Section 5 - 11 Photosynthesis Flashcards
In what form does energy enter plants?
- Energy in light is absorbed by chlorophyll
- Then transferred into the chemical energy of the molecules formed during photosynthesis.
Molecules used by the plant to produce ATP during respiration. Non-photosynthetic organisms feed on the molecules produced by plants and then also use them to make ATP during respiration.
What is the main photosynthetic structure un eukaryotic plants?
The leaf
Chloroplasts are the cellular organelles within the leaf where photosynthesis takes place.
Where does photosynthesis occur?
Chloroplasts inside the leaves.
What are the raw materials of photosynthesis?
water
carbon dioxide
light
What are the products of photosynthesis?
oxygen and glucose
List adaptations leaves have made for photosynthesis
What is the overall equation for photosynthesis?
What are the three main stages of photosythesis?
- Capturing of light energy
- The light-dependent reaction
- the light-independent reaction
Explain the first stage of photosynthesis
Capturing of light energy
By chloroplast pigments such as chlorophyll
Explain the second stage of photosynthesis
Light-dependent reaction
- Some of the light energy absorbed is conserved in chemical bonds.
- During the process an electron flow is created by the effect of light on chlorophyll causing water to split into protons, electorns and oxygen.
- The products are reduced NADP ATP and oxygen
During light-dependent photosynthesis what does water break down into
protons
electrons
oxygen
What is photolysis?
In light-dependent reaction of photosythesis
water splitting into protons, electrons and oxygen
What are the products of light-dependent reactions?
Reduced NADP
ATP
oxygen
What is the third stage of photosythesis?
Light-independent reaction
Protons - hydrogen ions used to prodcue sugars and other organic molecules
What are the products of light-independent reaction?
Sugars and other organic molecules
What are the two distinct regions inside the chloroplast membranes?
- The grana
- The stroma
What is grana?
Stacks of up to 100 disc-like structures of thylakoids.
What is thylakoids?
Where the light-dependent stage of photosynthesis occurs.
Contains the photosynthetic pigment chlorophyll.
What is intergranal lamellae?
Thylakoids that have tubular extentions that join up with thylakoids in adjacent grana.
What is the stroma?
A fluid-filled matrix where the light-independent stage of photosynthesis takes place.
Within the stroma are a number of other structures such as starch grains.
Where do light-dependent reactions of photosynthesis occur?
Thylakoids in the grana.
Where does the light-independent stage of photosynthesis occur?
The stroma
For what purposes is energy captured in the light-dependent reaction of photosynthesis?
- To add an inorganic phosphate molecule to ADP, thereby making ATP
- Split water into H+ ions (protons) and OH- ions, As the splitting is caused by the light it is known as photolysis.
What is oxidation?
When a substance gains oxygen or loses hydrogen.
What is the reduction?
The process when substance loses oxygen or gain hydrogen.
What is the result of oxidation?
Results in energy being given out
What is the result of reduction?
Energy being taken away.
How happens when chlorophyll absorbs light energy?
- boosts the energy of a pair of electrons within the chlorophyll
- This raises them to a higher energy level
- These electrons are in an excited state
- They become more energetic and leave the chlorophyll molecule
- The chlorophyll mole becomes ionised
What is the process of photoionisation?
- Light energy boosts the energy of a pair of electrons within the chlorophyll
- This raises them to a higher energy level
- These electrons are in an excited state
- They become more energetic and leave the chlorophyll molecule
- The chlorophyll mole becomes ionised
What happens to the electrons that leave the chlorophyll in photoionisation?
Taken up by an electron carrier.
The chlorophyll molecule is oxides and electron carrier is reduced.
Why do electrons in the membranes of the thylakoid lose energy?
- They pass through electron carriers in a series of oxidation-reduction reactions.
- These form an electron transfer chain.
- Each carrier is at a slightly lower energy level than the previous one in the chain
- so electrons lose energy at each stage.
What theory is used to explain the process of ATP production?
