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Biology Y13 > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

What is metabolism?

A

all chemical reactions take place in a cell

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2
Q

what is catabolism?
what is anabolism?

A

C - the break down of substances releasing energy
A - the synthesis of substances requiring energy

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3
Q
  1. What is ATP?
  2. What is ATP used for?
  3. How is ATP formed?
  4. ATP is broken down to form?
  5. how does ATP give an immediate source of energy?
  6. through what process can make a molecule more reactive?
  7. When can ATP be made or hydrolysed?
A
  1. AdenosineTriPhosphate
  2. immediate source of energy for biological processes
  3. Condensation reaction of ADP + Pi, catalysed by enzyme ATP synthase
  4. ADP + Pi vias a hydrolysis reaction, catalysed by ATP hydrolase
  5. inorganic phosphate group can be broken off to release energy and form ADP
  6. Phosphorylation
  7. during photosynthesis or respiration
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4
Q

Why is ATP a good energy source?

A
  • energy is released quickly from ATP in a 1 step hydrolysis reaction
  • energy is released on small, manageable amounts
  • ATP is small and water soluble, so can be easily moved around the cell
  • ATP can’t pass out the cell, always has an immediate source of energy
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5
Q

Photosynthesis

A
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6
Q

what is photosynthesis?

A
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7
Q

what is the word and symbol equation for photosynthesis?

A

Carbon dioxide + water —-light energy –> glucose and oxygen

6CO2 + 6H20 —-LIGHT ENERGY —> C6H12O6 + 6O2

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8
Q

When and where does photosynthesis occur in plants?

A
  • only in green plants and algae, because chloroplasts contain chlorophyll pigments which trap light energy.
  • light energy is used to build up biological molecules
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9
Q

How are plants adapted to photosynthesis?

A

Chloroplasts packed into palisade layer which means more photosynthesis/ absorb more light energy needed for photosynthesis

Transparent cuticle and upper epidermis which means light can pass through for photosynthesis

Thin which means light can pass through

Large surface area which means more chlorphyll can absorb light for photosynthesis

Air spaces which means gases like co2 can diffuse needed for photosynthesis

Stomata which means o2 can diffuse out and co2 diffuse in

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10
Q

what does chlorophyll allow?

A

provides a large surface area for maximum light absorption

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11
Q

what is a photosystem?

A

Pigment + proteins

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12
Q

what is the stroma (part of chloroplast)?

A

jelly like substance which contains DNA & ribosomes to enable proteins to be made quickly.

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13
Q

Photosynthesis: Light Dependent reaction stage

A
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14
Q

What are the two stages in photosynthesis?

A
  • light dependent reaction (LDR)
  • light independent stage (LIR)
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15
Q

Where does the Light dependent stage occur?

A

on the thylakoid membrane or grana

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16
Q

what is required for the LDR?

A

light energy or energy is provided for by photolysis of water

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17
Q

what does the LDR make?

A

makes ATP and NADPH (reduced NADP) needed for the second stage of photosynthesis

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18
Q

what consists of the thylakoid membrane?

A
  • photosystems - light-harvesting systems where chlorophyll is found.
  • electron carries, forming an electron transport chain, which pick up electrons and pass them down energy levels
  • also ATP synthase present - (in form of an chanel/carrier proteins i think)
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19
Q

why is photosystem 2 first and not photosystem 1?

A

photosystem 2 was discovered first and photosystem 1 was found later

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20
Q

what differs between the two photosystems?

A

They absorb different wavelengths of light. Both have chlorophyll at their centres.

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21
Q

draw a thylakoid membrane, include the photosystems, electron carries and ATP synthase

A
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22
Q

what are the 4 key stages in photosynthesis?

A
  • Photo- ionisation (of chlorophyll) - light energy causes electrons to be lost from chlorophyll
  • Photolysis - splitting of water
  • Chemiosmosis - movement of H+ ions
  • Production of ATP and reduced NADP (NADPH)
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23
Q

what is a electron transport chain?

A

a chain of proteins (in which excited electrons flow)

