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A-Level Biology A2 > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

What is energy needed for?

A

Biological processes

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2
Q

Why do plants need energy?

A

For things like photosynthesis, active transport, DNA replication, cell division and protein synthesis.

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3
Q

Why do animals need energy?

A

For muscle contraction, maintenance of body temperature, active transport, DNA replication, cell division and protein synthesis.

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4
Q

What is photosynthesis?

A

The process where energy from light is used to make glucose from H2O and CO2 (the light energy is converted to chemical energy in the form of glucose).

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5
Q

How does photosynthesis produce the oxygen we breathe?

A

By releasing it from water molecules

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6
Q

What does life depend on?

A

The continuous transfer of energy

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7
Q

In the plant, what is the energy in light absorbed by?

A

the chlorophyll

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8
Q

What do non-photosynthetic organisms feed on?

A

Molecules produced by plants and use them to make ATP during respiration.

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9
Q

What is ATP?

A

Adenosine triphosphate.

It’s the immediate source of energy in a cell.

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10
Q

Give the specific properties of ATP that make it a good energy source

A
  • Stores and releases only small amount of energy at a time so no energy wasted as heat.
  • Small and soluble so easily transported.
  • Easily broken down.
  • Quickly re-made
  • Make other molecules more reactive by transferring one of the Pi groups.
  • Can’t pass out of cell so always provides cell with immediate supply of energy.
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11
Q

Why is the energy released from glucose used to make ATP?

A
  • A cell can’t get its energy directly from glucose.
  • ATP carries energy around the cell to where it’s needed.
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12
Q

What is ATP synthesised with?

A

A condensation reaction between ADP and Pi using energy from an energy-releasing reaction.

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13
Q

What is the energy stored as?

A

Chemical energy in the phosphate bond.

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14
Q

What enzyme catalyses the reaction of ATP into ADP + Pi

A

ATP snythase

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15
Q

What happens once the ATP diffuses to the part of the cell that’s needed?

A

It’s hydrolysed back into ADP and Pi.

Chemical energy is released from the phosphate bond and used by the cell.

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16
Q

What enzyme catalyses the reaction of ADP + Pi into ATP?

A

ATP hydrolase

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17
Q

Where does photosynthesis store energy?

A

In glucose

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18
Q

What is the overall equation for photosynthesis?

A

6CO2 + 6H2O + Energy -> C6H12O6 (glucose) + 6O2

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19
Q

How do cells release energy from glucose?

A

By respiration:

  • Aerobic respiration - respiration using oxygen
  • Anaerobic respiration - respiration without oxygen
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20
Q

What is the equation for aerobic respiration?

A

C6H12O6 (glucose) + 6O2 -> 6CO2 + 6H2O + Energy

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21
Q

What does anaerobic respiration produce?

A

in plants = ethanol and carbon dioxide

releases energy

in humans = lactate

releases energy

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22
Q

Definition of metabolic pathway

A

A series of small reactions controlled by enzymes

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23
Q

Definition of phosphorylation

A

Adding phosphate to a molecule

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24
Q

Definition of photophosphorylation

A

adding phosphate to a molecule using light

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25
Q

Definition of photolysis

A

The splitting (lysis) of a molecule using light (photo) energy

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26
Q

Definition of photoionisation

A

When light excites electrons in an atom or molecule, giving them more energy and causing them to be released.

The release of electrons causes the atom or molecule to become a positively charged ion.

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27
Q

Definition of hydrolysis

A

The splitting of a molecule using water

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28
Q

Definition of decarboxylation

A

The removal of carbon dioxide from a molecule

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29
Q

Definition of dehydrogenation

A

The removal of hydrogen from a molecule

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30
Q

Definition of redox reactions

A

Reactions that involve oxidation and reduction

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31
Q

Definition of a co enzyme

A

A molecule that aids the function of an enzyme.

They work by transferring a chemical group from one molecule to another.

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32
Q

What is the co enzyme used in photosynthesis

A

NADP (transfers hydrogen from one molecule to another).

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33
Q

What is the co enzyme used in respiration

A

NAD

FAD

coenzyme A (transfers acetate)

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34
Q

describe the structure of chloroplasts

A

flattened organelles surrounded by a double membrane.

thylakoids stacked up to form grana which linked by lamellae.

