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AQA A Level Biology > 3.5 Chapter 11- Photosynthesis > Flashcards

3.5 Chapter 11- Photosynthesis Flashcards

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1
Q

Why is energy important?

A
  • Life depends on continuous transfers of energy.
  • Needed in plants and animals for biological processes
  • e.g. active transport, DNA replication, cell division, protien synthesis, maintainance of body temperature, muscle contraction.
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2
Q

How is energy generated in plants?

A
  • By photosynthesis.
  • Energy from light is absorbed by chlorophyll, and then transferred/ converted into chemical stores (usually glucose).
  • These chemicals are then used by plants to produce ATP during respiration.
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3
Q

How is energy produced in non-photosynthetic organisms?

A

Feed on molecules produced by plants and use them to make ATP in respiration.

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4
Q

What is a simplification of the process of photosynthesis?

A

Energy from light- used to make glucose from water and CO2.

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5
Q

What type of reaction is photosynthesis?

A

A metabolic pathway- a series of small reactions controlled by enzymes.

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6
Q

Why is photosynthesis important?

Hint: 4 Points

A
  • Stores energy in the form of glucose for use in respiration.
  • Produces energy in the form of glucose for animals to respire (who either feed on plants or other animals that have eaten plants to gain glucose).
  • Stores energy for other uses e.g. fossil fuels, wood to produce energy has it’s energy stored by photosynthesis.
  • Provides oxygen we breathe.
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7
Q

Where does photosynthesis occur and what is this evidence for?

A
  • In all photoautotrophic organisms.
  • Indirect evidence for evolution.
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8
Q

Where does photosynthesis occur?

A
  • In chloroplasts.
  • Mainly in the leaves (In eukaryotic plants)
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9
Q

Why do leaves need to have adaptions?

A

To absorb the raw materials of photosynthesis (water, carbon dioxide and light) and release the products (oxygen and glucose).

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10
Q

Describe the adaptions of leaves for photosynthesis.

Hint: 10 points

A
  • Large surface area for light absorbtion.
  • Arranged to avoid overlapping to prevent shadows and maximise light absorbtion.
  • Thin- most light is absorbed on the surface of the leaf and keeps diffusion distance for gases short.
  • Transparent cuticle and epidermis let light into the mesophyll cels.
  • Upper mesophyll cells are packed with chloroplasts to collect sunlight.
  • Large numbers of stomata for gas exchange so all mesophyll cells have a short diffusion pathway.
  • Stomata- open and close with light intensity.
  • Air spaces in lower mesophyll to allow rapid diffusion of carbon dioxide and oxygen.
  • Xylem that brings water to the leaves.
  • Phloem that carries away sugars produced.
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11
Q

Describe the structure of chloroplasts.

Hint: 6 points

A
  • Small and flat.
  • Double membrane and thylakoid space.
  • Grana- stacks of up to 100 discs called thylakoids- fluid filled sacs with photosystems in their membrane that contain chlorophyll (photosynthetic pigment). Where light absorbtion happens. Granal membranes increase the surface area for photosynthesis- chlorophyll and enzymes can attatch.
  • Lamaellae- tubular extensions that join adjacent grana.
  • Stoma- matrix where light independent stage happens. Contains starch grains (made up of carbohydrates produced in photosynthesis not used up straight away), enzymes for photosynthesis, and amino acids for protien synthesis.
  • DNA and ribosomes- manufacture protiens and enzymes needed for photosynthesis
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12
Q

What is the role and adaptions of photosynthetic pigments?

A
  • Absorb light energy needed for photosynthesis.
  • Plants- contain different photosynthetic pigments- absorb different wavelengths of light for photosynthesis.
  • More pigments= more wavelengths of light.
  • Other pigments- have other roles e.g. protect from UV radiation
  • Different proportions and mixtures in different plants- adaptions to different conditions e.g. shade vs. no shade.
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13
Q

Where are photosynthetic pigments and give examples?

