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Life of Earth 2 > Leaves & photosynthetic pathways > Flashcards

Leaves & photosynthetic pathways Flashcards

1
Q

What are the main parts of a leaf?

A 
Blade =
>apex
>margin
>vein
>base

Petiole
Axial bud
Stipule

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2
Q

Which fibres strengthen the leaf?

A

Sclerenchyma

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3
Q

What does the spongy mesophyll contain?

A

Xylem + phloem surrounded by bundle sheath cells

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4
Q

What is phyllotaxy?

A

Leaf arrangement

- efficiently distributing leaves to reduce overlap and maximise light capture

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5
Q

What type of phyllotaxy do most angiosperms have?

A

Alternate phyllotaxy

= leaves arrange din ascending spiral around stem - each leaf emerging 137.5 degrees from the previous one

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6
Q

What are the 3 general types of dicotyledonous leaves?

A

Simple
Compound
Doubly compound

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7
Q

How do veins differ in monocots & dicots?

A

Monocots: parallel veins

Dicots: branched network of major veins

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8
Q

During the redox reaction of photosynthesis, which compound is reduced and which is oxidised?

A

CO2 reduced into glucose

H2O oxidised into O2

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9
Q

Chlorophyll absorbing light results in what?

A

Water splitting into protons + electrons

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10
Q

How many protons + electrons are transferred to NADP+?

What is produced?

A

1 proton + 2 electrons

NADPH
reduced NADP

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11
Q

Light energy is initially converted into chemical in the form of which 2 compounds?

A

NADPH
= source of electrons as ‘reducing power’ that can be passed on to another electron acceptor

ATP
by photophosphorylation of ADP

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12
Q

Photosynthesis is made of which 2 reactions?

A

Light reaction

Calvin cycle

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13
Q

What is the main objective of the Calvin cycle?

A

Forms sugar (G3P) from CO2 using ATP + NADPH

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14
Q

What do photosynthetic pigments do?

A

Absorb light

- diff pigments absorb diff wavelengths

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15
Q

What happens to wavelengths that aren’t absorbed?

Give an example.

A

Reflected

Green (500-600nm) = why plants are green

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16
Q

What is the main photosynthetic pigment?

What are the 2 accessory pigments?

A

Chlorophyll a

> Chlorophyll b - broadens spectrum for photosynthesis

> Carotenoids - absorb excessive light that would damage chlorophyll

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17
Q

Describe the excitation of chlorophyll by light

A
  1. chlorophyll absorbs light
  2. energy from absorbed photons excites electrons
  3. electrons move from ground state = unstable
  4. electrons drop back to ground state releasing heat/light
18
Q

What are light-harvesting systems made up of?

What function do they carry out?

A

chlorophyll a, chlorophyll b + carotenoids bound to proteins

transfer photon energy to reaction centre

19
Q

What is the reaction centre?

A

An organised association of proteins holding a special pair of chlorophyll a molecules

20
Q

Describe how a photosystem harvests light

A
  1. photon excites electron in pigment
  2. energy transferred through other pigments
  3. excited electron transferred to special pair of chlorophyll a molecules in reaction centre
  4. pass excited electron to primary electron acceptor - becomes reduced
21
Q

What are the 2 photosystems and the wavelengths they absorb?

A

PS II = 680nm

PS I = 700nm

22
Q

What happens in PS II once an electron is passed from the P680 chlorophyll a to the primary electron acceptor?

A

P680 with a missing electron
= P680+
(has an electron hole)

23
Q

An enzyme then catalyses the photolysis of what…?

A

H2O
–>
2 e + 2 H+ + 1/2 O2

24
Q

What are the products of the photolysis of water used for?

A

Electrons supplied to the P680+ –> replacing those passed to primary electron acceptor

H+ released into thylakoid lumen

O atom immediately combines w/ another O atom

25
Q

What is the 1st ETC made up of?

A

> Plastoquinone
a cytochrome complex
Plastocyanin

26
Q

What happens as electrons pass through the cytochrome complex?

A

H+ (protons) are pumped into thylakoid lumen

–> contributes to proton gradient used in chemiosmosis

27
Q

What happens in PS I when P700 transfers an excited electron to the primary electron acceptor?

A

P700 converted to electron deficient form = P700+

electrons replaced via ETC

28
Q

What is the 2nd ETC made of?

A

Ferredoxin

29
Q

What does NADP+ reductase do?

A

Catalyses the transfer of e from ferredoxin to NADP+

30
Q

What happens in the conversion of NADP+ to NADPH?

A

2 electrons required for the reduction

Removes 1 H+ from stroma

31
Q

What are the 3 main phases of the Calvin cycle?

A
  1. Carbon fixation (using Rubisco)
  2. Reduction
  3. Regeneration of RuBP
32
Q

What is the sugar produced in the Calvin cycle?

A

G3P = glyceraldehyde 3-phosphate

33
Q

What happens in hot, arid environments?

These conditions favour what process?

A

Stomata close
–> O2 builds up

photorespiration

34
Q

What happens in photorespiration?

A

Rubisco adds O2 instead of CO2 in the Calvin cycle

–> produces 2-C compound

35
Q

Why isn’t photorespiration good?

A

Consumes O2 + organic fuel
Releases CO2
Doesn’t produce ATP or sugar

36
Q

Why might photorespiration be an evolutionary relic?

A

Rubsico 1st evolved at a time when atmosphere had much less O2 + more CO2
It limits damaging products of light reactions that build up in absence of Calvin cycle

37
Q

Why are C4 plants special?

A

Minimise cost of photorespiration by incorporating CO2 into 4C compounds in mesophyll cells.

  • -> 4C compounds exported to bundle-sheath cells
  • -> release CO2 for Calvin cycle
38
Q

Which enzyme do C4 plants need?

A

PEP carboxylase

- higher affinity for CO2 than Rubisco

39
Q

What do CAM plants do?

A

Use crassulacean acid metabolism to fix carbon

  1. Open stomata at night
    - -> incorporate CO2 into organic acids
  2. Close stomata in day
    - -> CO2 released & used in Calvin cycle
40
Q

What are the pros of C4 plants?

A

Beneficial in high light, low nutrient envrios as require less Rubisco

41
Q

What are the cons of C4 plants?

A

Regeneration of PEP in C4 pathway requires more ATP than in C3 photosynthesis
–> bad for low light enviros

42
Q

What are CAM plants usually associated with and why?

A

Succulence & low photosynthetic capacity

As photosynthesis is proportional to vacuolar storage

Life of Earth 2 (20 decks)

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