Photosynthesis (5) Flashcards
What kinds of processes do plants need energy for?
- photosynthesis
- active transport
- DNA replication
- cell division
- protein synthesis
What kind of organisms are plants? (food)
They are autotrophs/phototrophs
What is photosynthesis and what is it’s word equation?
Photosynthesis is the process where energy from light is used to make glucose from H2O and CO2.
Carbon dioxide + water + energy —-> glucose and oxygen
What is a metabolic pathway?
A metabolic pathway is a series of samll reactions controlled by enzymes
What is phosphorylation?
This is the process of adding phosphate to a molecule
What is photophosphorylation?
This is the process of adding phosphate to a molecule using light
What is photolysis?
The splitting of a molecule using light energy
What is hydrolysis?
The splitting of a molecule using water
What is decarboxylation?
The removal of carbon dioxide from a molecule
What is dehydrogenation?
The removal of hydrogen from a molecule
What is a redox reaction?
Reactions that involve both oxidation and reduction
What is a coenzyme and how do they work?
A coenzyme is a molecule that aids the function of an enzyme. They usually work by transferring a chemical group from one molecule to another
What is the coenzyme used in photosynthesis?
NADP
It transfers hydrogen from one molecule to another.
What are chloroplasts?
Chloroplasts are small, flattened organelles found in plant cells. They are the location for photosynthesis in plant cells.
What are the main structures in a chloroplast?
- double membrane (chloroplast envelope)
- thylakoids stacked into grana linked together by lamellae
- photosynthetic pigments
What are the photosynthetic pigments in chloroplasts?
These are colored substances that absorb the light energy needed for photosynthesis. The pigments are found in the thylakoid membranes- attached to proteins. The protein and pigment are called a photosystem.
What are the specific photosynthetic pigments in chloroplasts?
- chlorophyll a
- chlorophyll b
- carotene
What is the structure of a photosystem?
contains both primary and accessory pigments.
What are primary pigments?
Primary pigments are reaction centers, where electrons are excited during the light-dependent reaction.
What are accessory pigments?
Accessory pigments make up light-harvesting systems. These surround reaction centers and transfer light energy to them to boost the energy available for electron excitement to take place.
What are the differences between photosystem I and II?
Photosystem I: absorbs light best at 700nm wavelength
Photosystem II: absorbs light best at 680nm wavelength
What is the stroma in chloroplasts?
Contained with the inner membrane of the chloroplasts and surrounding thylakoids is a gel-like substance called the stroma. It contains enzymes, sugars and organic acids.
Where is the DNA in chloroplasts?
Chloroplasts have their own DNA, which is found in the stroma and is often circular. There can be multiple copies in each chloroplast.
Where are carbohydrates stored in the chloroplast?
Carbohydrates produced by photosynthesis and not used straight away are stored as starch grains in the stroma.
What are the two steps in photosynthesis?
- The light dependent reaction
- The light independent reaction
Where does the light dependent reaction take place?
The thylakoid membranes of the chloroplasts
What happens during the light dependent reaction?
- light energy is absorbed by photosynthetic pigments in the photosystems and converted to chemical energy
- the light energy is then used to add a phosphate group to form ATP and to form reduced NADP
- ## during the process water is oxidized to oxygen
What is the process of photolysis?
the breaking up of water into oxygen, hydrogen and electrons via light
Where does the Calvin cycle/light independent reaction take place?
It occurs in the stroma of the chloroplasts
What happens as an overview of the light dependent reaction?
The ATP and reduced NADP from the light dependent reaction supply the energy and hydrogen to make glucose from CO2.
How can you separate the pigments in plants?
Thin layer chromatography. The stationary phase of this is a thin layer of gel called a chromatography plate
What are the steps in TLC to separate photosynthetic pigments?
- grind up some leaves with anhydrous sodium sulfate and propanone
- transfer the liquid to a test tube and add some petroleum ether
- add some of the liquid from the top layer into another test tube with more anhydrous sodium sulfate
Draw a baseline using a pencil on a chromatography plate and add drops of the sample, letting them dry before adding more to create a concentrated single spot. - put the plate into a beaker with the chosen solvent so it is below the baseline. put a lid on the beaker while it develops
- when the solvent has nearly reached the top, take the plate out and mark the solvent front with a pencil
- calculate the rf values of the different spots
In the light-dependent reaction, what is the light energy absorbed by the photosystems used for?
- making ATP (photophosphorylation)
- making reduced NADPH
- splitting water into oxygen, protons and electrons (photolysis)
What are electron carriers?
