3.5.3 | ENERGY AND ECOSYSTEMS

Question 1

define biomass

Answer 1

the total mass of living material in a specific area at a given time

Question 2

describe how biomass is formed in plants

Question 3

how can biomass be measured

Answer 3

mass of carbon or dry mass of tissue per given area

Question 4

describe how dry mass of tissue can be measured

Answer 4

sample of tissue is dried in an oven set to a low temperature (to not burn sample)
mass weighed at regular intervals until the mass becomes constant

Question 5

explain why dry mass is more representative than fresh (wet) mass

Answer 5

water volume in wet samples will vary but will not affect dry mass

Question 6

describe how the chemical energy stored in dry biomass can be estimated

Answer 6

using calorimetry:
known mass of dry biomass is fully combusted (burnt)
heat energy released heats a known volume of water
increase in temperature of water is used to calculate
chemical energy of biomass

Question 7

explain how features of a calorimeter enable
valid measurement of heat energy released

Answer 7

stirrer → evenly distributes heat energy (in water)
air / insulation → reduces heat loss & gain to & from surroundings
water → has a high specific heat capacity

Question 8

what is gross primary production (GPP)

Answer 8

chemical energy store in plant biomass, in a given area or volume, in a given time
- total energy transferred into chemical energy from light energy during photosynthesis

Question 9

what is net primary production (NPP)?

Answer 9

chemical energy store in plant biomass after respiratory losses to environment taken into account

Question 10

state the formula for NPP

Answer 10

NPP = GPP – R
R = respiratory losses to the environment

Question 11

explain the importance of NPP in ecosystems

Answer 11

NPP is available for plant growth and reproduction
NPP is also available to other trophic levels in the ecosystem, such as herbivores and decomposers

Question 12

name factors which contribute to energy losses at each trophic level

Answer 12

not all solar energy is captured by leaves or is of the correct wavelength for photosynthesis.
energy is lost during photosynthetic reactions.
not all parts of biomass are edible or digestible by consumers.
energy is lost as heat during movement or respiration.
energy is lost in excretory materials, such as urine and faeces.

Question 13

define net production/secondary production

Answer 13

amount of ingested food that is converted into biomass