Plant Hormones Flashcards
Auxins
Plant hormones that coordinate and control cell growth in response to light and gravity
Tropism
When an organism such as a plant responds to a stimulus by turning or growing in a certain direction
Phototropism
A change in the direction of a plant in response to light
Gravitropism
A change in the direction of a plant in response to gravity
Positive phototropism
Most plant shoots grow towards a light source to increase the rate of photosynthesis
Negative phototropism
Plant roots grow away from light sources as darker conditions such as the soil are more likely to provide moisture and minerals
Positive gravitropism
Plant roots grow towards the centre of gravity to increase the chances of obtaining water and minerals from the soil
Negative gravitropism
Plant shoots grow away from the centre of gravity to increase exposure to sunlight for photosynthesis
Tips of shoots and roots
Known as apical meristems, where auxins are produced in plants
Effect of auxins in shoots
Auxins accumulate on the shaded side of plant shoots and promote cell elongation, causing the shoots to grow towards light
Effect of auxins in roots
Auxins accumulate on the lower side of plant roots and inhibit cell growth, causing the roots to grow towards gravity
Cell elongation in shoots
Shaded cells stretch more in plant shoots so that the shaded side becomes longer than the light side, resulting in the shoots growing towards light
Inhibition of cell growth in roots
Cells on the lower side of plant roots stretch and grow less than cells on the upper side, causing the roots to grow down towards gravity
Diffusion
Auxin molecules are originally equally distributed from the tips of shoots and roots via diffusion
Unequal distributions
Gravity and light causes auxins to diffuse unevenly and move towards a shaded side or a side closer to the centre of gravity
