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Biology (Grade 12) > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

For the carbon fixation in the calvin cycle, how many turns of the cycle is needed to make 1 glucose molecule?

A

2

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2
Q

What electron carriers/complexes are involved in the electron transport chain for light-dependent reactions?

A

Primary electron acceptor
↓
plastoquinone (PQ)
↓
b6f complex
↓
plastocyanin (PC)

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3
Q

How much NADPH and ATP is made for every 2 electrons that pass through the electron transport chain for light-dependent reactions

A

1 NADPH and 1ATP is made by ATP synthase complex

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4
Q

When is a proton gradient created in the light-dependent reactions?

A

by the b6f complex in the ETC and the splitting of water

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5
Q

part of a leaf: chloroplasts are abundant, location of most of photosynthesis

A

palisade mesophyll cells

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6
Q

Where do light-dependent reactions take place

A

in the thylakoid

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7
Q

protein-rich semiliquid material in the interior of chloroplast

A

stroma

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8
Q

what enzyme is involved in photorespiration

A

rubisco

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9
Q

For reduction reactions of the calvin cycle, how many NADPH are needed for every 6 CO2

A

12

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10
Q

What is photoexcitation

A

electrons in chlorophyll molecules are initially at ground state however when a molecule absorbs a photon, one of the electrons is elevated to an orbital where it has more potential energy

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11
Q

What’s the purpose of the Calvin cycle?

A

to make glucose

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12
Q

part of a leaf: regulates exchange of CO2 and O2, allow water to escape by transpiration AND allows CO2 to diffuse into air spaces within the leaf’s mesophyll layers

A

stomata (stoma for singular)

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13
Q

What is photophosphorylation?

A

synthesizing ATP in the presence of light

ADP is phosphorylated in the stroma using light energy from photons

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14
Q

What is transpiration?

A

water loss; the evaporation of water from leaves

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15
Q

How might transpiration be harmful to a plant?

A

can cause dehydration; conditions that promote transpiration can cause guard cells to reduce the size of stomata

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16
Q

What are the 4 main stages of the light-dependent reactions?

A
  1. Photoexcitation (p680)
  2. Electron Transport Chain (chemiosmosis)
  3. Photoexcitation (p700)
  4. Splitting of Water
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17
Q

part of a leaf: creates openings called stomata

A

guard cells

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18
Q

unstacked thylakoids between grana

A

lamellae

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19
Q

Are the stomata open or closed during the day? Why is this so?

A

open; to ensure CO2 is available to the chloroplasts for photosynthesis

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20
Q

part of a leaf: transports water, minerals, carbohydrates

A

vein/vascular bundle

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21
Q

What is the final electron acceptor in light-dependent reactions?

A

NADP+

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22
Q

c4 plants: what is the role of bundle sheath cells? how do they help to limit the degree of photorespiration?

A

bundle-sheath cells are impermeable to CO2; as a result, CO2 is concentrated in the bundle-sheath cells where the calvin cycle takes place
~ this high CO2 concentration makes the Calvin cycle much more efficient than in C3 plants

23
Q

Describe the steps of the Calvin cycle.

A

PHASE 1: Carbon Fixation
~ CO2 joins to Ribulose 1,5 - bisphosphate (RuBP) to form a 6C intermediate however the intermediate is too unstable and splits into two 3C molecules called 3 - phosphoglycerate (PGA) (THIS IS CATALYZED BY RUBISCO)

PHASE 2: Reduction Reactions
~ 6 3- phosphoglycerate molecules are phosphorylated by ATP to produce 6 molecules of 1,3 - bisphosphoglycerate (ATP turns into ADP)
~ 6 1,3 bisphosphoglycerate molecules are reduced by NADPH to produce 6 molecules of glyceraldehyde-3-phosphate (NADPH turns into NADP+)
~ I molecule of G3P (aka 2 G3P as 2 G3P make 1 glucose) exits the cycle

PHASE 3: Regeneration
~ the remaining 5 G3P molecules are rearranged to form 3 molecules of Ribulose 1,5 -bisphosphate (RuBP)
~ ATP turns into ADP as 3 ATP are used in this process
~ the RuBP is now available to join with the next CO2 in the next cycle

24
Q

Size and shape of the guard cell changes with?