A
  • In the thylakoid membranes attatched to protiens called photosystems.
  • E.g. Chlorophyll a, Chlorophyll b, and carotene.
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14
Q

Describe photosystems and their role.

A
  • Two photosystems- photosystem II (PSII) and photosystem I (PSI)- each better absorb different wavelengths of light.
  • Contain photosynthetic pigments to absorb and capture light energy.
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15
Q

What is oxidation?

A
  • Gain of oxygen
  • Loss of electrons
  • Loss of hydrogen
  • Energy given out.
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16
Q

What is reduction?

A
  • Loss of oxygen.
  • Gain of electrons
  • Gain of hydrogen.
  • Energy taken in.
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17
Q

When do oxidation and reduction always take place and what is this called?

A
  • Together- oxidation of one molecule always involves the reduction of another.
  • Known as a redox reaction.
  • Occurs in photosynthesis and respiration.
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18
Q

What are coenzymes and give some examples.

A
  • Molecules that aid the function of enzymes.
  • Some enzymes require these molecules to function.
  • Transfer chemical groups from one molecule to another.
  • e.g. NADP (in photosynthesis), NAD, FAD (in respiration), acetyl coenzyme A - transfer hydrogen from one molecule to another- reduce and oxidise molecules.
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19
Q

What is the overall equation for photosynthesis?

A

6CO2+ 6H2O -> C6H12O6+ 602

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20
Q

What are the three main stages of photosynthesis?

A
  1. Capturing of light energy by chorophyll (or other pigments).
  2. Light- dependent reaction- electron flow created by light energy, causing water to split by photolysis into protons, electrons and oxygen. Products are reduced NADP, ATP and oxygen.
  3. Light independent reaction- protons (hydrogen ions) are used to produce sugars and other organic molecules.
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21
Q

What stage of photosynthesis do thylakoids perform?

A

The light dependent reaction.

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22
Q

How are grana structurally adapted to their function?

Hint: 6 points

A
  • Adapted to capturing sunlight and carrying out light dependent reaction:
  • Thylakoid membranes- large SA for attatchment of chlorophyll, electron carriers, and enzymes for the light dependent reaction.
  • Protiens in the grana- hold chlorophyll precisely to allow maximum absorbtion of light.
  • Granal membranes- ATP synthase channels to catalyse production of ATP- selectively permeable allowing the establishment of a proton gradient.
  • Contain DNA and ribosomes to manufacture protiens involved in the light dependent reaction.
  • Pigments- specific proportions depending on environmental conditions (see pigments card).
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23
Q

Where does the electron transfer chain occur and describe it’s features?

A
  • In the membrane of the thylakoids.
  • Photosystems are linked by electron carriers- protiens that transfer electrons.
  • Photosystems and electrons form an electron transport chain- chain of proteins where electrons flow.
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24
Q

What is required for the light-dependent reaction?

A
  • Light energy.
  • Water
  • NADP
  • ADP and Pi
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25
Q

Describe the electron transfer chain.

A
  • Photosystems are linked by electron carriers- protiens that transfer electrons.
  • Photosystems and electrons form an electron transport chain- chain of proteins where electrons flow.
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26
Q

What is the purpose of the light dependent reaction?

A
  • To make ATP.
  • To split water into hydrogen ions (protons), electrons and oxygen through photolysis.
  • To form reduced NADP for the light independent reaction.
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27
Q

What are the processes used in the light dependent reaction?

A
  • Photoionisation.
  • Photolysis.
  • Chemiosmosis.
  • Photophosphorylation (cyclic and non-cyclic)
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28
Q

Describe photoionisation.

A
  1. Chlorophyll molecules (and other photosynthetic pigments) in the photosystems absorb light this boosts energy of 2 electrons making them excited.
  2. This results in the electrons leaving (are lost from) the chlorophyll and the chlorophyll becomes positively charged- resulting in it becoming ionised (it is now a positive ion) and oxidised (due to the loss of electrons).
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29
Q

How is the energy from electrons used after photoionisation?

