Movement Of Materials Through Plants

A maize plant standing in a dry field is moving water every second of the day. It pulls water from between the soil particles, lifts it metres up a hollow pipework of dead cells, and lets most of it escape as vapour from tiny pores under its leaves. At the same time it is building sugar out of air and sending that food down to its roots and grains. Nothing in the plant has a heart or a pump; the whole traffic is driven by diffusion, osmosis and the simple fact that water evaporates.

In this lesson you will follow materials all the way through a crop plant: in at the root hairs, up the xylem, into the leaf for photosynthesis, and back out through the phloem to the storage organs. You will see why a leaf is built the way it is, how the stomata trade gases, and why hot, dry, windy weather makes a crop wilt. These are the ideas a farmer uses every time they irrigate, space a crop or choose when to transplant.