plant responses

definitions

clinostat: a revolving platform to equalise light and gravity

chemotropism: growth response to chemicals

geotropism: growth response to gravity

growth regulator: a substance that controls the growth of a plant

hydrotropism: growth response to water

negative: grows away from stimulus

phototropism: growth response to light

positive: grows towards stimulus

stimulus: factor that causes a response

thigmotropism: growth response to touch

tropism: growth response of a plant to a stimulus

investigate the effect of IAA on plant tissue

take some petri dishes

place 5 cress seeds on an acetate grid

place filter paper and cotton wool on top of the seeds

pour a different concentration of IAA solution into each dish

different concentrations acheived by serial dilution

add water to one dish as a control

cover and seal dishes

stand on edge so roots grow downwards

incubate at room temperature

measure the length of roots and shoots each dish

calculate average growth

control had little growth

low concentration of IAA promote root growth

high concentration of IAA promote shoot growth

safety precaution wear gloves

Serial Dilution

make stock solution of 1 ppm auxin

put 10cm³ into test tube

remove 1cm³ and add to next tube

add 9cm³ distilled water to the 1cm³ and mix well

remove 1cm³ from this tube

repeat until all tubes are used

growth regulation

external factors: temperature day length intensity nutrients water etc

internal factors: production of growth regulators

tropism

phototropism: growth response to light

a. stem grow towards light postive

b. roots away from light

geotropism: growth response to gravity

a. stems grow away from gravity negative

b. roots grow towards gravity positive

thigmotropism: growth response to touch

pea tendrils

hydrotropism: growth response to water

chemotropism: growth response to chemicals

growth regulators

promoter: increase growth

1. auxins: cell elongation

2. gibberellins: breaks dormancy cell elongation and division

3. cytokines: cell division cell differentiation

inhibitor: retards growth

1. abscisic acid: inhibits shoot growth

2. ethylene: ageing processes

similar to animal hormones

1. chemical

2. transported through the vascular system

3. slow acting and and have a long lasting effect

4. produced

effect of concentration

an auxin concentration that promotes growth in one part of a plant can inhibit growth in another part

roots are more sensitive than shoots

a concentration of 10^-1 p.p.m will promote the growth of the shoots and inhibit the growth of roots

uses of plant regulators

1. auxins used in rooting powders

2. ethene is used to ripen fruit

3. micropropagation

4. producing seedless fruit

adaptions that protect plants

1. hawthorn has thorns

2. chillies have oils that cause a burning sensation

3. nettles have stings

4. gorse has stiff pointed leaves

5. holly has thick wax cuticles protect against water loss

auxins

examples: IAA- indole acetic acid

production site- auxins is produced in apical meristems

function: causes cell elongation

effects: phototropism and apical dominance

phototropism

auxin is produced at the tip of the shoot

unilateral light causes more auxins diffuse down the shadded side

cells on the shaded side elongate more higher concentration of auxin

tip growing towards the light

demonstrating phototropism

1. plant 2 sets of seeds

2. place one in a box with light shining from one side

3. place the other on clinostat in a similar box

4. leave for 1 week

5. examine both sets of seedlings to see the direction of growth

results

• the seedlings in the box without the clinostsat grow towards the light

conclusion

seedling shoots are positively phototrophic

apical dominance

high auxin concentration near the tip inhibits growth of lateral buds

auxin concentration drops as one goes down the stem

lateral buds begin to develop

apical bud is removed the IAA production stops

all lateral buds develop making the plant bushy