5.3 energy and ecosystems

Question 1

how’s biomass formed in plants

Answer 1

during photosynthesis plants make organic compounds from atmospheric or aquatic co2
most sugars synthesised are used by plant as respiratory substrates
rest used to make groups of other bio molecules

Question 2

how can we measure biomass

Answer 2

mass of carbo or dry mass of tissue

Question 3

describe how to measure dry mass of tissue

Answer 3

sample dried in oven at 100
sample weighed and reheated at regular intervals until mass remains constant

Question 4

why’s dry mass more representative than fresh wet mass

Answer 4

water samples will vary in wet mass but won’t affect dry mass

Question 5

how can chemical energy in dry biomass be estimated

Answer 5

using calorimetry
know mass of dry biomass is fully combusted
heat energy released used to heat a known volume of water
increase in temp of water is used to calculate the chemical energy in biomass

Question 6

features of calorimeter enabling valid measurement of heat energy released

Answer 6

stirrer - evenly distributes heat energy
air or insulation reducing heat loss and gain from surroundings
water which has a high specific heat capacity

Question 7

GPP

Answer 7

chemical energy store in plant biomass in given area volume and time
total energy transferred into chemical energy from light energy during photosynthesis

Question 8

NPP

Answer 8

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

Question 9

importance of NPP in ecosystems

Answer 9

NPP is available for plant growth and reproduction
also available to trophic levels in ecosystem like herbivores and decomposers

Question 10

units for primary and secondary productivity and why are they used

Answer 10

kJ ha-1 year-1
per unit area enables comparison between environments since they may vary in size
per year takes into account effect of seasonal variation so more representative and enables comparison

Question 11

why is most light falling on producers not used in photosynthesis

Answer 11

light reflected
wrong wavelength
light misses chlorophyll
co2 conc or temp are limiting factors

Question 12

net production of consumers formula

Answer 12

n= I-(f+r)
I being the chemical energy store in ingested food
F is the chemical energy lost to environment in faeces and urine

Question 13

formula for efficiency of energy transfer

Answer 13

energy or biomasss available after transfer \ energy or biomass available before transfer
times 100

Question 14

why is energy transfer between trophic levels inefficient

Answer 14

heat energy lost via respiration
energy lost via parts of organisms not eaten like bones
energy lost via food not digested
energy lost via excretion

Question 15

crop farming practices to increase efficiency of energy transfer

Answer 15

herbicides kill weed so less competition so more energy to create biomass
pesticides to kill insects which reduce loss of biomass from crops
fungicides to reduce fungal infections so more energy to create biomass

Question 16

livestock farming practices to increase efficiency of energy transfer

Answer 16

restrict movement and keep warm less energy lost as heat in respiration
slaughter animals while young and growing as most their energy is used for growth
treat with antibiotics prevent loss of energy due to pathogens
selective breeding to produce breeds with higher growth rates