GoConqr has a new look! Let us know what you think.

Sign up free

Flashcards

Photosynthesis Flashcards

Rhea Sekhon Biology A level English 66 cards

Photosynthesis Flashcards

Cards in this deck (66)

  1. 1What is photosynthesis?This is the process whereby LIGHT ENERGY from the sun is transformed into CHEMICAL ENERGY and used to synthesise LARGE ORGANIC MOLECULES, from INORGANIC substances eg. CO2 and H2O
  2. 2Give the word and chemical equation for photosynthesisGive the word and chemical equation for photosynthesis
  3. 3What are the two stages of photosynthesis?1. The light-dependent stage
    2. The light-independent stage
  4. 4What is the glucose produced in the light-independent stage of photosynthesis converted into and why? (2 things)- A disaccharide for TRANSPORT
    - To starch for STORAGE
  5. 5Define an autotrophThese are organisms that use light energy and inorganic molecules (CO2 and water) to synthesise complex organic molecules, by converting the light energy into chemical energy (synthesise their own food)
  6. 6Define a heterotrophThese are organisms that ingest and digest complex organic molecules, RELEASING (not synthesising) the chemical potential energy that is stored in them (don't synthesise their own food)
    They obtain energy from the products of digestion, through respiration
  7. 7Define a photoautotrophThese are organisms that synthesise complex organic molecules using energy derived from the SUN
    Eg. photosynthetic organisms
  8. 8Define a chemoautotrophThese are organisms that synthesise complex organic molecules using energy derived from CHEMICAL REACTIONS
    Eg. bacteria such as nitrobacter
  9. 9What are saprotrophs a type of?They are a type of heterotroph!
  10. 10How are photosynthesis and respiration related to one another?During respiration, organisms will OXIDISE the organic molecules that have been previously synthesised by photosynthesis and stored (what the glucose produced is converted into), releasing CHEMICAL ENERGY
    The products of respiration are the starting materials for photosynthesis and the products of photosynthesis are the starting materials for respiration
  11. 11What is the compensation point?Plants RESPIRE all the time but only photosynthesise during DAYLIGHT
    Plants will compete for LIGHT, but the RATE of photosynthesis has to replenish the carbohydrate debt from respiration
    The compensation point is the point at which the rate of photosynthesis = the rate of respiration
  12. 12What is the compensation period?This is the time it takes for a plant to reach its compensation point
    The compensation period is different for different plant species - shade plants can utilise light of a lower intensity than sun plants can
    When exposed to light after being in darkness, shade plants 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
  13. 13Graph for compensation points of sun and shade plantsGraph for compensation points of sun and shade plants
  14. 14What are the main areas of a chloroplast to be aware of?- Grana
    - Thylakoids (+ their membranes)
    - Stroma
    -Intermembrane space
    - Intergranal lamellae
    - Outer membrane
    - Inner membrane
    - Circular DNA
    - Starch grains
    - Ribosomes
  15. 15Components of chloroplasts - granaThis is the inner part of chloroplasts, made of stacks of thylakoid membranes, where the LIGHT-DEPENDENT stage of photosynthesis takes place
  16. 16Components of chloroplasts - StromaThis is the fluid-filled matrix of chloroplasts, where the LIGHT-INDEPENDENT stage of photosynthesis takes place. It contains ENZYMES, STARCH GRAINS, DNA and RIBOSOMES
  17. 17Components of chloroplasts - ThylakoidsThese are flattened membrane-bound sacs (fluid-filled) found inside chloroplasts, containing photosynthetic pigments/photosystems and is the site of the LIGHT-DEPENDENT stage of photosynthesis
  18. 18Is the outer or inner membrane of chloroplasts more permeable?The outer membrane is PERMEABLE (including being permeable to H+ ions)
