5.1 photosynthesis Flashcards
What is the overall equation of photosynthesis?
6CO2 + 6H2O ——> C6H12O6 + 6O2
What are the 2 stages of photosynthesis?
Light dependent and light independent
Where does the light dependent stage occur?
Thylakoid membrane
What is the first stage of photosynthesis?
Light dependent stage
What does the light dependent stage require?
Light
What happens in the photolysis of water?
- Light energy is absorbed by chlorophyll
- Splits water into oxygen, H+ and e-
What is the equation for the photolysis of water?
H2O —> 1/2O2 + 2e- + 2H+
What happens to the H+ produced in the photolysis of water?
The H+ is picked up by NADP to form NADPH
What happens to the e- produced in the photolysis of water?
The e- are passed along a chain of electron carrier proteins
What happens to the oxygen produced in the photolysis of water?
Either used for respiration or diffuses out of the leaf via the stomata
What is the photoionisation of chlorophyll?
- Light energy is absorbed by the chlorophyll
- Electrons are excited and move up an energy level to leave chlorophyll
- Chlorophyll is ionised by light
What happens when electrons have gained energy?
They move along a series of proteins embedded within the thylakoid membrane
What happens when the electrons move along the proteins in the membrane?
- They release energy
- Some energy is used to pump protons across the chloroplast membranes
What does moving protons across the chloroplast membranes do?
Creates an electrochemical gradient
How do protons move across the membrane?
They pass through the enzyme ATP synthase, producing ATP
What do the protons do once they have moved across the membrane?
Combine with the co-enzyme NADP to become reduced NADP (NADPH)
Where does the light independent reaction occur?
Stroma
What catalyses the light independent reaction?
RuBisCo
Where is RuBisCo found?
Stroma
Why is the light independent reaction temperature sensitive?
Because of the enzymes
What does the Calvin cycle do?
Uses CO2, NADPH and ATP to form a hexose sugar
What happens first in the Calvin cycle?
- CO2 reacts with RuBP to form GP
How many molecules of GP are formed when CO2 reacts with RuBP?
TWO
What is RuBP?
Ribulose biphosphate
What is GP?
Glycerate-3-phosphate
What catalyses the first stage of the Calvin cycle?
RuBisCo
What happens second in the Calvin cycle?
GP is reduced to TP
What is TP?
Triose phosphate
How is GP reduced to TP in the second stage of the Calvin cycle?
- Using energy from ATP
- Accepting a H+ from reduced NADP
What happens in the Calvin cycle after GP has been reduced to TP?
1/6 carbons from TP leave the cycle each turn to be converted into useful organic substances
What are useful organic substances?
Substances that contain carbon
What happens in the Calvin cycle to the rest of the molecule?
- The rest of the molecule (5 carbons) is used to regenerate RuBP
- With the energy from ATP
How many carbons in RuBP?
5
How many carbons in GP?
3
How many carbons in TP?
3
What is a limiting factor?
Any factor that reduces the rate of photosynthesis
What are the limiting factors for photosynthesis?
- Temperature
- Light intensity
- CO2 concentration
Why does the rate of photosynthesis increase as light intensity increases?
- Greater light intensity means more light energy is absorbed by the plant
- Faster LDR stage occurs
- Produces more ATP and NADPH for the Calvin cycle
Why does the rate of photosynthesis increase as [CO2] increases?
- CO2 is required for the LIR stage
- More CO2 means faster Calvin cycle
What is it called when CO2 is combined with RuBP?
Carbon fixation
Why does the rate of photosynthesis increase as temperature increases?
- Rate increases with temperature due to enzymes
- Rate decreases if temperature exceeds a certain value due to enzyme denaturation
Describe what happens during photoionisation in the light-dependent reaction.
- Chlorophyll absorbs light
- Electrons are lost and move to electron transport chain
Explain why heat stress decreases the light-dependent reaction of photosynthesis. Heat stress is a condition that often occurs in plants exposed to high temperatures for a prolonged period of time. Heat stress is a major factor in limiting the rate of photosynthesis.
- Less ATP
- Less NADPH
Explain why a decrease in the activity of the enzyme RuBisCo would limit the rate of photosynthesis.
- Less CO2 reacts with RuBP
- Less GP
Where precisely is RuBisCo found in a cell?
Stroma
How does Atrazine affect the rate of photosynthesis in weeds? Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.
