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BIOL 225 > Lesson 11: Leave it to Leaves (and Hormones) > Flashcards

Lesson 11: Leave it to Leaves (and Hormones) Flashcards

1
Q

What is the only gateway for carbon dioxide to enter inside the leaf?

A

Stomatas

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2
Q

What is a pitfall of stomatas as a gateway for carbon dioxide to enter the leaf?

A

Stomatas are also gateways for water to escape out from plant leaves

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3
Q

Have stomata changed across 4000 million years?

A

Stomata have remained largely unchanged
BUT the operational efficiency of guard cells controlling the size of the apparatus has improved

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4
Q

What controls the size of the apparatus of stomata?

A

Guard cells

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5
Q

The success of seed vascular plants over seedless vasculars has been hypothesized to be because:

A

The sophistication of the guard cells of seed vascular plants minimizes water loss while optimizing carbon gains

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6
Q

Guard cells develop from:

A

Epidermal cells following assymetric cytokinesis

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7
Q

The size of the stomata is controlled by:

A

Changing the turgidity of the guard cells (using potassium or sucrose)

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8
Q

The stomata can be controlled by:

A

potassium, sucrose

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9
Q

Explain how stomata can be controlled by potassium/sucrose

A

SEE NOTES

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10
Q

How do plants avoid the partial pressure gradient problem ?

A

By negotiating the optimal stomatal density as a function of the amount of CO2 in the air

Following the mitotic cell division of the guard mother cell, the derivative guard cells produce a signalling molecule that diffuses in the surrounding area preventing neighbouring epidermal cells from differentiating into guard cells

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11
Q

Why can’t plants maximize stomatal density if area improves rates of diffusion (Fick’s law of diffusivity)

A

Partial pressure gradient of carbon dioxide:
With so little CO2 in the air, the concentration of carbon dioxide inside the leaf will quickly match or exceed that of the outside air –> plants must therefore tightly control, even limit area, to ensure that the net diffusion is always in and not out of the leaf.

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12
Q

True or false: Over the course of 400 MYRs, changes in the concentration of CO2 in the atmosphere have led to changes in the density of stomata on a leaf surface

A

True!

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12
Q

What is rubisco ?

A

Rubisco is the enzyme that pulls CO2 into the calvin cycle and fixes it into a 3-carbon sugar molecule

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13
Q

*What is the problem with rubisco?

A

readily binds to oxygen
when it binds to oxygen it generates CO2 instead of sugar as a by product while consuming the ATP from the light reactions in the thylakoid membranes of the chloroplast – this wasteful process is called cellular respiration

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14
Q

Light reactions take place in:

A

Thylakoid membranes of the chloroplast

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15
Q

The standard pathway for photosynthesis is:

A

C3 pathway

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16
Q

What happens to carbon dioxide in C3 plants? (most plants exclusively use the C3 pathway)

A

The carbon dioxide molecules taken up enter straight into the calvin cycle, producing a 3-carbon sugar molecule

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17
Q

What is the anatomy of the leaves of C3 plants?

A

Leaves of C3 plants are organized with :
upper layer:
-palisade mesophyll cells
bottom layer:
-loosely arranged spongy mesophyll cells
-air chambers

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18
Q

What is the anatomy of the leaves of C4 plants?

A

Large air chambers are found on the inside of the stomata where the concentration of carbon dioxide is kept very low
Mesophyll cells
bundle sheath cells

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19
Q

Mesophyll cells of C4 plants lack:

A

The machinery to operate the calvin cycle

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20
Q

What happens to carbon dioxide in C4 cells

A
  • Carbon dioxide diffuses into the air chambers and is immediately taken up by the surrounding mesophyll cells
    (mesophyll cells of C4 plants lack the machinery to operate the calvin cycle)
  • mesophyll cells fix CO2 into malate –> a 4 - carbon sugar molecule
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21
Q

C4 plants get their name from:

A

The 4-carbon sugar molecule they produce

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22
Q

What ensures that the CO2 concentration in the chambers is kept low and well below that of the outside air?

A

The ability to quickly pickup CO2 by

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23
Q

True or false: When the stomata of C4 plants open, CO2 diffuses in at a faster rate than C3 plants

A

True –> in C3 plants, CO2 often accumulates because of Rubisco’s fumbling around with oxygen

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24
Q

The calvin cycle in C4 plants occurs in :

A

The bundle sheath cells

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25
Q

What happens to malate in C4 plants?

A

Malate received from adjacent mesophyll cells is cleaved into one molecule of CO2 and pyruvate

Rubsico then pulls CO2 into the calvin cycle to make a 3-carbon sugar molecule in the same way as with C3 plants

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26
Q

What does the concentration of CO2 in the chloroplast of bundle sheath cells look like ?

