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OCR Biology A Level > 5.2.1 Photosynthesis > Flashcards

5.2.1 Photosynthesis Flashcards

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1
Q

Give a brief overview of photosynthesis

A
  • transforms light energy from the sun into chemical energy
  • builds complex organic molecules from inorganic molecules
  • energy released from complex molecules during respiration
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2
Q

What is the word and balanced chemical equation for photosynthesis?

A

Carbon dioxide + water = glucose + oxygen
6CO2 + 6H20 + C6H12O6 + 6O2

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3
Q

Define an autotroph

A

An organism that can macke organc molecules from inorganic molecules using light or chemical energy

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4
Q

Define a heterotroph

A

Organisms that have to botain organic molecules that have been made by another organism

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5
Q

Give an overview of the endosymbionet theory

A
  • aerobic respiration relies on microchonrida
  • photosynthesis relies on chloroplasts
  • both have small prokaryotic 70s ribosomes
  • it’s thought cells englufed bacteria which were then incorporated into the cells
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6
Q

Where does msot photosynthesis occur?

A

Palisade msophyll in upper section of the leaf

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7
Q

What is the function of the upper epidermis

A
  • allows light to reach the mesophyll layers
  • no chloroplasts
  • thin waxy cuticle to protect leaf
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8
Q

What is the function of palisade mesophyll?

A
  • absorbs the majority of light energy for photosynthesis
  • lots of chloroplats
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9
Q

What is the function of spongy mesophyll?

A
  • absorbs light not absorbed by palisade msophyll layer
  • air spaces let CO2 diffuse out and 02 diffues in
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10
Q

What is the function of lower epidermis

A
  • contains guard cells to open + close stomata depending on water availability
  • open stomata for gas exchange
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11
Q

What is the function of the xylem?

A

Transports water + mineral ions to leaf in the transpiration stream

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12
Q

What is the function of the phloem?

A

Transports sucrose form the leaf to other parts of the plant

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13
Q

Explain the structure of chloroplasts (6)

A
  • two membranes
  • fluid-filled called stroma containign rubisco enzyme
  • thylakoid discs tacked up into grana
  • thylakoid membranes contain photosynthetic pigemnts e.g. chlorophyll, ATPsynthase, electron carriers
  • have their own DNA + ribosomes for protein synthesis
  • contain oil droplets used for making/repairing membranes
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14
Q

Explain chloroplast’s DNA + ribosomes

A
  • circular DNA
  • 70s ribosomes
  • DNA contains genes that code for proteins needed for photosynthesis e.g. enzymes ATPase + rubisco
  • ribosomes for protein synthesis
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15
Q

Explain what thylakoids contain

A
  • enzymes: ATPsynthase for making ATP
  • pigment molecules e.g. chlorophyll forming photosystems
  • electron carriers for electreon transport
  • large surface area for light abosorption for light dependant reaction + electron transport
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16
Q

Explain the structure and function of photosytems

A
  • primary pigment at reaction centre - chlorophyll a
  • accessory pigments surround reaction centre - chlorophyll b, cartenoids
  • accessory pigments transfer energy to primary pigments
  • light energy of different wavelengths is absorbed/harvested then passed to reaction centre
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17
Q

Explain the types of chlorophyll a

A

P700
- found in photosystem I
- absorbs 700nm
- mainly found in intergranal lamellae

P680
- found in photosystem II
- absorbs 680nm
- almost exclusively in grana

Chlorophyll a absorbs blue light of wavelength of around 450-480nm

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18
Q

Where are photosystems found?

A

The surface of internal membrane of chloroplasts(grana)

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19
Q

Give key details about accessory details

A
  • chlorophyll B: 500nm-640nm
  • carotenoids (absorbs wavelengths chlorophyll doesn’t) 520nm
  • xanthophylls
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20
Q

Explain how seaweeds pigments are different

A
  • contains pigmen ts other than chlorophyll
  • deeper water has lower light intensities
  • only shorter wavelengths can pass through
  • pigments absorb these wavelengths
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21
Q

Give a brief overview of the stages of photosynthesis (5)

A

Light dependent reaction/stage (LDR)
- energy from sunlight absorbed
- ATP made
- hydrogen from water used to form reduced NADP/NADPH

