energy + ecosystems

Question 1

what is an ecosystem?

Answer 1

: An ecosystem is formed from a community and the non-living (abiotic) components of its
environment.

Question 2

what is biomass?

Answer 2

mass of organic material in a plant, made from biological molecules such as starch, cellulose, lipids + amino acids.

Question 3

what 2 things can biomass be measured as?

Answer 3

1. Dry mass of tissue, per unit area, per unit time. I.e. the mass of living tissue with all water removed. This
   is because the amount of water of the living tissue can vary.
2. Mass of carbon, per unit area, per unit time.

Question 4

how to measure dry mass

Answer 4

1. The sample of organism is heated in an oven to evaporate the water
   (normally below 100oC to prevent combustion and loss of mass via CO2).
2. The sample is weighed after a certain amount of time e.g. 24 hours
3. The sample is heated again and re-weighed until the mass remains
   constant, which means all the water has been removed.

Question 5

how to use calorimetry to estimate the chemical energy in biomass in joules (J) + what 3 ways allow accurate results?

Answer 5

1. The sample of living tissue is burnt in a combustion chamber.
2. The heat energy released is transferred to a known volume of water surrounding the tissue.
3. The rise in temperature of the water is measured and used to calculate chemical energy in the biomass.
   Cool ways to allow accurate results:
   * The stirrer distributes the heat energy evenly.
   * The insulation reduces heat loss/gain by conduction/ convection.
   * Water has a high specific heat capacity.

Question 6

what is the definition of GPP+ units?

Answer 6

Gross primary production (GPP) is the chemical energy store in plant biomass in a given area or volume, in a given time. It represents total light energy which is converted into stored biomass during photosynthesis.
Units: e.g. kJ m-2 year-1

Question 7

why isn’t all light energy from photosynthesis converted into chemical energy store?

Answer 7

only about 2% is converted because:
1) some light is the wrong wavelength for photosynthesis
2) some light misses the chlorophyll and transmits
through/ a lot of light is reflected off the surface of the leaf
3) temperature or CO2 concentration are a
limiting factor.

Question 8

what is the definition of NPP+ how can it be calculated?

Answer 8

Net primary production (NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account.
NPP=GPP-respiratory losses

Question 9

what do food chains show+ what do organisms represent?

Answer 9

the flow of energy between organisms.
each organism represents a trophic level- Due to losses of energy through the food chain, there is not enough energy to sustain populations at high trophic levels, so trophic levels are not unlimited.

Question 10

why are more complex food webs more stable?

Answer 10

The more complex the food web, any large changes in a population of one species, will have less of an effect on the other populations, making the food web more stable.

Question 11

what is net production+ give equation?

Answer 11

Net production (N) in a consumer is the energy available to the next trophic level. The N reduces as you
go from one trophic level to the next due to the energy loss at each level.
N= Chemical energy from ingested food- (CE lost in faeces and urine + energy lost thru respiration)

Question 12

what is primary productivity?

Answer 12

the rate of primary production It is measured as biomass in a given area
at a given time e.g. in kJ ha-1 year-1

Question 13

what is secondary productivity?

Answer 13

the rate of secondary production. It is measured as
biomass in a given area at a given time e.g. kJ ha-1 year-1.
Secondary production refers to the net quantity of energy transferred and stored in the tissues of
heterotrophs.

Question 14

how to calculate efficiency of energy transfer?

Answer 14

% efficiency of energy transfer =( N of trophic level / N of previous trophic level) x100

Question 15

how can simplifying food webs increase efficiency in food chains with farming practices

Answer 15

1) Simplifying food webs- involves getting rid of food chains that don’t include humans. This can increase the proportion of energy transferred to humans as less is eaten by other organisms. Little insects and stuff can be removed to reduce competition with humans for stuff like wheat by:
chemical control: insecticides + herbicides to kill weeds, removing interspecific competition for the crop
for abiotic factors such as light and also removes a food source for the aphids reducing their numbers.
biological control: e.g. adding ladybirds to ecosystem to eat insects.

Question 16

how does reducing respiratory losses increase efficiency of food chains?

Answer 16

Reduces R in the equation, increasing N, so more energy for growth + biomass.
* Movement can be restricted by keeping animals in pens so less respiration occurs, so less energy is released muscle contraction.
* Animals can be kept indoors or heated rooms so less respiration occurs so less heat energy is released to
maintain body temperature