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A-Level EDUQUAS Biology > Component 1: Photosynthesis > Flashcards

Component 1: Photosynthesis Flashcards

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1
Q

What is the general formula for photosynthesis?

A

6CO2 + 6H2O -> C6H12O6 + 6O2

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2
Q

What are the 2 stages of photosynthesis?

A
  1. Light dependent reaction (light energy converted to chemical energy)
  2. Light independent reaction (ATP and NADPH reduce CO2 and produce glucose)
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3
Q

Where does photosynthesis occur?

A
  • in chloroplasts
  • chloroplast found in any part that is exposed to light
  • chlorophyll is contained in the thylakoids (green pigment)
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4
Q

What are the adaptations of leaves for photosynthesis?

A
  • AIR SPACES between spongy mesophyll allows CO2 to diffuse to photosynthesising cells
  • LARGE SA to capture as much light as possible
  • THIN to let light penetrate all the way through
  • STOMATAL PORES to allow CO2 diffusion
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5
Q

What are the adaptations of chloroplasts for photosynthesis?

A
  • More chloroplasts is palisade than spongy mesophyll cells allows for them to be exposed to more light
  • Large SA allows more maximum CO2 and light absorption
  • Thylakoid stacking maximises light catchment
  • Single pigment layher in thylakoid membrane allows for pigments to maximise light absorption
  • Chloroplasts can move within palisade cells allows for maximum absorption of light and protection from bleaching
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6
Q

Name all photosynthetic pigments

A
  • Chlorophyll a
  • Chlorophyll b
  • Carotenes (carotenoid)
  • Xanthophylls (carotenoid)
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7
Q

Why is there more than one photosynthetic pigments?

A
  • Different pigments absorb photons at different wavelengths of light
  • Function is to absorb light energy and start conversion into storable chemical energy
  • More than one pigment allows for a large range of wavelengths to be absorbed
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8
Q

What is the role of the stroma in the chloroplast?

A
  • site of the light independent reaction (requires enzymes)
  • CO2 is fixed to produce sugar
  • ATP and NADPH is required
  • Contains starch grains that store the products of pss
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9
Q

What is the role of thylakoids in the chloroplast?

A
  • site of the light dependent reactions
  • chlorophyll absorbs light energy
  • ATP, NADPH and O2 produced
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10
Q

What is the role of the granum/grana in the chloroplast?

A

provides surface area of the absorption of light energy

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11
Q

What is the role of the starch grain in the chloroplast?

A
  • excess carbs stored as a starch grain

- starch doesn’t affect water potential

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12
Q

What is the role of the double membrane in the chloroplast?

A

Controls movement of substances in and out of the chloroplasts

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13
Q

Why are plants green?

A

reflect green wavelengths on the leaf

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14
Q

What is an absorption spectra?

A

A graph showing how much light is absorbed at different wavelengths (degree of light absorption by a pigment)

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15
Q

What is an action spectrum?

A

A graph showing the rate of of photosynthesis at different wavelengths

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16
Q

What is the relationship between an absorption spectra and an action spectrum?

A

Together they can suggest that the pigments responsible for absorbing a specific wavelength of light are used in photosynthesis

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17
Q

What happened in the engelmann’s experiment?

A
  • As the spiral chloroplast of Spirogyra photosynthesises oxygen gas is produced as a waste product
  • The mobile aerobic bacteria move towards the parts of the chloroplasts exposed to red and blue parts of the spectrum
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18
Q

What is an overview statement of photosynthesis?

A

The process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water

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19
Q

Describe the structure of photosystems?

A
  • located in the thylakoid membranes
  • antenna complex are the groups/clusters of photosynthetic pigments, held together by protein molecules
  • reaction centre contains 2 molecules of chlorophyll a
20
Q

What are the 2 types of photosystems?

A
  1. Photosystem 1 (PS1) is arranged around a chlorophyll a molecule with a maximum absorption at a wavelength of 700nm (P700). Mostly found on intergranal lamellae
  2. Photosystem 2 (PS2) is arranged around a chlorophyll a molecules with and absorption peak of 680nm (P680), found on the granal lamellae
21
Q

What is a photosystem?

A

Each photosystem is a collection of accessory pigments which absorb light at various wavelengths and transmit the energy to a reaction centre

22
Q

What stage of photosynthesis is non-cyclic and cyclic photophosphorylation apart of and where does it happen?

A

Light dependent stage (first stage)

thylakoid membrane

23
Q

What happens in the first part of cyclic-photophosphorylation?

A
  • photon hits PSI and is absorbed by accessory pigments in the antenna complex
  • they transfer energy to the primary pigment and this excites an electron (higher energy level)
  • the excited electron moves down the electron transfer chain (ETC)
  • as it moves down the ETC is loses energy and at the end of the ETC returns to the primary pigment in PSI
24
Q

What happens in the second part of cyclic-photophosphorylation?

A
  • energy released by the electron is used by the proton pumps to pump protons from the stroma into the thylakoid space
  • this creates a proton gradient (pH and electrochemical gradient also)
  • to back down the gradient protons move through ATPsynthase
  • energy released is used to make ATP from ADP and Pi
  • this process is called chemiosmosis
25
Q

What is the definition of cyclic photophosphorylation?

