A Discussion on Glucose as an Alternative for Sunlight for Plant Growth

Biology Research Project

Can a plant survive without sunlight, if its fed the glucose that the sunlight provides?

In my project, I explored the concept of the necessity of sunlight in the survival of plants. Sunlight provides plants with energy that, in turn, will produce sugars through the carbon fixation cycle in the form of glucose. Glucose is used as the food of plants, and is broken down by cell respiration and gives the plant energy to grow and thrive. I always heard people say that plants needed plenty of sunlight, but if the sunlight only produced glucose, could you just give the glucose to it and not give it any sunlight? I wondered if plants were capable of staying alive without sunlight if I just gave them the glucose that the sunlight wasnt there to give for them.

In carrying out this experiment, I started by collecting two Styrofoam planting pots and soil to put in the pots. I put cotton wicks in the holes of the pots to suck up water for the plants. I got some fast plants that grow quickly obviously, and planted three seeds in each hole for the seeds. I put three fertilizer seeds on a half full pot of soil, I then filed up the rest of the pot with the soil and put the plant seeds on the top of the soil and pushed them down a little bit. I then got two Tupperware boxes and taped down the tops of the boxes sideways so you could see into the box. In the box, I put water and draped a cotton sheet across the top into the water but over the taped down tops. These cotton sheets would absorb the water, and through osmosis it would soak up and would defy gravity by getting the whole cotton sheet wet. Because the pots are placed on these sheets, and because they have the wicks to absorb the water and pull them into the pot, the plant can get water. I planted the plants and put them both into the sun so I could make sure that both the plants are growing. After two days both of the plants were growing, so I took one and labeled it glucose, and labeled the other one sun. The sun plant I left the sun, and the glucose plant I put in my desk drawer. In the glucose plants box, I didnt put only water, because I needed to give it the glucose remember?, but I put in a glucose concentration. The glucose concentration was 97% water, and 3% glucose. This is the concentration necessary because plants are 97% water and putting any more glucose in this concentration would kill the plant, or would at least harm it. For the next fifteen days I let the plants grow, the glucose-fed one in my desk, and the sun plant in my window. Everyday I would take pictures of each plant and make observations of their growth, color and shape, and how the glucose plant was growing differently from the sun plant.

In the first few days, the sun plant grew constantly while the glucose plant barely grew. At this point I thought that the glucose, plant had died and my experiment was useless. Time would prove me wrong though. The next two days or so, the glucose plant grew at a furious rate while the sun plant grew at a still constant rate. It then stopped growing for a couple of days and stayed at a constant height. It would then grow again and stop for a few days. After about the third time this happened, the glucose plant stopped growing entirely and died. I assumed that it died by the observation of its height shrinking by a few millimeters. Meanwhile, the sun plant was constantly growing about three or four millimeters a day, depending on how much sun it got. The leaves on the sun plant were very big and green throughout the whole experiment and the stems were green and healthy-looking. The glucose plants leaves we very small and shriveled, and later they got burnt edges. The stem for the glucose plant was white and I kept observations and they are on the attached sheet, I also made a table of the heights of the two plants and how they changed as days went on.

