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N Biology A Level > Topic 5 (Photosynthesis) > Flashcards

Topic 5 (Photosynthesis) Flashcards

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1
Q

What are the 2 stages of photosynthesis? + where

A

Light-dependent stage (occurs in thylakoid membranes)
Light-independent (occurs in stroma)

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2
Q

What are grana joined together by?

A

Lamallae

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3
Q

What is chloroplasts made up of?

A

Grana (stack of thylakoids)
Starch grains
Stroma
Double membrane

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4
Q

Why do plants have different colours?

A

Photosynthetic pigments
Absorb certain wavelengths of light
What we see is what’s being reflected

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5
Q

What are the types of photosynthetic pigments?

A

Chlorophylls (a and b) (blue/green/yellow)
Carotenoids (xanthophyll and carotenes) (yellow/orange)

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6
Q

What is the structure of chlorophyll?

A

Magnesium in the middle
Hydrophilic porphyria ring group (lies flat on surface of thylakoids)(head)
Hydrophobic hydrocarbon chain (attaches to lipid membrane)(tail)

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7
Q

How is energy being absorbed by chlorophyll?

A
  • excites pair of electrons with the Mg
  • pass along electron transport chain
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8
Q

Why is the hydrophilic head lied flat on the thylakoids?

A

To maximise light absorption

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9
Q

How can you tell if a plant is magnesium deficient?

A

Yellow leaves - can’t make enough chlorophyll
Aka chlorosis

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10
Q

What are accessory pigments?

A

Carotenoids
They absorb wavelengths that aren’t well absorbed by chlorophylls and pass energy to chlorophyll a
Reflect yellow and orange light, absorb blue light

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11
Q

Why are there more colours in autumn months?

A
  • cold nights: low temp destroy chlorophyll, enhancing red ccolour
  • dry weather, sugars more concentrated in leaves , hence redder
  • bright sunny days: more anthrocynin
    = more colours like red and orange
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12
Q

What’s a photosystem?

A

Funnel shaped structures
Embedded in thylakoids membranes
Proteins holding them in place

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13
Q

What are the 2 types of photosystem?

A

PS1 AND PS2
wavelength of light they absorb out of visible spectrum of light
(Has a primary pigment reaction centre, at either P680 or P700)

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14
Q

What are PSI AND PSII

A

Photosystem I - absorbs light at 700 nm (found on inter-granal lamallae)
Photosystem II - at 680nm (found on grana)

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15
Q

What are the layers in plants? From top to bottom

A

Waxy cuticle
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Lower epidermis

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16
Q

Why is accessory pigment necessary?

A

Accessory pigments allow energy from light at a wider range of wavelengths to be used in the light-dependent reactions.

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17
Q

Why is the absorption spectrum the shape it is?

A
  • chlorophyll a and b absorb strongly at blue and red ends
  • chlorophyll a peaks at 430nm
  • b peaks at 470
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18
Q

Why are there a variety of pigments in chlorophyll to take up different wavelengths of light?

A

To maximise light absorbed
as greater range of wavelengths can be absorbed

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19
Q

How do you explain the peaks of wavelength absorbed at 680 and 700?

A

P680 - photosystem 2
P700 - photosystem 1

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20
Q

Explain why seaweeds have different absorption spectra and action spectra. (3 marks)

A

Because…
- Each pigment absorbs diff wavelengths
- Diff amounts of wavelengths
- action spectra shows rate of p/s absorbing diff wavelengths of light

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21
Q

Explain why seaweeds occupy different positions of a submerged rock and have different colours. (3 marks)

A
  • positioned differently to reduce competition
  • shallow water seaweeds: cannot absorb green light, so reflects green and looks green. Can absorb red and blue
  • height of diff wavelengths
  • so on
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22
Q

Compare light dependent and independent reactions

A

light dependent / independent
thylakoid / stroma
light needed / not needed
Makes ATP and Red NADP / uses ATP and red NADP

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23
Q

describe the light dependent stage of photosynthesis

A
  • enables photolysis: water split into H+, e- and O
  • light energy is converted into chemical energy in the form of ATP and reduced NADP
    ….
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24
Q

where does light dependent stage of photosynthesis take place

A

across thylakoid membrane

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25
Q

what is NADP

A
  • a type of molecule called a coenzyme
  • role is to transfer hydrogen between molecules
  • When NADP gains hydrogen it becomes reduced NADP / NADPH
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26
Q

what are 2 types of photophosphorylation

A

cyclic
non cyclic

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27
Q

What is chemiosmosis

A

Flow of H+ ions down the conc gradient through ATP synthase

28
Q

where does the light independent cycle take place

A

Stroma of chloroplasts

29
Q

What does rubisco do

A

Combine RuBP and Carbon dioxide
Aka fixation of carbon

30
Q

What are 3 steps of Calvin cycle

A
  1. Carbon fixation
  2. Reduction
  3. Regeneration
31
Q

What is the role of RuBP?

A
  • 5C compound
  • CO2 acceptor
  • found in stroma
32
Q

What is the role of Rubisco?

A
  • enzymes that catalyses the reaction between RuBP and CO2
33
Q

What is GP made from ?

A
  • 3C products of RuBP and CO2
34
Q

What is the role of GALP?

