5.2.1 Photosynthesis Flashcards
why do plants need energy
photosynthesis, active transport, DNA replication, cell division, protein synthesis
why do animals need energy
muscle contraction, maintaining body temperature, active transport, DNA replication, cell division, protein synthesis
why do microorganisms need energy
DNA replication, cell division, protein synthesis and sometimes movement
how do plants make their own food and what is it
- via photosynthesis
- make glucose
what is photosynthesis
- process where energy from light is used to make glucose from H2O and CO2
- light energy is converted to chemical energy in the form of glucose
what is the overall equation of photosynthesis
6CO2 + 6H2O → C6H12O6 + 6CO2
how do plants obtain energy from photosynthesis
- the energy is stored in glucose until plants release is via respiration
how do animals gain energy, given they cannot make their own food
- via eating plants or other animals
- then they too respire this glucose to release energy
what is respiration
living cells releasing energy from glucose
- this energy is used to power all biological processes in a cell
what are the two types of respiration
- aerobic, using oxygen
- anaerobic, without using oxygen
what is the equation of aerobic respiration
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
what is a metabolic pathway
a series of small reactions controlled by enzymes, e.g. photosynthesis and respiration
what is phosphorylation
adding phosphate to a molecules, e.g. ADP is phosphorylated to ATP
what is photophosphorylation
adding phosphate to a molecule using light
what is photolysis
the splitting of a molecule using light energy
what is hydrolysis
the splitting of a molecule using water
what is decarboxylation
the removal of CO2 from a molecule
what is dehydrogenation
the removal of hydrogen from a molecule
what are redox reactions
- reactions that involves oxidation and reduction:
Oxidation
Is
Loss of an electron (lose hydrogen and gain oxygen too)
Reduction
Is
Gain of an electron (gain hydrogen and lose oxygen too)
what is a coenzyme
- a molecule that aids in the function of an enzyme
- usually work by transferring a chemical group from one molecule to another
what is the coenzyme used in photosynthesis called
- NADP
- transfers hydrogen from one molecule to another
- it can reduce (give hydrogen) or oxidise (take hydrogen) from a molecule
what are the coenzymes involved in respiration
- NAD
- coenzyme A
- FAD
what are chloroplasts
- small flattened organelle
- found in plant cells
- location for photosynthesis
name the parts of a chloroplast
- the inner and outer membrane, combine to make envelope (double membrane structure)
- thylakoid membrane
- thylakoid
- lamellae
- granum/grana (thylakoid stack)
- starch grain
- stroma
- circular DNA
explain the membranes inside a chloroplast
- the chloroplast membrane around
- thylakoids (fluid filled sacs) are stacked up in the chloroplast into structures called grana, and these are linked by bits of thylakoid membrane called lamellae (lamella singular)
explain the stroma inside the chloroplasts
- contained within the inner membrane of the chloroplasts
- surround the thylakoids
- gel-like substance
- contains enzymes, sugars and organic acids
explain the chloroplasts having their own DNA
- found in the stroma
- often circular
- can be multiple copies in each chloroplast
what are the starch grains in chloroplasts
-carbohydrates produced by photosynthesis and not used straight away are stored as these grains
- in the stroma
what are photosynthetic pigments
- coloured substances that absorb light energy needed for photosynthesis
- found in the thylakoid membranes, attached to proteins
- the protein plus the pigment is called a photosystem
give examples of photosynthetic pigments
chlorophyll a, chlorophyll b and carotene
what are the two types of accessory pigments that make up a photosystem
primary and accessory
what are primary pigments
- reaction centres, where electrons are excited during the light-dependent reaction
what are accessory pigments
- make up light harvesting systems
- they surround reaction centres and transfer light energy to them to boost the energy available for photosynthesis to take place
what are the two photosystems
- used by the plant to capture light energy
- photosynthesis I, or PSI absorbs light best at wavelength 700nm
-photosystem II, or PSII, absorbs light best at wavelength 680nm
what are the two stages of photosynthesis
- light independent and dependent stage
briefly overview the light dependent stage of photosynthesis
