Energy and Ecosystems Flashcards
In any ecosystem, plants synthesise ________________ compounds from atmospheric, or aquatic, carbon dioxide.
organic
ost of the sugars synthesised by plants are used as respiratory substrates. The rest are used to make other groups of biological molecules. These biological molecules form the ______________ of the plants.
biomass
Primary consumers obtain their energy by feeding on ___________.
producers
____________________ are a group of microorganisms that break down the organic materials in dead organic matter and faeces into simple ones.
Saprobionts / decomposers
n natural ecosystems, most of the light energy falling onto producers is NOT used in photosynthesis. Explain why (2 marks).
- Light being reflected
- Pigments may not absorb the wavelength of light received
- Light may miss the chlorophyll
- There is another limiting factor that means that the light cannot be used e.g. carbon dioxide concentration
Farming cattle for humans to eat is less efficient than farming crops because of energy transfer. Explain why (2 marks).
- Energy lost during transfer between trophic levels;
(Humans eating cattled adds a trophic level)
- Energy lost via respiration / heat loss / maintaining temperature / muscle contraction / movement
Also accept: excretion / faeces / parts of food not eaten e.g. roots/bones;
Give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem.
- Heat loss from respiration;
- Food not digested / not all eaten OR faeces;
- Excretion OR urine;
Energy efficiency equation
(energy available after transfer / energy available before transfer) x 100
Biomass definition
Total mass of carbon per given area per given time
The chemical energy stored in dry biomass can be estimated using _____________.
calorimetry
Suggest how you could determine the dry mass of a sample of plant material (2 marks).
- Heat at 100°C to evaporate water;
- Weigh and heat until no further change in mass
What is the advantage of using dry mass and not fresh mass to compare the yield of plants (2 marks).
- Water content present will vary in fresh mass;
- This issue will not affect dry mass;
Gross primary production (GPP) is the ____________ energy store in plant biomass, in a given area or volume.
chemical
The higher GPP, the higher the rate of ______________
photosynthesis
Net Primary Production (NPP) equation
NPP = GPP-R
Where:
GPP = Gross primary production
R = respiratory losses
Net production of consumers (N) equation
N = I - (F+R)
What does I represent?
N = I - (F+R)
I = Chemical energy/store of ingested/consumed food
What does F represent?
N = I - (F+R)
energy loses due to
F = faeces AND urine
What does R represent?
N = I - (F+R)
R = respiratory losses
Units for the energy stored in biomass
KJ m^-2 year ^-1
Describe how calorimetry can estimate the energy stored in biomass.
Sample of (dry) biomass is combusted;
This releases heat energy;
This warms the surrounding water;
The larger the temperature increases of water, the more energy stored in the biomass;
Water is used because it has a high specific heat capacity
(we know much energy is required to heat 1cm3 of water by 1oC).
To increase the net productivity (N) of domestic livestock, farmers aim to decrease energy losses due to ________.
Respiration / heat loss / maintaining body temperature / movement;
Explain why farmers try to reduce respiratory losses (e.g. by keeping animals indoors during the winter)
More energy is available for growth/biomass
Explain why simplifying food webs reduces energy losses to non-human food chains (2 marks).
- Insecticides/pesticides/fungicides are used to exclude competitors who may feed on crops;
- This means a higher N (net production of consumers) / more energy available for growth/biomass of crops
