Photosynthesis Flashcards
What is photosynthesis
A physiological process used by producers to convert light energy into chemical energy
Autotrophic nutrition
An organism that makes its own food (organic compounds) from inorganic molecules using energy (chemical/sunlight)
-Producers
Types of autotrophs
-Chemoautotrophs
-Photoautotrophs
Chemoautotrophs
Life that gets energy from chemicals
-Produce energy from simple organic compounds
Chemoautotrophs example
Nitrifying bacteria in the recycling of nitrogen obtain their energy from oxidizing ammonia to nitrite or oxidizing nitrite to nitrate
Photoautotrophs
Produce energy from sunlight
Heterotroph
Consumer
-Organism that cannot make organic compounds from inorganic sources, needs a ready-made supply of organic compounds
-Obtains by consuming other organisms
Equation for photosynthesis
6CO2 + 6H20 + energy from photons = C6H1206 + 602
Carbon-fixation
The process by which carbon dioxide is converted to other sugars
-Endothermic so needs energy
- Needs electrons so reduced reaction
How photosynthesis and respiration correlate
Products of one process are the raw materials for the next process
-Balance between rate of respiration and photosynthesis
Glucose in a plant
-Stored as starch
-Respiration
Why is glucose transported in sucrose
Sucrose is soluble so can be transported in sap
-Metabolically inactive so won’t be used by the plant
Compensation point
Plants respire all the time but only photosynthesise during the day
= point at which rate of photosynthesis are respiration are balanced
Compensation period
The time it takes to reach the compensation point
Why does the compensation change dependant on the plant
Shade plants can utilise light of lower intensity than sun plants can
-When exposed to light after darkness the shade plants reach their compensation point sooner to reach their optimum rate of photosynthesis
Different layers of a leaf
1) Waxy cuticle
2) Upper epidermis
3) Palisade mesophyll
4) Spongy mesophyll (large air spaces)
5) Guard cells+ stomata in the lower epidermis
What is present in the palisade mesophyll layer
-Chloroplasts that can move dependant on the amount of sunlight
- Large vacuoles for water storage
-Where photosynthesis mainly happens
The Light dependant stage
Converts solar energy to chemical
-Produce ATP and NADPH
The light independent stage
Makes sugar from CO2 in the Calvin cycle
-ATP provides energy for sugar synthesis
-NADPH provides electrons for the reduction of CO2 to glucose
Different structures within a chloroplast
-Disc shaped
-Double membrane with an inter-membrane space between inner and outer membrane
-Outer membrane is highly permeable
-Inner membrane folded with stacks of thylakoids
- Grana - consists of stacks of thylakoid membranes where LD stage takes place
-Stroma - fluid-filled matrix - LI takes place
-Contains loops of DNA and starch granules
Grana
Where the light dependant stage takes place
-Thylakoids within may be connected to thylakoids within another granum by intergranal thylakoids
-Thylakoid membrane less permeable and folded into flattened discs named thylakoids that form stacks
One stack - granum
Why is there a large SA in chloroplasts
-For a large distribution of the photosystems
-Electron carriers/ ATP synthase
Adaptions of the stroma
-Proteins embedded in thylakoids membrane hold photosystems in place
-Surrounded by the stroma = short diffusion distance
Stroma
- fluid-filled matrix
-Contains enzymes to catalyse reactions, starch grains, oil droplets, small ribosomes
-Loop of DNA to code for proteins at chloroplast ribosomes
Photosystem
Contain photosynthetic pigments that trap light energy
-Funnel-shaped so light energy can be concentrated down into the primary pigment
Photosynthetic pigments
Initial requirement of photosynthesis is the trapping of sunlight energy by photosynthetic pigments
-Allow the maximum absorption of light
-Pigment absorbs light of a particular wave length and reflects other wave lengths of light
-Each pigment appears to our eyes and brain the colour that it is reflecting
What happens to the energy associated with the different wave-lengths of light
It is captured and funneled down the primary pigment reaction centre,which consists of a type of chlorophyll a at the base of the photosystem
What is chlorophyll
Mixture of pigments
