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A2 BIOLOGY > photosynthesis > Flashcards

photosynthesis Flashcards

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1
Q

what is photosynthesis

A

the process by which carbohydrates are synthesised from carbon dioxide and water using light energy

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2
Q

where does photosynthesis take place

A

in the chloroplast

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3
Q

draw and label a chloroplast

A

-outer membrane
-inner membrane
-stroma
-granum (stack of thylakoids)
inter-grana; thylakoid/lamella
starch grain
lipid droplet
ring of DNA

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4
Q

adaptions of a chloroplast
4

A
  • stacked thylakoids: increase surface area for light absorption
    -chloroplass are abundant in the palisade layer: this is near the upper surface of the leaf where more light to be captured
    -chloroplast have many grana: large SA for photosynthetic pigments, electron carriers and ATP synthetase involved in photosytnesis
    -they can move around within palisade mesophyll cells to optimise light absorption by the thylakoids
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5
Q

draw and label angiosperm

A
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6
Q

where is the main site of photosynthesis in plant leaves

A

palisade mesophyll cells/tissues

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7
Q

what part of the leaf has the most chloroplast

A

top of the leaf
in the palisade cells

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8
Q

why are chloroplasts often described as transducers

A

can be called ‘energy transducers’ because they change energy from one form into another
they turn the energy in photons of light into chemical energy which is incorporated into molecules like glucose

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9
Q

adaptions of leaves for photosynthesis

A

-leaf is thin so light penetrates through the leaf, there is a short diffusion distance for carbon dioxide to travel from the stomata to the palisade mesophyll cells
- the cuticle and upper epidermis are transparent which allows light to pass through to chloroplasts in the mesophyll layers of the leaf
-spongy mesophyll layer contains loosely packed cells with air spaces between them to allow the diffusion of carbon dioxide to photosynthesising cells in the leaf

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10
Q

what do plants do to absorb as much light energy as possible

A

they have a variety of different pigments in their chloroplast

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11
Q

what is a photosynthetic pigment

A

is a chemical substance that is present in chloroplasts to absorb the light energy necessary for photosynthesis

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12
Q

2 groups of photosynthetic pigments found in green plants

A

chlorophyll
carotenoids

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13
Q

2 types of chlorophyll
(green and in all green plants)

A

a
b

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14
Q

carotenoids..

A

carotene (orange and in all plants)
xanthophyll (yellow and in most plants)

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15
Q

where are photosystems found

A

embedded in the thylakoid membrane

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16
Q

what is an absorption spectrum

A

a graph to show the absorbance of different wavelengths of light by a pigment

17
Q

what is an action spectrum

A

a graph to show the rate of photosynthesis at different wavelengths of light

18
Q

relationship between the two graphs

A

very Similar shape proves link between absorption of light energy by pigment and the process of photosynthesis
more absorption of light=faster the rate of photosythesis

19
Q

what do the peaks of the graph in absorption spectra show

A

show the wavelengths that are almost totally absorbed

20
Q

what do the troughs show in absorption spectra

A

none of the pigments absorb light particularly strongly instead they reflect it

21
Q

describe what Theodor Engelmann found

A
  • placed motile and aerobic bacteria and long strand of a photosynthetic alga on a microscope slide. he illuminated the slide using light that had travelled through a prism
    -bacteria clustered at point where the most oxygen was produced (where the greatest rate of photosynthesis was: action spectrum)
    -showed the wavelengths shone on those areas are the most efficient for photosynthesis (similar to absorption spectrum)
22
Q

what are the 2 stages of photosynthesis

A

light dependent stage
light independent stage

23
Q

what’s light-dependent stage

A

absorbs light energy producing ‘excited high-energy electrons. energy from these is used to power proton pumps and produce ATP

24
Q

what’s light-independent stage

A

takes the products of the light-dependent stage (ATP and reduced NADP) ties carbon dioxide and reduces it, forming glucose

25
Q

what are photosystems used for

A

to show energy from a board range of wavelengths, absorbed by an antenna complex of accessory pigments, is ‘funnelled down’ to a reaction centre

26
Q

examples of accessory pigments

A

chlorophyll b an carteroids

27
Q

what does the antenna complex contain

A

many different light absorbing pigments

28
Q

what does a reaction centre contain

A

a pair of chlorophyll a molecules

29
Q

explain photophosphorylation

A

-electrons (lost from the reaction centre) pass along a chain of electron acceptors which power a H pump that carries a H+ ion from the storm to the thylakoid lumen
-the H+ ion will eventually diffuse down a conc gradient back into the storm through an ATP synthetase enzyme molecule and generate some ATP
-the energy to move H+ ions across the membrane before they formed ATP came originally from light, so this process in known as photophosphorylation

30
Q

what are the 2 separate photosystems

A

photosystem 1 and photosystem 11

31
Q

difference between 2 photsystes
(chlorophyll a)

A

chlorophyll a molecules absorb at slightly different wavelengths PSI at 700nm and PSII at 680nm

32
Q

explain the cyclic pathway

A

PSI will lose high-energy electrons to electron acceptors which will generate a single molecule of ATP as the pass along the ETC before returning to the PSI

33
Q

explain non-cyclic pathway

A

involves electrons lost from PSII
electrons pass to an electron acceptor and along the ETC in the same way as those from PSI but these electrons don’t return to the photosystem they started at instead they end up in PSII

34
Q

where will the electrons that originated in PSII end up

A

leaving the z-scheme
they will pass from PSII to an electron acceptor and then leave b being accepted by a molecule of NADP

35
Q

what happens to the electrons lost from PSI

A

will eventually be replaced wither by electrons from itself or by electrons that have come from PSII

36
Q

problem with PSII

A

continually losing its electrons to PSI it needs these electrons to be replaced otherwise it will run short and photophosphorylation will stop
the electrons that replace those lost to PSI come from water in a process called photolysis

37
Q

what does photolysis involve snd what does it generate

A

water being split
-an oxygen atom that will eventually form molecular oxygen
-2 electrons that will replace those lost from PSII
-2H+ ions

A2 BIOLOGY (4 decks)

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