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35
Q

what do chloroplasts contain?

A

photosynthetic pigments; chloropyll a and b and carotene.

they are coloured substances that absorb light energy for photosynthesis.

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36
Q

where are photosynthetic pigments found?

A

the pigments are found in the thylakoid membranes - they are attached to proteins.

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37
Q

photosystem meaning

A

protein and pigment

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38
Q

what are the two photosystems used by plants to capture light energy and the wavelenghts?

A
  • photosystem I (PSI) absorbs light best at a wavelength of 700nm.
  • photosystem II (PSII) absorbs light best at 680nm.
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39
Q

photosystem I wavelength

A

700nm

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40
Q

photosystem II wavelength

A

680nm

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41
Q

what is the stroma

A

it surrounds thylakoids and contains enzymes, sugars and organic acids.

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42
Q

what are the three main stages of photosynthesis?

A
  1. capturing of light energy by chloroplasts pigments such as chlorophyll.
  2. the light dependent reaction which same of the light energy absorbed is conserved in chemical bonds.
  3. the light independent reaction - protons (hydrogen ions) used to produce sugars and other organic molecules.
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43
Q

what effect does photolysis have on the concentration of inside the thylakoid space?

A

photolysis of water produces protons which increases their concentration inside.

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44
Q

how do H+ pass across the Thy. Mem.

A

through ATP synthase channel proteins which causes a change in the structure of enzymes which catalyses combination of ADP with Pi -> ATP

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45
Q

what does the light DEPENDENT reaction involve?

A

capturing light by chlorophyll in photosynthesis.

  1. adds inorganic phosphate molecule to ADP -> ATP (photophosphorylation)
  2. light splits water into H+ ions and OH- ions (photolysis)
  3. some used to reduce NADP to form NADPH
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46
Q

where does the light DEPENDENT reaction take place in?

A

the thylakoid membranes of chloroplasts.

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47
Q

what are the two types of photophosphorylation?

A

non cyclic

cyclic

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48
Q

explain process of gaining an oxygen but losing a hydrogen

A

oxidation

loses electron

energy given out

49
Q

explain process of losing an oxygen but gaining a hydrogen

A

reduction

electron gained

energy taken in

50
Q

what are the products of non-cyclic photophosphorylation?

A

produces ATP, reduced NADP and oxygen

51
Q

what are electron carriers

A

proteins that transfer electrons

they form an electron transport chain with photosystems

52
Q

explain non cyclic photophosphorylation

A
  1. PSII absorb light energy, exciting the electrons in the chlorophyll.
  2. Them electrons move to a higher energy level.
  3. The high energy electrons are then released from the chlorophyll and move down the electron transport chain to PSI.
  4. the excited electrons must be replaced so the light energy splits water into H+ ions, electrons and O2 = photolysis.

H2O -> 2H+ + 1/2O2

  1. as the excited electrons move down the electron transport chain, they lose energy.
  2. that energy lost is used to transport protons into the thylakoid membrane, so has a higher concentration of protons than the stroma.
  3. A proton gradient is formed across T. mem and protons move down the conc. gradient into the stroma via. the enzyme ATP synthase which is embedded in the T. mem.
  4. energy combines to form ATP.
  5. PSI absorbs light energy nd excites electrons to higher energy level.
  6. electrons transferred to NADP along with the proton from stroma to form NADPH.
53
Q

How is ATP made in photophosphorylation?

A
  1. Energy absorbed used to excite electrons within the chlorophyll.
  2. electrons leave chlorophyll - photoionisation.
  3. electron carrier accepts electrons.
  4. electrons passed along electron carries in a series of oxidation reduction reactions.
  5. electrons lose energy at each stage end = ATP
54
Q

How does the NADP become reduced?

A

takes up protons and electrons

55
Q

what is light energy needed for?

A
  1. adding Pi to ADP to make ATP.
  2. split water into H+ ions and OH- ions.
56
Q

define chemiosmosis

A

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

57
Q

what does cyclic photophosphorylation produce?

A

only produces ATP

58
Q

what photosystem cyclic photophosphorylation use?

