C6 (Plant Responses)

Question 1

Plants not passive objects
Define Tropism:

Answer 1

Plants not passive objects. They respond to abiotic stimuli in terms of directional growth - this is a tropism.

Question 2

What are some limitations for plants and how do they compensate for it?

Answer 2

Limitations of plants include lack of mobility and nervous system. They use hormones secreted from cells to respond to their environment.
Hormones are less immediate than the responses nervous systems animals provide, but their effects are often more long-term.​

Question 3

What can plant hormones be used for (3)?

Answer 3

Plant hormones can be used to protect themselves from pests,

produce chemical defences against herbivores,

communicate with other plants and more.

Question 4

Hormone: Auxin
Role and Importance
(5)

Answer 4

1) Cell elongation

2) Preventing abscission

3) Maintaining apical dominance

4) Involved in tropisms

5) Stimulate the release of ethene

-Plants would not grow as rapidly
-Lack of photosynthesis/gaseous exchange
-Plants would not be tall enough to get sunlight for photosynthesis
-Plants would not have reactants required for photosynthesis.
-See importance of ethene

Question 5

Hormone: Gibberellin
Role and Importance
(3)

Answer 5

1) Stem elongation
2) Trigger mobilisation of food stores in seed a germination
3) Stimulate pollen tube growth at fertilisation

-Plants would not grow
-Plants would not be able to reproduce sexually

Question 6

Hormone: Ethene
Role and Importance
(2)

Answer 6

1) Fruit ripening
2) Promotes abscission in deciduous trees

-Pollinators would not be attracted to plants, so would not be able to sexually reproduce
-Deciduous trees chance of surviving winter would plummet

Question 7

Hormone: Abscisic Acid
Role and Importance
(3)

Answer 7

1) Maintains seed and bud dormancy
2) Stimulates cold protective responses such as antifreeze production
3) Stimulates stomatal closure

-Seeds would sprout at inopportune times, and die
-Plants would not survive throughout winter
-Plants would suffer extreme water loss in hot periods

Question 8

Seed Germination Process:
A seed embryo is activated when…

Answer 8

-A seed embryo, activated when absorbs water, producing gibberellins.

-Gibberellins turn on the genes, code for amylases and proteases which break down food stores found in the seed, (Cotyledons in dicotyledonous seeds, and endosperm in monocotyledonous seeds).

-The embryo plant uses these food stores to produce ATP for building materials to grow and break through the seed coat.

-Abscisic Acid (ABA) works against gibberellins to determine when the seed will germinate.

Question 9

Experimental Evidence for the Role of Gibberellins in Germination:

Answer 9

-Mutant breeds of seeds lacking gibberellins have not been able to germinate until gibberellins were applied externally.
-Seeds with gibberellin biosynthesis inhibitors do not germinate until the inhibitor is removed.​