    The inner membrane is SELECTIVELY PERMEABLE and contains transport proteins (is impermeable to H+ ions)
  19. 19What is a starch grain?A starch grain is a STORAGE POLYSACCHARIDE
  20. 20What does the stack of thylakoid membranes provide the grana with?This provides the grana with a HIGH SURFACE AREA for:
    - The distribution of photosystems, containing photosynthetic pigments that trap light energy
    - The electron carriers and ATP synthase enzymes needed to convert that light energy into ATP
  21. 21Under light microscopes, what do the chloroplasts look like, as opposed to under electron microscopes?Under the light microscope, chloroplasts appear as BICONVEX DISCS, with little detail
    However, electron microscopes have better resolution and magnification, therefore, MORE DETAIL can be seen
  22. 22What is the diameter of chloroplasts?2 - 10 micrometres
  23. 23Do starch grains affect the water potential of chloroplasts?No, as starch grains are INSOLUBLE so don't affect the water potential
  24. 24How many membranes do chloroplasts have, so, how many compartments do they have?Chloroplasts have THREE MEMBRANES, making THREE COMPARTMENTS
    - The inner and outer chloroplast membranes form a DOUBLE MEMBRANE that surrounds the stroma, with an INTERMEMBRANE SPACE (outer membrane is highly permeable)
    - The THYLAKOID MEMBRANES - the thylakoid space is a fluid-filled sac - the membranes are LESS permeable and hold pigments (photosystems), electron carriers and enzymes
  25. 25What is a photosynthetic pigment?This is a pigment that absorbs specific wavelengths of light and traps the energy associated with light eg. chlorophylls a and b, carotene and xanthophyll
    The other wavelengths of light, that aren't absorbed by the pigment, are REFLECTED by the pigment
  26. 26What is a photosystem?This is a system of photosynthetic pigments found in thylakoids of chloroplasts
  27. 27How do the colours reflected by photosynthetic pigments correlate to the colours absorbed?The colours REFLECTED determine the colour the pigment APPEARS
    eg. if green and blue light is reflected, red and orange light is absorbed (opposites)
  28. 28Each photosynthetic pigment has a different absorption spectrum What are the 5 pigments to know?- Chlorophyll a
    - Chlorophyll b
    - Carotenoids
    - Carotene (a carotenoid)
    - Xanthophyll (a carotenoid)
  29. 29What are chlorophylls and what are their structures?Chlorophylls are a MIXTURE of pigments
    All have a similar molecular structure, consisting of a long hydrocarbon chain and a PORPHYRIN GROUP, which contains a MAGNESIUM ATOM (Mg is required as part of the chlorophyll molecule so a plant deficient in Mg would appear yellow)
    Chlorophyll is the PRIMARY PIGMENT, at the base of the funnel-shaped photosystems, in the primary pigment reaction centre
  30. 30What are the two forms of chlorophyll a?Both forms of chlorophyll a APPEAR BLUE-GREEN and both are situated at the centre of photosystems. Both absorb RED LIGHT but have different absorption peaks
    P680 is found in photosystem II (peak of absorption is light of wavelength 680nm)
    P700 is found in photosystem I (peak of absorption is light of wavelength 700nm)
    Chlorophyll a also absorbs some blue light of wavelength around 440nm
  31. 31How does chlorophyll b appear and what does it absorb?Chlorophyll b absorbs light of wavelength 400-500nm and around 640nm and it appears yellow-green
  32. 32Describe the structure of photosystems and where the photosynthetic pigments are distributedThe pigments are found within photosystems in the thylakoid membrane
    Photosystems I and II are FUNNEL-SHAPED clusters of photosynthetic pigments, held in the membrane by PROTEINS
    ENERGY associated with the wavelengths of light is funnelled down to the PRIMARY PIGMENT REACTION CENTRE (made of chlorophyll a) at the BASE (to EXCITE electrons)
    ACCESSORY PIGMENTS surround the primary pigment reaction centre and absorb different wavelengths and PASS THE ENERGY to the primary pigments
