Plant Hormones

Question 1

What are tropisms

Answer 1

when plants moves/directional growth to a response of the external stimuli in the environment

Question 2

Hormones and their Roles -
Auxins

Answer 2

control cell elongation, prevent leaf fall, maintain apical dominance, involved in tropisms, stimulate the release of ethene and involved in the ripening of fruit.

Question 3

Hormones and their Roles - Gibberellin

Answer 3

causes stem elongation, triggers the mobilisation of food stores in a seed at germination, stimulate pollen tube growth in fertilisation

Question 4

Hormones and their Roles - Ethene

Answer 4

causes fruit ripening, promotes abscission in deciduous trees

Question 5

Hormones and their Roles - ABA (Abscisic Acid)

Answer 5

maintains dormancy of seeds and buds, stimulates cold protective responses (e.g. antifreeze production), stimulates stomatal closing.

Question 6

Why are scientists unsure about the details of plant hormones?

Answer 6

1. plant hormones work at low concentrations, so isolating them and measuring changes is difficult
2. The multiple interactions between different chemical control system also make it very difficult for researchers to isolate the role of a signal chemical in a specific response.

Question 7

Plant Hormones and Seed Germination - how does a seed germinate?

Answer 7

1. when the seed absorbs water, the embryo is activated and begins to produce gibberellins.
2. Stimulate the production of enzymes that break down the food stores found in the seed. The food store is in the cotyledons in dicot seeds and the endosperm in monocot seeds.
3. The embryo plant uses these food stores to produce ATP, so it can grow and break through the seed coat.

Question 8

Plant Hormones and Seed Germination: Experimental evidence - How was gibberellin used in the mutants?

Answer 8

• Mutant varieties of seeds have been bred which lack the gene that enables them to make gibberellins.
• These seeds don’t germinate, so if gibberellins are applied to the seeds externally, they then germinate normally.

Question 9

Plant Hormones and Seed Germination: Experimental evidence - Gibberellin in biosynthesis inhibitors

Answer 9

• If gibberellin biosynthesis inhibitors are applied to seeds, they don’t germinate as they can’t make the gibberellins needed for them to break dormancy.
• If the inhabitation is removed, or gibberellins are applied, the seeds germinate

Question 10

Commercial use of Plant Hormones - how can auxins be used?

Answer 10

Auxins can be used in the production of seedless fruit

Question 11

Commercial use of Plant Hormones - how can ethene be used?

Answer 11

used to promote fruit dropping in plants

Question 12

Commercial use of Plant Hormones - how can cytokinins be used?

Answer 12

used to prevent ageing of ripened fruit and products such as lettuces and in micropropagation to control tissue development

Question 13

Commercial use of Plant Hormones - how cab gibberellins be used?

Answer 13

can be used to delay ripening and ageing in fruit, to improve the size and shape of fruits, and in beer brewing to speed up the malting process.