5.6 Photosynthesis Flashcards
What is carbon fixation?
The process by which CO2 is fixed into organic compounds, and regulates the amount of CO2 in the atmosphere.
Photosynthesis is ________.
Endothermic
What is the compensation point?
When photosynthesis and respiration take place at the same rate, no net change in amount of carbohydrate.
What is a compensation period?
The amount of time it takes a plant to reach its compensation point.
Where does the light dependant stage take place?
Thylakoid membrane
What is a photosynthetic pigment?
Pigment that absorbs specific wavelengths of light and trap their energy.
What are examples of photosynthetic pigments?
Chlorophyll a, Chlorophyll b, carotene
Where does the light independant stage take place?
Stroma
What is the stroma?
Fluid filled matrix in the chloroplasts
What is a granum?
Stack of thylakoid membranes
What is a thylakoid?
Flattened membrane bound sac found in chloroplasts, contains photosystems and photosynthetic pigments.
Where are photosystems found?
Thylakoid membranes
Why do granum have such a high surface area?
Space for more photosystems and photosynthetic pigments, and electron carriers and ATP Synthase
What is a coenzyme?
Molecule that aids the function of an enzyme, by transferring a group from one molecule to another
What are the two types of photosynthetic pigments in photosystems?
Primary pigments and accessory pigments.
What do primary photosynthetic pigments do?
They are reaction centres where electrons are excited in the light dependant reaction.
What do accessory photosynthetic pigments do?
They are light harvesting systems surrounding reaction centres, transferring light energy to them to increase electron excitement.
What wavelength of light is best absorbed by PSI?
700nm
What wavelength of light is best absorbed by PSII?
680nm
Chloroplasts contain their own ____ and _____.
DNA and small ribosomes.
What happens to carbohydrates that are made but not used in chloroplasts?
Stored as starch grains in stroma.
How is ATP made in the light dependant reaction?
Photophosphorylation
What is photolysis?
Using light energy to split water into protons, electrons and oxygen
When does photolysis occur?
The light dependant reaction
When does cyclic and non-cyclic photophosphorylation occur?
Light dependant reaction
What are the products of non-cyclic photophosphorylation?
ATP, NADPH, O2
What links photosystems in thylakoid membranes?
Electron carriers
What are electron carriers?
Proteins that transfer electrons
What is an electron transport chain?
A chain of proteins through which excited electrons flow
What makes up the electron transport chain in non-cyclic photophosphorylation?
The electron carriers and the photosystems
What is the first step of non-cyclic photophosphorylation?
Light energy is absorbed by PSII, exciting electrons in chlorophyll until they move down the electron transport chain to PSI
What is the second step of non-cyclic photophosphorylation?
Photolysis of water to replace the electrons lost from PSII.
What is chemiosmosis?
The process of electrons flowing down an electron transport chain to provide energy to pump protons creating a proton gradient to drive ATP synthesis
What is the third step of non-cyclic photophosphorylation?
Energy from excited electrons moving along an electron transport chain is used to pump protons into thylakoid creating a conc gradient, then making ATP by chemiosmosis
What is the fourth and final step of non-cyclic photophosphorylation?
Light energy excites electrons in PSI, then they are transferred to NADP with a proton to make NADPH
What can be used to separate photosynthetic pigments?
Thin layer chromatography
What photosystem is used in cyclic photophosphorylation?
Only PS1
What happens in cyclic photophosphorylation?
e- from chlorophyll are passed back to PS1, and repeatedly flow through PS1, only making a small amount of ATP
What are the products of cyclic photophosphorylation?
Small amounts of ATP
When does CO2 fixation take place?
Calvin cycle / light independant reaction
What makes up a photosystem?
Membrane protein and photosynthetic pigments
How does the light independant reaction rely on the light dependant reaction?
ATP and NADPH are required to keep it going, which are made in the light dependant reaction
What does RuBisCO catalyse?
RuBP + CO2 > 2GP
What is the order of the Calvin cycle?
RuBP > GP > TP > RuBP
What are the uses of TP?
As a starting material for synthesis of carbs, lipids and proteins
How many turns of the Calvin cycle are needed to make 1 hexose sugar (glucose) ?
6 turns
How is RuBP regenerated?
5 out of 6 TPs made are used to regenerate RuBP
How many of each light dependant reaction product are needed to make 1 glucose?
18 ATP and 12 NADPH
What is needed to go from GP to TP?
2ATP and 2NADPH
What is used to go from TP back to RuBP?
1ATP
What makes GP?
RuBP + CO2 > GP
What is chemiosmosis?
The process of e- flowing down an e- transport chain to create a H+ gradient across a membrane to drive ATP synthesis
What is the role of water in photosynthesis?
Photolysis of water makes electrons, H+ and O2 gas. The e- are used to replace the excited ones lost from chlorophyll
What is the effect of intense light on the Calvin cycle?
High levels of RuBP and TP, low levels of GP
What is the effect of dim light on the Calvin cycle?
Low levels of RuBP and TP and high levels of GP as it cannot be reduced to TP without the LDR
What is the effect of low CO2 concentration on the Calvin cycle?
RuBP accumulates as it can’t accept CO2, and GP and TP cannot be made
What is the effect of high CO2 concentration on the Calvin cycle?
Low amount of RuBP as it is combined with CO2, high levels of GP and TP
What is a limiting factor of photosynthesis?
The factor which is at its least favourable level will limit photosynthesis rate, even when the other factors are at the most favourible.
What factors affect rate of photosynthesis?
Light intensity, Carbon dioxide concentration, and Temperature
How does light intensity affect photosynthesis rate?
Light of blue-red wavelength is used in photosynthesis, so as you increase the intensity the rate increases.
How does CO2 concentration affect photosynthesis rate?
Increasing CO2 concentration increases photosynthesis rate, but not too high as this causes stomatal closure.
How does temperature affect photosynthesis rate?
Photosynthesis rate is highest when temp is at around 30C. Too high/too low and the rate decreases
What does ATP Synthase do?
An enzyme that aids H+ moving down their concentration gradient back to the stroma, and the energy from this movement makes ATP from ADP +Pi
What happens to stomata at high temperatures and how does this affect photosynthesis?
They close to avoid losing water, stopping CO2 from entering the leaf and decreasing photosynthesis rate
What happens to thylakoid membranes under high temperatures?
May become damaged and reduce rate of LDR by reducing electron transfer via electron carriers
What happens to the chloroplasts outer membrane when at high temp?
They become damaged and cause enzymes such as RuBP to be released into cell, reducing LIR
What happens to chlorophyll at high temp?
Could become damaged and reduce amount of pigment that can absorb light energy, reducing LDR
What is the saturation point?
Where a factor is no longer limiting the reaction, and something else is
What happens to the Calvin cycle at extreme temperatures?
RuBP, GP and TP levels will all fall because the enzymes used to make them will either be denatured or inactive.
What is water stress?
When a plant has insufficient water to supply itself and the transpiration stream
What affect does water stress have on photosynthesis?
Decreases rapidly as leaves wilt and stomata close due to cells becoming plasmolysed and tissues becoming flaccid.
What causes stomatal closure?
Abscisic acid release in times of water stress
How do you measure the rate of photosynthesis?
Measure the rate of uptake of raw material e.g. CO2 or the rate of production of product, O2
How does a photosynthometer work?
It is an airtight apparatus that measures the volume of O2 produced by a plant, by measuring the length of an air bubble in a capillary tube