- what it needs
- where it takes place
- what happens
- the chemicals formed and why needed
- needs light energy
- takes place in the thylakoid membrane of the chloroplasts
- here, light energy is absorbed by photosynthetic pigments in the photosystems and converted to chemical energy
- light energy is used to add a phosphate group to ADP to form ATP
- reduce NADP to reduced NADP (or NADPH), which is an energy rich molecule because it can transfer hydrogen, and so electrons, to other molecules
- ATP is used to transfer energy and NADPH is used to transfer hydrogen in the light-independent reaction
- H2O is also oxidised to form O2
briefly overview the light-independent reaction:
- another name for it
- what it relies on
- where it takes place
- the chemicals involved
- also called the Calvin cycle
- doesn’t use light energy directly
- does still rely on the products of the light-independent reaction
- takes place in the stroma
- ATP and NADPH supply energy and hydrogen to make glucose from CO2
PAG: how can you separate out the photosynthetic pigments in plants
- using thin layer chromatography TLC
PAG: what two phases does thin layer chromatography involve
- the mobile phase, a liquid solvent
- the stationary phase, a solid such as glass, plate with thin layer of gel/silica gel on it(a chromatography plate)
PAG: explain the steps involved in TLC of photosynthetic pigments
1) grind up leaves with anhydrous sodium sulfate and propanone
2) transfer liquid to test tube and add petroleum ether and gently shake
3) should form 2 distinct layers, top layer is needed
4) transfer top layer into second test tube with anhydrous sodium sulfate
5) draw a horizontal pencil line near the bottom of the chromatography plate
5) carry on adding several drops once the one before has dried to make sure the spot is concentrated - makes the point of origin
5) once the point is completely dry, put plate into a prepared solvent, so the point of origin is slightly above the solvent
6) put lid on beaker and leave to develop
7) as solvent moves up, so do the pigments at different rates and separate out
8) when its nearly reached the top, take out the plate and mark the solvent front with a pencil and leave to dry
9) should show several coloured spots on plate, which are the separated pigments
10) find Rf values and look them up in database to identify the values
how do you calculate Rf values
distance travelled by solute/distance travelled by solvent
what is light energy needed for in the light-dependent reaction
- making ATP from ADP and inorganic phosphate (photophosphorylation)
- making reduced NADP from NADP
- splitting of water via photolysis into H+, e- and O2
what are photosystems linked by
electron carriers
what are electron carriers
proteins that transfer electrons
what is an electron transport chain
a chain of proteins through which excited electrons flow, made of photosystems and electron carriers
explain the set up where the light-dependent reaction takes place
- thylakoid membrane
- the stroma
- inside the thylakoid
- electron carriers in the thylakoid membrane
- photosystems I and II, with chlorophyll found at the bottom
- light energy entering from above
what is the first step of non-cyclic photophosphorylation
1) light energy is absorbed by PSII
2) this excited the electrons in the chlorophyll
3) and they move to a higher energy level
4) these high-energy electrons move along the electron transport chain to PSI
(chlorophyll fluorescence occurs when plants absorb too much light energy, and release excess by emitting fluorescent light)
what is the second step of non-cyclic photophosphorylation
1) as excited electrons from the chlorophyll leave PSII to move along the electron transport chain, they must be replaced
2) light energy splits water into protons, electrons and oxygen (this is why photosynthesis produces O2, as it comes from the water)
3) H2O → 2H+ +1/2O2 + 2e-
what is the third step of non-cyclic photophosphorylation
1) the excited electrons lose energy as they move along the electron transport chain
2) this energy is used to transport protons into the thylakoid, via membrane proteins called proton pumps
3) this means the thylakoid has a higher concentration of protons than the stroma
4) forms a proton gradient across the membrane
5) protons move down their concentration gradient into the stroma via an enzyme called ATP synthase
6) the energy from this movement combines ADP with inorganic phosphate to form ATP
- CHEMIOSMOSIS
what is chemiosmosis
