5.6- Photosynthesis Flashcards
Name 4 types of nutrition
- heterotrophic
- autotrophic
- chemoautotrophic
- photoautotrophic
describe heterotrophs
- cannot make organic compounds from inorganic sources
- obtain organic compounds by digesting complex organic molecules of food to smaller molecules that they can use as respiratory substrates
- they obtain energy from the products of digestion by respiration
- almost all animals, fungi, and some Protista and bacteria
- Consumers or decomposers
Describe autotrophs
- An organism that makes their own food (complex organic compounds)- synthesise large molecules- from inorganic molecules using energy (chemical or light)
- Producers in an ecosystem
Describe chemoautotrophs
- Produce energy from simple inorganic compounds
- The first life forms on Earth were chemoautotrophs
- Prokaryotes that synthesise complex organic molecules using energy derived from exergonic chemical reactions
- Many bacteria are chemoautotrophs; nitrifying bacteria in the recycling of nitrogen obtain their energy from oxidising ammonia to nitrite or oxidising nitrite to nitrate
Describe photosutotrophs
- Organisms that photosynthesise are described as photoautotrophs- producers
- Their energy source is sunlight and the raw materials are inorganic molecules: carbon dioxide and water
Describe the sun
The sun is the ultimate source of energy for ALL living organisms- photosynthesis is the only means available to use this energy
Outline photosynthesis
- physiological process used by plants, algae, and some types of bacteria to convert light energy from sunlight into chemical energy
- this is used to synthesise large organic molecules from inorganic substances (O2 and CO2), which form the building blocks of living cells
- main product is monosaccharide sugar, which can be converted to disaccharide for transport, and then to starch for storage
- It releases oxygen, from water, into the atmosphere, so all aerobes depend on it for aerobic respiration
general equation of photosynthesis
What are Photons
- a particle of light
- each photon contains an amount (a quantum) of energy
What process is photosynthesis an example of
carbon fixation
Describe carbon fixation
- the process by which carbon dioxide is converted into sugars
- the carbon for synthesising all types of organic molecule is provided by carbon fixation
- endothermic- needs energy
- also needs electrons- addition of electrons is reduction
- helps to regulate the concentration of CO2 in atmosphere and oceans
- most forms of life rely directly or indirectly on photosynthesis
Outline respiration (photosynthesis topic)
- plants and other organisms that photosynthesise also respire- during respiration, they oxidise the organic molecules that they have previously synthesised by photosynthesis and stored, releasing chemical energy
- during respiration from non-photosynthetic organisms, glucose and other organic compounds are oxidised to produce carbon dioxide and water
- releases chemical energy (exothermic) that can drive the organisms metabolism
Describe the interrelationship between photosynthesis and respiration
- both are important in cycling CO2 and O2 in the atmosphere
- the products of one process are the raw materials for the other process- aerobic respiration removes O2 from the atmosphere and adds CO2, while photosynthesis removes CO2 and adds O2
Describe the balance between photosynthesis and respiration in plants
- plants respire constantly
- only photosynthesise during daylight
- plants often compete with each other for light- light intensity has to be sufficient to allow photosynthesis at a rate that replenishes the carbohydrate stores used up by respiration
- when photosynthesis and respiration proceed at same rate, so there is not net gain or loss of carbohydrate, the plant is at its compensation point
- the time a plant takes to reach its compensation point is the compensation period
Describe the compensation period for different types of plants
- shade plants can utilise light of lower intensity than sun plants can
- when exposed to light after being in darkness, shade plants will reach their compensation point sooner- have a shorter compensation period- than sun plants (which require a higher light intensity to achieve their optimum rate of photosynthesis)
Balance between photosynthesis and respiration in plants diagram
Briefly outline chloroplasts
