How Do Plants Feed and Breathe?

Plants nourish themselves not only with nutrients found in the soil and water but also with the energy found in light. Just as some bacteria and algae do, photosynthesis is the way plants capture the energy of sunlight to produce food. The process is rather complex but basically, plants convert CO2 (carbon dioxide) into carbohydrates and oxygen with the use of water and energy (provided by light). During the day, light is absorbed by different pigments, especially chlorophyll. Since chlorophyll does not absorb the wavelength of green light, it is reflected by the leaves. This is why most plants are green.

Carbohydrates are chemical forms of energy necessary to feed living organisms. Oxygen is necessary for respiration of living organisms, including plants. During plant respiration, carbohydrates combine with oxygen which are reduced to carbon dioxide and water, the reverse of photosynthesis. This process goes on night and day, but is counterbalanced by photosynthesis during daytime.

Of course, plants also need small amounts of mineral nutrients they absorb along with water through their roots. Carnivorous plants have developed an original way of ingesting nutrients by capturing insects and feeding on their decomposing bodies.

Try an experiment with two same-size potted plants (you can sow your own peas or beans and wait until they are a few weeks old to do this experiment). Since plants need light and carbon dioxide for photosynthesis, you can demonstrate this by depriving some of the plants of these vital elements and then observe the effects. Deprive light from one and leave the other one as a control plant in order to compare the results.

The "no light" plant should be put in a dark closet or anywhere where the plant will get no light. Observe and water the plants for two weeks to see the effects of these experiments. You can also keep a daily log of this experiment and note all the changes as well as the time span. You can also take pictures of the two potted plants at various stages of your experiment and include them in your log.