the process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis
- described by the chemiosmotic theory
what is the 4th and last step of non-cyclic photophosphorylation
1) light energy is absorbed by PSI, which excited the electrons again to an even higher energy level
2) the electrons are transferred to NADP, along with a proton H+ from the stroma to form reduced NADP
3) NADP + e- + H+ → NADPH
what happens in cyclic photophosphorylation
- only uses PSI
- electrons from the chlorophyll molecule once excited aren’t passed onto NADP, but pass back to PSI via electron carriers
- electrons are recycled and can repeatedly flow through PSI
- doesn’t produce O2 or NADPH
- only produces small amounts of ATP
what are the alternative names of the light-independent reaction
- the Calvin cycle
- carbon dioxide fixation ( because carbon from CO2 is fixed into an organic molecule)
what are the products of the Calvin cycle
- triose phosphate TP from CO2
- ribulose bisphosphate RuBP, which is the starting compound but is also regenerated, forming a cycle
why is making TP a useful product
can be used to make glucose and other useful organic substances
what is needed for the Calvin cycle
- energy (via ATP)
- H+ ions (via NADPH)
what happens in the first stage of the Calvin cycle
- CO2 [1] + RuBP [5] → 2GP[2x3] (rubisco)
1) CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast
2) it combines with RuBP (a 5 carbon compound)
3) this forms an unstable 6 carbon compound which quickly breaks down into two molecules of a 3 carbon compound called GP (glycerate 3-phosphate)
4) the reaction between CO2 and RuBP is catalysed by enzyme RuBisCO
what is the second step in the Calvin cycle
- 2GP [2x3] → 2TP [2x3] (NADPH/ATP)
(all TIMES 2)
1) the 3-carbon compound GP is turned into a different 3-carbon compound called TP
2) requires energy provided from ATP→ADP+Pi
3) requires H+ ions provided by NADPH → NADP + H+ (the NADP can then be recycled for use again in the light-dependent reaction)
4) the TP produced can then be converted into many useful organic compounds
what is the third and final stage in the Calvin cycle
1) 5 out of every 6 molecules of TP produced in the cycle aren’t used to make hexose sugars, but the regenerate RuBP
2) this reaction requires the rest of the ATP produced in the light-dependent reaction
explain the Calvin CYCLE and the number of C present
1) RuBP + CO2 → 2GP [5C + 1C → 2(3) C]
2) 2GP → 2TP [ 2(3)C →2(3)C]
3) TP → RuBP [ 2(3)C → 5C ] (+C)
why is the Calvin cycle needed for
- the starting point for making all the organic substances a plant needs
what useful organic substances can be made from TP (and GP)
- CARBOHYDRATES: hexose sugars such as glucose are made by joining 2 TP molecules together and larger ones are made by joining these hexose sugars together
- LIPIDS: are made using glycerol, which is synthesised from TP, and fatty acids which are synthesised from GP
- AMINO ACIDS: some amino acids are made from GP
how many times does the Calvin cycle need to turn to make one hexose sugar
- 6 times
explain why the Calvin cycle needs to turn 6 times to produce one hexose sugar
- 3 turns of the cycle produce 6 molecules of TP, because 2 molecules of TP are produced for every CO2 used
- 5/6 of these TP is used to regenerate RuBP
- so for every 3 turns, only 1 TP is produced
- one hexose sugar has 6 carbons, so TWO TP molecules are needed to form one sugar
- so the cycle must turn 6 times to produce 2 molecules of TP which can be used to make one hexose sugar
how much ATP and NADPH is needed to make one hexose sugar
6 turns means:
- 18 ATP
- 12 NADPH
what are the optimum light conditions for photosynthesis
- light is needed to provide the energy for the light dependent reaction of photosynthesis, so HIGHER THE INTENSITY, the more energy it provides
- only certain wavelengths of light are used for photosynthesis
- photosynthetic pigments chlorophyll a (violet, red) ,b (blue) and carotene (violet, blue, green) only absorb red and blue sunlight (green light is reflected, which is why plants appear green)
explain the optimum temperature for photosynthesis
- around 25°C
- photosynthesis involves enzymes, like ATP synthase and RuBisCO
- if temp falls below 10, they become inactive, and if above 45 they will denature
- at high temp, stomata close to avoid losing too much water, so photosynthesis slows as less CO2 can enter the leaf when the stomatal aperture is closed
- at high temp, the thylakoid membranes might become damaged, reducing the rate of the LDS by reducing the number of sites available for electron transfer
