AQA A Level Biology
3.5 Energy transfers in and between organisms
3.5.1 photosynthesis
3.5.2 respiration
3.5.3 Energy and ecosystems
3.5.4 nutrient cycles
, Energy and Ecosystems
Part 1. Biomass
ecosystem: the community and the non-living components of its environment
How does energy enter an ecosystem and what is Biomass: the mass of organic molecule
it converted to? (containing carbon)
• during photosynthesis, plants synthesise
organic compounds (e.g. glucose from carbon what can biomass be represented as?
dioxide, using light energy) • dry biomass (per unit area per unit time)
• the energy is stored within these organic • mass of carbon
compounds
Dry Biomass
What are the organic compounds produced in • dry biomass is the mass of organic material
photosynthesis used for in the plant? with all the water removed.
• most of the sugars made by plants are used in • biomass is not measured as wet (fresh) mass
respiration because the amount of water can vary
• the rest make other organic biological
How would you measure the dry biomass of
molecules, which form the biomass of the plant
some grass?
(stored)
• heat the grass to evaporate the water (not so
hot that it would burn it)
• measure the mass of the grass
• reheat and reweigh until a constant mass is
units of biomass are: mass of carbon per unit area reached
per unit time e.g. Kgm-2year-1
Part 2. Calorimetry
A calorimeter is used to estimate the energy in biomass in joules:
method:
• the sample of living tissue is burnt in a combustion chamber
• the heat energy released is transferred to a known volume of water surrounding the tissue
• the increase in temperature of the water is measured and used to calculate chemical energy in the
biomass
energy released = volume of water x temperature increase x specific heat capacity of water (4.2J)
Simple Colorimetry vs Enclosed calorimeter
Why does this simple calorimetry apparatus cause Explain the features of the enclosed calorimeter
an inaccurate measurement for the energy content which allow it to accurately measure the total heat
of the combusted biomass? energy released from the combusted biomass
• Heat energy can escape to the surrounding and • The container is insulated preventing heat loss by
does not enter the water conduction
• Heat energy can escape from the water due to • The stirrer ensures the heat energy evenly
the calorimeter not being insulated/no lid to distributed
prevent evaporation • Water has a high specific heat capacity
, Lesson 2 – GPP, NPP and N
Gross Primary Production (GPP)
GPP: the chemical energy store in plant biomass, in a given area or volume, in a given time
GPP related directly to rate of photosynthesis
(the greater the rate of photosynthesis, the greater the GPP as more organic molecules are formed)
only about 2% of the light energy is converted to biomass (GPP) in photosynthesis. Why so low?
• light is reflected off the leaf
• light misses the chlorophyll
• some light is the wrong wavelength for photosynthesis
Net Primary Production (NPP)
NPP: the chemical energy store in plant biomass after respiratory losses to the environment
NPP = GPP – R Units: KJm-2year-1
The NPP is the energy available to the plant for growth and reproduction
it is also the energy available to the primary consumer and decomposers when thy feed on the plant
only about 10% of the NPP is transferred to the consumer, 90% is lost
How can the energy be lost between trophic levels?
• energy is lost as heat due to respiration of organic molecules
• some organic molecules are excreted in urine
• some organic molecules are not absorbed and are lost in faeces (egestion)
Farming cattle for humans to eat is less efficient than farming crops because of energy transfer. Explain
why [2]
1. energy is lost between trophic levels
2. energy is lost via respiration etc
Net primary Production of consumers (N) Exam tip: NPP refers to the net
N is the chemical energy stored as biomass in a consumer (primary) production in a producer, N
which is available to the next trophic level refers to the net production in higher
trophic level consumers
N = I - (F + R)
I = chemical energy in ingested food
R = energy lost through respiration
F = chemical energy lost in faeces and urine
3.5 Energy transfers in and between organisms
3.5.1 photosynthesis
3.5.2 respiration
3.5.3 Energy and ecosystems
3.5.4 nutrient cycles
, Energy and Ecosystems
Part 1. Biomass
ecosystem: the community and the non-living components of its environment
How does energy enter an ecosystem and what is Biomass: the mass of organic molecule
it converted to? (containing carbon)
• during photosynthesis, plants synthesise
organic compounds (e.g. glucose from carbon what can biomass be represented as?
dioxide, using light energy) • dry biomass (per unit area per unit time)
• the energy is stored within these organic • mass of carbon
compounds
Dry Biomass
What are the organic compounds produced in • dry biomass is the mass of organic material
photosynthesis used for in the plant? with all the water removed.
• most of the sugars made by plants are used in • biomass is not measured as wet (fresh) mass
respiration because the amount of water can vary
• the rest make other organic biological
How would you measure the dry biomass of
molecules, which form the biomass of the plant
some grass?
(stored)
• heat the grass to evaporate the water (not so
hot that it would burn it)
• measure the mass of the grass
• reheat and reweigh until a constant mass is
units of biomass are: mass of carbon per unit area reached
per unit time e.g. Kgm-2year-1
Part 2. Calorimetry
A calorimeter is used to estimate the energy in biomass in joules:
method:
• the sample of living tissue is burnt in a combustion chamber
• the heat energy released is transferred to a known volume of water surrounding the tissue
• the increase in temperature of the water is measured and used to calculate chemical energy in the
biomass
energy released = volume of water x temperature increase x specific heat capacity of water (4.2J)
Simple Colorimetry vs Enclosed calorimeter
Why does this simple calorimetry apparatus cause Explain the features of the enclosed calorimeter
an inaccurate measurement for the energy content which allow it to accurately measure the total heat
of the combusted biomass? energy released from the combusted biomass
• Heat energy can escape to the surrounding and • The container is insulated preventing heat loss by
does not enter the water conduction
• Heat energy can escape from the water due to • The stirrer ensures the heat energy evenly
the calorimeter not being insulated/no lid to distributed
prevent evaporation • Water has a high specific heat capacity
, Lesson 2 – GPP, NPP and N
Gross Primary Production (GPP)
GPP: the chemical energy store in plant biomass, in a given area or volume, in a given time
GPP related directly to rate of photosynthesis
(the greater the rate of photosynthesis, the greater the GPP as more organic molecules are formed)
only about 2% of the light energy is converted to biomass (GPP) in photosynthesis. Why so low?
• light is reflected off the leaf
• light misses the chlorophyll
• some light is the wrong wavelength for photosynthesis
Net Primary Production (NPP)
NPP: the chemical energy store in plant biomass after respiratory losses to the environment
NPP = GPP – R Units: KJm-2year-1
The NPP is the energy available to the plant for growth and reproduction
it is also the energy available to the primary consumer and decomposers when thy feed on the plant
only about 10% of the NPP is transferred to the consumer, 90% is lost
How can the energy be lost between trophic levels?
• energy is lost as heat due to respiration of organic molecules
• some organic molecules are excreted in urine
• some organic molecules are not absorbed and are lost in faeces (egestion)
Farming cattle for humans to eat is less efficient than farming crops because of energy transfer. Explain
why [2]
1. energy is lost between trophic levels
2. energy is lost via respiration etc
Net primary Production of consumers (N) Exam tip: NPP refers to the net
N is the chemical energy stored as biomass in a consumer (primary) production in a producer, N
which is available to the next trophic level refers to the net production in higher
trophic level consumers
N = I - (F + R)
I = chemical energy in ingested food
R = energy lost through respiration
F = chemical energy lost in faeces and urine
