PHOTOSYNTHESIS

3.8 Standard Level8.2 Additional Higher Level

8.2.1 DRAW & LABEL a diagram showing the structure of a chloroplast as seen in electron micrographs.

(a) Cell wall(b) Double membrane(c) Starch grain(d) Grana(e) Thylakoid(f) Stroma

3.8.1 State that photosynthesis involves the conversion of light energy into chemical energy.

Need carbon dioxide, water, w/light and chlorophyll...

glucose and oxygen

3.8.2 State that light from the Sun is composed of a range of wavelengths (colors).

Sunlight = white light (all colors, λ)

3.8.4 Outline the differences in absorption of red, blue, and green light by chlorophyll.

Shine white light through a chlorophyll solution

Some absorbed, some not absorption spectrum

Orange-red & blue mostly absorbed

Green mostly reflected/transmitted

8.2.7 Explain the relationship between the action spectrum and the absorption spectrum of photosynthetic pigments in green

plants.

• Not all wavelengths are equally used in photosynthesis

• Action spectrum shows how well used

• Blue, red are peaks for absorption & action b/c rate of photosynth

• Low abs green b/c reflection from chlorophyll...green appearance

3.8.3 State that chlorophyll is the main photosynthetic pigment.

Green, reflects green light & absorbs all others

Several (chl a, chl b ,etc)

Each has own absorption spectrum

3.8.5 State that light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen.

Light dependent reactions

8.2.2 State that photosynthesis consists of light-dependent and light-independent reactions.

light-dependent reactionsNEED lightOn thylakoid membrane

light-independent reactionsAny time, depending on

reactants (ATP and NADPH from light-dependent)

In stroma

8.2.3 Explain the light-dependent reactions.

Use light energySplit water

H+, e- Produce ATP, NADPH (go to light-indep rxns)

O2 = waste, leaves chloroplastThylakoid membrane

Non-cyclic photophosphorylationCyclic photophosphorylation

8.2.3 Explain the light-dependent reactions.

Cyclic photophosphorylationE- go to 2nd e- acceptor, but don’t

produce NADPHInstead, go thru membrane, ETC,

redox rxns, returned to PSIPSII not involvedDoesn’t produce NADPH

Doesn’t drive Calvin CycleWon’t produce carbs for energy

storageDoes produce ATP

8.2.3 Explain the light-dependent reactions.Non-cyclic photophosphorylation

Light absorbed by PSII (grana)Excites e-

(higher energy level, move away from nucleus) (“photoactivation of PSII”)

E- taken up by e-acceptorChl a gets + chargeseveral e-carriers in membrane (redox rxns), to PSI

(ETC)Photolysis: Chl a+ induces lysis of waterLight also absorbed in PSI,

photoactivation of PSI; different e- acceptor, passed on, taken up by NADP+ Reduced to NADPH

Chl a+ of PSI receives e- from ETC (from PSII) & becomes uncharged

8.2.4 Explain photophosphorylation in terms of chemiosmosis.

E- from photolysis taken up by Chl a+ (PSII)Chl a+ Chl aOxygen released (waste)

H+ pumped to inside grana, accumulate (thyl space), conc gradient

ATP synthase: phosphorylation of ADP + P ATP

“photophosphorylation” b/c light involved

e-

3.8.6 State that ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.

Light-independent reactions

ATP High energy bonds

between P groups Reversible

8.2.5 Explain the light-independent reactions.

ATP, NADPH, H+ from lt-dep rxnsCalvin CycleCombine 3 CO2s into 1 triose phosphate

(3C)2 of these combine to form glucose (6C)Stroma

8.2.5 Explain the light-independent reactions.

RuBP: CO2 acceptorRuBP carboxylase: Rubisco (catalyst)Takes up CO2, forms GP (G3P)GP reduced to TP but needs energy from

ATP and reducing power from NADPHTP converted to glucose, sucrose, starch,

fatty acids, amino acids, ...RuBP regenerated (use ATP) to keep it

going

3.8.7 Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass.

Production of oxygen Enclosed/controlled expt

Shine bright light on water plant Measure oxygen in water

Uptake of carbon dioxide Enclosed/controlled expt

Measure CO2 before/after or pH of water

Increase in biomass Change in organic matter, not water Indirect measurement of photosynth. Dehydrate the plant before massing

3.8.8 Outline the effects of temperature, light intensity, and carbon dioxide concentration on the rate of photosynthesis.

Temperature: Optimal ranges

for enzymes Kinetic energy

of reactants denaturation

Light intensity: Increases, rate

increases Too high can

damage chlorophyll

[Carbon dioxide]: Reactant (like

[substrate]) Saturation level =

max rate Shaded on graph

8.2.6 Explain the relationship between the structure of the chloroplast and its function.

Large thylakoid sfc areaIncreased area for light absorptionMany light-dep rxns take place @ same time

Small space inside thylakoidsAccumulation and concentration of H+Small change big effect in conc.

Fluid-filled stromaLight-indep rxns here, need enzymes (Rubisco)Enzyme concentrationpH facilitates rxns too

8.2.8 Explain the concept of limiting factors in photosynthesis, with reference to light intensity, temperature, and concentration of carbon dioxide.

Light intensityIncreases rate to certain level, then no longer

a limiting factor[CO2]

sameTemperature

Low – lim factor b/c kinetic energyOptimumHigh – lim factor b/c enzymes denature

•Iron is limiting – seeding algae with iron stimulates algal blooms. •used in ferroxidase – responsible for reduction of NADP+ in the light dependent reactions.

•Results with CO2 were short-term. Levels dropped in the immediate area, but the seeding is too expensive to work.

•Pros: possible reduced CO2 levels, algal blooms provide food for grazers and thus fisheries.

•Cons: large blooms block light to lower levels, may cause eutrophication; Diatoms block gills of some species; iron seeding may encourage blooms of toxic algae; who owns the ocean?