1. Name the two ways biomass can be measured.
Answer
Mass of carbon or dry mass of tissue per given area.
2. What is gross primary production (GPP) ?
Answer
Gross primary production is the chemical energy store in a plant's biomass for a given volume or area.
3. How does net primary production differ from GPP ?
Answer
This is when the respiratory losses to the environment have been taken away from the gross primary production.
4. The net production of consumers can be calculated using the equation: N = I – (F + R). What do each of these letters represent ?
Answer
I = chemical energy store in food that has been ingested
F = chemical energy that has been lost to the environment or energy lost as faeces or urine
R = respiratory losses to the environment.
5. Describe how primary and secondary productivity are measured.
Answer
Measured as biomass in a given area in a given time.
6. The figure below shows the net primary productivity in a lake ecosystem in May. Explain the shape of the line at each of the points numbered.
Answer
At point 1: net productivity is constant because light is not a limiting factor for photosynthesis. High light intensity for photosynthesis occurring at maximum rate.
At point 2: productivity rapidly decreases because of the decreasing levels of light, so rate of photosynthesis decreases.
At point 3: the rate of respiration = rate of photosynthesis so net productivity is 0.
At point 4: the photosynthesis is limited by poor light availability, so rate of photosynthesis is less than respiration.
7. The same measurements were collected in October. Explain how you would expect the net primary productivity at different depths of water to be different.
Answer
Line would be lower because of lower light intensity and lower temperature. Would reach 0 quicker because rate of photosynthesis = rate of respiration is easier due to lower light levels. Decrease after 0 would be steeper as the rate of photosynthesis would be far less than rate of respiration
8. A scientist measured the rate at which oxygen is being produced by photosynthetic organisms. Water samples from a pond were taken containing only photosynthetic organisms. One bottle was exposed to light and the other was left in darkness. The concentration of dissolved oxygen was measured at both the start and then after 24 hours. The table below shows the results. Calculate the gross primary productivity.
Answer
Calculating net productivity in light was 0.15 and respiratory loss in dark as 0.8;
9. The results of the investigation were then plotted on a graph shown in the figure below. Identify A, B and C.
Answer
10. Find a way to calculate A, B and C.
Answer
A = L − I, B = I − D,
11. The table below shows the area and the plant biomass of different ecosystems. Calculate how many times more productive a tropical rain forest is than a temperate coniferous forest.
Answer
440 ÷ 200 = 2.2 times more productive.
12. The figure below shows the energy transfer in cattle farming, for both milk and beef. Give two ways in which energy is lost at A and B.
Answer
A = energy lost through waste (could mention faeces, urine)
B = energy lost as heat
13. Describe measures that could be taken in order to reduce the energy losses at A and B.
Answer
A - Feed provided is easier to digest and absorb, so less is wasted.
B - Provide warmer surroundings for the animals to reduce energy loss through heat generation. Restrict movement of the animals to reduce energy loss through respiration.