mrajan
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Trouble with "How Do Plants Change the Buildup of Greenhouse Gases?"

Postby mrajan » Mon Jan 06, 2020 7:05 pm

My elementary school son has taken on this project for the science fair and is using the suggestion/outline provided in the summary. He took 6 identical glass jars and in 3 of them he placed containers containing soil and fenugreek plants and in the remaining 3 he has just placed containers containing soil. We have thermometers in each jar and have sealed the jars and placed on a window sill and recorded the temperatures in them. We expected the temperatures to be lower in the jars with the plants in them; however, they are actually recording a higher temperature than the jars with no plants. Is this to be expected? We actually had a slight variation in the purpose of the experiment as we wanted to prove that houseplants lower energy costs (due to the cooling effect). However, with the higher temperatures recorded in the jars with plants we can obviously not prove this. The soils in the jars with the plants are a tad bit more moist than the soil in the jars without the plants. Also, the fenugreek plants are themselves a bit small (perhaps 8 cms tall) and the leaves are tiny. Are these factors influencing the increased temperature? Please help (as he only has a few days until his project is due)! Thanks!!

cnoonan180
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Re: Trouble with "How Do Plants Change the Buildup of Greenhouse Gases?"

Postby cnoonan180 » Tue Jan 07, 2020 6:20 pm

Hello and welcome to the forums!

It sounds like the jars you are using for this experiment are airtight. This would make sense since you mentioned that the soil in the jars containing the plants is more moist. Since the jar is most likely air tight, the water vapor from the soil is not able to escape the jar. The water vapor stuck in the jar is causing the temperature in the jar to rise. This is because water vapor is a greenhouse gas itself. So, the water vapor is causing a small scale greenhouse effect, or trapping of the sun’s heat, in the jar with the plants. The trapping of heat from the sun by the water vapor in the jars causes the inside temperature of the jars to rise, especially since the jars were placed near a window where sunlight could provide heat to be trapped.

So, your experiment is a small representation of the effect of greenhouse gases in Earth’s atmosphere!

The reason the plants are not cooling the air inside the jars from the effect of the greenhouse gas, water vapor, is because when the atmosphere becomes warmer, or in this case the air inside the jar due to heating by sunlight, plants release water from their leaves, in the attempt to cool down their surroundings with water. However, in the airtight jars this would cause the soil to be more moist, and for the temperature inside the jar to rise. This is because as sunlight heats the jar, the water molecules turn to water vapor, which as a greenhouse gas will trap the sun’s heat inside the closed jars.

This process of plants releasing water almost like humans release sweat is called transpiration. The jars without the fenugreek plants will not experience these effects as there are no plants to release water when the sun heats the jar to create water vapor to conceal the heat. So, the soil is less moist and the air temperature in the jars without the plants is lower.

I hope this helps and feel free to ask more questions!
-cnoonan180

mrajan
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Re: Trouble with "How Do Plants Change the Buildup of Greenhouse Gases?"

Postby mrajan » Wed Jan 08, 2020 10:00 am

Thank you and this helps greatly! We did read about the fact that water vapor is a major greenhouse gas. As you say, this is a good representation of the effect of greenhouse gases. However, since we have chosen to do use a plant, not sure of what we can actually title this experiment. Because it appears that with this set-up are we then proving that plants actually contribute to the production of greenhouse gas effect which is not really true, correct? I guess this is a sealed environment which is different from reality.

We had planned to test if houseplants reduce energy costs by this set-up. There are plenty of articles that state that houseplants actually cool the house in summer and warm the house up in winter. If we demonstrate that the temperature in a sealed jar with a plant is higher (presumably due to condensation of the moisture given out by the plants, thereby releasing heat energy since the process of condensation releases heat) in addition to the water vapor effect of retention of heat are we proving that the plants are actually warming up a home (since a sealed jar environment is similar to a sealed house environment).

Conversely, in summer, due to the moisture becoming water vapor and evaporating (they wouldn't condense since the environment would be hot), plants are actually drawing away the heat. So are we on the right track with this question and experiment?

Thanks again for your input.

cnoonan180
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Re: Trouble with "How Do Plants Change the Buildup of Greenhouse Gases?"

Postby cnoonan180 » Wed Jan 08, 2020 4:43 pm

No problem!

