Photosynthesis Flashcards
In natural ecosystems, most of the light falling on producers is not used in photosynthesis. Suggest two reasons why
Light misses chlorophyll
Not correct wavelength
Light is reflected
Co2 conc or temp is limiting
Atrazine binds to proteins in the electron transfer chain in chloroplasts of
weeds, reducing the transfer of electrons down the chain.
Explain how this reduces the rate of photosynthesis in weeds.
- Reduced transfer of protons across thylakoid membrane
OR
Reduced chemiosomotic gradient / proton gradient across thylakoid
membrane;
AQA Biology A-Level - Photosynthesis MS PhysicsAndMathsTutor.com - (So) less ATP produced;
- (So) less reduced NADP produced;
Accept NADPH / NADPH2 / NADPH+
Reject reduced NAD - (So) light-independent reaction slows / stops;
OR
Less reduction of GP to triose phosphate.
Atrazine binds to proteins in the electron transfer chain in chloroplasts of
weeds, reducing the transfer of electrons down the chain.
When treated with Atrazine, weeds have been shown to give off small
amounts of heat.
Suggest an explanation for this observation.
) Idea that energy is released from high energy / excited electron/s (that
were lost from chlorophyll)
Explain how chemicals which inhibit the decolourisation of DCPIP could
slow the growth of weeds.
. Less / no ATP produced;
2. Less / no reduced NADP produced;
3. Less / no GP reduced / converted to TP;
2, Accept: less / no NADPH / NADPH2 / NADPH +
H
where is rubisco found in a cell?
Stroma
Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction
(Less/no) ATP;
2. (Less/no) reduced NADP;
Accept NADPH, NADPH + H, NADPH2 NADPH +
H+
Reject reduced NAD, NADH etc,
Another effect of heat stress is a decrease in the activity of the enzyme
rubisco. A decrease in the activity of an enzyme means that the rate of the
reaction it catalyses becomes slower.
A decrease in the activity of the enzyme rubisco would limit the rate of
photosynthesis.
Explain why.
(Less/no) carbon dioxide (reacts) with RuBP;
2. (Less/no) GP;
The pigments in leaves are different colours. Suggest and explain the
advantage of having different coloured pigments in leaves
(Absorb) different/more wavelengths (of light) for photosynthesis;
Accept wider/larger range of wavelengths.
Accept frequency for wavelength.
Accept light-dependent reaction /photophosphorylation
/photoionisation for photosynthesis
Explain why the student marked the origin using a pencil rather than using
ink
Ink and (leaf) pigments would mix
OR
(With ink) origin/line in different position
OR
(With pencil) origin/line in same position
OR
(With pencil) origin/line still visible;
Describe the method the student used to separate the pigments after the
solution of pigments had been applied to the origin
Level of solvent below origin/line;
Reject water or any named aqueous solution.
Accept named organic solvent.
2. Remove/stop before (solvent) reaches top/end
Describe what happens during photoionisation in the light-dependent
reaction
- Chlorophyll absorbs light
OR
Light excites/moves electrons in chlorophyll;
Ignore photosystems. - Electron/s are lost
OR
(Chlorophyll) becomes positively charged;
Ignore site/molecule from where electrons are lost.
Accept electrons go to electron transport/carrier chain for
‘electrons lost’.
Describe the light dependent reaction
- A photon of light is absorbed by chlorophyll in Photosystem II. The energy from this photoexcites an electron which jumps from chlorophyll to an electron carrier.
- The electron jumps to the proton pump. It’s energy is used to transport protons form the stroma to the thylakoid lumen.
- Protons flow from the thylakoid lumen to the stroma through ATP synthase (via chemiosmosis). The energy provided by the protons allows ATP synthase to catalyse ADP + Pi to ATP.
- Chlorophyll in PSII is now oxidised. PSII breaks water into 2e- 2H+ and 1/2 O2. The electrons released reduce chlorophyll. This is called the photolysis of water.
- A photon of light photoexcites an electron at PSI. This electron is lost from chlorophyll and reduces the co-enzyme NADP+ + 2e- + H+ goes to NADPH.
Describe the Light independent reaction
Co2 reacts with RuBP to form 2x G-3-P. Thid reaction is catalysed by the enzyme rubisco.
GP is reduced to TP using energy from ATP and by accepting a H from reduced NADP. Some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances.
The rest of the molecule is used to regenerate RuBP, with energy from ATP.
(Whilst glucose is the product, the monosaccaride can join to form disaccharides such as sucrose, and polysaccharides such as cellulose and starch It can also be converted into glycerol and therefore combine with fatty acids to make lipids for the plant)
For maximum PS, common agricultural practices incorporate techniques to remove limiting factors like…
The extent to which each technique is used needs to be considered in terms of…
artificial lighting
heating
burning fuel (for Co2)
profit. Needs to be cost effective.