- organelles within plant cells where photosynthesis takes place
- algae have them, but photosynthetic bacteria don’t
- most plant ones are disc shapes and around 2-10um long
- each surrounded by double membrane- the envelope, with an intermembrane space (10-20mm) between the inner and outer membrane
- outer membrane is highly permeable
- 2 distinct regions on electron micrographs- the storm and the grana (consists of stacks of thylakoid membranes)
Name the 3 distinct membranes and internal compartments of chloroplasts
Membranes:
- outer
- inner
- thylakoid
Compartments:
- intermembrane space
- stroma
- thylakoid space
Describe the grana
- where the light-dependent stage (1st stage) of photosynthesis occurs
- the thylakoids within a grain may be connected to thylakoids in another geranium by intergranal lamellae (aka intergranal thylakoids)
- the thylakoid membrane of each chloroplast is less permeable and is folded into flattened disc-like sacs (thylakoids) that form stacks - each stack is a geranium
- one granum may contain up to 100 thylakoids
Adaptations of the grana
- many grana in every chloroplast, many chloroplast in every photosynthetic cell- large SA for the distribution of the photosystems that contain the photosynthetic pigments that trap sunlight energy, and for the electron carriers and ATP synthase enzymes needed to convert that light energy into ATP
- proteins embedded in the thylakoid membranes hold the photosystems in place
- the grana are surrounded by the storm, so the products of the light-dependent stage can easily pass to the storm to be used in the light-independent stage
Describe the stroma
- the fluid filled matrix
- contains the enzymes needed to catalyse the reactions of the light-independent stage
- also contains starch grains, oil droplets, small ribosomes similar to those found in prokaryotes cells and DNA
- the loop of DNA contains genes that code for some of the proteins needed for photosynthesis
- these proteins are assembled at the chloroplast ribosomes
What are the structures within the thylakoid membranes called
Photosystems
Describe photosystems
- funnel-shapes
- contain photosynthetic pigments
- each pigment absorbs light of a particular wavelength and reflects other wavelengths of light
- each pigment appears to us the colour of the wavelength of light its reflecting
- the energy associated with the wavelengths of light captured is funnelled down o the primary pigment reaction centre, consisting of a type of chlorophyll at the base of the photosystem
Describe chlorophylls
- a mixture of pigments
- all have similar molecular structure- consist of porphyrin group- in which is a magnesium atom and a long hydrocarbon chain
Types:
- chlorophyll a
- Chlrophyll b
Describe chlorophyll a
- two types
- both appear blue-green
- both situated at centre of photosystems
- both absorb red light, but have different absorption peaks
- P680- found in photosystem II- peak of absorption is light of 680nm WL
- P700- found in photosystem I- peak of absorption is light of 700nm WL
- chlorophyll a also absorbs some blue light (around 440nm WL)
describe chlorophyll b
- absorbs 400-500nm WL and around 640nmWL
- escapers yellow green
Describe accessory pigments
- carotenoids- absorb blue light of 400-600nm WL, reflect yellow and orange light
- xanthophylls- absorb blue and green light- 375-550nm WL, reflect yellow light
photosynthetic pigments graph
Rf values of photosynthetic pigments
Name the steps of the light-dependent stage of photosynthesis
1) light harvesting at the photosystems
2) photolysis of water
3) photophosphorylation (the production of ATP in the presence of light)
4) the formation of reduced NADP
Describe the 2 types of photosystem
- photosstem I- pigment at primary reaction centre is P700 (peak red light, 700nm)
- photosystem II- pigment at primary reaction clemyrr is P680 (peak red light 680nm)
Describe the role of water in the light-dependent stage of photosynthesis
- splits- photolysis
- in PSII there is an enzyme that, in the presence of light, splits water molecules unto protons (hydrogen ions), electrons, and oxygen
- the protons are used in photophosphorylation
- the electrons are donated to chlorophyll to replace those lost when light strikes chlorophyll
- oxygen is by-product
- water also keeps plant cells turgid, enabling them to function
Describe the role of the oxygen produced in photolysis
- some of oxygen produced is used by plant cells for aerobic respiration
