B1.6 Nervous System and Hormones - 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
Positive phototropism
Positive phototropism
Negative phototropism
Plant roots grow away from light sources as darker conditions such as the soil are more likely to provide moisture and minerals
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
Foil covering plant shoot tips
Plant shoots grow upwards but do not grow towards light if foil covers plant tips, suggesting the tips of shoots are sensitive to light
Foil covering plant shoot stems
Plant shoots continue to grow towards light if foil covers stems, suggesting the stems and lower parts of shoots are not sensitive to light