  33. 33What are the accessory pigments?- Chlorophyll b
    - Carotenoids
    - Carotene
    - Xanothophyll
  34. 34What do carotenoids and xanthophylls reflect and absorbCarotenoids absorb blue light of wavelengths 400 - 500 nm. They reflect yellow and orange light
    Xanthophylls absorb blue and green light of wavelengths 375-550nm. They reflect yellow light
  35. 35What does the light-dependent stage of photosynthesis (photophosphorylation) involve?1) Light harvesting at the photosystems
    2) Photolysis of water (forming H+ and O2)
    3) Photo-phosphorylation - production of ATP in the presence of light
    4) The formation of reduced NADP (NADPH) - a coenzyme and electron and hydrogen carrier
  36. 36What is cyclic vs non-cyclic photophosphorylation?Non-cyclic photophosphorylation involves photosystems I and II, producing ATP, O2 and reduced NADP (NADPH)
    Cyclic photophosphorylation involves photosystem I only and produced only ATP, and LESS of it
  37. 37What are the light-dependent reactions of photosynthesis also called?The Z-scheme
  38. 38Describe the process of non-cyclic photophosphorylation (up to where protons are pumped across the thylakoid space)1) When a photon of light strikes PSII, its energy is channeled to the primary pigment reaction centre
    2) The light energy excites a pair of electrons in the chlorophyll molecule
    3) The energised electrons escape from the chlorophyll molecule and are captured by an ELECTRON CARRIER, which is a protein with IRON at its centre, embedded in the thylakoid membrane
    4) These in the photosystems are replaced by electrons derived from PHOTOLYSIS
    5) When this iron ion combines with an electron, it becomes REDUCED (Fe2+) - it can then DONATE the electron, becoming REOXIDISED to Fe3+, to the next carrier in the chain
    6) As electrons are passed along a chain of electron carriers embedded in the thylakoid membrane, at each stage, some energy associated with the electrons is RELEASED
    7) This energy is used to PUMP PROTONS across the thylakoid membrane, into the thylakoid space, from the stroma
  39. 39Describe the rest of non-cyclic photophosphorylation8) Eventually, the electrons are captured by another molecule of chlorophyll a in PSI - these electrons replace those lost from PSI due to excitation by light energy
    9) A protein-iron-sulfer complex called FERREDOXIN accepts the electrons from PSI and passes them to NADP in the STROMA
    10) As protons accumulate in the thylakoid space, a PROTON GRADIENT forms across the membrane
    11) Protons diffuse down their concentration gradient, through special channels in the membrane associated with ATP synthase enzymes and, as they do, the flow of protons causes ADP and Pi to join, forming ATP
    12) As the protons pass through the channel, they're accepted, along with electrons, by NADPH, which becomes REDUCED - the reduction of NADP is catalysed by the enzyme NADP REDUCTASE
  40. 40Give the equation for the photolysis of water2H2O ==> 4H+ + 4e- + O2
  41. 41Describe the process of cyclic photophosphorylation- This only involves PSI
    - The excited electrons at PSI pass down an electron transport chain, until they get back to PSI, allowing SOME H+ to be pumped in through PROTON PUMPS, into the thylakoid space, from the stroma
    - As there is NO PHOTOLYSIS (PSII not involved), NO H+ or O2 are formed
    - A SMALL AMOUNT of ATP is formed (using the H+ diffusing through the channel associated with ATP synthase) but no NADPH as the electrons are retuned back to the chlorophyll in PSI
  42. 42What singular photosystem do chloroplasts in guard cells contain?Chloroplasts in guard cells contain ONLY PSI
    They produce ONLY ATP, which actively brings K+ ions into the cells, lowering the water potential so that water follows by osmosis, causing the guard cells to swell and open the stoma
  43. 43What does the light-independent stage of photosynthesis (the Calvin Cycle) involve?1) Fixation of CO2