- However, during periods of high light intensity the rate of photosynthesis is greater than the rate of respiration in the plant, so much of the oxygen by-product will diffuse out of the leaves, through the stomata, into the surrounding atmosphere
Define photophosphorylation
The generation of ATP from ADP and inorganic phosphate in then presence of light
Outline the 2 types of photophosphorylation
- non-cyclic- involves PSI and PSII- produces ATP, oxygen, and reduced NADP
- cyclic- just PSI- produces ATP but in smaller quantities
- both involve iron-containing proteins embedded in the thylakoid membranes that accept and donate electrons and form an electron transport system
Outline the beginning non-cyclic photophosphorylation
1) Photon of light strikes PSII (P680)
2) It’s energy is channeled to the primary pigment reaction centre
3) The light energy excites a pair of electrons inside the chlorophyll molecule
4) The energised electrons escape from the chlorophyll molecule- these electrons are replaced by electrons derived from photolysis
Describe what happens to the energised electrons that have escaped from the chlorophyll molecule in PSII (non-cyclic photophosphorylation)
1) They are captured by an electron carrier (a protein embedded in the thylakoid membrane)
2) When this iron ion combines with an electron but becomes reduced to Fe2+
3) It can then donate the electron to the next electron carrier in the chain, becoming re-oxidised to Fe3+
4) As electrons are passed along a chain of electron carriers embedded in the thylakoid membrane, at each step some energy associated with the electrons is released- this energy is used to pump protons across the thylakoid membrane into the thylakoid space
5) Eventually the electrons are captured by another molecule if chlorophyll in PSI- these electrons replace those lost from PSI due to excitation by light energy
Describe what happens to the electrons after being captured by PSI (non-cyclic photophosphorylation)
1) a protein-iron-sulfur complex (called ferredoxin) accepts the electrons from PSI and passes them to NADP in the stroma
2) As protons accumulate in the thylakoid space, a proton-gradient forms across the membrane
3) Protons diffuse down their concentration gradient through special channels in the membrane associated with ATP synthase enzymes
4) As they do so, the flow of protons causes ADP and inorganic phosphate to join- forming ATP
5) As the protons pass through the Chanel they are accepted, along with electrons, by NADP, which becomes reduced
- The reduction of NADP is catalysed by the enzyme NADP reductase
Non-cyclic photophosphorylation diagram
Briefly outline what has happened by the end of non-cyclic photophosphorylation
- the light energy has been converted into chemical energy in the form of ATP by photophosphorylation
- ATP and reduced NADP are now in the storm ready for the light independent stage
Outline cyclic photophosphorylation
- only uses PSI (P700)
- As light strikes PSI,, a pair of electron in the chlorophyll molecule at the reaction centre gain energy and become excited
- They escape from the chlorophyll and pass to an electron carrier system then pass back to PSI
- During the passage of electrons along the electron carriers, a small amount of ATP is generated
Describe an example of where cyclic photophosphorylation occurs
- chloroplasts in guard cells contain only PSI
- They produce only ATP which actively brings potassium ions into the cells, lowering the water potential so that water follows by osmosis
- This causes the guard cells to swell and opens the stoma
Z-scheme diagram
Briefly outline the light-independent stage of photosynthesis
- occurs in the stroma
- doesn’t directly use light energy, but uses the products of the light-dependent state
- if the plant is not illuminated, the LD state soon ceases as ATP and hydrogen are not available to reduce the carbon dioxide and synthesise large complex organic molecules
Describe the role of carbon dioxide
- the source of carbon for the production of all organic molecules found in all the carbon-based life forms on earth
- these organic molcules may be used a s structures (e.g. cell membranes, antigens, enzymes, muscle proteins, cellulose cell walls), or act as energy stores (starch and glycogen)
Describe how carbon dioxide enters the leaf (calivn cycle)