A

PSI

59
Q

why is cyclic photophosphorylation called “cyclic”

A

the electron from chlorophyll molecules aren’t passed onto NADP, but are passed back to PSI via. electron carriers.

the electrons are recycled and repeatedly flow through PSI.

60
Q

whats the point of photolysis?

A

when light hits chlorophyll it loses electrons

electrons need to be replaced to continue light absorption

photolysis replaces electrons.

61
Q

describe the role of the electron transport chain in the light dependent reactions of photosynthesis (6 marks)

A
  1. electron chain accepts excited electrons.
  2. from chlorophyll/ photosystem
  3. electron loses energy down the chain
  4. ATP produced from ADP + Pi.
  5. NADPH formed when electrons and hydrogens combine with NADP.
  6. The H+ is from photolysis.
62
Q

Where does the light INDEPENDENT reaction take place?

A

in the stroma of chloroplasts

63
Q

Describe the way in which ATP and reduced NADP are produced in the light-dependent reaction of photosynthesis.

A
  1. light raises energy level of / excites electrons;
  2. pass through carriers;
  3. energy released;
  4. ATP formed from ADP + P;
  5. producing reduced NADP
  6. protons / H+ ions;
  7. from photolysis / water; electrons;
64
Q

Explain how ATP and reduced NADP are used in the light-independent reaction of photosynthesis.

A
  1. GP converted to triose phosphate / GALP;
  2. this involves reduction;
  3. reduced NADP provides reducing power / hydrogens; ATP supplies energy for this reaction;
  4. phosphate from ATP;
  5. for production of RuBP
65
Q

what can triose phosphate be used to make?

A

Glucose and other useful organic substances.

66
Q

what two things are required in a light independent reaction?

A

ATP

H+ ions

67
Q

how is Ribulose bisphosphate regenerated?

A

the reactions are linked in a cycle

68
Q

why can the calvin cycle be known as CO2 fixation?

A

the carbon in CO2 is fixed into an organic molecule.

69
Q

What products from the light DEPENDENT stage are used to reduce Glycerate 3- phosphate in the second stage of photosynthesis; the light INDEPENDENT reaction

A
  1. ATP and NADPH

doesnt require light directly.

70
Q

what happens in stage one of the calvin cycle; light independent

A
  1. CO2 enters the leaf through the stomata and into the stroma of the chloroplast.
  2. combined with RuBP, a 5 carbon molecule. The enzyme rubisco catalyses this reaction.
  3. That gives an unstable 6 carbon compound which breaks down into two molecules of GP (glycerate 3-phosphate) (3C).
71
Q

what happens in stage two of the calvin cycle; light independent

A
  1. Hydroylsis of ATP from the light dependent reaction provides energy to turn (3C) GP into TP (3C).
  2. This requires H+ ions from NADPH from the light dependent reaction.
  3. NADPH is recycled into NADP which goes back to the LD. R. to be reduced again, accepting H+.
  4. Some TP is converted into useful organic substances and some continues in the calvin cycle to regenerate RuBP.
72
Q

what happens in stage three of the calvin cycle; light independent

A
  1. 5/6 molecules of every six molecules of TP produced aren’t used to make hexose sugars, but to regenerate RuBP.
  2. RuBP is regenerated and uses the rest of the ATP produced by the light dependent reaction.
73
Q

How many turns does the calvin cylce need to have to produce a hexose sugar?

A

6 turns

74
Q

why does the calvin cylce need to turn 6 times to make one hexose sugar?

A
  1. three turns of the cycle produces six molecules of triose phosphate, because two molecules of TP are made for every one CO2 used.
  2. 5/6 of those TP molecules are used to regenerate RuBP.
  3. This means that for three turns of the cycle only one TP is produced that’s used to make a hexose.
  4. A hexose sugar has six carbons so two TP molecules needed to form one hexose sugar.
  5. So must turn 6 times to produce two molecules of TP.
  6. Six turns means it needs 18 ATP and 12 NADPH from the light dependent reaction.
75
Q

what are limiting factors in photosynthesis?

A
  1. High light intensity of a certain wavelength - light needed to provid energy for light - dependent reaction. The higher the intensity of light, the more energy it provides. Only certain wavelength of light are used for photosynthesis.

