Photosynthesis Flashcards
Adaptations of leaf
Large surface area = as much sunlight absorbed as possible
Arrangement of leaves = avoids shadowing
Thin = most sunlight absorbed in first micrometres and short diffusion distance for gases
Transparent cuticle and epidermis = let light through to photosynthetic mesophyll cells beneath
Long narrow upper mesophyll cells packed with chloroplast = collect sunlight
Stomata open and close = diff light intensities
Air spaces in lower mesophyll = rapid diffusion
Network of xylem = brings water to leaf cells and phloem carries sugar
Number equation of photosynthesis
6CO2 + 6H2O ->(light)-> C6H12O6 + 6O2
Word equation of photosynthesis
Carbon dioxide + water -> glucose + oxygen
Label chloroplast
Outer membrane and inner membrane
Stroma (outter shell bit)
Thylakoid (one circle)
Granum (stack of thylakoids)
Intergranal lamella (connects thylakoids)
What are the 2 main types of pigment
1) Chlorophylls A and B
2) Carotenoids
What are the 2 stages of photosynthesis
The light-dependent reaction
The light-independent reaction
How is the primary pigment shown
Light enters cartenoids and goes to chlorophyll b then a (these are the antenna complexes) when it reaches the reaction centre
What are the three stages of the light dependent reaction
Photolysis
Photoionisation
Electron transfer chain (chemiosmotic theory)
What happens in photolysis
electrons replace those lost in photoionisation
When light energy hits water molecules they split into H+ (protons), e- and O2
Protons produced pass out of the thylakoid through ATP synthase channels taken up by NADP
What happens in photoionisation
1) Light hits chlorophyll and excites electrons
2) chlorophyll loses electrons and is oxidised
3) electrons leave chlorophyll and are taken up by electron carrier
Describe the process of the electron transfer chain
1) As electrons pass along electron carrier (oxidation-reduction reactions) a transfer chain is formed in thylakoid membranes
2) Electrons lose energy at each stage lowering each carriers energy
3) H+ ions are pumped into the thylakoid from stroma using proton pumps
4) A proton concentration gradient is formed (thylakoid high conc, stroma low)
5) Protons pass through ATP synthase channels, changing enzymes structure catalysing the formation of ATP
Where is chlorophyll found
Thylakoids
Where does the light-dependent stage of photosynthesis take place
In the grana, where thylakoids are stacked up. Thylakoids contain chlorophyll used for the reaction.
Where does the light-independent stage take place
The stroma
Describe the way in which ATP and reduced NADP are produced in the light-dependent reaction of photosynthesis.
Protons pass through ATP synthase from proton pumps
Changing enzymes structure catalysing formation of ATP by addition of ADP + Pi
NADP is the electron carrier, when the electrons leave is becomes reduced during electron transfer chain
Using the information in the passage, describe how the structure of a chloroplast is adapted to its function in photosynthesis. [3 marks]
Membranes shape provides large surface for light absorptio;
(permeable) membrane allows diffusion of gases
Describe the role of water in the light-dependent reaction of photosynthesis
Provides protons / hydrogen ions for reduction of NADP
Describe how plants absorb light energy from the sun and use this energy to produce useful substances in the light-dependent stage of photosynthesis. [5 marks]
Light absorbed by chlorophyll electrons excited
pass down chain of carriers
energy released producing ATP from ADP + Pi
NADPH formed with electrons
photolysis of water
supplies H+ ions to reduce NADP
Describe how the products of the light-dependent stage of photosynthesis are used in the Calvin cycle and how carbohydrate is synthesised as a result of the cycle. [6 marks]
RuBP converted to GP
RuBP binds with carbon dioxide
GP converted TP
reduced NADP provides hydrogen
ATP provides energy
some TP converted to glucose/carbohydrate
some TP used to produce RuBP
ATP supplies phosphate for this reaction
Describe the similarities between photosynthesis and respiration. [6 marks]
Both processes involve:
Transfer of energy
Use and produce ATP
chain of electron carriers
located on membranes
involve cycle of reactions
oxidation and reduction reactions involved
coenzymes
processes are controlled by enzymes
some common intermediates/GALP is common to both;
explain why red seaweeds are usually found in deeper water (further down the shore) than green seaweeds.
