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Biology A Level Unit 3 > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

Photosynthesis definition

A

Process whereby plants (+ some other organisms) synthesise carbohydrates from CO2 and water using light energy as an energy source

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2
Q

Photosynthesis equation

A

6CO2 +6H2O –> C6H12O6 + 6O2

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3
Q

Site of photosynthesis

A

Organ - leaf, tissue - palisade mesophyll layer, cell - palisade mesophyll cells, organelle - chloroplasts

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4
Q

Adaptations for photosynthesis

A
  • Thin leaf - short diffusion distance for CO2
  • Transparent cuticle + upper epidermis - light passes through
  • Air spaces in spongy mesophyll - CO2 diffuses easily
  • Chloroplasts in palisade mesophyll layer - absorbs lots of light
  • Chloroplasts contain many grana - carry ATP synthetase for ATP synthesis
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5
Q

Main photosynthetic pigments found in grana of chloroplasts

A

Chlorophyll a
Chlorophyll b
Beta carotene *
Xanthrophyll *

*carotenoids

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6
Q

Function of photosynthetic pigments

A

Absorb photons of light energy

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7
Q

Results of Englemann’s experiment

A

-Motile bacteria clustered near chloroplasts at blue + red wavelengths as these wavelengths increased photosynthesis by the alga producing more oxygen for bacteria to use for aerobic respiration

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8
Q

Absorption spectra

A

Graph that shows how much light energy is absorbed (by plant pigments) at different wavelengths

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9
Q

Action spectra

A

Graph that shows the rate of photosynthesis at different wavelengths

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10
Q

Relationship between absorption spectra + action spectra

A

Similar shape, suggests light absorbed by pigments allows photosynthesis to occur

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11
Q

Why do plants appear green?

A

Plant pigments don’t really absorb green/yellow wavelengths so it’s reflected back

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12
Q

Advantage to having more than 1 photosynthetic pigment

A

Each pigment absorbs light from a limited part of spectrum so additional pigments allow light from a range of different wavelengths to be absorbed. Increased rate of photosynthesis, more carbohydrates made.

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13
Q

What is a photosystem for?

A

‘Light harvesting’

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14
Q

Photosystem

A

Funnel shaped light harvesting cluster of photosynthetic pigments held in place by proteins in thylakoid membrane (antenna complex). Primary pigment in reaction centre is chlorophyll a. Accessory pigments = chlorophyll b and carotenoids

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15
Q

Chlorophyll a

A

“Primary” pigment = passed energy from light to subsequent reactions of photosynthesis

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16
Q

Where does light-dependent stage occur?

A

Thylakoid (membrane)

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17
Q

Where does the light-independent stage occur?

A

Stroma

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18
Q

What diagram shows light dependent stage of photosynthesis?

A

Z-scheme

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19
Q

Electron transport chain (ETC)

A
  • Light energy reaches PS2, chlorophyll a emits 2 ‘excited electrons’ leaving chlorophyll a oxidised
  • Electrons raised to higher energy level, electron acceptor accepts
  • Electrons pass along a chain of electron carriers and a proton (H+) pump which generates ATP from ADP (phosphorylation)
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20
Q

What does light-dependent stage consist of?

A
  • Electron transfer through Z-scheme
  • NADP reduction
  • Photolysis of water
  • ATP synthesis by phosphorylation (non-cyclic + cyclic)
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21
Q

Where does NADP production occur?

A

Stroma

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22
Q

Production of NADP

A

Electrons from PS1 may combine with H+ ions (from photolysis of water) and NADPH2 to form reduced NADP

NADPH2 + H+ ions + electrons –> reduced NADP

23
Q

What is photolysis of water?

A

Splitting of a water molecule (light is responsible)

24
Q

Where does photolysis of water occur?

A

Thylakoid space/lumen

25
Q

Uses of photolysis of water

A

Electrons replace those lost in PS2.

Hydrogen ions contribute to higher H+ ion concentration inside the thylakoid. Also used to reduce NADPH2 (in stroma)

26
Q

Photophosphorylation

A

Generate ATP from ADP + Pi

Occurs in chloroplasts during light-dependent reactions

27
Q

What happens to electrons in non-cyclic photophosphorylation?

A

Electrons in PS1 replaced by PS2
Electrons not returned to PS1, chlorophyll left with positive charge neutralised by electrons from PS2, electrons excited to higher energy level by light absorption, electron acceptor picks up, passed down ETC to PS1 (energy down ETC = phosphorylation of ADP)

28
Q

What happens to electrons in cyclic photophosphorylation?

