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biology paper 2 > 3.5.1 photosynthesis > Flashcards

3.5.1 photosynthesis Flashcards

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1
Q

write the photosynthesis equation

A

6CO2 + 6H2O ——– C6H12O6 + 6O2

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2
Q

describe the site of photosynthesis

A

the dicotyledon leaf is the main photosynthetic structure in eukaryotic plants

chloroplasts are the cellular organelles where photosynthesis takes place

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3
Q

describe the structure of the leaf and the adaptations present

A
  • large SA that absorbs as much sunlight as possible
  • an arrangement of leaves on the plant that minimises overlapping and so avoids the shadowing of other leaves
  • thin - more light absorbed
  • diffusion distances are short
  • transparent cuticle to let light through to the photosynthetic mesophyll cells
  • long, narrow and upper mesophyll cells packed with chloroplasts collect sunlight
  • numerous stomata for gas exchange so that all mesophyll cells
  • air spaced in the lower mesophyll layer to allow rapid diffusion
  • network of xylem that brings water to leaf cells
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4
Q

3 main stages of photosynthesis

A
  1. capturing of light energy = by chloroplast pigments such as chlorophyll
  2. light dependant reactions = some of the energy is absorbed and converted into chemical bonds
    electron flow is created by the effect of light in chlorophyll, causing water to split (photolysis) into protons, electrons and oxygen
    products: NADP, ATP and O2
  3. light independent reactions = hydrogen ions (protons) are used to produce sugars and other organic molecules
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5
Q

what is the structure and role of chloroplasts?

A

typically disc shaped

2-10um long and 1um in diameter

surrounded by double membrane inside:
- grana = stacks of 100 disc like structures called thylakoids, where light dependent stage of photosynthesis takes place

  • thylakoids = hold photosynthetic pigments (chlorophyll)
    some thylakoids have tubular extensions that join up with the thylakoids in adjacent grana (inter granal lamellae)
  • stroma = fluid filled matrix where light independent reactions of photosynthesis takes place
    also starch grains

MEMBRANE PROVIDES A LARGE SA FOR LIGHT ABSORBTION
MAY CONTAIN MULTIPLE COPIES OF CIRCULAR DNA TO MAKE THEIR OWN PROTEINS
MADE IN CYTOSOL

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6
Q

describe photosynthetic pigments

A

as light meets it may be reflected, transmitted, absorbed

pigments are substances that absorb visible light, different pigments absorb different wavelengths

colour we see is the colour that is reflected/ transmitted

CHLOROPHYLL ABSORBS RED ANS BLUE LIGHT WHISLT REFLECTING/TRANSMITTING GREEN LIGHT

MAINLY CONSISTS OF CHLOROPHYLL A, HOWEVER THERE ARE CHLOROPHYLL B, ORANGE AND YELLOW CAROTENOIDS

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7
Q

how do plants harness energy from sunlight?

A

through photosynthetic pigments

mainly chlorophyll a (main photosynthetic pigment)

accessory pigments = chlorophyll b + carotenoids

CHLOROPHYLL A = MG IN MIDDLE

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8
Q

how is the absorption spectra made?

A

made by putting a solution of a pigment in a spectrophotometer

spectrophotometer = measures ability of pigment to absorb certain wavelengths

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9
Q

what is an action spectra’s function?

A

shows how different wavelengths of light affecting the rate of photosynthesis

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10
Q

describe light dependant reactions, on thylakoid membranes

A

light energy is required for these and pigments which absorb certain wavelengths of light

ATP AND REDUCED NAPD IS PRODUCED

water is split (photolysis) and O2 is produced

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11
Q

describe light independent reactions, stroma

A

involves reduction of CO2 to carbohydrate, using ATP

reduced NADP is produced in light dependant reactions

OILRIG

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12
Q

what are photosystems?

A

arranged in light harvesting cultures called photosystems, imbedded into thylakoid membranes

accessory pigments (chlorophyll b) pass light energy to a primary pigment

PHOTOSYSTEMS I P700 = CONTAINS A PRIMARY PIGMENT WITH A PEAK ABSORBTION AT 700NM

PHOTOSYSTEM II P680 = CONTAINS A PRIMARY PIGMENT WITH A PEAK ABSORPTION AT 680NM

REACTIONS HAPPEN AT CHLOROPHYLL A, OTHERS PASS TO CHLOROPHYLL A

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13
Q

photoionisation + photo phosphorylation

A

light is absorbed, a pair of excited electrons are emitted (photoionisation) from chlorophyll in both photosystems

from photosystem II they pass to electron acceptors and then along chains of electron carriers in a series of REDOX reactions

energy is lost as electrons as they pass from carrier to carrier to produce ATP

CHEMIOSMOTIC THEORY

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14
Q

photolysis

A

photosystems are left positively charged

photosystem 1 absorb electrons from photosystem II

photosystem II gains electrons from photolysis of water by water splitting enzyme

H2O ——- 2H+ + 2e- + 1/2 O2

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15
Q

how is NADP reduced?

