Energy & Ecosystems (A Level only) (AQA A Level Biology): Flashcards
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Define the term primary producer.
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Define the term primary producer.
Plants are described as primary producers because they produce their own organic molecules during photosynthesis.
Why do living organisms need a supply of organic compounds?
To respire and to build their tissues.
Name three groups of organic compounds that living organisms need.
Carbohydrates
Proteins
Lipids
By which process do plants synthesise organic compounds?
Photosynthesis.
Which element present in carbon dioxide do plants use to produce organic molecules?
Carbon.
Where do plants in terrestrial ecosystems obtain their carbon dioxide?
From the atmosphere.
In what form do plants in aquatic ecosystems obtain their carbon dioxide?
As dissolved carbon dioxide.
How are the organic compounds produced by plants passed to other organisms in an ecosystem?
When herbivores consume plant tissue.
True or False?
All organisms are able to synthesise their own organic compounds.
False.
Only producers, such as plants, can synthesise their own organic compounds; consumers must obtain them by eating other organisms.
In ecosystems, organic compounds are synthesised by during the process of .
In ecosystems, organic compounds are synthesised by plants during the process of photosynthesis.
What do plants synthesise during photosynthesis?
Sugars.
What is most of the sugar produced in photosynthesis used for?
As respiratory substrates.
Name the four groups of biological molecules that photosynthetic sugars can be used to make.
Starch
Cellulose
Lipids
Proteins
What is the function of starch in plant cells?
A complex carbohydrate that acts as an energy storage molecule inside plant cells.
What is the function of cellulose in plants?
A complex carbohydrate that forms a structural component of plant cell walls.
State two functions of lipids in plants.
Energy storage
Formation of the waxy cuticle on leaves
Plant cells combine sugars with nitrates to make which molecules?
Amino acids, which are then used to produce proteins.
Give two examples of proteins made by plant cells.
Membrane proteins
Enzymes
True or False?
Cellulose functions as an energy storage molecule in plant cells.
False.
Cellulose is a structural molecule in plant cell walls; starch is the energy storage molecule.
Plant cells combine sugars with to make , which are used to build proteins.
Plant cells combine sugars with nitrates to make amino acids, which are used to build proteins.
Define the term biomass.
The mass of living material present in an organism or tissue sample.
Why is dry mass a more reliable measure of biomass than fresh mass?
Because the water content of living tissue can vary; dry mass is the mass after water has been removed.
State the units used for the dry mass of biomass.
Mass per unit area, e.g. kg m^-2.
The mass of carbon in a sample is taken to be what percentage of the dry mass?
50 % of the dry mass.
True or False?
Biomass is a measure of the number of organisms present.
False.
Biomass is a measure of the mass of living tissue, not the number of organisms present.
Dry mass is the mass of a tissue sample after has been removed.
Dry mass is the mass of a tissue sample after water has been removed.
Why should an oven be set to a low temperature when finding the dry mass of a sample?
If the temperature is too high, the sample may burn and lose biomass.
During drying, how do you know when a sample is fully dehydrated?
When the mass of the crucible and sample stops decreasing between weighings.
Which technique is used to estimate the chemical energy stored in a dried plant sample?
Calorimetry (using a calorimeter).
State the equation used to calculate the energy transferred per gram in calorimetry.
Energy transferred per gram = (mass of water × temperature change × 4.2) ÷ mass of sample.
Give one limitation of using a simple calorimeter to estimate stored energy.
Heat energy from the burning sample may be transferred to the surrounding environment rather than to the water, giving an underestimate.
A calorimeter estimates the energy in a dried sample by it and measuring the rise of a known mass of water.
A calorimeter estimates the energy in a dried sample by burning it and measuring the temperature rise of a known mass of water.
Define gross primary production (GPP).
The chemical energy stored in plant biomass, in a given area or volume.
State two units in which the GPP of terrestrial plants can be expressed.
Energy per unit area, e.g. J m^-2
Mass per unit area, e.g. g m^-2
Why can a measure of mass be used to represent energy when expressing GPP?
Because biomass = stored chemical energy, so a measure of mass can represent the energy stored.
In what units might GPP be expressed for an aquatic environment?
Energy or mass per unit volume, e.g. kJ m-3 or kg m-3.
True or False?
The units for GPP should include a measure of time.
False.
GPP is not a rate, so its units do not include time; if a unit includes time it is a measure of productivity, not production.
Gross primary production is the chemical energy stored in plant , in a given area or .
Gross primary production is the chemical energy stored in plant biomass, in a given area or volume.
