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Biology A level > (11) Photosynthesis > Flashcards

(11) Photosynthesis Flashcards

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1
Q

overall equation of photosynthesis

A

6CO2 + 6H2O (+ energy) = C6H12O6 + 6O2

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2
Q

how is energy released after photosynthesis

A

plants store the energy in glucose until it is released during respiration

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3
Q

define metabolic pathway

A

a series of small reactions controlled by enzymes eg respiration and photosynthesis

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4
Q

define photophosphorylation

A

adding phosphate to a molecule using light

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5
Q

define photolysis

A

splitting of a molecule using light energy

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6
Q

define photoionisation

A

when light energy excites electrons in an atom or molecule giving them more energy and causing them to be released so the atom or molecule becomes a positive ion

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7
Q

define hydrolysis

A

the splitting of a molecule using water

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8
Q

define decarboxylation

A

the removal of carbon dioxide from a molecule

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9
Q

define dehydrogenation

A

removal of hydrogen from a molecule

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10
Q

what is a coenzyme and what is the coenzyme in photosynthesis

A

coenzyme is a molecule that aids the function of an enzyme by transferring a chemical group from one molecule to another
eg in photosynthesis NADP transfers hydrogen from one molecule to another

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11
Q

what are chloroplasts

A

flattened organelles surrounded by a double membrane found in plant cells

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12
Q

what are thylakoids

A

fluid filled sacs stacked up in the chloroplast into grana structures. grana are linked together by thylakoid membrane called lamellae

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13
Q

what are the differences between photosystem 1 and 2

A

PS1 absorbs light best at a wavelength of 700nm and PS2 absorbs light best at 680 nm

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14
Q

what is the stroma

A

gel like substance that surrounds the thylakoids within the inner membrane of the chloroplast
contains enzymes, sugars and organic acid

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15
Q

how do plants store carbohydrates

A

stored as starch grains in the stroma

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16
Q

outline briefly the steps of the light dependant reaction

A

takes place in the thylakoid membrane

  1. light is absorbed by chlorophyll in the photosystems. light energy excites electrons in chlorophyll leading to their eventual release from the molecule (chlorophyll has been photoionised)
  2. some of the energy released from the electrons is used to add a phosphate group to ADP to form ATP
  3. some energy is also used to reduce NADP to NADPH and this then transfers hydrogen to the light independent reaction.
  4. in this process H2O is also oxidised to O2
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17
Q

outline the light independent reaction / calvin cycle

A
  1. doesn’t use light directly but relies on the products of the light dependent reaction
  2. takes place in the stroma of the chloroplast
  3. ATP and NADPH from light dependent reaction supply the energy and hydrogen to make simple sugars from CO2
  4. makes triose phosphate from CO2 and ribulose biphosphate which can be used to make glucose and organic substances
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18
Q

what is the energy from the photoionisation of chlorophyll in the light dependent reaction used for

A
  1. making ATP from ADP and inorganic phosphate (photophosphorylation)
  2. making reduced NADP from NADP
  3. splitting water into protons (H+), electrons and oxygen (photolysis)
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19
Q

what is an electron transport chain

A

made up of photosystems and electron carriers to form a chain of protons through which excited electrons flow

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20
Q

what is chemiosmosis

A

the process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis

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21
Q

what does non cyclic photophosphorylation produce

A

ATP, reduced NADP and O2

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22
Q

what are the 4 stages of non cyclic photophosphorylation

A
  1. light energy excites electrons in chlorophyll- they are released and move down electron transport chain to PS1
  2. photolysis of water produces H+, electrons and O2 in order to replace the lost electrons from chlorophyll
  3. ATP is produced- excited electrons lose energy as they move down the electron transport chain, protons transport into thylakoid forming proton gradient so protons move into stroma. energy from this movement combines ADP and Pi to make ATP
  4. light energy absorbed by PS1 which excites eelctrons to even higher level so electrons are transferred to NADP to form NADPH
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23
Q

what is cyclic photophosphorylation

A

only produces ATP
only uses PS1- electrons from chlorophyll aren’t passed onto NADP but are passed back to PS1 by electron carriers so no NADPH or O2 is produced, only ATP

24
Q

outline stage 1 of the light independent reaction/ calvin cycle

A

CO2 enters leaf via stomata and diffuses into the stroma, combines with RuBP (catalysed by rubisco) this forms an unstable 6 carbon compound which quickly breaks down into 2 molecules of glycerate 3 phosphate

25
Q

outline stage 2 of the light independent reaction

A

hydrolysis of ATP provides energy to turn 3 carbon GP into 3 carbon TP (triose phosphate) also requires H+ ions which come from NADPH
some triose phosphate is then converted into organic compounds to regenerate RuBP

26
Q

outline stage 3 of the independent reaction

A

RuBP is regenerated
- 5/6 molecules of TP produced aren’t used to make hexose sugars but to regenerate RuBP and regenerating RuBP uses the rest of the ATP produced by the light dependent reaction

27
Q

how are carbohydrates made

A

hexose sugars eg glucose are made by joining 2 triose phosphate molecules together and larger carbohydrates are made by joining hexose sugars together in different ways

28
Q

how are lipids made

A

using glycerol (synthesised from triose phosphate) and fatty acids (synthesised from glycerate 3 phosphate)

