coordination and control in plants

Question 1

what is phytochrome

Answer 1

a pigment system found in the leaves of flowering plants

Question 2

what is a photoperiod

Answer 2

the duration of light / day length

Question 3

what are long day plants LDPs

Answer 3

plants which only flower is the length of day exceeds the certain minimum length aka critical level eg.cabbage and petunia

Question 4

what are short day plants SDPs

Answer 4

species which only flower if the length of day is shorter than the critical value
(nights exceed certain minimum length)
eg.chrysanthemum and strawberries

Question 5

describe the two forms of phytochrome

Answer 5

phytochrome acts as a photoreceptor
P660- absorbs red light with an absorption peak of 660nm
P730- absorbs far red light with an absorption peak of 730nm

Question 6

how are the phytochrome affected by light

Answer 6

if subject to red light P660 is rapidly converted to P730 form
if P730 is subjected to far red light it is rapidly converted to P660

Question 7

how does darkness affect phytochrome

Answer 7

in darkness P730 will slowly concert to p660 form
the amount of p730 eventually reaches a critical level that initiates flowering
-intensity of light after effects speed

Question 8

which type of light does sunlight contain more of

Answer 8

more red than far red, p660 is converted to p730 during the day

Question 9

hat is the physiologically active form of phytochrome

Answer 9

p730
p730 either promotoes flowering of ldps or places an inhibitory effect on sdps which must be removed before flowering can take place

Question 10

how can the photoperiod be manipulated

Answer 10

by a light regime to stimulate flowering process
using artificial light in glasshouses or using screens to reduce lightperiod

Question 11

in sdp what must the critical period of darkness be?

Answer 11

continuous
even a shirt flash of light will rapidly convert p660 to p730 whereas conversion of p730 to p660 in darkness is slow

Question 12

auxin

Answer 12

auxin is produced in the tip of the shoot
it is stimulated by unilateral light
it diffuses down the shaded side of the stem
phototropism occurs as the cells on the shaded side elongate more than the cells on the light side so they bend towards the light to retrieve more light for photosynthesis
main function: promote growth by cell elongation in the zone of elongation

Question 14

cytokinins

Answer 14

produced in the meristematic tissues in the zone of division
promote growth by increased cell division in the apical meristems (zone of division)

Question 15

Gibberellins

Answer 15

produced in leaves
promote growth by cell elongation in the internodes