Plant Hormones

Question 1

The opening and closing of stomata are due to changes in environmental conditions. Hydrogen ions (H+) and potassium ions (K+) are involved in the opening of stomata.
Describe how hydrogen ions and potassium ions are involved on the opening of a stoma.

Answer 1

H+ pumped out of guard cell / into cell wall of guard cell;
Inside of cell becomes negatively charged;
K+ enters cell by facilitate diffusion;
Water potential of cell decreases;
Water enters cell by osmosis;
Cell expands / increases in volume / becomes turgid;
Stoma opens due to thick inner wall

Question 2

Outline the role of amylase in seed germination.

Answer 2

Hydrolyses / breaks down starch;
In endosperm;
To glucose;
Glucose used by embryo;
Glucose used for respiration / growth

Question 3

During seed gemination gibberellin stimulates the synthesis of enzymes.
State the name of one of these enzymes and the precise location of its synthesis.

Answer 3

Amylase / protease / maltase;
Aleurone layer

Question 4

Explain how the Le/le gene and gibberellin are involved in affecting the height of plant stems.

Answer 4

Short / dwarf plants:
Are homozygous recessive / lele;
le / recessive allele codes for non-functioning enzyme;
le / recessive allele / non-functional enzyme gives inactive gibberellin;
DELLA proteins not broken down / stay bound to PIF;
PIF cannot bind to promoter / start transcription;
Of genes that promote growth / cell division / cell elongation

Question 5

Define phytochrome and explain what it does.

Answer 5

Plant pigments;
React to different types of light which lead to different plant responses;

Question 6

Describe the sequence of events that lead to the production of amylase during germination of barley seeds.

Answer 6

Embryo absorbs water;
Embryo stimulated to produce gibberellin;
Gibberellin moves to aleurone layer;
Gene coding for amylase expressed;
Translation of mRNA to produce amylase;
Gibberellin binds to receptor and destroys DELLA protein

Question 7

Explain the control of gibberellin synthesis and outline how gibberellin stimulates stem elognation.

Answer 7

Dominant allele / Le codes for functional enzyme;
Enzyme produces active gibberellin ;
DELLA inhibits transcription factor / PIF;
Gibberellin binds to receptor;
Causes DELLA destruction;
Transcription factor / PIF / RNA polymerase binds to DNA / promoter;
Growth genes switched on / expressed OR transcription occurs;
Cell walls loosen / acid growth;
So cells can expand when water enters;