29
Q

how are some amino acids made

A

some (not all) are made from glycerate 3 phosphate

30
Q

why does the calvin cycle need to turn 6 times to make 1 hexose sugar

A
  1. 3 turns of the cycle produces 6 molecules of TP because 2 TP are made for every 1 CO2 used
  2. 5/6 of these TP molecules are used to regenerate RuBP
  3. so for 3 turns only one TP is produced thats used to make a hexose sugar
  4. and 2 TP are needed to form 1 hexose
  5. 6 turns need 18 ATP and 12 NADPH from the light dependent reaction
31
Q

what are the optimum conditions for photosynthesis

A
  1. high light intensity of a certain wavelenght- higher intensity = more energy
    chlorophyll a, b and carotene only absorb red and blue light in sunlight and reflect green
  2. temp around 25c- optimum enzyme activity (rubisco and ATP synthase) too high temp causes stomata to close
  3. CO2 at 0.4%- higher rate of photosynthesis but any higher causes stomata to close
  4. constant supply of water
32
Q

what is the saturation point

A

the point where a factor is no longer limiting a reaction and something else has become the limiting factor

33
Q

how do farmers overcome limiting factors

A

CO2 conc- CO2 is added to the air by burning a small amount of propane in a CO2 generator
Light- glasshouse/ lamps at night
temperature- glasshouses trap heat from sunlight, heaters, coolers, air circulation systems

34
Q

what is the difference between the stationary and mobile phase

A

mobile- liquid solvent

stationary- glass plate with thin layer of gel (silica) on top

35
Q

what is a photosystem

A

photosynthetic pigments attached to proteins within thylakoid membrane

36
Q

what 3 reactions use the energy from the photoionisation of chlorophyll

A

photophosphorylation- making ATP from ADP and Pi
reduction- making NADPH from NADP
photolysis- splitting H2O into H+, e- and O2

37
Q

what does non cyclic photophosphorylation produce

A

NADP and ATP

38
Q

what does cyclic photophosphorylation involve

A

PS1
when PS1 absorbs light energy, the electrons in the chlorophyll are absorbed and move to a higher energy level (photoionisation)
electrons then coninuously cycle from PS1 to electron carriers and back

39
Q

what are the differences between cyclic and non cyclic photophosphorylation

A

cyclic: ATP produces, no NADPH produced, electrons are continuously recycled, photolysis doesn’t take place

non cyclic: ATP and NADPH produced
eelctrons in PS2 are replaced by photolysis

40
Q

what does the light independent reaction (calvin cycle) use and produce

A

uses ATP, reduced NADP, CO2 and RuBP to produce triose phosphates

41
Q

what is carbon fixation

A

the combination of CO2 to RuBP after CO2 diffuses into the leaf through stomata, combines with RuBP catalysed by rubisco to produce an unstable 6 carbon compound that then splits into 2 molecules of glycerate 3 phosphate

42
Q

what happens in the reduction of GP

A

GP is reduced to TP (driven by the energy from 2 molecules of ATP and protons from NADP that are made in the LDR and recycled)

43
Q

what happens to the molecules of TP after they are produced

A

1/6 are converted into hexose sugars but most continue in the calvin cycle and are used to regenerate RuBP (driven by one molecule of ATP that is then recycled)

44
Q

what are the hexose sugars produced in the calvin cycle used for

A

(produced from 2 molecules of TP) glucose is a hexose sugar. many hexose sugars can be joined together to form larger carbohydrates eg starch and cellulose

45
Q

how are lipids made from the light independent reaction (calvin cycle)

A

both components of lipids (glycerol and fatty acids) are synthesised from products of the calvin cycle:
TP is used to synthesise glycerol and fatty acids are formed from GP

46
Q

how are amino acids linked to the calvin cycle

A

GP is used in the synthesis of some amino acids

47
Q

at what temperature does the rate of photosynthesis start to fall

A

45c

48
Q

in what way does temperature affect photosynthesis

A

at low temp enzymes (rubisco) has less kinetic energy and so less likely to successfully collide with the substrate so fewer enzyme substrates are formed
above optimum temp enzymes start to denature so rate falls

49
Q

in what way does light intensity affect photosynthesis

A

higher light intensity = faster rate, more energy
in low light, LDR can’t take place so levels of ATP and NADPH start to fall these are necessary to convert GP to TP and regenerate RuBP so calvin cycle can’t take place and rate falls

50
Q

how does CO2 conc affect photosynthesis

A

high CO2 = more carbon available for carbon fixation in calvin cycle so more GP and TP are produced and more RuBP regenerated but very high CO2 conc can cause stomata to open too wide causing water loss so stomata close again and rate falls

51
Q

how does chlorophyll concentration affect photosynthesis

A

more chlorophyll means light can be absorbed at a faster rate so rate of LDR increases

52
Q

how many ATP are used to produce one molecule of glucose

A

18

53
Q

what is the purpose of a control experiment

A

to validate your results by proving that the change you are observing is not due to other factors

54
Q

describe how the synthesis and breakdown of ATP meets the energy needs of the cell (6 marks)

A

ATP is synthesised from ADP + Pi using energy from an energy releasing reaction eg respiration
The energy is stored as chemical energy in the phosphate bond (catalysed by ATP synthase)
ATP then diffuses to the part of the cell that needs the energy where it is broken down into ADP and Pi (catalysed by ATP hydrolase). Chemical energy is then released from the phosphate bond and used by the cell

55
Q

why is the increase in dry mass of a plant less than the mass of hexose produced over the same period

A

some parts of the plant are eaten/ decompose

some CO2 produced is lost to the air

some hexose produced is lost in respiration

Biology A level (20 decks)

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