A
  • Photophosphorylation (adding a phosphate to a molecule using light) adds a phosphate group (Pi) to ADP to form ATP-
  • To reduce NADP to form NADPH.
  • Photolysis- splits water into protons (H+) ions, electrons, and oxygen. (H2O is oxidised to O2.)
  • Some may be lost as heat.
30
Q

Name and briefly describe the two processes of photophosphorylation in the light-dependent stage:

A
  • Non-cyclic photophosphorolyation- produces ATP, reduced NADP and oxygen. Involves the electron transport chain, ATP synthase, PSI and PSII.
  • Cyclic photophosphorylation- only produces ATP and only uses PSI and ATP synthase (but maybe not ATP synthase- ask teacher).
31
Q

Describe non-cyclic photophosphorylation.

Hint: 6 steps

A
  1. Light energy is absorbed by photosynthetic pigments in PSII and this causes photoionisation (2 electrons are released).
  2. Electrons are then taken up by an electron carrier which becomes reduced (due to the gain of electrons).
  3. Electrons are passed along electron carriers which form an electron transfer chain, in a series of oxidation-reduction reactions. At each new carrier protein- the electrons lose energy which is used in chemiosmosis to form ATP.
  4. While this occurs, photolysis replaces the electrons in the chlorophyll.
  5. The electrons eventually reach PSI and light energy is absorbed by PSI which excites the electrons to an even higher energy level.
  6. The 2 electrons are then transferred to NADP, along with 2 protons from the stroma to form reduced NADP using the enzyme dehydrogenase. NADP is the final electron acceptor.
32
Q

Describe photolysis.

A
  • Chlorophyl’s electrons need to be replaced after light strikes it if it is to continue absorbing light energy.
  • The electrons are replaced by water molecules split using light energy, which produces electrons, protons and oxygen.
  • H2O (+ light energy) –> 2H+ + ½O2
33
Q

Name the mechanism by which ATP is produced in the light dependent stage?

A

Chemiosmotic theory (chemiosmosis)

34
Q

Describe chemiosmotic theory.

Hint: 8 steps

A
  1. The electrons loose energy flowing down the electron transport chain.
  2. This energy is used to pump protons across the thylakoid membrane into the thylakoid space, so the thylakoid has a higher concentration of protons than the stroma.
  3. Photolysis also produces protons which increases their concentration inside the thylakoid.
  4. This creates a chemiosmotic gradient of protons across the thylakoid membrane.
  5. The protons can only cross thylakoid membrane through ATP synthase channel proteins (aka. stalked granules) embedded in the thylakoid membrane.
  6. Protons move down the concentration gradient into the stroma via ATP synthase.
  7. As protons pass through ATP synthase they change it’s tertiary structure to catalyse ADP and Pi to form ATP.
  8. Protons are then used to reduce NADP.
35
Q

Describe cyclic phosphorylation.

A
  • Produces ATP but only uses PSI.
  • Electrons from photosynthetic pigments aren’t passed onto NADP but back to PSI via electron carriers.
  • This means electrons are recycled and repeatedly flow through PSI.
  • This doesn’t produce any reduced NADP or oxygen- only small amounts of ATP.
36
Q

What are the products of light-dependent reaction used for?

A
  • Reduced NADP transfers hydrogen to the light-independent reaction and is also used as a source of chemical energy in the plant.
  • ATP transfers energy (including to the light-independent reaction)
  • Waste oxygen is either used in respiration or leaves through the leaf.
  • The products are required for the light independent raction to produce triose phosphate.
37
Q

What is required for the light independent reaction?

A
  • The products of the** light dependent stage** NADP and ATP (doesn’t require light but does need the light-dependent stage).
  • ATP and reduced NADP are used to reduce glycerate 3 phosphate (GP).
38
Q

Give an overview of the light independent reaction.