    2) The building of complex carbon-based organic molecules
  44. 44Describe the two carbon fixation stages of the Calvin Cycle1) CO2 diffuses into the stomata and eventually the stroma and combines with a 5C compound called RIBULOSE BISPHOSPHATE (RuBP), catalysed by RuBisCO
    The RuBP is CARBOXYLATED, accepting COO- from CO2; the enzyme is acting as a CARBOXYLASE, rather than an OXYGENASE - the product is an UNSTABLE 6C comoound
    6RuBP (15C) + 6CO2 (3C) ==> 6 x unstable 6C compounds
    2) The unstable 6C compound breaks down immediately into 2x 3C compounds called GP (glycerate-3-phosphate) So, 6 unstable 6C compounds will break down into 12 GP
  45. 45Describe the reduction and regeneration stages of the Calvin Cycle3) REDUCTION = GP is REDUCED using H+ from NADPH and energy from ATP (from the light-dependent stage) to make TP (triose phosphate)
    2ATP and 2NADPH are used for EVERY CO2 molecule inputted into the Calvin Cycle
    12GP (3C) ==> 12TP (3C)
    So, 12 ATP and 12 NADPH are needed per formation of one glucose molecule
    4) REGENERATION = 10 of the 12 triose phosphate molecules are rearranged to regenerate 6 RuBP (5C) - this requires Pi from ATP!! (5 ATP needed - 1 needed per 2 triose phosphates)
    The other two are used to make 1 glucose molecule
  46. 46How many times does the Calvin Cycle run per molecule of glucose formed?As glucose is a 6C compound, to make one glucose molecule, the cycle must run 6 TIMES!
  47. 47The Calvin Cycle as a diagramThe Calvin Cycle as a diagram
  48. 48What are the uses of the triose phosphates produced in the Calvin Cycle that aren't used to regenerate RuBP?- Some TP is used to make amino acids, fatty acids and glycerol
    - Some TP (to glucose first, then...) is converted to SUCROSE (for transport), STARCH (storage) or CELLULOSE (structural)
  49. 49Give some reasons as to why the Calvin Cycle only runs in daylight?- ATP and NADPH are needed for the Calvin Cycle
    - During the light-dependent stage, H+ ions were pumped into the thylakoid space to make ATP and NADPH, increasing the pH in the stroma to around 8, which is the optimum pH of RuBisCO in the Calvin cycle
    - Extra ATP in the stroma, produced in the light-dependent reactions, activates RuBisCO
    - Also, during daylight, Mg2+ increases in the stroma, which attaches to the active sites of RuBisCO and acts as COFACTORS
    - Reduced ferredoxin from PSI also activates Calvin Cycle enzymes
  50. 50What practical method can be used to separate photosynthetic pigmentsTLC - thin layer chromatography
  51. 51What happens to the oxygen produced in photolysis?- It can be used by the plant during respiration
    - It can diffuse out of the plant as a waste gas, through the stomata
  52. 52What are the 4 main limiting factors of photosynthesis?- Light energy (could be insufficient energy transferred to the glucose)
    - CO2 concentration (insufficient reactant concentration)
    - H2O concentration (insufficient reactant concentration)
    - Temperature (affects the optimum activity of enzymes)
  53. 53What is a limiting factor?The limiting factor for a metabolic process is the factor that is present at the lowest or least favourable value eg. light intensity, CO2 concentration, temperature or water stress
  54. 54A graph to show the affect of light intensity on the RATE of photosynthesisA graph to show the affect of light intensity on the RATE of photosynthesis
  55. 55How does light intensity affect the rate of photosynthesis?Light intensity affects:
    - The light-dependent stage for ATP and NADPH production
    - Stomatal opening during daylight - increasing transpiration and water uptake and delivery to leaves as well as increased gas exchange (more CO2) when higher light intensity
    At a certain point, even when light intensity increases, the rate of photosynthesis does not increase - now, a factor other than light intensity is limiting the process
