What impressions of plants are we giving? Part 1. The needs of the plant. June 12 2019, 1 Comment

The botany impressionistic charts are a set of about 18 images and stories that have been described as showing what Maria Montessori thought children should know about plants. The concept of these charts is an excellent one because plants are harder than animals for children (and adults) to understand. The originals are likely over 70 years old now. There have been some changes over the years, particularly in the illustrations, but a good deal of the content is quite similar to the originals.

I have been looking at these charts and asking myself what else children today need to know about plants, and whether everything shown on the original charts is still considered valid. I’ve come up with several chart ideas that are different from the usual content of the set.

As you read my ideas below, please note that I am not advocating doing away with the botany impressionistic charts although I would like to give them a name that is more understandable in today’s language. I am critiquing the content, not the basic idea of helping children understand the biology of plants. I’ve been looking at current knowledge about plants and will tell you about some changes or new charts that I think are important.

The “needs of the plant,” the first chart in the original set, is really the “matter and energy needs of the plant.” The usual graphic shows a plant with the names of some of the chemical elements around its roots. It shows carbon dioxide, water, and sunlight as well. These are the basic building blocks of a plant’s body and its fundamental energy source.

Note that the list of chemical elements should include the major nutrients for plants – nitrogen, potassium, phosphorus, magnesium, calcium, and sulfur, as well as carbon, oxygen, and hydrogen from water and carbon dioxide. There are eight other elements that are needed in small amounts as well, but I don’t think the chart has to be encyclopedic. These can be mentioned in the text. The chart needs to get over the concept that plants need building block substances.

The text should also clarify that plants are not taking in uncombined elements through their roots. They are taking in soluble compounds of the elements. Sometimes the ions of the nonmetal elements are given – sulfate, phosphate, and nitrate, for example. The ions of the metallic elements can be labeled as ions – potassium ions, for example.

The “matter and energy needs of the plant” as shown on the original chart has one glaring omission. It should also include oxygen gas (O2). I’ve come across many students and adults who didn’t realize that plants need oxygen. The usual misconception is that plants produce oxygen, but they do not use it. All macroscopic organisms need oxygen, and plants are no different.

Plants need oxygen to extract energy from the food they have made for themselves. They make sugars, but they also use the energy stored in sugar’s chemical bonds. With their amazing chemical synthesis abilities, plants also take sugar molecules and modify them to make all the other molecules in their bodies. All that synthesis requires a lot of energy.  

Oxygen starvation is not usually a problem for the shoot system, but it can happen in the roots. The underground parts cannot use food for their energy needs if they do not have oxygen seeping down into the soil. Each cell has to transform energy for itself. The energy carrier molecule, ATP, cannot be made in the shoot and sent to the roots. When a soil is water-saturated, it greatly decreases the oxygen available to the roots, and this can kill them. This is why overwatering can be lethal. Plant roots differ in their tolerance to low oxygen. Some can handle soggy soils; others find such conditions quickly lethal.

A chart that shows plants’ other needs would be an excellent addition to these charts. It could include an appropriate environment in which to live, complete with the necessary partner organisms, and an appropriate range of physical conditions, such temperature. The soil needs of a plant are vitally important, and the characteristics of soil include pH, particle sizes, organic material, and those all-important microorganisms.

I’ll continue with ideas about other of the botany impressionistic chart in my next article. You are welcome to suggest a better name for set. If you have questions about this or other of my blog articles, please feel free to send them to me. See the “Contact Us” tab on my website for my email address.

Priscilla Spears