A

The light-independent reaction uses reduced NADP from the light-dependent reaction to form a simple sugar. The hydrolysis of ATP, also from the light-dependent reaction, provides the additional energy for this reaction.

39
Q

Where does the light independent reaction occur?

A

In the stroma of the chloroplasts.

40
Q

What is the light independent stage also referred to as?

A

The Calvin cycle

41
Q

What molecules are needed for the light independent reaction to occur?

A
  • CO2
  • Ribulose biphosphate (RuBP).
  • ATP
  • Reduced NADP (or another source of H+ ions)
  • Rubisco
42
Q

What is produced by the light independent reaction?

A

Triose phosphate.

43
Q

Describe the Calvin Cycle.

Hint: 6 steps

A
  1. CO2 diffuses into the leaf through stomata and dissolves in water around the walls of the mesophyll. It then diffuses through the mesophyll cell into the stroma of chloroplasts.
  2. The CO2 reacts with RuBP (ribulose bisphosphate) a 5 carbon compound, catalysed by rubisco. This produces two molecules of GP (glycerate 3-phosphate) - a three carbon molecule.
  3. 2 reduced NADP from the light dependent reaction reduce the 2 glycerate 3-phosphate to two triose phosphate (TP) using energy from the hydrolysis of two ATP.
  4. NADP is reformed and goes back to the light-dependent reaction to be reduced again by accepting more protons.
  5. Some triose phosphate molecules are kept to be converted **into organic substances **that the plant requires e.g. starch, cellulose, lipids, glucose, amino acids and nucleotides.
  6. Most triose phosphate molecules are used to regenerate RuBP using one molecule ATP from the light dependent reaction.
44
Q

How is the light independent reaction cyclical?

A
  • The starting compound, ribulose biphosphate is regenerated using triose phosphate.
  • The regeneration of RuBP keeps the cycle going so RuBP is always ready to combine with CO2.
45
Q

What does one turn of the Calvin Cycle require?

A
  • 3 ATP
  • 2 reduced NADP.
  • To produce 2 triose phosphate.
46
Q

What is triose phosphate used for?

A
  • Some triose phosphate molecules are converted into organic substances that the plant requires e.g. starch, cellulose, lipids, glucose, amino acids and nucleotides.
  • Triose phosphate helps produce all the organic substances a plant needs.
  • Most triose phosphate molecules are used to regenerate RuBP using ATP from the light dependent reaction.
47
Q

How is the Calvin Cycle used to make hexose sugars?

A
  • One hexose sugar (e.g. glucose) is made by joining two molecules of triose phosphate together.
  • The Calvin cycle needs to turn 6 times to make one hexose sugar.
  • 3 turns of the cycle produce 6 TP.
  • 5/6 are used to regenerate RuBP- only one TP is able to be used to make hexose sugar.
  • Therefore 6 turns are needed to generate two TP.
  • This requires 18 ATP and 12 reduced NADP from the light-dependent reaction.
48
Q

How are carbohydrates formed by the Calvin Cycle?

A

Hexose sugars made from two triose phosphates can be used to make larger carbohydrates by joining them together in condensation reactions (e.g. sucrose, starch, cellulose).

49
Q

How are lipids formed from the Calvin cycle?

A
  1. Glycerol synthesised from triose phosphate.
  2. Fatty acids synthesised by glycerate 3-phosphate.
50
Q

How are amino acids formed from the Calvin Cycle?

A

Some made from glycerate 3-phosphate.

51
Q

How are chloroplasts adapted for carrying out the light independent reaction of photosynthesis.

Hint: 4 points

A
  • Stroma contains all the enzymes needed.
  • Stroma- membrane bound in the chloroplast- maintains a chemical environment with a high concentration of enzymes and substrates- distinctly different from the cytoplasm.
  • Stroma- surrounds the grana so the products of the light dependent reaction can readily diffuse.
  • Contains DNA and ribosomes to quickly and easily manufacture protiens involved.
52
Q

What are the factors that affect photosynthesis called and describe?