A

water concentration

25
Q

What enzyme catalyzes the calvin cycle?

A

ribulose bisphosphate carboxylase; RUBISCO

26
Q

part of a leaf allows light to pass to mesophyll

A

upper epidermis

27
Q

Describe the consequence of photorespiration in terms of photosynthetic efficiency for plants

A
  • as a result of photorespiration, all of the energy used to regenerate ribulose 1,5 bisphosphate is wasted which reduces the efficiency of photosynthesis
  • atmospheric conditions influence the reduction of efficiency due to photorespiration
  • for ex: in hot conditions, leaves begin to lose water through the stomata; to prevent further loss of water, stomata close and while it is closed, the oxygen formed in the light dependent reactions accumulates inside the leaves and carbon dioxide cannot enter; with this high ratio of oxygen to carbon dioxide, photorespiration increases significantly.
28
Q

What is photorespiration

A

the reaction of oxygen with ribulose 1,5 bisphosphate in a process that reverses carbon fixation and reduces the efficiency of photosynthesis

29
Q

what is C4 photosynthesis

A

C4 plants separate the initial uptake of carbon dioxide from the Calvin cycle into different types of cells

ex. corn

30
Q

What enzyme causes the split of water into 1/2 Oxygen and 2 H+) for light-dependent reactions?

A

z complex

31
Q

What is stomatal closing regulated by in the evening/night?

A

decrease in sucrose in guard cells

32
Q

What is stomatal opening regulated by in the morning?

A

water and K+ ions

33
Q

NADPH and ATP are used in the light independent reactions to fix CO2 into?

A

Glucose

34
Q

part of a leaf: waxy and water resistant, protection

A

cuticle

35
Q

Where do light-independent reactions occur (ex. calvin cycle)?

A

stroma of chloroplast

36
Q

one of the two protein-based complexes composed of clusters of pigments that absorb light energy

A

photosystems

37
Q

Describe the “temporal” adaptation in CAM plants and how the stomata are involved in this adaptation?

A
  • CAM plants like water-storing plants (eg. cactus) use a biochemical pathway like the C4 plants, but the rxns take place in the same
    ~ carbon fixation is separated from the calvin cycle by time of day, rather than by different cell types
  • for plants that thrive in hot, desert conditions, their stomata remain CLOSED during the day and OPEN and night to prevent water loss
    ~ CO2 is then fixed while stomata are open
    ~ the rxns proceed until malate is formed which is stored in a large vacuole
    ~ malate exits the vacuole & is decarboxylated, freeing the CO2 which is then fixed again by rubisco and enters the Calvin cycle (when enough ADP and NADPH is made by light dependent rxns)
38
Q

What are the 3 main stages of Light independent reactions (calvin cycle)?

A
  1. Carbon Fixation –> 2 turns of the cycle are needed to make 1 glucose molecule
  2. Reduction Reactions –> requires 12 NADPH for every 6 CO2
  3. RuBP Regeneration –> enzymes convert G3P into RIbulose 1,5 Bisphosphate
39
Q

Describe the light-dependent reactions in detail.

