PLSC 210 - Horticulture Science
Fall Semester, 2010
Homework #2
Name____________________________
(Total 25 points, due Friday, October 16)
1. Using the information provided below, answer the following questions:
Gas
Nitrogen (N2)
Oxygen (O2)
Argon (A)
Carbon Dioxide (CO2)
Other gases (C2H4, SO2, other pollutants)
Concentration
78.09% (780,900 ppm)
20.94% (209,400 ppm)
0.93% (9,300 ppm)
0.03% (300 ppm)
0.01% (100 ppm)
____
a. You have 30 umbrella plants that are 2' tall in your bedroom (dimension 8'x10'x10') and keep the
door partly open at night, worrying that plants could deplete oxygen in the dark. Assuming that an
average 2'-tall umbrella plant consumes 0.25 ft3 oxygen for respiration over a 12-hour dark period
and the condition of anoxia for human develops when the ambient oxygen level falls below 16%.
Do you have to keep your bedroom door propped open for replenishing oxygen or it is safe to go
to sleep with your bedroom door closed? Provide logic for your conclusion. (4 points)
b. Plot a general pattern of the fluctuating CO2 concentrations inside a tightly sealed tomato
greenhouse over a 24-hour time course for a typical clear day. On your graph, show when CO2
can best be enriched to enhance crop yield and explain your logic. (4 points)
c. The generally perceived phenomenon of “global warming” may become more real as CO2
concentration in the atmosphere keeps increasing. Which of the following practices would be the
most desirable way of keeping the atmospheric carbon dioxide levels in check? Provide reasons
for your conclusion. (2 points)
a)
b)
c)
d)
Heating a greenhouse with #2 heating oil from petroleum source
Using natural gas as a fuel source
Burning coal as a fuel source
Heating the greenhouse with a biomass feedstock from renewable sources.
2. The carbon dioxide compensation point is lower in C4 plants than in C3 plants. Design an experiment
to demonstrate that one of the two crops given (corn, soybean) is a C4 or a C3 plant, and provide the
logic for your decision. (4 points)
3. What would be the wet-bulb temperature of an air having 80 oF dry-bulb temperature at 10% relative
humidity (RH) and 50% RH, respectively? (6 points)
Wet-bulb temperature:
___________ oF at 10% RH
___________ oF at 50% RH
4. Which of the following locations would have a lower greenhouse temperature when a pad-and-fan
evaporative cooling system is in operation? (5 points)
a. Tucson (Arizona), on a summer day with 120 oF air temperature and 10 % RH
b. Washington, D.C., on a summer day with 85 oF air temperature and 90% RH
Psychrometric Chart
2