Biomass and productivityAQA A-Level Biology: Flashcards
Card 1 of 130 of 13 known
Question
Where does the carbon in plant biomass come from?
Tap or press Space to reveal
Tap card or press Space to flip
See all 13 cards
- Where does the carbon in plant biomass come from?
- Atmospheric or aquatic carbon dioxide, fixed in photosynthesis.
- What happens to most of the sugars a plant makes?
- They are used as respiratory substrates.
- What are the remaining sugars used for?
- To make other biological molecules (cellulose, lipids, proteins) that form the plant's biomass.
- Why use dry mass to measure biomass?
- Water content varies, so dry mass is a reliable measure of the organic material.
- How do you know a sample is fully dry?
- Its mass is constant when reweighed at intervals.
- Give two ways of expressing biomass.
- Mass of carbon, or dry mass of tissue, in a given area.
- How is the energy store in dry biomass estimated?
- By calorimetry: burn a sample under water and measure the temperature rise.
- What is the equation for energy transferred to water?
- Energy = mass of water × specific heat capacity × temperature change.
- Why does calorimetry tend to underestimate the energy store?
- Heat is lost to the surroundings and combustion may be incomplete.
- Define gross primary production (GPP).
- The chemical energy store in plant biomass, in a given area or volume, made by photosynthesis.
- State the equation for NPP.
- NPP = GPP − R, where R is respiratory loss.
- What is NPP available for?
- Plant growth and reproduction and to other trophic levels, such as herbivores and decomposers.
- What is productivity?
- The rate of production, measured as biomass in a given area in a given time, e.g. kJ ha⁻¹ year⁻¹.
Exam questions on Biomass and productivity
- An ecologist estimates the biomass of a meadow. She cuts all the vegetation from several 1.0 m² quadrats, dries it in an oven at 80 °C and reweighs it at intervals until the mass stops changing. The mean dry mass of vegetation per quadrat is 240 g.The ecologist's quadrats are 1.0 m² and 1 ha = 10 000 m². Calculate the mean dry mass of the meadow vegetation in kg ha⁻¹.2 marks
- A student measures the chemical energy stored in dried meadow plants using calorimetry. She burns 0.50 g of dried, ground plant material beneath a boiling tube containing 100 g of water. The temperature of the water rises by 19.0 °C. The specific heat capacity of water is 4.2 J g⁻¹ °C⁻¹.Calculate the energy released per gram of dried plant material, in kJ g⁻¹.2 marks
- A conifer plantation of area 1 ha has a gross primary production (GPP) of 21 000 kJ m⁻² year⁻¹. The trees lose 8 400 kJ m⁻² year⁻¹ to the environment as a result of respiration. A second plantation (B) of the same area has the same GPP but a net primary production (NPP) of 15 750 kJ m⁻² year⁻¹.Calculate the net primary production (NPP) of the first plantation in kJ m⁻² year⁻¹, and state what this energy is available for.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).