Chapter 18- Photosynthesis Flashcards
Why are there different pigments in chloroplasts?
- different pigments absorb different wavelengths of light
- so a wider range of pigments available in leaf means more light is absorbed and available for photosynthesis.
What are the pigments called that surround chlorophyll?
Accessorie pigments
What is it called when pigments and chlorophyll are together in chloroplasts?
LIGHT HARVESTING CLUSTERS
What happens to wavelengths of light that aren’t absorbed?
They are reflected
- visible to human eye
What do chloroplasts contain even though they are not cells?
Own strand of DNA and mitochondria
How is the glucose stored after being made by photosynthesis?
They are combined together to make starch and is temporarily stored in the chloroplasts.
Why do chloroplasts contain ribosomes?
- They are there to perform protein synthesis
- They are important in order to make the enzymes required for phtosynthesis.
- DNA chloroplasts code for the enzymes
What is the sight for the light dependent reaction?
Thylakoid membrane
What is the structure called when thylakoids are staked up?
GRANUM
What connects the thylakoids that are staked in the structure called the granum?
Intergranum lemella
Where is the site of the light independent reaction?
STROMA
What do thylakoid membranes contain?
Photosystems
How many photosystems are there?
Photosystem 1 and photosystem 2
What are photosystems made up of?
Photosynthetic pigments
What is the primary pigment?
Key one which absorbs the sun light - CHLOROPHYLL A
What are accessory pigments?
CHLOROPHYLL B, XANTHOPHYLLS and CAROTENOIDS
- They are all supplementary pigments which help absorb energy when chlorophyll A nitrogen functioning well
What is the first important molecule produced in the light dependent reaction?
ATP
Why enzyme in the thylakoid membrane catalyses the reaction between ADP and an inorganic phosphate group to produce ATP?
ATP synthase
How is energy provided for the reaction to produce ATP?
Energy is provided by H+ ions (protons)
Describe CHEMIOSMOSIS
Explain the proton gradient in the thylakoid membrane
There is a higher concentration of protons in the thylakoid space compared to the STROMA
- protons diffuse down the proton concentration gradient through ATP synthase
- so protons move from thylakoid space to STROMA
- move through partially permeable membrane
What is the method of producing ATP known as?
PHOTOPHOSPHORYLATION
How is the proton gradient maintained in the thylakoid?
Protons are actively transported from the STROMA to the thylakoid space.
However energy is required due to it being actively transported.
Describe PHOTOIONISATION
- energy that is used for active transport of protons from the stoma to thylakoid space is supplied but electrons.
- the energy supplying electrons are supplied by chlorophyll.
- when light hits left, chlorophyll absorbs light
- light energy then transferred to a pair of electrons in the chlorophyll
-electrons gain energy- now in excited state .
- energy then propels the electrons OUT of chlorophyll
- chlorophyll oxidised (as lost electrons)
THIS PROCESS DOESN’T PROVIDE ENERGY FOR ACTIVE TRANS[ORT OF PROTONS
Describe the process that provides the energy for active transport of protons.
-After PHOTOIONISATION has occurred and elections left chlorophyll, they get transferred to next molecule + into protein complex
- this carries on until last molecule along electron transfer chain
- Electrons move through electron transfer chain through series of oxidation reduction reactions
- these reactions release energy
- energy transferred to first protein complex which allows active transport of protons from stoma to thylakoid space
What happens when electrons (travelling along electron transport chain) reach end protein complex in the membrane?
- they can’t just stay there (if did, would prevent it from being involved in other oxidative reduction reactions)
- so NADP (coenzyme) reacts with electrons in that molecule and a proton form the STROMA, in a reduction reaction to produce REDUCED NADP
What is the second important molecule produced in the light dependent reaction?
Reduced NADP
Describe PHOTOLYSIS
- In order for electron transport chain to continue after chlorophyll in thylakoid membrane looses electrons (during photoionisation) electons need to be replaced.
- electons replaced by water
- when light hits leaf, it spilts water up into PROTONS, ELECTRONS and OXYGEN.
What are the three products of PHOTOLYSIS and what are they used for?
ELECTRONS:
- Replace the electrons lost from chlorophyll
PROTONS:
- maintain the high concentration of protons in the thylakoid space
OXYGEN:
- diffuses out of the plant or used in respiration
Describe CYCLIC PHOSPHORYLATION
- The light energy gets transferred to SINGLE electron.
- WHICH excites it out of the chlorophyll
- This electron then moves to next molecule in electron transport chain.
- However IT DOESNT REACT with NASP to form reduced NADP
- Instead the molecule carries the electron back to the molecule after photosytem 2
- Then travels through the electron transfer chain taking part in oxidation reduction reactions like normal process.
- This energy released is transferred to the next compound and the energy is used to enable the protein complex to actively transport protons into thylakoid space. Maintains the proton gradient for synthesis of ATP
- Finally electron goes back to photosystem 1 and as electron replaced itself, doesn’t need to take part in photolysis
Describe NON- PHOTOPHOSPHORYLATION
- When photosystem 2 absorbs light, electrons at end of electon transport chain react with NADP and a proton to produce reduced NADP
What molecules des the light independent reaction need form the light dependent reaction?
ATP and reduced NADP
Why does cyclic photophosphylation take place if it doesn’t produce reduced NADP?
Because photosystems 1 and 2 absorb light at different wavelengths lengths
So which type of PHOTOPHOSPHORYLATION takes place depends on the light wavelength
Why is CYCLIC PHOTOPHOSPHORYLATION helpful?
When there is enough reduced NADP for the light dependent reaction but not enough ATP.
How are chloroplasts adapted for photosynthesis?
- LARGE SURFACE AREA : for molecules involved in light- dependent reaction, maximises amount of ATP and reduced NADP made at one time
- THYLAKOID MEMBRANES CONTAIN ATP SYNTHASE- for efficient ATP production
- THYLAKOID MEMBRANE = SELECTIVELY PERMEABLE: allows them to establish and maintain proton gradient
Where does the Calvin cycle/ light independent reaction take place?
STROMA
Describe the first step of the Calvin cycle:
- carbon dioxide enters STROMA, reacts with molecule called RIBULOSE BISPHOSPHATE (containing 5 carbons and 2 phosphates)
- carbon dioxide and RIBULOSE bisphosphate react to form 2 identical Glycerate 3- phosphate
- reaction is catalysed by enzyme : RIBISCO
In the reaction to produce Glycerate 3 phosphate, why is carbon dioxide said to be fixed?
- because it is removed from the environment and fixed in a molecule of Glycerate 3 phosphate
What happens in the light independent reaction after Glycerate 3 phosphate is produced?
- Glycerate 3 phosphate needs to be converted into Triose phosphate.
- Glycerate 3 phosphate has to lose oxygen and gain hydrogen
- the hydrogen needed comes from reduced NADP
- reduced NADP donates hydrogen to Glycerate 3 phosphate to produce TRIOSE PHOSPHATE and NADP
- energy required for this reaction
- energy provided by ATP (from light dependent reaction)
- ATP broke down into ADP and inorganic phosphate molecule.
What happens after Triose phosphate is produced in the light independent reaction?
- 80% of Triose phosphate converted into RIBULOSE BISPHOSPHATE to ensure cycle continues
- for this, energy in form of ATP is need, it breaks down into ADP and Pi
- Remaining 20% produces 3 different organic molecules
What are the 3 organic molecules produced in the light independent reaction?
GLUCOSE
AMINO ACIDS
LIPIDS