- the membrane around the chloroplast itself could become damaged, which can cause enzymes important to Calvin cycle to be released into the cell, reducing the LIS reactions
- chlorophyll could be damaged, reducing the amount of pigment that can absorb light energy, reducing the rate of the light-dependent stage reactions
explain the optimum CO2 concentration for photosynthesis
- CO2 makes up 0.04% of the gases in the atmosphere
- if increased to 0.4%, we have a higher rate of photosynthesis, but any higher and the stomata start to close
how can photosynthesis be limited
- light intensity and wavelength, CO2 concentration and temperature all have to be at the right level for photosynthesis to occur quickly as possible
- if any factor is too high or too low, it will slow down photosynthesis
- even if other two factors are at perfect level, it will not matter
- on warm, sunny, windless day, CO2 concentration is usually limiting factor, at night light intensity
- any factor could be limiting, depending on the environment
explain the light intensity limiting factor graph
- on the slope, the rate of photosynthesis is limited by the light intensity
- as light intensity increases, so does rate of photosynthesis
- when it levels off, you reach a saturation point (where the factor is no longer the limiting factor, but something else is)
- increasing light intensity will make no difference to rate
explain the temperature limiting factors graph on light intensity axis
- at both temperatures, will level off when light intensity no longer the limiting factor
- at 25°C, will level off at a higher point than at 15°C, showing that temp must be limiting factor
explain the CO2 concentration graph on limiting factor on a light intensity axis
- both graphs will level off when light intensity is no longer the limiting factor
- at 0.4% will level off higher than 0.04% as the CO2 conc must be limiting factor
how does water affect the rate of photosynthesis
- when plants don’t have enough water
- the stomata will close to preserve the little water they do have
- so less CO2 enters the leaf for the Calvin cycle
- photosynthesis slows down
what do the limiting factors of photosynthesis also impact
- the levels of GP, RuBP and TP in the Calvin cycle
how does light intensity impact components of the Calvin cycle
- in low light intensity, the products of the LDS (ATP and NADPH) will be low
- so the conversion of GP into TP and RuBP will be low
- so the levels GP will rise as its still being made
- and levels of TP and RuBP will fall as they are being used up to make GP
how does temperature affect the components of the Calvin cycle
- all the reactions of the Calvin cycle are catalysed by enzymes like RuBisCO
- so at lower temperature, all the reactions will be slower as the enzymes work more slowly
- levels of GP, TP and RuBP will fall
- same for very high temperature, as enzymes will start to denature
how does carbon dioxide concentration affect the components of the Calvin cycle
- at low CO2 concentration
- the conversion of RuBP to GP is slow
- as there is less CO2 to combine with RuBP
- so the levels of RuBP will rise as its still being made
- and levels of GP and TP will fall as they are being used up to make RuBP
PAG: what can you measure to find out the rate of photosynthesis
the rate at which oxygen is produced by pondweed
PAG: what is the equipment you need to find out the rate of photosynthesis using pondweed
- a ruler
- light source if this is the independent variable
- test tube containing pondweed
- clamp
- capillary tube and syringe
PAG: how would you measure how light intensity affects the rate of photosynthesis
- connect test tube containing pondweed and water to a capillary tube containing water
- connect the tube to a syringe
- use a source of white light, and place the pondweed at a specific distance away
- leave the pondweed to acclimatise for a set amount of time once acclimatised
- as it photosynthesises, oxygen released is collected in the capillary tube
- once time has ran out, you use the syringe to draw up the oxygen bubble in the tube alongside a ruler, and measure the length of the bubble produced
- this is proportional to the volume of O2 produced
- control all other variables (temperature, CO2 conc.)
- repeat the experiment and calculate the average length the bubble - MORE PRECISE
- repeat the whole experiment but with the pondweed at different lengths to the light source
- can figure out the exact volume of the O2 via radius of the capillary tube