A
  • formed from reduction + photophosphorylation of GP
  • ATP + reduced NADP from light independent reaction used
35
Q

what is photolysis

A

splitting water into H+, e- and O

36
Q

What is NADP and what does it do?

A

NADP is a coenzyme
- transfers hydrogen from one molecule to another
- becomes reduced NADP

37
Q

Describe the (non-cyclic) light dependent stage of photosynthesis

A
  • light hits PSI and PSII
  • e-s excited
  • accepted by e- proton chain
  • takes place in thylakoid membrane
  • flow of H+ thru ATP synthase via chemiosmosis
  • rotates ATP synthase
  • ADP + Pi → ATP
  • movement of e-s from water to PSII
  • replacement of e-s from photolysis
  • NADP + H+ + e-s - → Reduced NADP
38
Q

Describe the cyclic light dependent stage of photosynthesis

A

Light hits PSI
e-s are excited and leave PS
and returns to e- transport chain, e-s rejoin PSI

39
Q

Compare the non cyclic and cyclic photophosphorolation

A

Non cyclic / cyclic
doesnt / e-s come back to same molecule
first e- donor is water / PSI
involves PSI and II / PSI only
last e- acceptor is NADP / PSI
Net products ATP, NADPH, O2 / ATP only
reduction of NADP / no

40
Q

What are NAD and FAD?

A

Coenzymes

41
Q

Coenzymes are not…

A

ENZYMES!!
They just bind to them / help

42
Q

What is the structure of ATP

A

It is a phosphorylated nucleotide
- adenosine (adenine + ribose sugar)
- three phosphate groups (T= triphosphate)

43
Q

What are 2 ways of ATP production

A
  1. Substrate level phosphorylation
  2. Oxidative phosphorylation
44
Q

What is substrate level phosphorylation?

A

Simply
ADP + Pi -> ATP

45
Q

What are some limiting factors for photosynthesis?

A
  • temp
  • light intensity
  • CO2 conc
  • number of chloroplasts
46
Q

Increasing the light intensity will increase the production of which 3 products in the light dependent stage?

A

ATP, reduced NADP, O2

47
Q

Why will the light independent cycle be affected by the level of production from light dependent cycle?

A

More energy from ATP and NADP to reduce GP into GALP, driving cycle forward

48
Q

Why does GP increase in dim light?

A

Less ATP and Red NAPD from LDC to change into GALP

49
Q

Why does increasing CO2 conc lead to more proteins, polysaccharides and lipids being made?

A

More carbon is fixed by rubisco
So more GP = more GALP = more products

50
Q

Why may an increase in CO2 conc lead to the plant wilting?

A

Stomata’s open to increase gas exchange,
To increase rate of transpiration

51
Q

Why does temp have little effect on the light dependent cycle but huge effect on Calvin cycle?

A

Calvin is more dependent on enzyme e.g. Rubisco

52
Q

Above 25C photorespiration occurs, how does this reduce the rate of photosynthesis?

A

When O2 enters Rubisco’s active site, blocking it from fixing carbon
Also wastes ATP and red NADP

53
Q

Increased temp also increases water loss during transpiration. Why does this also then affect photosynthesis?

A

When plants lose too much water, stomata closes, = reduces CO2 intake
= cannot photosynthesise

54
Q

what is an absorption spectrum?

A

graph to show the % of wavelengths of light absorbed by each pigment

55
Q

what is an action spectrum?

A

graph of overall rate of p/s at each wavelength of light

56
Q

what are 2 main groups of photosynthetic pigments?

A

chlorophyll (a and b)
carotenoids (carotene and xanthophylls)

57
Q

where are photosynthetic pigments found

A

thylakoid membrane of chloroplasts

58
Q

what are roles of chlorophyll a and b?

A

a- primary photosynthetic pigment
b- accessory pigment

59
Q

why do plants have such a variety of photosynthetic pigments?

A

to widen range of wavelengths they absorb to maximise light absorption hence max rate of p/s

60
Q

what does light do in photosynthesis?

A

excites e-s , causing release from chlorophyll
then they go in the e- transport chain

61
Q

how is ATP produced? (in terms of chemiosmosis)

A

H+ ions move down the conc gradient from thylakoid into stroma, spinning the ATP synthase
ADP+Pi -> ATP

62
Q

What does NADP act as in non-cyclic photophosphorylation?

A

final e- acceptor

63
Q

what are the purposes of cyclic and non-cyclic photophosphorylation?

A

cyclic: produce ATP
non: produce ATP and Red NADP

64
Q

what are e-s used for in photophosphorylation when they are produced from photolysis?

A

replaces e-s lost from chlorophyll

65
Q

what is needed to convert GP into GALP?

A

2 Red NADP -> 2x NADP +
2 ATP -> 2 (ADP+Pi)

66
Q

Explain why a wider/more stomata increases their yield. (3 marks)

A
  • more carbon dioxide intake to be fixed
  • faster rate of photosynthesis so more GALP produced in Calvin cycle and more biomass produced
  • increased rate of transpiration also
  • so more Mg for chlorophyll
67
Q

Why does the thylakoid have higher pH than stroma, and what is the significance?

A

Energy from an e- transport chain is used to actively transport protons from the stroma to the thylakoid lumen
So that more H+ can be used to produce more ATP via chemiosmosis through the ATP synthase as it travels from a higher to lower H+ concentration.

N Biology A Level (18 decks)

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