Is gross primary production a rate?
No.
GPP is not a rate and so does not include a unit of time.
The total biomass of grass in a 200 m^2 field is 1000 kg. Calculate the GPP of the field, with units.
Step 1: find the biomass in 1 m^2 (1/200th of the field):
1000 ÷ 200 = 5
Step 2: give appropriate units (mass per unit area):
GPP = 5 kg m^-2
When calculating GPP for aquatic algae, why are the units expressed per unit volume?
Because aquatic organisms occupy a volume of water rather than an area, so units such as J m^-3 are used.
If a unit of production also includes , then it is a measure of rather than production.
If a unit of production also includes time, then it is a measure of productivity rather than production.
Define net primary production (NPP).
The chemical energy stored in plant biomass after respiratory losses to the environment have been taken into account.
State the equation for net primary production.
NPP = GPP − R
In the equation NPP = GPP − R, what does R represent?
The respiratory loss to the environment.
Why is NPP important in an ecosystem?
It represents the energy available to consumers in the ecosystem.
In what form is energy typically lost from a plant, reducing GPP to NPP?
As waste heat generated during respiration.
True or False?
The concept of NPP applies to both plants and animals.
False.
NPP applies only to producers; this is why the NPP equation includes only respiratory loss and not losses in faeces and urine.
A plant has a GPP of 10 000 kJ m^-2 and respiratory losses of 6000 kJ m^-2. Calculate its NPP.
Step 1: write the equation and substitute values:
NPP = GPP − R
NPP = 10 000 − 6000
Step 2: calculate NPP with units:
NPP = 4000 kJ m^-2
In what units is NPP expressed?
Energy per unit area or volume, e.g. J m-2 or J m-3.
True or False?
NPP is always greater than GPP.
False.
Because NPP = GPP − R, NPP is always less than GPP once respiratory losses are subtracted.
Net primary production is the energy that remains in plant tissues after losses, and is available to .
Net primary production is the energy that remains in plant tissues after respiratory losses, and is available to consumers.
Within a plant, which two processes is NPP available for?
Growth
Reproduction
How is the energy in NPP transferred to consumers at other trophic levels?
When plant biomass is eaten by herbivores (or broken down by decomposers).
Net primary production is available for plant growth and , or for transfer to at other trophic levels.
Net primary production is available for plant growth and reproduction, or for transfer to consumers at other trophic levels.
Define net production of consumers.
The chemical energy transferred to and stored in the tissues of consumers after energy losses (also known as secondary production).
State the equation for the net production of consumers.
N = I − (F + R)
In the equation N = I − (F + R), what does I represent?
The chemical energy in ingested food.
In the equation N = I − (F + R), what does F represent?
The chemical energy lost to the environment in faeces and urine.
Why is energy lost from a consumer in faeces?
Consumers cannot digest all of the food they eat, so some is egested as faeces (e.g. cellulose, fur and bones).
Why is energy lost from a consumer in urine?
Energy stored in the bonds of excess amino acids, which are converted into urea for excretion in the urine.
In what form is energy lost from a consumer during respiration?
As heat, which is radiated into the environment.
Caterpillars ingest 2000 kJ m^-2, losing 1200 kJ m^-2 in faeces and urine and 600 kJ m^-2 in respiration. Calculate their net production.
Step 1: write the equation and substitute values:
N = I − (F + R)
N = 2000 − (1200 + 600)
Step 2: calculate N with units:
N = 2000 − 1800 = 200 kJ m^-2
The net production of consumers is also known as production.
The net production of consumers is also known as secondary production.
Define productivity.
The rate of primary or secondary production.
What is meant by primary production?
The transfer of energy to the tissues of plants.
What is meant by secondary production?
The transfer of energy to the tissues of consumers (also known as the net production of consumers).
What is the key difference between productivity and production?
Productivity is a rate, so its units include time
Production has no unit of time and is just energy or mass per unit area or volume
State two possible units for productivity.
e.g. g m^-2 day^-1
e.g. kJ ha^-1 yr^-1
True or False?
Productivity must have an associated time period.
True.
Productivity is a rate, so it must include a unit of time.
In an aquatic environment, why might productivity be measured per unit volume?
Because aquatic organisms, such as algae, occupy a volume of water, so units such as g m^-3 yr^-1 are more suitable.
True or False?
Production has an associated unit of time.
False.
Production has no unit of time; it is just energy or mass per unit area or volume. Adding time makes it productivity.