A

hydrogen ions from photolysis combine with electrons from photosystem 1 and NADP to give reduced NADP

2H+ + 2e- + NADP ——– REDUCED NADP

NADP AND ATP ARE USED IN LIGHT INDEPENDENT REACTIONS

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16
Q

synthesis of ATP - chemiosmosis

A

as electrons pass from one electron carrier to the next, energy is released which is used to pump proteins across the thylakoid membrane into the thylakoid space

creates a electrochemical gradient (proton motive force) across the thylakoid membrane

protons can flow back into the stroma through an enzyme which spans the membrane - ATP SYNTHASE

flow of three protons allows the production of one ATP from ADP and organic phosphate

17
Q

discuss light independent reactions

A

occur in the stroma

calvin cycle

each step is catalysed by different enzymes: rate, temp and enzyme dependent

use ATP and reduced NADP made in light dependent reaction

18
Q

describe the process of light independent reactions (calvin cycle)

A
  1. carbon dioxide diffuses into the stroma of the chloroplast
  2. CO2 combines with an acceptor molecule that fixes it in place = carbon fixation
  3. 5 carbon sugar called ribulose biphosphate RuBP
    enzyme ribulose biphosphate carboxylase RUBISCO catalyses this reaction
  4. new 6 carbon product splits into glycerate 3 phosphate GP
    ATP and reduced NADP is reduced to triose phosphate TP
  5. rest is regenerated in RuBP, regenerates store

IMPORTANT DIAGRAM

19
Q

what organic substances are formed during photosynthesis?

A

glucose

sucrose

starch for storage

cellulose for cell wall construction

amino acids + lipids

20
Q

main limiting factors

A

light intensity

carbon dioxide

concentration

temperature

chlorophyll

21
Q

how much C02 is in the atmosphere?

A

0.04% CO2 in atmosphere

burning fossil fuels, clearing up rainforests increases this

22
Q

what is the compensation point?

A

rate of photosynthesis is measured by volume of O2 released by plants/ volume of CO2 taken up by plant

light intensity = volume of oxygen produced + CO2 absorbed is exactly balanced by O2 absorbed + CO2 is produced in cellular respiration

no net exchange of gases - light compensation point

RATE OF PHOTOSYNTHESIS = RATE OF RESPIRATION
AMOUNT OF CO2 USED = AMOUNT OF CO2 PRODUCED
AMOUNT OF O2 USED = AMOUNT OF O2 PRODUCED

IMPORTANT DIAGRAM IN NOTES

23
Q

how is photosynthesis measured?

A
  1. apparatus is set up, taking care not to introduce any air bubbles into it and the apparatus is completely air tight
  2. the water bath is used to maintain a constant temperature throughout the experiment and can be adjusted necessary
  3. potassium hydrogen carbonate solution is used around the plant to provide a source of carbon dioxide
  4. a source of light, whose intensity can be adjusted, is arranged close to the apparatus, which is kept in an otherwise dark room
  5. apparatus is kept in the dark for two hours before the experiment
  6. light source is switched on and the plant left for 30 minutes to allow air spaces in the leaves to fill with oxygen
  7. oxygen released by the plant during photosynthesis collects in the funnel end of the capillary tube above the plant
  8. after 30 minutes this oxygen is drawn up the capillary tube by gently withdrawing the syringe until its volume can be measured and calibrated by mm3
  9. gas is drawn up the syringe, which is depressed again, before the process is repeated at the same light intensity four or five times
    MEAN VOLUME IS CALCULATED PER HOUR
  10. apparatus is left in the dark for 2 hours before the procedure is repeated with the light source set a different light intensity
24
Q

what is practical 7?

A

chromatography of photosynthetic pigments

25
Q

what is the purpose of chromatography?

A

to separate different components in a sample

26
Q

state the factors affecting the rate of migration of different pigments

A

solubility
mass
affinity to the paper

27
Q

what is the formula of the RF value?

A

distance moved by pigment / distance moved by solvent

28
Q

what is the purpose of finding the RF value of a pigment?

A

Experimental RF value can be compared to a standard value in a database to identify the pigment.

The standard value should be measured using the same paper and solvent.

29
Q

outline the procedure of using chromatography to separate photosynthetic pigments

A
  1. Draw a horizontal pencil line 1cm above the bottom of the filter paper.
  2. Add some acetone and use the mortar and pestle to grind up the leaf sample and release the pigments.
  3. Use a capillary tube to transfer the pigment onto the pencil line.
  4. Suspend the paper in the solvent so that the level of the liquid does not lie above the pencil line and leave the paper until the solvent has run up the paper to near the top.
  5. Remove the paper from the solvent and draw a pencil line marking where the solvent moved up to.
  6. Calculate the Rf value for each spot.
30
Q

state the hazards and precautions in practical 7?

A

solvents are irritant and flammable

keep away from naked flames, wear eye protection and avoid constant with skin

leaf extract may be a biohazard
wash hands after use

31
Q

what is practical 8?

A

dehydrogenase activity in chloroplasts

32
Q

what is the function of dehydrogenase in chloroplasts?

A

it catalyses the acceptance of electrons by NADP in the light dependant reactions

33
Q

what is the purpose of DCPIP?

A

it is a redox indicator dye and acts as an alternative electron acceptor instead of NADP

TURNS BLUE TO COLOURLESS WHEN REDUCED

34
Q

why is the plant extract chilled in an ice-water bath?

A

to lower the activity of enzymes to prevent them from breaking down the chloroplasts

35
Q

how is the control set up?

A

fill a cuvette with chloroplast extract and distilled water

36
Q

how is light intensity controlled?

A

adjust the distance of the lamp from set up

perform the practical in a dark room so that light source is the lamp

37
Q

what is the function of the muslin cloth?

A

to filter out any debris in the ground leaf mixture but allowing chloroplasts to pass through

38
Q

why are the stalks of leaves removed before grinding?

A

the stalks do not contain many chloroplasts

39
Q

outline the procedure of investigating the effect of light intensity, after chloroplast extract has been obtained

A
  1. Set the colorimeter to the red filter. Zero using a cuvette containing chloroplast extract and distilled water.
  2. Place test tube in the rack 30cm from light source and add DCPIP.
    Immediately take a sample and add to cuvette. Measure the absorbance of the sample.
  3. Take a sample and measure its absorbance every 2 minutes for 10 minutes.
  4. Repeat for different distances from lamp up to 100 cm.

biology paper 2 (12 decks)

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