23.2- Biomass transfer through an ecosystem Flashcards
Explain trophic levels
Producer – 1st trophic level
Organism that converts light energy to chemical energy by photosynthesis
Consumer – (primary, secondary, tertiary…)
Organisms that obtain energy by feeding on other organisms
(Primary consumer feeds on producer)
Decomposers: break down dead organisms, releasing nutrients back into ecosystem.
What is biomass?
The mass of living material present in a particular place/organisms.
Can be equated to energy content.
How do you calculate biomass at each trophic level?
Biomass (gm-2) = biomass in each organism x number of organisms.
What must be done before calculating the biomass of aquatic organisms?
- the water content must be disregarded so scientists calculate the dry mass.
1. Organisms must be killed. Placed in an 80*C oven until all water has evaporated.
2. Only a small sample is taken to minimise destruction.
Biomass measured in gm-3 (water)
Explain energy transfer between the trophic levels.
- the biomass of each level is always less than the trophic level below.
- this is because biomass consists of all the cells and tissues of the organism (including carbs and any other carbon compounds).
- as carbon compounds are a store of energy, biomass can be equated to energy content.
- when animals eat, only a small proportion of the food they ingest is converted into new tissue, only this part of the biomass is available for the next trophic level to eat.
What is the energy available at each trophic level measured in?
Kilojoules per metre squared per year (kJm-2yr-1)
- this allows for changes in photosynthetic production and consumer feeding patterns throughout the year
What is ecological efficiency? (Formula)
The efficiency with which biomass is transferred from one trophic level to the next.
Biomass at higher level(after transfer) / biomass at lower level (before transfer)
X100
Efficiency at consumer levels?
Consumers at each trophic level convert at most 10% of the biomass in their food to their own tissue because:
- Energy lost through respiration (for movements, active transport etc.)
- Energy lost through photosynthetic reactions
- Tissue that cannot be eaten or easily digested (e.g. cellulose, bone)
- Energy help in excreted substances (e.g. urea and carbon dioxide)
- Organisms grow and are not eaten by organisms in the successive trophic level
Efficiency at producer level?
Producers only convert 1-3% of the sunlight they receive into chemical energy/biomass. Due to:
- not all solar energy available is used in photosynthesis (approx 90% reflected)
- other factors may limit photosynthesis.
- energy used up for photosynthetic reactions.
Total solar energy that plants convert to organic matter is gross production (some used in respiration)
Remaining energy is converted to biomass – energy available to the next trophic level is net production
net production = gross production - respiratory losses
What human activity can manipulate biomass transfer through an ecosystem?
-Biomass flow can be manipulated by growing foods:
Involves diverting energy to food growth and creating artificial ecosystems.
-Improving Growth Conditions
-Improving Efficiency of Energy Conversion to Food
-Reducing Competition
How can humans improve growth conditions?
Greenhouses - crops grow in artifical conditions to enhance growth (extra light, warm temperatures, extra CO2)
- Irrigation
- Fertilisers
- Crop rotations
How can humans improve efficiency of energy conversion to food?
- Use faster-growing crop
- Selective breeding or GM
- Introduce fungus/disease resistance
- Harvest animals as soon as fully grown
- Keep animals in small enclosures, or indoors to reduce energy loss by respiration used to move and keep warm
How can humans reduce competition?
- Control pests
- Use selective weedkillers
- Use antibiotics to treat illness