A crop has a total primary production of 900 kJ ha^-1 over 5 years. Calculate its average primary productivity.
Step 1: productivity is production per year, so divide by the number of years:
900 ÷ 5 = 180
Step 2: give appropriate units (mass or energy, area and time):
= 180 kJ ha^-1 yr^-1
Productivity is a , so its units must include a measure of .
Productivity is a rate, so its units must include a measure of time.
Which equation is used to calculate the net productivity of producers?
NPP = GPP − R
(where NPP = net primary productivity, GPP = gross primary productivity, R = respiratory losses)
Which equation is used to calculate the net productivity of consumers?
N = I − (F + R)
(where I = ingested energy, F = energy lost in faeces and urine, R = respiratory losses)
What is meant by the efficiency of energy transfer?
The percentage of energy that is transferred between trophic levels.
State the formula for the percentage efficiency of energy transfer.
% efficiency = (productivity of trophic level ÷ energy available from the level below) × 100
A wheat crop has a GPP of 10 000 kJ m^-2 yr^-1 and loses 5500 kJ m^-2 yr^-1 in respiration. Calculate its net primary productivity.
Step 1: write the equation and substitute values:
NPP = GPP − R
NPP = 10 000 − 5500
Step 2: calculate NPP with units:
NPP = 4500 kJ m^-2 yr^-1
Wheat has an NPP of 112 500 kJ m^-2 yr^-1; insect pests eating it have a net productivity of 10 000 kJ m^-2 yr^-1. Calculate the % efficiency of transfer to the insects.
Step 1: write the equation and substitute values:
% efficiency = (productivity of trophic level ÷ energy available from level below) × 100
= (10 000 ÷ 112 500) × 100
Step 2: calculate the efficiency:
= 0.089 × 100 = 8.9 %
Rabbits have a net productivity of 2400 kJ m^-2 yr^-1 and ingest 18 900 kJ m^-2 yr^-1 of grass. Calculate their total energy loss (F + R).
Step 1: rearrange N = I − (F + R) to make (F + R) the subject:
(F + R) = I − N
Step 2: substitute the known values:
(F + R) = 18 900 − 2400
Step 3: calculate the total energy loss with units:
= 16 500 kJ m^-2 yr^-1
In a calculation, how can you tell whether a value is a productivity rather than a production?
Productivity includes a unit of time, whereas production is just energy or mass per unit area or volume.
True or False?
The efficiency of energy transfer is expressed as a percentage.
True.
The efficiency of energy transfer is the percentage of energy transferred between trophic levels.
Percentage efficiency = (productivity of a trophic level ÷ energy available from the level ) × .
Percentage efficiency = (productivity of a trophic level ÷ energy available from the level below) × 100.
State two ways in which farming practices increase production.
Simplifying food webs
Reducing respiratory loss
How does removing pests increase the energy available to humans from a crop?
Pests reduce crop biomass and make crops expend energy on herbivory defences rather than growth, lowering NPP; removing pests increases the NPP available to humans.
Name two methods used to remove pests from crops.
Chemical pesticides
Biological pest control
How does restricting the movement of livestock increase net production?
Keeping animals in pens reduces the energy needed for muscle activity, reducing respiratory loss and leaving more energy for biomass production.
How does keeping livestock warm increase net production?
A heated environment reduces the energy used for temperature regulation, leaving more energy for biomass production.
Why might antibiotics be given to healthy livestock to increase production?
To prevent infection, reducing the energy used by the immune system and leaving more energy for biomass production.
State one ethical concern raised by intensive livestock farming practices.
They raise concerns about animal welfare.
The net production of livestock can be increased by reducing losses, which maximises the energy available for production.
The net production of livestock can be increased by reducing respiratory losses, which maximises the energy available for biomass production.
Define theoretical yield.
The yield that is theoretically possible under ideal conditions.
State the formula for percentage yield.
% yield = (actual yield ÷ theoretical yield) × 100
A wheat crop has a theoretical NPP of 200 kg m^-2 yr^-1 and an actual NPP of 50 kg m^-2 yr^-1. Calculate the percentage yield.
Step 1: write the equation and substitute values:
% yield = (actual yield ÷ theoretical yield) × 100
= (50 ÷ 200) × 100
Step 2: calculate the % yield:
= 0.25 × 100 = 25 %
Give two reasons why the percentage yield of a crop may not be 100 %.
Any two of:
Temperature too low or too high
Light intensity lower than ideal
Carbon dioxide concentration too low
Pests consuming part of the crop
The crop has a disease or infection
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