-All have similar molecular structures consisting of a porphyrin group, in which there is a magnesium atom and a long hydrocarbon chain
Chlorophyll a
Primary pigment (always chlorophyll a at primary reaction centre)
Similarities/ differences between two types of chlorophyll a
Similarities:
-appear blue-green
- centre of the photosystem
- absorb red light
Differences:
-Different absorption peaks
Two types of chlorophyll a and where are they found
P700 is found on photosystem 1 and has a peak absorption of 700nm
P680 is found on photosystem 2 and has a peak absorption of 680nm
What can chlorophyll a also absorb
Some blue light at 440 nm
What are the accessory pigments
-Chlorophyll b
-Carotenoid
-Xanthophyll
-Phaeophytin
Function of the accessory pigments
Help the light energy to be transferred to chlorophyll a
Chlorophyll b (accessory pigment)
Absorbs light at wavelengths 400-500nm and around 640 nm
-Appears yellow-green
Carotenoids (accessory pigment)
Absorbs blue-light between 400-500 nm and reflect yellow-orange light
Xanthophylls (accessory pigment)
Absorbs blue and green light between 375-550 nm
-reflect yellow light
What are the benefits of accessory pigments
Allow absorption of light from different wavelengths
What is the graph from a calorimeter called
The absorption spectrum
-Combining the absorption spectrum of all photosynthetic pigments gives the action spectrum of overall photosynthesis
Peaks of chlorophyll A/B
2 peaks at a lower wavelength and then a higher
- A has first and last peaks
- B follows shortly after
-Accessory pigments in the middle
Where does the LD stage occur
Grana (thylakoids)
-Involves photosystems
-Involved direct use of light energy
What does the LD consist of:
-Light harvesting at the photosystems
-Photolysis of water
-Photophosphorylation
-The formation of reduced NADPH
Photophosphorylation
The production of ATP in the presence of light
-O2 is also produced as a by-product
Photolysis
PS2 there is an enzyme that in the presence of light, splits water into protons, electrons and oxygen
Photolysis equation
2H20 = (4H+) + (4E-) + (O2)
What is the oxygen used for
-Some are used by plant cells for aerobic respiration
-When photosynthesis exceeds respiration at periods of high light intensity most of the O2 will diffuse out of the stomata
Water uses in the plant
-The source of protons - used in photophosphorylation
-Donates electrons to chlorophyll to replace those lost when light strikes the chlorophyll
-Source of the by-product O2
-Keeps plant cells turgid, enabling them to function
What are the two types of photophosphorylation
-Non cyclic
-Cyclic
What does non-cyclic photophosphorylation involve and produce
Involves: PS1 and PS2
Produces: ATP, Oxygen, reduced NADP
What does cyclic photophosphorylation involve and produce
Involves: only PS1
Produces: ATP but in smaller quantities than non-cyclic
What is a similarity of non/cyclic photophosphorylation
Both involve iron-containing proteins embedded in the thylakoid membrane that accept and donate electrons and form an electron transport system
Non-cyclic photophosphorylation 1-3
1) When photon of light hits PS2 energy is channelled to the primary pigment reaction centre and excites 2 electrons in the chlorophyll
2) Energised electrons escape from chlorophyll and are captured by an electron carrier embedded in the thylakoid membrane
3) Meanwhile electrons lost from chlorophyll are replaced by those derived from photolysis
Non-cyclic photophosphorylation 4-5
(How does the electron transport system work?)
4) When iron ion in the electron carriers combines with an electron, it becomes reduced. It then donates the electron to the next electron carrier and becomes oxidised
5) Each time electron is donated energy is released and provides energy for chemiosmosis
= allows protons (derived from photolysis) to be pumped across the thylakoid membrane into thylakoid space
Non-cyclic photophosphorylation 6-7 (PS1?)
6) Electrons eventually captured by chlorophyll A in PS1
-Replace those lost from PS1 by excitation of light energy
7) Ferredoxin accepts electrons from PS1 and passes them to NADP in the stroma
Non-cyclic photophosphorylation 8-9 (protons)
8) Chemiosmotic gradient forms as protons accumulate in thylakoid space
9) Protons diffuse down the concentration gradient through ATP synthase and as they do ( ADP+ pi=ATP)
Non-cyclic photophosphorylation 10 (electrons and protons- what finally happens?)
