Coordination and Control in Plants

Question 1

what is the pigment called that is found in the leaves of flowering plants? and what is its job?

Answer 1

-phytochrome is the pigment system
-it is involved in the timing of flowering in plants

Question 2

how is the flowering process initiated? what triggers it?

Answer 2

-when average temps reach a certain level
-most common trigger is the duration of light or day length

Question 3

what is another term to describe the duration of day light?

Answer 3

-photoperiod

Question 4

what are the two species/ types of plants that are controlled by light?

Answer 4

-long day plants
-short day plants

Question 5

when do long day plants flower?

Answer 5

-when day length exceeds a certain minimum length

Question 6

when do short day plants flower?

Answer 6

-when day lengths are shorter/ dark period is longer

Question 7

what is the term used to describe how the photochrome pigment responds to light?

Answer 7

-acts as a photoreceptor

Question 8

what is the two forms that phytochrome can be found?

Answer 8

-P660
-P730

Question 9

what type of light does P660 absorb and what is its absorption peak?

Answer 9

-red light with a peak of 660nm

Question 10

what type of light does P730 absorb and what is its absorption peak?

Answer 10

-far red light with a peak of 730nm

Question 11

what happens if the plant is subjected to red light in-terms of the pigment conversions? what about far red light?

Answer 11

-the P660 is rapidly converted to the P730 form
-if there is far red light P730 is rapidly converted to the P660 form

Question 12

in darkness which pigment is more stable and what does this result in?

Answer 12

-P730 is much less stable in darkness than P660
-P730 will therefore convert to the P660 form slowly

Question 13

what type of light does daylight contain more of and what is the effect of this in-terms of the pigments?

Answer 13

-more red than far red light
-meaning P660 is converted to P730 so as day length/ light gets longer the amount of photochrome in the form P730 increases

Question 14

what is the effect of a longer day length in flowering in LDPs?

Answer 14

-as day length increases the amount of P730 increases too until it reaches a critical level which then initiates flowering

Question 15

what happens are day length increases in short day plants and why is this?

Answer 15

-the inhibitory effect of high levels of P730 must be removed before flowering can take place
-this is due to P730 being physiologically active

Question 16

what is the phytochrome response in LDP when there is a short day and a long night?

Answer 16

-P660 converted to P730 rapidly in the day
-the night/ dark is long enough for sufficient P730 to be converted back into P660
-this prevents P730 reaching critical level and so prevents flowering

Question 17

what is the phytochrome response in LDP when there is a long day and a short night?

Answer 17

-long day means P660 can rapidly convert to P730
-dark period is not long enough for P730 to convert back to P660
-P730 stays at critical level and so the plant flowers

Question 18

what is the phytochrome response in SDP when there is a short day and a long night?

Answer 18

-P660 converted to P730 in the day
-dark period is long enough for a sufficient level of P730 to be converted back to P660
-this removes inhibitory effect of high amounts of P730
-the plant flowers

Question 19

what is the phytochrome response in SDP when there is a long day and a short night?

Answer 19

-P660 converted to P730 during the day
-dark period is not long enough for a sufficient level of P730 to be converted back into P660
-high amounts of P730 results in flowering being inhibited

Question 20

what is done by flower suppliers to ensure that flowers are available during the whole year?

Answer 20

-the photoperiod is manipulated

Question 21

what are the two ways that the photoperiod can be manipulated?

Answer 21

-using artificial light
-using screens to reduce the light period

Question 22

what is the effect of the light and the dark period in LDPs being the same length?

Answer 22

-the length of day is not long enough to build up a supply of P730 to initiate flowering

Question 23

what is the effect of having a longer light period and a shorter dark period in LDPs?

Answer 23

-flowering is initiated as the light period is long enough for sufficient amount of P730 to reach the critical level
-the dark period is not long enough to break down a sufficient amount of the P730

Question 24

what is the effect of light period being longer than dark period but the light period is interrupted by a short period of darkness?

Answer 24

-the short amount of darkness does not reduce the amount of P730 level enough so that it falls below the critical level and inhibits flowering
-this is because the conversion of P730 to P660 in darkness is a slow process

Question 25

what is the effect of having light and dark period the same in a SDP?

Answer 25

-darkness is long enough to allow enough P730 to be converted back into P660
-removes the inhibitory effects of P730

Question 26

what is the effect of having light and dark period the same in a SDP but the dark period is interrupted by a short flash of light?

Answer 26

-the short flash of light is enough to inhibit flowering as the P660 will be rapidly converted to P730
-therefore there is not a sufficiently long continuous period of darkness to allow for flowering

Question 27

in SDP what must the period of darkness be to ensure flowering?

Answer 27

-continuous

Question 28

why do some scientists believe that a hormone is involved in flowering?

Answer 28

-there must be some form of communication between where the light stimulates the phytochrome and where flowering actually occurs

Question 29

there have been no plant hormones identified but what has been found in plants?

Answer 29

-plant growth substances

Question 30

what is different about growth in plants compared to animals?

Answer 30

-growth in plants is localised in specific zones at the tips of roots and shoots called apical meristems

Question 31

what occurs in the meristems of plants/ regions of localised growth?

Answer 31

-mitosis takes place to produce more cells

Question 32

how else can plant growth occur besides mitosis of cells in the roots? what does this mean that the two zones are in roots and shoots?

Answer 32

-cell elongation
-zones of division and zones of elongation

Question 33

where else might growth occur in certain plants beside the roots, shoots and tips?

Answer 33

-the internodal regions
-these are parts of the stem between points that leaves develop

Question 34

what are the three main plant growth substances?

Answer 34

-auxins
-cytokines
-gibberellins

Question 35

where is the site of production and the main function of auxins?

Answer 35

-produced in the tip and moves down the stem (decreases concentration)
-promotes cell elongation

Question 36

where is the site of production and the main function of cytokinins?

Answer 36

-produced in the meristem tissues (zones of division)
-promote cell division in internodes

Question 37

where is the site of production and the main function of gibberellins?

Answer 37

-produced in leaves
-promotes cell elongation