A

It is 10x above that of the outside air
The constant stream of malate than enters bundle sheath cells helps to increase the concentration of CO2 in the chloroplast of bundle sheath cells to ten times that of the outside air

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27
Q

How much water do C3 plants lose in comparison to C4 plants

A

C4 plants lose only half as much water for every gram of CO2 fixed in comparison to C3 plants

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28
Q

Which is most common: C3 or C4 plants

A

C3 plants despite C4 gains in water use efficiency

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29
Q

C4 photosynthesis is limited to :

A

plants that grow in high light environments

plants growing in the shade, C4 pathways could never produce enough sugar to sustain the whole plant

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30
Q

How are CAM plants similar to C4 plants?

A

CAM plants fix carbon dioxide into a 4-carbon sugar molecule exclusively at night

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31
Q

Where are CAM plants found?

A

In dessert environments

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32
Q

Stomata of CAM plants open when?

A

Stomata open only at night when the risk of water loss through transpiration is minimal
Carbon dioxide taken in at night

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33
Q

What happens in CAM plants during the day?

A

Stomata remain closed (minimize water loss)
The 4 carbon molecules are broken down and carbon dioxide enters the C3 pathway

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34
Q

CAM plants have highest water use efficiency (compared to C3 and C4), do they fix a lot of carbon?

A

no, they fix very little carbon –> XXXX

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35
Q

What is phyllotaxy

A

Phyllotaxy is the art of leaf placement on a stem to reduce self-shading

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36
Q

How are the leaves or needles of most angiosperms and gymnosperms arranged?

A

Alternate phyllotaxy: where leaves or needles are arranged in a spiral where the angle between the successive leaves is positioned 137.5degrees from the previous one

37
Q

The number of spirals on a leaf bud always converge to :

A

A fibonacci number

38
Q

What is the leaf index area (or LAI)?

A

Is a proxy for primary productivity at the individual or stand level

The leaf index is the ratio of the total upper leaf surface divided by the surface area of land on which they grow

39
Q

At the stand level, LAI numbers can climb up to a maximum of :

A

7

40
Q

Why is the LAI number maximum 7?

A

Above this value, branches in the sub-canopy are in deep shade, unable to intercept any useful radiation to drive photosynthesis –> At this point, trees must die or whole branches must be abscised.

41
Q

What wavelengths can plants photosynthesize?

A

400 - 750 nm
wavelengths below 400 nm have too much energy and wavelengths above 750 nm have too little

42
Q

Where does the conversion of radiant energy to chemical energy occur?

A

Occurs through specific pigments within plant leaves - most notably the chlorophyll pigment

43
Q

What two specific regions of the visible light spectrum does chlorophyll a absorb?

A

Blue range : around 430 nm
Red band range: around 680 nm

44
Q

Chlorophyll doesn’t absorb anything beyond:

A

700 nm - what we call far-red light

45
Q

Why isn’t far-red light absorbed by chlorophyll?

A

Far-red light has too little energy to excite electrons in the photosystem – this band of light is therefore rejected

46
Q

What are two accessory pigments

A

Chlorophyll b and carotenids

47
Q

What is chlorophyll b?

A

Accessory pigment that captures light as wavelengths adjacent to those of chlorophyll a

48
Q

What are carotenoids?

A

Carotenoids are another class of accessory pigments that work with wavelengths in the blue-green range to drive photosynthesis

49
Q

By midday, the only useful light available to excite the electrons of chlorophylls a and b is:

A

Red light

50
Q

Light in the understory of a forest comes in as:

A

Diffused light and sun flecks

51
Q

What is diffused light?

A

indirect light that has been scattered after passing through a medium (leaves in the canopy or particles in the atmosphere that scatter light into many directions)

Diffused light, for many plants in the understory, contains some suitable wavelengths to drive photosynthesis

52
Q

What is preferred between sun flecks and diffused light?

A

sun flecks are much prefered because these are unfiltered rays of direct light that strike the ground

53
Q

What are sun flecks ?

A

Sunflecks reach the ground from holes in the canopy and the shifting position of leaves.
Intermittent sunflecks are a lifeline for the forest understory.

54
Q

Leaves can get how much hotter than ambient air temperatures ?

A

10 - 20 degrees celsius hotter

55
Q

How does leaf shape help reduce the dangers of overheating?

A

Leaf shape is often a trade off between having enough surface area available for photosynthesis and maximizing the area available for conductive heat transfer with the surrounding air

56
Q

Plants respond to their environment by:

A

Producing hormones that regulate their growth and development

57
Q

When an epidermal cell differentiates into guards cells:

A

A hormone diffuses out preventing neighbouring epidermal cells from becoming themselves, guard cells

58
Q

What is the external stimulus that drives the production of this signalling molecule (the one that prevents epidermal cells from becoming themselves, guard cells)?

A

Concentration of carbon dioxide in the air

59
Q

Stomatal density is a response to an ___ mediated by an ____ that reaches its target tissue by ____

A

Stomatal density is a response to an external stimulus but mediated by an internal stimulus that reaches its target tissue by diffusion

60
Q

Hormones control stomatal density and :

A

Phyllotaxy in shoot apical meristems

61
Q

How is phyllotaxy in shoot apical meristems controlled?