A

Limiting factors- the factor whose level is least favourable and limits the rate at which the process can occur.

53
Q

What are limiting factors of photosynthesis (in order of how they affect it)?

A
  1. Light intensity (directly proportional).
  2. Carbon Dioxide
  3. Temperature.
54
Q

What is the relationship between photosynthesis and it’s limiting factors?

A

Directly proportional.

55
Q

What is important to consider with limiting factors and draw graphs to demonstrate this.

A
  • If one factor is to high or two low- limits photosynthesis despite other factors.
  • Any factor could become the limiting factor due to changes in environmental conditions.
  • Need to be balanced for photosynthesis to be at the optimum rate.
  • Look at which factor may be the main limiting factor e.g. after one graph levels off, another graph may become the limiting factor, with a higher rate reached than the previous one, until the optimum- example graph on revision card.
56
Q

What must you consider when analysing data on limiting factors?

Hint: 8 points

A
  • You may be asked to evaluate data relating to common agricultural practices used to overcome the effect of these limiting factors.
  • Remember steeper curve= faster rate.
  • State on average… compare control with new value.
  • Look at changes over time e.g. where levels out- change in limiting factor.
  • Explain why in relation to q e.g. CO2- independent reaction, light- dependent and independent reaction.
  • Remember to link to plant growth if necessary.
  • More glucose/ sugars= respire more= more ATP/energy for for DNA replication, cell division and protein synthesis= growth. Also can synthesise organic molecules from triose phosphate e.g. lipids, faster for growth.
  • Remember control factors e.g. potassium hydrogencarbonate for CO2.
57
Q

Why is considering limiting factors important in agriculture?

A

Increasing plant growth- agricultural growers adjust the limiting factors of photosynthesis that limits plant growth to the optimum (within a reasonable budget) to increase yields e.g. by using glasshouses, heaters, lights, and CO2 emitters such as propane.

58
Q

What are the optimum conditions for photosynthesis?

A
  • Vary from plant to plant.
  • High light intensity of a certain wavelength (most photosynthetic pigments only absorb red and blue sunlight).
  • Temperature- usually around 25°C for enzymes- if falls below- too slow, above e.g. 40°C—enzymes denature. High temperatures- stomata close to avoid water loss- less CO2.
  • Carbon dioxide- atmospheric 0.04%, usually best at 0.4%- after that stomata close.
  • Water- constant supply. Too much- soil becomes waterlogged- reduces minerals and causes anaerobic respiration- alcohol damages plants.
59
Q

What are the ways to measure the rate of photosynthesis?

A
  • Oxygen release using a potometer. (Oxygen produced in light dependent reaction- faster produced= faster reaction.)
  • Oxygen release using a gas syringe and aquatic plants.
  • DCPIP turning from blue to colourless.
60
Q

Explain the use of DCPIP in investigating the rate of photosynthesis.

A
  • NADP- electron acceptor- reduced by electrons- catalysed by dehydrogenase in the chlorophyll from the light dependent reaction.
  • Redox indicators e.g. DCPIP- act as electron acceptors- change colours when get reduced- from blue to colourless.
  • DCPIP can therefore be used to measure dehydrogenase activity in chloroplasts (aka. the rate of photosynthesis).
  • Measure rate of dehydrogenase activity by measuring rate DCPIP loses colour- can use colorimeter to measure this.
  • This can then be used to investigate the effects of factors on the rate of dehydrogenase activity.
61
Q

Describe the process of investigating the activity of dehydrogenase in chloroplasts.

