There is a conflict between van Helmont's data on willow tree growth and the data on essential nutrients listed in Table 36.1. According to the table, nutrients other than C, H, and O should make up about 4 percent of a willow tree's mass. Most or all of these nutrients should come from soil. But van Helmont claimed that the soil in his experiment lost just 60 g, while the tree gained 74,000 g. Calculate the percentage of the added mass accounted for by soil, and compare it to the predicted 4 percent. State at least one hypothesis to explain the conflict between expected and observed results. How would you test this hypothesis?

Video transcript

Welcome back everyone. Let's look at our next problem. It says, assume you fill a pot with 45 kg of soil. Plant a one kg sapling in it and simply water it on a regular basis. After five years, the soil and plant weights were 44.97 kg and 37 kg respectively. As determined by you Based on this observation, which of the following do you believe is responsible for most of the additional 36 kg in the plant? Well, when we think about um what makes up the bulk of the plant, about 95 of the dry weight of a plant is made up of carbon, hydrogen and oxygen. So let's keep that in mind. As we look at our answer choices, choice A says water. Um water is necessary. It's necessary for the reactions of photosynthesis to be carried out and it provides the hydrogen to the plant, but that wouldn't be responsible for most of the mass of that plant. So not responsible for most of its growth. So we can rule out choice A is our correct answer. Choice B. says carbon dioxide. Well, as we recall, the plant uses the carbon and carbon dioxide fixes the carbon um as photosynthesis to provide to make all those sugars, all those carbohydrates it needs that are going to make up 95% of its dry weight. So carbon dioxide is our correct answer for being the source of most of the growth of the plant. Choice C says micronutrients. Micronutrients are nutrients needed in tiny amounts like vitamins um the plant obtains that from the soil but they're only needed in tiny amounts and therefore not responsible for most of the growth. And finally, choice to eat macronutrients, macronutrients are needed in large amounts for plants. Um that would be nitrogen Um is necessary and the nitrogen it would be mainly getting from the soil, but again, 95% of its weight are carbon, hydrogen and oxygen not nitrogen. So it is very necessary but it's not going to be responsible for most of its growth. And we see that reflected in the fact that the soil mass only went down by a tiny bit from 45 kg to 44.97. So that confirms that observation. So choice d is not a correct answer. What's responsible for most of the additional 36 kg in the plant? Choice be carbon dioxide. Hope to see in the next video