Plant Responses - Chp 32

Stimulus

anything that causes a reaction in an organism

Response

activity in a cell or organism that occurs as a result of the stimulus

How does the way plants respond differ from how animals respond?

• only have a chemical response;animals have a chemical, nervous and immune system

• their responses are slow; animals are capable of fast and slow responses

• plant reponses include; growth, flowering, production of enzymes

• animals responses include movement, feeding etc

What are the external factors that stimulate plant responses?

Light intensity - provides energy for photosynthesis

Day length - causes plants to flower, seed and fruit formation, and seed germination

Gravity - causes roots to grow downwards, and shoots to grow upwards

What are the internals factors that stimulate a plant response?

plants produce chemicals, growth regulators, in the meristematic regions of the plant

Tropism

a change in the growth of a plant in response to an external stimulus to obtain more favourable growing conditions

Phototropism

change of growth in response to light

Geotropism

change of growth in response to gravity

Thigmotropism

change of growth in response to touch

Hydrotropism

change of growth in response to water

Chemotropism

change of growth in response to chemicals

Growth regulator

a chemical that controls the growth of a plant

Where are growth regulators produced?

meristem → travel through vascular tissue to different parts of the plant

What impacts the affect of growth regulators?

• concentration - usually active in small amounts; can have opposite effect at higher or lower concentrations

• location - can have opposite effects in shoot or root

Promoters + example

• increase the rate of growth for the plant

• auxin (IAA)

Inhibitors

What does IAA stand for? not sure if need to know

indoleacetic acid

Where is Auxin made

in shoot tips, young leaves, seeds

What are the functions of auxin?

• stimulates cells to grow longer, causing stem elongation and root growth

• develops fruit

• causes phototropism and geotropism

• moves through plant by active transport

What are the effects of auxin?

Tropisms - causes growth as the cells elongate

Apical dominance - apical bud releases auxins and stops the lateral buds from growing; if the apical bud is removed the side branches will develop and a low bushy plant will form

Fruit formation - stimulate the growth of food in the fruit around the seed, this results in seedless fruits

Root growth - at low concentrations only will cause roots to grow

What is another name for seedless fruits?

parthenocarpic

How does auxin cause cell elongation?

auxin helps break down the cell walls in a plant, allowing them to expand

Describe the role of Auxin in phototropism

diffuses down the shaded side

bends due to the unequal distribution

Draw a graph to show the behaviour of roots and shoots in response to auxins

Give 2 commercial uses for growth regulators:

• ethene is used to commercially ripen fruits

• auxins are used to produce seedless fruits

• root powders such as NAA stimulates root growth from plant cuttings

Name 4 methods of plant protection

Anatomical

• epidermis prevents the entry of pathogens and prevents excessive water loss

• guard cells close to prevent water loss in high temperatures

• abscisic acid produced in mesophyll cells also cause stomata to close to conserve water

Chemical

• cabbages produce mustard oils to deter animals

• oak trees produce tannins to deter caterpillars

• rhubarb contains oxalic acid, which is fatal to animals in high doses