23.2 biomass transfer through an ecosystem

Question 1

what is a trophic level

Answer 1

each stage in a food chain

Question 2

what is the first trophic level

Answer 2

producers - organism which converts light energy into chemical energy by photosynthesis

Question 3

what are the subsequent trophic levels

Answer 3

consumers - organism that obtains energy by feeding on other organisms

Question 4

define biomass

Answer 4

mass of the living material present in a particular place or in particular organisms

Question 5

how do you calculate biomass at each trophic level

Answer 5

biomass present in each organism X total number of organisms present

Question 6

what is biomass measured in

Answer 6

grams per square meter (g/m²)

grams per cubic meter (g/m³)

Question 7

how do you measure biomass

Answer 7

• measure the mass of fresh material present
• water content has to be discounted
• dry mass has to be calculated

Question 8

how do you calculate dry mass

Answer 8

1. organisms are killed and dried
2. placed in an oven at 80C until all water is evaporated
3. to minimise destruction, only a small sample is taken BUT it may not be representative

Question 9

define ecological effieciency

Answer 9

the efficiency with which biomass or energy is transferred from one trophic level to the next

Question 10

define gross production

Answer 10

• total solar energy that plant converts into organic matter

- around 20-50% of energy is used in respiration

Question 11

how do you calculate net production

Answer 11

gross production - respiratory losses

Question 12

efficiency at producer level

Answer 12

producers only convert 1-3% of light into biomass because:

• not all solar energy is available for photosynthesis (90%=reflected and some is transmitted)
• other factors list photosynthesis
• proportion of ‘energy’ is lost as it is used in photosynthesis rezctions

Question 13

efficiency at consumer levels

Answer 13

consumers covert 10% of biomass into their own organic tissue because:

• not all biomass of an organism is eaten
• energy is transferred to the environment as metabolic heat due to movement/respiration
• some parts of organisms are indigestible and are egested
• energy is lost in excretory materials such as urine

Question 14

how much of energy from sunlight is embodied as biomass in a tertiary consumer

Answer 14

0.001%

Question 15

how do you calculate ecological efficiency

Answer 15

biomass available after transfer/biomass available before transfer
X100

Question 16

what do humans depend on which manipulates the environment

Answer 16

• agriculture manipulates environment to favour crops and rear animals for food/produce
• provided with necessary abiotic conditions
• competition from other species and predators are removed

Question 17

how does agriculture affect food chains

Answer 17

simplifies food chains as fewer trophic levels are present so as much energy as possible is transferred into biomass

Question 18

farming animals for food - TROPHIC LEVELS

Answer 18

producers - animal feed
primary consumers - livestock
secondary consumers - humans

Question 19

cultivating plants for human consumption - TROPHIC LEVELS

Answer 19

producers - crops

primary consumers - humans