Plant Hormones And Growth In Plants

Question 1

what are tropisms?

Answer 1

directional growth in response to environmental cues.

Question 2

what are the key limitations of plants?

Answer 2

• they are rooted (immobile.)
• do not have rapidly responding nervous systems.

Question 3

are plant responses faster or slower than animal responses?

Answer 3

slower.

Question 4

what are hormones?

Answer 4

chemicals that are produced in one part of the plant and are transported cell to cell or through transport tissues to have an effect on another part of the plant.

Question 5

what are the important plant hormones?

Answer 5

• Auxins
• Giberellin
• Abscisic acid.
• Ethene.

Question 6

what are the roles of auxin?

Answer 6

• control cell elongation.
• prevent abscission.
• maintain apical dominance.
• stimulate the release of ethene.

Question 7

what are the roles of gibberellin?

Answer 7

• cause stem elongation.
• trigger the mobilisation of food stores in a seed at germination.
• stimulate pollen tube growth in fertilisation.

Question 8

What are the roles of ethene?

Answer 8

• causes fruit ripening
• promotes abscission in deciduous trees.

Question 9

What is the role of abscisic acid?

Answer 9

• maintains dormancy of seeds and buds.
• stimulates cold protective responses.
• stimulates stomatal closing.

Question 10

why are chemicals essential?

Answer 10

plants may use chemicals to signal to other species and produce chemicals in defences against herbivory.

Question 11

why are scientists unsure about the details of plant responses?

Answer 11

• plant hormones work in very low concentrations so isolating and measureing concentration changes is difficult.
• multiple interations between different chemical control systems makes it difficult for researchers to isolate the role of a single chemical in a response.

Question 12

how does a seed germinate?

Answer 12

1. the seed absorbs water and the embryo is activated and begins to produce gibberellins.
2. gibberellins then stimulate the production of enzymes that break down food stores found in the seed.
3. The embryo plant uses these food stores to produce ATP so it can grown and break out through the seed coat.

Question 13

where is the food store in dicot seeds?

Answer 13

in the cotyledons

Question 14

where is the food store in monocot seeds?

Answer 14

in the endosperm.

Question 15

what experimental evidence supports the role of gibberellins in the germination of seeds?

Answer 15

• mutant varieties of seed have been bred which lack gene to make gibberellin. the seeds do not germinate.
• if gibberellin biosynthesis inhibitors are applied, they cannot germinate.

Question 16

where are auxins made?

Answer 16

cells of tips of roots and shoots and in meristems.

Question 17

how does auxin affect the plasticity of the cell wall?

Answer 17

• more auxin, cell wall stretches more easily.
• auxin molecules bind to specific receptor sites in plant cell membrane, causing pH to fall to 5.
• 5 is optimum pH for enxymes to keep walls flexible and plastic.
• auxin is destroyed as cells mature so pH rises so enzymes controlling plasticity are inactive.
• plant is more fixed in shape and can no longer expand and grow.

Question 18

what are the internodes?

Answer 18

the regions between leaves on a stem

Question 19

how were gibberellins discovered?

Answer 19

they were produced by a fungus that affects rice. The infected seedlings grew extremely tall and thin.

Question 20

how can you investigate the effect of plant hormones on the growth of plants?

Answer 20

• growing seedlings hydroponically
  (nutrient solution rather than soil) in serial dilutions of different hormones.
• applying different concentrations of hormones to the cut ends of stems or roots and observing the results.
• once measurements have been completed, standard deviation should be calculated to measure the spread of data.

Question 21

what is synergism?

Answer 21

when different hormones work together and give a greater response than it would on its own.