A

ATP can be produced by electrons that take a cyclical pathway and are recycled back into the chlorophyll a is PSI

26
Q

What is the first part of non-cyclic photophosphorylation?

A
  • photon hits PSII and the energy excites an electron in chlorophyll a
  • electron travels down the ETC, releasing energy as it goes and travels to the chlorophyll a in PSI
  • energy from the electron is used by the proton pump to pump H+ from the stroma to the thylakoid space
  • proton gradient is used by ATP synthase to make ATP by chemiosmosis
27
Q

What is the second part of non-cyclic photophosphorylation? (final electron acceptor)

A
  • light energy hits PSI and excites an electron from chlorophyll a and travels down the ETC
  • at the end it joins to the final electron acceptor NADP (nucleotide)
    NADP + e- + H+ -> NADPH
28
Q

What is the third part of non-cyclic photophosphorylation? (photolysis)

A
  • for PSII to replace the lost electron it splits water in photolysis (2H2O -> 4H+ + 4e- + O2)
  • the electrons replace those lost is PSII in chlorophyll a and the protons add to the proton gradient
  • the O2 diffuses away as a waste product
29
Q

What are the three things contributing to the proton gradient in the light dependent stage?

A

photolysis
proton pump
NADP removing H+ from stroma

30
Q

What is the definition of non-cyclic photophosphorylation?

A

ATP can be produced by electrons that take a linear pathway from water, through PSII and PSI to NADP, which they reduce

31
Q

What is the definition of photolysis?

A

the splitting of water molecules by light producing hydrogen ions, electrons and oxygen

32
Q

What does the electrochemical gradient produce?

A
  • the electrochemical gradient produced by protons becomes a source of potential energy
  • when H+ diffuses back it makes available derived from light
33
Q

Draw the calvin cycle

A

Ribulose Bisphosphate (5C)
CO2 + RUBISCO enzyme
Unstable 6C compound
(splits)
2 x Glycerate-3-Phosphate (3C0
ATP -> ADP + Pi (energy released), NADPH -> NADP
2 x Triose Phosphate (3C)
1/6 of TP = manufactures glucose -> lipids -> amino acids with the addition of nitrogen obtained from nitrates
5/6 of TP = Ribulose Phosphate (5C)
ATP -> ADP (inorganic phosphate group added)
RuBP (start of cycle)

34
Q

What stage of photosynthesis is the calvin cycle?

A

The light-independent stage

35
Q

What is chromatography?

A

a separation technique to separate pigments in plant leaves

36
Q

What does an Rf value show?

A

shows how far a component has travelled compared with the solvent front
- a ration of distance solvent moved to solvent front

37
Q

What are the limiting factors for plant metabolism?

A

inorganic nutrients: nitrogen and magnesium

38
Q

What happens when nitrogen is in short supply?

A
  • limits metabolism
  • nitrogen is required to synthesise proteins and nucleic acids
  • usually transported as nitrates in the xylem and as a.a. in the phloem
  • a lack of N = stunted growth of all organs, hindered cell division and chlorosis (inadequate chlorophyll production)
39
Q

What happens to plants when magnesium is in short supply?

A
  • limits metabolism
  • transported as Mg2+ in the xylem
  • Magnesium is required to make chlorophyll and for the activation of ATPase
  • lack of Mg2+ leads to chlorosis (inability to photosynthesise)
40
Q

What are the 3 limiting factors of photosynthesis?

A

Light intensity, carbon dioxide concentration and temperature

  • if one of these factors is restricted the rate of photosynthesis will be blow the maximum possible rate, restricted factor is the limiting factor
41
Q

What happens to the rate of photosynthesis as light intensity is increased?

A
  • as the amount of light increases so does pss rate, light is therefore the limiting factor
  • eventually the rate will plateau no matter how much the light intensity is increasing, light intensity is no longer the limiting factor
42
Q

What happens to the rate of photosynthesis as carbon dioxide concentration increases?

A
  • initially as the amount of CO2 increases, so does the pss rate, CO2 is therefore the limiting factor
  • eventually increasing CO2 conc has no effect on the rate, CO2 conc is no longer the LF
43
Q

What happens to the rate of photosynthesis as temperature is increased?

A
  • initially as temp increases so does the rate of photosynthesis because photosynthetic enzymes work best in the warmth (temp is LF)
  • most plant enzymes are destroyed at about 45 degrees, rate stops and falls to 0, temp is still the LF
44
Q

What is a compensation point?

A

Where the rate of photosynthesis and the rate of respiration ar equal
- the net carbon uptake is 0 at compensation poi

45
Q

Why would the compensation point never be reached at night?

A

The light dependent reaction of photosynthesis can’t take place while respiration will occur through the night

46
Q

Why can water also act as a limiting factor?

A
  • photolysis can’t happen in severely short water supply

- stomata will close, less gas exchange and pss is limited

47
Q

What happens in photosystems?

A

-photons of light that hit the PS excite pigments in the antenna complex, transfer light energy until it reaches the primary pigment (chlorophyll a in the reaction centre) and an electron is excited and raised to a higher energy level

A-Level EDUQUAS Biology (24 decks)

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