Hint: 9 steps

A
  1. Cut leaves into pieces and grind then with isolation solution (sucrose, potassium chloride and phosphate buffer of pH 7)- filter liquid.
  2. Transfer into centrifuge and gather chloroplasts in the pellet at the bottom, remove the supernatant on top.
  3. Suspend the pellet in chilled isolation solution.
  4. Set up colorimeter, set it to a red filter and zero it using a cuvette containing chloroplast extract and distilled water.
  5. Set up test tubes at a set distance from a lamp filled with set volumes of chloroplast extract and DCPIP. Mix.
  6. Set up two control tubes- one with only DCPIP and isolation solution to show chloroplasts are required and light does not affect DCPIP, and one with only DCPIP and chloroplast extract- wrapped in tin foil so no light enters to act as a control to show light is required for the chloroplasts to perform photosynthesis and change the colour of DCPIP. No change should happen in controls.
  7. Take samples and add it to cuvette, add to colorimeter and record the absorbance every 2 minutes for 10 minutes to measure rate of colour change. Absorbance will decrease as DCPIP gets reduced and loses its colour. Faster= faster rate of dehydrogenase activity.
  8. Repeat with e.g. different distances of the lamp.
  9. You can plot a graph of absorbance against time for each distance to compare results.
62
Q

Why is a colorimeter used to measure the colour change of DCPIP?

A

Makes the answers comparable and provides a standard reference point

63
Q

What is the compensation point?

A
  • The rate of photosynthesis is partly dependent on light intensity.
  • The point of light intensity at which the rate of photosynthesis matches the rate of respiration exacly is the compensation point for light intensity.
64
Q

How can compensation point be measured?

A
  • Measuring the rate at which oxygen is produced and used by a plant at different light intensities.
  • The compensation point is the light intensity at which oxygen is being used as quickly as it is being produced, therefore net oxygen generation is 0.
  • The same could be done with CO2 concentration.
65
Q

What is chromatography used for?

A

Used to separate mixtures to identify components.

66
Q

What components does chromatography have?

A
  • Mobile phase- molecules can move- e.g. liquid solvent.
  • Stationary phase- where molecules can’t move- paper chromatography= chromatography paper, thin-layer chromatography= thin layer of solid e.g. silica gel on glass/plastic plate.
67
Q

How does chromatography work?

A
  1. Mobile phase moves through/ over the stationary phase.
  2. Components in the mixture spend different amounts of time in the mobile/ stationary phase dependent on how attracted they are to each section.
  3. Components that spend longer in the mobile phase travel further- separating the mixture.
68
Q

What safety should be considered with chromatography?

A

Wear eye protection, lab gloves and coat to protect from solvent.

69
Q

What is chromatography used for in plants?

A
  • Plants- contain different photosynthetic pigments- absorb different wavelengths of light.
  • Pigments can be separated through chromatography, then identified using Rf values- specific to different pigments under specific conditions.
70
Q

Describe the process of chromatography to seperate pigments in plants.

A
  1. Grind leaves with anhydrous sodium sulfate and propane.
  2. Transfer liquid to test tube, add some petroleum ether and shake.
  3. Transfer liquid into tube with anhydrous sodium sulfate.
  4. Draw pencil line on paper (not ink to ensure ink and leaf pigments don’t mix). Build up concentrated spot of the liquid in the centre by applying drops and drying them before the next is added- forms point of origin.
  5. Once dry, place in solvent so that the point of origin is above the solvent. Add a lid and leave it.
  6. Solvent spreads up the plate, pigments move with it but at different rates- separate.
  7. Remove the plate before the solvent reaches the top and mark the solvent front with a pencil. Leave to dry.
  8. Measure the different coloured spots from how far they are from the origin.
  9. Calculate Rf using the formula Rf= distance travelled by solute/ distance travelled by solvent (gives a no. below 1).
  10. Compare Rf values to data to find the name of the solvent.
  11. Repeat using different variables e.g. different type of plants- shade-tolerant and shade intolerent, and compare results of different proportions of solvent.
71
Q

What is the Rf value and his formula?

A

Rf= solute distance/ solvent distance
Distance travelled through the stationary phase in relation to the solvent-

AQA A Level Biology (11 decks)

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