ch16 - plant hormones

name the 4 types of plant hormones

auxins

gibberellins

ABA (abscisic acid)

ethene

state one reason why plants need hormones

since plants are rooted to the ground they cannot move

> hormones enable them to respond to stimuli by moving/ growing towards or away

what is one thing that all 4 hormones are used for

commercial usage

What are the two ways that plant hormones interact with each other

Synergism 

Antagonism

What is synergism

When the hormones work together giving greater response than they would on their own

What is antagonism

when the hormones have opposing effects

> the balance between the hormones will determine the response of a plant - hormone with higher concentration present is the response the plant will have

state the different roles of gibberellins

-promoting stem elongation

-promoting seed germination

what does lateral shoots mean

refers to side branches

what occurs in stem elongation

gibberellins cause the stem of a plant to grow by increasing the length of the internodes (the region/ distance between leaves/ lateral shoots on a stem)

give reason why is stem elongation beneficial

helps plants grow upwards and taller to compete for more sunlight

give a reason why farmers may reduce stem elongation

shorter plants will be less vulnerable to being damaged by the weather

what is a cause of dwarf plants

mutations in the gene which produces gibberellins can result in low levels of the gibberellins - there will be little stem elongation

define germination

process in which a seed grows into seedling

define dormancy and why is it important for plants

the period of time when a seed is still alive but inactive

- plant has reduced metabolic rate > little respiration occurs so energy stores are not used up

— this conserves energy enabling the plant to survive during harsh environmental conditions e.g. winter

why is germination important

it ends dormancy state which enables the plant to start growing again

name the features of a seed

embryo

endosperm

aleurone layer

what are the roles of these features

embryo - will grow into a new plant once the seed has germinated

aleurone layer - contains many storage proteins, surrounds endosperm

endosperm - acts as energy storage that contains starch, surrounds embryo

where are gibberellins made

in the embryo of a seed

outline how germination occurs in a seed

1. water is absorbed and enters the seed & stimulates the embryo to produce gibberellins

2. gibberellins diffuse into aleurone layer & stimulates storage proteins to produce the digestive enzymes: amylase and maltase

3. digestive enzymes diffuse into endosperm

4. amylase hydrolyses starch > maltose

5. maltase hydrolyses maltose > glucose

6. glucose is transported back into the embryo where it is used during respiration to produce ATP, enabling the embryo to grow

what can be done to enable seeds with low levels of gibberellin to germinate

gibberellins can be applied to a seed externally

state the role of ethene

promotes leaf abscission

what is leaf abscission

when a plant looses its leaves

state the different roles of ABA

-maintains dormancy of seeds and buds which stops them germinating 

-stimulates protective responses when plant is under abiotic stress

state the different roles of auxins

1. promotes cell elongation 

2. maintains apical dominance

3. involved in tropism 

name an example of an auxin

IAA

name the 2 sites where auxins are produced

produced in the tips of shoots and roots by meristem cells (plant stem cells)

where are auxins mostly produced

in the shoot tips

What are the 3 zones in cell elongation 

-meristematic cell zone 

-zone of elongation 

-zone of differentiation 

Describe the process of cell elongation 

1. Auxins are produced by meristematic cells in shoot tips and diffuse downward into zone of elongation

2. A plant cell starts off very simple (only consist of plasma membrane, cell wall, nucleus) with receptors on the plasma membrane  

3. Auxins bind to these receptors which opens protein channels allowing hydrogen ions to be pumped in, this decreases pH causing cell wall to become more flexible  

4. Water moves into cell via osmosis and vacuole forms which expands cell wall (without busting since its flexible) allowing cell to elongate 

5. Once cell has matured auxins are removed and broken down causing cell wall to become rigid 

what two effects can auxin concentrations have

High auxin conc - promote shoot growth, inhibit root growth

Low auxin conc - inhibit shoot growth, promote root growth

what is the apical shoot

refers to the main vertical stem

what is apical shoot also referred to as

apical bud

explain how auxins maintain apical dominance

auxins favour growth of apical shoot which suppresses growth of the lateral shoots

what does apical dominance cause and why is this useful

causes lateral shoots near the top of plant to be shorter whereas further down lateral shoots are longer, as there is less auxins present 

> this is beneficial for the plant as it enables all shoots to compete and absorb light for photosynthesis

what happens when you remove the apical bud

plant will grow much bushier since lateral shoot growth will no longer be suppressed

outline the stages of plant growth and development 

seed germination > cell elongation > stem elongation & apical dominance

what type of interaction do gibberellins and auxins have

…

what type of interaction do gibberellins and ABA have - why

antagonistic

ABA maintains dormancy whereas

what type of interaction do auxins and ethene have - why

antagonistic