Essay On Phototropism

Phototropism and Location in Brassica narinosa

Background

Phototropism is the tendency for a plant to react to the light in its surrounding environment. In plant shoots, this effect is created by the synthesis and transport of Auxin, a hormone that stimulates the growth of cells. Photoreceptors called phototropins sense certain wavelengths of light, and they cause the auxin to move away from the lit side of the plant. The auxin causes the cells on the dark side of the cell to grow larger than the lit side, causing the shoot to bend towards the light source. This adaptation allows plants to optimize the amount of light that they receive. Experiments done by Charles Darwin have shown the tips of coleoptiles to be especially photosensitive.

Aim

2. Fill the plant tray almost to the top with garden soil and make sure the soil creates a relatively level surface.

3. Use your finger to make indentations in the soil about one half of an inch deep. Evenly space these indentations throughout the tray, in a 5X6 grid. Leave at least two inches between the edges of the tray and any of the indentations.

4. Let the water out of the jar without losing the seeds.

5. Place 3-5 seeds in each indentation, then push some soil over top of them to cover them and make the surface relatively level.

6. Poke a hole in the cap of the plastic water bottle, and use this to lightly water the seeds, making the soil damp.

7. Place the tray under the grow light, parallel with it, and center it so that each plant gets as similar an amount of light as possible.

8. Let this sit, watering lightly just enough to keep the soil slightly damp, until the plants grow to around one inch tall.

9. Use the scissors to cut any extra plants, leaving only one per each spot on the grid. Cut the ones that seem the most flimsy or that are already growing at an angle, not perpendicular to the ground. Cut the stem as low to the soil as