- Reduced transfer of protons across thylakoid membrane
- Less ATP produced
- Less NADPH produced
- LIR slows
Why do weeds treated with Atrazine give off small amounts of heat? Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.
Energy is released for excited electrons
Describe how crop plants use light energy during the light-dependent reaction.
- Excites electrons (electrons removed from chlorophyll)
- Electrons move along electron transport chain, releasing energy
- Energy used to join ADP and Pi to form ATP
- Photolysis of water produces protons, electrons and oxygen
- NADP reduced by electrons
Explain the relationship between stomatal opening and photosynthesis.
- Stomata allow uptake of CO2
- CO2 used in photosynthesis
A student used chromatography to separate the different photosynthetic pigments in a chlorophyll solution. She had the following materials:
Chromatography paper
A ruler and pencil
Suitable glassware
A solvent (solvent A)
2 cm³ of the chlorophyll solution
(a) Describe how she could use these materials to separate the photosynthetic pigments by chromatography.
1- Draw a line on chromatography paper using ruler and pencil
2- Use pipette add chlorophyll to origin
3- Add solvent A below line
4- Remove from glassware before solvent
5- Make where solvent reaches front
(b) Using solvent A, the student separated five pigments. She then repeated her method using a different solvent, solvent B. Using solvent B, she separated six pigments.
Explain the difference between these results.
Two pigments have the same solubility in A but different in B
one pigment is soluble in B bit not in A
pigments have different solubiliteis in solvents A and B
one pigment Is insoluble in A
In the following passage, the numbered spaces can be filled with biological terms.
During photosynthesis, plants produce (1) ________ compounds, which contain carbon, such as carbohydrates, lipids, and proteins. Most of the sugars synthesized by plants are used by the plant in (2) ________. The rest are used to make other groups of biological molecules. These biological molecules form the biomass of plants. Biomass can be measured in terms of mass of (3) ________ per given area per given time. The chemical energy stored in dry biomass can be estimated using (4
Organic
Respiration
Biomass
Calorimetry
(b) Describe the light-independent reaction of photosynthesis.
1- Co2 combines with RUBP
2- Produces 2 glycerine 3 phosphate using Ribuscio
3- Gp reduced to Tp
4- Using reduced NADP
5- using energy from ATP
6- TP converted to hexose/ or other useful organic substances
In this species of tree, very high light intensity can inhibit the release of electrons from chlorophyll
less ATp
Less NADPH
less GP reduced to TP
less TP regenerate to make RUBP
Less RUBP is regenerated
Less RUBP to react with co2
mature leaves from slow growing shade plants produce poisonous chemicals that are a defence against being eaten by herbivores
Suggest how this benefits slow growing shade tolenet plants
slower rate if photosynthesis
slow growing so would take a long time to replace mature leaves
leaves more likely to reach maturity
plants can maintain a large enough SA for photosynthesis
Plants can absorb enough light
explain why the student marked the origin using a pencil rather than using ink
ink and pigements would mix
Origin line in different positions with ink
with pencil origin still visible
Describe the method the students used to separate the pigments are the solution of pigments has been applied to the origin
level of solvent below origin
Remove before reaches top
the pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves
more wavelengths of light for photosynthesis
the solution that the student used to produce the chloroplast suspension has the same water potential as the chloroplast. Explain why it was important that these water potentials were the same
osmosis doesn’t occur
chloroplast dont burst/ shrivel
explain why the student measured the rate of production of oxygen in this investigation
oxygen produced in LDR
the faster oxygen is produced, the faster the light dependent reaction
the student did not use a buffer to maintain the Ph of the solution. Explain what would happen to the pH of the solution during this investigation
Ph would increase
as CO2 Is removed
suggest and explain why the rate of photosynthesis was low between 525m and 575 nm wavelength of light
less absorption of these wavelength of light
no green light absorbed
light required for LDR- photolysis
represents green light
the experiements were carried out at a high carbon dioxide conc. Explian whty
So co2 not limiting factor
explain why it was important to grow the plants under the same conditions up to ten days before the experiment
any diffennce is due to iron
Iron defincency results in a decrease in the uptake of c02. Explain why
less Tp converted to RUBP
co2 combines with RUbP
In leaves at the top of trees in a forest, c02 is often the limiting factor for photosnyrheis. Use your knowledge of photosynthesis to suggest and explain one reason why
1- light not limting - lots of light
for LDR not limiting
temp not limiting
fast reactions of enzymes in LIR
high use of C02
light independent reaction is limiting