Electron carriers are proteins that transport electrons.
What are the steps in non-cyclic photophosphorylation?
- light energy excites electrons in chlorophyll as it is absorbed in PSII
- these high energy electrons move along the electron transport chain to PSI
- the photolysis of water produces electrons to replace the electrons displaced at PSII
- the electrons in the ETC lose energy as they move along which is used to transport protons into the thylakoid using proton pumps
- via chemiosmosis, the protons move back out of the thylakoid through the enzyme ATP synthase to produce ATP
- light energy absorbed by PSI excites electrons which are transferred to NADP along with a proton from the stroma to produce reduced NADP.
What is cyclic photophosphorylation?
Cyclic photophosphorylation only uses PSI. It is called this as the electrons that are not passed onto NADP are passed back to PSI via electron carriers which means they are recycled and can continously flow through PSI.
Why is the Calvin cycle also called carbon fixation?
The carbon from CO2 is fixed into an organic molecule
What compound is regenerated in the Calvin cycle?
Ribulose bisphosphate
What are the steps when carbon dioxide is combined with ribulose bisphosphate to form two molecule of glycerate 3 phosphate?
- CO2 enters the stomata and diffuses into the stroma of the chloroplast
- It is then combined with RuBP, a 5 carbon compound. This gives an unstable 6 carbon compound, which quickly breaks down into two molecules of G3P
- RuBisCO catalyses the reaction between CO2 and ribulose bisphosphate
What does G3P stand for?
Glycerate 3 phosphate
What does RubisCO stand for?
Ribulose bisphosphate carboxylase
What are the steps in which ATP and reduced NADP are required for the reduction of GP to TP?
- ATP from the light dep reaction provides energy to convert GP to TP
- this reaction also uses H+ ions which come from the reduced NADP
- triose phosphate is then converted into many useful organic compounds like glucose etc.
How is ribulose bisphosphate regenerated?
- five out of every six molecules of TP produced in the cycle are not used to make hexose sugars but to regenerate RuBP
- this uses the rest of the ATP produced by the light dependent reaction
How many turns of the Calvin cycle do you need to make one hexose sugar?
six
- needs 2x TP
- 18 ATP
- 12 Reduced NADP
Why does high light intensity of a certain wavelength increase the rate of photosynthesis?
- light is needed to provide the energy for the LDR - the higher the intensity of the, the more energy it provides.
- only certain wavelengths of light are used for photosynthesis. The photosynthetic pigments chlorophyll a, chlorophyll b and carotene only absorb the red and blue light in sunlight.
Why is carbon dioxide at 0.4% optimum conditions for photosynthesis?
Carbon dioxide makes up 0.04% of the gases in the atmosphere. By increasing this to 0.4% it gives a higher rate of photosynthesis, but any higher and the stomata start to close.
Why does temperature around 25 degrees provide optimum conditions for photosynthesis?
- optimum conditions for enzyme activity
- stomata close at high temps so less CO2 can enter
- at high temps the thylakoid membranes may be damaged
- chlorophyll could be damaged in high temperatures
What are the limiting factors of photosynthesis?
- light intensity
- temperature
- CO2 concentration
- chlorophyll concentration
Why can water stress also affect photosynthesis?
When plants don’t have enough water, their stomata will close to preserve what little water they do have, leading to less CO2 entering the leaf for the Calvin cycle and slowing photosynthesis down.
How does light intensity affect the levels of GP, RuBP and TP?
- In low light intensities, the products of the light dependent stage will be in short supply.
- this means that the conversion of GP to TP and RuBP is slow
- so the level of GP will rise and levels of TP and RuBP will fall
How does temperature affect the levels of GP, RuBP and TP?
- all the reactions in the Calvin cycle are catalyzed by enzymes
- at low temperatures all the reactions will be slower as the enzymes work more slowly
- This means the levels of RuBP, GP and TP will fall as they are affected in the same way at very high temperatures, because the enzymes will start to denature.
How does carbon dioxide concentration affect the levels of GP, RuBP and TP?
- at low CO2 concentrations conversion of RuBP to GP is also slow
- so the level of RuBP will rise and the levels of GP and TP will fall.
How can you measure the limiting factors of photosynthesis?
- a test tube containing pondweed water is connected to a capillary tube full of water
- the tube of water is connected to a syringe
- the pondweed is left for a set time and oxygen will collect in the capillary tube - measure the distance travelled by the bubble
- control the variables
- repeat and calculate the average length of gas bubble produced
- repeat the experiment with the light source placed at different distance