A
  1. Photoexcitation (p680)
    ~ two photons strike photosystem II and excite 2 electrons from chlorophyll p680
    ~ the excited electrons are there captured by a primary electron acceptor and are then transferred to plastoquinone (PQ) and the Electron Transport Chain
  2. Electron Transport Chain (chemiosmosis)
    ~ the 2 electrons pass through a proton pump which transports 4 protons from the stroma into the thylakoid lumen to create a proton gradient
    ~ this electrochemical gradient drives the PHOTOPHOSPHORYLATION of ADP to ATP
    ~ 1 ATP forms for every 4 protons that pass through ATPase
    ~ the electrons then flow to P700 to make ATP
  3. Photoexcitation (p700)
    ~ two photons strike photosystem I and excite 3 electrons from chlorophyll p700 (replaced by electrons from p700)
    ~ these electrons then pass through another ETC (primary electron acceptor → carrier → 2H + NADP+ → NADPH)
    ~ the enzyme NADP reductase uses the 2 electrons and 1 proton from the stroma to reduce NADP+ into NADPH
    ~ NAP+ is the final electron acceptor
  4. Splitting of Water
    ~ a z protein/complex splits water into 2 protons, 2 electrons, and 1 oxygen atom
    ~ the protons remain in the thylakoid space to add to the proton gradient
    ~ oxygen leaves as a byproduct
    ~ electrons are used for replacement to p680+
40
Q

C4 photosynthesis: what happens in the mesophyll cells?

A

POMCPP

  • In the outer layer of mesophyll cells, carbon dioxide is fixed by addition to phosphoenolpyruvate (PEP).
  • This forms the product oxaloacetate which is then converted to malate and transported into the bundle sheath cells
  • In the bundle sheath cells, malate is decarboxylated.
  • The resulting pyruvate is transported back into the mesophyll cells and converted into phosphoenolpyruvate (PEP)
41
Q

C4 photosynthesis: what is the product of carbon fixation

A

oxaloacetate

42
Q

Describe the idea of stomata and electrochemical gradient.

A
  • blue light activates receptors that stimulate proton pumps to actively drive protons out of guard cells
  • this creates a H+ ion gradient
  • the electrochemical gradient causes K+ ions to diffuse into the guard cells and water then follows by osmosis
  • as the guard cells fill up with water and swell, they open due to a thicker cell wall on the inner side
43
Q

What are carotenoids?

A

a large class of pigments which absorb blue and green light, making them yellow, orange, and red in colour.

44
Q

Where does photosynthesis occur

A

in the chloroplast

45
Q

How might transpiration be helpful to a plant?

A
  • creates a transpiration pull that helps to move water, minerals, and other substances upwards
  • produces an evaporative cooling effect that PREVENTS OVERHEATING
46
Q

membrane-bound, flattened sacs that stack to form granum (columns)

A

thylakoid

47
Q

What do chlorophyll molecules contain (in terms of structure)? Describe.

A

a porphyrin Ring and a phytol tail

Porphyrin Ring: magnesium ion in the centre, surrounded by hydrocarbon ring. This ring contains the electrons that absorbs light energy

phytol tail: hydrocarbon tail that anchors the molecule to a membrane

48
Q

What is a pigment?

A

a compound that absorbs certain wavelengths of visible light while reflecting others.

49
Q

What is cyclic phosphorylation?

A

** only happens in photosystem I
~ allows chloroplasts to make more ATP to drive the light-independent reactions
~ however, this does not release electrons to generate NADPH and without NADPH, carbon fixation cannot occur

50
Q

Briefly outline the relationship between beta-carotene, vitamin A and retinal

A

Beta carotene is a pigment/carotenoid responsible for the orange colour of carrots. It can be converted into vitamin A which can then be converted into retinal which is the visual pigment in our eyes

51
Q

Why are plants green?

A

Chlorophyll absorbs blue and red light while reflecting green light, making the plants green in colour

52
Q

Describe the role of the reaction centre and antenna complex

A
  • the antenna complex includes all the surrounding pigment molecules that gather light energy
    ~ transfers light energy to the reaction centre
  • the reaction centre is a complex of proteins and chlorophyll a molecules
    ~ when a reaction centre has recieved energy from the antenna complex, an electron becomes excited and is raised to a higher energy level
53
Q

What is the value of accessory pigments?

A

pigments expand light absorption, protect chlorophyll from damage, and transfer absorbed energy to chlorophyll for photosynthesis.

Biology (Grade 12) (8 decks)

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