, Plant responses
The limitations for plants are:
they are rooted (not mobile)
they do not have a rapidly responding nervous system, therefore
plant responses are slower than animal responses
However they are coordinated organisms that show clear responses
to their environment & communication between cells & different
plants.
Plants have evolved a system of hormones- chemicals produced in one
region of the plant & transported both through the transport tissue
& cell to cell to have an effect in another part of the plant.
Chemicals such as auxin & gibberellins are considered to be plant
hormones as they're similar to animal hormones, involved in
coordination of the plant & made in one place & carried through the
transport system to another region where they have an effect.
Synergism- Interaction of different hormones which complement
each other.
Antagonism- Interaction of different hormones that have opposing
effects. E.g. 1 hormone preventing growth & the other promoting it.
, Plant hormones and seed germination
Germination is the process by which a plant starts growing from a seed.
When the seed absorbs water, the embryo is activated & begins to produce
gibberellins. They in turn stimulate the production enzymes by switching on the gene
that codes for amylases & proteases which break down the food stores found in the
seed. The food store is in the cotyledon in dicot seeds & endosperm in monocot
seeds. The embryo plant uses these food stores to produce ATP for building
materials so it can grow & break out through the seed coat.
Evidence suggests that plant hormone ABA
acts as an antagonist to gibberellins
(interferes with action of gibberellins). The
levels of the 2 hormones determine when the
seed will germinate.
Experiments to provide evidence of the action
of gibberellins have been conducted. E.g.
mutant seeds lacking gibberellin have been
bred. These seeds do not germinate unless
gibberellins are applied externally.
Gibberellins are important in the elongation
of plant stems during growth as they
affect the length of the internodes (regions between the leaves on a stem). Plants
with short stems produce few or no gibberellins. Short plant stems reduce waste &
make plants less vulnerable to damage by weather & harvesting.
The limitations for plants are:
they are rooted (not mobile)
they do not have a rapidly responding nervous system, therefore
plant responses are slower than animal responses
However they are coordinated organisms that show clear responses
to their environment & communication between cells & different
plants.
Plants have evolved a system of hormones- chemicals produced in one
region of the plant & transported both through the transport tissue
& cell to cell to have an effect in another part of the plant.
Chemicals such as auxin & gibberellins are considered to be plant
hormones as they're similar to animal hormones, involved in
coordination of the plant & made in one place & carried through the
transport system to another region where they have an effect.
Synergism- Interaction of different hormones which complement
each other.
Antagonism- Interaction of different hormones that have opposing
effects. E.g. 1 hormone preventing growth & the other promoting it.
, Plant hormones and seed germination
Germination is the process by which a plant starts growing from a seed.
When the seed absorbs water, the embryo is activated & begins to produce
gibberellins. They in turn stimulate the production enzymes by switching on the gene
that codes for amylases & proteases which break down the food stores found in the
seed. The food store is in the cotyledon in dicot seeds & endosperm in monocot
seeds. The embryo plant uses these food stores to produce ATP for building
materials so it can grow & break out through the seed coat.
Evidence suggests that plant hormone ABA
acts as an antagonist to gibberellins
(interferes with action of gibberellins). The
levels of the 2 hormones determine when the
seed will germinate.
Experiments to provide evidence of the action
of gibberellins have been conducted. E.g.
mutant seeds lacking gibberellin have been
bred. These seeds do not germinate unless
gibberellins are applied externally.
Gibberellins are important in the elongation
of plant stems during growth as they
affect the length of the internodes (regions between the leaves on a stem). Plants
with short stems produce few or no gibberellins. Short plant stems reduce waste &
make plants less vulnerable to damage by weather & harvesting.