The photosynthetic pigments chlorophyll a and b and carotene only absorb blue and red. green lights reflected.

  1. Temperature around 25oC - photos involves enzymes so if the temperature falls below 10 then they are inactive.

if the enzymes are more than 45oC they may start to denature.

high temp, stomata closes = less water loss, so photosynthesis slows down as less CO2 enters leaf when stomata closes.

  1. CO2 at 0.4% - CO2 makes up 0.04% of gases in the atm. increasing it to 0.4% gives a higher photosynth. rate but any higher and stomata closes.
  2. Constant supply of water - too little, photo stops, too much and soil is waterlogged (reducing uptake of minerals such as Mg which is needed to make chlorophyll a).
76
Q

why do plants look green

A

The photosynthetic pigments chlorophyll a and b and carotene only absorb blue and red. green lights reflected.

77
Q

What factors can limit photosynthesis?

A

light intensity

temperature

carbon dioxide concentrations

78
Q

what is the limiting factor and a warm, sunny, windless day?

A

carbon dioxide

79
Q

what is the saturation point?

A

when increasing a limiting factor has no effect and levels off due to something else being a limiting factor.

that factor is no longer limiting the reaction

80
Q

how do growers incease the plant growth?

A

they know about the limiting factors so create optimum conditions in the glasshouse.

light intensity - light thru glass during day, lamps provided at night.

temperature - glasshouse tramps heat which warms the air, heaters and cooling systems used to keep constant optimum temp, and air circulation systems make sure the temp is even throughout the glasshouse.

carbon dioxide - added to the air by burning a small amount of propane in a CO2 generator.

81
Q

what do the plants use carbon dioxide for?

A

making glucose by photosynthesis.

82
Q

why is it good when they have a high concentration of CO2 provided to the plant?

A

the more CO2 the more glucose that can be made during photosyn. so the more they cn respire and make more ATP for DNA replication, cell division and protein synthesis.

83
Q

How can you investigate the pigments in the leaves?

A

using thin layer chromatography (TLC)

because all plants have different photosynthetic pigments in their leaves

and each one has a different wavelength of light,

so having more than one pigment type increases the range of wavelengths of light that a plant can absorb.

84
Q

what do different species of plants contain

A

different proportions and mixtures of pigments.

85
Q

what does TLC involve?

A

a mobile phase

a stationary phase

86
Q

what is a mobile stage

A

where molecules can move in the TLC, this is a liquid solvent.

87
Q

what is a stationary phase?

A

where molecules can’t move, in TLC this involves a solid plate with a thin layer of gel on top.

88
Q

explain the set up of TLC

A

a small sample of pigments can be extracted from the plant and put on a TLC plate.

when the plate is placed vertically in the solvent, the solvent moves upwards through the gel, carrying the dissolved pigments with it.

some pigments will travel faster or further through the gel than others which separates them out.

89
Q

how would you calculate the Rf value?

A

the distance a substance has moved through the gel in relation to the solvent.

90
Q

how can TLC be used to compare the pigments in different plants?

A
  1. grind up several leaves from the shade-tolerant plant you’re investigating with some anhydrous sodium sulfate and then add a few drops of propanone.
  2. transfer the liquid to a test tube and add some petroleum ether and gently shake. Two distinct layers will form in the liquid - the top layer is the pigments mixed in with the petrolum ether.
  3. transfer some of the liquid from the top layer into a second test tube with some anhydrous sodium sulfate.
  4. draw a horizontal pencil line near the bottom of the TLC plate. build up a concentrated spot of the liquid, making sure each time you drop it it is dry.
  5. once point of origin completely dry, place plate into small glass container with some prepared solvent but just enough so its slightly below point.
  6. put lid on container and leave to develop.
  7. diff pigments move at diff rates as solvent spreads.
  8. when solvent nearly reached the top, take the plate out, and mark the solvent front with a pencil and leave the plate to dry in a well ventilated place.
  9. calculate Rf values by measuring distance travelled by spot (from pencil line to pigment)/ distance travelled by solvent (from pencil line to solvent front)
91
Q

what can you investigate in the chloroplast

A

the activity of dehydrogenase

92
Q

how can you measure the activity of the dehydrogenase enzyme?