- CO2 in air enters the leaf through the stomata and diffuses through the spongy mesophyll layer to the palisade layer, into the palisade cells, through their thin cellulose cell walls, and then through the chloroplast envelope into the stroma
- the fixation of CO2 in the stroma maintains a concentration gradient that aids in diffusion
- Carbon dioxide that is a by-product of reparation in plant cells may slo be used for this stage of photosynthesis
Define the Calvin cycle
The metabolic pathway of the light independent stage of photosynthesis whereby carbon dioxide is fixed, with the products of the LD state, to make organic molecules
Describe the process of carbon fixation in the Calvin cycle
1) Carbon dioxide combines with a carbon dioxide acceptor- 5C compound ribulose bisphosphate (RuBP)
- This enzyme is catalysed by the enzyme RuBisCo (ribulose bisphosphate carboxylase-oxygenase)
2) By accepting the carboxyl (COO-) group, RuBP becomes carboxylated
3) This forms an unstable intermediate 6C compound
4) This immediately breaks down into 2 3C compounds- GP (glycerate-3-phosphate)
Describe what happens after carbon fixation in the Calvin cycle
1) The GP is reduces, using hydrogens from the reduced NADP made during the light-dependent stage
2) forms triose phosphate (TP)
3) Two molecules of ATP are converted to ADP To release energy
Describe the products of the Calvin cycle
- produces 2 triose phosphate, which can be converted into 1 molecule of glucose
- however, in 10 of every TP molecules produced, the atoms are rearranged to regenerate 6 molecules of RuBP
- this process requires phosphate groups
- chloroplasts contain only low levels of RuBP, as it is continually being concerted to GP, but is also continually being regenerated
- the remaining 2 of the 12 TP are the product
- means 6 turns of the cycle are needed for the formation of 2 TP that can then be used to make 1 molecule of glucose
Calvin cycle diagram
Describe the relation between the Calvin cycle and daylight
- the products of the LD stage (ATP ad reduced NADP are continuously needed for the cycle to run)
- in the LD stage, H ions are pumped from the stroma into the thylakoid paces, so the concentration of free protons in the storma falls, raising the pH to around 8- this is the optimum pH for enzyme RuBisCO
- RuBisCO activated by presence of extra ATP in the stroma
- in daylight, they concentration of magnesium ions increases in the stroma- these attach to the active site of RuBisCO, acting as cofactors
- the ferredoxin that is reduced by electrons from PSI activates enzymes involved in the reactions of the Calvin Cycle
Describe the uses of the triose phosphate produced in the cabin cycle
- glucose- some converted to sucrose, starch and cellulose
- some TP used to synthesise amino acids, fatty acids, and glycerol
- the rest of the TP is recycled to regenerate the supply of RuBP- 5 molecules of 3C TP interact to form 3 molecules of 5C compound RuBP
What does the rate of photosynthesis depend on
Limited by the factor that is present at its least favourable level
Name limiting factors of photosynthesis
- Light intensity
- Carbon dioxide concentration
- Temperature
- Water stress
Name limiting factors of photosynthesis
- Light intensity
- Carbon dioxide concentration
- Temperature
- Water stress
Describe the effect of light intensity on the rate of photosynthesis
- light provides energy to power the first stage and produce ATP and reduced NADP needed for the next stage
- also causes the stomata to open so that gaseous exchange can occur
- when the stomata are open, transpiration occurs- egads top uptake of water and delivery to leaves
Describe how light intensity acts as a limiting factor
- at content favourable temperatures and constant suitable carbon dioxide concentration, light intensity is the limiting factor
- when light intensity is low, the rate of photosynthesis is low, as light intensity increases, the rate of photosynthesis increases
- at a certain point, even when light intensity increases, the rate of photosynthesis does not increase- factor other than light intensity is limiting the process
Effect of light intensity on photosynthesis multiple factors graph
Describe what happens to the Calvin cycle when there is little/no light
1) GP can’t be reduced to TP
2) TP levels fall and GP accumulates
3) If TP levels fall, RuBP cannot be regenerated
Describe the effects of carbon dioxide concentration on photosynthesis
