7.4 Trophic Levels in an Ecosystem

Question 1

what does a food chain show?

Answer 1

it describes the feeding relationships between organisms and the resultant stages of biomass transfer.

Question 2

what are trophic levels?

Answer 2

the stages in a food chain`

Question 2

what is trophic level 1?

Answer 2

plants and algae which make their own food (through photosynthesis) - called producers.

Question 2

how are trophic levels represented?

Answer 2

trophic levels are represented by numbers, starting from 1. after 1, trophic levels are numbered according to far along the organism is in the food chain.

Question 3

what is trophic level 2?

Answer 3

herbivores which eat producers - called primary consumers.

Question 3

what is trophic level 3?

Answer 3

carnivores that eat herbivores - called secondary consumers.

Question 4

what is an apex predator?

Answer 4

a carnivore with no predators

Question 4

what is trophic level 4?

Answer 4

carnivores that eat other carnivores - called tertiary consumers.

Question 5

how do decomposers break down dead matter?

Answer 5

decomposers release enzymes which catalyse the breakdown of dead material into smaller molecules. soluable small food molecules then diffuse into the microorganisms.

Question 6

what is biomass?

Answer 6

thew dry mass of all of the living organisms in an area.

Question 7

why is dry mass used for biomass?

Answer 7

because the wet mass varies as the volume of water in the organism varies.

Question 8

what percentage of the incident energy from light for photosynthesis do producers transfer?

Answer 8

1%

Question 8

how do you calculate the efficiency of biomass transfer?

Answer 8

efficiency = (energy transferred/total energy available) x 100

Question 8

what percentage of the biomass from one trophic level is transferred to the level above it in feeding?

Answer 8

approximately 10%

Question 9

what is the producer in a pyramid of biomass?

Answer 9

the bottom of the pyramid is the producer

Question 9

why are biomass transfers not 100% efficient?

Answer 9

energy is lost through:
- egestion (removal of faeces)
- excretion (removal of waste products e.g. urine containing urea and water)
- respiration (loss of carbon dioxide and water) in which large amounts of glucose are used
- the production of inedible bones and shells

Question 10

how does the efficiency of biomass transfers affect the number of trophic levels in a biomass pyramid?

Answer 10

the less efficient the transfers, the fewer trophic levels and the fewer organisms in higher trophic levels.

Question 11

what is a biomass pyramid?

Answer 11

a pryamid that shows the total dry mass of organisms at each trophic level
trophic level 1 is at the bottom of the pyramid

Question 12

what is a pyramid of numbers?

Answer 12

a pyramid of numbers shows the number of organisms at each trophic level

Question 13

why are some pyramid of numbers not pyramid shaped?

Answer 13

pryamids of numbers don’t take size and mass of organisms into account.

Question 14

calculate the efficiency of this biomass transfer from the flowers to the caterpillar:
flowers are eaten by caterpillers using 800kJ, and 4000kJ energy is lost through the flowers

Answer 14

efficiency = (energy transferred/total energy available) x 100
total energy available = 800kJ + 4000kJ = 4800kJ
energy transferred = 800kJ
800/4800 x 100 = 16.67%