Plant Hormones

What are the three key hormones in plants?

• auxins

• ethene

• gibberellins

What can hormones do in plants?

control anything related to growth

• roots & shoots

• seed germination

• leaf fall

• disease resistance

• fruit fermentation & ripening

• flowering time

• bud formation

tropism

• plants respond to stimuli of Light, Gravity and Water

• the growth response of a plant to a directional stimulus

• if a plant grows towards the stimuli is positive tropism but if plant grow away its negative tropism

phototropism

stem/shoots moving towards light (positive)

geotropism

• roots moving towards the direction of gravity (positive)

• move into the soil and anchor the plant

• allows plant to get water and minerals

hydrotropism

plants moving towards a water source

auxins

a group of chemicals that influence the growth and development of plants

• are made in tip of roots and shoots

• in shoots it make the cells grow faster → cell elongation

• in roots it makes cells grow slower → inhibits growth

What happens when light is shone directly above a plant?

growth is equal towards light source → auxins diffuse downwards causing cell elongation on both sides

What happens when plants receive light from an angle?

• sunlight causes auxins to diffuse away from the side with light on it

• therefore most direct sunlight cause the least amount of auxin

• more auxin leads to more growth by cell elongation

• so the side of the tip that has the most direct sunlight will have the least amount of auxin

• more growth occurs on the shaded side

• lopsided growth occurs & the plant bends towards light

What happens to auxin in a root?

• when it grows sideways auxins will increase on its lower side

• extra auxin inhibits growth and the root bends downwards

other auxin uses

• killing weeds → use auxins to disrupt growth of weeds

• rooting powder → leads to rapid growth of cuttings so a new plant develops

• added to tissue culture in labs to ensure growth of

Gibberellins

• initiate germination (when a seed becomes a plant)

• end dormancy → seed no longer requires perfect conditions

• flowering → allows plants to flower quicker

• larger fruit

Ethene

• gas produced by plants

• controls growth of plants

• controls ripening of fruits

• used in storage and fruits to ensure ripening doesn’t happen too quickly

Germination required practical Equipment

• newly germinated seeds

• three petri dishes

• cotton wool

• ater and pipette

Germination required practical variables

Independent variable - light intensity

Dependent variable - length of plants

control - temperature, volume of water

Germination required practical method

• three petri dishes containing 5 newly germinated seedling growing in a layer of cotton wool

• measure length of each shoot then right measurement in results table

• draw seedling in results table

• place one petri dish in direct sunlight, one in partial light and one in no light

• leave experiment for a week adding same amount of water throughout

• after a week measure the length of each shoot then write measurements in results table

• repeat?

Germination required practical expected results

• plant in partial light would have bent towards light

• in full sunlight would have grown the most straight up

• in no sunlight would have grown upwards but te least