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PLBI 403 > Midterm 1 > Flashcards

Midterm 1 Flashcards

1
Q

What is diffusion

A

spontaneous movement of solutes from regions of higher to lower concentration

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2
Q

What is osmosis

A

diffusion of water across a selectively permeable barrier

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3
Q

What is free-energy

A

represents the potential for performing work, force x distance, in J mol-1

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4
Q

What is Chemical potential

A

a relative quantitative expression of free energy associated with a substance

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5
Q

What is Water potential

A

the free energy of water per unit volume
the chemical potential of water divided by the volume of 1 mol of water

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6
Q

What are the major factors influencing water potential in plants

A

concentration, pressure, gravity

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7
Q

Water potential equation

A

Yw = Ys + YP + Yg

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8
Q

What is reference state

A

pure water at ambient temperature and standard atmospheric pressure

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9
Q

How do solutes impact water potential

A

Reduce free energy of water by diluting the water
Lower Yw

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10
Q

How does pressure impact water potential?

A

Positive hydrostatic pressure raises Yw

Negative hydrostatic pressure lowers Yw

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11
Q

What is positive pressure called?

A

Turgor

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12
Q

What is negative pressure called

A

Tension

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13
Q

What is the water potential of flaccid cells

A

Negative

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14
Q

Why does water move in and out of cells, or from one plant part to another

A

In response to a water potential gradient

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15
Q

How is the direction of flow determined

A

By Yw gradient (from regions of higher to lower Yw) with rate proportional to magnitude

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16
Q

What else influences the rate of movement?

A

hydraulic conductivity

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17
Q

What do aquaporins do?

A

Provide water-specific channels to facilitate water movement across membranes

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18
Q

How do solutes in, and drying of, soil lower Yw into the negative range

A

by lowering Ys and Yp, respectively

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19
Q

What happens as soil dries?

A

water recedes into intersticies between soil particles

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20
Q

What are root hairs?

A

outgrowths of epidermal cells that increase surface area (represent ~60%)

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21
Q

What happens to water under a curved surface

A

develops a negative YP

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22
Q

What is curvature of air-water surfaces a balance of?

A

Minimizing surface area (surface tension) and attraction of water to soil particles

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23
Q

What is Apoplast?

A

Continuous system of cell walls, intercellular air spaces, and lumens of non-living cells (xylem and fibres)

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24
Q

What is symplast

A

Entire network of cell cytoplasm interconnected by plasmodesmata

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25
Q

What does transmembrane pathway alternate between

A

Apoplast and symplast

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26
Q

What is the casparian strip

A

a band of hydrophobic suberin in the radial cell walls of the endodermis (inner cell layer of the cortex)

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27
Q

What are the functions of the casparian strip?

A
  • Blocks the apoplastic pathway in the endodermis and requires symplastic movement through these cells
  • Forces water and solutes into transmembrane pathway
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28
Q

What is guttation

A

the formation of liquid droplets (dewdrops) at the edges of leaves through hydrathodes

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29
Q

What does absorption of solutes from the soil leads to?

A

decreases in Ys and Yw in roots

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30
Q

What does lowering of Yw provide?

A

driving force for water absorption, leading to positive hydrostatic pressure in root xylem

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31
Q

When does absorption of solutes from the soil occur?

A

when transpiration is low and soil solute concentration is high

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32
Q

What are tracheids?

A

Tracheary elements found in all plants.
Long spindle-shaped cells in overlapping vertical files
Pits, pit membranes, tori (singular torus)
Radius less than 50 mm

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33
Q

What are vessel elements?

A

Tracheary elements found in angiosperms, Gnetales, some ferns
Shorter, wider than tracheids with perforated end walls
Perforation plate
Stacked end-to-end form a vessel
Radius up to 500 mm

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34
Q

How does water move?

A

Bulk flow
Long-distance transport through the xylem and from the soil

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35
Q

Is water movement extremely sensitive to the radius of the tracheary element?

A

Yes

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36
Q

Is waster movement independent of solute concentration?

A

Yes

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37
Q

What is the pressure difference required to overcome frictional drag?

A

0.01 MPa m-1

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38
Q

What is cohesion tension theory?

A
  • Positive to negative pressure gradients from the base to apex of a plant could move water in the xylem
  • a large tension (negative pressure) develops at the top of a plant
  • requires cohesive properties of water to sustain this tension
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39
Q

What does water adhere to in the xylem?