A

Hormones control phyllotaxy in shoot apical meristems
As the hormone diffuses away from the developing leaf primordia, neighbouring cells are prevented from differentiating into embryonic leaves.

62
Q

What is the most important kind of external signal perceived by plants?

A

light

63
Q

What is the general function of the major plant hormones ?

A

Function as internal stimuli, hormones are synthesized in response to external signals.

64
Q

Define plant hormones

A

Plant hormones are defined as chemical signals that modify or control one or more physiological processes

65
Q

How do the signalling molecules of plants (hormones) travel to reach receptors on target tissues and trigger a signal transduction pathway&

A

These signalling molecules travel through the symplast and apoplast

66
Q

What is involved in the signal transduction pathway

A

Transduction involves many relay proteins and second messengers that ultimately lead to the activation of some cellular-level response

67
Q

Can plant hormones be active at very low concentrations?

A

Most plant hormones are active at very low concentrations and have many multiple functions depending on the target tissue and developmental stage of the plant

68
Q

Do plant hormones work together?

A

Hormones work in concert and in combination with other plant hormones

69
Q

What are the range of responses to a hormone?

A

The range of responses to a hormone can be depending on its relative concentrations, type of tissue and particular life stage of the plant

70
Q

What are the five classic plant hormones (known to science for over 100 years)

A

1- Auxin
2- Cytokinis
3- gibberellins
4- Abscisic acid
5- Ethylene

71
Q

What are the three newly discovered hormones (past 20 years)

A

1- brassinosteroids
2 - jasmonates
3 - strigolactones

72
Q

Where does auxin production take place?

A

In shoot apical meristems and young leaves

73
Q

How does the auxin hormone travel?

A

Hormone travels unidirectionally from site of production down towards the root system

74
Q

What are the major functions of auxin:

A

1- Stem elongation,
2 - Apical dominance
3 - Promoting vascular differentiation
4- delaying leaf abscission

75
Q

Auxin’s role in stem elongation is derived from:

A

The stimulation of proton pumps embedded in the plasma membrane of cells:

The acidification of cell walls activates expansin proteins that reside in the cell wall
Once activated, they loosen the fabric of the cell wall by disrupting the linkages between the pectin and cellulose microfibrils.

This loosening of the cell wall allows the cell to swell when more water is imbibed.

76
Q

Cytokinins control:

A
  • cell division and differentiation
  • mobilize nutrients to sink tissues
77
Q

What is the site of production of cytokinins?

A

Meristematic regions of roots, fruits and seeds

78
Q

What hormone is critical in the development of fruits?

A

cytokinins

79
Q

why are cytokinins critical in the development of fruits?

A

If an ovary has too few fertilized ovules, nutrients will not be invested in the development of that seedless fruit.

Only ovaries with seeds will develop into fruits and the chemical signal that is responsible for mobilizing nutrients to fruits and seeds is cytokinin.

80
Q

The primary sites of gibberellin synthesis include:

A

Apical buds in roots and shoots, young leaves and seeds

81
Q

Giberellins function in:

A

Stem elongation, fruit growth, and seed germination

82
Q

Unlike aucin and cytokinins, giberellins encourage growth by:

A

promoting both cell elongation and cell division

83
Q

What happens to plants with up-regulated production of giberellins:

A

Plants will gtow much taller than varieties producing less of the hormone (Thompsom seedless grapes)

Longer stalks –> ventilation

84
Q

How do gibberellins promote seed germination?

A

The radical inside the seed is a rich source of gibberellins. As water is imbibed into the seed, gibberellins diffuse out of the plant embryo and into the surrounding endosperm, triggering the release of alpha-amylase.
Just like salivary amylase is responsible for digesting starch in the oral cavity, this enzyme is responsible for digesting the starch within the endosperm. Once reduced to monosaccharides and disaccharides, these energy rich sugars are used to power the growth of the germinant

85
Q

Abscisic acid is synthesized:

A

throughout the plant

86
Q

Function of abscisic acid

A

Prevents premature germination (chemical block to seed germination)
mediates the rapid closure of stomata in drought-stressed plants

87
Q

Hoe does abscisic acid mediate the rapid closure of stomata during times of excessive transpirational water loss

A

Abscisic acid triggers guard cells to move potassium ions into the cell wall.
With a lowering of the solute potential of the cell wall, water rushes out of the guard cells.
As the cells become flaccid, the stomatal pores close and water is better conserved

88
Q

For most plant tissues, ethylene is releases in :

A

gaseous form

89
Q

Ethylene is responsible for :

A

Leaf abscission and fruit ripening

90
Q

How does ethylene trigger the fruit ripening process?

A

Ethylene activates enzymes like pectinase to break down the pectin in cell walls to soften fruits and make them more palatable.

Ethylene also drives the synthesis of anthocyanins–pigments that are responsible for
the vibrant colors of ripe fruit

91
Q
A

BIOL 225 (3 decks)

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