The plants were both growing in height during this fifteen day period, but the sun plant was much healthier. I have found a reason for why, even though the glucose, which sun provides, is already given to the plant, the plant is still doomed. I found that glucose, water, soil, and oxygen arent the only things which plants need to survive, but that is all I gave to the glucose plant. The essential elements which plants need to survive are nitrogen, phosphorus, and potassium, but too much of these elements can lead to bad things. For example: when there is evidence of burnt edges to the leaves, it can mean there is an unhealthily high level of nitrogen. In addition to the base elements, plants also need at least 10, of what are called, trace elements. Some examples of trace elements are, sulfur, iron, manganese, zinc, copper, magnesium, calcium, chorine, molybdenum, and boron. Plants also cant survive in soil whos pH levels are much higher than 7. The comfort level for them, is between 5.6 and 6.5. I found that sunlight is a good neutralizer of the base elements (nitrogen, phosphorus, potassium) so the levels dont get too high. This means it can increase the element levels if it is insufficient as well as kill it off it is too much. Sun also provides neutralization of the pH levels in the soil as well as element levels. Neither of these things could happen for the glucose plant, and is a good explanation of why there was burnt edges on the glucose plant. Nitrogen provides chlorophyll and plant proteins to give strong stems and roots, potassium helps plants reserve food and fights of disease. Phosphorus provides an increase in seed production, and gives plants more color. When there is no sun to provide any more of these elements they loose these additions. Soil can provide the elements for some time but eventually they will die out. Potassium is usually needed a lot in indoor plants, and my glucose plant obviously didnt get much. It had no color and the leaves were weak. The plant didnt get any, but at the same time, got too much of these minerals. There were only small deposits of the minerals that were way to rich in them. That is why the plant had an unusually stiff stem, and looked so dead. It grew at the beginning because the soil provided healthy amounts of the minerals but they culminated in areas where the soil then became very dense in the minerals. The plant had no defense for disease as well, and any subjection to a disease would result in contraction of it. The plant showed all the signs of mineral deficiency. Some signs for mineral deficiency are stunted growth (the glucose plant had stopped growing and stayed at the same height for long periods of time), deformed leaves (they werent the usual raindrop-shaped leaves, but were attached together), leaves with unusual red, purple, or yellow splotches (they were light yellow with off yellow splotches). The mineral dense areas were created, when the water was absorbed by the roots. The minerals were all needed and culminated in that area, and only salts were left over. This also happened with the glucose. It was all used and then it was left in the soil as sodium and sucked the plant dry of the water. Wick-watering techniques (what I used) are known to leave salt deposits on the surface of the soil. These are all reasons for the water loss. I saw that even though the water was evaporated faster when the plant was in the sun, more water was absorbed of the glucose solution.

This experiment had a lot of room for error, but none that really influences the outcome that much, if there really is a different result for each variable. On two occasions the pot for the sun plant was blown over by the wind when I left the window open. The plant fell out with the soil, but when I replanted it, the plant was still taller than the glucose plant. This only affected the numbers corresponding to the plants height on the data table. In the end I still knew that the glucose plant wasnt as tall as the sun plant, and it didnt grow as constantly. The possibility of the glucose solution being the incorrect mixture of glucose and water was another error. It was estimated that the correct ratio was 97% water and 3% glucose, but its an approximation and I dont know if that could have made any difference because it was such a small difference. Even if it did make a difference, it again, couldnt have made the experiment change so dramatically that the entire outcome would be totally different from what it is now. Another error is the glucose plant getting light when I would take it out of the dark to take its picture and make observations on it. This could have given it enough light for a little growth but, like I said before, it wouldnt be enough to make a difference in the outcome of my experiment. The last somewhat significant error was made by me. I didnt measure the glucose plant correctly for a day or two, but I recovered and estimated the total. This makes a difference but I still knew what would have happened approximately and it didnt really affect my last observations anyway. Other than that, there isnt anything which is anymore of an error than these things, but none of these make a significant impact anyway.

In conclusion, I think glucose-fed, sunless plants, are capable of growing, but not capable of maintaining homeostasis. They are not healthy, green, normal, or even capable of surviving a short period of time. They cant grow or even have a chance of surviving at all, unless they have a good amount of minerals in its soil like I used the little fertilizer pellets. The glucose plant is only capable of growing for a little bit and then it dies. So basically you will have to consistently feed it the perfect amount of minerals and keep the pH at the perfect level, while monitoring the sodium deposits on the top soil. After doing these things a whole lot more care is also necessary to let a plant stay healthy without sunlight. Even when you do everything perfectly, the sunless plant is still not going to be as successful as one grown by sun. So in concluding the project, plants do need sunlight to survive, and feeding it glucose isnt an okay substitute for sunlight.