The levels of CO2 in the atmosphere and in aquatic habitats are high enough that CO2 is not usually a limiting factor
Describe potential effects of global warming on the rate of photosynthesis
- As a result of human activity, such as burning fossil fuels increasing the carbon dioxide in the air and oceans, it has been proposed that this could increase crop production as it may increase the rate of photosynthesis
- However, it also leads to warming and, when the environmental temperature increases, oxygen competes successfully with carbon dioxide for the active site of the enzyme RuBisCo
- This phenomenon, called photorespiration, reduces the growth in plants by inhibiting the Calvin cycle
- The ATP and reduced NADP generated in the light-dependent stage are wasted
Describe what happens to the Calvin cycle is the concentration of carbon dioxide falls below 0.01%
1) RuBP cannot accept it, and it accumulates
2) GP cannot be made
3) Therefore TP cannot be made
Describe the Calvin cycle at temperatures from low to 25-30°C
*From low temperatures to temperatures of 25-30 °C, if plants have enough water and carbon dioxide and a sufficient light intensity, the rate of photosynthesis increases as temperature increases
Describe the Calvin cycle at temperatures above 30°C
- growth rates may reduce due to photorespiration
- oxygen competes with carbon dioxide for the enzyme RuBisCO’s active site
- this reduces the amount of carbon dioxide being accepted by RuBP and subsequently reduces the quantity of GP and therefore of TP being produced, whilst initially causing an accumulation of RuBP
- however, due to lack of TP, RuBP cannot be regenerated
Describe the Calvin cycle at temperatures above 45°C
- enzymes involved in photosynthesis may be denatured
- would reduce the concentrations of GP and TP
- eventually of RuBP as it could not be regenerated due to lack of TP
Describe the effects of water stress on photosynthesis
- if a plat has access to sufficient water in the soil, the transpiration stream has a cooling effect on the plant
- the water passing up the Xylem to leaves also keeps plant cells turgid so they can function
- turgid guard cells keep the stomata open for gaseous exchange
What happens to photosynthesis if not enough water is available to the plant (water stress)
- the roots are unable to take up enough water to replace that lost via transpiration
- cells lose water and become plasmolysed
- plant roots produce abscisic acid that, when translocated to leaves, causes stomata to close, reducing gaseous exchange
- tissues become flaccid and leaves wilt
- the rate of photosynthesis greatly reduces.
name different ways to measure the rate of photosynthesis
- rate of uptake of raw materials e.g. carbon dioxide
- the rate of production of the by-product oxygen
- in each case, to measure the rate we need to calculate the quantity taken up or produced per minute
What is the issue with using the volume of oxygen produced per minute by an aquatic plant to measure rate of photosynthesis
- Some of the oxygen produced by the plant will be used for its respiration
- there may be some dissolved nitrogen in the gas collected
Name the apparatus used to measure respiration
Photosynthometer- also known as an Audus microburette
Describe how photosynthometers work
- set up so that it is air tight and there are no air bubbles in the capillary tubing
- Gas given off by the plant, over a known period of time, collects in the flared end of the capillary tube
- As the experimenter manipulates the syringe, the gas bubble can be moved into the part of the capillary tube against the scale and its length measured
- if the same apparatus his used throughout the investigation, the radius of the tube bore is content, so comparison can be made using just the bubble lengths
Describe how photosynthometers can be used to measure the volume of gas collected
If the radius of the capillary tube bore is known, then this length can be converted to volume:
Describe what you need to do before using a photosynthometer to investigate factors that effect rate of photosynthesis
- make and justify a prediction
- state the IV and DV
- state the variables you will need to control, why you need to control them and how you will
control them - write a plan and ask your teacher to check it
Why is sodium hydrogen carbonate often added to the photosynthometer
to supply carbon dioxide - a reactant in photosynthesis
Non-cyclic phosphorylation diagram