  56. 56A graph to show the affect of light intensity on the relative concentrations of RuBP, TP and GPA graph to show the affect of light intensity on the relative concentrations of RuBP, TP and GP
  57. 57Explain the graphIn BRIGHT LIGHT = more electrons excited, more photophosphorylation, more ATP and NADPH, more GP is reduced TP, more RuBP is regenerated from TP
    In DIM LIGHT = no light-dependent reactions, no conversion of GP to TP as no ATP or NADPH, conc. of GP rises and conc. of TP and RuBP falls, fixation of CO2 eventually ceases (as levels of RuBP fall and this is required for CO2 fixation)
  58. 58Why are CO2 levels not usually a limiting factor? What could increase/decrease CO2 levels?CO2 levels and water availability are usually NOT limiting factors (as, they're readily available)
    However, BURNERS could INCREASE CO2 levels (through combustion), which would directly increase photosynthesis
    Also, photosynthesis could be decreased due to a DECREASE in CO2 levels, due to STOMATAL CLOSURE to conserve water (at high temperatures and low humidity)
    So, if water is scarce, this will affect CO2 levels too
  59. 59A graph to show the effect of changing the level of CO2 concentration on relative concentrations of GP, TP and RuBPA graph to show the effect of changing the level of CO2 concentration on relative concentrations of GP, TP and RuBP
  60. 60Explain the graphWhen there is a lower concentration of CO2, there is LESS ACCEPTANCE of CO2 by RuBP so RuBP accumulates
    Consequently, LESS GP can form and, therefore, less TP as less GP is present to reduce to TP
  61. 61A graph to show the affect of temperature on the RATE of photosynthesisA graph to show the affect of temperature on the RATE of photosynthesis
  62. 62Explain the shape of the graphLow temperatures affect the SPEED of enzyme action (RuBisCO)
    Optimum temperature = 25-30 degrees celsius
    High temperatures (>45 degrees) causes the enzymes to DENATURE, which reduces GP and TP concentration and eventually, RuBP, as it would not regenerate
  63. 63What phenomenon happens at temperatures greater than 30 degrees celsius?PHOTORESPIRATION!
    This happens due to stomatal closure, to reduce water loss, reducing CO2 levels
    Less GP and TP are formed as RuBisCO is 'sharing' its activity between photosynthesis and respiration
    At this temperature, RuBisCO is NOT denatured to reduce activity
  64. 64Describe what happens during photorespirationThis occurs when CO2 levels are VERY LOW (stomata have usually closed to cause this, to reduce water loss)
    So, plants STOP photosynthesising as CO2 levels fall and O2 levels INCREASE
    - O2 COMPETITIVELY INHIBITS RuBisCO and stops it catalysing the production of GP
    - RuBisCO then catalyses the production of PHOSPHOGLYCOLATE (it acts as an oxygenase), which feeds into RESPIRATION
    - This REDUCES the efficiency of RuBisCO in photosynthesis
    - The products of photorespiration are CO2 and water, but NO ATP
    - Photorespiration initially causes an accumulation of RuBP as GP and TP cannot form, but, due to a lack of TP, RuBP cannot be regenerated
  65. 65In school labs, how is the rate of photosynthesis usually measured and what are the 2 limitations of this method?By measuring the volume of oxygen produced per minute by an aquatic plant
    Limitations
    - Volume of oxygen collected may not be directly proportional with rate of photosynthesis as some oxygen produced by the plant will be used in respiration
    - There may be some dissolved nitrogen in the gas collected
  66. 66What can be used to measure the effects of light intensity, temperature or CO2 availability on the rate of photosynthesis?A photosynthomer (look in textbook page 126 for more details)
    Volume of gas collected = length of bubble x (pi x r squared)

Information

Description
A level Biology Flashcards on Photosynthesis Flashcards, created by Rhea Sekhon on 28/05/2022.
Created by
Rhea Sekhon
Views
0
Rating

Feedback

What is it about?

What do you think of the new look?

How do you like it?