Phytochrome

Question 1

What stimulus controls the flowering of plants

Answer 1

-The stimulus of night length controls the flowering of plants
-For example spring and summer have short night lengths while autumn and winter have long night lengths
-Some plants flower during long nights and others flower during short nights

Question 2

How does night length control flowering in plants in terms of transcription/genes

Answer 2

-When the night length reaches a certain point, genes that control flowering in plants are either switched on or switched off, leading to activation or inhibition of flowering
-When the genes are switched on, they are expressed, and the polypeptides that they code for are produced
-However, if the gene is switched off, it is not expressed, and the polypeptide that they code for will not be produced

Question 3

How can the length of night be determined by plants

Answer 3

Length of night can be determined by plants as they can detect the quantities of the different forms of phytochrome in the leaves

Question 4

Two Forms of phytochrome

Answer 4

-PR- PR is the inactive form of phytochrome and absorbs light from the red part of the spectrum (660nm)
-PFR is the active form of phytochrome and absorbs light from the far red part of the spectrum

Question 5

Reversible conversion

Answer 5

-When Pr absorbs red light (660nm) it converts into PFR
-When PFR absorbs far red light (730nm), it converts back into PR
-In the absence of light PFR slowly converts back into PR

Question 6

Which form of phytochrome is more abundant in the daytime and why

Answer 6

-In the daytime, there are higher levels of PFR
-This is because sunlight contains more 660nm wavelengths than 730nm wavelengths
-This means that PR if converted to PFR more rapidly in the daylight than PFR converts to PR

Question 7

What form of phytochrome is more abundant at night and why

Answer 7

-PR is at a higher level at night
-This is because red light wavelengths are not available in darkness
-In an absence of light, PFR slowly converts back to PR

Question 8

Long day Plants

Answer 8

-Long day plants flower when the night is short
-High levels of the active form of phytochrome activate flowering in long day plants
-PR is converted to PFR more rapidly than PFR to PR because there are more red light (660nm) wavelengths present in daylight
-This means there are higher levels of PFR present
-Higher levels of PFR activate flowering in long day plants

Question 9

How do high levels of PFR cause flowering in long day plants

Answer 9

-High levels of PFR allow the gene to be switched on and expressed
-This gene is then transcribed and translated
-The resulting protein then causes flowering