Light independent reaction/stage (LIR)
- hydrogen from reduced NADP + carbon dioxide used to build organic molecules
- ATP needed

22
Q

Give key details of NADP (4)

A
  • coenzyme
  • becomes NADPH by accepting hydrogen
  • reduced NADP carries hydrogen to calvin cycle in stroma
  • important in converting carbon dioxide into glucose
23
Q

Define photophosphorylation (3)

A
  • the making of ATP from ADP and Pi
  • using light energy
  • two types: cyclic + non-cyclic
24
Q

Explain the light independent stage (non-cyclic)

A
  1. Light strikes PSII, exciting 2 electrons which leave chlorophyll and pass down electron carriers
  2. Electrons release energy that pumps hydrogen into thylakoid space
  3. PSII has an enzyme that performs photoslysis of water forming 2H+, 2e-, 1/2 O2
  4. 2e- reduces oxidised chlorophyll in PSII that originally lost electrons
  5. Light hits PSI and excites 2 electrons which leave the chlorophyll and pass down electron carriers
  6. Electrons accepted by NADP
  7. Electrons from PSII replace those lost from PSI
    8.H+ flow through ATP synthase enzyme, creating ATP
  8. H+ along with 2e- from PSI join with NADP to form NADPH
25
Q

Explain the process of cyclic photophosphorylation

A
  1. Light hits PSI and excites 2 electrons trhat leave chlorophyll and pass down electron carriers
  2. Electrons move back through carriers to create ATP
    - no photolysis/no reduced NADP
    - PSII not involved
26
Q

How does weed killer work>

A
  1. It binds to electrons in PSI
  2. This stops non-cyclic + cyclic photophosphorylation
  3. No NADPH can form
  4. So calvin cycle stops
27
Q

Where does the light dependent part take palce?

A

The stroma in the chloroplast

28
Q

Explain the process of the light depenent cycle (calvin cycle)

A
  1. Carbon Fixation: Rubisco enzyme fixes 3 CO2 to the 3 5-carbon RuBPs to form 3 unstable 6-carbon molecules
  2. The 3 6-carbon molecules breaks down into 6 3-carbon molecule GP
  3. ATP used for energy + hydrogen from reduced NADP to convert GP into TP- 6TP Formed
  4. 1 out of 6 TP used to form glucose
  5. 5 remaining TP used to regenerate RuBP
  6. ATP used to convert 5 TP into 3 RuBP
29
Q

What is GP used to produce?

A

Fatty acids + amino acids

30
Q

How does rubisco work/ what else can it do?

A
  • can fit both oxygen and carbon dioxide into its active site
  • as temp increases it works more on oxygen (photorespiration) as it uses o2 and produces CO2, also needing light
31
Q

What is a limiting factor

A

A factor that will limit a rate when at a sub-optimal level

32
Q

Name limiting factors of photosynthesis

A
  • CO2 concentration
  • temperature
  • light intensity
33
Q

Explain how carbon dioxide can be a limiting factor of photosynthesis

A
  • CO2 is fixed by the enzyme Rubisco in the calvin cycle
  • enzyme found in the stroma
  • without CO2 RuBP can’t be cconverted to GP
34
Q

Explain how temperature can be a limit factor of photosynthesis

A
  • temp affects enzyme controlled reations
  • increases rate of reaction until enmzymes denature
  • BUT, photorespiration increases above 25 degrees which reduces rate of photosynthesis
  • even before enzymes denature, rate of photosynthesis may never be as high as it could be due to photorespiation
35
Q

Explain how light intensity can be a limit factor of photosynthesis

A
  • lifht is needed as energy sources
  • as light intensity increases ATP + NADPH are produced at a higher rate
36
Q

Why isn’t water thought of as a limit factor of photosynthesis?

A
  • during dry spells plants undergo water stress
  • close their somatats reduicing water loss + CO2 intake, eventaully stopping photosynthesis
  • water not thought of as limiting factor as plants close stomata before water potential reached low enough level to reduce photosynthesis rate
37
Q

What is compensation point?

A

When respiration = photosynthetic rate
- Carbon dioxide produiction in respiration = carbon dixoide absoprtion in photosynthesis
- No net exchange of CO2 in/out of plant

38
Q

How is rate of photosynthesis measured?