The chemiosmotic theory
What is the chemiosmotic theory?
Makes ATP
- Each thylakoid is an enclosed chamber where protons are pumped from the stroma using proton pumps.
- The energy to drive process comes from electrons released when water molecules are split by light - photolysis
- This produces protons increasing conc. inside thylakoid space
- creating and maintaining conc. gradient - high in thylakoid space and low in the stroma
- Protons cross thylakoid membrane using ATP synthase channel proteins
- As travel through the protons change the structure which catalyses the combination of ADP with inorganic phosphate to form ATP
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Why is the chlorophyll short of electrons?
They lose electrons when light strikes a chlorophyll molecule.
What is the equation for photolysis of water?
Explain the process of photolysis of water
- protons are passed through ATP synthase channels and taken up by an electron carrier called NADP
- This makes NADP reduced
- Reduced NADP is the main product of the light-dependent stage and it enters the light-independent reaction taking electrons from chlorophyll molecules.
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Why is reduced NADP important?
It is a further potential source of chemical energy to the plant.
What is a by-product of photolysis of water?
oxygen
What is the oxygen from photolysis of water used for?
- Either Respiration
- Or diffuses out of the leaf as a waste product of photosynthesis.
In what ways has chloroplasts been structurally adapted to their function of capturing sunlight and carrying out the light-dependent reaction of photosynthesis?
- Thylakoid membrane - large SA for attachment of chlorophyll, electron carriers and enzymes
- Network of proteins hold chlorophyll to enable maximum absorption of light
- Granal membranes have ATP synthase channels - catalysing the production of ATP and creating a proton gradient
- Chloroplasts contain DNA and ribosomes so can produce proteins involved in IDR
What are the products of the light-dependent reaction of photosynthesis?
ATP and reduced NADP
What are the products of the light-dependent reaction of photosynthesis used for?
Products - ATP and reduced NADP
Used to reduce glycerate 3-phosphate in the second stage of photosynthesis. - this is in the light-independent reaction.
Where does the light-independent reaction of photosynthesis take place?
In stroma of the choloplasts.
What process explains the light-independent reactions of photosynthesis?
Calvin Cycle
Worked out by Melvin Calvin
What are the stages of the Calvin Cycle?
- CO2 from the atmosphere diffuses into leaf - stomata - dissolves in water around walls of mesophyll cells.
- Then diffuses through cell-surface membrane, cytoplasm and chloroplast membranes into the stroma of the Coloplast
- In stroma, CO2 reacts with 5-carbon compound ribulose biphosphate (RuBP) a reaction catalysed by enzyme - ribulose bisphosphate carboxylase AKA rubisco
- Reactions between CO2 and RuBP produces two molecules of 3-carbon glycerate 3-phosphate (GP)
- Reduced NADP from light-dependent reaction is used to reduce glycerate 3-phosphate to triose phosphate using energy supplied by ATP.
- NADP is reformed and used again in light-dependent reaction to be reduced again by accepting more protons
- some triose phosphate molecules are converted to organic substances that the plant requires such as starch, cellulose, lipids, glucose, amino acids and nucleotides.
- Most triose phosphate molecules are used to regenerate riboluse bisphophate using ATP from the light-dependent reaction.
What reacts with CO2 in the light-independent reaction of photosynthesis?
5-carbon compound ribulose biphosphate (RuBP)
What enzyme is present in the light-independent reaction of photosynthesis?
ribulose bisphosphate carboxylase AKA rubisco
What is produced in the reaction between CO2 and RuBP?
two molecules of 3-carbon glycerate 3-phosphate (GP)
In what ways is the chloroplast adapted to carry out the light-independent reaction of photosynthesis?
- Matrix contains enzymes for IIR - this is membrane bound in chloroplast so the chemical environment is maintained
- Stroma fluid surrounds the grana so products of LDR can easily diffuse into the stroma
- Containing both DNA and ribosomes so protein manufacturing is effecient.