Yellow / green OR approx. 500-600mm 1. Penetrates water better;
2. Absorbed by phycoerythrin ;
3. Red seaweeds have phycoerythrin;
4. Red seaweeds photosynthesise in deep water;
Blue AND red OR approx. 460 and 670mm 5. Penetrate water poorly;
6. Absorbed by chlorophyll;
7. Green have only chlorophyll;
8. Green seaweeds can‘t photosynthesise in deep water
9. Red seaweeds have less competition from green in deeper water / converse in shallow water;
What is oxidation
Gain of oxygen
Loss of electrons
Loss of hydrogen atoms
Energy given out
What is an oxidising agent
Compounds that remove electrons or hydrogen atoms
Or add oxygen and is oxidised
What is reduction
Loss of oxygen
Gain of electrons
Gain of hydrogen atoms
Energy produced
What is a reducing agent
Compounds that supply electrons or hydrogen atoms
or remove oxygen and is reduced
What is the chemical reaction that photosynthesis does
Turns light energy into chemical potential energy
And produces ATP which is used to release energy in order to main compounds (like glucose)
What are some advantages of ATP making is useful
Releases small amounts of energy so none is wasted
Small soluble molecule (easy to transport)
Easily broken down (energy easy to release)
Can transfer energy to other molecules
Cannot pass out of cell
Immediate supply of energy
What does the light-dependent stage require
Light
What does the light-dependent stage produce
NADPH and ATP
What is NADPH
Reduced NADP
The process of photoionisation
1) Light hits pigment and it passed through the photosystem to a chlorophyll molecule
2) Chlorophyll A absorbed the light energy and boosts the energy of its electrons
3) This means electrons can get enough energy to leave their atoms leaving a positively charged ion (H+ ion)
4) So chlorophyll A ejects electrons
What are the two staged in the light-dependent stage
Cyclic and non-cyclic
Bb
Fgg
Which reaction produces oxygen
Light dependent
Which reaction is carbon dioxide fixed
Light independent
Which reaction uses NADPH and H
Light independent
Which reaction produces ATP
Light dependent
Stages of the calvin cycle/light independent reaction
1) CO2 diffuses into stroma
2) 1C binds with RuBP catalysed by Rubisco
3) 6 Carbons attach to enzyme rubisco
4) Release and breakdown into 2x GP molecules
5) GP is reduced by NADPH into triose phosphate using ATP
6) RuBP is regenerated (5C), 1 carbon is lost for production of carbs, lipids, proteins etc
Explain how a pair of electrons move from chlorophyll to the electron carrier system
1) Chlorophyll is excited by light
2) Electrons are excited
3) Chlorophyll is oxidised
4) Electrons get picked up by another molecule
Explain how electrons lost from chlorophyll are replaced
1) Photolysis of water occurs
2) 2OH + 2e-
3) Cyclic photophosphorylation
4) Hydroxide ions as source of electrons
Name the process of the light dependent reaction in 8 stages
1) Light energy is absorbed by chlorophyll. Electrons are excited to a higher energy level
2) Electrons are lost form the chlorophyll molecule (and pass to electron carriers in the thylakoid membrane)
3) Electrons are passed between carriers in the electron transport chain
4) Energy released during the transfer of electrons in the electron transport chain used to generate ATP
5) Photolysis occurs
6) Electrons from water replace those lost during electron transport chain
7) NADP is reduced by adding electrons and H+ ions on the electron transport chain
8) Oxygen from splitting of water is lost as a waste product
Summarisation of the two light reactions
6H2O -> Light dependent -> 6O2
↓ ↓
ATP NADPH
6CO2 -> Light independ -> C6H12O6
Lollipop light independent reaction experiment
1) Algae grown under light in thin transparent lollipop
2) Radioactive 1C in form of hydrogencarbonate is injected
3) Intervals samples of photosynthesising algae are dropped into hot methanol to stop chemical reactions
4) Compounds separated by 2 way chromatography
5) Radioactive compounds identified
Equation for photolysis
2H2O -> 4H+ (protons) + 4e- (electrons) + O2 (oxygen)
What is nadph
A reduced electron carrier
What happens when NADP takes up electrons
It becomes reduced
What occurs with the electrons during photolysis of water
Light hits the chlorophyll
Loses electrons
Photolysis splits water molecules using light energy
Electrons from the split water molecule are used to replace those lost
What happens to the protons in photolysis
When water molecules split protons are produced
Protons pass out of the thylakoid space through ATP synthase channels, taken up by NADP
What happens to the reduced NADP at the end of the light dependent stage
It enters the light independent stage
What happens to the oxygen from photolysis
Used in respiration or diffused out of leaves as waste product
What four sites are adapted in the light dependent reaction
Thylakoid membrane
Chloroplast
Proteins
Granal membranes
How is the thylakoid membrane adapted for the light dependent reaction
Large surface area
For attachment of chlorophyll, electron carriers and enzymes
How are the proteins adapted for in the light dependent reaction
Hold chlorophyll in specific way to allow maximum absorption
How are the granal membranes adapted for in the light dependent reaction
Have atp synthase channels to catalyse ATP production
Selectively permeable to establish proton gradient
How are the chloroplasts adapted for in the light dependent reaction
Contain DNA and ribosomes so they can quickly manufacture proteins
What happens to the NADP formed from the light independent reaction
NADP is reformed and goes back to the light dependent reaction to be reduced again
What happens to the remaining triose phosphate molecules in the light independent reaction
Converted to organic substances e.g. starch, cellulose, lipids
Most regenerate to ribulose bisphosphate using ATP
What in the light independent reaction are adapted
Chloroplast
Specifically the fluid of the stroma
How is the chloroplast adapted in the light independent reaction
Contains both DNA and ribosomes to quickly and easily manufacture some of the proteins
How is the fluid of the stoma adapted in 2 ways
1) contains all enzymes needed to carry out the reaction and is membrane-bound so the chemical environment has a high concentration of enzymes
2) Fluid surrounds the grana so products from the light-dependent reaction can diffuse into the stroma readily
The solution that the student used to produce the chloroplast suspension
had the same water potential as the chloroplasts.
