3.5.3 - ENERGY + ECOSYSTEMS

Question 1

freshwater marshes have one of the highest rates of gross primary production (GPP) and net primary production (NPP) of all ecosystems.

carbon use efficiency (CUE) is the ratio of NPP:GPP. freshwater marshes have a high CUE.

use your knowledge of NPP to explain why freshwater marshes have high CUE and the advantage of this (2)

Answer 1

1. low respiration (less energy lost in respiration)
2. more growth/biomass

Question 2

explain why a increase in shoot biomass can be taken as a measurement of net primary productivity (2)

Answer 2

1. represents dry mass/mass of carbon
2. represents GPP - R

Question 3

farming cattle for humans to eat is less efficient than farming crops because of energy transfer.

explain why (2)

Answer 3

1. energy lost between trophic levels
2. energy lost via respiration/excretion/faeces

Question 4

give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem (3)

Answer 4

1. not all eaten OR food not digested
2. heat loss from respiration
3. excretion

Question 5

what is biomass? (2)

Answer 5

1. the mass of carbon or dry mass of tissue
2. per a given area

Question 6

describe the process of calorimetry (4)

Answer 6

1. dry the sample, and burn it
2. use this to heat a known volume of water
3. measure the temperature change
4. use this to calculate the chemical energy store in the biomass

Question 7

define gross primary production (GPP) (2)

Answer 7

the chemical energy store in plant biomass, in a given area or volume

Question 8

define net primary production (NPP) (2)

Answer 8

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

Question 9

what is the equation for NPP (1)

Answer 9

GPP - R = NPP

Question 10

what is net primary production available for? (3)

Answer 10

1. for plant growth and reproduction
2. available to other trophic levels in the ecosystem
3. such as herbivores and decomposers

Question 11

what is the equation for net production of consumers? (1)

Answer 11

I - (F + R) = N

Question 12

how is are primary and secondary productivity measured? give an example (2)

Answer 12

1. measured as biomass in a given area in a given time
2. for example, kJ ha^-1 year^-1

Question 13

why is the efficiency of energy transfer considered low? explain why energy is lost at each trophic level (4)

Answer 13

1. some light energy is reflected by plants
2. some light energy is not absorbed by plants as it may be the wrong wavelength
3. energy is lost to surrounds as heat from respiration
4. energy is lost in faeces and urine
5. not all parts of an organism are consumed/ingested

Question 14

describe one way in which farmers may increase efficiency in a non-human food chain (2)

Answer 14

1. simplifying food webs
2. with the use of pesticides

Question 15

describe one way in which farmers may increase efficiency in a human food chain (2)

Answer 15

ANY PAIR

1. restricting movement
2. so less energy is lost as heat from respiration

OR
1. keep them warm
2. so less energy used to generate heat