A

by adding a redox indicator dye

93
Q

why do you see a colour change when investigating activity of dehydrogenase

A

the dye acts as an electron acceptor and gets reduced by the dehydrogenase.

94
Q

how can you measure the rate of the dehydrogenase activity?

A

measuring the rate at which DCPIP loses its blue colour.

use a colorimeter

95
Q

what does a colorimeter measure?

A

how much light a solution absorbs when a light source is shone directly through it.

a coloured solution absorbs more light than a colourless solution.

96
Q

write the steps for investigating the effect of light intensity on dehydrogenase activity in the extracts of chloroplasts

A
  1. cut a few leaves into pieces and remove any tough stalks.
  2. use a pestle and mortar, grind up the leaf pieces with some chilled isolation solution. filter the liquid you make into a beaker through a funnel lined with muslin cloth.
  3. transfer the liquid to centrifuge tubes and centrifuge at high speeds for 10 mins. This will make the chloroplasts gather at the bottom of each tube in a pellet.
  4. get rid of the liquid from the top of the tubes leaving pellet.
  5. resuspent pellet in fresh chilled isolation solution. thats the chloroplast extract. store it on ice.
  6. set up colorimeter with red filter and zero it using cuvette containing chloroplast extract and distilled water.
  7. set up test tube rack at set distance from a bench lamp and switch it on.
  8. put a test tube in the rack add a set volume of chloroplast extract to the tube and a set volume of DCPIP. mix the contents of the tube together.
  9. immediately take sample of mixture from the tube and add it to clean cuvette. then place in colorimeter and record the absorbance. do this every 2 mins for 10 mins.
  10. repeat 7 to 9 for each distance.
97
Q

if there is dehydrogenase activity taking place what happens?

A

the absorbance would decrease as the DCPIP gets reduced and loses its blue colour.

the faster the absorbance decrease, the faster the rate of activity.

98
Q

Using the information in the passage, describe how the structure of a chloroplast is adapted to its function in photosynthesis.

A
  1. Membranes / (disc) shape provides large surface for light absorption;
  2. layering of membrane allows a lot of pigment;
  3. (permeable) membrane allows diffusion of gases / carbon dioxide;
  4. membranes provide surface for attachment of electron / hydrogen acceptors;
  5. stroma / matrix containing enzymes for Calvin cycle / light–independent reactions;
99
Q

Explain why the amount of GP increases after a photosynthesising plant has been in darkness for a short time.

A
  1. GP (accumulates as) cannot be converted to triose phosphate;
  2. since this requires ATP / reduced NADP /products of light-dependent reaction;
100
Q

Describe the role of water in the light-dependent reaction of photosynthesis.

A
  1. Provides protons / hydrogen ions / H+;
  2. for reduction of NADP;

OR

  1. provides electrons;
  2. which replace those lost from chlorophyll / photosystem (I or II);
101
Q

Describe how plants absorb light energy from the sun and use this energy to produce useful substances in the light-dependent stage of photosynthesis. (5)

A
  1. Light absorbed by/strikes,chlorophyll/photosystem/PSI/PSII; electrons excited;
  2. pass down chain of carriers;
  3. energy released/transferred;
  4. producing ATP from ADP and phosphate;
  5. reduced NADP/formed with electrons;
  6. photolysis of water /allow light splits water;
  7. (water) supplies protons/H+ ions to reduce NADP;
102
Q

Describe how the products of the light-dependent stage of photosynthesis are used in the Calvin cycle and how carbohydrate is synthesised as a result of the cycle. (6)

A
  1. RuBP converted to GP;
  2. RuBP as carbon dioxide acceptor/combines with carbon dioxide;
  3. GP converted to triose phosphate/TP/GALP;
  4. this reaction is a reduction;
  5. reduced NADP provides hydrogen;
  6. ATP provides energy;
  7. some triose phosphate/TP/GALP converted to glucose/carbohydrate;
  8. some triose phosphate used to produce RuBP
  9. ATP supplies phosphate for this reaction;
103
Q

Describe the similarities between photosynthesis and respiration. (6)