Explain why it was important that these water potentials were the same.
1) Osmosis doesn’t occur
2) Chloroplast / organelle does not burst / lyse / shrivel / shrink;
Summarise the light independent reaction
1) Carbon dioxide fixation - CO2 binds with RuBP using Rubisco forming 2 glycerate 3-phosphate
2) Reduction phase - GP is reduced to triose phosphate
3) Regeneration of RuBP - 5C of triose phoshate are used to regenerate RuBP, 1C is used for other productions (proteins, lipids)
What chemicals are needed for the light dependent reaction?
NADP, ADP, Pi and water
Describe what happens during photoionisation in the light-dependent reaction.
1) Chlorophyll absorbs light
OR
Light excites/moves electrons in chlorophyll;
2) Electron/s are lost
OR
(Chlorophyll) becomes positively charged;
Ignore site/molecule from where electrons are lost.
Accept electrons go to electron transport/carrier chain for ‘electrons lost’.
Explain why the student marked the origin using a pencil rather than using ink
Ink and (leaf) pigments would mix
OR
(With ink) origin/line in different position
OR
(With pencil) origin/line in same position
OR
(With pencil) origin/line still visible;
Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin.
1) Level of solvent below line;
2. Remove/stop before (solvent) reaches top of paper
The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves.
Absorb) different/more wavelengths (of light) for 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.
Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction. [2 marks]
Less/no) ATP;
(Less/no) reduced NADP;
Another effect of heat stress is a decrease in the activity of the enzyme rubisco. A decrease in the activity of an enzyme means that the rate of the reaction it catalyses becomes slower.
A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis.
Explain why
Less/no) carbon dioxide (reacts) with RuBP; (Less/no) GP;
Where precisely is rubisco found in a cell?
Stroma (in chloroplast)
Graph shows mutant plants grow faster than normal plants in both high and low light.
The scientists suggested that mutant plants producing more chlorophyll b would grow faster than normal plants in all light intensities.
Explain how these data support this suggestion.
1) Have faster production of ATP and reduced NADP;
2) Have faster / more light-independent reaction;
3) Produce more sugars that can be used in respiration;
4) Have more energy for growth;
5) Have faster / more synthesis of new organic materials.
name products of the calvin cycle and its uses
1) Amino acids -> protein synthesis
2) Lipids -> build cell membranes
3) ADP/NADP -> enter back into light dependent reaction
Explain why lower light intensity leads to a reduced rate of photosynthesis (practical with lamp pointing to seaweed in water attached to gas synringe)
1) Light energy is needed for photoionisation to excite electrons to enter electron transport chain
2) Light energy needed for photolysis to split water into H+, e- and O2
3) If the light dependent reaction cannot take place then no ATP/NADPH can be passed to the light independent reaction
Why is CO2 concentration a limiting factor in photosynthesis
1) Needed in the light independent reaction
2) It combines with RuBP to form GP
3) Provides carbon fixing to other organic molecules (sugar, amino acids, glycerol)
Describe the trend between the rate of photosynthesis and carbon dioxide concentration
As carbon dioxide increases so does the rate of photosynthesis
It eventually plateaus when a certain concentration is reached
Identify another possible limiting factor which causes carbon dioxide to plateau
Temperature
Light intensity
How the energy of light is converted into chemical energy in the light dependent reaction
1) Electrons raised to high energy levels
2) Use electron transfer chains to transfer and diffuse down the atp synthase channel
3) To form atp from ADP + Pi
Heat stress decreases the light dependent reaction of photosynthesis
Explain why this leads to a decrease in the light-independent reaction
Less atp and nadph is formed so the reduction of GP into TP cannot occur
A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis explain why
Carbon dioxide binds with RuBP using rubisco as the catalyst
So less gp can be produced