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24
Q

What happens in photosynthesis in the LDR? - non-cyclic photophosphorylation

A
  1. Photo-Ionisation - A photon of light actually hit’s chlorophyll in photosystem 2 and this light energy is then picked up by electrons, becoming excited and raising up in an energy level to break free and leave chlorophyll
  2. Chlorophyll has now been ionised by light (lost an electron)
  3. The excited electron then get’s passed on to electron carriers and passed down the electron transport chain, loosing energy as it goes.
  4. this energy is used to Pump H+ ions across from Stroma into Thylakoid lumen (via active transport)
  5. once the electron has reached photosystem 1, energy has been lost, so another photon of light is needed to re-excite the electron that’s lost it’s energy.
  6. so more light energy is needed (at photosystem 1) to re-excite the electron back to a higher energy state
  7. the electron then get’s passed down though another electron transport chain where it combines with NADP+
  8. the electron then combines with NADP+ to become NADPH (used for LIR)
  9. Now an electron has been lost, to replace lost electron we can get it from Photolysis - (water)
  10. So at photosystem 2, light energy is absorbed by chlorophyll and splits water into O2, H+ and e- (H2O —> 1.5 O2 + 2e- + 2h+ . the electron has enough energy, leaves chlorophyll and joins the electron transport chain once again. As the electron leaves, it releases energy to pump H+ ions across (from thylakoid lumen to stroma)
  11. Oxygen is produced as a waste gas, so diffuses out of the cell. Furthermore, this is also going to add H+ ions into the thylakoid lumen as well, which creates an electrochemical gradient where there’s a high conc. in the lumen and a low conc. in the stroma.
  12. so these H+ ions are actively transported, across ATP synthase via facilitated diffusion, As protons diffuse through ATP synthase, it actually causes a chain in shape of the protein, and the change in shape of the protein provided energy to catalyse the reaction of ADP +Pi to make ATP.
  13. How reduced NADPH is made
  14. So protons (H+) , which have been moved into the stroma, will be recycled back and pumped back around, so the cycle continues.
  15. But some H+ ions/ protons will be picked up by co-enzyme NADP to become reduced NADP -> NADPH . however it has also picked up a electron (e-) at the end of the electron transfer chain thus becoming reduced
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25
Q

What is required for Non-cyclic photophosphorylation LDR to happen?

A

ATP and NADP+

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26
Q

When does Cyclic-photophosphorylation occur?

A

when the plant has become short in NADP+

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27
Q

which processes do not occur in Cyclic-Photophosphorylation?

A
  • process where NADP+ is used to make NADPH
  • Splitting of water - photolysis
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28
Q

Describe the process of cyclic-photophosphorylation in the LDR?

A
  1. Photo-ionisation - A photon of light actually hit’s chlorophyll in photosystem 2 and this light energy is then picked up by electrons, becoming excited and raising up in an energy level to break free and leave chlorophyll
  2. Chlorophyll has now been ionised by light (lost an electron)
  3. The excited electron then get’s passed down an electron transport chain, loosing energy as it goes.
  4. this energy is used to Pump H+ ions across from Stroma into Thylakoid lumen
  5. once the electron has reached photosystem 1, there is no NADP+ to accept the electron, and so the electron is then passed down again to photosystem 2, where it get’s re-excited.
  6. can then be passed along (across electron transport chain) and release more energy to pump more H+ ions into the lumen.
  7. Then these H+ ions can then go through the lumen and generate more ATP
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29
Q

What is NADPH?

A

Nicotinamide Dinucleotide Phosphate
a co-enzyme important in the process of photosynthesis (& respiration) as carriers of H+ and electrons

30
Q

what are co-enzymes?

what is important about co-enzymes?

A

Coenzymes bind with a specific enzyme or substrate, helping to catalyze a reaction.

Breaking the bonds between coenzyme and product after a reaction is crucial, otherwise coenzyme concentration will drop.

31
Q

Explain how chloroplasts are adapted to their function of photosynthesis (LDR)

A
  • thylakoid membrane - large SA for attachment of chlorophyll, electron carriers and enzymes that carry out the light-dependent reaction
  • network of proteins in grana hold chlorophyll in a precise manner that allows the maximum absorption of light
  • Granal membranes have ATP synthase, so catalyse production of ATP
  • Granal membranes are selectively permeable allows establishment of a proton gradient
  • chloroplasts contain both DNA + ribosomes so they can quickly and easily manufacture some of the proteins involved in the LDR
32
Q

Light - Independent Reaction (LIR)

A
33
Q

where does the Light-independent reaction occur?

A

occurs in the stroma (fluid filled centre of chloroplast)

34
Q

what is required for the light-independent reaction?

A

ATP and NADPH from the LDR

35
Q

what are the 4 phases of the Calvin cycle?

A
  1. CO2 fixation (carboxylation)
  2. Glycerate-3-phosphate to Triose Phosphate (reduction)
  3. Reformation of acceptor molecules (regeneration)
  4. Triose phosphate converted to carbohydrates, lipids, amino acids (product synthesis)
36
Q

Describe the Calvin cycle?

A

Carboxylation - Ribulose Bisphosphate (RuBP) is reacted with Carbon dioxide (from the atmosphere that diffuses into the stroma) which is catalysed by enzyme Rubisco. This gives an unstable 6 Carbon compound which quickly breaks down into two molecules of a 3 carbon compound glycerate tri/3-phosphate.

