Net Primary Productivity Lab
Name __________
Materials
(Note - derived from Molnar Lab 15)
Trays of growing grass
wheat grass - ¼ ' spaced (3 packages)
red/orange yarn, paper clips large, scissors, drying oven, aluminum trays for drying, balance
PreLab BZ 54-62 or Miller P 70
1. What does NPP mean and how is it different from GPP?
Procedure
We will use the clipped grass Method - simulates effect of grazing
animals
1. After the grass has grown for 2/3 weeks in each grass tray define
Planting
Date
Grass
type
Area
2 areas 20cm x 20 cm with approx. equal growth so far. Mark with
yarn and opened paper clips
Wheat grass
date
height
Dry
mass
XXXXX
XXXXX
XXXXX
XXXXX
2. In the first area clip the grass 0.5 cm above the soil
First
Harvest
Second
Harvest
Mass
difference
Extra
Days
3. Place clipped grass in an aluminum tray and dry for 48 hours at
temp (90-95C)
4. Record mass of dried grass in your data table
5. Let the other section(s) grow for one more week
6. Harvest the second area and dry it as in 2,3 above.
7. Record mass in grams
Calculations
Analysis
1. Use grams increase and days to find
grams /year
2. 1 cm = ______ m; 1 cm2= ______ m2
1
Calculate growth /day
= Mass increase/day
x days per year
Your area = __________cm2
= __________ m2
3
3. Calculate the growth for a full square meter
g/year
divide by your area to
convert to g/ m2 yr
g/ m2 yr
4. Each gram of grass produces 17kJ
- convert to kJ /m2year
4
NPP in
k J/ m2year
4. How does this data compare with NPP numbers in your text books?
Part 2 Bioenergy Math problems:
from Tom LaHue, revised October, 2011
1. Net Productivity (NSP) of rabbits is 1200 kJ/m2/year and Net Primary Productivity (NPP) of the grasses they eat is
12,000 kJ/m2/year. What is the % trophic level efficiency?
2. It takes 7 lb of grains and other plant material to produce 1 lb of livestock.
What is the growth efficiency of livestock?
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Net Primary Productivity Lab
Name __________
PYRAMID OF BIOMASS (Questions 3-7) 3. Complete missing names and levels
4. Calculate the level to level % efficiency and put answers in table
Level name
type - example
Trophic
level
large carnivore - fish
primary consumer
producer
small carnivore invertebrates /small fish
herbivore
turtles/invertebrates
autotroph plants and algae
g dry biomass/m3
efficiency from prev
level
1.5
11
2
37
1
809
XXXXXXXXXXX
5. Calculate the average of the 3 efficiencies
6. Calculate the overall efficiency from plants to large carnivores
7. Why aren’t there more levels in this ecosystem?
8. Human who eat large fish could be considered super carnivores in this system. Use the average efficiency and add
one more level to find the overall efficiency from plants to humans
9. Draw a biomass pyramid for this
- include numbers but scale does NOT
need to be exact
10. Why is it preferable to eat at a lower trophic level?
11. What % of your diet comes from the higher trophic levels?
12. Why is it not a good idea to eat too many predatory fish?
( third or 4th trophic level) Give 2 reasons
Part 3 - Related Problems
1. How much more efficient in is an estuary (9000 kcal /m2 year) than taiga (3500 kcal per meter2 per year)?
Give kcals AND approx. ratio
2. How much more efficient is temperate forest (6000 kcal /m2 year) than agricultural land (2800 kcal /m2 year)?
Give kcals AND approx. ratio
3. About 3% of the food eaten by growing manatees is converted into body mass. If a manatee eats 70 lbs of food per
week, how much mass will the manatee gain in one week?
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