A

hydrophillic components such as cellulose microfibrils

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40
Q

How can air enter the xylem?

A

to injury, leaf abscission, or adjacent damaged conduits

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41
Q

Can water form if there is breaks in the xylem?

A

No

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42
Q

Features that reduce cavitation?

A

Pit membranes
Interconnectivity
Finite lengths of tracheary elements
Reduced tension at night
New growth of xylem tissues

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43
Q

What is the driving force of transpiration?

A

The difference in water vapor concentration difference between the inside of the leaf and the outside air

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44
Q

Factors that affect rate of transpiration?

A
  • Leaf temperature
  • Stomatal resistance (number and diameter)
  • Boundary layer resistance (wind speed and leaf size)
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45
Q

Dumbbell shaped guard cells are in what kind of plant?

A

Grasses

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46
Q

Kidney shaped guard cells are in what kind of plants?

A

All other plants

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47
Q

What opens the stomata?

A

Increase in guard cell turgor

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48
Q

What aspect of guard cells is responsible for opening stomata?

A

Specific alignment of cellulose

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49
Q

How are microfibrils oriented in guard cells?

A

fan out radially from the pore

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50
Q

What factors influence guard cell opening?

A

Light intensity and quality
Temperature
Water status
Intracellular CO2 concentration

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51
Q

Why does water loss occur?

A

as a result of allowing sufficient CO2 uptake for photosynthesis

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52
Q

What is the transpiration ratio due to?

A
  • Concentration gradient (inside and outside the leaf) of water 50 times greater than than of CO2
  • CO2 diffuses 1.6 times slower in air than water
  • Assimilation of CO2 requires transport across plasma membrane, cytoplasm and chloroplast envelop
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53
Q

How many essential plant nutrients are there?

A

17

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54
Q

Why are nutrients required?

A

Essential for structure or metabolism
Absence causes abnormal growth, development, or reproduction

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55
Q

Macronutrients?

A

N, K, Ca, Mg, P, S, Si

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56
Q

What is Passive Transport

A

Spontaneous movement of molecules down a chemical potential gradient
At equilibrium, no further movement occurs without an input of energy

57
Q

What is active transport?

A

Movement of substances against a chemical potential gradient
Not spontaneous, requires that energy is applied

58
Q

What can diffusion of salts across a membrane can produce

A

electrical membrane potential

59
Q

What is the membrane potential of plant cells

A

-200 to -100 mV

60
Q

Where does energy for proton transport come from?

A

ATP

61
Q

What are the types of transport proteins?

A

channels, carriers, and pumps

62
Q

What do channels do?

A

Selective pores that extend completely across membrane and enhance diffusion

63
Q

What do carriers do?

A

Do not have pores that extend across membrane, but bind and transport specific molecules

64
Q

What do you pumps do?

A

Require energy
Primary active transport is couple directly to ATP hydrolysis
Secondary active transport uses the proton motive force, which is stored energy created by H+ gradients
Two types: symports and antiports

65
Q

Symport

A

Both H+ and substrate A travel in the same direction from low to high

66
Q

Antiport

A

H+ travels from High to Low
Substrate A travels from low to high

67
Q

How are most transport processes energized?

A

by one primary active transport system coupled to ATP hydrolysis by generating ion gradients

68
Q

Where is the phloem found?

A

on the outer side of xylem in vascular bundles or In plants with secondary growth, phloem is the inner bark

69
Q

What do sieve elements do?

A

conduct sugars and organic compounds

70
Q

What do sieve cells lack?

A

nuclei and vacuoles, Golgi bodies, ribosomes, microfilaments and microtubules

71
Q

Sieve element cell walls

A

contain pores that interconnect cells

72
Q

Companion cells

A

Highly branching plasmodesmata connect cells
Take over critical functions from sieve elements
protein synthesis
ATP supply

73
Q

What is each sieve element associated with?

A

One or more companion cells

74
Q

What are Transfer cells

A

Companion cells that cells have finger-like wall ingrowths
Efficient for solute transfer with sieve elements

75
Q

What are Intermediary cells

A

COmpanion cells that have many connections to surrounding cells, unlike ordinary and transfer cells

76
Q

What do sources and sinks do?