12) As protons pass through the channel they are accepted along with electrons by NADP which then becomes reduced
-Reduction of NADP is catalysed by NADP reductase
What are the products of non-cyclic photophosphorylation
Light energy is now in the form of chemical energy (ATP)
ATP and reduced NADP = in the stroma
Cyclic photophosphorylation
-Uses only PS1
- Produces less ATP
-No photolysis / reduced NADP
Cyclic photophosphorylation steps
1) As light strikes PS1 pair of electrons become excited
2) Escape from electron carrier systems and pass back to PS1
- During passage of electrons along carriers small amount of ATP generated
Chloroplasts in the guard cells
Contain only PS1:
-Produces only ATP to bring potassium ions into cells lowering the WP so water follows by osmosis
-This causes the guard cells to swell and open the stoma
Comparisons between cyclic and non-cyclic photophosphorylation
Cyclic Non-Cyclic
- PS1 - PS1 + PS2
-Photolysis
-Electrons pass back - PS2 along ECTC to PS1 to NADP
to PS1
- produces ATP - ATP , reduced NADP, O2
Peaks of chlorophyll A/B
2 peaks at a lower wavelength and then a higher
- A has first and last peaks
- B follows shortly after
-Accessory pigments in the middle
Where does the light-independent stage occur
- Stroma
-Uses products from LD stage
Why does CO2 need to be produced
Source of carbon for the production of all organic molecules found in all carbon-based life forms on Earth
1) Structures: cell membranes, antigens, enzymes, muscle proteins
2) Energy stores: Starch, glycogen
Path of CO2 into the chloroplast
Stomata - spongy mesophyll - palisade layer - cell walls - chloroplast envelope - stroma
What happens to the CO2 in the stroma
Calvin cycle:
Series of reactions where CO2 is converted to organic molecules
The Calvin cycle
1) 6CO2 diffuses through stomata and combines with 6RuBP
= 30C + 12P
(catalyzed by RuBisCO) (carbon is fixed)
2) RuBP becomes carboxylated (highly unstable and breaks down)
3) Produces 12x G-3-P’s
4) G-3-P reduced
- 12NADPH2 = 12NADP
-12 ATP = 12 ATP+ pi
5) 12 TP
6) 10 TP are rearranged to regenerate 6RuBP
( 6ATP = 6ADP + 6pi) as 10 TP (3x10) RuBP (6x5) =30c
7) 2 TP that remain are the product used to makes amino acids/glucose etc.
Carbon fixation?
Taken carbon from its gaseous form and fixed it
Why do chloroplasts only contain low levels of RuBP
-RuBP is continuously being re-generated by TP
Why can the Calvin cycle only happen in the daylight
1) H+ in LD pumped into thylakoid space and thus raises pH in stroma to 8
= optimum pH for RuBisCO (also activated by presence of extra ATP in stroma)
2) In the daylight conc of magnesium ions in stroma increases in stroma and act as co-factors to RuBisCO
3) Ferredoxin in LD activates enzymes involved in the Calvin cycle
Uses of product TP from Calvin cycle
-Some TP used to synthesise organic compounds i.e. glucose is converted to starch; sucrose; cellulose
-Synthesise amino acids; fatty acids; glycerol
- Rest of TP is recycled and used to regenerate supply of RuBP
Examples of limiting factors
-CO2 and H20
- Light intensity
-Availability of chlorophyll
-Electron carriers
- Relevant enzymes
-Temperature
-Turgidity of cells
Light intensity
-Needed at LD
-Causes stomata to open (LI)
= At favourable temperature and CO2 concentration light intensity will be the limiting factor
=Light intensity low photosynthesis low
Note: Light intensity as a LF
At a certain point even when light intensity increases the rate of photosynthesis does not increase and another factor is limiting the process
The effect of changing light intensity on the Calvin cycle
-As no products from LD
1) G-3-P cannot be reduced to TP
2) TP falls; G-3-P accumulates
3) If TP falls RuBP cannot be regenerated so falls; G-3-P falls
CO2 as a LF
Not usually a LF as in atmosphere and aquatic environments
Benefits and disadvantages of CO2 of Climate change
+CO2 = +Crop rotation +photosynthesis
YET
climate change also leads to increased temperature
+Temp = O2 inhibits RuBisCO = photorespiration
-This reduces the growth in plants as it inhibits the Calvin cycle
-ATP + NADPH2 wasted
The effect of changing CO2 concentration on the Calvin cycle
If the concentration of CO2 falls below 0.01%
1) RuBP cannot be made
2) GP cannot be made
3) TP cannot be made
Temperature
Calvin cycle involves many enzymes so sensitive to changes in temperature
Effects of low temperature on the Calvin cycle
low - 25/30C
The rate of photosynthesis increases with temperature if plant has sufficient water, CO2, light
Effects of medium temperature on the Calvin cycle
30C+ most plants growth rates may reduce to photorespiration
