5.1.6 Plant responses- Plant responses using TM

Plants need to response to their environment from abiotic stress or herbivory as well as tropisms that affect the plants direction growth

Tropisms- Directional responses to abiotic factors e.g light and are towards or away from stimuli

When they grow towards a stimuli’s this is positive the opposite is negative

Light Phototropism- Positive shoots negative roots

Gravity Geotropism- Positive roots negative shoots

Others are hydrotropism and thigmotropism e.g Mimosa Pudica

This is controlled by hormones in the plant

Growth factors like auxin promote cell elongation- IAA Indole ascetic acid (Promote shoots inhibits growth in roots) also inhibit leaf loss

this only occurs in the tip where meristem cells are present for growth, this growth factor diffuses down into the rest of the shoot

IAA is on the shaded side cause the cells to elongated in the presence of it so the cell walls stretch bending the shoot towards the light

Roots exhibit negative phototropism to IAA inhibits growth so the shaded side will not elongated as much but on the lighter side elongated inside so the roots grow away

Older cells are no effected by IAA as they become more ridged as active transport of hydrogen ions allow elongation