A

Defines direction of phloem transport

77
Q

What are sources?

A

Exporting organs such as mature leaves and storage roots

78
Q

What are sinks

A

Organs that do not produce enough photosynthetic product to support their own growth or storage needs
Roots
Tubers
Developing Fruits
Immature leaves

79
Q

What is the pressure-flow model

A

Passive mechanism
Bulk flow of phloem sap driven by an osmotically generated pressure gradient between source and sink
Nevertheless, energy is required in sources and sinks for the synthesis and consumption of photosynthate, which in required for active phloem loading and unloading

80
Q

What is flow of pholem sap driven by?

A

pressure gradient between source and sink

81
Q

What do phloem loading at the source and unloading at the sink establish

A

Change in pressure potential

82
Q

What are the three mechanisms generate high sugar concentration in sieve elements of the source

A

Photosynthesis in mesophyll
Conversion of photoassimilate to sugars in intermediary cells
Active membrane transport

83
Q

Pressure Gradient at the Sink

A

phloem unloading lowers sugar concentrations in sieve elements generating higher (more positive) Delta Yp

84
Q

What maintains change in water potential in the sink?

A

Cross walls (sieve plates) of sieve elements

85
Q

Pressure Flow model predictions

A

Sieve plate pores must be totally unobstructed
Flow cannot be bidirectional at the same time in the same sieve element

Limitations in ATP supply should not immediately stop phloem transport,

Pressure gradient must be greater than the resistance in sieve elements for bulk flow to occur

86
Q

What happens during phloem loading?

A

Sucrose moves from mesophyll to vicinity of sieve elements (across only a few cells)

Sugars transported into sieve elements and companion cells

Can occur via symplast or apoplast, or both

87
Q

Apoplastic phloem loading

A

Difference results from phloem loading of sucrose by active transport (against its chemical gradient)
ATP-dependent process by a sucrose-H+ symporter
Uses energy generated by the proton pump

88
Q

How can diffusion-dependent symplastic loading account for selectivity and accumulation of sugars against a concentration gradient?

A

Polymer-trapping model
Sucrose is converted to raffinose and stachyose in intermediary cells, which diffuse into sieve elements
Larger size compared with sucrose prevents these sugars from diffusing back into mesophyll cells

89
Q

Phloem unloading

A

can be symplastic or apoplastic
Sugars move to sink cells
Symplastic pathways predominate
Apoplastic pathways occur in some sinks with high sucrose accumulation

90
Q

Energy Required for symplastic Phloem Unloading

A

Sucrose metabolism results in a low sucrose concentration in sink cells, maintaining the required concentration gradient for diffusion

91
Q

Energy Required for apoplastic Phloem Unloading

A

Utilize transporters that may require energy

92
Q

Physiological and anatomical changes of Source to Sink Transition

A

Plasmodesmatal closure
Fewer plasmodesmata
Reduced symplastic continuity

93
Q

What is allocation

A

Regulation of the distribution of fixed carbon into different metabolic processes
Synthesis of storage compounds
Metabolic utilization
Synthesis of transport compounds

94
Q

What is partitioning

A

Differential distribution of photosynthates within a plant
Turgor pressure could be the means of communication between sources and sinks, coordinating rates of loading and unloading
Hormones, mineral nutrients, and sugars could be messengers
Important for maximizing crop yield

95
Q

What is the most active photosynthetic cell

A

Mesophyll

96
Q

What is the photosynthesis equation

A

6 CO2 + 6 H2O -> C6H12O6 + 6 O2

97
Q

Internal membranes of chloroplasts produce

A

ATP and NADPH

98
Q

Where do carbon fixation reactions occur?

A

Stroma

99
Q

What is Absorption spectrum of chlorophyll a ?

A

the portion used by plants

100
Q

Why does chlorophyll appear green

A

Absorbs mainly red and blue light
Only light enriched in green (550 nm) is reflected

101
Q

What does absorption of a photon cause?

A

transition to a higher-energy state

102
Q

What are the 4 ways to dispose of extra energy

A
  1. Re-emit a photon, known as fluorescence
  2. Convert excitation energy to heat
  3. Participate in energy transfer
  4. Photochemistry, or transfer of energy directly to chemical reactions
103
Q

What chlorophyll is in green plants

A

A and B

104
Q

What chlorophyll is in protists /cyanobacteria

A

C and D

105
Q

what is the porphyrin ring?