= O2 successfully competes with CO2 for RuBisCO’s active site
-Reduces the amount of CO2 being accepted by RuBP -G3P -TP
- Initially causes an accumulation of RuBP but die to insufficient amount of TP = RuBP cannot be regenerated
Sufficient water supply
-Transpiration stream has a cooling affect on the plant
-Plant cells kept turgid so plant cells can function (keeps stomata open for gaseous exchange)
If not enough water is available
1) Roots unable to take up enough water to replace the water lost via respiration
2) Cells lose water and become plasmolysed
3) Plant roots produce abscisic acid = when translocated to the leaves causes stomata to close which decreases gaseous exchange
4) Tissues become flaccid and leaves wilt
5) Rate of photosynthesis decreases
Flaccid vs plasmolysed
Cells become plasmolysed but tissue becomes flaccid
What does the photosynthometer do
Measure the rate of photosynthesis
-Measure the volume of O2 produced by the Aquatic plant per min
What are some limitations of the photosynthometer
-Some of the O2 produced by the plant will be used for respiration
-May be some dissolved nitrogen in the gas collected
How are the limitations of the photosynthometer overcome
Measuring other effects i.e. light intensity/ CO2 availability on the rate of photosynthesis / temp
Photosynthometer experiment steps
1) Photosynthometer set up so that it is air tight and there are no air bubbles in the capillary tubing
2) Gas is given off by the plant over a known period of time, collects in the flared end of the capillary tube
3) Experimenter manipulates syringe so gas bubble can be moved into the part of the capillary tube against the scale so can measure the length of the gas bubble
4) If the radius of the capillary bore is known then this length can be converted to volume
How do you calculate the volume of the gas collected
Length of bubble x (pi)2
What is the solution
Sodium hydrogencarbonate ions = source of CO2
Greater conc = greater conc of CO2 available
What must you do at the beginning of the experiment
Wait for a period of equilibration
What is DCPIP
Replicates the electron transport and reduction of NADP in the light-dependant stage of the reaction
Photorespiration
O2 involved/ CO2 excreted
Only occurs in the light
Involves the Calvin cycle
Describe and explain the likely effect on photosynthesis
of an increase in the oxygen concentration
Reduces photosynthesis and increases the rate of photorespiration
In the test tube which is exposed to green light the hydrogen-carbonate solution is green
Explain the changes observed
Chlorophyll absorbs little green light of this wavelength
Green light cannot be used in photosynthesis
= no photolysis / no CO2 for the Calvin cycle
How can factors other than light conditions be controlled to increase the rate of
photosynthesis and maximise production in a greenhouse
photosynthesis is controlled by enzymes ;
temperature can be increased by heater /
reduced by ventilation (or fan) / maintained by air conditioning (or other method) ;
increase CO2 concentration (in environment) by burning,
fuel / gas / paraffin ;
idea that increased / more / higher, CO2 (conc),so CO2 no longer a limiting factor /
increases CO2 fixation / (or described)increases Calvin cycle (or described) ;
idea that easier to control,
water supply / irrigation (to prevent wilting) / humidity /
minerals / fertiliser ;
idea that easier to control use of,
pesticides / pest control / biological control
How is light harvested in the chloroplast membranes
1) (primary & accessory) pigments , are in / form a(n) ,
photosystem / complex / antenna complex ;
2) photon / light energy , absorbed by
pigment (molecule(s)) ;
3) electron , excited / moves to higher energy level /
delocalised , and returned to pigment ;
4 (energy / photon) passed from one pigment
to another ;
5 (energy / photon) passed to ,
reaction centre / chlorophyll a / P680 / P700 /
PSI / PSII / primary pigment ;
6 range of / accessory , pigments allow
range of wavelengths to be absorbed
How is light harvested in the chloroplast membranes
1) (primary & accessory) pigments , are in / form a(n) ,
photosystem / complex / antenna complex ;
2) photon / light energy , absorbed by
pigment (molecule(s)) ;
3) electron , excited / moves to higher energy level /
delocalised , and returned to pigment ;
4 (energy / photon) passed from one pigment
to another ;
5 (energy / photon) passed to ,
reaction centre / chlorophyll a / P680 / P700 /
PSI / PSII / primary pigment ;
6 range of / accessory , pigments allow
range of wavelengths to be absorbed