A

PS1 absorbs photons, excites electrons, electron acceptor picks up, passed down energy carriers (energy as electrons pass through ETC phosphorylates ADP to ATP) to PS1

29
Q

Non-cyclic- Source and path of electrons

A

Electrons derived from water

Pass through Z-scheme until end up in reduced NADP

30
Q

Cyclic - Source and path of electrons

A

Electrons derived from PS1

Pass along first ETC and return to PS1

31
Q

Photosystems involved in non-cyclic photophosphorylation?

A

PS1 & PS2

32
Q

Photosystems involved in cyclic photophosphorylation?

A

PS1

33
Q

Is NADP produced in non-cyclic?

A

Yes, electrons from PS1 + H+ ions reduce NADPH2

34
Q

Is NADP produced in cyclic?

A

No, electrons return to PS1 so no reduction

35
Q

Products of non-cyclic

A

ATP, reduced NADP, oxygen

36
Q

Products of cyclic

A

ATP

37
Q

How is ATP synthesised in the chloroplast?

A
  • Photolysis of water produces higher H+ concentration inside thylakoid lumen than in stroma generating a H+ gradient
  • Electrons passed along ETC by electron carriers provide energy for pumping of H+ ions from stroma into thylakoid lumen
  • NADP reduction lowers H+ concentration in in stroma, H+ flow out of thylakoid through protein channels down gradient into stroma providing energy to form ATP from ATP synthetase (on stroma side of protein channels)
38
Q

What diagram shows light independent stage of photosynthesis?

A

Calvin cycle

39
Q

What is the Calvin cycle?

A

A biochemical pathway incorporated by light independent reactions. CO2, energy from ATP and reduced NADP consumed to produce organic chemicals (carbohydrates)

40
Q

Where does Calvin cycle take place?

A

Stroma of chloroplasts

41
Q

Stages of Calvin cycle

A

1) Fixation:
3RuBP + 3CO2 -(catalysed by Rubisco)-> 6Glycerate-3-phosphate
2) Reduction:
6Glycerate-3-phosphate + 6ATP + 6NADPH –> 5G3P (RuP) (to stage 3)
–> 1G3P (2TP) yield to glucose/fructose
3) Regeneration:
5G3P (RuP) +3ATP –> 3RuBP

42
Q

Calvin cycle explained

A
  • CO2 combines with 5C acceptor molecule RuBP catalysed by Rubisco
  • Unstable 6C compound forms, splits into 2 GP molecules. CO2 ‘fixed’ into an organic molecule
  • 2GP modified using energy from ADP and NADP reduction (both from light dependent stage). 2TP (3C carbohydrate) form.
  • Most TP regenerate RuBP via a series of reactions involving more ATP. RuBP regenerated for cycle to continue
  • Some TP makes carbohydrates (glucose, sucrose), lipids, amino acids (after Nitrogen from nitrates added)
43
Q

Calvin’s ‘lollipop’ experiment

A
  • Cultures of Chlorella (green alga) grown in a ‘lollipop’ vessel
  • Radioactive isotope 14CO2 added
  • Algae cultures dropped into hot alcohol at different intervals to instantly prevent further metabolic reactions (kills algae)
  • Identify compounds after each time interval using 2D chromatography. Positions on chromatography using autoradiography. Compounds identified from position of radioactive spots
44
Q

Results of lollipop experiment

A

5secs after 14CO2 added:
-large, dark intense GP spot indicates it’s the first product formed after addition of 14CO2
-smaller sugar phosphate quantities indicates they were produced later
30secs after:
-more sugar phosphates + triode phosphates
-other compounds present indicated by presence of amino acids e.g glycine
-sucrose present

45
Q

Calvin cycle + Calvin’s lollipop experiment - sequence of compounds reveals CO2 path

A
  • First RuBP carboxylated (enzyme Rubisco) to yield a 6C hexose phosphate
  • Hexose phosphate (6C) breaks down into 2Glycerate-3-phosphate (3C)
  • Eventually creates glucose
46
Q

Example of limiting factors of photosynthesis

A

Light intensity, CO2 concentration, temperature

47
Q

Limiting factor definition

A

Limits rate of physical process by being in short supply

48
Q

What can increase CO2 concentration in some algae cells?

A

Carbonic anhydrase

49
Q

Nitrates from soil are a source of Nitrogen used for synthesis of…

A

Amino acids, nucleotides and chlorophyll

50
Q

If a plant is yellow?

A

Plant has chlorosis (Magnesium + Nitrates not synthesised enough chlorophyll)

51
Q

Nitrate deficiency…

A

Hinders cell division causing stilted growth

52
Q

Magnesium used for synthesis of…

A

Chlorophyll

53
Q

Phosphates used for synthesis of…

A

Phospholipids, nucleotides

Biology A Level Unit 3 (8 decks)

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