A

structure related to hemoglobins and cytochromes
Involved in electronic transition and redox

106
Q

What are the components of chlorpophyll

A

Central magnesium atom surrounded by a nitrogen-containing structure called a porphyrin ring; attached to the ring is a long carbon–hydrogen side chain, known as a phytol chain

107
Q

What are carotenoids?

A

An accessory pigment
Linear molecules with many conjugated double bonds
Absorb between 400 – 500 nm
Characteristic orange to yellow color

108
Q

What is an action spectrum?

A

shows response of a biological system to light as a function of wavelength

109
Q

What serves as an antenna complex?

A

Pigments

110
Q

What does some light energy absorbed by Chl get stored as?

A

Chemical bonds

111
Q

What is the role of antenae?

A

Collect light and transfer energy to reaction centers

112
Q

What are reaction centers the site of?

A

Redox reactions that lead to long-term energy storage

113
Q

What is quantum yield?

A

(ϕ) is a definitive measure of the energetic efficiency of photoautotrophy
0 if process does not respond to light
1 if every absorbed photon contributes to the process
0.95 in dim light with fluorescence at 0.05

114
Q

What reduces NADP+ to NADPH

A

light

115
Q

NADP+ reduction is what kind of process

A

redox reaction where Electrons are moved from one chemical species to another

116
Q

What is the recycling agent for carbon reactions like the Calvin-Benson cycle

A

NADP+

117
Q

What led to the discovery of PS1 and PS2

A

Red drop and enhancement effect

118
Q

What does PS1 prefer?

A

Far red > 680nm

119
Q

What does PS1 produce?

A

Produces strong reductant; can reduce NADP+
And a weak oxidant

120
Q

What does PS2 prefer?

A

Red 680nm

121
Q

What does PS2 produce?

A

Produces a strong oxidant; can oxidize water
And a weak reductant

122
Q

What is the Z scheme?

A

Reductant of PSII re-reduces the oxidant of PSI

123
Q

Where do light reactions occur

A

Thylakoids

124
Q

What is a stack of thylakoids called?

A

grana lamellae

125
Q

What is a non-stacked thylakoid called?

A

Stroma lamellae

126
Q

What do thylakoids contain?

A

Contain Chl and integral membrane proteins
Reactions centers, antenna pigment-protein complexes and electron transport chain proteins

127
Q

Where do carbon reactions (dark) occur?

A

Stroma

128
Q

How many lipid bi-layers do chloroplasts contain?

A

Two

129
Q

What do chloroplasts also contain?

A

DNA RNA and ribosomes

130
Q

WHat is the role of PS1 in thylakoids

A

antennae Chl, e transfer proteins and ATP synthase in stroma lamellae

131
Q

What is the role of PS2 in thylakoids

A

antennae Chl e transfer proteins in grana lamellae

132
Q

What are the diffusible carriers of electrons?

A

Plastocyanin and Plastoquinone

133
Q

What is Plastocyanin

A

Blue-colored copper protein

134
Q

What is plastoquinone

A

Organic redox cofactor

135
Q

Electron Transport

A
  • PSII oxidizes H2O to O2 in thylakoid lumen releasing protons
  • Excited PSII P680 transfers e to pheophytin
  • Cytochrome b6f oxidizes plastohydroquinone (PQH2)
  • Pheophytin transfers e to plastoquinones QA and QB
  • Cytochrome b6f complex transfers e to plastocyanin (PC)
  • PC reduces P700 of PSI
  • e transferred to a Chl (A0), a quinone (A1), a series of iron sulfer proteins (FeSX, FeSA, FeSB), and to ferredoxin (Fd)
  • Ferredoxin-NADP reductase reduces NADP+ to NADPH
  • ATP synthase functions as H+ diffuses from lumen to stroma
136
Q

PSII is only biochemical system capable of doing this reaction

A

2 H2O -> O2 + 4 H+ + 4 e

137
Q

What is PS2 damaged by

A

Excess light (photoinhibition)

138
Q

WHat are the three stages of Calvin-Benson Cycle

A

Carboxylation of CO2 acceptor
Reduction of triose phosphate 3-phosphoglycerate (NADPH)
Regeneration of CO2 acceptor

PLBI 403 (2 decks)

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