Reduction - Reduced NADP from the LDR is used to reduce glycerate-3-phosphate into triose phosphate (TP) using energy supplied/provided from the hydrolysis of ATP.
(the NADP is reformed and goes back to the LDR to be reduced again by accepting more protons)

Regeneration - Most of the Triose Phosphate (5 molecules) is used to regenerate RuBP using energy from ATP. The rest (1 molecule) is used to form Glucose and other useful compounds such as starch, cellulose, DNA, proteins and lipids. 5 of every 6 carbons from Triose phosphate is used to regenerate Ribulose Biphosphate. 1 carbon goes towards making hexose sugar.

37
Q

Triose Phosphate is really useful and can be turned into other things the plant needs such as..?

A
  • some used in glycolysis + krebs cycle in respiration to make ATP for the cell
  • glucose made via gluconeogenesis can be converted into other carbohydrates such as: starch, sucrose, cellulose
  • Addition of nitrates from the soil is used to form Amino Acids
  • Addition of phophates from the soil can result in the production of nucleic acids such as DNA/RNA
  • Triose phosphate that goes into glycolysis can be converted into acetyl coenzyme A, which can be used to make fatty acids which can be used to make phospholipids + other key lipid molecules for the plant
38
Q

Explain hoe the chloroplast is adapted to carry out the LIR of photosynthesis?

A
  • stroma contains enzymes needed for photosynthesis
  • stromal fluid is membrane bound which means a chemical environment which has a high concentration of enzymes and substrates can be maintained within it - as distinct from the environment of the cytoplasm
  • the stroma fluid surrounds the grana do the products of the LDR can readily diffuse in
  • contains both DNA + ribosomes so can quickly assemble proteins involved in the LIR
39
Q

The Calvin Experiment

A
40
Q

what was Calvin’s aim?

A

Calvin shone light on the lollipop and used a radioactive form of carbon called carbon-14 to trace the path that carbon took through the algae’s chloroplast, the part of the cell where photosynthesis occurs.

41
Q

Describe how the ‘Lollipop experiment was carried out?

A
  • single celled algae grown under light in a thin transparent lollipop
  • radioactive carbon 14 in the form of hydrogen carbonate is injected
  • at intervals (seconds - minutes) samples of the photosynthesising algae are dropped into the hot methanol to stop chemical reactions instantly
  • the compounds in the algae are separated by two-way chromatography
  • the radioactive compounds are then identified
42
Q

what were the results of the experiment?

A
  • at 0 seconds found to be only CO2
  • at 5 seconds found to be GP
  • at 10 seconds found to be GP and TP
  • at 15 seconds found to be GP, TP and glucose
  • at 20 seconds found to be GP,TP, glucose and RuBp
43
Q

Explain why each apparatus was used:
funnel -
Flat-sided flask -
Algae -
syringe with CO2 + C14 -
rapid action tap
tube containing hot ethanol

A
  • Funnel - add/ introduce algae into the flask
  • flat sided flask - to increase the surface area, so more light hits the flask/chlorophyll, so more photosynthesis
  • Algae - is a photosynthetic organism
  • allows us to track organic products of the calvin cycle
  • allows sample to be collected quickly - allows us to gain/ control precise timings
  • Kills and denatures enzymes in the algae, s stops the photosynthesis reaction, also allows precise timings to be recorded
44
Q

why was his experiment carried out in a closed system?

A

to ensure that there is only carbon dioxide with C14 incorporated available within the system

45
Q

why was there more apparatus for maintaining pH and nutrient concentration?

A

so we can control the factors of photosynthesis, so that there is no other factor limiting affecting the production of organic compounds

46
Q

explain the method used by Calvin in his Lolipop experiment

A
  1. isolated chloroplasts - Ultracentrifugation so to isolate the chloroplast they would have to homogenize a sample of cells so break open the cells, would then have to filter the large debris and then they could centrifuge to isolate out the different pellets and the chloroplasts come to the second pellets so that’s how they could isolate the chloroplasts
  2. Use of radioactive isotopes - carbon is being injected in in the form of carbon dioxide into the apparatus and they would need to leave the apparatus set period of time under the exact conditions that they want to do the experiment in to allow that carbon dioxide to be fully incorporated into all of those carbon-containing compounds in the Calvin cycle
  3. perfusion of chloroplasts - the perfusion stage is referring to the fact that they can then simultaneously continue to inject in that carbon 14 isotope in the form of the carbon dioxide whilst also taking samples through that rapid action tap and in that way they can get multiple samples at precise periods of time and measure the exact quantity of that carbon isotope in all of the different carbon-containing compounds
  4. Measurement of radioactivity - would be using autoradiography for and for that, that is basically a way to measure the quantity of radioactive substances in each of those carbon-containing compounds
  5. Analysis of the data - using graph
47
Q

Draw the results of Calvin’s Lollipop experiment in a graph form, using the graph answer the next few questions

A
48
Q

explain why there is a high amount of GP in the light compared to the other substances?

