Plant tropisms and hormonal control Chapter 14 – pg’s 264 - 276
Aims: • > describe the hormonal system of plants & list the 5 main groups • > environmental stimuli & plant response • > phototropism, geotropism & thigmotropism = movements • > how light effects seedlings • > rel’ship btw photoperiod & flowering in plants • > turgor (water pressure) leads to movement in plants • > describe bud dormancy, seed dormancy & vernalisation
Plants • > fixed position (therefore have to make do with the environment) • > have to become ______ of changes • > communication btw cells is controlled by __________
What is a Hormone? • A c_____ produced by cells in the plant that can be transported to other cells in the plant. • Hormones help with the TIMING of responses (eg. when to flower or produce new buds) • Hormones TARGET particular cells for them to ________. Less specific in plants than in animals.
Tropisms • A DIRECTIONAL growth response of a plant to a stimulus. • Growth is either towards or away from a stimulus
The 5 things that PLANT hormones are responsible 4: • 1) Phototropism – growth in response to light. Photo = light. • 2) Geotropism (Growth in response to Gravity) • 3) Apical dominance – stopping lateral branches from growing – gardeners would rely on this hormone if they wanted their plant to grow TALL without side branches • 4) Ripening of fruit • 5) Abscission – shedding of leaves and flowers (particularly • with deciduous trees – in autumn)
5 types of HORMONES to affect the changes of the plant • > 1) Auxins: produced in the _________ (tip of plant), concentrates on the opposite side of the plant to the light source & when in excess it INHIBITS buds on the sides • > 2) Gibberellins – whole plant growth • > 3) Cytokinins – cell division • > 4) Inhibitors – one type = abscisic acid (ABA) – helps plants to adapt to their enviro. STOPS growth. Concentration increases in stressed conditions. Therefore conserve resources. • > 5) Ethylene – for ripening fruits and flowers. It’s a gas.
Environmental Stimuli • What is a stimuli? • 2 types: chemical & physical • PHOTOTROPISM – seed growth towards light – mostly BLUE light. What wavelength? • GEOTROPISM – shoots grow away from gravity (negatively geotropic) • THIGMOTROPISM – touch & contact with a surface (eg. vines twirl around objects). • Read page 272 on the Venus fly trap.
Photoperiod • Length of the NIGHT affects growth = ____________. Short day & long day plants. Therefore can only flower in certain environments with the RIGHT night length. • Note: Day length does NOT affect growth
Turgor • Turgor = water pressure. • Stomata -> respond to the pressure by opening or closing. • Respond to the levels of CO2, light, humidity (water in the air)
Dormancy • Seeds remain dormant until conditions are RIGHT (dormant during winter). • Vernalisation = exposure to cold conditions to break seed dormancy
Questions: • How do we use plant responses to our advantage in agriculture? • What is the advantage of being anchored to the ground if you are alive?