Some options for a title for this project are:
1. Earth's Natural Air-Conditioners: How Plants Affect The Buildup of Greenhouse Gases
2. Power Plants: Are Plants Reducing Our Yearly Energy Costs?

Additionally, it is correct that plants do NOT contribute to the greenhouse effect globally, however; in the jar, the greenhouse effect does take place as it is a sealed environment, much different from Earth's atmosphere. It is also correct that water molecules lose heat energy as they condense, as they are releasing heat to transform from a hotter state (gas) to a cooler state (water). So, to answer your question: plants actually warm homes in the winter months and cool homes in the summer months. In a warm room when transpiration takes place, this will have a cooling effect. Plants release water from their leaves through transpiration as you know, and to do this the water on the leaves absorbs heat from the surrounding air, cooling the air, in order for the water to become a vapor (gas) or evaporate into the atmosphere or flow outside of a window or door in the home, when opened. This vapor will eventually condense into a cloud form outside, which provides cover to warm areas, cooling the Earth's surface. The cloud will then produce rain to nourish more plants outdoors. All of these phases that the water molecules go through make up different parts of Earth's natural water cycle. Keep in mind: none of these contribute to the greenhouse effect. In fact, global warming intensifies the water cycle so that an excessive amount of water evaporates, which does contribute to the greenhouse effect since the excess water vapor acts as a greenhouse gas.

As for colder environments, plants will again release water through transpiration and the moisture in the air from the water released by transpiration tends to hold more heat, as moist air holds more heat. The moisture in the air has not vaporized into a gas, so no heat has been taken away from the air (no cooling of air) as vaporization/evaporation do remove heat from the air so water can transform into a gas. So, more moisture in the air causes water to take longer to become a gas because the air is already saturated with water molecules so heat energy is simply held in the air which has a warming effect inside the home.

I hope this helps, and you are on the right track with this experiment. If you have any other questions, feel free to ask!
-cnoonan180

mrajan
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Re: Trouble with "How Do Plants Change the Buildup of Greenhouse Gases?"

Postby mrajan » Wed Jan 08, 2020 8:20 pm

Thanks so much for the detailed explanation. This greatly helps!! Love the suggestions for the titles as well!

mrajan
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Re: Trouble with "How Do Plants Change the Buildup of Greenhouse Gases?"

Postby mrajan » Thu Jan 09, 2020 5:44 pm

Sorry, don't mean to go on about this, but for the last day and a half the jars with the plants are consistently recording a lower temperature than the jars without. Not sure about the reason, but thought I would let you know because this is interesting and in case you know of the reason. One thing is for sure..plants do affect the ambient temperature. :)

cnoonan180
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Re: Trouble with "How Do Plants Change the Buildup of Greenhouse Gases?"

Postby cnoonan180 » Thu Jan 09, 2020 8:17 pm

Hello again!

Have you screwed on the jar lids as tightly as you did before if you have removed them? It is possible that water vapor is able to escape the jar if there are any openings or the jar is no longer air tight, so that the plant inside has a cooling effect due to the escape of the water vapor as it is no longer keeping the heat in the jar and acting as a greenhouse gas.

If the lid has been removed and re-placed on top of the jar, this would also allow moist, heat-carrying air to escape, lowering the temperature upon putting the lid back on.

Additionally, have any significant weather changes or large changes in temperature taken place? Or has the temperature of the environment where you have the jars set up changed in a notable way (ex. heating or air-conditioning)? These environmental factors may also cause the temperature difference from your previous results as explained before.

Hope this helps!
-cnoonan180

mrajan
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Joined: Mon Jan 06, 2020 6:50 pm
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Re: Trouble with "How Do Plants Change the Buildup of Greenhouse Gases?"

Postby mrajan » Fri Jan 10, 2020 8:49 am

Thanks again! No significant changes had occurred since the jars are in same location and the weather had been pretty much the same outside (and of course we are climate controlled inside). It might have more cloudy on the day that the temperatures had been lowered in the jar with the plants and maybe that had something to do with it. We did put the lid back on the jars, but not 100% sure how airtight we made it.
But it is interesting to see that the plants definitely affect the temperature inside the jar (since they consistently raise or lower)!


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