The Tree That Ate Air

Start: a 2.3 kg willow sapling in 90.8 kg of dried soil. Five years of nothing but water. End: a 76.7 kg tree — and the soil has lost just 0.06 kg.

1. Mass gained by the tree: 76.7 − 2.3 = ___ kg

2. Convert the soil's loss to grams, then to kg. Soil loss in kg: 60 g = ___ kg

3. The ratio that ends the argument: tree gain ÷ soil loss = 74.4 ÷ 0.06 = ___. Finish the sentence: "The tree gained about ___ times more mass than the soil lost — so the tree is mostly NOT made of ___."

4. Van Helmont concluded it was all the water. He was half right — he couldn't weigh the other ingredient because it's invisible. What is it? (You met it in the steel wool.)

6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂
Trees rearrange air and water into sugar. Count every atom on both sides — the conservation law says the inventory must match exactly.

1. Respiration (you, right now) runs the exact same equation backwards. Write it flipped: glucose + oxygen → ___ + ___. What does it mean that life and air run the same books in opposite directions?

Food energy is chemistry you can eat. Walking burns about 4 kcal per minute. Labels: cookie = 220 kcal · apple = 95 kcal.

1. Minutes of walking to burn the cookie? The apple?

2. Fat stores 9 kcal per gram; carbohydrate stores 4 kcal per gram. A 20 g pat of butter vs. 20 g of sugar — energy of each? Why does the same mass of fat hold more than double the energy? (Which one is the denser storage, chemically?)

3. Your body is burning glucose all day just to stay alive — roughly 1,600 kcal before you move a muscle. At 4 kcal/g of carbohydrate, how many grams of glucose is a rest day? (Real bodies mix fuels — this is the simplified version.)

A big tree's dry mass is about 500 kg, and dry plant matter is about half carbon — call it 250 kg of carbon. All of it pulled from CO₂ in the air. CO₂ is 12/44 carbon by mass (C = 12, O₂ = 32, total 44).

1. Carbon fraction of CO₂: 12 ÷ 44 ≈ 0.27. As a percent?

2. CO₂ needed to deliver 250 kg of carbon: 250 ÷ 0.27 ≈ ___ kg

3. So one tree pulled ~900 kg of CO₂ out of the air. One sentence for the bridge to biology: why does "a tree is made of air" turn out to be literally, weighably true?