The Nitty Gritty With No Grit!
Plants, like all living things, have certain requirements that need to be met for them to grow and thrive. These include water, nutrients, light, air, and structural support for the roots. In traditional gardening, plants get root support, nutrients, water, and oxygen from the soil. Without soil, hydroponic growers must find ways to provide water and the right balance of nutrients directly to the plants' roots, enabling the plants to concentrate their energy on producing leaves and fruits rather than searching for water and nutrients. Another challenge is designing ways of providing the support and oxygen that plants need. Before reading more about plant needs and some of the innovative ways hydroponic gardeners meet them, read this refresher on plant plumbing.
Roots and Shoots
The most important function of plant roots is to absorb water and nutrients. How does it happen? Covering the growing tip of each root are hundreds of tiny root hairs. The cell walls and membranes of the hairs are porous thereby allowing water molecules containing dissolved minerals to enter. The movement of the molecules through the cell membranes is called osmosis. Osmosis occurs because the water seeks balance in the concentration of nutrients inside and outside of the plant.
Plant roots deliver the necessary water and nutrients (via the stem) to the plant's leaves where photosynthesis -- food (energy) production-- occurs. During photosynthesis carbon dioxide enters the plant through the leaf's surface. Carbohydrates (glucose) are produced from carbon dioxide and a source of hydrogen (water) in chlorophyll-containing plant cells when they are exposed to light. This process results in the production of oxygen. (Like animals, plants also require oxygen for respiration.) These carbohydrates fuel plant growth and reproduction. Only a small amount of the water sent to the leaves is used in photosynthesis; the rest is given off into the air through transpiration.
You can explore the phenomenon of osmosis with your students by inserting a clear straw into the hollowed-out top of a fresh carrot, dripping candle wax around the straw to serve as a seal. Set the carrot in a jar of water, then drop a small amount of sugar water down the straw and mark its position. Students should be able to see the fluid in the straw, which simulates the carrot stem, rising under osmotic pressure.