATP and NADPH in LDS, which regenerates RuBP in LIS quicker. More GP converted into TP.
high light intensity - more light than needed, so temperature becomes limiting factor and rate plateaus
carbon dioxide concentration:
co2 concentration limits lightindependentreaction
less co2 means there is less available to combine with RuBP