5.1 Photosynthesis Flashcards
Where does the light dependent stage occur?
thylakoid membranes
Where does the light independent reaction happen?
the stroma
What are the 2 stages of photosynthesis?
light dependent reaction
light independent reaction
What is used in the LDR?
water and light energy
What is prouced in the LDR?
ATP and reduced NADP
What are the 4 stages of the LDR?
- photolysis of water
- photoionisation of chlorophyll
- chemiosmosis
- production of ATP and reduced NADP
What is photolysis of water?
light energy is absorbed by photostem II on the thylakoid membrane and splits water into oxygen, H+ and e-
What is the equation for the photolysis of water?
H2O —-> 1/2 O2 + 2e- + 2H+
What happens to the H+ from the photolysis of water?
picked up by NADP to form reduced NADP which is used in the LIR
What happens to the e- from photolysis of water?
passed along a chain of electron carriers
What happens to the O2 from the photolysis of water?
used for resp or diffuses out of the leaf through the stomata
What is the photoionisation of chlorophyll?
light energy is absorbed by the chlorophyll and the energy excites electrons, raising their enery levels to leave chlorophyll
What is the energy released from the photoionisation of chlorophyll used for?
used to make ATP and reduced NADP in chemiosmosis
What is the LIR also known as?
the calvin cycle
What enzyme is involved with the calvin cycle?
RuBisCo
Why does temp only affect the calvin cycle not the LDR?
the calvin cycle involves enzymes
What does the calvin cycle use up?
carbon dioxide
reduced NADP
ATP
What is produced from the LIR?
a hexose sugar
What is the role of ATP in the calvin cycle?
provides energy for reaction
What is the use of reduced NADP in the calvin cycle?
donates hydrogen (protons) to reduce GP molecules
What is oxidation?
remove H+
What is reduction?
add hydrogen
Describe the process of the photoionisation of chlorophyll
Light energy isabsorbedby chlorophyll
Thisexcites2 electrons carrying them to leave thechlorophylland pass to an electron acceptor
The electrons pass along a series of electron carriers
As they pass theylose energy
This energy is used toproduce ATP from ADP and Pi by chemiosmosis
Describe the process of chemiosmosis
High energy electrons from thephotoionisationof chlorophyll passes along a series of electron carriers
As they pass they lose energy, which is used to pump protons (H+) from the stroma into the thylakoid space
The protons accumulate producing an electrochemical gradient
As a result the protons are diffuse by facilitated diffusion into the stroma via ATP synthase. This provides the energy to form ATP from ADP and Pi
Protons in the stroma and electrons at the end of the carrier chain combine with NADP to form NADPH
Describe the process of the calvin cycle
CO2 reacts with RuBP to form 2 molecules of G-3-P - this reaction is catalysed by RuBisCo
G-3-P is reduced to Triose phosphate using energy from ATP and accepting H from reduced NADP
some of the Triose phosphate leaves the cycle to be converted into useful organic substances = glucose/ sucrose
this leaves a 3C compound and a 2C compound = as 1C is removed each cycle
using ATP RuBP is regenerated from these compounds
cycle only produces 1 carbon, so it repeats
What is a limiting factor?
any factor that reduces the rate of photosynthesis
What are the 3 limiting factors of photosynthesis?
temp
CO2 conc
light intensity
Why is CO2 conc a limiting factor of photosynthesis?
it is a reactant in the calvin cycle
Why is light intensity a limiting factor of photosynthesis?
light energy is needed in the LDR for the photoionisation of chlorophyll and photolysis of water
How can each limiting factor be overcome in agriculture techniques?
light = artificial lighting
temp = heating greenhouses
CO2 conc = burning fuel
How many carbons are in G-3-P?
3
How many carbons are in RuBP?
5
How many carbons are in triose phosphate?
3
What colour is DCPIP when it is oxidised?
blue
What colour is DCPIP when it is reduced?
colourless
Describe how you would investigate the effect of light on the rate of deydrogenase activity in chloroplast extracts
x4 test tubes
x2 - chloroplast extract, DCPIP, buffer (dark green)
x1 - DCPIP, buffer (blue)
x1 - chloroplast, buffer (light green)
one of the tubes with everything in it is going to be placed in the dark, the other tubes will be plaed under a light
tube with everything under the light will turn a light green colour=DCPIP is reduced and turns blue–> colourless
tube with just chloroplast is used as a colour standard for comparisons of colour
DCPIP tube thats blue is the control for comparison of changes
What is DCPIP?
an artifical hydrogen acceptor
What is the relationship between light intensity and the rate of photosynthesis?
at low light intensity = it is the limiting factor
at high light intensity = other factors are limiting the rate of photosyn
Describe the relationship between temp and the rate of photosynthesis
at low temps = the enzymes work so slowly that photosyn virtually stops = not enough KE
as temp increases so does enzyme activity so the rate also increases
above the optimum temp = enzymes denature and the rate decreases rapidly
Describe the relationship between CO2 conc and the rate of photosynthesis
low CO2 = it is the limiting factor
high CO2 = other factors limiting the rate
What 2 measurements can be taken to determine the rate of photosynthesis while invesigating limiting factors?
the change in pH = more acidic –> more photosynthesis
volume of O2 produced
Why would increasing the CO2 conc increase the amount of glucose produced?
more GP is produced from RuBP
more GP results in more triphosphate
more TP = more glucose
Why is there an increase in photosynthesis even when no CO2 is being taken up by the plant?
plant uses CO2 from aerobic respiration for photosynthesis
How do you prepare a dilution series?
- use a known conc of extract/pigment
- prepare a dilution series
- compare with colour standards to give the concentration
When carrying out a TLC for photosynthetic pigments why is a pencil line used not ink?
the ink and the leaf pigments would mix
Describe the method the student used to separate pigments
- draw line of origin with pencil
- add pigments to chromotography paper
- level of solvent below the origin
- remove before solvents reaches the top
what is the advantage of having different coloured pigments in leaves?
absorb a greater range of different wavelengths of light in photosynthesis
What is the part played by chlorophyll in photosynthesis?
chlorophyll absorbs light
raises energy level of electrons/ electrons are excited
ATP formed
Describe and explain the relationship between light absorption and the rate of photosynthesis
more light absorption increases, rate of photosynthesis increases
light provides energy for light dependent reactions
Why does the blue colour of DcPIP disappear?
reduced NADP is formed which changes the colour of the dye
If ADP and Pi is added to a suspension of chloroplasts, why does the colour of DcPIP disappear more rapidly?
ADP and Pi are required to synthesise ATP
ADP is a limiting factor
