chapter 13 Flashcards
Where in the chloroplast does the light-dependent stage of photosynthesis occur?
In the thylakoids.
In which cell organelle does
photosynthesis occur?
In the chloroplasts of plant cells.
Where in the chloroplast does the light-independent stage of photosynthesis occur?
In the stroma.
Why are there many different photosynthetic pigments?
Each pigment absorbs light most efficiently at
specific wavelengths. Having multiple pigments
allows the organism to capture more energy from
the Sun, compared to having just one pigment.
Which photosynthetic pigment is found in all photosynthetic plants?
Chlorophyll a.
Which colours of light do chlorophyll pigments absorb, and which do they reflect?
Chlorophyll a and b absorb red light
(wavelength 650-700 nm) and blue light
(wavelength 400-450 nm).
The chlorophyll pigments reflect green
light (wavelength 500-550 nm). This is
why most plants are green.
Plants containing carotenoid pigments (xanthophyll and carotene) tend to be which colours?
Red, orange and yellow. The carotenoids absorb
blue light (wavelength 400-450 nm) and reflect red,
orange and yellow (wavelength 550-700 nm). The
presence of these pigments gives carrots, pumpkins
and tomatoes their colour.
Explain the difference between an absorption spectrum and an action spectrum.
An absorption spectrum measures
which wavelengths of light are
absorbed by the chlorophyll pigments.
An action spectrum measures the rate
of photosynthesis occurring at particular
wavelengths.
Name the technique used to separate chloroplast pigments.
Chromatography.
How is the Rf value calculated in chromatography?
Retention value = Distance travelled by component/Distance travelled by solvent
Define photoactivation.
The process by which two electrons in the
chlorophyll molecule become excited (due to
absorption of light energy) which causes them
to leave the molecule. This results in the
ionisation of the chlorophyll molecule.
What happens to the electrons that leave the chlorophyll molecule during photoactivation?
The two electrons are taken up by an electron
acceptor. From here, they move down electron
carriers within the thylakoid membrane in the
electron transfer chain (ETC). The electrons
release energy as they move down the ETC.
How is the energy from the ETC used in the light-dependent stage?
The energy lost from the electrons is used to pump
two H+ ions from the stroma into the thylakoid
space. This creates a H+ gradient across the
thylakoid membrane.
How is the H+ gradient used to make ATP?
The H+ ions in the thylakoid space exit via an ATP synthase enzyme in the thylakoid membrane. This enzyme catalyses the formation of ATP, using the energy in the H+ ion gradient.
Once in the stroma, NADP accepts the H+ ions becoming reduced NADP.
What happens to water during the light-dependent stage of photosynthesis?
Water is split using light energy (photolysis).
2H2O → 4H+ + 4e- + O2
State what happens to the products of the photolysis of water.
● H+ ions taken up by a hydrogen acceptor, NADP
● Electrons replace those lost from the chlorophyll
molecules during photoactivation
● O2 given off as a waste product
Outline cyclic phosphorylation.
● Excited electrons from photosystem I enter the ETC
● Energy from electrons used to produce ATP. The electrons return to photosystem I (hence the process is cyclic)
● There is no reduction of NADP, and no need to photolysis of water to
replace the electrons
● Cyclic photophosphorylation is performed to produce extra ATP for
immediate energy
Outline non-cyclic photophosphorylation.
● Electrons from photosystem II are excited and enter the ETC. This produces ATP and reduced NADP via generation of the proton gradient and subsequent
movement through the thylakoid membrane.
● The electrons then move to photosystem I, so photolysis of water is required to replace the lost electrons from photosystem II (hence the term non-cyclic).
● Non-cyclic photophosphorylation produces ATP and reduced NADP, which are important for the light-independent stage.
What are the two important products of the light-dependent stage that are used in the light-independent stage?
ATP and reduced NADP - these
compounds transfer energy from the
light-dependent stage which is used later.
Name the three stages of the Calvin cycle in the light-independent stage.
- Fixation of carbon dioxide
- Reduction
- Regeneration
During fixation, which molecule does CO2 combine with?
Ribulose bisphosphate (RuBP), a 5-carbon sugar.
Name the enzyme that catalyses the fixation of CO2.
Rubisco (in the stroma)
What is the product of the fixation of CO2
2 molecules of glycerate 3-phosphate (GP), a 3-carbon compound.
Describe the reduction step of the light-independent stage.
● Two molecules of GP are reduced to two molecules of triose phosphate (TP). ATP and reduced NADP are required for this step.
● ATP is hydrolysed to provide energy for the conversion. Reduced NADP is used to reduce GP.
● This results in two ADP molecules and two NADP molecules. NADP returns to the light-dependent stage to be reduced again.