A
  1. Transfer of energy/conversion of energy from one form to another;
  2. Use and produce ATP;
  3. chain of electron carriers;
  4. located on membranes;
  5. detail of process (eg ref to chemiosmotic theory);
  6. involve cycle of reactions;
  7. oxidation and reduction/redox reactions involved;
  8. and coenzymes;
  9. processes are controlled by enzymes;

some common intermediates/GALP is common to both;

104
Q

The weedkiller DCMU blocks the flow of electrons along the chains of electron carriers. Describe and explain the effect this will have on the production of triose phosphate in the light-independent reaction. (3)

A
  1. Fall in production of triose phosphate/no more triose phosphate produced;
  2. triose phosphate production requires ATP/reduced NADP;
  3. produced during passage of electrons along electron transport chain;
105
Q

DNP is a substance which allows electron transport to take place without the production of ATP. When DNP is given to rats, their body temperatures rise. Explain why.

A

Energy released as heat;
because not used to produce ATP;

106
Q

What is the function of each of the following in the reactions shown in the diagram?

Reduced NADP

ATP

A

Reduced NADP: to reduce GP / add H (to GP)

ATP: supply energy;

107
Q

Describe how you would select limpets at random.

A

Use of quadrat / nearest limpet to… ;

Grid / described – e.g. tape measures / walk to random coordinates;

Method of obtaining random coordinates – tables / calculator;

108
Q

In investigations like this, why is it necessary to collect data from a large number of specimens which are selected at random?

A
  1. Need representative / ̳typical‘ / ̳reliable‘ / ̳valid‘ value / anomalies less significant / chance variations less significant;
  2. Random sampling overcomes bias / independent of observer
109
Q

Use information from the graphs to explain why red seaweeds are usually found in deeper water (further down the shore) than green seaweeds.

A

Yellow / green OR approx. 500-600mm

  1. Penetrates water better;
  2. Absorbed by phycoerythrin ;
  3. Red seaweeds have phycoerythrin;
  4. Red seaweeds photosynthesise in deep water;

Blue AND red OR approx. 460 and 670mm

  1. Penetrate water poorly;
  2. Absorbed by chlorophyll;
  3. Green have only chlorophyll;
  4. Green seaweeds can‘t photosynthesise in deep water
  5. Red seaweeds have less competition from green in deeper water / converse in shallow water;
110
Q

The stomata close when the light is turned off.
Explain the advantage of this to the plant

A

water lost through stomata

(Closure) prevents / reduces water loss;

Maintain water content of cells.

111
Q

In both Treatment 1 and Treatment 2, the uptake of carbon dioxide falls to zero when the light is turned off.

Explain why.

A

No use of carbon dioxide in photosynthesis (in the dark);

No diffusion gradient (maintained) for carbon dioxide into leaf

there is now a diffusion gradient for carbon dioxide out of leaf (due to respiration).

112
Q

What measurements should the student have taken to determine the rate of photosynthesis?

A

Oxygen production / concentration and time.

113
Q

Suggest and explain why the rate of photosynthesis was low between 525 nm and 575 nm wavelengths of light.

A
  1. Less absorption / (more) reflection (of these wavelengths of light);
  2. (Light required) for light dependent (reaction) / photolysis

Accept: for excitation / removal of electrons (from chlorophyll)

  1. (Represents) green light / colour of chlorophyll.
114
Q

Explain why the scientists measured the rate of production of oxygen in this investigation.

A 
Oxygen produced in light-dependent reaction;
The faster (oxygen) is produced, the faster the light-dependent reaction.
115
Q

Explain the increase in the diversity of birds as the woodland developed.

A

Greater variety / diversity of plants / insects / more plant / insect species;

More food sources / more varieties of food;

Greater variety / more habitats / niches;

116
Q

Name the process that resulted in the development of woodland from farmland.

A

succession

117
Q

Explain why CO2 uptake is a measure of net productivity.

A

Shows (gross) photosynthesis / productivity minus respiration / more carbon dioxide used in photosynthesis than produced in respiration;

118
Q

The photolysis of water is an important part of the process of photosynthesis. Describe what happens in the photolysis of water.

A
  1. (Water) forms H+ /hydrogen ions and electrons/e– ;
  2. O2/oxygen formed;
  3. (Light) excites electrons / raises energy level of electrons / electrons to chlorophyll / to photosystem

A-Level Biology A2 (11 decks)

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