A
  • measure rate of oxygen production (cm3 min-1)
  • measure rate of CO2 uptake (cm3 min-1)
  • increase of dry mass of plant
39
Q

How is oxygen production measured?

A
  • using a photosynthometer
  • sodium hydrogencarbonate used as source of CO2
  • need diameter of capillary tube to get a volume
40
Q

How might results measuring oxygen production from photosynthesis differ from ther actual amount?

A
  • not all O2 collected
  • some O2 used in respiration
  • some dissolved in water
  • seom trapped in air space of leaf
  • air contains nitrogen so bubble might have nitrogen in from air space
  • CO2 as well from respiration and from hydrogen carbonate solution
41
Q

What are limitations of the method and how could they be overcome?

A
  • temp may fluctuate - use thermostatically controlled water bath to keep temp constant
  • ambient light may fluctuate - complete experiment in a room with no ambient light
  • errors with rimings, apparatus, reading meniscus - use gas syringe with data logging equipment for more precise measurement of volume/timing
42
Q

What is hydrogencarbonate indicator used for?

A

Measurses carbon dioxide lewvels in aquatic systems
- becoes more orange with increased CO2 levels
- becomes more purple as CO2 decreases

43
Q

What colour will hydrogencarbonate indicator go in different light levels and why?

A

Bright Light
- rate of photosynthesis > rate of respiration
- decreasing water CO2 concentration
- purple colour

Darker Light
- rate of photosynthesis < rate of respiration
- increasing water CO2 concentratrion
- orange colour

Neutral Light
- rate of photosynthesis = rate of respiration
- water CO2 concentration stays the same
- green colour

44
Q

How does hydrogencarbonate change colour?

A
  • green plants + algae use carbon dixoide - removing it from the indicator during photosyunthesis
  • respiration uses carbon dioxide from the indicator
45
Q

Why might measuring O2 production or CO2 not be accurate?

A
  • O2 only used in light dependent stage of photosynthesisa
  • O2 produced in respiration
  • CO2 only used in light independent stage of photosynthesis
  • CO2 produced in respiration might be used in photosynthesis
46
Q

How can rate of photosynthesis be controlled?

A
  • temperature controlled by heaters, ventilation for optimum enzyme activity
  • light wage length controlled if dark
  • higher light intesnity for more light dependant reaction
  • CO2 controlled by burning fuel - more CO2 fixed in calvin cycle
  • water supply controlled
  • fertilisers + pesticides used
47
Q

Explain the levels of RuBP, TP and GP in bright light

A
  • more light energy avaible to excite electrons
  • more light dependent cycle
  • more ATP + NADP produced for use in calvin cycle
  • more GP reduced to TP
  • more TP regenerate to RuBP
  • high RuBP + TP Levels
  • lower GP levels
48
Q

Explain the levels of RuBP, TP and GP in dark light

A
  • less light energy avaible to excite electrons
  • less light dependent cycle
  • less ATP + NADP produced for use in calvin cycle
  • less GP reduced to TP
  • less TP regenerate to RuBP
  • lower RuBP + TP Levels
  • higher GP Levels
49
Q

How does increased carbon dioxide concentration affect the calvin cycle?

A
  • increases rate of light dependent reaction
  • more CO2 available for CO2 fixation
  • more GP produced
  • lower RuBP levels
  • some GP convereted to fatty acid + amino acids
  • more GP reduced to TP
  • TP levels rise
  • some TP usedd to make glucose
50
Q

How does decreased carbon dioxide concentration affect the calvin cycle?

A
  • can be casued by closed stomata
  • less carbon fixation
  • decreased GP
  • less GP converted to TP
51
Q

How does increased temperature affect the calvin cycle?

A
  • increase rate of photosynthesis
  • enzyme molecules hafve more kinetic energy - more successsful collisions - more ESC formed
  • above 25 oxygenase activity of rubisco increases more than carboxylase activity - rate of photorespiration reduces rate of photosynthesis
  • enzymes denatuer by high temperatures - change 3D shape of enzymes, so no longer complementary to substrate

OCR Biology A Level (21 decks)

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