A

there is a higher GP amount as GP has more carbons and it is the carbon that is radioactive (6 carbons all together)

49
Q

what caused the amount of radioactively labelled glucose to decrease in the dark?

A

light dependent reactions would stop and that means you won’t be getting any reduced NADP or ATP and those two compounds are required in the Calvin cycle to reduce GP into TP.

50
Q

Why did GP levels rise in the dark

A

light dependent reactions would stop so there’d be no more ATP or reduced NADP being created and those two are both needed to reduce GP into TP therefore that doesn’t happen so you get a buildup of GP.

51
Q

Why did RuBP decrease in the dark?

A

RuBP is still able to combine with the carbon dioxide using the enzyme rubisco to form GP but that GP has not been converted into TP and therefore there’s no TP available to regenerate RuBP there’s also no ATP which is needed to regenerate the TP into RuBP so the RuBP is still being
used but it’s not been regenerated.

52
Q

Limiting factors of photosynthesis

A
53
Q

explain how the optimum conditions vary from one plant species to another?

A

only certain wavelengths of light are used for photosynthesis. for example pigments chlorophyll a,b and carotene only absorb the blue and red light in sunlight.`

54
Q

what happens when temperature exceeds and is below it’s limit of 25°C?

A
  • if temperature falls below 10°C, enzymes become inactive, and if temperature is more than 45°C they may start to denature.
  • Also at high temperatures stomata close to avoid losing too much water. this causes photosynthesis to slow down because less CO2 enters the leaf when the stomata are closed.
55
Q

what happens when the concentration of CO2 rises and falls?

A

Carbon dioxide makes up 0.04% of gases in the atmosphere.
- increasing this to 0.04% gives a higher rate of photosynthesis, but any higher and the stomata start to close.

56
Q

what happens when the water levels of a plant begin to exceed the limit and begin to fall?

A

plants need a constant supply of water.
- too little and photosynthesis has to stop but too much and the soil becomes waterlogged (reducing the uptake of minerals such as magnesium, which is needed to make chlorophyll a

57
Q

what are the 3 main factors which limit the rate of photosynthesis?

A

temperature, light intensity, carbon dioxide concentration

58
Q

Draw a graph to show how light intensity affects the rate of photosynthesis. describe what the graph shows

A

between points A and B the rate of photosynthesis is limited by light intensity. so as light increases so does the rate of photosynthesis. However, after point B (saturation point) Light intensity is no longer a limiting factor. And so there must be another factor affecting the rate of photosynthesis. so the rate levels off

59
Q

explain what this process affects and how?

A

LDR affected
- increased light
- more electrons excited and leave chlorophyll
- more pumping of H+ ions
-more ATP and NADPH produced

60
Q

Draw a graph to show how carbon dioxide concentration affects the rate of photosynthesis. describe what the graph shows?

A

From point 1 to 2 carbon dioxide is the limiting factor for the rate of photosynthesis. after point 2, carbon dioxide concentration increases but there is no difference in the rate of photosynthesis so there must be another limiting factor affecting the rate of photosynthesis.

61
Q

which process is affected and how?

A

LIR affected
- the more CO2
- the more RuBP binds with CO2 in presence of rubisco
- more GP and more TP
- more regeneration of RuBP

62
Q

Draw a graph to show how temperature affects the rate of photosynthesis

A

At point 1 , there is more binding between enzymes controlling photosynthesis, e.g rubisco + CO2 + RuBP, so more enzyme substrate complexes formed.
at point 2 - enzymes controlling photosynthesis denature.

63
Q

explain the economic importance of the rate of photosynthesis?

A

farmers need to know factors which limit photosynthesis + plant growth. because more plant growth = higher yield = more money

63
Q

check AQA textbook - page 31 - graphs

A
64
Q

how do farmers create optimum conditions in glasshouses/greenhouses?

A

CO2 conc - co2 added to air, burning small amounts of propane in co2 generator
Light - light passes through transparent glass and at night time, lamps
Temperarture - glasshouses trap heat energy from sunlight, keeps air warm. heaters + cooling systems can also be used to keep optimum conditions

65
Q

which process can happen at the same but different rates time as photosynthesis?

A

respiration

66
Q

what is the compensation point?

A

where the amount of carbon dioxide produced by respiration is equal to the amount of CO2 required for photosynthesis. there is not net loss or gain of CO2

67
Q

what is the gross rate of photosynthesis?

A

the total/true rate of carbon dioxide intake (carboxylation).

68
Q

what is and how is the net rate of photosynthesis calculated?

A

the gross rate - the production of CO2 by respiration

69
Q

DONE

A

Biology Y13 (13 decks)

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